Fullerene

From Wikipedia, the free encyclopedia

Model of the C60 fullerene (buckminsterfullerene).

 

Model of the C20 fullerene.

 

Model of a carbon nanotube.

 

C60 fullerite (bulk solid C60).

 

A fullerene is an allotrope of carbon whose molecule consists of carbon atoms connected by single and double bonds so as to form a closed or partially closed mesh, with fused rings of five to seven atoms. The molecule may be a hollow sphere, ellipsoid, tube, or many other shapes and sizes. Graphene (isolated atomic layers of graphite), which is a flat mesh of regular hexagonal rings, can be seen as an extreme member of the family.

Fullerenes with a closed mesh topology are informally denoted by their elemental formula C_n, often written Cn, where n is the number of carbon atoms. However, for some values of n there maybe more than one isomer.

The family is named after buckminsterfullerene (C60), the most famous member, which in turn is named after Buckminster Fuller. The closed fullerenes, especially C60, are also informally called buckyballs for their obvious resemblance to the standard ball of association football ("soccer"). Nested closed fullerenes have been named bucky onions. Cylindrical fullerenes are also called carbon nanotubes or buckytubes. The bulk solid form of pure or mixed fullerenes is called fullerite.

Fullerenes had been predicted for some time, but only after their accidental synthesis in 1985 were they detected in nature and outer space. The discovery of fullerenes greatly expanded the number of known allotropes of carbon, which had previously been limited to graphite, diamond, and amorphous carbon such as soot and charcoal. They have been the subject of intense research, both for their chemistry and for their technological applications, especially in materials science, electronics, and nanotechnology.

History

The icosahedral fullerene C
₅₄₀, another member of the family of fullerenes

Predictions and limited observations

The icosahedral C
₆₀H₆₀ cage was mentioned in 1965 as a possible topological structure. Eiji Osawa of Toyohashi University of Technology predicted the existence of C
₆₀ in 1970. He noticed that the structure of a corannulene molecule was a subset of the shape of a soccer ball, and hypothesised that a full ball shape could also exist. Japanese scientific journals reported his idea, but neither it nor any translations of it reached Europe or the Americas.

Also in 1970, R. W. Henson (then of the UK Atomic Energy Research Establishment) proposed the C
₆₀ structure and made a model of it. Unfortunately, the evidence for that new form of carbon was very weak at the time, so the proposal and was met with skepticism, and was never published. It was acknowledged only in 1999.

In 1973, independently from Henson, a group of scientists from the USSR made a quantum-chemical analysis of the stability of C
₆₀ and calculated its electronic structure. The paper was published in 1973, but the scientific community did not gave much importance to this theoretical prediction.

Around 1980, Sumio Iijima identified the molecule of C60 from an electron microscope image of carbon black, where it formed the core of a particle with the structure of a "bucky onion".

Discovery of C60

In 1985 Harold Kroto of the University of Sussex, working with James R. Heath, Sean O'Brien, Robert Curl and Richard Smalley from Rice University, discovered fullerenes in the sooty residue created by vaporising carbon in a helium atmosphere. In the mass spectrum of the product, discrete peaks appeared corresponding to molecules with the exact mass of sixty or seventy or more carbon atoms, namely C
₆₀ and C
₇₀. The team identified their structure as the now familiar "buckyballs".

The name "buckminsterfullerene" was eventually chosen for C60 by the discoverers as an homage to American architect Buckminster Fuller for the vague similarity of the structure to the geodesic domes which he popularized; which, if they were extended to a full sphere, would also have the icosahedral symmetry group. The "ene" ending was chosen to indicate that the carbons are unsaturated, being connected to only three other atoms instead of the normal four. The shortened named "fullerene" eventually came to be applied to the whole family. 

Kroto, Curl, and Smalley were awarded the 1996 Nobel Prize in Chemistry for their roles in the discovery of this class of molecules.

Further developments

Kroto and the Rice team already discovered other fullerenes besides C60, and the list was much expanded in the following years. Carbon nanotubes were first discovered and synthesized in 1991.

After their discovery, minute quantities of fullerenes were found to be produced in sooty flames, and by lightning discharges in the atmosphere. In 1992, fullerenes were found in a family of minerals known as shungites in Karelia, Russia.

The production techniques were improved by many scientists, including Donald Huffman, Wolfgang Krätschmer, Lowell D. Lamb, and Konstantinos Fostiropoulos. Thanks to their efforts, by 1990 it was relatively easy to produce gram-sized samples of fullerene powder. Fullerene purification remains a challenge to chemists and to a large extent determines fullerene prices. 

In 2010, the spectral signatures of C60 and C70 were observed by NASA's Spitzer infrared telescope in a cloud of cosmic dust surrounding a star 6500 light years away. Kroto commented: "This most exciting breakthrough provides convincing evidence that the buckyball has, as I long suspected, existed since time immemorial in the dark recesses of our galaxy." According to astronomer L. Stanghellini, "It’s possible that buckyballs from outer space provided seeds for life on Earth."

Types

There are two major families of fullerenes, with fairly distinct properties and applications: the closed buckyballs and the open-ended cylindrical carbon nanotubes. However, hybrid structures exist between those two classes, such as carbon nanobuds — nanotubes capped by hemispherical meshes or larger "buckybuds".

Buckyballs

upright=0.5C
₆₀ with isosurface of ground state electron density as calculated with DFT

 

Rotating view of C
₆₀, one kind of fullerene

Buckminsterfullerene

Buckminsterfullerene is the smallest fullerene molecule containing pentagonal and hexagonal rings in which no two pentagons share an edge (which can be destabilizing, as in pentalene). It is also most common in terms of natural occurrence, as it can often be found in soot. 

The structure of C
₆₀ is a truncated icosahedron, which resembles an association football ball of the type made of twenty hexagons and twelve pentagons, with a carbon atom at the vertices of each polygon and a bond along each polygon edge.

The van der Waals diameter of a C
₆₀ molecule is about 1.1 nanometers (nm). The nucleus to nucleus diameter of a C
₆₀ molecule is about 0.71 nm.

The C
₆₀ molecule has two bond lengths. The 6:6 ring bonds (between two hexagons) can be considered "double bonds" and are shorter than the 6:5 bonds (between a hexagon and a pentagon). Its average bond length is 1.4 angstroms.

