High-pressure ATR spectroscopic study on conformation and hydration of oxyethylene

采用高压红外光谱研究了非离子表面活性剂烷基/低聚（氧乙烯）二嵌段化合物H(CH_2)_n(OCH_2CH_2)_mOH （C_nE_n）在c_ne_m -水二元体系中的分子构象及其水化行为。使用金刚石衰减全反射池（DATRC）和金刚石砧池（DAC）研究了凝胶相中表面活性剂的分子构象、分子堆积和水合作用。由于在这个过程中没有标准的方法，我们有几种高压DATRC测量的采样方法。因此，我们获得了高达约30 MPa的压力，在DATRC元件和压力鞋之间设置了相反的顶砧。因此，使用DATRC和DAC，可以在从环境压力到约5 GPa的压力范围内进行红外测量。我们研究了C_nE_7化合物的压力依赖性分子形态和堆积，因为C_nE_7s的分子形态为*型，与m=3-6和m【大于或等于】8的其他C_nE_ms在固态时的*型不同。由于C_nE_7s的特殊形态是由于晶体中的分子堆积造成的，外部压力会干扰分子形态和堆积。对于C_<10>E_7-H_2O体系，氢键随着压力的增加而增强，在1 GPa左右发生了由*型到*型的构象转变。另一方面，对于C_<16>E_7-H_2O体系，虽然没有发生构象转变，但对低聚（氧乙烯）部分的红外波段进行了小波数筛选。

Molecular conformation of nonionic surfactants alkyl / oligo(oxyethylene) diblock compounds H(CH_2)_n(OCH_2CH_2)_mOH (C_nE_n) and their hydration behavior in the C_nE_m-water binary system have been studied by high-pressure infrared spectroscopy. Molecular conformation, molecular packing, and hydration of the surfactants in the gel phase have been studies using a diamond attenuated total reflection cell (DATRC) and a diamond anvil cell (DAC).We have first several sampling method for high-pressure DATRC measurement, because no standard method is available in this procedure. Consequently, we have obtained a pressure up to ca. 30 MPa with opposed anvils arrangement between a DATRC element and a pressure shoe. Accordingly, infrared measurements in pressure range from ambient pressure to ca. 5 GPa became possible with DATRC and DAC.We have studied pressure dependent molecular form and packing for the C_nE_7 compounds, because C_nE_7s assume the * form, which is the molecular form different from the * form for the other C_nE_ms with m=3-6 and m【greater than or equal】 8 in the solid state. As the peculiar form for C_nE_7s results from molecular packing in the crystal, external pressure should perturb the molecular form and packing.For C_<10>E_7-H_2O system, Hydrogen bonding was strengthened with increasing pressure and a conformational transformation from the * form to the * form has been observed at about 1 GPa. For C_<16>E_7-H_2O system, on the other hand, conformational transformation has not been occurred but small wavenumber sift for the infrared bands attributed to the oligo (oxyethylene) part been observed.