Chain orientation in deformed networks via NMR

Abstract

AbstractWe quantitatively simulate the deuterium NMR linshapes that result when labelled poly(dimethyl siloxane)‐d6 networks are uniaxially strained. The inferred microscopic reorientational processes that the chain segments exercise in (deformed) networks are indicative of dynamic heterogeneity wherein different parts of the network average the residual quadrupolar interaction to different degrees. The higher the molecular weight between crosslinks, the larger the fraction of slow reorienting species suggesting that chain disinterpersion may be the rate‐limiting contribution to segmental motion in long chains. Our depiction of the network at ambient temperature is that of a liquid wherein motionally distinct segmental domains are characterized by different rotational correlation times. However, under uniaxial extention the fluid network is similar to an anisotropic liquid having macroscopically homogeneous (nematic‐like) segmental orientational order that is characterized by a single order parameter. Order parameters extracted from the NMR simulation are discussed in terms of classical descriptions of how macroscopic strain induces microscopic orientational order in Gaussian networks.