Studying Stress and Conductivity Relaxations of CNT-Infused Rubber Materials*

Stress relaxation experiments are important to study polymer properties. We are focused on the parallel study of stress relaxation and conductivity relaxation in carbon nanotube (CNT) infused rubber composites. Observations of relaxations are essential for predicting future behavior, as the polymers retain memory in the form of elastic deformations with slow relaxation times. We constructed a specialized device for stress relaxation experiments. Our device applies calibrated strain in the form of stretching and measures conductivity and force responses over time. The setup is housed in an isothermal chamber whereby a proportional-integral controller maintains constant temperatures. Initial ambient temperature data shows clear force fluctuations corresponding to room temperature changes throughout a day. The several weeks of data needed to observe important relaxation features are thus only possible in the absence of temperature fluctuations. With this system, stress-relaxation data of various samples are obtained and compared with polymers of various CNT compositions. The setup design and relaxation data will be shown to demonstrate the measurement technique, the scales by which these relaxations occur, and how the force and conductivity relaxations of similar polymers compare.