G. Para

Encapsulation of liquid cores by layer-by-layer adsorption of polyelectrolytes.

The aim of this work was to develop the method of preparation of loaded, submicron nanocapsules based on the liquid core encapsulation by polyelectrolyte (PE) multilayer adsorption. The procedure of PE adsorption on the emulsion droplets requires a specific selection of surfactants, which have good properties as emulsifiers and provide a stable surface charge for sequential adsorption of PE without losing stability of emulsion. Using AOT as emulsifier this study obtained droplets, stabilized by AOT/PDADMAC surface complexes. These positively charged liquid cores were then modified by sequential adsorption of polyelectrolytes to obtain nanocapsules with the average size of 200 nm, with various combinations of polyelectrolytes (PDADMAC, CHIT, PAH, PSS, ALG). This study demonstrated the formation of consecutive layers of PE shells by measuring zeta potential of capsules after adsorption of each layer. It visualized the cores by dissolving fluorescent dye Coumarine6 in oil phase and multilayer shells by using FITC labelled polycation.

Effect of electrolytes on surface tension of ionic surfactant solutions

Abstract An improved model of ionic surfactant adsorption was developed by considering penetration of counterions into the interfacial Stern layer. Accordingly, the surface layer was treated as quasi two-dimensional electrolyte in which the electroneutrality condition was not fulfilled. Moreover, in the model the finite size of surfactant head-groups and counterions were taken into account as well as lateral electrostatic interactions. The model was confronted with experimental data obtained for cetyltrimethylammonium bromide in different electrolytes. It was found, that the model correctly reflected the variation in surface tension isotherms with the ionic strength of the solution. Contrary to previous models of ionic surfactant adsorption, our model allowed to account for the strong dependence of adsorption on type of counterion present in solution. Using the model a dependence of Stern layer potential and diffuse double layer potential on the concentration of surfactant in solution also was predicted.

Natural oil nanoemulsions as cores for layer-by-layer encapsulation

In this study, emulsions of three different natural oils were prepared using spontaneous emulsification technique. The effect of three emulsifiers, AOT, lecithin and cholesterol on emulsion properties was studied. Their influence on interfacial tension at oil/water interface was evaluated by the pendant drop shape analysis method. Then, the mean droplet size, zeta potential and stability of emulsions were investigated in relation with the type of oil, surfactant, oil-to-ethanol ratio and surfactant concentration. We found that in the case of linseed oil, fine emulsion droplets are formed without any surfactant due to its low oil/water interfacial tension. A hydrophobic dye (Coumarin 6) was encapsulated within oil cores and its presence was confirmed by fluorescence spectroscopy and microscopy. The obtained emulsions can be used alone or as the cores for layer-by-layer encapsulation, which was demonstrated by enclosing droplets within first layer of synthetic polycation poly(allyamine hydrochloride) (PAH).

Hydrolysis driven surface activity of esterquat surfactants

HYPOTHESIS Surface activity of selected cleavable esterquat cationic surfactants is determined by the synergistic effect of surface active products of their hydrolysis. EXPERIMENTS Interfacial behavior of two classes of esterquat surfactants, quaternary alkylammmoniumesters and amino acid betaine (trimethylglycine) esters of fatty acids were examined both experimentally and theoretically. The surface tension measurements at air/water interface were performed by the pendant drop shape analysis method, then the obtained isotherms were theoretically described by the model of adsorption of ionic/non-ionic surfactants mixtures taking into account the presence of surface active products of surfactant hydrolysis. FINDINGS We found that surface activity of the mixture of surface active compounds resulting from the esterquat basic hydrolysis increases with time and it is higher when the ester carbonyl group is connected with the quaternary amine by bridging oxygen than in the inverted (betaine ester type) arrangement. That is, in the first case, the consequence of strong synergistic effect between the cationic esterquat surfactant and the anionic product of its hydrolysis - dodecanoate ion, while in the second case, the non-ionic hydrolysis product - dodecanol exhibits much weaker synergy. The addition of side CH3 group into the esterquat head-group slows down the hydrolysis that leads to the lower surface activity of the resulting mixture.

Surface activity and mercury flotation in solutions of n-dodecanoic acid and n-dodecylamine

The flotation and adsorption properties of two ionic collectors (n-dodecylamine andn-dodecanoic acid) are compared on the bases of results of mercury flotation in the model flotation apparatus and electrochemical measurements of the double layer capacity.The flotation recovery and the adsorption parameters (standard free enthalpyΔG°A, the interaction coefficient of Frumkins isotherm, the surface area per molecule) have been determined within the pH range 2.5–12 in solutions of various collector concentrations containing 0.1 N KCl. The maxima of flotation recovery and surface excess have been found at pHs corresponding to pK values for both substances. The influence of the electrolyte on flotation recovery and the gas bubble size distribution dependent upon the pH of the solution is presented forn-dodecanoic acid. The maxima of flotation recovery are involved through the formation of ion-molecule associates (1∶1) as well as an optimum of the bubble size distribution.

Flotation and adsorption investigations of the systemn-dodecanoic acid/mercury at different pH values

The systemn-dodecanoic acid/mercury in 0,1 N KCl solutions has been investigated within pH range 4,0–10,5 in order to characterize the adsorption of surfactant and to determine its influence on the flotation of mercury. Flotation tests have been carried out in a model mercury flotation apparatus developed by Pomianowski and Para. Some characteristic parameters of adsorption (attraction constant of Frumkin isotherm, adsorption coefficient at maximum adsorption potential, free standard adsorption enthalpy and area per molecule) have been determined by a. c. polarographic capacity-potential and capacity-time curves. Flotation recovery as well as attraction constant, adsorption coefficient and surface excess reach maximum at pH≈5,1. It is explained by the assumption of an ion-molecule associate formation.