Preparation And Properties Of Photo Actuation Interpenetrating Networks Liquid Crystalline Elastomer

Azobenzene-based light actuation liquid crystalline elastomer(LCE)has characteristics of simple operation,long control distance,excellent stability and repeatability,can be used in the design and manufacture of high-tech products,such as artificial muscles and soft robots,and has attracted the attention of many researchers.However,problems such as insufficient material toughness and low actuation stress caused by the rigidity of azobenzene molecules restrict its further application.Polyurethane elastomer has become one of the most widely used polymer materials due to its excellent flexibility,chemical stability and aging resistance.Studies have shown that through the form of interpenetrating networks(IPN),the long chain of polyurethane molecules are introduced into the polymer matrix,which further increases the molecular weight,chain entanglement and the flexibility of material and device,and great potential in liquid crystalline elastomer's actuation ability improvement.Therefore,azobenzene-based polyurethane networks(Azo-PU)were innovatively designed and introduced into the liquid crystalline elastomer matrix synthesized by the thiol-ene click chemistry reaction containing four thiols with different structures as spacers.Four photo actuation interpenetrating liquid crystalline elastomers(IPN-LCE)are synthesized by two-step crosslinking reaction,then material structure,mechanical properties,actuation performance and application have been researched.Main work is introduced as follows:(1)Preparation of light actuation interpenetrating networks liquid crystalline elastomer film.A photo actuation interpenetrating networks liquid crystalline elastomer material was successfully synthesized with azobenzene-based polyurethane as the second network,1,8-Octanedithiol(ODT),2,2?-(Ethylenedioxy)diethanethiol(EDDET),1,4-Butanediol Bis(thioglycolate)(BDBTG)and Ethylene Glycol Bisthioglycolate(EGBTG)as spacers,by two-step cross-linking process.The effects of UV light irradiation,temperature changes and stretching conditions on the structure and properties of materials were investigated respectively.It is found that azobenzene groups in the material have strong ultraviolet light absorption ability;the rise of temperature will improve the interplanar spacing of molecular chains in the material,and facilitate the thermally actuation process from molecular order-disorder change.However,this process is affected by azobenzene,and the phase transition temperature of some IPN-LCEs have been risen.The orientation parameter depends on tensile strain.The introduction of Azo-PU can significantly improve the stability of orientation,but causes weak light transmittance,resulting in a small amount of free monomer remaining in the material after UV curing.Furthermore,the morphology inside became rough,and interpenetrating networks were formed.Finally,the use temperature of the material should be lower than 200 ?.(2)Research on physical,mechanical properties and high actuation performance of materials.The introduction of Azo-PU has greatly improved the tensile properties and UV light absorption capacity of the liquid crystalline elastomer,but has aggravated hysteresis in the temperature rise and fall process.The molecular structures based on four thiols show different mechanical properties.When the molar ratio of RM82(acrylate-based liquid crystal monomer)/BHHAB(azobenzene-based monomer)is 8:1,the tensile properties are the best,where the breaking stress and strain of BDBTG-IPN-LCE(BDBTG-based interpenetrating liquid crystalline elastomer)reached 4.5 MPa and 660 %,respectively.At the same time,the light response ability of azobenzene in the material has also been confirmed.The investigation of light actuation ability shows that the actuation stress of EDDET-IPN-LCE(EDDET-based interpenetrating liquid crystalline elastomer)is the highest,reaching 1.1 MPa.Through the comparison of four thiol-based liquid crystalline elastomers,EDDET-IPN-LCE has the potential for application in artificial muscles.(3)Preliminary design of material application.Three types of actuators,such as light-actuated hook,cross-shaped swimmer and arrow swimmer by using EDDETIPN-LCE,were designed and prepared,which preliminarily showed the application prospects in flexible optical actuator field.