Labajos-Broncano L, Antequera-Barroso J A, González-Martín M L, Bruque J M
Department of Physics, University of Extremadura, Campus Universitario, Av. Elvas s/n, 06071 Badajoz, Spain.
J Colloid Interface Sci. 2006 Sep 1;301(1):323-8. doi: 10.1016/j.jcis.2006.04.076. Epub 2006 Jun 5.
The imbibition of aqueous solutions of Triton X-100 in calcium fluoride columns has been studied in order to determine the influence of the interfacial adsorption of the surfactant in the capillary rise of the solutions. This system has been chosen because this surfactant behaves as non-adsorbable at the surface of this solid when it is in aqueous solution. The experiments have consisted of the measurement of the increase in the weight of the porous columns caused by the capillary rise of the solutions. The analysis of the results has been made through a modified expression of Washburn's equation that takes into account that the experimental increase in the weight is caused by the imbibition as well as by the development of a liquid meniscus around the bottom base of the columns. From this analysis, it has been deduced that the surfactant concentration does not influence on the imbibition rate, it being equal to the observed for water. However, it has been also proved that the contact angle depends on the surfactant concentration, taking decreasing values as the surface tension of the solutions decreases. In order to justify these findings, a study about the influence of the interfacial adsorption on the imbibition has been carried out. By means of them, it has been proved that the absence of adsorption at the solid-liquid interface is the reason that explains both the independence of the imbibition rate from the surfactant concentration and the decrease of the contact angle. Moreover, this fact indicates that the depletion of the surfactant molecules from the advancing meniscus, which has been normally adduced as the phenomenon causing the observed behaviour, has to be ruled out as the physical cause that justifies the behaviour found from the analysis of the imbibition experiments. As a corollary, it has been also stated that only if the adsorption at the solid interfaces happened, the imbibition of aqueous solution of surfactant in hydrophilic media could be influenced by the surfactant concentration.
为了确定表面活性剂的界面吸附对溶液毛细上升的影响，研究了Triton X - 100水溶液在氟化钙柱中的吸液现象。选择该体系是因为这种表面活性剂在水溶液中时在该固体表面表现为不可吸附。实验包括测量溶液毛细上升引起的多孔柱重量增加。通过对沃什伯恩方程的修正表达式对结果进行分析，该表达式考虑到实验中重量的增加是由吸液以及柱底周围液体弯月面的形成引起的。从该分析中可以推断出，表面活性剂浓度对吸液速率没有影响，其与水的吸液速率相同。然而，也已证明接触角取决于表面活性剂浓度，随着溶液表面张力降低，接触角减小。为了证明这些发现，开展了关于界面吸附对吸液影响的研究。通过这些研究，已证明固液界面不存在吸附是解释吸液速率与表面活性剂浓度无关以及接触角减小的原因。此外，这一事实表明，通常被认为是导致观察到的行为的现象——表面活性剂分子从前进弯月面的耗尽，必须被排除作为从吸液实验分析中发现的行为的物理原因。作为一个推论，还指出只有当在固体界面发生吸附时，表面活性剂水溶液在亲水性介质中的吸液才会受到表面活性剂浓度的影响。
