Epoxy-Based Organogels for Thermally Reversible Light Scattering Films and Form-Stable Phase Change Materials

PUIG, JULIETA; DELL'ERBA, IGNACIO E.; SCHROEDER, WALTER F.; HOPPE, CRISTINA E.; WILLIAMS, ROBERTO J. J.

ACS APPLIED MATERIALS & INTERFACES

AMER CHEMICAL SOC

Año: 2017 vol. 9 p. 11126 - 11133

1944-8244

Alkyl chains of β-hydroxyesters synthesized by the capping ofterminal epoxy groups of diglycidylether of bisphenol A (DGEBA) withpalmitic (C16), stearic (C18), or behenic (C22) fatty acids self-assembleforming a crystalline phase. Above a particular concentration solutions of theseesters in a variety of solvents led to supramolecular (physical) gels below thecrystallization temperature of alkyl chains. A form-stable phase change material(FS-PCM) was obtained by blending the ester derived from behenic acid witheicosane. A blend containing 20 wt % ester was stable as a gel up to 53 °C andexhibited a heat storage capacity of 161 J/g, absorbed during the melting ofeicosane at 37 °C. Thermally reversible light scattering (TRLS) films wereobtained by visible-light photopolymerization of poly(ethylene glycol)dimethacrylate−ester blends (50 wt %) in the gel state at room temperature.The reaction was very fast and not inhibited by oxygen. TRLS films consistedof a cross-linked methacrylic network interpenetrated by the supramolecularnetwork formed by the esters. Above the melting temperature of crystallites formed by alkyl chains, the film was transparent dueto the matching between refractive indices of the methacrylic network and the amorphous ester. Below the crystallizationtemperature, the film was opaque because of light dispersion produced by the organic crystallites uniformly dispersed in thematerial. Of high significance for application was the fact that the contrast ratio did not depend on heating and cooling rates.