Rubber Surface Change and Static Charging under Periodic Stress

Abstract

Rubber materials play an important role in robotics, due to their sensing and actuating abilities, that are exploited in soft smart materials endowed with shape-adaptive and electroadhesive properties. The application of an electric field produces non-linear deformation that has been extensively modelled, but is not understood at the molecular level. The symmetric effect (the production of an electric field due to rubber deformation) was recently discovered and explained as follows: rubber surface chemical composition and adsorptive properties change during rubber deformation, allowing the surface to exchange charge with the atmosphere. The present work describes the complex surface morphology and microchemistry of tubing made from vulcanized natural rubber, showing that it is rough and made from two domain types: stiffer elevations containing Br or Al (depending on the sample used) and O, that rise above an elastic base that is exempt of elements other than C and H. The surface area fraction occupied by the elastic base is higher in the strained rubber than when it is relaxed. Electrostatic potential on rubber surfaces was measured as a function of the stretching frequency, using Kelvin electrodes and showing frequency-dependent potential variation. This is explained considering charge exchange between the atmosphere and rubber surface, mediated by water vapor adsorbed in the stretched rubber and trapped when it relaxes.Colloids Interfaces 2018, 2, 55 2 of 11 of rubber performance in many important situations, but this does not benefit from knowledge on the molecular mechanisms of the observed phenomena.Recent work from this group described a new finding on the electrostatic behavior of elastomers: in short, rubber tube stretching, followed by relaxation, provokes the appearance of transient excess charge that is more pronounced under higher relative humidity [14]. This effect is not related to any existing electrostatic charging phenomenon (piezoelectricity, flexoelectricity, triboelectricity, and contact charging) and a new mechanism was then proposed to explain charge pick-up and dissipation by stretched elastomers, as the result of water adsorption and the partition of water ions (H + and OH − ) in the rubber-air interface, due to periodic rubber surface modification.Other unexpected findings on electrostatic phenomena in dielectrics have been described recently, leading to a revision of widespread ideas on electrostatic charging and its mechanisms [15]. Important aspects of electrostatic phenomena are not well understood [16][17][18], but tribo-and piezoelectricity are important sources of the electrostatic potentials detected in anthropic environments, often reaching many-thousand volts. They are currently used in nanotribogenerators, with great success. This is creating new opportunities for energy scavenging [19][20][21], and it is probably relevant to the prevention of harmful electrostatic discharge.Knowledge of the electrostatic behavior of elastomers is more limited than in the case of semicrystallin...

FEM Based Elasto-Electric Analysis of Elastomers for Pharmaceutical Applications

“…7, it can be seen that the maximum deformation is about 50mm, whereas the maximum electric potential developed is 3100V. The results are within 2% of the results obtained in [27] and this similarity in the results proves the validity of the mechanism used for FEM analysis used in this research (Slight variation of deformation in the results from [27] is due to unavailability of width and height data of Silicon Rubber specimen). However, in the case of PVC, minimum deformation i.e.…”

“…Silicon Rubber, Nitrile (NBR) and Poly Vinyl Chloride (PVC) are studied in this work on COMSOL multi-physics software. At initial level, a model has been developed in COMSOL keeping in view the study carried out in [27]. Afterwards the same study has been carried out and the results are regenerated in order to evaluate / validate the developed model.…”

“…Recent development presents various research being carried out in electric field induced in elastomers by change in shapes. Detailed work on the complex surface morphology and of a tube of vulcanized natural rubber has been presented in [27]. Electric field effect develops a non-linear deformation which is modelled but is not studied at molecular level.…”