Preparation And Properties Of Side Chain Liquid Crystal Polymers/5CB Liquid Crystal Physical Gels

Liquid crystals possess both liquid fluidity and solid crystal orderliness.The fluidity of liquid crystals makes them have good stimulus responsiveness and liquid crystal can show quickly response under the application of external field.However,the fluidity also makes liquid crystals lose mechanical stability.Therefore,in the preparation of liquid crystal devices,liquid crystals are often encapsulated in liquid crystals cells or dispersed in polymers to obtain liquid crystal devices with good mechanical properties.In recent years,it has been found that the preparation of liquid crystal gels by gelation was another effective way to endow liquid crystals with good mechanical stability.Liquid crystal gel composites not only show good mechanical strength,but also retain the stimulus response of the liquid crystal to the external field.Compared with the preparation method of liquid crystal devices by encapsulating liquid crystals in liquid crystal cells,the liquid crystal gels discard the use of liquid crystal cells,and the structure of the device is simpler.The preparation process is simplified,and the preparation cost of the liquid crystal device is also reduced.Therefore,liquid crystal gels show great application values.Liquid crystal physical gels(LCPGs)are a novel class of gel materials.LCPGs have attracted the attention of researchers due to their responsiveness to external stimuli and thermal reversibility.LCPGs are mainly composed of two parts:one is the working material,which is usually a room temperature nematic liquid crystal molecules(such as 5CB),and the another is gelators,which mainly plays a supporting role,and inhibits the flow and deformation of the liquid crystals,so that the LCPGs can maintain a fixed shape on the macro view.Some of the reported gelators can form LCPGs in 5CB,however,the thermal stability and mechanical stability of the prepared LCPGs are still poor.Meanwhile,the influence of the structures of gelators on the properties of LCPGs is often neglected.It is still a big challenge to prepare LCPGs with good thermal stability,high modulus and fast response.In this paper,we have prepared a series of LCPGs with excellent thermal stability,good mechanical properties and fast photoelectrical response using side chain liquid crystalline polymers as the gelators.The influence of the structures of the side chain liquid crystal polymers on the stability,mechanical properties and electro-optical properties of the LCPGs has been studied in detail.The main research contents are as follows:1.Two kinds of side-chain liquid crystalline polymers PMmACB and PmACB(m=2,4,6)with different spacer length were synthesized by free radical polymerization.Polymers were blended with small molecule liquid crystal 5CB respectively,and then LCPGs were prepared by heating-cooling method.The influence of spacer length on the gelation ability of polymers and the properties of the LCPGs were studied in detail.The experimental results showed that only PM2ACB can form gels in 5CB,and all the other polymers were well dissolved in 5CB and could not form gels in 5CB.The minimum gelation concentration(MGC)of PM2ACB in 5CB was 4 wt%.With the increase of PM2ACB content,the driving voltage and contrast of LCPGs increased,the open-state response time remained basically unchanged,and the off-state response time of LCPGs decreased.The storage modulus G’ of LCPGs prepared by PM2ACB could reach about 103 Pa.2.Side chain liquid crystal polymers P0ACB and PM0ACB without flexible spacer were successfully prepared by polymerization.The chemical structures of P0ACB and PM0ACB were identical except for the main chain structure.P0ACB and PM0ACB were blended with 5CB respectively,and LCPGs were prepared by heating-cooling method.The effects of main chain structure on the gelation ability of polymers and the properties of the LCPGs were studied in detail.The experimental results showed that both P0ACB and PM0ACB can form LCPGs in 5CB.The MGC of P0ACB in 5CB was lower than PM0ACB,and the LCPGs formed by P0ACB showed better thermal stability and better mechanical properties than PM0ACB.With the increase of P0ACB and PM0ACB content,the driving voltage of LCPGs increased,the open-state response time remained basically unchanged,and the off-state response time of LCPGs decreased.At the same concentration,P0ACB/5CB