Tavana H, Jehnichen D, Grundke K, Hair M L, Neumann A W
Department of Mechanical and Industrial Engineering, University of Toronto, 5 King's, College Road, Toronto, Ontario, Canada M5S 3G8.
Adv Colloid Interface Sci. 2007 Oct 31;134-135:236-48. doi: 10.1016/j.cis.2007.04.008. Epub 2007 May 1.
Contact angle hysteresis of liquids with different molecular and geometrical properties on high quality films of four fluoropolymers was studied. A number of different causes are identified for hysteresis. With n-alkanes as probe liquids, contact angle hysteresis is found to be strongly related to the configuration of polymer chains. The largest hysteresis is obtained with amorphous polymers whereas the smallest hysteresis occurs for polymers with ordered molecular chains. This is explained in terms of sorption of liquid by the solid and penetration of liquid into the polymer film. Correlation of contact angle hysteresis with the size of n-alkane molecules supports this conclusion. On the films of two amorphous fluoropolymers with different molecular configurations, contact angle hysteresis of one and the same liquid with "bulky" molecules is shown to be quite different. On the surfaces of Teflon AF 1600, with stiff molecular chains, the receding angles of the probe liquids are independent of contact time between solid and liquid and similar hysteresis is obtained for all the liquids. Retention of liquid molecules on the solid surface is proposed as the most likely cause of hysteresis in these systems. On the other hand, with EGC-1700 films that consist of flexible chains, the receding angles are strongly time-dependent and the hysteresis is large. Contact angle hysteresis increases even further when liquids with strong dipolar intermolecular forces are used. In this case, major reorganization of EGC-1700 chains due to contact with the test liquids is suggested as the cause. The effect of rate of motion of the three-phase line on the advancing and receding contact angles, and therefore contact angle hysteresis, is investigated. For low viscous liquids, contact angles are independent of the drop front velocity up to approximately 10 mm/min. This agrees with the results of an earlier study that showed that the rate-dependence of the contact angles is an issue only for liquids with high viscosity.
研究了具有不同分子和几何性质的液体在四种含氟聚合物高质量薄膜上的接触角滞后现象。确定了导致滞后现象的多种不同原因。以正构烷烃作为探针液体时，发现接触角滞后与聚合物链的构型密切相关。非晶态聚合物的滞后现象最大，而分子链有序的聚合物滞后现象最小。这可以从固体对液体的吸附以及液体渗入聚合物薄膜的角度来解释。接触角滞后与正构烷烃分子大小的相关性支持了这一结论。在两种具有不同分子构型的非晶态含氟聚合物薄膜上，同一种具有“庞大”分子的液体的接触角滞后现象表现出很大差异。在分子链刚性的特氟龙AF 1600表面，探针液体的后退角与固液接触时间无关，所有液体都获得了相似的滞后现象。提出液体分子在固体表面的滞留是这些体系中滞后现象最可能的原因。另一方面，对于由柔性链组成的EGC - 1700薄膜，后退角强烈依赖于时间且滞后现象较大。当使用具有强偶极分子间力的液体时，接触角滞后甚至会进一步增大。在这种情况下，认为是由于与测试液体接触导致EGC - 1700链发生重大重组所致。研究了三相线移动速率对前进接触角和后退接触角的影响，进而对接触角滞后的影响。对于低粘度液体，接触角在液滴前沿速度达到约10毫米/分钟之前与速度无关。这与早期一项研究的结果一致，该研究表明接触角的速率依赖性仅对高粘度液体才是一个问题。
