J. Soc. Cosmet. Chem., 28, 549-569 (September 1977) The electrostatic properties of human hair ANTHONY C. LUNN and ROBERT E. EVANS, American Cyanamid Company, Chemical Research Division, Stamford, CT 06904. Received October 12, 1976. Presented, Ninth IFSCC Congress, Boston, MA.,June 1976. Synopsis Three factors have been studied which are significant in the development of ELECTROSTATIC CHARGE on HAIR FIBERS: (1) the charge generated by separation between hair fibers and brush or comb (2) the mobility of charge on the fibers and (3) the distribution of charge along the fiber length. Instrumentation has been developed to measure each of these parameters, and the effect upon them of quaternary ammonium compounds and other fiber treatments. Quaternary antistatic agents are found to reduce substantially the charge generated on the fibers the half-life of charge mobility varies with the quantity of agent on the hair. The density of charge is greatest near the fiber tips, corresponding to the region of a peak in the combing force. It is concluded that the mechanism of action of these antistatic agents is primarily one of lubrication: a reduction in combing force leads to a reduc- tion of static charge generated on the hair. INTRODUCTION While the phenomenon of static electrification, first recorded by the ancient Greeks, has intrigued physicists over the centuries, our knowledge and understanding of electrostatics as related to practical problems remains even today at an elementary level. Yet problems associated with the buildup of electrostatic charge on a body are of commercial importance in many industries. For example, static electrification has been of major concern to textile manufacturers and users, especially since the development of synthetic polymers, and, of course, to the plastics industry itself. In the hair-care in- dustry, problems arise from static charges in brushed or combed hair, particularly at low humidity levels. The fibers are mutually repelled by these charges, thereby show- ing the phenomenon of "flyaway" which is unattractive and which makes hair hard to comb or to keep in place. 549

550 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Substantial efforts have been made to develop means to ameliorate electrostatic prob- lems. On human hair, cationic quaternary ammonium compounds are in common use for this purpose. Little is known of the mechanism of action of such antistatic agents, however, and in such circumstances it is difficult to develop improved materials. Hypothetical reasoning led us to believe that 3 principal factors contribute to the severity of the "flyaway" of human hair. The first is the magnitude of charge which is generated by the contact and subsequent separation of hair and comb. The second fac- tor is the mobility of charge and its rate of dissipation from the fibers. The third factor is the distribution of charge along the length of the combed fibers. In principle, the desired objective of reduced electrostatic effects can be approached by altering each one of these factors. Either a reduction in the magnitude of charge generated or an increase in the mobility of that charge can be effective. Mutual repulsion of fibers can also be altered by changing the distribution of charge density along the length of the fiber. The generation of static charges when unlike objects are rubbed together arises from an unequal transfer of charges across the interface between two bodies in contact. When the bodies are separated, they are each left with net charges of opposite sign and of magnitude equal to the differential charge transferred. Theoretical aspects of this process are discussed by Vick (1), Arthur (2), and Hersh and Montgomery (3). The charge generated by rubbing filaments together has been studied experimentally by Hersh and Montgomery (4). Henry eta/. (5) measured both charge magnitude and the rate of its decay from rubbed textile fabrics. Barber and Posner (6) measured the charge generated by combing human hair. Mills et aL (7) also attempted to measure the charge generated by combing hair, but the method employed did not permit a distinc- tion to be made between generation and dissipation mechanisms. The rate of dissipation of charge to electrical ground depends on the ease of movement of charges on the body, a property which we here call "charge mobility." A comple- mentary phenomenon, the rate at which charge develops on the body in the presence of an electrostatic potential, is similarly determined by the charge mobility. Charge mobility is itself dependent primarily on the conductivity of the material (5,8). Sha- shoua (9) measured the rates of build up and decay of charge from films and fabrics. Ballou (10) measured decay rates from textiles he also considered charge generated on moving yarns. Unfortunately, little information is available on the mobility of charge on human hair. The distribution of charge along the length of a fiber, although noted by Ballou (10) as important, has received very little investigation. The only other discussion of such phenomena is by Sprokel (11), who studied the variation of charge along a running textile yarn. In a published work, the relative importance of charge generation, mobility, and dis- tribution to the incidence and control of electrostatic charges is rarely considered, and a clear distinction between them is not always drawn. Instrumentation has, therefore, been developed at these laboratories to study each of these parameters separately, on treated and untreated hair, with the intention of evaluating their relative importance and of elucidating the mechanism of action of antistatic agents on human hair.