Basic research on soft opal crystal films and control of their structural color

软蛋白石晶体是一种具有柔性和柔软力学性能的胶体晶体。软蛋白石晶体由有序排列的单分散颗粒组成，其中填充弹性聚合物。本文报道了用软蛋白石晶体薄膜制备的两种结果。1. 膨胀现象及基础研究：一种测定未知弹性体溶解度参数的简便方法。在给定溶解度参数σ的条件下，我们用大约20种溶剂测量了膨胀条件下Bragg衍射的峰移△λ。然后绘制出σ和△λ之间的关系，并给出了σ max处△λ的最大值。该σ max估计了未知弹性体的溶解度参数。在参考数据的基础上，我们利用弹性体块体的伸长率L/L0研究了同一弹性体的溶解度参数。弹性体的溶解度参数在最大时对应于σ (L/L0)。这两个值也几乎相同。在几秒钟内测量△λ us。该方法简单，易于确定弹性体σ的未知量。2. 弹性变形可调结构颜色：胶板表面涂覆软的蛋白石晶体。应变改变了胶体晶体中的粒子排列。这种新材料被命名为“光子橡胶片”，它的结构颜色通过拉伸可逆地从红色变为绿色。应变与峰值位移之间的关系可以应用于机械传感。结果，光子橡胶片被《物理基础》教科书（Wiley出版社，2007年第8版）收录。软蛋白石晶体就是一个很好的例子，由于可见波长的布拉格衍射和结构颜色的变化。

Soft opal crystal is a colloidal crystal with flexible and soft mechanical property. The soft opal crystal consists of a composite material ordered array of mono-dispersed particles and among them infilling with elastic polymer. Here we report two results using thin film of soft opal crystal. 1. Swelling phenomena and basic research: A new easy and simple method to determine solubility parameter of unknown elastomer. We measured peak shift of Bragg's diffraction, △λ, at swollen conditions using about twenty solvents with given the solubility parameter, σ. Then the relationship between σ and △λ was plotted and gave us the maximum of △λ at σ max. This σ max is estimate the solubility parameter of the unknown elastomer. On reference data, we investigated the solubility parameter of same elastomer using the elongation, L/L0 of an elastomer block. The solubility parameter of elastomer is corresponding to σ at the maximum (L/L0). Both values are also almost same value. The measurement of △λ us in a few seconds. The new method is simple and easy to determine unknown of σ the elastomer. 2. Tunable structural color by elastic deformation: soft opal crystal coated on surface of rubber sheet. The particle array in colloidal crystal is changed by strain. This new material named "Photonic Rubber sheet" reversibly change its structural color from red to green by stretch-out. The relationship between strain and peak shifting enable apply for mechanical sensing. As distinguished result, the photonic rubber sheet was picked up in a textbook of Physics (Fundamental of Physics, 8th Ed., Wiley, 2007). Soft opal crystal is a good example due to Bragg's diffraction in visible wavelength and change of structural color.