Preparation and characterization of side-chain liquid crystal polymer/paraffin composites as form-stable phase change materials

Abstract

A series of side-chain liquid crystal polymers (SCLCPs), named poly[ω-(4′-n-alkyloxybiphenyl-4-oxy) hexyl methacrylates] (P6biCm, m = 1, 2, 4, 6, 8, 10, 12, 14, 16 and 18), have been synthesized. Novel SCLCP/paraffin composite form-stable phase change materials (FSPCMs) were prepared by introducing P6biCm into paraffin. The minimum gelation concentration (MGC) and gel-to-sol transition temperature (T_GS) properties were tested by a “tube-testing method”. It was found that P6biCm (m = 1, 2, 4, 6, 8, 10) were insoluble in paraffin, while P6biCm (m = 12, 14, 16, 18) exhibited a low MGC (≤6 wt%) and high T_GS (T_GS of P6biC12/paraffin is 140 °C). The structure and morphology of FSPCMs were systematically investigated by FT-IR, POM, 1D WXAD and SEM. The experimental results revealed that paraffin was restricted in the three-dimensional P6biCm network, leading to the FSPCM without leakage even above its melting point. The thermal properties were studied by DSC and TG. The research showed that the P6biCm/paraffin exhibited excellent thermal stability and high heat storage density. The shape stability was assessed by rheological measurements, indicating that solid ↔ hard gel ↔ soft gel ↔ liquid was observed with the increase of temperature. This work is useful in comprehending the physical mechanism of shape stability and in the meanwhile provides a novel method for synthesis of FSPCMs.