LCPGs showed lower driving voltage,higher contrast and shorter off state response time than PM0ACB/5CB LCPGs.3.A series of side chain liquid crystal polymers P0ACB with different molecular weight and narrow molecular weight distribution were synthesized by RAFT polymerization.P0ACB with different molecular weight were blended with 5CB respectively,and LCPGs were prepared by heating-cooling method.The effects of molecular weight on the gelation ability of P0ACB and the properties of the LCPGs were studied in detail.The experimental results showed that the gelation ability of P0ACB increased,and the thermal stability of prepared LCPGs enhanced with the increasing of polymers molecular weight.However,when the molecular weight of P0ACB was more than 3.61 × 104g/mol,the gelation ability of P0ACB and thermal stability of prepared LCPGs kept unchanged with the increasing of polymer molecules.With the increase of molecular weight of polymers,the threshold voltage,saturation voltage and the contrast of LCPGs increased,but the off-state response time decreased.The storage modulus of LCPGs was also related to the molecular weight of P0ACB.With the increase of molecular weight of P0ACB,the storage modulus of LCPGs gradually enhanced,and the maximum value of G’could reach about 104 Pa.4.Copolymers P0ACB(x)-co-P6ACB(y)with different copolymerization ratios were prepared by free radical copolymerization.P0ACB was the rigid component and P6ACB was the flexible component.Copolymers with different copolymerization ratios were blended with 5CB respectively,and LCPGs were prepared by heating-cooling method.The effects of copolymerization ratios on the gelation ability of copolymers and the properties of the LCPGs were studied in detail.The experimental results showed that with the increase of the flexible component content,the MGC of copolymers in 5CB decreased firstly and then increased,while the thermal stability of LCPGs gradually became worse.When the content of flexible component exceeded 30%,the copolymers could not form gels in 5CB.With the increase of the flexible component content,the threshold voltage,saturation voltage and contrast of LCPGs increased firstly and then decreased.The LCPGs prepared by P0ACB(0.8)-co-P6ACB(0.2)showed the highest threshold voltage,saturation voltage and contrast.The storage modulus of LCPGs was also related to the copolymerization ratio of copolymers.With the increase of the flexible component content,the storage modulus of LCPGs gradually decreased.5.A series of side chain liquid crystal copolymers P0ACB(x)-co-PmACB(y)(m=2,4,6,8,10)were prepared by copolymerization.P0ACB(x)-co-PmACB(y)were blended with 5CB respectively,and LCPGs were prepared by heating-cooling method.The effects of flexible component spacer length on the gelation ability of copolymers and the properties of the LCPGs were studied in detail.The experimental results showed that with the increase of the flexible component spacer length,the TGs of LCPGs decreased firstly,then increased and then decreased.The MGC value of the copolymers was related to the content of two components in the copolymers.The threshold voltage and saturation voltage of LCPGs decreased first and then increased with the increase of the flexible component spacer length in the copolymer.The contrast and the off-state response time of the LCPGs decreased firstly,then increased and then decreased.The storage modulus of LCPGs also decreased firstly,then increased and then decreased with the increase of flexible component spacer length.6.A series of side chain liquid crystal polymers PMBimC without flexible spacer with different alkoxy tail length were synthesized by free radical polymerization.PMBimC with different alkoxy tail length were blended with 5CB respectively,and LCPGs were prepared by heating-cooling method.The effects of alkoxy tail length on the gelation ability of PMBimC and the properties of the LCPGs were studied in detail.The experimental results showed that the gelation ability of PMBimC and the thermal stability of LCPGs decreased with the increase of alkoxyl tail length.With the increase of alkoxyl tail length,the threshold voltage,saturation voltage and contrast of LCPGs decreasd,while the off-state response time increased.The mechanical properties of LCPGs were also related to the polymers alkoxyl tail length.With the increase of alkoxy tail length,the storage modulus G’ of LCPGs decreased gradually.