Thermal Properties Of Porous PDMS And Its Applications In Flexible Electronics

Flexible electronics refers to the electronic devices which fabricate organic/inorganic electronic components on the flexible substrates.Flexible electronic devices,which can be stretched,twisted and folded,not only guarantee the performance of traditional electronic devices,but also have excellent flexibility.In the field of clinical medicine,flexible electronics is frequently served as heat sensors or thermal heaters,so the thermal analysis of its components and skin tissue is much important.In this paper,we choose the porous PDMS(p-PDMS)substrate of flexible electronics as the main research object.Through emulsion polymerization reaction,we fabricated the p-PDMS samples with different porosities.Then we analyzed each sample's porosity and pore size experimentally,and used a flash method and a comparison method to measure p-PDMS thermal properties(thermal diffusivity,volumetric heat capacity,and thermal conductivity)under varying temperature(0-40?).The p-PDMS properties were also analyzed theoretically through homogenization method.Finally,on the basis of homogenization theory and experiment,we theoretically discussed the temperature field,thermal damage,and device strechability of flexible electronics(combined with human skin).The main research work and conclusions are as follows.(1)The porosity and pore size of p-PDMS samples were analyzed by using scanning electron microscope(SEM).The results show that,as the proportion of distilled water increases,the porosity of the samples increases,while the pore size remains basically unchanged.At the same time,thermal properties of p-PDMS with different temperatures were measured.Through the experimental values,we find that,as the temperature rises from 0? to 40?,the thermal conductivity and thermal diffusivity of p-PDMS decrease,while the volumetric heat capacity increases.And all the three thermal parameters decrease with the increase of porosity.(2)The experimental values of the three thermal parameters are consistent with the homogenized ones,which indicates the feasibility and applicability of homogenization theory.The influence of pore size and porosity on thermal properties of p-PDMS was discussed by this theory.It is found that the pore size has no effect on thermal properties,while the porosity has notable effect on them.Meanwhile,the prediction formulas of thermal properties were obtained through the theoretical values.(3)On the basis of the thermal analysis of p-PDMS,we theoretically calculated the temperature field and thermal damage caused by the flexible electronics combined with human skin.Under the discussion of each influencing factor,we find that,the form of external heat source,and p-PDMS substrate's thickness and porosity all have great effect on the temperature field and thermal damage.Optimizing the form of external heat source and increasing the thickness and porosity of p-PDMS substrate,can effectively reduce the thermal damage to skin.Combined with the temperature field,the effect of p-PDMS substrate's porosity on the strechability of flexible electronics was also analyzed.The results show that,when considering the effect of temperature field,the regulatory ability of p-PDMS substrate's porosity on the strechability will be reduced,and the regulatory ability will be affected by the thickness of substrate and the form of external heat source.The quantitative analysis of various influencing factors provides the basis for the optimization of thermodynamic properties of electronic devices.The research results in this paper can provide reference and ideas for the optimization of thermodynamic properties of flexible electronic devices,and also provide data basis for the subsequent analysis of material thermo-mechanical coupling,moisture-heat coupling and so on.