Cholesteric pitch of aqueous hydroxypropylcellulose in the presence of synthetic polyelectrolytes

Abstract

Cholesteric pitches (D) of mesophases of aqueous hydroxypropyl cellulose (HPC) have been measured by the reflection spectrum method in the presence of simple- and poly-electrolytes. The simple electrolytes used were sodium chloride and sodium sulphate, the polyelectrolytes were sodium poly(ethene sulphonate)(NaPES), sodium poly(styrene sulphonate)(NaPSS), polybrene (PB), poly(4-vinyl-N-benzylpyridinium chloride)(BzPVP), and a copolymer of 4-vinyl-N-hexadecylpyridinium bromide and 4-vinyl-N-benzylpyridinium chloride (C₁₆BzPVP). NaCl and Na₂SO₄ decrease D values, explained by the desolvation effect of the salts upon HPC molecules. Cationic macro-ions also decrease D values, and the strength of the effect is in the order PB > BzPVP > C₁₆BzPVP. This is due to the shrinkage of the HPC helicoid by the association of HPC with the macrocations. On the other hand, anionic polyelectrolytes increase D values in the order NaPSS > NaPES, which is ascribed to the intercalation of the macro-anions into the intra-chain space of the helicoidal HPC by the hydrophobic interaction.