Effect of Molecular Structure on Wetting Behavior at the Air-Liquid Interface of Water + Alcohol Mixtures

In this study, the wetting behavior of binary water + alcohol mixtures was carefully investigated by using eight different short-chain alcohols. These binary mixtures exhibit liquid-liquid equilibrium over the experimental temperature range 10-40°C. The wetting behavior of the upper liquid (alcohol-rich) phase at the surface of the lower liquid (aqueous) phase can be determined according to the wetting coefficient resulting from the interfacial tension measurements. Molecular structure of alcohols plays an essential role in the wetting behavior. The purpose of this study is threefold. (1) The effect of the hydrocarbon chain length of alcohols was examined by employing water + 1-butanol (C4E0), water + 1-pentanol (C5E 0), and water + 1-hexanol (C6E0) three systems, where CiEj is the abbreviation of a nonionic polyoxyethylene alcohol CiH2i+1(OCH2-CH 2)jOH. The shorter chain alcohol has a stronger tendency to wet the surface of the aqueous phase. (2) The effect of number of oxyethylene groups of alcohols was investigated by using three mixtures, water + C6E0, water + C6E1, and water + C6E2. An interfacial phase transition from partial wetting to nonwetting was observed for water + C6Ej mixtures as the number of oxyethylene groups j increases from 1 to 2. (3) The effect of isomeric structures of alcohols on wetting behavior was investigated by studying three mixtures, water + 1-pentanol, water + 2-pentanol (2-C 5E0), and water + tert-pentanol (t-C5E 0). An interfacial phase transition from partial wetting to complete wetting occurs while the molecular structure of alcohols evolves from linear (C5E0) to near spherical (t-C5E0) shape.