Hydrophobicity enhancement in micelles of Triton X-165 by the presence of the cosolvent 2,2,2 trifluoroethanol (TFE)

Adsorption and wetting properties of biosurfactants, Trtions and their mixtures in aqueous and water-ethanol environment

Adsorption of rhamnolipid (RL) and surfactin (SF) as well as their mixtures with Triton X-100 (TX100) and Triton X-165 (TX165) at the solution-air (S-A), PTFE (polytetrafluoroethylene)-S, PMMA (poly (methyl methacrylate))-S, Q (quartz)-S, PMMA-A, and Q-A as well as their wetting properties regarding the surface tension of the PTFE, PMMA and quartz and its components and parameters were discussed using the literature data. The mutual influence of biosurfactants and Tritons on the S-A, PMMA(quartz)-A and PTFE(PMMA, quartz)-S interfaces tensions was considered in terms of their adsorption at these interfaces for both aqueous and water-ethanol solutions of the biosurfactant mixtures with Tritons. For this purpose there were used different methods on the basis of which the S-A, PMMA(quartz)-A and PTFE(PMMA, quartz)-S interface tensions can be predicted and/or described in the function of concentration and composition of the mixtures. Changes of these interface tensions as a function of concentration and composition of the mixtures were compared to those affected by individual mixture components. In turn, these changes of the interface tension were considered as regards properties of the biosurfactants, Tritons and ethanol layers adsorbed at the S-A, PMMA(quartz)-A and PTFE(PMMA, quartz)-S interfaces. Based on the changes of the contact angle of the aqueous and water-ethanol solutions of the biosurfactants and Tritons as well as biosurfactants mixtures with Tritons on PMMA and quartz as a function of mixture concentration and composition, the changes of the PMMA and quartz surface tension were analyzed using various approaches to the surface and interface tension. The thermodynamic functions change as a results of RL, SF, TX100, TX165, ET as well as the mixtures of RL and SF with Tritons adsorption at different interfaces were also analyzed based on the literature data. These considerations allow to describe and/or predict changes of the interface tension, contact angle of the mixtures as a function of their composition based on these properties of individual mixture components.

Hexafluoroisopropanol/Brij-35 based supramolecular solvent for liquid-phase microextraction of parabens in different matrix samples

A novel supramolecular solvent (SUPRAS) based on hexafluoroisopropanol (HFIP)/Brij-35 was proposed for liquid-phase microextraction (LPME) of parabens in water samples, pharmaceuticals and personal care products. Brij-35 is a cost-effective and non-toxic non-ionic surfactant, but it has a high cloud point (>100 °C). HFIP, with the features of strong hydrogen-bond donor, high density and powerful hydrophobicity, was used as the cloud point-reducing agent and self-assembling and density-regulating solvent of Brij-35. Upon adding HFIP into the Brij-35 aqueous solution, the cloud point of Brij-35 was decreased to below room temperature, and the SUPRAS was formed in the bottom over a wide range of HFIP and Brij-35 concentrations at room temperature. The SUPRAS was composed of Brij-35, HFIP and water, having a density larger than water, and it showed a large spherical structure of positive micellar aggregates (2-8 μm). The HFIP/ Brij-35 SUPRAS-based LPME procedure was non-thermodependent and could be performed at room temperature with centrifugation using normal centrifuge tubes, being very simple. In the extraction of six parabens, the HFIP/ Brij-35 SUPRAS-based LPME method showed short extraction time (3.3 min), low solvent consumption (0.3 mL), and large enrichment factor (26-193). The method of HFIP/ Brij-35 SUPRAS-based LPME with HPLC-DAD gave good linearity for the quantification of parabens with correlation coefficients larger than 0.9990. The limits of detection based on a signal-to-noise ratio of 3 were from 0.042 to 0.167 μg L^-1. The recoveries for the spiked real samples were in the range of 90.2-112.4% with relative standard deviation less than 8.9%. Except for tap water, one or several paraben (s) were detected in all the other real samples.