Tkachenko and Rabin Reply
Tkachenko and Rabin Reply
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特卡琴科和拉宾 回复
DOI：
10.1103/physrevlett.79.532
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发表时间：
1997
影响因子：
8.6
通讯作者：
Y. Rabin
中科院分区：
文献类型：
--
作者：
A. Tkachenko;Y. Rabin
正构烷烃 [2, 3] 和其他链分子表面冻结的基于波动的场景。我们将此效应归因于与单层分子波动相关的自由能增益 D，单层分子的约束比块体分子的约束要小。西罗塔等人[4]指出即使 D 0，表面冻结也可以通过适当选择相关界面张力来解释为纯粹的润湿现象，并认为对于正构烷烃来说确实是这种情况。如果 gly 2 (gsl 1 gsy) 1D，预计会发生表面冻结。 0;即，它是由标准润湿理论已知的扩散压力P gly 2 (gsl 1 gsy)与波动修正D之间相互作用的结果而产生的。目前还没有足够的实验信息来确定上述不等式中出现的所有参数；只能直接测量 gly [3]，并且可以从接触角 (uc) 实验中提取组合 gsy 2 gsl gly cosuc。西罗塔等人[4]声称我们对 gsl 和 gsy 的值太高，他们的论点基于 Zisman、Mitchell 和 Elton、Mach 和 Hoffman 的数据（Sirota 等人的参考文献 [4, 6-8]）。这个论点是有缺陷的：与我们的问题直接相关的唯一数据是 Zisman 的数据，有关 C16 液体铺展在 C36 晶体上的数据。从方法论的角度来看，更有问题的是 Sirota 等人[4]使用表面冷冻实验的结果作为额外的输入来确定那些没有直接实验数据的界面能。由于这些计算假设 D 0，因此它们不能用于区分烷烃表面冻结的润湿和波动机制。下面我们提出了一种简单且相当通用的方法，可以确定是润湿还是波动情况导致了表面冻结。考虑在块状冻结点 g (Tb) gsy 1 gsl 2 D 覆盖有固体单分子层的液体的表面张力与链长的关系。在所考虑的系统中，没有物理原因可以预期链长为 n 的固体 gsy 的表面张力会有相当大的变化。因此，g (Tb) 的 n 依赖性仅由波动贡献 D 和固液界面张力 gsl 决定。由于后者的 n 相关部分可以从接触角测量中提取，因此可以确定 D 对 g (Tb) 的整体链长依赖性的贡献，并估计表面冻结波动的显着性。即，由于 gsy 独立于 n，我们得到
a fluctuation-based scenario for surface freezing of normal alkanes [2, 3] and other chain molecules. We attributed the effect to the free energy gain D associated with the fluctuations of the molecules in the monolayer, which are less constrained than in the bulk. Sirota et al.[4] point out that surface freezing can be explained as a purely wetting phenomenon by an appropriate choice of relevant interfacial tensions, even if D 0, and argue that this is indeed the case for normal alkanes. Surface freezing is predicted to occur if gly 2 (gsl 1 gsy) 1D. 0; ie, it arises as the result of the interplay between the spreading pressure P gly 2 (gsl 1 gsy) known from the standard wetting theory, and the fluctuational correction D. At present there is no sufficient experimental information to determine all the parameters that appear in the above inequality; only gly can be measured directly [3] and the combination gsy 2 gsl gly cosuc can be extracted from contact angle (uc) experiments. Sirota et al.[4] claim that our values for gsl and gsy are too high, basing their argument on the data of Zisman, Mitchell and Elton, Mach and Hoffman (Refs.[4, 6–8] in Sirota et al.). This argument is flawed: the only data which are directly relevant to our problem are those of Zisman, on C16 liquid spread on C36 crystal. What is even more problematic from a methodological point of view is that Sirota et al.[4] use the results of experiments on surface freezing as an additional input to determine those interfacial energies on which there are no direct experimental data. Since these calculations assume that D 0, they cannot be used to distinguish between wetting and fluctuational mechanism of surface freezing in alkanes. Below we propose a simple and quite general methodology which allows one to determine whether it is the wetting or the fluctuational scenario that is responsible for surface freezing.Consider the chain-length dependence of the surface tension of a liquid covered with a solid monolayer at the point of bulk freezing, g (Tb) gsy 1 gsl 2 D. There is no physical reason to expect considerable variation of the surface tension of a solid gsy with chain length n in the considered system. Thus, the n dependence of g (Tb) is determined only by the fluctuational contribution D and by the solid-liquid interfacial tension gsl. Since the n-dependent part of the latter can be extracted from contact angle measurements, it is possible to determine the contribution of D to the overall chain-length dependence of g (Tb), and to estimate the significance of fluctuations for surface freezing. Namely, since gsy is independent of n, we obtain