Monotropic Polymorphism in Ester-Based Phase Change Materials from Fatty Acids and 1,4-Butanediol

Abstract

This article reports on the synthesis, thermal behavior, and morphology of phase change materials based on diesters from 1,4butanediol with palmitic (BD16), stearic (BD18), or behenic (BD22) acid. The crystalline contents and melting enthalpies of all substances exceed 90% and 180 J/g, respectively. The molecules display monotropic polymorphism. The metastable β′ form is built from outstretched molecules, whereas the denser, stable β form is composed of molecules with a kinked conformation. BD18 and BD22 crystallize into the β′ form during cooling. Only BD18 transforms into the β form during subsequent heating via a solid−solid transition. The resistance of BD22 to convert into the β form is believed to originate from the lack of mobility associated with longer aliphatic chains. In contrast, the polymorphic conversion is thought to be very efficient and to take place during cooling for the shorter BD16 molecules. The hypothesis is put forward that the original BD16 β′ nuclei are rapidly overgrown by the β phase by which crystal growth is postponed to larger supercooling where the β phase can grow from the melt. Consequently, BD16 only occurs in the β form. The melt crystallization of BD18 and BD22 into the β′ form hardly requires any supercooling.

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Phase Behavior and Polymorphism of Saturated and Unsaturated Phytosterol Esters

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Polyester‐based phase change materials with flexible poly(ethylene glycol) chains for thermal energy storage

“…PCMs can reversibly absorb or release thermal energy through the melting or solidification of crystals. Some common crystalline compounds, including fatty acid, fatty alcohol, fatty acid ester, poly(ethylene glycol) (PEG), paraffin, and their eutectics are widely used as solid–liquid PCMs (SLPCMs). However, they experience a leakage problem during their melting state, which requires additional container or encapsulation materials in practical applications .…”

“…Some common crystalline compounds, including fatty acid, fatty alcohol, fatty acid ester, poly(ethylene glycol) (PEG), paraffin, and their eutectics are widely used as solid–liquid PCMs (SLPCMs). However, they experience a leakage problem during their melting state, which requires additional container or encapsulation materials in practical applications . A large number of inorganic, organic, and polymeric materials have been adopted as encapsulation materials to overcome the leakage problem …”

“…Recently, the synthesis of polymeric solid–solid PCMs (SSPCMs) has emerged as a promising strategy for thermal energy storage owing to the low cost and light weight of polymers. Moreover, polymeric solid–solid PCMs can be processed into arbitrary shapes and even used directly without additional packaging . There are two types of polymeric SSPCMs.…”