Negative Values Of Interaction Parameter Research Articles

Microstructure and mixing behavior of benzalkonium chloride with triblock polymers in aqueous medium

Interaction of cationic surfactant (benzalkonium chloride) with nonionic polymeric surfactants, triblock polymers (F127, P105, L64, P123) has been investigated using surface tension, dynamic light scattering (DLS), small angle neutron scattering (SANS) and viscosity measurements. Addition of triblock polymers to the micellar solution of benzalkonium chloride decreases the critical micellar concentration (cmc) and enhances the surface properties. This decrease in cmc values and negative values of interaction parameter show synergism in the binary mixtures of benzalkonium chloride and triblock polymer. Average dimensions of the mixed micelles like diffusion coefficient and hydrodynamic diameter measured from DLS indicate micellar growth in these binary mixtures. SANS data analysis reveal the prolate ellipsoidal shape and micellar growth for the mixed micelles of these binary mixtures. Resultant micellar growth for the proposed binary mixtures is attributable to reduced head group repulsions and hydrophobicity effect. Results from the present study can be helpful in the selection of surfactant mixtures for surfactant-based applications.

Micellization properties of mixed cationic gemini and cationic monomeric surfactants in aqueous-ethylene glycol mixture

The surface properties and mixed micellization behavior of binary combinations of cationic gemini (C 16-4-C 16, 2Br −) tetramethylene-1,4-bis(cetyldimethylammonium bromide) with cationic monomeric surfactants viz. cetyltriphenylphosphonium bromide (CTPB), tetradecyltriphenylphosphonium bromide (TTPB), cetyltributylphosphonium bromide (CTBuPB), cetyldiethylethanolammonium bromide (CDEEAB) and tetradecyldiethylethanolammonium bromide (TDEEAB) have been investigated by surface tension and conductivity measurements in (10%, v/v) ethylene glycol mixture at 300 K. The critical micelle concentration (cmc), surface properties, Γ max (maximum surface excess), A min (minimum surface area per molecule) and π cmc (surface pressure at the cmc) have been determined. The deviation from the ideal of the mixed micelles has been discussed on the basis of Clint theory. The results of the mixed systems were analyzed in the light of the regular solution theory (Rubingh) and Rosen's theory to evaluate the composition of the mixed micelle, the activity coefficient, the interfacial mole fraction of the surfactant at the mixed adsorbed film and the corresponding interaction parameters ( β and β σ). The negative values of interaction parameters ( β and β σ) for mixed micelle formation indicate the attractive interaction for all the system. The standard Gibbs free energies of adsorption (Δ G° ads), standard Gibbs free energies of micellization (Δ G° m), the excess free energies of micellization (Δ G ex) and minimum free energy of the surface (Δ G (s) min) of gemini with cationic monomeric surfactants were also evaluated. The Δ G° ads, Δ G° m and Δ G ex values are negative indicating the spontaneity and stability of the mixed micelle.

Cyclic voltammetry and viscosity measurements of aggregated assemblies of anionic surfactants with nonionic surfactants and triblock copolymers

Cyclic voltammetry (CV) and viscosity measurements have been employed to study the aggregation behavior of mixed micellar systems of anionic surfactant (dioctyl sulfosuccinate sodium salt, AOT) with conventional nonionic surfactants such as Brij 35/TritonX-100/Tween 20/Tween 80/Myrj 45 and two triblock copolymers (L64 and F68). Critical micelle concentration (cmc) values have been determined for various micellar systems from CV measurements using 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as an electroactive probe at 25 °C. Diffusion coefficient (D) has been evaluated from Randles–Sevcik equation which showed an overall decrease for most of the binary systems. The negative values of interaction parameters (β) obtained from regular solution theory suggest the synergistic behavior in all the binary systems except AOT + Tween 80 mixtures. The mixed systems of AOT with triblock copolymers showed stronger synergistic interactions than that of mixed systems of AOT with nonionic surfactants. A comparative evaluation of mixed systems of anionic surfactants AOT and sodium dodecyl sulfate with Myrj 45 and AOT + L64 and F68 has been made on the basis of different micellar parameters and structural properties of surfactants. Viscosity measurements also show similar type of interactions in the mixed micelles.

Miscibility of Solution Blends of Unsaturated Polyester Resin with Polystyrene and Polycarbonate

Miscibility studies of unsaturated polyester resin (UPR) blends with two different thermoplastics—polystyrene (PS) and polycarbonate (PC), in a common solvent, chloroform, were carried out by viscosity, ultrasonic velocity, density, and refractive index methods. Two interaction parameters, μ and α were calculated using viscosity data for these blends. The positive interaction parameter values (μ and α > 0) obtained for the UPR/PS blend and the negative interaction parameter values (μ and α < 0) obtained for the UPR/PC blend indicate that the former is a miscible blend and the latter is an immiscible blend. These results were further confirmed by the ultrasonic velocity, density, and refractive index measurements.

