Chuiko Institute of Surface Chemistry, Kiev, Ukraine.
Langmuir. 2013 Apr 2;29(13):4303-14. doi: 10.1021/la400392h. Epub 2013 Mar 21.
The interfacial and temperature behavior of n-decane bound to weakly hydrated nanosilica A-400 (initial, heated, or compacted) or silica gel Si-60 was studied using low-temperature (1)H NMR spectroscopy applied to static samples that allowed us to observe signals only of mobile decane and unfrozen water molecules. For deeper insight into the phenomena studied, interactions of n-decane, 1-decanol, and water with a set of nanosilicas and silica gels were analyzed using DSC and thermoporometry. Both NMR and DSC results demonstrated that during heating of frozen samples at a heating rate of 5 K/min a portion of decane or decanol remained frozen at temperature higher than the freezing point of bulk liquid (Tf). For decane and decanol adsorbed onto silica gels Si-40, Si-60, and Si-100, the number, position, and intensity of freezing and melting peaks observed in the DSC thermograms over the 170-300 K range during cooling and heating of samples depended on the pore size distribution of silicas as well as on the amounts and type of adsorbates. The position of the main freezing peak of decane for all samples was close to Tf because the alkane amount was greater than the pore volume; i.e., a fraction of decane was bulk liquid. According to (1)H NMR data, a portion of decane, which was in a quasi-crystalline solid state characterized by fast molecular exchange (i.e., short transverse relaxation time) and not observed in the spectra, was greater than a portion of decane frozen at temperatures close to Tf during cooling that appears in the DSC endotherms of heated samples.
用低温（1）H NMR 光谱研究了与弱水合纳米二氧化硅 A-400（初始、加热或压实）或硅胶 Si-60 结合的正癸烷的界面和温度行为，该方法适用于静态样品，使我们仅能观察到可移动的癸烷和未冻结水分子的信号。为了更深入地了解所研究的现象，使用 DSC 和热压法分析了正癸烷、1-癸醇和水与一组纳米二氧化硅和硅胶的相互作用。NMR 和 DSC 结果均表明，在以 5 K/min 的加热速率加热冷冻样品时，一部分癸烷或 1-癸醇在高于液体整体凝固点（Tf）的温度下保持冻结状态。对于吸附在硅胶 Si-40、Si-60 和 Si-100 上的癸烷和 1-癸醇，在冷却和加热过程中，在 170-300 K 范围内观察到的 DSC 热谱图中观察到的冻结和熔化峰的数量、位置和强度取决于硅胶的孔径分布以及吸附物的数量和类型。由于烷烃的量大于孔体积，因此所有样品的正癸烷的主要冻结峰的位置都接近 Tf；也就是说，一部分正癸烷是体相液体。根据（1）H NMR 数据，一部分处于快速分子交换（即短横向弛豫时间）特征的准晶固态的癸烷，没有在光谱中观察到，比在冷却过程中接近 Tf 温度冻结的部分癸烷多，在加热样品的 DSC 吸热中出现。
