Birefringence of Rubber during Creep and Recovery

Abstract

Measurements of creep and recovery of lightly cross-linked polybutadiene, carried out in both shear and compression geometries, reveal two deviations from the stress optical law: the birefringence increases during the constant stress creep, and the birefringence is not zero during the stress-free recovery. Most interestingly, the sign of the birefringence during recovery was found to be opposite to that during creep. This implies that the chain segments have a net orientation opposite to the macroscopic deformation.

Strain-Crystallization of Guayule and Hevea Rubbers

“…Although Equation (3) is often regarded as generally valid for amorphous polymers, 50 exceptions to this law are known. 28,51,52 The birefringence was measured for the four rubbers over a range of tensile strains ( Figure 9). At low strains, proportionality between ∆n and the uniaxial true stress is observed, yielding Fig.…”

Anisotropic thermal transport in a crosslinked polyisoprene rubber subjected to uniaxial elongation

“…The stress‐thermal rule in eq 2 is analogous to the stress‐optic rule, which provides a linear relation between the refractive index n and stress tensors20 where C o is the stress‐optic coefficient. The stress‐optic rule has been examined for a number of polymeric materials that include polymer solutions,21 polymer melts22, 23 and crosslinked polymers24–26 and found to be valid at moderate deformations. Violations of the stress‐optic rule have been observed at large deformations, which are believed be a consequence of the finite extensibility of polymer chain segments 20.…”

Relationship between Photoelasticity of Polyurethane and Dielectric Anisotropy of Diisocyanate, and Application of High-Photoelasticity Polyurethane to Tactile Sensor for Robot Hands

“…Thus far, various methods of detecting stress inside a polymer based on the birefringence of light have been studied. For example, methods of irradiating a flexible and transparent polymer sheet with circularly polarized light and observing the fringes in the transmitted light through a polarizing filter [ 1 , 2 , 3 , 4 , 5 , 6 ], and methods of measuring changes in refractive index by stretching the polymer [ 7 , 8 ] have been studied. A tactile sensor [ 9 ] for stress detection based on the polarized light and the photoelasticity of transparent, flexible, and robust polyurethane is expected to realize a highly sensitive robot hand tactile sensor that imitates the tactile sensation of a human finger, but the performance of the sensor has not yet been fully verified.…”

“…In addition, for hydrogels [ 7 ], polybutadiene [ 8 ], acrylic copolymers [ 12 ], nylon [ 13 , 14 ], and gelatin gels [ 15 ], the magnitude of their birefringence is proportional to the strain. The birefringence mechanism of these polymers is also considered to be the same as that of polyurethane.…”