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

Abstract

Alkyl chains of β-hydroxyesters synthesized by the capping of terminal epoxy groups of diglycidylether of bisphenol A (DGEBA) with palmitic (C16), stearic (C18), or behenic (C22) fatty acids self-assemble forming a crystalline phase. Above a particular concentration solutions of these esters in a variety of solvents led to supramolecular (physical) gels below the crystallization temperature of alkyl chains. A form-stable phase change material (FS-PCM) was obtained by blending the ester derived from behenic acid with eicosane. A blend containing 20 wt % ester was stable as a gel up to 53 °C and exhibited a heat storage capacity of 161 J/g, absorbed during the melting of eicosane at 37 °C. Thermally reversible light scattering (TRLS) films were obtained 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 consisted of a cross-linked methacrylic network interpenetrated by the supramolecular network formed by the esters. Above the melting temperature of crystallites formed by alkyl chains, the film was transparent due to the matching between refractive indices of the methacrylic network and the amorphous ester. Below the crystallization temperature, the film was opaque because of light dispersion produced by the organic crystallites uniformly dispersed in the material. Of high significance for application was the fact that the contrast ratio did not depend on heating and cooling rates.

Form-stable benzoxazine-urethane alloys for thermally reversible light scattering materials

“…High transparency of BA-a/PU alloys indicated that the alloy components, i.e. polybenzoxazine (poly(BA-a)) and urethane prepolymer, were miscible at elevated temperatures, forming a single phase [28]. The experimental bulk refractive indices of PU3K prepolymer was measured to be 1.465.…”

“…Thermally reversible light scattering (TRLS) materials are smart materials exhibiting the temperaturedependent transparency across some specific temperature ranges. TRLS materials with good optical contrasts based on β-hydroxyester organogels [28], eicosane dissolved in poly(dodecyl methacrylate) [29], polyether urethane diacrylate with dispersed 1octadecanol [30], epoxy resin modified with a low molecular weight liquid crystal [31], dispersed polystyrene/naphthalene domains in epoxy matrixes [32], epoxy resin modified with polystyrene-block-poly (ethylene oxide) and a low molecular weight liquid crystal [33], meso/nanocomposite films [34], dispersed diphenyl crystals in an epoxy matrix [35], and 4′-(hexyloxy)-4-biphenyl-carbonitrile and polystyrene in diglicydylether of bisphenol-A epoxy resin [36] were previously fabricated. The optical state transitions in these systems mainly based on melting/crystallization of organic crystals or nematic/isotropic transition of liquid crystals.…”

Facile Synthesis of Nitrogen-Rich Porous Organic Polymers for Latent Heat Energy Storage

“…To overcome these problems, the design and preparation of shape-stable PCMs via an encapsulation technique using porous materials have been proposed as one of the most effective methods. , Porous carbon-based materials (e.g., heteroatom-rich carbon, graphite foam, graphite oxide, graphene, − and carbon nanotubes), porous inorganic oxides (e.g., expanded perlite, vermiculite, and silicon dioxides), and porous organic polymers (POPs) − have been proposed for the encapsulation. Recently, POPs have attracted increasing interest for a range of applications including gas uptake, energy storage, and catalysis. − Due to their covalent bonds they usually exhibit high chemical and thermal stability, and their high surface areas and porosity make them feasible materials for encapsulating various substances and thus for PCMs.…”

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“…When the temperature is more than 40 ºC and then reduce below 35 ºC gelatine forms a gelled structure. Adding of gelatin in w/o microemulsion helps in the process of gellation of total solution that is micellar and the formed gel is clear in nature 21,22,23 . For the development of organogels which are stabilized in gelatin, w/o microemulsions are used due to its thermostability and ease of preparation 24 .…”

“…For the development of organogels which are stabilized in gelatin, w/o microemulsions are used due to its thermostability and ease of preparation 24 . isopropyl myristate (ipm), tween-85, AOT and water contains a typical pharmaceutical-grade w/o microemulsion preferably used in the preparation of MGB 22,23,24 . The MBGs are vehicle used for the topical and transdermal controlled delivery of hydrophobic bioactive agents 25 .…”