Synthesis, Antimicrobial Activity and Micellization of Gemini Anionic Surfactants in a Pure State as Well as Mixed With a Conventional Nonionic Surfactant

AbstractNew gemini anionic surfactants were prepared from sodium salts of monoalkyl sulfosuccinate esters of ethylene glycol having variably long tails (C12, C16, C18) and dichloroethane. The chemical structures of the prepared surfactants were confirmed using different spectroscopic techniques. The surfaces tension values of the synthesized surfactants were measured at 25 °C individually or mixing at different molar fractions with ethoxylated alkylphenol. In all cases, mixed micellar aggregates were formed and critical micellar concentrations of binary mixtures containing different mole fractions of the surfactants were measured. The micellization processes of the individual and mixed surfactants were investigated. The effect of different alkyl chains of gemini anionic surfactants on properties of binary systems and molar ratio in the mixed aggregates were deduced. The critical micelle concentration of mixed surfactants shifted to lower values compared to those of the single surfactants. Effectiveness values increased with decreases in the mole fraction of gemini anionic surfactants. The negative values of interaction parameter (β) increased with increases in the chain length of anionic surfactants. The activity coefficient (f1, f2) and total minimum surface area of mixed solution were calculated. Also, the gemini anionic surfactants prepared have moderate antimicrobial activity towards bacteria and not active towards fungi.

Wettability of a Polytetrafluoroethylene Surface by an Aqueous Solution of Two Nonionic Surfactant Mixtures

Measurements of the advancing contact angle (theta) were carried out for an aqueous solution of p-(1,1,3,3-tetramethylbutyl)phenoxypoly(ethylene glycol)s (Triton X-100 (TX100) and Triton X-165 (TX165) mixtures) on polytetrafluoroethylene (PTFE). The obtained results indicate that the wettability of PTFE depends on the concentration and composition of the surfactant mixture. The minimum of the dependence between the contact angle and composition of the mixtures for PTFE for each concentration at a monomer mole fraction of TX100, alpha = 0.8, points to synergism in the wettability of PTFE. This effect was confirmed by the negative values of interaction parameters calculated on the basis of the contact angle and by the Rosen approach. In contrast to Zisman, there was no linear dependence between cos theta and the surface tension of an aqueous solution of TX100 and TX165 mixtures for all studied systems, but a linear dependence existed between the adhesional tension and surface tension for PTFE over the whole concentration range, the slope of which was -1, indicating that the surface excess of the surfactant concentration at the PTFE-solution interface was the same as that at the solution-air interface for a given bulk concentration. Similar values of monomer mole fractions of the surfactants at water-air and PTFE-water interfaces calculated on the basis of the surface tension and contact angles showed that adsorption at these two interfaces was the same. It was also found that the work of adhesion of an aqueous solution of surfactants to the PTFE surface did not depend on the type of surfactant and its concentration. This means that for the studied systems the interaction across the PTFE-solution interface was constant and was largely of Lifshitz-van der Waals type. On the basis of the surface tension of PTFE, the Young equation, and the thermodynamic analysis of the adhesion work of an aqueous solution of surfactant to the polymer surface, it was found that in the case of PTFE the changes in the contact angle as a function of the mixture concentration of two nonionic surfactants resulted only from changes in the polar component of the solution surface tension.

Phase Behavior of Bis(Quaternary Ammonium Bromide)/Sodium Cholate/H2O System

Interactions in an oppositely charged surfactant mixture composed of a gemini surfactant (bis(quaternary ammonium bromide)) and a bile salt (sodium cholate) in water were studied at 30°C. A combination of techniques was used including surface tension, conductometry, light scattering, light microscopy, and microelectrophoretic measurements. A strong dependence of the phase behavior on the molar ratio and actual concentration of surfactants was found. The interplay between electrostatic effects, geometry of molecules, and dissimilar separation of the hydrophobic and hydrophilic moieties in the surfactants dictate the interaction mode and the microstructures formed. Instead of precipitation, in the equivalent mixtures formation of complexes, mixed micelles, vesicles, coacervates, and solid crystalline phases have been observed. The extent of interacting forces in mixed micelles formed in equivalent mixtures was evaluated by regular solution theory. A relatively high negative value of interaction parameter indicated a strong attractive interaction between surfactants. The compositions of both mixed micelles and mixed monolayer are found to be almost equimolar.

Effect of alkyl groups in anionic surfactants on solution properties of anionic‐nonionic surfactant system

AbstractThe effect of different alkyl chains of anionic surfactants on properties of binary anionic‐nonionic mixed surfactant systems was studied. These systems included ocytldodecyl‐, and cetylsulfoacetates mixed with isooctyl phenol nonyl ethoxylate. The critical micelle concentration of mixed surfactants shifted to lower values compared to those of the single anionic surfactants. Effectiveness values increased with decreases in the mole fraction of anionic surfactants. The negative values of interaction parameter (β) increased with increases in the chain length of anionic surfactants.