Solvent Permeation, Swelling Profiles and Mechanical Properties of Thin Polymer Films

本研究将研究薄硅氧烷和环氧树脂聚合物薄膜，这些薄膜将以线性链的形式自旋铸造到各种衬底（蓝宝石、BK7玻璃和二氧化硅）上，厚度从50纳米到几微米，然后交联形成刚性结构。研究的重点是这些膜吸收溶剂的机制，以及溶剂的渗透和膨胀如何影响膜与基底的附着力，以及膜的力学。溶剂渗透将使用全内反射荧光（TIRF）进行研究，该技术将薄膜粘附的衬底放置在光学棱镜上，激光束以掠掠角撞击衬底/聚合物薄膜表面，产生指数衰减的倏逝波，穿透薄膜。通过改变入射角，可以达到不同的侵彻深度。使用TIRF，将进行两种类型的实验。在第一种方法中，将自由染料扩散到平衡膨胀膜或部分膨胀膜中，然后在染料上放置发色团。由倏逝波引起的辐射使发色团发出荧光，通过检测薄膜的总荧光作为穿透深度的函数（通过改变掠角），可以通过反褶积计算染料浓度（参见公式3）。通过重复TIRF角度作为时间的函数，可以构建染料的时间依赖性浓度曲线。在第二种类型的实验中，未膨胀薄膜的聚合物网络将被标记。然后，薄膜的表面将暴露在渗透性溶剂中，随着薄膜因溶剂吸收而膨胀，聚合物链将变形，标签的浓度将发生变化。同样，通过使用时间分辨的TIRF角度，可以计算出标签的时间依赖浓度曲线，并从中了解标签在膨胀过程中的空间分布。将测量薄膜的动态力学响应，并使用显微硬度计来确定聚合物薄膜与衬底之间的结合。

This research will study thin siloxane and epoxy polymeric films which will be spin cast as linear chains onto a variety of substrates (sapphire, BK7 glass, and silica) to thicknesses of 50 nm to several microns, and then crosslinked to form a rigid structure. The study focuses specifically on the mechanisms by which these films uptake solvent, and how solvent permeation and swelling affects the adhesion of the film to the substrate, and the membrane mechanics. Solvent permeation will be studied using total internal reflectance fluorescence (TIRF), a technique in which the substrate onto which the film is adhered is placed on an optical prism, and a laser beam impinges at a grazing angle to the substrate /polymer film surface producing an exponentially decaying evanescent wave which penetrates through the film. By varying the angle of incidence, different penetration depths can be achieved. Using TIRF, two types of experiments will be undertaken. In the first, diffusion of a free dye into an equilibrium swollen film or a partially swollen film will be followed by placing a chromophore on the dye. The radiation due to the evanescent wave causes the chromophore to fluoresce, and by detection of the total fluorescence of the film as a function of the penetration depth (by changing the grazing angle), the dye concentration can be computed by deconvolution (cf. eq. 3). By repeating the TIRF angling as a function of time, the time dependent concentration profile of the dye can be constructed. In the second type of experiment, the polymer network of an unswollen film will be tagged. The face of the film will then be exposed to a permeating solvent, and as the film swells due to the solvent uptake, the polymer chains will deform and the concentration of the tag will vary. Again, by using time resolved TIRF angling, the time dependent concentration profile of the labels can be computed, and from these, insight into the spatial distribution of the labels during swelling can be obtained. The dynamical mechanical response of the membrane will be measured, and a microhardness tester will be used to determine the bond between the polymer film and the substrate.