Search Results (8)

This study was aimed at establishing the interactions prevailing in an anionic surfactant, sodium dodecyl sulfate, and dopamine hydrochloride in an alcoholic (ethanol) media by using volumetric, conductometric, and tensiometric techniques. Various methods were utilized to estimate the critical micelle concentration (cmc) values at different temperatures. The entire methods yielded the same cmc values. The corresponding thermodynamic parameters viz. the standard free energy of micellization ($G_{mic}^o$), enthalpy of micellization ($H_{mic}^o$), and entropy of micellization ($S_{mic}^o$) were predicted by applying the pseudo-phase separation model. The experimental density data at different temperatures (298.15 K, 303.15 K, 308.15 K, and 313.15 K) were utilized to estimate the apparent molar volumes ($V_{\varphi }^o$) at an infinite dilution, apparent molar volumes ($V_{\phi }^{cmc}$) at the critical micelle concentration, and apparent molar volumes ($\mathsf{\Delta }{V}_{\phi }^m$) upon micellization. Various micellar and interfacial parameters, for example, the surface excess concentration (${\mathsf{\Gamma }}_{\max }$), standard Gibbs free energy of adsorption at the interface ($\mathsf{\Delta }{G}^o{}_{ad}$), and the minimum surface area per molecule ($A_{\min }$), were appraised using the surface tension data. The results were used to interpret the intermolecular interactions prevailing in the mixed systems under the specified experimental conditions. Full article

The effect of temperature on the micellar properties of the alkylglucoside surfactant n-octyl-β-D-thioglucopyranoside (OTG) used for membrane protein solubilization has been investigated. Critical micelle concentration (CMC), apparent (${\varphi }_V$) and partial (${\overline{V}}_M$) molar volume changes of the studied surfactant, as well as thermodynamic functions (the standard Gibbs free energy ($\Delta G_{mic}^o$), the standard enthalpy ($\Delta H_{mic}^o$) and entropy ($\Delta S_{mic}^o$)) of the OTG micellization process were determined. The above-mentioned parameters were calculated on the basis of the results obtained from measurements of surface tension, density and viscosity of the aqueous solutions of n-octyl-β-D-thioglucopyranoside, as well as pyrene (Py) and 8-anilinonaphthalene-1-sulfonic acid (ANS) fluorescence intensity in aqueous solutions of OTG and dynamic light scattering of aqueous solutions of OTG. Basing on the obtained results it is stated that critical micelle concentration of OTG is much lower compared to that of the earlier studied n-octyl-β-D-glucopyranoside (OGP). The standard Gibbs free energy changes indicate that the tendency of OTG molecules to form aggregates increases with temperature increase. However, this increase is not so evident as in the case of some other sugar-based surfactants. The small temperature effect on the aggregation properties of OTG in water is probably connected with the presence and strength of the hydrogen bonds between the water molecules and sugar units, or the type of linkage between the hydrophobic and hydrophilic parts of the studied surfactant. In addition, the presence of S-linkage in the OTG molecule despite its high enzymatic stability also causes the hydrophobicity increase of the studied surfactant (compared to OGP), which directly influences its micellization process. Full article

The poor solubility of berberine (Ber) in water limits its practical use. Its solubility can be increased, among other ways, by the addition of surfactants. Of the surfactants, Kolliphor^® ELP (ELP) and Kolliphor^® RH 40 (RH40) can be very useful in this respect. The increase of Ber’s solubility in water in the presence of ELP and RH40 should be reflected in the composition of the surface layers at the water-air interface and the micelles. The determined composition is reflected in the Gibbs energy of interactions of berberine with ELP and RH40 through the water phase and the standard Gibbs free energy, enthalpy, and entropy of adsorption and micellization. These energies were determined from the equations proposed by us, based on the Gibbs surface excess concentration of the Ber mixture with ELP and RH40, the activity of these compounds in the surface layer at the water-air interface and in the micelles obtained by the Hua and Rosen method, and the contributions of Ber, ELP, and RH40 to the reduction in the water surface tension. For this determination, the measurements of the surface tension of the aqueous solution of the Ber mixture with ELP or RH40 and that of the Ber mixture with these two surfactants, as well as the density and conductivity were performed. Moreover, the fluorescence emission spectra for the Ber + surfactant mixtures were recorded. Full article

The studies on the behavior of Auramine O (AuO) at the water–air interface and in the bulk phase of the aqueous solution of Kolliphor^® ELP (ELP) and Kolliphor^® RH 40 (RH40) and their mixture were based on the results obtained from the measurements of the contact angle of water, formamide and diiodomethane on the polytetrafluoroethylene covered by the AuO layer, the surface tension of the aqueous solution of AuO, AuO + ELP, AuO + RH40, AuO + ELP + RH40, density and fluorescence intensity. Based on the obtained results, it was possible to determine components and parameters of the AuO surface tension, concentration and composition of the mixed monolayer, including AuO, ELP and RH40, as well as that of the mixed micelles, and to determine the Gibbs standard free energy of adsorption, micellization and AuO solubilization. The obtained results also showed that surface tension isotherms of the studied solutions can be described by the Szyszkowski equation and the exponential function of the second order and predicted by the Fainerman and Miller equation. In addition, the mixed surface layer composition can be predicted based on the contribution of the components of this layer to the water surface tension reduction. Full article