Other buckyballs

Another fairly common fullerene is C
₇₀, but fullerenes with 72, 76, 84 and even up to 100 carbon atoms are commonly obtained. 

The smallest fullerene is the dodecahedral C
₂₀. There are no fullerenes with 22 vertices. The number of fullerenes C_2n grows with increasing n = 12, 13, 14, ..., roughly in proportion to n⁹ (sequence A007894 in the OEIS). For instance, there are 1812 non-isomorphic fullerenes C
₆₀. Note that only one form of C
₆₀, the buckminsterfullerene alias truncated icosahedron, has no pair of adjacent pentagons (the smallest such fullerene). To further illustrate the growth, there are 214,127,713 non-isomorphic fullerenes C
₂₀₀, 15,655,672 of which have no adjacent pentagons. Optimized structures of many fullerene isomers are published and listed on the web.

Heterofullerenes have heteroatoms substituting carbons in cage or tube-shaped structures. They were discovered in 1993 and greatly expand the overall fullerene class of compounds. Notable examples include boron, nitrogen (azafullerene), oxygen, and phosphorus derivatives. 

Trimetasphere carbon nanomaterials were discovered by researchers at Virginia Tech and licensed exclusively to Luna Innovations. This class of novel molecules comprises 80 carbon atoms (C
₈₀) forming a sphere which encloses a complex of three metal atoms and one nitrogen atom. These fullerenes encapsulate metals which puts them in the subset referred to as metallofullerenes. Trimetaspheres have the potential for use in diagnostics (as safe imaging agents), therapeutics and in organic solar cells.

Carbon nanotubes

This rotating model of a carbon nanotube shows its 3D structure.

 

Carbon nanotubes are cylindrical fullerenes. These tubes of carbon are usually only a few nanometres wide, but they can range from less than a micrometer to several millimeters in length. They often have closed ends, but can be open-ended as well. There are also cases in which the tube reduces in diameter before closing off. Their unique molecular structure results in extraordinary macroscopic properties, including high tensile strength, high electrical conductivity, high ductility, high heat conductivity, and relative chemical inactivity (as it is cylindrical and "planar" — that is, it has no "exposed" atoms that can be easily displaced). One proposed use of carbon nanotubes is in paper batteries, developed in 2007 by researchers at Rensselaer Polytechnic Institute. Another highly speculative proposed use in the field of space technologies is to produce high-tensile carbon cables required by a space elevator.

Derivatives

Buckyballs and carbon nanotubes have been used as building blocks for a great varety of derivatives and larger structures, such as 

• Nested buckyballs ("carbon nano-onions" or "buckyonions") proposed for lubricants;
• Nested carbon nanotubes ("carbon megatubes");
• Linked "ball-and-chain" dimers (two buckyballs linked by a carbon chain);
• Rings of buckyballs linked together.

Heterofullerenes and non-carbon fullerenes

After the discovery of C60, many fullerenes have been synthesized (or studied theoretically by molecular modeling methods) in which some or all the carbon atoms are replaced by other elements. Inorganic nanotubes, in particular, have attracted much attention.

Silicon

Silicon buckyballs have been created around metal ions.

Boron

A type of buckyball which uses boron atoms, instead of the usual carbon, was predicted and described in 2007. The B
₈₀ structure, with each atom forming 5 or 6 bonds, is predicted to be more stable than the C
₆₀ buckyball. One reason for this given by the researchers is that B
₈₀ is actually more like the original geodesic dome structure popularized by Buckminster Fuller, which uses triangles rather than hexagons. However, this work has been subject to much criticism by quantum chemists as it was concluded that the predicted I_h symmetric structure was vibrationally unstable and the resulting cage undergoes a spontaneous symmetry break, yielding a puckered cage with rare T_h symmetry (symmetry of a volleyball). The number of six-member rings in this molecule is 20 and number of five-member rings is 12. There is an additional atom in the center of each six-member ring, bonded to each atom surrounding it. By employing a systematic global search algorithm, later it was found that the previously proposed B80 fullerene is not global minimum for 80 atom boron clusters and hence can not be found in nature. In the same paper by Sandip De et al., it was concluded that boron's energy landscape is significantly different from other fullerenes already found in nature hence pure boron fullerenes are unlikely to exist in nature.

Other elements

Inorganic (carbon-free) fullerene-type structures have been built with the disulfides of molibdenum (MoS₂), long used as a graphite-like lubricant, tungsten (WS₂), titanium (TiS₂) and niobium (NbS₂). These materials were found to be stable up to at least 350 tons/cm² (34.3 GPa).

Properties

Topology

Schlegel diagrams are often used to clarify the 3D structure of closed-shell fullerenes, as 2D projections are often not ideal in this sense.

In mathematical terms, the combinatorial topology (that is, the carbon atoms and the bonds between them, ignoring their positions and distances) of a closed-shell fullerene with a simple sphere-like mean surface (orientable, genus zero)can be represented as a convex polyhedron; more precisely, its one-dimensional skeleton, consisting of its vertices and edges. The Schlegel diagram is a projection of that skeleton onto one of the faces of the polyhedron, through a point just outside that face; so that all other vertices project inside that face.

• Schlegel diagrams of some fullerenes
• 

  C20 (dodecahedron)
  
• 

  C26
  
• 

  C60 (truncated icosahedron)
  
• 

  C70
  

The Schlegel diagram of a closed fullerene is a graph that is planar and 3-regular (or "cubic"; meaning that all vertices have degree 3.

A closed fullerene with sphere-like shell must have at least some cycles that are pentagons or heptagons. More precisely, if all the faces have 5 or 6 sides, it follows from Euler's polyhedron formula, V−E+F=2 (where V, E, F are the numbers of vertices, edges, and faces), that V must be even, and that there must be exactly 12 pentagons and V/2−10 hexagons. Similar constraints exist if the fullerene has heptagonal (seven-atom) cycles.

Open fullerenes, like carbon nanotubes and graphene, can consist entirely of hexagonal rings. In theory, a long nanotube with ends joined to form a closed torus-like sheet could also consist entirely of hexagons.

Bonding

Since each carbon atom is connected to only three neighbors, instead of the usual four, it is customary to describe those bonds as being a mixture of single and double covalent bonds.

Encapsulation

So-called endohedral fullerenes have ions or small molecules incorporated inside the cage atoms.

