STRUCTURAL-PROPERTIES AND ELASTICITY OF AMPHIPHILICS ON WATER
STRUCTURAL-PROPERTIES AND ELASTICITY OF AMPHIPHILICS ON WATER
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DOI：
10.1051/jp2:1991102
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发表时间：
1991-02-01
期刊：
影响因子：
--
通讯作者：
BENATTAR, JJ
中科院分区：
文献类型：
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作者：
DAILLANT, J;BOSIO, L;BENATTAR, JJ
用X射线反射率研究了吸附在空气-水界面上的两亲分子的单分子膜。这项技术允许准确和独立地确定厚度(通过测量等倾角的条纹)以及密度和粗糙度(因为这是绝对强度测量)；因此可以获得完整的电子密度分布。表面粗糙度是由热激发的毛细管波引起的，因此与界面的动力学有关，界面的动力学由层的弹性常数决定。用这种方法研究了C15、C21和C29脂肪酸和磷脂L-α-二苯基丙酸的相图，并对相变进行了分析。从结构上看，这类化合物吸附在水中的一个总体特征是在液体和固体相中的脂肪族介质密度不变。压力与油膜厚度的关系曲线与压力面积曲线相似。特别是，脂肪族介质厚度的突然增加给出了液体膨胀到液体冷凝转变的证据。这些数据表明，这种转变应该涉及构象变化。此外，随着分子倾角的减小，液体凝聚相内的分子面积减小。该相的结构也被证明与温度和极性头基的性质无关。观察到最长链化合物向多层结构的转变。结果表明，界面动力学在没有可调参数的简单毛细管波模型中是一致的。在向固态转变的过程中，粗糙度的强烈下降表明了抗弯曲刚性的开始。得到的高刚性模量值(约100k(B)T)对脂肪族链长很敏感，可以用固体单层的弹性行为的简单模型来解释。对于单层这样的刚性界面，毛细管波对X射线的散射进行了详细的描述。
Monolayers of amphiphilic molecules adsorbed at the air-water interface have been studied using X-ray reflectivity. This technique allows an accurate and independent determination of thicknesses (by the measurement of fringes of equal inclination) as well as densities and roughnesses (since this is an absolute intensity measurement); therefore a complete electron density profile can be obtained. The surface roughness is due to thermally excited capillary waves, and is thus related to the dynamics of the interface, which are conditioned by the elastic constants of the layer. The phase diagrams of the C15, C21 and C29 fatty acids and of the phospholipid L-alpha-DPPC have been investigated using this method, and an analysis of the phase transitions has been performed. From the structural point of view, a general feature of this class of compounds adsorbed on water is an unchanging aliphatic medium density within the liquid and solid phases. If follows that the pressure vs. film thickness curves mimic the pressure area curves. In particular evidence for the liquid-expanded to liquid-condensed transition is given by an abrupt increase of the aliphatic medium thickness. The data suggest that this transition should involve conformational changes. Furthermore the decrease in molecular area within the liquid condensed phase is revealed by a decreasing molecular tilt angle. The structure of this phase is also shown to be independent of the temperature and of the nature of the polar head-group. A transition to a multilayer structure is observed with the longest chain compound. We show that the dynamics of the interface are consistent in the liquid phases with a simple capillary wave model, with no adjustable parameter. A strong drop in the roughness at the transition to the solid state reveals the onset of a rigidity against bending. The high values of the rigidity modulus obtained (on the order of 100 k(B) T) are sensitive to the aliphatic chain length and can be interpreted using a simple model for the elastic behavior of the solid monolayer. The scattering of X-rays by capillary waves in detailed for a rigid interface such as a monolayer.