Reinforcement in the mechanical properties of shape memory liquid crystalline epoxy composites

Abstract

In this work, novel thermoresponsive shape memory composites based on glass fiber and nanosilica‐modified liquid crystalline epoxies (LCEs) with lateral substituent were prepared and characterized. According to the comprehensive analysis of polarized optical microscopy, wide‐angle X‐ray diffraction measurements, and tan δ data, the orientation of mesogen units were hindered by the introduction of nanosilica and lateral substituents of liquid crystalline epoxies, so that additional physical cross‐links except for similar chemical cross‐links emerged with the introduction of surface‐treated nanosilica. And the increased cross‐links could enhance the shape memory properties of the composites which could recover to their original state quickly in a time shorter than 30 s with high shape fixing ratios (>96%) and high shape recovery ratios (>98%), which indicated the composites could be applied into self‐deployable structural materials. Moreover, the reinforcement in the dynamic storage moduli, tensile modulus, and the tensile strength and shape memory properties indicated that glass fiber and nanosilica‐modified shape memory liquid crystalline epoxy composites could be high‐performance composites and could be used as new candidates for aerospace smart materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42616.

Review of Progress in Shape Memory Epoxies and Their Composites

“…In the literature many examples can be found for the combinations of hydroepoxy (cycloaliphatic type) and aliphatic EP [ 40 , 41 , 42 ], aromatic diepoxide and aromatic monoepoxide [ 21 ], aromatic and aliphatic EPs [ 43 ], similar epoxies with different molecular weights [ 44 ], synthesis of EPs containing rigid and flexible units [ 45 ], and the like. High-temperature resistant novel EPs with and without liquid crystalline characteristics were also synthesized and their SM behaviour checked [ 46 , 47 , 48 ].…”

“…Parallel to that the critical bending strain, not causing observable damage, was highly reduced compared to neat EP (from >6% to 1%) [ 155 ]. Guo et al [ 47 ] incorporated one single GF fabric layer with and without additional nanosilica coating in a liquid crystalline EPs. R f was improved by this surface treatment of the GF fabric without affecting the R r values.…”

High thermal conductivity epoxies containing substituted biphenyl mesogenic

“…Liquid crystalline epoxides (LCEs), formed from curing of low molecular weight, rigid rod epoxy monomers, are superior to common amorphous epoxies in the performance of low dielectric constant, good water resistance properties, better mechanical properties, better thermal stability and noticeable high temperature properties [22][23][24][25][26][27][28][29]. It was reported that a highly crystallized polymer possessed a obviously better thermal conductive property than amorphous polymers, owing to the more effective thermal-energy transmission of the lattice vibration (phonon) in the crystals [30,31].…”

Reprocessable Shape Memory Epoxy Resin Based on Substituent Biphenyl Structure

“…Thus, SMPs can realize good shape recovery and good repeatability, which is challenging but exceedingly important. Some special structures have been designed to improve the shape memory performance, such as including well‐controlled network structure, [ 21 ] semi‐interpenetrating network structure, [ 22 ] liquid crystal unit, [ 23 ] star network structure, [ 24 ] and topological slide‐ring structure. [ 25 ] For instance, our group synthesized topologically well‐controlled poly(ethyl methacrylate) structures [ 21 ] and semicrystalline slide‐ring shape‐memory polycaprolactone‐based polyurethane network, [ 25 ] which both showed excellent shape memory performance.…”

“…also studied PMMA/PEG semi‐interpenetrating network [ 26 ] and PMMA‐PCL copolymer networks [ 27 ] possessed excellent shape memory ability with R f higher than 95% and R r over 96%. Lu's group fabricated some epoxy resin composites containing liquid crystal unit of aromatic ester, which had excellent shape memory performance, [ 23b ] in that the liquid crystal unit could be oriented along the direction of external forces, reducing the entropy and increasing the entropy elasticity in the epoxy network so as to improve the shape recovery ability. Similarly, Lu's group fabricated some high thermal response epoxies network containing diphenyl group, which improved the shape memory performance by the introduction of diphenyl structure, but any kind of reprocessing is impossible due to the permanently crosslinked network.…”