THE RATE OF EVAPORATION OF WATER THROUGH FATTY ACID MONOLAYERS
THE RATE OF EVAPORATION OF WATER THROUGH FATTY ACID MONOLAYERS
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DOI：
10.1021/j150525a002
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发表时间：
1955-01-01
影响因子：
--
通讯作者：
LAMER, VK
中科院分区：
文献类型：
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作者：
ARCHER, RJ;LAMER, VK
本文通过测定固体干燥剂在水面上的吸湿速率，研究了脂肪酸单分子膜对水蒸发速率的影响。数据报告为单层的蒸发比阻，其等于通过膜冷凝的比速率常数的倒数。这些数据建立了一种污染效应，蒸发的延迟强烈依赖于这种效应，这在以前的所有工作中引入了严重的错误。我们的结果给出了通过单分子膜的蒸发速率的描述，这与以前的工作有根本的不同。测量了四种饱和脂肪酸Cu、C18、C18和C20的单层的蒸发阻力作为表面压力、链长、单层相、亚相组成和表面温度的函数。在液相凝聚相中，单分子层阻力与表面压力和亚相pH无关，其对数是链长的线性函数。另一方面，在含钙离子的碱性亚相上的固相中，电阻的对数是链长和表面压力的线性函数。C12酸单分子层的液体凝聚相中的电阻的对数是绝对温度的倒数的线性函数，这证实了用指数能垒描述蒸发电阻。提出了一个理论的能量势垒的来源，计算其大小的汽化热数据与实验值吻合得很好。所有研究的单分子膜都使水的蒸发速率降低约104倍。
The influence of fatty acid monolayers on the rate of evaporation of water has been studied by measuring the rate of ab-sorption of water vapor by a solid desiccant supported above the water surface. The data are reported as the specific resistance of the monolayer to evaporationwhich is equal to the reciprocal of the specific rate constant for condensation through the film. These data establish a contamination effect upon which the retardation of evaporation is strongly de-pendent and which has introduced serious error in all previous work. Our results give a description, of the rate of evapora-tion through monolayers, which is fundamentally different from earlier work. The resistance to evaporation of monolayers of the four saturated fatty acids Cu, Cis, Cis and C20 was measured as a function of surface pressure, chain length, monolayer phase, subphase composition and surface temperature. In the liquid condensed phase, monolayer resistance is independent of surface pressure ana subphase pH; its logarithm is a linear function of chain length. On theother hand, in the solidphase on an alkaline subphase containing calcium ions, the logarithm of resistanceis a linear function of both chain length and surface pressure. The logarithm of the resistance in the liquid condensed phase of Ci2 acid monolayers is a linear function of the reciprocal of the absolute temperature, which substantiates the description of evaporation resistance in terms of an ex-ponential energy barrier. A theory is proposed for the source of the energy barrier; calculation of its magnitude from heats of vaporization data agrees well with the experimental values. All of the monolayers studied decrease the rate of evaporation of water by a factor of about 104.