Prediction of multicomponent liquid adsorption using excess quantities. II. Calculations for the liquid/solid interface

The utilization of excess quantities as the basis for a thermodynamic approach can simplify the prediction of multicomponent liquid adsorption from binary data. A new method for predicting liquid adsorption on solids is suggested, which is different from the existing equations with respect to the theoretical background and formulation. The applicability of the new model is tested with three ternary adsorption systems. The predicted surface excesses are discussed and compared with experimental ones and with those of other prediction models in the literature. The accordance between measured and predicted ternary data is convincing.     

Studies on UNIQUAC and SAFT equations for nonionic surfactant solutions

The segment-based UNIQUAC and SAFT equations are established to calculate the activity coefficients of surfactants in aqueous solutions. The critical micellar concentrations of single aqueous surfactant systems are correlated and predicted. The predicted values are satisfactory. Both equations have good accuracies and good prediction functions, and the SAFT equation is more successful.     

Thermodynamic consideration of the mixed micelle of surfactants

In conformity with the conclusion obtained previously, the mixed micelle formation of surfactants was treated thermodynamically as the appearance of a macroscopic bulk phase with the aid of the excess thermodynamic quantities similar to those used for the adsorbed film. The composition of surfactant in the mixed micelle and the thermodynamic quantities of micelle formation were found to be evaluated by applying the thermodynamic equations derived. These equations were extended so as to be applicable to any kind of surfactant mixture. It was shown that the critical micelle concentration vs. composition of surfactant curves form a diagram analogous to the phase diagram of binary mixture. Applying the equation to the published data on typical surfactant systems, this thermodynamic approach was proved to be useful to clarify the miscibility of surfactants in the micellar state.     

Power-law stage of slow relaxation in solutions with spherical micelles

General (independent of models selected for surfactant molecular aggregates) analytical relations are derived to describe the initial stage of slow relaxation in micellar solutions with spherical micelles. This stage precedes the final stage of the relaxation occurring via an exponential decay of disturbances with time. The relations obtained are applicable throughout the interval of micellar solution concentrations from the first to the second critical micellization concentration. It is shown that the initial stage is characterized by power laws of variations in the concentrations of monomers and micelles with time, these laws being different for the relaxation processes proceeding from above and below toward equilibrium values of micellar solution parameters. Relations are derived for the duration of this stage, and the effect of initial conditions is studied. Characteristic times of the power-law stage are determined and compared with the characteristic time of the final exponent-law relaxation stage. The behavior of these times is investigated at surfactant solution concentrations in the vicinity of, and noticeably above, the first critical micellization concentration. On the basis of the droplet and quasi-droplet thermodynamic models of surfactant molecular aggregates, numerical solutions are found for nonlinearized equations of slow relaxation for the time dependence of surfactant monomer concentrations at all stages of the slow relaxation. Numerical results obtained from the models are compared with the results of a general analytical study.     

Thermodynamic Investigation of the Micellization and the Adsorption of Short Perfluoroalkylated Diols via Fluorescence Spectroscopy and Tensiometry

The micellization and adsorption of two short chain perfluorodiols 3,3,4,4,5,5,6,6,6-nonafluorohexane-1,2-diol (nFHD) and 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctane-1,2-diol (tFOD) are examined from a thermodynamic point of view as a function of temperature and methanol content. The microenvironment of the fluorinated aggregates is evaluated by the fluorescence probe method using pyrene and a molecular rotor 1,1-dicyano-4-p-dimethylaminophenyl)-1,3-butadiene (DMAPhC). The formation of micellar aggregates being evidenced, the results are discussed in terms of the polarity and of the cohesion behavior of the micellar aggregates by taking into account the methanol (MeOH) effect. The critical micellization concentrations thus determined are compared with those given by surface tension measurements. Micellar and adsorption thermodynamic parameters such as Gibbs free energies, enthalpies, and entropies are determined together with the surface areas. The results are compared with literature data and discussed. A model for describing the adsorption process of the fluorinated compounds upon the influence of methanol is finally proposed. Copyright 2001 Academic Press.     

