S. M. Levachev

Properties of Interfacial Layers in Multicomponent Systems Containing Gelatin

The review is devoted to the analysis of the effect of the addition of various surfactants on the composition, structure, and the properties of the interfacial adsorption layers (IALs) formed at equilibrium in the aqueous gelatin solution–hydrocarbon system. Associates of variable compositions that are determined by the component ratio and the concentration of added surfactant are formed due to the interaction between gelatin and surfactant. The formation of associates is equivalent to the modification of gelatin. The properties of the IALs of modified gelatins are discussed on the basis of our own results and published data on the interfacial tension, the mass accumulation of surface-active components at the interfaces during the IAL formation, the IAL rheological properties and the stability of emulsion films varied with the conditions of IAL formation (the nature of low-molecular-weight surfactant, component concentrations, pH of aqueous phase, and temperature). It was concluded that modified gelatins can be considered as new surfactants governing the dynamics of the formation and fracture mechanism of the IALs and the stability of emulsion films. The properties of the IALs of modified gelatins are compared with those of IALs formed by gelatin and low-molecular-weight surfactants under the conditions when associates are formed directly at the interface due to the use of oil-soluble surfactants.

Non-Newtonian behavior of concentrated emulsions stabilized with globular protein in the presence of nonionic surfactant

Changes in the rheological properties of a model concentrated oil-in-water emulsion stabilized with globular protein (bovine serum albumin) upon the addition of nonionic surfactant polyoxyethylene (20) sorbitan monooleate (Tween 80) are studied. Non-Newtonian behavior is typical of the emulsions in question; moreover, they are characterized by the existence of yield stress. At stresses above the yield stress, the viscosity drops not immediately but after the intermediate Newtonian region at the flow curve. For all systems studied, the total flow curve is exhibited with the minimum Newtonian viscosity that is adequately described by the Cross formula. An increase in the Tween 80 concentration leads to a decrease in the viscosity of emulsion. Two threshold phenomena on the concentration dependences of rheological properties are revealed: at low concentration of added nonionic surfactant, the yield stress drops abruptly, whereas the viscosity lowers considerably with an increase in surfactant concentration to 1 × 10−3 mol/l and the emulsion becomes unstable. The effects observed can be explained by the gradual displacement of high-molecular-weight stabilizer from interfacial layers and its replacement by nonionic surfactant.

Novel Approach to Synthesis of Monodisperse Polymeric Microspheres: Heterophase Polymerization of Styrene and Methyl Methacrylate in Presence of Water-Insoluble Functional PDMSs

Water-insoluble polydimethylsiloxanes (PDMSs) with functional organic substituents at the silicon atom are promising surface-active substances for the synthesis of monodisperse polymeric microspheres. In this regard a number of PDMS oligomers bearing different functional chain ends (amino, carboxylic and epoxy groups) were synthesized by conventional approaches. Solubility of PDMS in both the monomers (styrene (St) or methyl methacrylate (MMA)) and water as well as their surface-active properties at the water-toluene interface were investigated. Heterophase polymerization of St and MMA was carried out in the presence of functional PMDS and the resulting suspensions of polymeric microspheres were characterized using scanning electron microscopy (SEM). It was shown that the polymeric suspensions obtained have a very narrow particle size distribution and high stability in electrolyte solutions. The mechanism of the interfacial layer formation which explains the observed results is proposed.

Viscoelasticity of concentrated emulsions stabilized by bovine serum albumin in the presence of a nonionic surfactant

Viscoelastic properties of highly concentrated toluene-in-water emulsions stabilized by mixtures of bovine serum albumin and a nonionic surfactant, polyoxyethylene(20)sorbitan monooleate, are studied by a dynamic method in a wide frequency range. It is shown that an increase in the relative content of the surfactant results in a suppression of the system elasticity and a decrease in the relaxation time. A direct correlation is found between the dynamic and steady rheological characteristics of the systems under examination. The latter fact confirms indirectly that the viscoelasticity of the emulsions is due to the presence of the high-molecular-mass component in interfacial layers.

