| Actuators have been widely applied for their function of energy coversion.However,the current research of the actuator mainly focuses on photo,thermal and electrical-responsive actuators with less attention on that actuated by water.In the research of humidity and water-responsive actuators,actuators made of single-layered or composite membrane are mainly types researched.Nevertheless,these two types of actuators suffer from the difficult control of stimuli and interlayer issues.In addition,some actuators with one single deformation mode which cannot be altered after production may cause the waste of raw material.In this paper,PVA was functionalized by anthracene derivatives through esterification reaction.Then the reprogrammable gradient cross-linked membrane and hydrogel actuators were fabricated via 365 nm UV-induced dimerization of anthracene groups.In chapter two,PVA-AN was fabricated first,and then blended with THBP to prepare PVA-AN/THBP composite membrane,followed with 365 nm UV treatment so as to obtain the PVA-AN/THBP humidity-responsive actuator.The FT-IR and fluorescence spectra were used to prove the synthesis of PVA-AN,while the liquid UV-vis spectrum was used to estimate the functionalized degree of anthracene,of which the result was 1.94%.The transmittance of PVA-AN/THBP composite membrane to 365 nm UV was characterized by solid UV-vis spectrum.The results show that the transmittance of the composite membrane can be reduced to less than 0.5%through the addition of THBP.According to the result of tensile test,PVA-AN/1.5%THBP has the maximum modulus of 2.84 GPa.Therefore,the ratio was determined to fabricate the actuator.The PVA-AN/THBP membrane irradiated by 365 nm UV was characterized by fluorescence spectrum and SEM.It was proved that a gradient crosslinking structure along the thickness direction was formed in the irradiated membrane.Taking advantage of this structure,the humidity-responsive PVA-AN/THBP actuator was constructed which can bend at an average speed of 2.36°·s-1 to the maximum bending angle of 53.0°under the stimulation of uniform humidity field and at an average bending speed of 22.78°·s-1 to the maximum bending angle of 182.2°under the stimulation of nonuniform humidity field.Since the reversible dimerization of anthracene can be induced by UV,the photomask combined with alternating irradiation of 365 nm and 254 nm UV was applied to prove the patterned reprogrammablity of the actuator.In chapter three,9-SA-AN was first synthesized and graft onto the PVA through esterification so that the PVA-SA-AN was fabricated.The reaction was proved by ~1H NMR and the grafting rate of anthracene was calculated.The PVA/PVA-SA-AN hydrogel was prepared by treating the mixture of PVA and PVA-SA-AN with cyclic freezing and thawing.The optimum ratio of PVA to PVA-SA-AN,which is 3:1,was determined by sol-gel transformation test and data of water content and ESR.Furthermore,TA was introduced into the PVA/PVA-SA-AN system to form multiple physical crosslinking to prepare highly stretchable PVA/PVA-SA-AN/TA hydrogel.Through FT-IR and fluorescence spectra,the formation of multiple non-covalent crosslinking in the hydrogel system was proved.The result of tensile test showed that PVA/25%AN/8%TA had the best mechanical properties compared with hydrogel without TA.Compared with PVA/25%AN/0%TA,the tensile strength of PVA/25%AN/8%TA increased by 175.73%,tensile strain increased by 270.12%,and toughness increased by 698.43%.The hydrogel was further treated by CTAB aqueous solution.The treated hydrogel could form a gradient cross-linking structure along the thickness direction after UV irradiation at 365 nm wavelength,and the existence of the structure was confirmed by SEM characterization.The actuator was constructed based on the gradient crosslinking structure.Under the induction of water-responsive swelling,the actuator can bend uniaxially at an average speed of2.51°·s-1 until the maximum angle is 226.3°.The patterned reprogrammablity and controllable deformation of the actuator are realized by combining specific pattern photomasks with alternately irradiation of 365 nm and 254 nm UV. |
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