Study On Preparation And Properties Of Liquid Crystal Elastomers

As an important branch of liquid crystal polymers,the liquid crystal elastomer(LCE)combines the ordering properties of liquid crystals with the elastic properties of elastomers,which has attracted the attention of chemists and physicists.As a category of advanced material,the LCE has the excellent potential applications in multifunction sensors,shape memory materials,etc.LCEs that can be applied to shape memory materials are generally referred to as shape memory LCEs.The shape memory LCE can generate a change in shape by changing the arrangement of liquid crystal elements under the stimulation of an external field(electric field,temperature,light,etc.)and has become a hot topic during the LCE research area.In this thesis,the research on the LCEs mainly focuses on two aspects.One is on the design and preparation of new types of LCEs,including a type of shape memory nematic side-chain LCE,a type of shape memory cholesteric side-chain LCE and two types of nematic main-chain LCEs.The other aspect is to study the relationship between the structure and performance and further develop the practical application.Firstly,the P1,a new type of side-chain LCE,was prepared by 6-(4'-(4-(allyloxy)benzoyloxy)biphenyl-4-yloxy)-6-oxohexanoic(Ml),sebacic acid,glycerol,etc.The structures of monomers and liquid crystal polymers were characterized by Fourier transform infrared spectroscopy(FT-IR)and nuclear magnetic resonance(1H-NMR).The polarized light microscopy(POM)and X-ray diffraction(XRD)were used to study liquid crystalline properties of the monomers and the LCEs.And the Ml and LCEs were proven to be nematic liquid crystals.The thermal properties analysis through differential scanning calorimetry(DSC)and thermogravimetric analysis(TGA)demonstrated the glass transition temperature(Tg)and decomposition temperature(Td)of LCEs increased with the increasing of crosslinker.The shape memory performance of P1 was illustrated by the shape recovery experiments.When the temperature reached to clearing point temperature(Ti),the shape recovered to the origin.To further explore the environmental performance and application conditions of P1 which contained ester bonds,the degradation properties and hydrophilicity were investigated.The results showed that the P1 was a type of hydrophobic shape memory side-chain LCE and was degradable under alkaline conditions.Secondly,the P2,a new type of side-chain LCE,was prepared by cholest-5-en-3-ol(3?)-,3-(hydrogen hexanedioate)(M2),sebacic acid,citric acid,etc.The chemical structures and properties of LCEs were characterized and analyzed by various techniques including FT-IR,1H-NMR,POM,XRD,DSC,TGA,contact angle tester,etc.The structure-property relationships were discussed in detail.It showed that M2 and P2 were cholesteric liquid crystals.The cross-linked structure can significantly improve the thermal stability of the materials.The P2 revealed properties of hydrophilia,and was degradability in phosphate solutions at pH=7.4.The shape recovery experiments were carried out on P2.The results showed that the cholesteric P2 also had shape memory properties.Finally,in order to study the effects of the types and amount of crosslinkers on the properties of main-chain LCEs,the following studies were carried out.Mid product LCP was prepared by using 4,4'-dihydroxy-?,?'-dimethylbenzylazide(M3),adipic acid and 2,5-dihydroxybenzoic acid.Glycerol and hexanediol were used as crosslinkers to prepare two kinds of main-chain LCEs,which refered to P3 and P4,respectively.The chemical structures and properties of P3 and P4 were characterized and analyzed with FT-IR,1H-NMR,POM,XRD,DSC,TGA,etc.According to the results,P3 and P4 were both nematic liquid crystals.The Tg and Td of the LCEs increased with the increasing of crosslinkers.In addition,the type effects of the crosslinkers on the properties of LCEs were investigated.As a result,the Tg and Td of P3 with glycerol as crosslinker were higher than those of P4 with adipic acid as crosslinker with the same mass fraction of the crosslinker.The preparation of P3 and P4 enriches the types of main-chain LCEs.The study also revealed that the LCEs with the target properties can be prepared by changing the types and amount of crosslinkers,which provided guidance significance in design of functional LCEs.