Thermally changing lattice distance of lamella in the hydrated solid of octadecyltrimethylammonium chloride.
Thermally changing lattice distance of lamella in the hydrated solid of octadecyltrimethylammonium chloride.
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DOI：
10.1021/jp802313c
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发表时间：
2008-06
期刊：
影响因子：
--
通讯作者：
S. Sasaki
中科院分区：
文献类型：
--
作者：
S. Sasaki
对水合十八烷基三甲基氯化铵（OTAC）固体进行了温度扫描小角x射线散射测量。逐步改变lamella-like晶格间距的结构从40 nm在5摄氏度到20 nm在18摄氏度观察融化过程中孵化的水化固体在4摄氏度的24 h水溶液,虽然变化不大的晶格间距约20 nm观察在同一进程中孵化的水化固体在4摄氏度一段大约10分钟。这表明水合固体在4℃孵育和熔化过程中的结构变化。差扫描量热法测量结果显示，与纳米结构的变化相对应，前者在温度为13 ~ 22℃时，后者在温度为15 ~ 21℃时，观察到广泛的吸热峰。在温度低于13℃时，由于没有观察到吸热峰，结构变化被认为是无热的。在频率约为10 kHz时，观察到水合固体悬浮液有较大的介电色散，而溶解固体的溶液没有。结果表明，水合固体悬浮液的电导率远低于溶解固体溶液的电导率。观察到的电学性质表明，游离氯离子的数量非常少，与铵基结合的氯离子通过响应外加电场在水合固体中移动。在4℃孵育10 min的水合固体悬浮液的电导率是在相同温度孵育24 h的水合固体悬浮液的4倍。这表明OTAC水合固体在4℃时的结构变化与氯离子与水合固体的结合有关。上述实验结果表明，在远低于熔点的温度下，OTAC水合固体中的片层呈波动状，波动波长随孵育时间的增加而增加。
A temperature scanning small-angle X-ray scattering measurement was carried out for the hydrated solids of octadecyltrimethylammonium chloride (OTAC). A gradual change of the lattice spacing of lamella-like structure from 40 nm at 5 degrees C to 20 nm at 18 degrees C was observed in the melting process of the hydrated solid that was incubated at 4 degrees C for a period of 24 h in the aqueous solution, while little change of the lattice spacing of about 20 nm was observed in the same process of the hydrated solid that was incubated at 4 degrees C for a period about 10 min. This indicates structural changes of the hydrated solid during the incubation at 4 degrees C and in the melting process. Corresponding to the nanostructure changes, broad endothermic peaks were observed at temperatures from 13 to 22 degrees C for the former hydrated solid and at temperatures from 15 to 21 degrees C for the latter hydrated solid in difference scanning calorimetry measurements. The structure change at temperatures below 13 degrees C is considered to be athermal from the fact that no endothermic peak is observed there. Large dielectric dispersions at frequencies at about 10 kHz were observed for the suspensions of hydrated solids but not for the solutions of dissolved solids. It was found that the electric conductance of the hydrated solid suspensions was much lower than that of the solutions of dissolved solids. The observed electric properties indicate that an amount of the free chloride ion is very small and that the chloride ions binding to the ammonium groups are movable in the hydrated solids by responding to an applied electric field. The electric conductance of suspension of the hydrated solid being incubated at 4 degrees C for 10 min was 4 times as large as that of a suspension of the hydrated solid being incubated at the same temperature for 24 h. This indicates that the structural change of the OTAC hydrated solid at 4 degrees C is related to the chloride ion binding to the hydrated solid. The experimental results described above suggest that the lamella in the hydrated solid of OTAC is undulated and that the wavelength of undulation increases with the incubation at a temperature much lower than the melting temperature.