Research

In the early 2000s, the chemical and physical properties of fullerenes were a hot topic in the field of research and development. Popular Science discussed possible uses of fullerenes (graphene) in armor.

In the field of nanotechnology, heat resistance and superconductivity are some of the more heavily studied properties.

There are many calculations that have been done using ab-initio quantum methods applied to fullerenes. By DFT and TD-DFT methods one can obtain IR, Raman and UV spectra. Results of such calculations can be compared with experimental results.

Fullerene is an unusual reactant in many organic reactions such as the Bingel reaction discovered in 1993.

Aromaticity

Researchers have been able to increase the reactivity of fullerenes by attaching active groups to their surfaces. Buckminsterfullerene does not exhibit "superaromaticity": that is, the electrons in the hexagonal rings do not delocalize over the whole molecule. 

A spherical fullerene of n carbon atoms has n pi-bonding electrons, free to delocalize. These should try to delocalize over the whole molecule. The quantum mechanics of such an arrangement should be like one shell only of the well-known quantum mechanical structure of a single atom, with a stable filled shell for n = 2, 8, 18, 32, 50, 72, 98, 128, etc.; i.e. twice a perfect square number; but this series does not include 60. This 2(N + 1)² rule (with N integer) for spherical aromaticity is the three-dimensional analogue of Hückel's rule. The 10+ cation would satisfy this rule, and should be aromatic. This has been shown to be the case using quantum chemical modelling, which showed the existence of strong diamagnetic sphere currents in the cation.

As a result, C
₆₀ in water tends to pick up two more electrons and become an anion. The nC
₆₀ described below may be the result of C
₆₀ trying to form a loose metallic bond.

Reactions

Polymerization

Under high pressure and temperature, buckyballs collapse to form various one-, two-, or three-dimensional carbon frameworks. Single-strand polymers are formed using the Atom Transfer Radical Addition Polymerization (ATRAP) route.

"Ultrahard fullerite" is a coined term frequently used to describe material produced by high-pressure high-temperature (HPHT) processing of fullerite. Such treatment converts fullerite into a nanocrystalline form of diamond which has been reported to exhibit remarkable mechanical properties.

Fullerite (scanning electron microscope image)

Chemistry

Fullerenes are stable, but not totally unreactive. The sp²-hybridized carbon atoms, which are at their energy minimum in planar graphite, must be bent to form the closed sphere or tube, which produces angle strain. The characteristic reaction of fullerenes is electrophilic addition at 6,6-double bonds, which reduces angle strain by changing sp²-hybridized carbons into sp³-hybridized ones. The change in hybridized orbitals causes the bond angles to decrease from about 120° in the sp² orbitals to about 109.5° in the sp³ orbitals. This decrease in bond angles allows for the bonds to bend less when closing the sphere or tube, and thus, the molecule becomes more stable.

Other atoms can be trapped inside fullerenes to form inclusion compounds known as endohedral fullerenes. An unusual example is the egg-shaped fullerene Tb₃N@C
₈₄, which violates the isolated pentagon rule. Recent evidence for a meteor impact at the end of the Permian period was found by analyzing noble gases so preserved. Metallofullerene-based inoculates using the rhonditic steel process are beginning production as one of the first commercially viable uses of buckyballs.

Solubility

C
₆₀ in solution

 

C
₆₀ in extra virgin olive oil showing the characteristic purple color of pristine C
₆₀ solutions

 

Fullerenes are soluble in many organic solvents, such as toluene, chlorobenzene, and 1,2,3-trichloropropane. Solubilities are generally rather low, like 8 g/L for C60 in carbon disulfide. Still, fullerenes are the only known allotrope of carbon that can be dissolved in common solvents at room temperature. Among the best solvents is 1-chloronaphthalene, which will dissolve 51 g/L of C60.

Solutions of pure buckminsterfullerene have a deep purple color. Solutions of C
₇₀ are a reddish brown. The higher fullerenes C
₇₆ to C
₈₄ have a variety of colors. 

Millimeter-sized crystals of C
₆₀ and C
₇₀, both pure and solvated, can be grown from benzene solution. Crystallization of C60 from benzene solution below 30 °C (when solubility is maximum) yields a triclinic solid solvate C
₆₀·4C
₆H₆. Above 30 °C one obtains solvate-free fcc C
₆₀.

Quantum mechanics

In 1999, researchers from the University of Vienna demonstrated that wave-particle duality applied to molecules such as fullerene.

Superconductivity

Fullerenes are normally electrical insulators, but when crystallized with alkali metals, the resultant compound can be conducting or even superconducting.

Chirality

Some fullerenes (e.g. C
₇₆, C
₇₈, C
₈₀, and C
₈₄) are inherently chiral because they are D₂-symmetric, and have been successfully resolved. Research efforts are ongoing to develop specific sensors for their enantiomers.

Stability

Two theories have been proposed to describe the molecular mechanisms that make fullerenes. The older, “bottom-up” theory proposes that they are built atom-by-atom. The alternative “top-down” approach claims that fullerenes form when much larger structures break into constituent parts.

In 2013 researchers discovered that asymmetrical fullerenes formed from larger structures settle into stable fullerenes. The synthesized substance was a particular metallofullerene consisting of 84 carbon atoms with two additional carbon atoms and two yttrium atoms inside the cage. The process produced approximately 100 micrograms.

However, they found that the asymmetrical molecule could theoretically collapse to form nearly every known fullerene and metallofullerene. Minor perturbations involving the breaking of a few molecular bonds cause the cage to become highly symmetrical and stable. This insight supports the theory that fullerenes can be formed from graphene when the appropriate molecular bonds are severed.

Systematic naming

According to the IUPAC, to name a fullerene, one must cite the number of member atoms for the rings which comprise the fullerene, its symmetry point group in the Schoenflies notation, and the total number of atoms. For example, buckminsterfullerene C60 is systematically named (C
₆₀-I_h)[5,6]fullerene. The name of the point group should be retained in any derivative of said fullerene, even if that symmetry is lost by the derivation. 

To indicate the position of substituted or attached elements, the fullerene atoms are usually numbered in spiral pathway, usually starting with the ring on one of the main axes. If the structure of the fullerene does not allow such numbering, another starting atom was chosen to still achieve a spiral path sequence. 

The latter is the case for C70, which is (C
₇₀-D_5h(6))[5,6]fullerene in IUPAC notation. The symmetry D_5h(6) means that this is the isomer where the C₅ axis goes through a pentagon surrounded by hexagons rather than pentagons.

