本研究藉由表面壓-面積及表面電位-面積等溫線、鬆弛曲線和布魯斯特角顯微鏡（Brewster angle microscope）影像，分析分子間交互作用和混合單分子層的穩定性，以探討添加雙十六碳鏈磷酸鹽（dihexadecyl phosphate, DHDP）及膽固醇對於離子對雙親分子（ion pair amphiphile, IPA）hexadecyltrimethylammonium-dodecylsulfate（HTMA-DS）單分子層行為的影響。
對HTMA-DS/DHDP混合單分子層而言，等溫線與熱力學分析顯示DHDP具有與膽固醇相似的凝縮效應，且HTMA-DS與DHDP分子間以吸引作用為主。此外，在表面壓30 mN/m時，隨著DHDP添加量的增加，混合單分子層在氣/液界面上的穩定性越高。
從HTMA-DS/膽固醇混合單分子層的等溫線可看出，在分子排列鬆散的狀態下，膽固醇具有相當顯著的凝縮效應。而熱力學分析顯示添加膽固醇於HTMA-DS單分子層中，能增加分子間的吸引作用，且分子排列的規則性較高。此外，由DHDP/膽固醇混合單分子層的等溫線及BAM影像可知，膽固醇似乎會擾亂混合單分子層中分子的排列，熱力學分析則顯示DHDP與膽固醇分子間的作用，小於二者各別相同分子間的作用。
添加膽固醇於不同莫耳比的HTMA-DS/DHDP混合單分子層中，由等溫線可知當HTMA-DS含量較高時，隨著膽固醇的莫耳分率增加，凝縮效應越明顯。在DHDP含量較高的混合單分子層中，膽固醇的凝縮效應則較不顯著。造成此結果的可能原因為膽固醇與DHDP的分子間作用小於膽固醇與HTMA-DS的分子間作用，或膽固醇分子擾亂了DHDP分子排列的規則性。此外，由單分子層的鬆弛行為可知，添加膽固醇於HTMA-DS/DHDP混合單分子層後，在表面壓30 mN/m的狀態下，混合單分子層的穩定性並不佳，推測是因為膽固醇的固醇環和短碳氫鏈插排在HTMA-DS及DHDP分子間會產生立體障礙，使單分子層中分子排列的配位性不佳。

This study investigated the effects of added dihexadecyl phosphate (DHDP) and cholesterol on the monolayer behavior of ion pair amphiphile (IPA), hexadecyltrimethylammonium-dodecylsulfate (HTMA-DS), by analyzing the molecular interaction and mixed monolayer stability with the surface pressure-area and surface potential-area isotherms, relaxation curves, and Brewster angle microscopy (BAM) images.
For the mixed monolayers of HTMA-DS/DHDP, the isotherms and thermodynamic analysis indicated that DHDP possessed the similar condensing effect as cholesterol and the interactions between HTMA-DS and DHDP were mainly attractive. In addition, at a surface pressure of 30 mN/m, the stability of a monolayer at the air/water interface was higher with the increased amount of DHDP.
From the isotherms of mixed HTMA-DS/cholesterol monolayers, one can find that cholesterol possessed a significant condensing effect when the molecular arrangement was at an expanded state. The thermodynamic analysis indicated that with the addition of cholesterol into the HTMA-DS monolayer, the attractive interaction between the molecules was enhanced and the molecular arrangement became ordered. Besides, the isotherms and BAM images of mixed DHDP/cholesterol monolayers suggested that cholesterol might disturb the molecular packing in the mixed monolayers, and the thermodynamic analysis implied that the interaction between DHDP and cholesterol was smaller than that between the same molecules of DHDP and cholesterol, respectively.
When adding cholesterol into mixed HTMA-DS/DHDP monolayers with different mixing ratios, one can find from the isotherms that with a higher content of HTMA-DS, the condensing effect became pronounced with increased molar fraction of cholesterol. However, the condensing effect of cholesterol was less significant with a higher content of DHDP in the mixed monolayers. This is probably because the molecular interaction between cholesterol and DHDP was smaller than that of cholesterol and HTMA-DS , or cholesterol might disturb the molecular packing of DHDP molecules. Furthermore, from the monolayer relaxation behavior, one can find that by adding cholesterol into mixed HTMA-DS/DHDP monolayers, the stability of the mixed monolayers at a surface pressure of 30 mN/m was poor. This probably resulted from the mismatch of the molecule arrangement due to the steric barrier induced by inserting the sterol ring and short hydrocarbon chain of cholesterol between HTMA-DS and DHDP molecules.

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