多孔基底柔性电子器件的力学分析与优化

The clinical application of flexible electronics has opened new avenues for biological function monitoring. During the long-term and real-time services, flexible electronics should have little disturbance on hygro- and thermo- exchange between human skin and its surroundings. Flexible electronics encapsulated with porous substrates are therefore proposed, which are very different from continuous substrates populated at present. The present proposal focuses on the mechanical analysis and optimization of flexible electronics encapsulated with porous substrates. To do so, a homogenization theory will be employed firstly to estimate the parameters, e.g. thermal conductivity and penetration coefficient, of a porous PDMS, which will be also measured by experiments. Secondly, static and dynamic responses of flexible electronics will be investigated once the distributions of temperature and humidity in porous PDMS integrated on human skin are determined. The following characteristics of porous PDMS will be taken into account, (1) the dependence of mechanical properties on its temperature and humidity (which will be measured by experiment), (2) the pre-stresses or pre-strains due to the gradient of temperature and humidity, (3) the nonlinear and visco-elastic mechanical properties. Finally, the inter-action between mechanical deformation and performance on hygro- and thermo- exchange will be studied, and mechanical optimization on flexible electronics will be studied, so that the integrated structures have good performance on hygro- and thermo- exchange as well as satisfying the mechanical deformation. Conclusions of present research are expected to provide strategies for the optimal structural designs of flexible electronics encapsulated with porous substrates.

柔性电子在医疗领域的应用，是一个崭新的课题。为了在长期、实时的监测中，保证人体热量、汗液的正常释放，需采用多孔柔性基底。它不同于目前广泛研究的连续柔性基底，也不同于力学物性参数不受湿、热影响的多孔无机材料。项目研究多孔基底柔性电子器件，在湿、热环境中的结构力学性能与优化：首先，利用均匀化理论与实验手段，确定多孔PDMS的导热系数、渗透系数等宏观参数。其次，在求得多孔PDMS基底中的温度、湿度场的基础上，进一步分析柔性电子器件的结构静、动力响应。其中既考虑高分子材料的静、动力学物性参数，受温度与湿度的影响特性（由实验测定），也考虑温度与湿度场在多孔基底中建立的应变、应力场。既考虑多孔PDMS的材料非线性、也考虑材料粘弹性。最后，研究结构变形对多孔基底传热传质性能的影响；通过优化设计，使得该类器件同时满足力学变形性能与传热传质性能要求。研究结果，可为该类器件的力学优化设计提供理论指导。

为了使柔性电子器件在对人体长期、实时的监测中，不影响人体组织正常的传热传质等生理活动，项目组提出了多孔柔性基底替代密封柔性基底制备柔性电子器件的设想。为此开展了如下研究：利用乳液聚合反应，制备了不同孔隙率的多孔PDMS。利用多种实验手段，测得多孔PDMS在不同孔隙率、不同温度与湿度下力、热、湿等多个材料参数。利用均匀化理论，从理论上预测了多孔PDMS的各项参数性能，并与实测结果吻合良好；进一步提出了各自的拟合公式，为后续的器件结构分析提供依据。采用数值或解析方法，分析、优化多孔PDMS基底柔性电子器件的静力、动力特性，以及温度、湿度环境中多孔PDMS基底柔性电子器件的响应性能。基于数值分析结果的数据拟合，提出了多个近似公式，供器件设计时方便选用。研究结果表明：多孔PDMS的多个物性参数，对孔隙率很敏感，尤其是在温、湿环境中；采用多孔PDMS基底不仅有利于传热传质等生理活动的正常进行，而且可以通过改变孔隙率有效调节、优化柔性电子器件的多项性能指标。项目研究中得到的具体研究结果，对柔性电子医疗器件的设计与优化具有较高的参考价值，可为其在健康监测领域的应用提供理论依据。研究工作涉及多孔软材料在湿热环境中的材料性能参数实验测量与理论预测；涉及多孔软材料与结构的机械性能、湿热性能分析等。研究方法与研究成果在热学、多孔材料力学、湿热力学等方面具有较高的学术价值。