Experimental methods and prediction with COSMO-RS to determine partition coefficients in complex surfactant systems

Surfactant-based separation processes are a promising alternative to conventional organic solvent processes. A crucial parameter to describe the efficiency of such processes is the partition coefficient between the surfactant aggregates (micelles) and the aqueous bulk phase. In this work, several experimental methods to determine these partition coefficients (micellar liquid chromatography, micellar enhanced ultrafiltration, and cloud point extraction) are evaluated and compared. In addition, these results are compared to predictions with the thermodynamic model COSMO-RS. In particular, systems with the nonionic surfactant TritonX-100 are studied. The partition equilibria of various solutes (pyrene, naphthalene, phenanthrene, phenol, 3-methoxyphenol, and vanillin) and the influence of different additives (alcohols) are investigated. All experimental methods show very good reproducibility. Moreover, the results from different methods are in good agreement, supplementing one another concerning the temperature ranges. Notably, the COSMO-RS model is capable of predicting partition coefficients between micelles and water in the investigated temperature range and at different alcohol concentrations. The results demonstrate the potential of the model COSMO-RS to facilitate the selection of optimized process parameters for a given separation problem. By predicting partition equilibria in multicomponent systems, the selection of surfactant, temperature, and appropriate additives can be facilitated.     

Separation of beta-lactam antibiotics by micellar electrokinetic chromatography

The retention behaviour of beta-lactam antibiotics in micellar electrokinetic chromatography (EKC) was investigated. Sodium dodecyl sulphate (SDS) and sodium N-lauroyl-N-methyltaurate were used an anionic surfactants at concentrations of 0.05-0.3 M. It was found that the retention of ionic substances in micellar EKC is determined by the following three factors: the electrophoretic migration of the ionic substances, the interaction between the ionic substances and ionic surfactants and solubilization of the solute by the micellar phase. A difference in the retention behaviours of cationic substances was observed between the two anionic surfactants, which have different groups neighbouring the charge-bearing groups. The effect of an ion-pairing reagent was also investigated to make the effect of the micelle clearer. All test solutes were successfully separated by micellar EKC at SDS concentrations above 0.1 M, with theoretical plate numbers ranging from 70,000 to 260,000.     

Formation and Physicochemical Features of Hybrid Threadlike Micelles in Aqueous Solution

We investigate the construction of long, stable hybrid threadlike micelles consisting of polyelectrolytes and oppositely charged surfactants in aqueous solution and examine the physicochemical features such as their structure and viscoelastic behavior in aqueous solution. The most important point for their construction is the careful control of interactions, especially electrostatic interactions, caused between the surfactants and polyelectrolytes. Incorporated polyelectrolytes are fully extended in these hybrid threadlike micelles irrespective of the molecular weight of the polymer. The viscoelastic behavior of the hybrid threadlike micellar solution is similar to that of ordinary threadlike micellar systems consisting of low‐molecular‐weight substances. However, the inclusion of polymers in the micelles causes differences in their mechanical properties.     

The use of the terms formal element,initial and detailed components,and phase and chemical form in modeling of the states of homo- and heterogeneous systems

The terms formal element, initial and detailed components, and phase and chemical form and their use in chemical thermodynamic modeling of the state of substances in homo- and heterogeneous systems with taking into account local and partial equilibria are considered. The detailed component concept is introduced into fundamental equations. The use of the concept of formal elements is illustrated.     

Clouding phenomenon and SANS studies on tetra-n-butylammonium dodecylsulfate micellar solutions in the absence and presence of salts

Clouding phenomenon in aqueous micellar solutions of an anionic surfactant tetra-n-butylammonium dodecylsulfate (TBADS) has been observed as a function of surfactant concentration. Small-angle neutron scattering (SANS) experiments in these systems show clustering of micelles as the temperature approaches the cloud point (CP). The individual micelles and the clusters of micelles coexist at CP. The clustering of micelles depends on the surfactant concentration and temperature. It is proposed that clustering is due to depletion of H-bonded water present around the butyl chains at the micellar surface. This is associated with entropy gain which is considered to be the major thermodynamic factor related to micellar aggregation. The structures (clusters) that emerge depend on the relative lengths of the alkyl chains of the counterion and can be tuned by the temperature.     

Quantitative treatments of protonation equilibria shifts in micellar systems.

The paper reviews the theoretical models and equations used for the interpretation of weak acid dissociation equilibria in the presence of micellar systems. The models and the equations of the literature can be rewritten and reinterpreted in terms of the generalized pseudophase model, for which the basic equations are reported. Some new relationships for the titration of weak acids in micellar systems are presented.     

