Study On Photothermal Vulcanization And Composite Properties Of Polydimethyl Siloxane

Silicon rubber,as a special rubber,is widely used in aerospace,electrical and electronic,and industrial production fields due to its excellent properties such as low temperature resistance,high temperature resistance,aging resistance,corrosion resistance,chemical resistance and low surface energy.However,the poor mechanical properties of silicone rubber highly limit its applications.Therefore,the research on reinforcement of silicone rubber has been widely concerned.High temperature vulcanized?HTV?silicone rubber is the most widely used silicon rubber.Whereas,its practical applications are subjected to uneven vulcanization caused by poor thermal conductivity of silicone rubber.Herein,we focus on photothermal vulcanization process of HTV based on photothermal materials via taking polydimethyl siloxane?PDMS?as a silicone rubber model to solve the forementioned problems in the applications of silicone rubber.The specific research content mainly includes the following aspects:1.Study on synthesis and photothermal properties of novel photothermal materials?1?Copper phosphate?CuPO?photothermal materials with two kinds of morphology were designed and synthesized based on d-d transition mechanism of 3d electrons in transitional metals,which strongly absorbed the energy of near-infrared?NIR?light and then converted it to heat with a high efficiency.?2?The phase and composition and morphology were characterized by XRD and TEM.The results indicated that the prepared products were amorphous copper phosphate with floss-like morphology?FCuPO?and crystalline rod-like copper phosphate with a chemical composition of Cu₂?OH?PO₄.?3?Results of investigations on optical properties demonstrated that FCuPO strongly absorbed NIR light of 600¹000 nm with?_max=760/849 nm,while RCuPO absorbed the energy of NIR light in the band of 600¹600 nm with?_max=1144 nm.?4?Photothermal properties of the prepared products were investigated,and the light-to-heat conversion efficiency performed by an 808 nm laser was calculated to be27.17%and 26.64%for FCuPO and RCuPO,respectivley.RCuPO was found to convert the energy of 980 nm laser into heat with an efficiency of 35.59%.2.Effects of photothermal heating and external heating mode s on vulcanization rate and mechanical properties of CuPO/PDMS composite materials.?1?FCuPO/PDMS composite was fabricated in which FCuPO served as a photothermal filler.The effects of photothermal heating and external heating modes on the curing rate of PDMS was investigated by measuring the cross-linking density via swelling method.The results showed that cross-linking density of FCuPO/PDMS cured by photothermal heating mode was higher than that cured by oven heating,suggesting that photothermal heating could significantly accelerate the heating rate of PDMS and achieve uniform and rapid curing.?2?Results of mechanical property tests indicated that both FCuPO and RCuPO could reinforce PDMS,and the CuPO/PDMS composites reinforced by RCuPO was more stronger than that by FCuPO.The reason might lie in the fine crystallinity and rod-like morphology of FCuPO,which enhanced the tensile strength of the polymer matrix in the way of carbon nanotubes.The reason was interpreted as even heating benefited by uniform distribution of the photothermal filler in the matrix.However,one can find localized cold spots that can affect crosslinking process in the conventional process.?3?The tensile strength of CuPO/PDMS composites cured via photothermal heating mode was significantly higher than that via oven heating.SEM was used to characterize the tensile fracture profiles of RCuPO/PDMS composites heated by two different modes.It was found that for oven heated samples many RCuPO rods stretched from the matrix could be observed,and the surface of the rods was smooth without adhesion of matrix,which was indicative of poor interface adhesion between RCuPO and PDMS.On the contrary,few RCuPO rods were found to be stretched out from the matrix for the photothermal heated samples,and the length of the stretched part was very small.Moreover it was very clear to observe that the tiny stretched parts of the RCuPO was wholly wrapped by the PDMS matrix,strongly suggesting better interface adhesion between the RCuPO filler and the matrix.The reason was attributed to the fact that the photothermal filler could act as internal heat sources under laser irradiation,which resulted in heat transfer from inside to outside.The temperature of adjacent matrix could reach to a value higher than the matrix's average temperature,and achieve better vulcanization,which improved the interface adhesion significantly.3.Applications of floatable CuPO-PDMS composite photothermal membranes in solar evaporation of simulating seawater.Porous bilayer photothermal membranes were prepared for accelerating solar evaporation of simulated seawater.The results indicated that the membranes made from RCuPO could achieve a higher water evaporation rate of salt water due to its wider and stronger absorption in NIR band.In addition,the design of double layer structure limited the flow of heat.The heat was well confined within the water-air interface zone,which significantly accelerated the evaporation of seawater.Under the simulated solar light source with a power density of 1000 W/cm²,the evaporation rate was measured to be1331 g·m^-2h^-1 for the porous double-layer membranes made by RCuPO,which was²19.2%higher than that measured for ordinary seawater without membrane.Moreover,a very high solar thermal conversion efficiency of 83.06%was obtained.