Surface Structure of Polymer Gels and Emerging Functions

在这项研究中，我们使用原子力显微镜（AFM）研究了聚合物凝胶的介观表面结构（如表面粗糙度和特征长度），以及它在决定宏观功能（如粘附、表面张力和摩擦）中的作用。利用原子力显微镜研究了聚n -异丙基丙烯酰胺（NIPA）凝胶在水中的表面结构，确定了其表面构象为亚微米尺度的海绵状结构域。我们研究了体网络的不均匀性对畴结构的影响，以及温度变化的影响。从自相关函数和从形貌计算的功率谱密度的角度讨论了海绵状畴引起的表面粗糙度。为了探讨表面粗糙度与宏观表面性质之间的关系，以具有疏水相互作用的NIPA凝胶为模型，测量了水中无根气泡的静态接触角。静态接触角随温度的变化取决于体网的不均匀性。我们表明，静态接触角不仅可以由化学（在本例中，疏水-亲水相互作用的平衡）控制，还可以由疏水聚合物凝胶响应温度变化的物理性质控制。在考虑的各种有效物理因素中，以下因素在确定静态接触角时是必不可少的：聚合物密度、表面粗糙度和网络均匀性。我们认为，本研究对基于聚合物凝胶表面基础研究获得的基本概念的新技术的未来开发和应用具有至关重要的意义。

In this study, we investigated the mesoscopic surface structure of polymer gels (such as surface roughness and characteristic length) using an atomic force microscopy (AFM), as well as its role in determining the macroscopic functions (such as adhesion, surface tension, and friction).1. Surface structure of poly(N-isopropylacrylamide) (NIPA) gels in water was studied using AFM, and it was established that the surface conformation is characterized by the sponge-like domains with submicrometer scale. We investigated the effect of the inhomogeneities of the bulk networks on the domain structure, as well as the effect of the temperature change. Surface roughness due to the sponge-like domains was discussed in terms of the auto-correlation function and of the power spectral density calculated from the topographies.2. In order to discuss the relation between the surface roughness and the macroscopic surface properties, the static contact angle of sessile air bubbles in water was measured for NIPA gels as a model gel with hydrophobic interactions. The static contact angle versus temperature was found to depend on the inhomogeneities of the bulk networks. We showed that the static contact angle can be governed not only by the chemical (in the present case, the balance of the hydrophobic-hydrophilic interactions) but also by the physical properties of hydrophobic polymer gels in response to a temperature change. Of the various effective physical factors being considered, the following would be essential in determining the static contact angle : the polymer density, the surface roughness, and the network homogeneity.We believe that the present study is of crucial importance for the future development and application of new technologies based on the basic concepts gained from the fundamental studies of polymer gel surfaces.