Concentration selective hydration and phase states of hydroxyethyl cellulose (HEC) in aqueous solutions.

Solution behaviour of hydroxyethyl cellulose (HEC) is reported in the polymer concentration range spanning over two decades (c=0.002-5% (w/v)). The results conclude the following: (i) dilute solution regime prevailed for c<0.2% (w/v), flexible HEC fibres of typical length ≈ 1 μm and persistence length ≈ 10 nm were found here, (ii) for 0.2<c<1% (w/v), a semidilute phase comprising soluble aggregates of hydrated HEC fibrils were observed with the material exhibiting viscoelastic behaviour and (iii) when 1<c<5% (w/v) the solution behaved with melt-like attributes with substantial embedded heterogeneity; viscous to elastic transition was observed in this region. Raman spectral, and DSC data indicated distinctive hydration of HEC fibres in the aforesaid concentration regimes. Cole-Cole plots revealed phase homogeneity and miscibility was limited to concentrations less than ~2% (w/v). For higher polymer concentrations, strong fibre-fibre interactions prevailed and samples became heterogeneous.