期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1999
卷号：96
期号：14
页码：7756-7759
DOI：10.1073/pnas.96.14.7756
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Amphiphiles are molecules such as surfactants or lipids that have a polar head group (hydrophilic) attached to nonpolar hydrophobic alkyl chains. Because of this characteristic they self-assemble in water and give rise to a wide range of phases with different structures and properties. Aqueous dispersions of amphiphiles are present in every aspect of day-to-day life--e.g., forming biological cell membranes, stabilizing emulsified food, or being used as soap. Time-resolved x-ray diffraction has been used to study the hexadecylhexa(oxyethylene glycol) ether (C16EO6)/water system, which shows an intermediate phase whose structure depends on the thermal path between lamellar and hexagonal structures. Heating the hexagonal phase from room temperature leads to a lamellar phase via an Ia3d cubic structure. Cooling from the lamellar phase initially leads epitaxially to an intermediate R[IMG]f1.gif" ALT="3" BORDER="0">m before the hexagonal phase is reached. Both cubic and R[IMG]f1.gif" ALT="3" BORDER="0">m phases are formed by very similar rod units, but the overall structures differ because of their spatial distribution and they both bridge morphologically the hexagonal and lamellar phases. The Ia3d does so on heating, whereas the R[IMG]f1.gif" ALT="3" BORDER="0">m does on cooling. The structural path during the phase transitions is determined by topological similarities between the forming phase and the one from which it originates. Although the estimated curvature energies for these two phases are similar, on cooling, kinetics and topology are initial factors determining the path for the phase transitions, whereas on heating energy is the dominant factor.