• 

  (C
  ₆₀-Ih)[5,6]fullerene carbon numbering.
  
• 

  (C
  ₇₀-D_5h(6))[5,6]fullerene carbon numbering.
  
• 

  (C
  ₇₀-D_5h(6))[5,6]fullerene; non-equivalent bonds shown by different colours.
  
• 

  3'H-Cyclopropa[1,2](C
  ₇₀-D_5h(6))[5,6] fullerene.
  
• 

  3'H-Cyclopropa[2,12](C
  ₇₀-D_5h(6))[5,6]fullerene.
  
• 

  C
  ₇₁-PCBM, [1,2]-isomer. IUPAC name is methyl 4-(3’-phenyl-3’H-cyclopropa[1,2](C
  ₇₀-D_5h(6))[5,6]fullerene-3’-yl)butyrate.
  

In IUPAC's nomenclature, fully saturated analogues of fullerenes are called fulleranes. If the mesh has other element(s) substituted for one or more cabons, the compound is named a heterofullerene. If a double bond is replaced by a methylene bridge –CH
2–, the resulting structure is a homofullerene. If an atom is fully deleted and missing valences saturated with hydrogen atoms, it is a norfullerene. When bonds are removed (both sigma and pi), the compound becomes secofullerene; if some new bonds are added in an unconventional order, it is a cyclofullerene.

Production

Fullerene production generally starts by producing fullerene-rich soot. The original (and still current) method was to send a large electric current between two nearby graphite electrodes in an inert atmosphere. The resulting electric arc vaporizes the carbon into a plasma that then cools into sooty residue. Alternatively, soot is produced by laser ablation of graphite or pyrolysis of aromatic hydrocarbons. Combustion is the most efficient process, developed at MIT.

These processes yield a mixture of various fullerenes and other forms of carbon. The fullerenes are then extracted from the soot using appropriate organic solvents and separated by chromatography. One can obtain milligram quantities of fullerenes with 80 atoms or more. C₇₆, C₇₈ and C₈₄ are available commercially.

Applications

Fullerenes have been extensively used for several biomedical applications including the design of high-performance MRI contrast agents, X-ray imaging contrast agents, photodynamic therapy and drug and gene delivery, summarized in several comprehensive reviews.

Medical research

In April 2003, fullerenes were under study for potential medicinal use: binding specific antibiotics to the structure to target resistant bacteria and even target certain cancer cells such as melanoma. The October 2005 issue of Chemistry & Biology contained an article describing the use of fullerenes as light-activated antimicrobial agents.

Tumor research

While past cancer research has involved radiation therapy, photodynamic therapy is important to study because breakthroughs in treatments for tumor cells will give more options to patients with different conditions. Recent experiments using HeLa cells in cancer research involves the development of new photosensitizers with increased ability to be absorbed by cancer cells and still trigger cell death. It is also important that a new photosensitizer does not stay in the body for a long time to prevent unwanted cell damage.

Fullerenes can be made to be absorbed by HeLa cells. The C
₆₀ derivatives can be delivered to the cells by using the functional groups L-phenylalanine, folic acid, and L-arginine among others.

Functionalizing the fullerenes aims to increase the solubility of the molecule by the cancer cells. Cancer cells take up these molecules at an increased rate because of an upregulation of transporters in the cancer cell, in this case amino acid transporters will bring in the L-arginine and L-phenylalanine functional groups of the fullerenes.

Once absorbed by the cells, the C
₆₀ derivatives would react to light radiation by turning molecular oxygen into reactive oxygen which triggers apoptosis in the HeLa cells and other cancer cells that can absorb the fullerene molecule. This research shows that a reactive substance can target cancer cells and then be triggered by light radiation, minimizing damage to surrounding tissues while undergoing treatment.

When absorbed by cancer cells and exposed to light radiation, the reaction that creates reactive oxygen damages the DNA, proteins, and lipids that make up the cancer cell. This cellular damage forces the cancerous cell to go through apoptosis, which can lead to the reduction in size of a tumor. Once the light radiation treatment is finished the fullerene will reabsorb the free radicals to prevent damage of other tissues. Since this treatment focuses on cancer cells, it is a good option for patients whose cancer cells are within reach of light radiation. As this research continues, the treatment may penetrate deeper into the body and be absorbed by cancer cells more effectively.

Safety and toxicity

Lalwani et al. published a comprehensive review on fullerene toxicity in 2013. These authors review the works on fullerene toxicity beginning in the early 1990s to present, and conclude that very little evidence gathered since the discovery of fullerenes indicate that C
₆₀ is toxic. The toxicity of these carbon nanoparticles is not only dose- and time-dependent, but also depends on a number of other factors such as:

• Type (e.g.: C
  ₆₀, C
  ₇₀, M@C
  ₆₀, M@C
  ₈₂;
• Functional groups used to water-solubilize these nanoparticles (e.g.: OH, COOH);
• Method of administration (e.g.: intravenous, intraperitoneal).

The authors therefore recommend assessing the pharmacology of every new fullerene- or metallofullerene-based complex individually as a different compound.

Popular culture

Examples of fullerenes in popular culture are numerous. Fullerenes appeared in fiction well before scientists took serious interest in them. In a humorously speculative 1966 column for New Scientist, David Jones suggested that it may be possible to create giant hollow carbon molecules by distorting a plane hexagonal net by the addition of impurity atoms.

On 4 September 2010, Google used an interactively rotatable fullerene C
₆₀ as the second 'o' in their logo to celebrate the 25th anniversary of the discovery of the fullerenes.

Wage slavery

From Wikipedia, the free encyclopedia

Wage slavery is a term used to draw an analogy between slavery and wage labor by focusing on similarities between owning and renting a person. It is usually used to refer to a situation where a person's livelihood depends on wages or a salary, especially when the dependence is total and immediate.

 

The term "wage slavery" has been used to criticize exploitation of labour and social stratification, with the former seen primarily as unequal bargaining power between labor and capital (particularly when workers are paid comparatively low wages, e.g. in sweatshops) and the latter as a lack of workers' self-management, fulfilling job choices and leisure in an economy. The criticism of social stratification covers a wider range of employment choices bound by the pressures of a hierarchical society to perform otherwise unfulfilling work that deprives humans of their "species character" not only under threat of starvation or poverty, but also of social stigma and status diminution.

