Effect of dilution on the orientational order induced in strained polymer networks, as measured by 2H nuclear magnetic resonance

Abstract

The orientational order generated in uniaxially strained rubbers is investigated as a function of the degree of swelling. This study is performed on polydimethylsiloxane (PDMS) networks diluted either with conventional solvents (such as chloroform) or with linear PDMS chains. Deuterium ( 2H) nuclear magnetic resonance is used to monitor selectively the ordering of each component of the solution (the network chains or the diluent molecules). The concentration dependence of the order in the range of network volume fractions larger than 80% is similar for both networks and diluents but depends on the nature of the diluent: the order decreases steeply when chloroform is added whereas it remains unaltered in the presence of free chains. These results mean that the orientational couplings between chain segments (introduced previously by Deloche et al. to account for the free chain orientation) are variably screened according to the nature of the diluent molecules. Introducing these interchain effects in a mean-field description of polymer networks allows one to discuss these observations quantitatively.