聚合物薄膜分子松弛与液滴在其表面润湿行为的关系研究

The macroscopic property of polymer was determined by the motion of their molecular chain. The glass transition temperature (Tg) is defined as the temperature at which the dynamics of molecules dramatically slow down and the molecular liquid falls out of equilibrium, manifested as a dramatic increase of the mechanical modulus, an increase in relaxation times, and also in the rise of viscosity by many orders of magnitude. It is a key parameter for characterizing the mobility of polymer chains and determines the temperature range for application of many materials. Because of the finite size effects, surface and interface effects and other impacts with decreasing of film thickness, the glass transition dynamics of nanometers-thick polymer films significantly deviates from that in bulk. With the recent advances in nanotechnology, increasing interest in thin film coatings and nano-devices of polymer materials exacerbate our concerns on the precise understanding of the physical properties and performances of nano-devices related to the segmental dynamics of polymers under confinement. Consequently, there is a great demand for novel techniques to characterize the thin film dynamics such as the glass transition, molecular mobility, flow dynamics, and mechanical response. In our previous work, the wetting behavior of liquid on polymer surface has found to be affected by the viscoelascity of the polymer film. Base on this background, the dynamic wetting of liquid on polymer surface was firstly developed to be a sensor investigating the chain relaxation of thin polymer films in the current proposal. In the glass transition region, the wetting of liquid on polymer surface exhibits "stick-slip" phenomenon and a quantitative parameter "jumping angle" was put forward to scale the "stick-slip" behavior. By detecting variation in the "jumping angle" as a function of film temperature, the relaxation dynamics of supported thin films such as Tg and viscoelascity can be accessed, and substrate effect can also be determined by detecting the liquid wetting on film surface. The aim of this project is to develop an original method for in situ characterizing the chain relaxation of thin polymer films and that influenced by the substrate, as well quest the theoretical foundation of this method. Our preceded results have proven this project to be feasible in both theory and experiment.

聚合物的分子运动决定其宏观性质。当高分子薄膜厚度从微米级别降低到分子水平，其分子松弛行为将与本体发生偏离，如Tg下降。纳米技术的快速发展迫切希望深入了解聚合物超薄膜分子运动的相关规律。发展原位研究聚合物薄膜分子松弛行为如玻璃化转变的新方法是目前的当务之急。本项目首次提出利用液滴在聚合物薄膜表面润湿行为与其粘弹性之间的关系来研究聚合物薄膜的分子松弛。以聚苯乙烯、聚甲基丙烯酸甲酯等薄膜为研究对象，通过液滴在膜表面润湿行为中stick-slip现象所产生的跳跃角与膜温度的关系原位研究基底支撑的聚合物薄膜、超薄膜分子松弛行为如玻璃化转变，粘弹响应及力学损耗等；研究基底效应对超薄膜分子运动的影响及其影响的临界厚度等。从本质上解决液滴润湿行为中相关参数如跳跃角，与聚合物膜力学性能的关系。发展一种全新的原位研究高分子超薄膜玻璃化转变的手段。解决该方法的理论基础。前期研究已经证明本项目是完全可行的。

纳米技术的快速发展迫切希望深入了解纳米受限聚合物材料分子运动的相关规律。发展原位研究聚合物薄膜分子松弛行为如玻璃化转变的新方法是目前当务之急。本项目研究了在液滴表面张力作用下，聚合物表面产生形变形成“润湿脊”，由此对液滴润湿行为产生影响。发展了一种利用力学方法研究聚合物超薄膜玻璃化转变、黏弹性及分子松弛的新方法并为之奠定理论基础，为原位研究受限聚合物分子运动行为提供了新的研究手段。项目研究了基底表面化学、自由表面、聚合物结构等对聚合物超薄膜的分子松弛行为的影响。获得了以下结果：1)发现了聚合物表面液滴润湿行为与其黏弹性及分子松弛行为之间的内在联系，实现了力学方法原位研究聚合物膜玻璃化转变、黏弹性与分子松弛行为。该法操作简单、灵敏度高，特别适合基底支撑聚合物薄膜黏弹性及玻璃化转变的研究。2) 阐明了利用stick-slip行为研究薄膜玻璃化转变及分子松弛的机理；建立了液滴stick-slip过程中聚合物表面形变的简化模型，借助流变学中的Deborah number概念，提出了衡量液滴stick-slip过程中聚合物表面黏弹性（或黏弹耗散）的参数ξ。建立了聚合物黏弹性与液滴跳跃角的本质关系。3）利用该方法研究深入研究了受限高分子薄膜分子动力学。阐明了基底性质、界面吸附层结构、聚合物分子量等对聚合物超薄膜分子运动行为影响的本质。发现了聚合物在基底表面的吸附层厚度可作为衡量受限聚合物薄膜基底效应的参数。4)获得了聚合物分子刷玻璃化转变行为规律，成膜溶液浓度以及聚合物结构对膜表面结构以及表面分子运动行为的影响。这些研究成果为受限聚合物材料分子运动行为偏离本体原因争论的解决，基底效应向本体传播的机理研究提供新的技术手段和实验证据。也为聚合物纳米材料结构设计、性能预测、加工条件优化等实际应用提供理论指导。项目发表论文19篇，SCI收录论文16篇（IF大于4.0的13篇）；申请发明专利6项。培养博士1名，硕士11名。期间承办第九届全国高聚物分子与结构表征研讨会。