Similarities between wage labor and slavery were noted as early as Cicero in Ancient Rome, such as in De Officiis. With the advent of the Industrial Revolution, thinkers such as Pierre-Joseph Proudhon and Karl Marx elaborated the comparison between wage labor and slavery, while Luddites emphasized the dehumanization brought about by machines. Before the American Civil War, Southern defenders of African American slavery invoked the concept of wage slavery to favorably compare the condition of their slaves to workers in the North. The United States abolished slavery after the Civil War, but labor union activists found the metaphor useful and appropriate. According to Lawrence Glickman, in the Gilded Age "[r]eferences abounded in the labor press, and it is hard to find a speech by a labor leader without the phrase".

The introduction of wage labor in 18th-century Britain was met with resistance, giving rise to the principles of syndicalism. Historically, some labor organizations and individual social activists have espoused workers' self-management or worker cooperatives as possible alternatives to wage labor.

History

Emma Goldman famously denounced wage slavery by saying: "The only difference is that you are hired slaves instead of block slaves"

 

The view that working for wages is akin to slavery dates back to the ancient world. In ancient Rome, Cicero wrote that "whoever gives his labor for money sells himself and puts himself in the rank of slaves".

In 1763, the French journalist Simon Linguet published an influential description of wage slavery:

The slave was precious to his master because of the money he had cost him ... They were worth at least as much as they could be sold for in the market ... It is the impossibility of living by any other means that compels our farm labourers to till the soil whose fruits they will not eat and our masons to construct buildings in which they will not live ... It is want that compels them to go down on their knees to the rich man in order to get from him permission to enrich him ... what effective gain [has] the suppression of slavery brought [him ?] He is free, you say. Ah! That is his misfortune ... These men ... [have] the most terrible, the most imperious of masters, that is, need. ... They must therefore find someone to hire them, or die of hunger. Is that to be free?

The view that wage work has substantial similarities with chattel slavery was actively put forward in the late 18th and 19th centuries by defenders of chattel slavery (most notably in the Southern states of the United States) and by opponents of capitalism (who were also critics of chattel slavery). Some defenders of slavery, mainly from the Southern slave states, argued that Northern workers were "free but in name – the slaves of endless toil" and that their slaves were better off. This contention has been partly corroborated by some modern studies that indicate slaves' material conditions in the 19th century were "better than what was typically available to free urban laborers at the time". In this period, Henry David Thoreau wrote that "[i]t is hard to have a Southern overseer; it is worse to have a Northern one; but worst of all when you are the slave-driver of yourself".

Some abolitionists in the United States regarded the analogy as spurious. They believed that wage workers were "neither wronged nor oppressed". Abraham Lincoln and the Republicans argued that the condition of wage workers was different from slavery as laborers were likely to have the opportunity to work for themselves in the future, achieving self-employment. The abolitionist and former slave Frederick Douglass initially declared "now I am my own master", upon taking a paying job. However, later in life he concluded to the contrary, saying "experience demonstrates that there may be a slavery of wages only a little less galling and crushing in its effects than chattel slavery, and that this slavery of wages must go down with the other". Douglass went on to speak about these conditions as arising from the unequal bargaining power between the ownership/capitalist class and the non-ownership/laborer class within a compulsory monetary market: "No more crafty and effective devise for defrauding the southern laborers could be adopted than the one that substitutes orders upon shopkeepers for currency in payment of wages. It has the merit of a show of honesty, while it puts the laborer completely at the mercy of the land-owner and the shopkeeper".

African American wage workers picking cotton on a plantation in the South

 

Self-employment became less common as the artisan tradition slowly disappeared in the later part of the 19th century. In 1869, The New York Times described the system of wage labor as "a system of slavery as absolute if not as degrading as that which lately prevailed at the South". E. P. Thompson notes that for British workers at the end of the 18th and beginning of the 19th centuries, the "gap in status between a 'servant,' a hired wage-laborer subject to the orders and discipline of the master, and an artisan, who might 'come and go' as he pleased, was wide enough for men to shed blood rather than allow themselves to be pushed from one side to the other. And, in the value system of the community, those who resisted degradation were in the right". A "Member of the Builders' Union" in the 1830s argued that the trade unions "will not only strike for less work, and more wages, but will ultimately abolish wages, become their own masters and work for each other; labor and capital will no longer be separate but will be indissolubly joined together in the hands of workmen and work-women". This perspective inspired the Grand National Consolidated Trades Union of 1834 which had the "two-fold purpose of syndicalist unions – the protection of the workers under the existing system and the formation of the nuclei of the future society" when the unions "take over the whole industry of the country". "Research has shown", summarises William Lazonick, "that the 'free-born Englishman' of the eighteenth century – even those who, by force of circumstance, had to submit to agricultural wage labour – tenaciously resisted entry into the capitalist workshop".

The use of the term "wage slave" by labor organizations may originate from the labor protests of the Lowell Mill Girls in 1836. The imagery of wage slavery was widely used by labor organizations during the mid-19th century to object to the lack of workers' self-management. However, it was gradually replaced by the more neutral term "wage work" towards the end of the 19th century as labor organizations shifted their focus to raising wages.

Karl Marx described capitalist society as infringing on individual autonomy because it is based on a materialistic and commodified concept of the body and its liberty (i.e. as something that is sold, rented, or alienated in a class society). According to Friedrich Engels:

The slave is sold once and for all; the proletarian must sell himself daily and hourly. The individual slave, property of one master, is assured an existence, however miserable it may be, because of the master's interest. The individual proletarian, property as it were of the entire bourgeois class which buys his labor only when someone has need of it, has no secure existence.

