Correlating Material Transfer and Charge Transfer in Contact Electrification

Static charge on surfaces of materials is generated when two solid surfaces come into contact and are then separated. It is important to understand the phenomenon because the influence of static charge on surfaces is widely felt in our daily lives and can have a wide range of applications or undesirable effects in industry. Although the phenomenon has been observed since antiquity, the fundamental mechanism that underlies the generation of charge on insulating surfaces is still not known. After many decades of research, different mechanisms have been proposed, including electron and ion transfer. One other possibility has been discussed to a lesser extent: material transfer (i.e., the transfer of quantities of charged materials). This study seeks to investigate the significance of material transfer by correlating the amount of charge transferred and the amount of material transferred from one surface to another after contact. The investigation involved varying the degree of softness of a polymer (polydimethylsiloxane; PDMS), contact-charging it against another reference material, and analyzing the surfaces of the materials after contact. Results showed that when more material transferred, more charge was generated. An explanation for these results is that the surface of PDMS experienced heterolytic cleavage of bonds, which resulted in the generation of charge. When more cleavage of bonds occurred, more charge was generated, and more materials were transferred. Hence, material transfer seems to have an important contribution for the generation of charge by contact.