Nonionic diethanolamide amphiphiles with unsaturated C18 hydrocarbon chains: thermotropic and lyotropic liquid crystalline phase behavior
作者:Sharon M. Sagnella、Charlotte E. Conn、Irena Krodkiewska、Calum J. Drummond
DOI:10.1039/c1cp21808e
日期:——
The neat and lyotropic liquid crystalline phase behavior of three nonionic diethanolamide amphiphiles with C18 hydrocarbon chains containing one, two or three unsaturated bonds has been examined. This has allowed the effect of degree of unsaturation on the phase behavior of diethanolamide amphiphiles to be investigated. Neat linoleoyl and linolenoyl diethanolamide undergo a transition from a glassy liquid crystal to a liquid crystal at ∼−85 °C, while neat oleoyl diethanolamide undergoes a transition at ∼−60 °C to a liquid crystalline material before re-crystallizing at −34 °C. Oleoyl diethanolamide then undergoes a third transition from a crystalline phase to a smectic liquid crystalline phase at ∼5 °C. In the absence of water, the transition temperature from a smectic liquid crystal to an isotropic liquid decreases with increasing unsaturation. The addition of water results in the formation of a lamellar phase (Lα) for all three amphiphiles. The lamellar phase is stable under excess water conditions up to temperatures of at least 70 °C. Approximate partial binary amphiphile-water phase diagrams generated for the three unsaturated C18 amphiphiles indicate that the excess water point for each amphiphile occurs at ∼60% (w/w) amphiphile.
考察了三种非离子型二乙醇酰胺表面活性剂的纯净状态和溶致液晶相行为,它们含有C18碳氢链,分别带有一个、两个或三个不饱和键。这使得可以探讨不饱和度对二乙醇酰胺表面活性剂相行为的影响。纯净的亚油酰基和亚麻酰基二乙醇酰胺在约−85 °C时发生从玻璃态液晶到液晶的相变,而纯净的油酰基二乙醇酰胺在约−60 °C时发生相变形成液晶材料,然后在−34 °C时再结晶。油酰基二乙醇酰胺随后在约5 °C时发生第三次相变,从晶态相转变为碟状液晶相。在没有水的情况下,从碟状液晶到各向同性液体的转变温度随着不饱和度的增加而降低。加入水会导致所有三种表面活性剂形成层状相(Lα)。层状相在水过量条件下至少在70 °C下稳定。为这三种不饱和C18表面活性剂生成的近似部分二元表面活性剂-水相图表明,每种表面活性剂的过量水点出现在约60%(重量比)表面活性剂。