Similarities of wage work with slavery

Critics of wage work have drawn several similarities between wage work and slavery:

1. Since the chattel slave is property, his value to an owner is in some ways higher than that of a worker who may quit, be fired or replaced. The chattel slave's owner has made a greater investment in terms of the money paid for the slave. For this reason, in times of recession chattel slaves could not be fired like wage laborers. A "wage slave" could also be harmed at no (or less) cost. American chattel-slaves in the 19th century had improved their standard of living from the 18th century and – according to historians Fogel and Engerman – plantation records show that slaves worked less, were better fed and whipped only occasionally – their material conditions in the 19th century being "better than what was typically available to free urban laborers at the time". This was partially due to slave psychological strategies under an economic system different from capitalist wage-slavery. According to Mark Michael Smith of the Economic History Society, "although intrusive and oppressive, paternalism, the way masters employed it, and the methods slaves used to manipulate it, rendered slaveholders' attempts to institute capitalistic work regimens on their plantation ineffective and so allowed slaves to carve out a degree of autonomy".
2. Unlike a chattel slave, a wage laborer can (barring unemployment or lack of job offers) choose between employers, but those employers usually constitute a minority of owners in the population for which the wage laborer must work while attempts to implement workers' control on employers' businesses may be considered an act of theft or insubordination and thus be met with violence, imprisonment or other legal and social measures. The wage laborer's starkest choice is to work for an employer or to face poverty or starvation. If a chattel slave refuses to work, a number of punishments are also available; from beatings to food deprivation – although economically rational slave-owners practiced positive reinforcement to achieve best results and before losing their investment by killing an expensive slave.
3. Historically, the range of occupations and status positions held by chattel slaves has been nearly as broad as that held by free persons, indicating some similarities between chattel slavery and wage slavery as well.
4. Like chattel slavery, wage slavery does not stem from some immutable "human nature", but represents a "specific response to material and historical conditions" that "reproduce[s] the inhabitants, the social relations… the ideas… [and] the social form of daily life".
5. Similarities became blurred when proponents of wage labor won the American Civil War of 1861-1865, in which they competed for legitimacy with defenders of chattel slavery. Each side presented an over-positive assessment of their own system while denigrating the opponent.

According to American anarcho-syndicalist philosopher Noam Chomsky, workers themselves noticed the similarities between chattel and wage slavery. Chomsky noted that the 19th-century Lowell Mill Girls, without any reported knowledge of European Marxism or anarchism, condemned the "degradation and subordination" of the newly-emerging industrial system and the "new spirit of the age: gain wealth, forgetting all but self", maintaining that "those who work in the mills should own them". They expressed their concerns in a protest song during their 1836 strike: 

Oh! isn't it a pity, such a pretty girl as I
Should be sent to the factory to pine away and die?
Oh! I cannot be a slave, I will not be a slave,
For I'm so fond of liberty,
That I cannot be a slave.

Defenses of both wage labor and chattel slavery in the literature have linked the subjection of man to man with the subjection of man to nature – arguing that hierarchy and a social system's particular relations of production represent human nature and are no more coercive than the reality of life itself. According to this narrative, any well-intentioned attempt to fundamentally change the status quo is naively utopian and will result in more oppressive conditions. Bosses in both of these long-lasting systems argued that their respective systems created a lot of wealth and prosperity. In some sense, both did create jobs, and their investment entailed risk. For example, slave-owners risked losing money by buying chattel slaves who later became ill or died; while bosses risked losing money by hiring workers (wage slaves) to make products that did not sell well on the market. Marginally, both chattel and wage slaves may become bosses; sometimes by working hard. The "rags to riches" story occasionally comes to pass in capitalism; the "slave to master" story occurred in places like colonial Brazil, where slaves could buy their own freedom and become business owners, self-employed, or slave-owners themselves. Thus critics of the concept of wage slavery do not regard social mobility, or the hard work and risk that it may entail, as a redeeming factor.

Anthropologist David Graeber has noted that historically the first wage-labor contracts we know about – whether in ancient Greece or Rome, or in the Malay or Swahili city-states in the Indian Ocean – were in fact contracts for the rental of chattel slaves (usually the owner would receive a share of the money and the slaves another, with which to maintain their living expenses). According to Graeber, such arrangements were quite common in New World slavery as well, whether in the United States or in Brazil. C. L. R. James (1901-1989) argued that most of the techniques of human organization employed on factory workers during the Industrial Revolution first developed on slave plantations. Subsequent work "traces the innovations of modern management to the slave plantation".

Decline in use of term

By the end of the 19th century, both the use of the term wage slavery and its meaning declined

 

The usage of the term "wage slavery" shifted to "wage work" at the end of the 19th century as groups like the Knights of Labor and American Federation of Labor shifted to a more reformist, trade union ideology instead of worker's self-management. Much of the decline was caused by the rapid increase in manufacturing after the Industrial Revolution and the subsequent dominance of wage labor as a result. Another factor was immigration and demographic changes that led to ethnic tension between the workers.

As Hallgrimsdottir and Benoit point out:

[I]ncreased centralization of production ... declining wages ... [an] expanding ... labor pool ... intensifying competition, and ... [t]he loss of competence and independence experienced by skilled labor" meant that "a critique that referred to all [wage] work as slavery and avoided demands for wage concessions in favor of supporting the creation of the producerist republic (by diverting strike funds towards funding ... co-operatives, for example) was far less compelling than one that identified the specific conditions of slavery as low wages.

Treatment in various economic systems

Adam Smith

 

Some anti-capitalist thinkers claim that the elite maintain wage slavery and a divided working class through their influence over the media and entertainment industry, educational institutions, unjust laws, nationalist and corporate propaganda, pressures and incentives to internalize values serviceable to the power structure, state violence, fear of unemployment, and a historical legacy of exploitation and profit accumulation/transfer under prior systems, which shaped the development of economic theory. Adam Smith noted that employers often conspire together to keep wages low and have the upper hand in conflicts between workers and employers:

The interest of the dealers ... in any particular branch of trade or manufactures, is always in some respects different from, and even opposite to, that of the public... [They] have generally an interest to deceive and even to oppress the public ... We rarely hear, it has been said, of the combinations of masters, though frequently of those of workmen. But whoever imagines, upon this account, that masters rarely combine, is as ignorant of the world as of the subject. Masters are always and everywhere in a sort of tacit, but constant and uniform combination, not to raise the wages of labor above their actual rate ... It is not, however, difficult to foresee which of the two parties must, upon all ordinary occasions, have the advantage in the dispute, and force the other into a compliance with their terms.

Capitalism

The concept of wage slavery could conceivably be traced back to pre-capitalist figures like Gerrard Winstanley from the radical Christian Diggers movement in England, who wrote in his 1649 pamphlet, The New Law of Righteousness, that there "shall be no buying or selling, no fairs nor markets, but the whole earth shall be a common treasury for every man" and "there shall be none Lord over others, but every one shall be a Lord of himself".

