Hannon Theresa E, Chah Soonwoo, Zare Richard N
Department of Chemistry, Stanford University, Stanford, California 94305-5080, USA.
J Phys Chem B. 2005 Apr 21;109(15):7435-42. doi: 10.1021/jp050045s.
Evanescent-wave cavity ring-down spectroscopy (EW-CRDS) is used to measure interfacial phenomena when methanol or water is placed in contact with a film of poly(dimethylsiloxane) (PDMS), which is attached to the face of a fused-silica prism that constitutes part of a ring cavity. In the first few minutes after contact, the uptake of methanol is slower than that of water, but after this initial period the methanol diffuses more rapidly in the film than water does. Bulk weight-gain measurements confirm this result and yield diffusion coefficients of (25.1 +/- 0.7) x 10(-7) cm(2)/s for methanol in PDMS and (7 +/- 2) x 10(-7) cm(2)/s for water in PDMS. The interfacial optical losses found in the EW-CRDS measurements result primarily from scatter. In particular, we find that delamination of the film from the fused-silica substrate dominates the optical losses in the case of methanol. This conclusion is confirmed by separate surface plasmon resonance experiments.
倏逝波腔衰荡光谱法（EW-CRDS）用于测量甲醇或水与聚二甲基硅氧烷（PDMS）薄膜接触时的界面现象，该薄膜附着在构成环形腔一部分的熔融石英棱镜表面。在接触后的最初几分钟内，甲醇的吸收速度比水慢，但在此初始阶段之后，甲醇在薄膜中的扩散速度比水快。整体增重测量证实了这一结果，并得出甲醇在PDMS中的扩散系数为(25.1±0.7)×10⁻⁷ cm²/s，水在PDMS中的扩散系数为(7±2)×10⁻⁷ cm²/s。EW-CRDS测量中发现的界面光学损耗主要源于散射。特别是，我们发现在甲醇的情况下，薄膜与熔融石英基底的分层主导了光学损耗。这一结论得到了单独的表面等离子体共振实验的证实。
