Research On Controllable Fabrication,structure And Performance Of Multifunctional Polydimethylsiloxane Foam

With the progress of the era,it is difficult for traditional single-component flexible polymer composites to break through the bottleneck in terms of high performance and multi-functionality,and it is also hard to meet increasing demand for high standards of smart devices.Generally,both the reasonable structures and functional fillers could be adopted in order to achieve the high performance of the flexible polymer.In terms of structural design,porous structure as the effective mean is usually selected in the composite system.However,traditional strategies for constructing porous materials are often difficult to control the pore size and distribution.Then,it exists the shortcoming of poor mechanical properties,which makes it still face great challenges in practical applications.Besides,the use of high-performance functional fillers is constrained by high economic costs,time-consuming and complicated technological processes,impeding the large-scale industrial application.In addition,although structured flexible polymers and their composites could enhance their performance to a certain extent,they are usually single and simplification,existing the drawback of functional expansion and diversification.In this case,the development of foam composites with economic adaptability,facile preparation,high mechanical properties and multi-functional characteristics shows great research significance and practical value.In this article,the temperature-sensitive microspheres(TSM)with the hollow and closed cell structure,were introduced into the silicone rubber elastomer to obtain a mechanically reinforced silicone rubber foam composite.We conducted a systematic study on its structure and performance,and carefully discussed the influence of the internal structure evolution on the multifunctional characteristics.The main research contents were included into the following three aspects:(1)By using a facile and controllable foaming method,the heated-expandable TSM were directly added to the polydimethylsiloxane(PDMS),and then the temperature-sensitive microspheres/polydimethylsiloxane(TSM/PDMS)foam composites were successfully prepared.It was found that the TSM/PDMS foam exhibited strengthened mechanical performance with unique softening behavior and excellent ideal energy absorption efficiency.Specifically,the compressive modulus of pure PDMS at 10%strain was only 4.3 MPa and the compressive strength got 0.5 MPa.Here,the modulus of TSM/PDMS(1:2)foam sample with hollow and closed structure was 10.2 MPa while the strength achieved 0.8 MPa,meaning that the mechanical properties had been improved by 237%and 160%,respectively.Besides,after a large compression strain of 70%,the modulus of the PDMS foam decreased from 10.2 MPa to 2.5 MPa,revealing the unique softening phenomenon.Furthermore,the ideal energy absorption efficiency of TSM/PDMS(1:2)foam samples was as high as 73.7%,while the value of pure PDMS was only 15.8%.Since the closed-cell TSM as a rigid support in the composite underwent structural evolution,it exhibited a stress-softening behavior,endowed itself with good toughness and consumed the impacted energy effectively.(2)Based on the work above,the TSM were directly introducing to the PDMS with multi-walled carbon nanotubes(CNT)in order to prepare the functional conductive silicone rubber foam composites(PDMS/TSM/CNT),realizing the enhancement of piezoresistive sensing and exhibiting the special temperature-sensitive response characteristic.Firstly,the introduced cell structure significantly improved the piezoresistive sensing performance of the composite.Compared with the response value of current change(I/I₀)in the PDMS/CNT sample,it achieved a great improvement of1800%,effectively enhancing the sensing sensitivity of the sample.Secondly,the PDMS/TSM/CNT foam sample showed a superior sensing response of 60 ms while it also exhibited excellent stability and outstanding reliability during cyclic compression.Thirdly,through the combination of softening behavior and sensing properties,conductive silicone rubber foam composites have shown great potential in strain alerting devices.Furthermore,due to the structural characteristics of TSM,the PDMS/TSM/CNT sample exhibited special temperature-sensitive response,having potential application in the area of temperature sensing materials.(3)Additionally,the introduction of TSM brought many cavities and interfaces to the PDMS/CNT composites,greatly benefiting the multiple scattering and reflection of electromagnetic waves in the interior.Herein,the unique stress softening phenomenon and temperature-sensitive response in the silicone rubber foam were closely related to the internal structure of microspheres.Further research found that the microsphere structure in the PDMS/TSM/CNT composite could be effectively regulated by specific temperature and strain,which caused the rearrangement of the CNT conductive network,exhibiting different electrical conductivity and electromagnetic interference(EMI)shielding effectiveness(SE).Specifically,the EMI SE of the PDMS/TSM/CNT composite controllably decreased after the treatment at 120?,and then partially recovered after heating at 150?;based on the heated samples at 120?,the shielding performance got controllably reduced after the compression to 70%;the compressed composite was heated again at 120?,and the shielding performance was also controllably restored.Finally,the morphological evolution of the microspheres in the PDMS/TSM/CNT composite together with the changes of the internal conductive network were discussed,and the mechanism of tunable EMI shielding was analyzed in depth.