Equilibrium contact angles as a function of the concentration of nonionic surfactants on quartz plate

Modification of adsorption, aggregation and wetting properties of surfactants by short chain alcohols

The adsorption of methanol, ethanol and propan-1-ol at the solution-air and solid-solution interfaces, their aggregation in the aqueous media as well as wetting properties regarding their applications as additives or co-surfactants in the surfactants aqueous solution were discussed based on the literature data. Mutual influence of alcohols and surfactants on the solution-air and solid-solution interface tension was considered. For this purpose there were used different methods allowing to describe or predict changes of water surface tension as a function of alcohols concentration. These, in turn, as a function of alcohol and/or surfactant concentration were also analyzed by means of the methods applied for prediction of surface tension of aqueous solution of the classical surfactants mixture. The same considerations related to the behaviour of alcohol and surfactant at the solid-solution and solution-air interfaces were made. To explain the behaviour of alcohols and surfactants mixture at the solution-air and solid-solution interfaces the components and parameters of water, alcohols, surfactants and solids surface tension as well as the Gibbs free energy changes during the adsorption process were taken into account. It was proved that wettability of some solids can be predicted based on alcohol and surfactants adsorption as well as surface tension components and parameters. As follows the mutual influence of alcohol and surfactant on their adsorption at the solution-air and solid-solution interfaces as well as on the wetting properties at the alcohol concentration from zero to its critical aggregation concentration (CAC) is different from that at its concentration higher than CAC.

Adsorption of triton X-100 on silica gel: effects of temperature and alcohols

Adsorption of Triton X-100 (TX-100) on silica gel has been studied as a function of temperature (308–328 K) and composition for mixtures of water with ethanol or t-butanol. The adsorption capacity of silica gel for TX-100 decreases with increase in alcohol content. Adsorption isotherms of TX-100 on silica gel are four-region and were analyzed using the ARIAN (adsorption isotherm regional analysis) model. Data in regions 2, 3 and 4 were fitted to the Temkin, bilayer and reverse desorption isotherms, respectively. The results show that adsorption of TX-100 on silica gel in water and alcohol-water binary mixtures occurs mainly through formation of monolayer surface aggregates or low bilayer coverage.

Surface properties of Toxoplasma gondii oocysts and surrogate microspheres

The physical properties that govern the waterborne transmission of Toxoplasma gondii oocysts from land to sea were evaluated and compared to the properties of carboxylated microspheres, which could serve as surrogates for T. gondii oocysts in transport and water treatment studies. The electrophoretic mobilities of T. gondii oocysts, lightly carboxylated Dragon Green microspheres, and heavily carboxylated Glacial Blue microspheres were determined in ultrapure water, artificial freshwater with and without dissolved organic carbon, artificial estuarine water, and artificial seawater. The surface wettabilities of oocysts and microspheres were determined using a water contact angle approach. Toxoplasma gondii oocysts and microspheres were negatively charged in freshwater solutions, but their charges were neutralized in estuarine water and seawater. Oocysts, Glacial Blue microspheres, and unwashed Dragon Green microspheres had low contact angles, indicating that they were hydrophilic; however, once washed, Dragon Green microspheres became markedly hydrophobic. The hydrophilic nature and negative charge of T. gondii oocysts in freshwater could facilitate widespread contamination of waterways. The loss of charge observed in saline waters may lead to flocculation and subsequent accumulation of T. gondii oocysts in locations where freshwater and marine water mix, indicating a high risk of exposure for humans and wildlife in estuarine habitats with this zoonotic pathogen. While microspheres did not have surface properties identical to those of T. gondii, similar properties shared between each microsphere type and oocysts suggest that their joint application in transport and fate studies could provide a range of transport potentials in which oocysts are likely to behave.

Surface tension and contact angle on enamel of surfactant solutions for caries diagnosis with dyes

We measured the surface tension of solutions of five surfactants in water, ethanol, and a 50% water/ethanol mixture at 25 degrees C, as well as the contact angle of these solutions on ground and polished bovine enamel in vitro and on intact pellicle-covered human enamel in vivo. All surfactants lowered the surface tension of water. In ethanol, no reduction of the surface tension was achieved by any of the five surfactants. In the water/ethanol mixture, only Fluorad lowered the surface tension from 29.2 to 19.7 mJ.m-2 at 25 degrees C. On bovine dental enamel, all surfactant solutions showed a significantly lower contact angle than did distilled water. On pellicle-covered human enamel, Rewoteric in distilled water showed no significantly lower contact angle than did pure distilled water, but all other solutions did. Both in vitro and in vivo, ethanol spread instantaneously over the enamel surface. Based on these measurements, we concluded that several surfactants may be used to spread aqueous dye solutions. In a 50% mixture of water and ethanol and in pure ethanol, no surfactant is necessary for enhanced spreading of the solution, but surfactants may be considered for adhesive properties.