選擇不同烷基鏈長度之雙烷基二甲基溴化銨(dialkyldimethylammonium bromides, DXDAB)陽離子型界面活性劑，即雙十四烷基二甲基溴化銨(dimyristyldimethylammonium bromide, DMDAB)、雙十六烷基二甲基溴化銨(dihexadecyldimethylammonium bromide, DHDAB)和雙十八烷基二甲基溴化銨(dioctadecyldimethylammonium bromide, DODAB)以改善化合物A分散液之穩定性。利用粒徑分佈和界面電位、穿透式電子顯微鏡(transmission electron microscope, TEM)、螢光偏極化和微分掃描熱卡計(differential scanning calormetry, DSC)分析分別探討混合A/DXDAB分散液的物理穩定性、粒子型態及雙層內的流動性。此外，量測24℃下混合A/DXDAB單分子層在氣/液界面上之表面壓-每分子佔據面積(surface pressure-per molecular area, π-A)之等溫線，並透過螢光顯微鏡直接觀察單分子層的型態。在TEM圖中可看到混合A/DXDAB分散液會形成粒子結構。由DSC和π-A等溫線結果推測A和DXDAB在雙層結構中及在氣/界面上具有部份混合現象。物性結果顯示混合A/DHDAB = 8/2分散液在室溫下的穩定天數最高，但混合A/DXDAB分散液的界面電位似乎不隨DXDAB比率的提高而有明顯改變。螢光偏極化結果顯示在XDHDAB = 0.2~0.4之混合分散液中雙層內分子疏水端區域的作用最為顯著。 We choose cationic lipid, dialkyldimethylammonium bromides (DXDAB) with differing in dialkyl chain length－dimyristyldimethylammonium bromide (DMDAB), dihexadecyldimethylammonium bromide (DHDAB), and dioctadecyldimethylammonium bromide (DODAB) to improve stability of compound A dispersions. The physical stability, particles morphology and bilayer fluidity of mixed A/DXDAB dispersions were investigated by size distribution, zeta-potential, transmission electron microscope (TEM), fluorescence polarization and differential scanning calormetry (DSC) analysis, respectively. Furthermore, surface pressure-per molecular area (π-A) isotherms of mixed A/DXDAB monolayers at the air/water interface were measured at 24℃, and fluorescence microscopy was utilized to directly observe morphology of mixed A/DXDAB monolayers. TEM images show that mixed A/DXDAB dispersions can form particles structures. DSC and π-A isotherms results show that A and DXDAB are partial miscible in the bilayer structures and at the air/water interface. Results of physical properties show that the best storage stability was found for mixed A/DHDAB = 8/2 dispersions. However, the zeta potential of the mixed A/DXDAB dispersions did not change significantly with the increase in XDXDAB. Fluorescence polarization results show that the best pronounced alkyl chain interaction in the bilayer was found for the mixed dispersions with XDHDAB = 0.2~0.4.
