本研究利用反射吸收式紅外光譜分析技術（infrared reflection-absorption spectroscopy, IRRAS），探討於動態壓縮-擴張氣/液界面的情況下，離子對雙親分子(ion pair amphiphile, IPA)單分子層的穩定性。IPA是由十六烷基三甲基溴化銨(hexadecyltrimethylammonium bromide, HTMAB)與十二烷基硫酸鈉(sodium dodecylsulfate, SDS)製備而成的HTMA-DS，純HTMA-DS單分子層的穩定性因受到界面壓縮-擴張的影響而顯著下降。由單分子層之IRRAS分析所得的CH2非對稱性吸收峰的吸收值與頻率，可發現添加正十六碳醇或正十八碳醇能夠促進HTMA-DS單分子層的穩定性，添加膽固醇則無明顯效果。此外，在壓縮單分子層後於固定面積下令單分子層鬆弛兩小時的過程中，發現添加正十六碳醇之混合單分子層的鬆弛損失率比添加正十八碳醇的小，添加膽固醇之混合單分子層的鬆弛損失率則最高。添加正十六碳醇或正十八碳醇於HTMA-DS單分子層中，可能因醇類分子頭基較小而無立體障礙，所以混合單分子層中分子長碳氫鏈間的凡得瓦爾作用較明顯，而提高單分子層的穩定性。且由於正十六碳醇的碳氫鏈長度與HTMA-DS其中的一條碳氫鏈等長，而可能使得單分子層中分子之間能有較緊密的排列。添加膽固醇時，則可能因其環狀結構較硬，分子之間排列不易緊密，導致HTMA-DS單分子層穩定性無法提升。

This study investigated the stability of an ion pair amphiphile (IPA) monolayer at the air/water interface during interfacial compression and expansion by the infrared reflection-absorption spectroscopy (IRRAS). IPA, HTMA-DS, was prepared from hexadecyltrimethylammonium bromide (HTMAB) and sodium dodecylsulfate (SDS). It was found that the stability of a pure HTMA-DS monolayer was significantly reduced due to the interfacial compression-expansion effect. With the reflectance-absorbance intensity and wavenumber of the νasCH2 band obtained from the IRRAS analysis of monolayers, the HTMA-DS monolayer stability could be enhanced by the presence of n-hexadecanol or n-octadecanol. With the addition of cholesterol, however, no obvious enhancement of the HTMA-DS monolayer stability could be detected. In addition, when the monolayer was compressed to a fixed area and then was relaxed for two hours, it appeared that the relaxation loss of a mixed HTMA-DS/n-hexadecanol monolayer was less than that of a mixed HTMA-DS/n-octadecanol monolayer. The most pronounced relaxation loss was found for a mixed monolayer of HTMA-DS with cholesterol. The headgroups of n-hexadecanol or n-octadecanol might be small enough to avoid the steric hindrance, resulting in stronger van der Waals interactions between the alkyl chains of molecules in the mixed monolayers with higher stability. Moreover, since the alkyl chain length of n-hexadecanol is the same as one of the HTMA-DS alkyl chains, the molecules in the monolayer may pack closely. With the presence of cholesterol, the rigid cyclic structure of cholesterol might lead to loose packing between molecules and thus no enhancement in the monolayer stability could be detected.

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