Adsorption Properties of Alumina Modified with Nickel Oxide Nanoparticles and Silver–Nickel Oxide Bimetallic Nanoparticles

The adsorption properties of γ-Al2O3, both in the original form and as modified with NiO nanoparticles and [NiO+Ag] bimetallic nanoparticles, were studied using the dynamic sorption method. n-Alkanes (C6–C8), benzene, chloroform, diethyl ether, toluene, and ethylbenzene were used as test adsorbates. The adsorption isotherms were measured, and the isosteric heats of adsorption of the tested adsobates were calculated. The surface of the original γ-Al2O3 was found to mostly have electron-accepting (acidic) properties, while the surface of alumina modified with NiO nanoparticles exhibits electron-donating (basic) properties. The adsorption isotherms of all adsorbates onto γ-Al2O3 at all specified temperatures lie higher than onto the original γ-Al2O3. Nanocomposite 5% NiO/γ-Al2O3 exhibits the highest adsorption activity with respect to aromatic hydrocarbons.

ORGANOSILICON SURFACTANTS: EFFECTS OF STRUCTURE ON THE KINETICS OF HETEROPHASE POLYMERIZATION OF METHYL METHACRYLATE AND BEHAVIOR IN LANGMUIR FILMS ON THE SURFACE OF WATER

The kinetics of methyl methacrylate polymerization in the presence of α,ω-functional polydimethylsiloxanes is investigated. The formation of polymer suspensions with a narrow particle-size distribution is explained by the ability of the surfactants to form strong adsorption layers in the interfacial layers of polymer–monomer particles. This assumption is confirmed by data obtained via the Langmuir method with the use of model systems: thin films of the mentioned organosilicon compounds.

Properties of Spreaded Collagen I Monolayers on the Surface of Aqueous tert-Butanol and n-Hexanol Solutions

Properties of the monolayers of collagen isolated from the sclera of pigs eye are studied at the air–water interface with increasing tert-butanol or n-hexanol concentrations in a subphase. In the case of aqueous n-hexanol solutions, its adsorption on the subphase surface results in the formation of mixed monolayer whose properties depend on n-hexanol concentration in the subphase and the ratio between the number of alcohol and collagen molecules in the monolayer. At higher n-hexanol surface concentration, the phase separation of the monolayer into the domains of the condensed phase of alcohol and fibrous collagen occurs. A decrease in water activity in the presence of tert-butanol leads to a drastic reduction of collagen surface activity. This effect can be explained by both the constrained collagen spreading on the surface of tert-BuOH solutions and adsorption of alcohol molecules on collagen resulting in macromolecule hydrophilization. Alcohol critical concentrations are disclosed above which collagen monolayers are not formed.

Heterophase Polymerization of Styrene in the Presence of Biodegradable Surfactants

Linear and branched copolylactides of various structures are synthesized and characterized. Polystyrene suspensions with various particle diameters are obtained via heterophase polymerization with the use of copolylactides as biodegradable surfactants. The influence of the surfactant structure on the polymer microsphere size and the type of size distribution is studied.

Styrene polymerization in the presence of different initiators and properties of polymer suspensions

It is shown that the nature of an initiator affects the molecular mass and molecular-mass distribution of a polymer and, thus, substantially contributes to the strength and rheological characteristics of the interfacial adsorption layer formed on the surface of polymer-monomer particles and the stability of these particles during polymerization.

Collagen Denaturation in Spread Monolayers at the Air-Water Interface: Experiments and a Possible Model of the Process

Spread monolayers of the fibril protein collagen were studied at the air-water interface in the presence of denaturants, urea and thiourea. The most prominent feature of spread collagen monolayers at the air-water interface is the ability to form supramolecular structures (fibrils), which themselves can form monolayers with collapse points of their own. The surface pressure isotherms of collagen monolayers have two “quasi-linear” centers, which are separated by a plateau and correspond to liquid-expanded and liquid-condensed states; this unique capability makes collagen different from other proteins. When in monolayer, collagen acquires the same level of structural organization as in the bulk. In the presence of denaturants, subphase characteristics of collagen monolayers change rapidly and irreversibly. Thiourea exerts more pronounced denaturing action on collagen monolayers than urea; this effect increases with exposure time and denaturant concentration. A hypothetical mechanism of thiourea-induced denaturation of fibril proteins is proposed according to which interactions between hydrophobic C=S groups of thiourea and nonpolar surface groups of the protein lead to reorientation of carbonyl groups to formation of intrinsic hydrogen bonds with NH2-groups of thiourea eventually resulting in the rupture of intrinsic hydrogen bonds and denaturation of the protein.