The surface tension of aqueous solutions of Triton X-165 with rhamnolipid or surfactin mixtures was measured. The obtained results were applied for the determination of the concentration and composition of the Triton X-165 and biosurfactants mixture at the water–air interface as well as the contribution of the particular component of the mixtures to water surface tension reduction and the mutual influence of these components on the critical micelle concentration. The determination of these quantities was based on both the commonly used concepts and a new one proposed by us, which assumes that the composition of the mixed monolayer at the water–air interface depends directly on the pressure of the monolayer of the single mixture component and allows us to determine the surface concentration of each mixture component independently of surface tension isotherms shape. Taking into account the composition of the mixed monolayer at the water–air interface, the standard Gibbs adsorption free energy was considered. The obtained results allow us to state that the concentration of both mixture components corresponding to their saturated monolayer and the surface tension of their aqueous solution can be predicted using the surfactants’ single monolayer pressure and their mole fraction in the mixed monolayer determined in the proposed way. Full article

In this study, we investigated the behaviour of rhamnolipid and Greenzyme in brine solutions relevant to hydrocarbon reservoir. Prior to this work, several studies only reported the behaviour of the biosurfactants dissolved in sodium chloride solutions of varied salinity. The results of this study are relevant to the application of the biosurfactants in enhanced oil recovery, during which the compounds are injected into reservoir saturated with formation water, typically of high salinity and complex composition. Surface tension and conductivity methods were used to determine the critical micelle concentrations of the biosurfactants, Gibbs surface excess concentrations and standard free energy at water-air interface. The results show that rhamnolipid and Greenzyme could reduce the surface tension of water from 72.1 ± 0.2 mN/m to 34.7 ± 0.4 mN/m and 47.1 ± 0.1 mN/m respectively. They were also found to be stable in high salinity and high temperature with rhamnolipid being sensitive to brine salinity, composition and pH while Greenzyme showed tolerance for high salinity. Furthermore, the Gibbs standard free energy of micellisation shows that rhamnolipid and Greenzyme have the tendency to spontaneously form micelles with rhamnolipid showing more surface adsorption. However from maximal Gibbs surface excess concentration calculations, Greenzyme monomers tend to favour aggregation more than that of rhamnolipid. Full article

The wettability of solids is important from both practical and theoretical viewpoints. In this study, we measured the contact angle of aqueous solutions of polysorbates (Tween 20, Tween 60, and Tween 80) on polytetrafluoroethylene (PTFE), polyethylene (PE), polymethyl methacrylate (PMMA), polyamide (nylon 6), and quartz. Based on the obtained results, the adsorption of Tween 20 (T20), Tween 60 (T60), and Tween 80 (T80) at the solid-water interface was determined based on the structure and size of their molecules. Next, the tendency of polysorbates to adsorb at the solid-water interface was considered based on the Gibbs standard free energy of adsorption ($\Delta G_{ads}^o$). This energy was evaluated using various methods, including a method we propose based on the critical micelle concentration (CMC) and the contact angle of water and solution at the CMC, as well as their surface tension. The $\Delta G_{ads}^o$ values obtained by this method were comparable to those calculated from the Langmuir equation. Taking into account the Tweens tendency to adsorb at the solid-water interface, the measured contact angle, the components and parameters of surface tension of Tweens solutions and solids, and the surface tension of water and its Lifshitz-van der Waals component that we determined, the wetting process in the solid-solution drop-air system was analyzed. The results based on the mentioned parameters showed that it is possible to predict the wettability of apolar, monopolar, and bipolar solids using the aqueous Tweens solution and their solution adhesion. Full article

The critical micelle concentrations (c.m.c.) of alkyloxy homologs of local anesthetic N-[2-(2-alkyloxyphenylcarbamolyoxy)-ethyl]-piperidinium chloride (CnA) with n=3, 5, 7, 8, 10 and 12 carbons in alkyloxy substituent determined by surfactant ion sensitive electrode (ISE) depend exponentially on n: lnc.m.c.=0.70+0.49n and lnc.m.c.=0.57+0.62n at t=25 °C and pH≈4.5 in water and 0.1 mol.l-1 NaCl solution, respectively, where the free energy of transfer of the alkyloxymethylene group from the aqueous phase into the micelle hydrophobic interior is ΔG0=(-0.49±0.008)RT in water and ΔG0=(-The critical micelle concentrations (c.m.c.) of alkyloxy homologs of local anesthetic N-[2-(2-alkyloxyphenylcarbamolyoxy)-ethyl]-piperidinium chloride (CnA) with n=3, 5, 7, 8, 10 and 12 carbons in alkyloxy substituent determined by surfactant ion sensitive electrode (ISE) depend exponentially on n: lnc.m.c.=0.70+0.49n and lnc.m.c.=0.57+0.62n at t=25 °C and pH≈4.5 in water and 0.1 mol.l^-1 NaCl solution, respectively, where the free energy of transfer of the alkyloxymethylene group from the aqueous phase into the micelle hydrophobic interior is ΔG⁰=(-0.49±0.008)RT in water and ΔG⁰=(-0.62±0.06)RT in the 0.1 mol.l^-1 NaCl solution. The enthalpic and entropic contributions to the standard Gibbs energy of micellization of heptacainium chloride (heptyloxy homologs of C_nA) in 0.1 mol.l^-1 NaCl solution were calculated according to the phase separation model in the temperature range of 25-45 °C.0.62±0.06)RT in the 0.1 mol.l-1 NaCl solution. The enthalpic and entropic contributions to the standard Gibbs energy of micellization of heptacainium chloride (heptyloxy homologs of CnA) in 0.1 mol.l-1 NaCl solution were calculated according to the phase separation model in the temperature range of 25-45 °C. Full article