MOLECULAR MECHANISMS ASSOCIATED WITH ADHESION AND CONTACT-ANGLE HYSTERESIS OF MONOLAYER SURFACES
MOLECULAR MECHANISMS ASSOCIATED WITH ADHESION AND CONTACT-ANGLE HYSTERESIS OF MONOLAYER SURFACES
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DOI：
10.1021/j100179a041
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发表时间：
1991-12-26
影响因子：
--
通讯作者：
ISRAELACHVILI, JN
中科院分区：
文献类型：
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作者：
CHEN, YL;HELM, CA;ISRAELACHVILI, JN
使用表面力装置技术和接触角测量技术在各种表面活性剂涂层的云母表面上进行了实验。这些实验旨在阐明粘附性滞后(在加载-卸载循环期间)和接触角滞后(前进/后退液体)的分子机制，并探索这两种能量耗散现象之间的任何可能关系。我们发现，磁滞效应不仅仅是由于表面的缺陷，如粗糙度或化学不均匀造成的。即使是最初光滑且化学成分均匀的表面，也会表现出很大的粘附力和接触角滞后效应。我们的结果表明，对于这样的表面，由于它们接触后在固-固或固-液界面上发生了分子重排，所以出现了滞后现象。这导致在接近两个表面期间(或在展开期间)的表面自由能低于在分离(或收回)期间的表面自由能。我们研究了一些增强磁滞的因素：(I)增加表面分子重新排序的自由度，(Ii)增加负载和允许表面保持接触的时间，以及(Iii)增加分离(或收回)的速度。这些发现突出了大多数加载-卸载和湿-去湿循环的内在非平衡性质，并提出了减少与此类过程相关的能量耗散滞后的方法。我们的结果进一步表明，半径为R的两个曲面之间的粘附力或拉脱力F与Johnson-Kendall-Roberts理论中的表面能-伽马有关，例如，对于平面上的球体，F=3-pi-R-伽马，但仅当分离发生在平衡条件下。初步结果还表明，粘合滞后和摩擦/粘滞之间存在相关性。
Experiments were carried out on a variety of surfactant-coated mica surfaces using the surface forces apparatus technique and contact angle measurements. The experiments were designed to clarify the molecular mechanisms underlying adhesion hysteresis (during loading-unloading cycles) and contact angle hysteresis (of advancing/receding liquids), and to explore any possible relationship between these two energy-dissipating phenomena. We found that hysteresis effects are not simply due to surface imperfections, such as roughness or chemical heterogeneity. Even surfaces that are initially smooth and chemically homogeneous can exhibit large adhesion and contact angle hysteresis effects. Our results indicate that, for such surfaces, hysteresis arises because of molecular rearrangements occurring at solid-solid or solid-liquid interfaces after they have come into contact. This results in a lower surface free energy during the approach of two surfaces (or during spreading) than during separation (or retraction). We have studied a number of factors that enhance hysteresis: (i) increasing the freedom of the surface molecules to reorder, (ii) increasing the load and time surfaces are allowed to remain in contact, and (iii) increasing the rate of separation (or retraction). These findings highlight the inherent nonequilibrium nature of most loading-unloading and wetting-dewetting cycles and suggest ways for reducing the energy-dissipating hysteresis associated with such processes. Our results further indicate that the adhesion or pull-off force F between two curved surfaces of radius R is related to the surface energy-gamma by the Johnson-Kendall-Roberts theory, for example, F = 3-pi-R-gamma for a sphere on a flat surface, but only when the separation occurs under equilibrium conditions. Preliminary results also indicate a correlation between adhesion hysteresis and friction/stiction.