Aristotle stated that "the citizens must not live a mechanic or a mercantile life (for such a life is ignoble and inimical to virtue), nor yet must those who are to be citizens in the best state be tillers of the soil (for leisure is needed both for the development of virtue and for active participation in politics)", often paraphrased as "all paid jobs absorb and degrade the mind". Cicero wrote in 44 BC that "vulgar are the means of livelihood of all hired workmen whom we pay for mere manual labour, not for artistic skill; for in their case the very wage they receive is a pledge of their slavery". Somewhat similar criticisms have also been expressed by some proponents of liberalism, like Silvio Gesell and Thomas Paine; Henry George, who inspired the economic philosophy known as Georgism; and the Distributist school of thought within the Catholic Church. 

Pinkerton guards escort strikebreakers in Buchtel, Ohio, 1884

 

Red Army troops attack Kronstadt libertarian socialist "wage slavery" critics who had demanded among other things that "handicraft production be authorized provided it does not utilize wage labour"

 

To Karl Marx and anarchist thinkers like Mikhail Bakunin and Peter Kropotkin, wage slavery was a class condition in place due to the existence of private property and the state. This class situation rested primarily on:

1. The existence of property not intended for active use;
2. The concentration of ownership in few hands;
3. The lack of direct access by workers to the means of production and consumption goods; and
4. The perpetuation of a reserve army of unemployed workers.

And secondarily on:

1. The waste of workers' efforts and resources on producing useless luxuries;
2. The waste of goods so that their price may remain high; and
3. The waste of all those who sit between the producer and consumer, taking their own shares at each stage without actually contributing to the production of goods, i.e. the middle man.

Fascism

Fascist economic policies were more hostile to independent trade unions than modern economies in Europe or the United States. Fascism was more widely accepted in the 1920s and 1930s, and foreign corporate investment (notably from the United States) in Italy and Germany increased after the fascists took power.

Fascism has been perceived by some notable critics, like Buenaventura Durruti, to be a last resort weapon of the privileged to ensure the maintenance of wage slavery:

No government fights fascism to destroy it. When the bourgeoisie sees that power is slipping out of its hands, it brings up fascism to hold onto their privileges.

Psychological effects

Wilhelm von Humboldt

 

According to Noam Chomsky, analysis of the psychological implications of wage slavery goes back to the Enlightenment era. In his 1791 book The Limits of State Action, classical liberal thinker Wilhelm von Humboldt explained how "whatever does not spring from a man's free choice, or is only the result of instruction and guidance, does not enter into his very nature; he does not perform it with truly human energies, but merely with mechanical exactness" and so when the laborer works under external control, "we may admire what he does, but we despise what he is". Because they explore human authority and obedience, both the Milgram and Stanford experiments have been found useful in the psychological study of wage-based workplace relations.

Self-identity problems and stress

According to research, modern work provides people with a sense of personal and social identity that is tied to:

1. The particular work role, even if unfulfilling; and
2. The social role it entails e.g. family bread-winning, friendship forming and so on.

Thus job loss entails the loss of this identity.

Erich Fromm argued that if a person perceives himself as being what he owns, then when that person loses (or even thinks of losing) what he "owns" (e.g. the good looks or sharp mind that allow him to sell his labor for high wages) a fear of loss may create anxiety and authoritarian tendencies because that person's sense of identity is threatened. In contrast, when a person's sense of self is based on what he experiences in a state of being (creativity, love, sadness, taste, sight and the like) with a less materialistic regard for what he once had and lost, or may lose, then less authoritarian tendencies prevail. In his view, the state of being flourishes under a worker-managed workplace and economy, whereas self-ownership entails a materialistic notion of self, created to rationalize the lack of worker control that would allow for a state of being.

Investigative journalist Robert Kuttner analyzed the work of public-health scholars Jeffrey Johnson and Ellen Hall about modern conditions of work and concludes that "to be in a life situation where one experiences relentless demands by others, over which one has relatively little control, is to be at risk of poor health, physically as well as mentally". Under wage labor, "a relatively small elite demands and gets empowerment, self-actualization, autonomy, and other work satisfaction that partially compensate for long hours" while "epidemiological data confirm that lower-paid, lower-status workers are more likely to experience the most clinically damaging forms of stress, in part because they have less control over their work".

Wage slavery and the educational system that precedes it "implies power held by the leader. Without power the leader is inept. The possession of power inevitably leads to corruption ... in spite of ... good intentions ... [Leadership means] power of initiative, this sense of responsibility, the self-respect which comes from expressed manhood, is taken from the men, and consolidated in the leader. The sum of their initiative, their responsibility, their self-respect becomes his ... [and the] order and system he maintains is based upon the suppression of the men, from being independent thinkers into being 'the men' ... In a word, he is compelled to become an autocrat and a foe to democracy". For the "leader", such marginalisation can be beneficial, for a leader "sees no need for any high level of intelligence in the rank and file, except to applaud his actions. Indeed such intelligence from his point of view, by breeding criticism and opposition, is an obstacle and causes confusion". Wage slavery "implies erosion of the human personality ... [because] some men submit to the will of others, arousing in these instincts which predispose them to cruelty and indifference in the face of the suffering of their fellows".

Psychological control

Higher wages

In 19th-century discussions of labor relations, it was normally assumed that the threat of starvation forced those without property to work for wages. Proponents of the view that modern forms of employment constitute wage slavery, even when workers appear to have a range of available alternatives, have attributed its perpetuation to a variety of social factors that maintain the hegemony of the employer class.

In an account of the Lowell Mill Girls, Harriet Hanson Robinson wrote that generously high wages were offered to overcome the degrading nature of the work:

At the time the Lowell cotton mills were started the caste of the factory girl was the lowest among the employments of women. ... She was represented as subjected to influences that must destroy her purity and self respect. In the eyes of her overseer she was but a brute, a slave, to be beaten, pinched and pushed about. It was to overcome this prejudice that such high wages had been offered to women that they might be induced to become mill girls, in spite of the opprobrium that still clung to this degrading occupation.

In his book Disciplined Minds, Jeff Schmidt points out that professionals are trusted to run organizations in the interests of their employers. Because employers cannot be on hand to manage every decision, professionals are trained to "ensure that each and every detail of their work favors the right interests–or skewers the disfavored ones" in the absence of overt control:

The resulting professional is an obedient thinker, an intellectual property whom employers can trust to experiment, theorize, innovate and create safely within the confines of an assigned ideology.

