Calorimetric and rheological studies of 12-hydroxystearic acid / digycidyl ether of bisphenol A blends

Summary

Above a concentration c^* close to 0.3 wt%, blends of 12-hydroxystearic acid (HSA) with diglycidyl ether of bisphenol A (DGEBA) prepolymer mixed at 80°C give thermally reversible physical gels (organogels) on cooling.

According with the literature, the turbidity of the gels indicates fibres of rectangular cross-sectional shapes. The slope of the linear melting heats versus concentration is equal to the melting heat of the pure HSA (-182 ± 4 J.g^-1).

The blends are gels as the elastic modulus G’ is about ten times larger than the loss one G” and G’ is practically independent of the frequency at a given concentration.

The sharp variation of the temperature of the endothermic peak T _peak , of the time to reach the rubbery plateau t _r , of the exponent Δ (G’∝ω^Δ) and of the limiting strain γ _l of the linear viscoelastic domain below 2.5 wt%, is attributed to smaller crystallites in the blend.

At a given frequency, G’ follows a scaling law with the concentration ($G^{\prime}\propto{c}^{\beta_1}$), the scaling exponent β₁ being equal to 3.87 ± 0.02 at 1 rad.s^-1. This indicates that the gel structure is independent of the concentration.