Preparation And Application Of High Deformation And Hydrophobic Polysiloxane Flexible Materials

Polysiloxane(PDMS)has been studied extensively in many fields for its unique properties such as high and low-temperature resistance,weather resistance,low surface energy,low surface tension,and hydrophobicity,especially in the field of dielectric elastomers and leather finishing agents.As a dielectric elastomer material,polysiloxane has a rather low elastic modulus and high speed of response,but its relatively low dielectric constant also severely limits the actuation strain.In addition,because of its excellent hydrophobic properties,the polysiloxane is often used to modify waterborne polyurethane to obtain hydrophobic leather finishing agents,but its hydrophobicity can no longer meet the increasing technical requirements.In view of the above problems,we have modified polysiloxane to improve its actuation strain and hydrophobicity.The specific research content is as follows.Firstly,a new LM/TiO2/PDMS three-phase composite material was prepared with both TiO2 and eutectic gallium-indium liquid metal(LM)as fillers and PDMS as matrix.It was found that TiO2 could significantly increase the dielectric constant of PDMS,while LM could reduce the elastic modulus of composites.When the amount of TiO2 and LM was 20 wt%and 15 wt%,respectively,the dielectric constant of LM/TiO2/PDMS composite material increased to 5.34(1 kHz),and the elastic modulus was 0.375 MPa.In addition,the LM/TiO2/PDMS composite exhibited a large actuated strain of 21.96%at an electric field of 40.21 kV/mm without pre-stretch,which is 5.3 times that of pure PDMS.Secondly,to prepare PDA@SiO2@GO hybrid,ethyl orthosilicate was used to modify GO sheet,followed by modified with polydopamine.And then it was physically compounded with PDMS.The results showed that PDA@SiO2@GO hybrids could significantly increase the dielectric constant of PDMS and effectively reduce the dielectric loss.Therefore,by introducing 5 wt%of PDA@SiO2@GO hybrids into PDMS,the dielectric constant of PDA@SiO2@GO/PDMS composite increased to 5.92(1 kHz),the elastic modulus was 0.558 MPa,and the actuation strain of composite achieved the best,it exhibited a large actuated strain of 14.23%at a relatively low electric field of 33.19 kV/mm without any pre-stretch,which is 5.9 times that of pure PDMS.Finally,to improve the hydrophobicity of polysiloxane,n-dodecyl mercaptan was grafted onto the side chain of hydroxy-terminated polysiloxane using a click chemistry method to obtain PDMS-SH,which was subsequently used to modify waterborne polyurethane.The effects of the content of PDMS-SH on the hydrophobic properties and mechanical properties of waterborne polyurethane were systematically studied.The results showed that when the amount of PDMS-SH was 6%,the PDMS-SH-WPU film had the best performance,its tensile strength was 31.65 MPa,the elongation at break was 554.46%,the water contact angle could reach 143.1,and the water absorption reduced to 6.92%.