Parecon (participatory economics) theory posits a social class "between labor and capital" of higher paid professionals such as "doctors, lawyers, engineers, managers and others" who monopolize empowering labor and constitute a class above wage laborers who do mostly "obedient, rote work".

Lower wages

The terms "employee" or "worker" have often been replaced by "associate". This plays up the allegedly voluntary nature of the interaction while playing down the subordinate status of the wage laborer as well as the worker-boss class distinction emphasized by labor movements. Billboards as well as television, Internet and newspaper advertisements consistently show low-wage workers with smiles on their faces, appearing happy.

Job interviews and other data on requirements for lower skilled workers in developed countries – particularly in the growing service sector – indicate that the more workers depend on low wages and the less skilled or desirable their job is, the more employers screen for workers without better employment options and expect them to feign unremunerative motivation. Such screening and feigning may not only contribute to the positive self-image of the employer as someone granting desirable employment, but also signal wage-dependence by indicating the employee's willingness to feign, which in turn may discourage the dissatisfaction normally associated with job-switching or union activity.

At the same time, employers in the service industry have justified unstable, part-time employment and low wages by playing down the importance of service jobs for the lives of the wage laborers (e.g. just temporary before finding something better, student summer jobs and the like).

In the early 20th century, "scientific methods of strikebreaking" were devised – employing a variety of tactics that emphasized how strikes undermined "harmony" and "Americanism".

Workers' self-management

Noam Chomsky has written in support of labour movements

Some social activists objecting to the market system or price system of wage working historically have considered syndicalism, worker cooperatives, workers' self-management and workers' control as possible alternatives to the current wage system.

Labor and government

The American philosopher John Dewey believed that until "industrial feudalism" is replaced by "industrial democracy", politics will be "the shadow cast on society by big business". Thomas Ferguson has postulated in his investment theory of party competition that the undemocratic nature of economic institutions under capitalism causes elections to become occasions when blocs of investors coalesce and compete to control the state.

Noam Chomsky has argued that political theory tends to blur the 'elite' function of government:

Modern political theory stresses Madison's belief that "in a just and a free government the rights both of property and of persons ought to be effectually guarded." But in this case too it is useful to look at the doctrine more carefully. There are no rights of property, only rights to property that is, rights of persons with property,...

[In] representative democracy, as in, say, the United States or Great Britain […] there is a monopoly of power centralized in the state, and secondly – and critically – […] the representative democracy is limited to the political sphere and in no serious way encroaches on the economic sphere […] That is, as long as individuals are compelled to rent themselves on the market to those who are willing to hire them, as long as their role in production is simply that of ancillary tools, then there are striking elements of coercion and oppression that make talk of democracy very limited, if even meaningful.

In this regard, Chomsky has used Bakunin's theories about an "instinct for freedom", the militant history of labor movements, Kropotkin's mutual aid evolutionary principle of survival and Marc Hauser's theories supporting an innate and universal moral faculty, to explain the incompatibility of oppression with certain aspects of human nature.

Influence on environmental degradation

Loyola University philosophy professor John Clark and libertarian socialist philosopher Murray Bookchin have criticized the system of wage labor for encouraging environmental destruction, arguing that a self-managed industrial society would better manage the environment. Like other anarchists, they attribute much of the Industrial Revolution's pollution to the "hierarchical" and "competitive" economic relations accompanying it.

Employment contracts

Some criticize wage slavery on strictly contractual grounds, e.g. David Ellerman and Carole Pateman, arguing that the employment contract is a legal fiction in that it treats human beings juridically as mere tools or inputs by abdicating responsibility and self-determination, which the critics argue are inalienable. As Ellerman points out, "[t]he employee is legally transformed from being a co-responsible partner to being only an input supplier sharing no legal responsibility for either the input liabilities [costs] or the produced outputs [revenue, profits] of the employer's business". Such contracts are inherently invalid "since the person remain[s] a de facto fully capacitated adult person with only the contractual role of a non-person" as it is impossible to physically transfer self-determination. As Pateman argues:

The contractarian argument is unassailable all the time it is accepted that abilities can 'acquire' an external relation to an individual, and can be treated as if they were property. To treat abilities in this manner is also implicitly to accept that the 'exchange' between employer and worker is like any other exchange of material property . . . The answer to the question of how property in the person can be contracted out is that no such procedure is possible. Labour power, capacities or services, cannot be separated from the person of the worker like pieces of property.

In a modern liberal capitalist society, the employment contract is enforced while the enslavement contract is not; the former being considered valid because of its consensual/non-coercive nature and the latter being considered inherently invalid, consensual or not. The noted economist Paul Samuelson described this discrepancy:

Since slavery was abolished, human earning power is forbidden by law to be capitalized. A man is not even free to sell himself; he must rent himself at a wage.

Some advocates of right-libertarianism, among them philosopher Robert Nozick, address this inconsistency in modern societies arguing that a consistently libertarian society would allow and regard as valid consensual/non-coercive enslavement contracts, rejecting the notion of inalienable rights:

The comparable question about an individual is whether a free system will allow him to sell himself into slavery. I believe that it would.

Others like Murray Rothbard allow for the possibility of debt slavery, asserting that a lifetime labour contract can be broken so long as the slave pays appropriate damages:

[I]f A has agreed to work for life for B in exchange for 10,000 grams of gold, he will have to return the proportionate amount of property if he terminates the arrangement and ceases to work.

Schools of economics

In the philosophy of mainstream, neoclassical economics, wage labor is seen as the voluntary sale of one's own time and efforts, just like a carpenter would sell a chair, or a farmer would sell wheat. It is considered neither an antagonistic nor abusive relationship and carries no particular moral implications.

Austrian economics argues that a person is not "free" unless they can sell their labor because otherwise that person has no self-ownership and will be owned by a "third party" of individuals.

Post-Keynesian economics perceives wage slavery as resulting from inequality of bargaining power between labor and capital, which exists when the economy does not "allow labor to organize and form a strong countervailing force".

The two main forms of socialist economics perceive wage slavery differently:

1. Libertarian socialism sees it as a lack of workers' self-management in the context of substituting state and capitalist control with political and economic decentralization and confederation.
2. State socialists view it as an injustice perpetrated by capitalists and solved through nationalization and social ownership of the means of production.