Crossover Equation of State and Microstructural Properties of Infinitely Dilute Solutions Near the Critical Point of a Pure Solvent

Microstructural (correlation integrals, cluster size) and related thermodynamic (partial molar volume, Krichevskii parameter) properties of infinitely dilute solutions near the critical point of a pure solvent are studied in terms of nonclassical (crossover) equations of state. The Krichevskii parameter was evaluated for a number of binary solutions by analyzing the initial slopes of the critical lines and the properties of a pure solvent. Qualitative explanation is offered for the physicochemical mechanism of the anomalously high solubility of slightly volatile substances in a supercritical solvent based on microstructural and thermodynamic characteristics of a supercritical fluid mixture.     

Fully biodegradable polymeric micelles based on hydrophobic‐ and hydrophilic‐functionalized poly(lactide) block copolymers

Novel amphiphilic diblock copolymers from a combination of hydrophobic‐functional poly(lactides) (PLAs) with hydrophilic‐functional PLAs or poly(malic acid), respectively, toward fully biodegradable materials for medical applications, such as micellar drug delivery systems, are reported for the first time. The presented PLA‐based polymeric micelles are characterized by their small size below 100 nm, low critical micellar concentrations, good in vitro stabilities at room and body temperature, and efficient incorporation capability of hydrophobic compounds, particularly with regard to potential drug substances. Moreover, the advantage of being totally degradable with different rates at different pH values, as investigated in medical cancer treatment, is demonstrated. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3244–3254, 2010     

Electrostatic charging of nonpolar colloids by reverse micelles

Colloids dispersed in a nonpolar solvent become charged when reverse micelles are added. We study the charge of individual sterically stabilized poly(methyl methacrylate) spheres dispersed in micellar solutions of the surfactants sodium bis(2-ethyl 1-hexyl) sulfosuccinate [AOT], zirconyl 2-ethyl hexanoate [Zr(Oct)2], and a copolymer of poly(12-hydroxystearic acid)-poly(methyl methacrylate) [PHSA-PMMA]. Although the sign of the particle charge is positive for Zr(Oct)2, negative for AOT, and essentially neutral for PHSA-PMMA, the different micellar systems display a number of common features. In particular, we demonstrate that over a wide range of concentrations the particle potential is a constant, independent of the number of micelles added and independent of the colloid size. A simple thermodynamic model, in which the particle charge is generated by the competitive adsorption of both positive and negative micelles, is in good agreement with the experimental data.     

Chiral polymerization: symmetry breaking and entropy production in closed systems

We solve numerically a kinetic model of chiral polymerization in systems closed to matter and energy flow, paying special attention to its ability to amplify the small initial enantiomeric excesses due to the internal and unavoidable statistical fluctuations. The reaction steps are assumed to be reversible, implying a thermodynamic constraint among some of the rate constants. Absolute asymmetric synthesis is achieved in this scheme. The system can persist for long times in quasi-stationary chiral asymmetric states before racemizing. Strong inhibition leads to long-period chiral oscillations in the enantiomeric excesses of the longest homopolymer chains. We also calculate the entropy production σ per unit volume and show that σ increases to a peak value either before or in the vicinity of the chiral symmetry breaking transition.     

The mass action law theory of micellar solutions

Theories of micellization based on the application of the mass action law to aggregation processes in surfactant solutions are reviewed. The rigorous thermodynamic justification of the approach, explanation of the critical micelle concentration, inter-relations between the main micellization parameters, and an analysis of the surface tension isotherm of a micellar solution are given. Properties of ionic micellar systems, including counterion binding and the behavior of free monomeric ions, are discussed in detail with illustrative estimations for sodium dodecylsulfate and other surfactants.     

Photo-induced electron transfer in surfactant solutions containing thionine dye

The mechanism of photovoltage generation in the micellar solution of nonionic surfactants incorporating thionine dye involves charge-transfer (CT) or electron donor acceptor (EDA) interaction; the dye acts as the electron acceptor and the surfactants act as the electron donors. This is well corroborated by the spectral studies of the systems. The thermodynamic and spectral properties of the complexes are presented. The photovoltage generation, the spectral shifts due to complexation, and the thermodynamic properties of the complexes are found to be well correlated.