Triboelectric effect
Triboelectric charge plays a major role in industries such as packaging of pharmaceutical powders,[3][7] and in many processes such as dust storms[8] and planetary formation.
While many aspects of the triboelectric effect are now understood and extensively documented, significant disagreements remain in the current literature about the underlying details.
The name ēlektron (ἤλεκτρον) is Greek for amber,[10][11] which is connected to the recording of electrostatic charging by Thales of Miletus around 585 BCE,[12] and possibly others even earlier.
[11] Syrian women used amber whorls in weaving and exploited the triboelectric properties, as noted by Pliny the Elder.
Archbishop Eustathius of Thessalonica, Greek scholar and writer of the 12th century, records that Woliver, king of the Goths, could draw sparks from his body.
[16][18] He discovered that many more materials than amber such as sulphur, wax, glass could produce static electricity when rubbed, and that moisture prevented electrification.
Others such as Sir Thomas Browne made important contributions slightly later, both in terms of materials and the first use of the word electricity in Pseudodoxia Epidemica.
[21][22] These names corresponded to the glass (vitreous) rods and bituminous coal, amber, or sealing wax (resinous) used in du Fay's experiments.
In a series of papers he: was one of the first to mention some of the failings of the triboelectric series, also showing that heat had a major effect on tribocharging;[29] analyzed in detail where different materials would fall in a triboelectric series, at the same time pointing out anomalies;[1] separately analyzed glass and solid elements[30] and solid elements and textiles,[31] carefully measuring both tribocharging and friction; analyzed charging due to air-blown particles;[32] demonstrated that surface strain and relaxation played a critical role for a range of materials,[33][34] and examined the tribocharging of many different elements with silica.
[35] Much of this work predates an understanding of solid state variations of energies levels with position, and also band bending.
An example is rubbing a plastic pen on a shirt sleeve made of cotton, wool, polyester, or the blended fabrics used in modern clothing.
For instance, as early as 1910, Jaimeson observed that for a piece of cellulose, the sign of the charge was dependent upon whether it was bent concave or convex during rubbing.
[42] In 1926, Shaw pointed out that with two pieces of identical material, the sign of the charge transfer from "rubber" to "rubbed" could change with time.
[57] An alternative view (beyond the Born–Oppenheimer approximation) is that sliding acts as a quantum mechanical pump which can excite electrons to go from one material to another.
[60] Other papers have considered that local bending at the nanoscale produces voltages which help drive charge transfer via the flexoelectric effect.
The triboelectric charge density of the tested materials was measured with respect to liquid mercury in a glove box under well-defined conditions, with fixed temperature, pressure and humidity.
Combined, the dipole and the MIP lead to a potential barrier for electrons to leave a material which is called the work function.
[88][89][90][91] If the additional polarization due to strain (piezoelectricity) or bending of samples (flexoelectricity) is included[61][62] this can explain observations such as the effect of curvature[41] or inhomogeneous charging.
The debate remains to this day with, for instance, George M. Whitesides advocating for ions,[92] while Diaz and Fenzel-Alexander[93] as well as Laurence D. Marks support both,[61][62] and others just electrons.
[94] In the latter half of the 20th century the Soviet school led by chemist Boris Derjaguin argued that triboelectricity and the associated phenomenon of triboluminescence are fundamentally irreversible.
[95] A similar point of view to Derjaguin's has been more recently advocated by Seth Putterman and his collaborators at the University of California, Los Angeles (UCLA).
[96][97] A proposed theory of triboelectricity as a fundamentally irreversible process was published in 2020 by theoretical physicists Robert Alicki and Alejandro Jenkins.
[58] Alicki and Jenkins argue that such an irreversible pumping is needed to understand how the triboelectric effect can generate an electromotive force.
[58][98] Generally, increased humidity (water in the air) leads to a decrease in the magnitude of triboelectric charging.
Increasing humidity may lead to the formation of water bridges between contacting materials that promote the transfer of ions.
[101] Friction[106] is a retarding force due to different energy dissipation process such as elastic and plastic deformation, phonon and electron excitation, and also adhesion.
There is evidence for a retarding Coulomb force between asperities of different charges,[110] and an increase in the adhesion from contact electrification when geckos walk on water.
[111] There is also evidence of connections between jerky (stick–slip) processes during sliding with charge transfer,[44] electrical discharge[112] and x-ray emission.
[124] These are analogous to the electromechanical terms for solids where electric fields can occur due to elastic strains as described earlier.
some examples are: While the simple case of stroking a cat is familiar to many, there are other areas in modern technological civilization where triboelectricity is exploited or is a concern:
