Elena A. Amelina

Influence of the nature of non-polar phase on the mechanical stability of adsorption layers of hydrocarbon and fluorocarbon surfactants at the interface between their aqueous solutions and non-polar media☆

Abstract A variety of experimental approaches has been used for companson of the stabilizing effect with respect to droplets coalescence caused by the interfacial adsorption layers (IAL) of a nunber of hydrocarbon and fluorocarbon surfactants at the boundary between their aqueous solutions and various non-polar hydrocarbon and fluorocarbon liquids: (I) compression of two individual droplets in surfactant solution up to their coalescence and consequent tension and rupture of a newly formed drop; (II) evaluation of the free energy of interaction between non-polar surfaces by measuring the contact rupture force for smooth spherical particles; (III) rheological study of IAL by torque pendulum method; (IV) SEM observation of the IAL morphology; (V) study of the stability with respect to the Ostwald ripening. These observations reveal the predominant role of the lyophilic structure-mechanical barrier formed by the IAL as a factor of strong stabilization with respect to coalescence and particular dependence of the mechanical strength of such layer on the nature of the non-polar liquid and on the interaction between this liquid phase and hydrophobic parts of the surfactant molecules.

Effect of cationic polyelectrolyte and surfactant on cohesion and friction in contacts between cellulose fibers

Abstract The methodics and devices are presented for quantitative study of the characteristics of interaction in contact between individual fibers: friction force F in shear test, and cohesion force, i.e. contact strength p in rupture test. In experiments with cellulose fibers in various liquid media, the friction coefficient μ has been estimated, and the molecular component of friction force related only to attraction of fibers, in the absence of any external normal load has been found. The specific free energy of interaction U has been evaluated in measurements using model samples with the nature of surface similar to that of cellulose fibers. The effects of cationic polyelectrolyte and surfactant: polyethyleneimin and tetrabuthylammonium iodid on these parameters have been quantitatively determined. Complicated, non-monotonic (with several extrema) dependence have been estimated between values F , μ , p , U and surfactant concentration C . Comparison of these data with the ζ -potential measurements of cellulose fibers in the same surfactant solutions allows one to propose an explanation of the mechanisms of these polyelectrolyte and surfactant influence on fiber interactions.

Surface Modification and Contact Interaction of Particles

Abstract The effects of particle surface modification by ambient media and surfactant adsorption on the cohesive forces in the immediate contacts between individual particles have been studied with the CF (cohesive force) apparatus. The values of the free energy of interaction in direct coagulation contacts between particles of various types in liquids of different polarity and in the presence of various surfactants have been measured. They cover a broad range of several orders of magnitude; these interactions define the rheological properties of concentrated thixotropic systems and their stability with respect to peptization. A similar experimental technique has been used for studying active media influences on various physico‐chemical processes of particle bridging and formation of the phase contacts responsible for the mechanical properties of related solid structures and their resistance to fracture. The effect of the adsorption induced decrease in strength and durability of such porous structures with phase contacts and compact solids is considered.

Investigation of residual internal stresses of the I and II modes in cement-hardening structures

Abstract Since the discovery of X-ray diffraction techniques, this has enabled the detection of internal microstresses (of mode II) caused by capillary forces during the removal of pore-confined water for the first time. The effect of polyethylene glycol and polypropylene glycol on residual internal stresses was studied quantitatively. The results were discussed within the basic concepts of physicochemical mechanics.

Contact Interactions between Individual Fibers of Cellulose and Its Derivatives: Mechanism of Cationic Surfactant Action

The effect of cationic surfactants (cetyltrimethylammonium bromide and tetrabutylammonium iodide) and cationic polyelectrolyte polyethylenimine on the coefficient of friction μ and adhesion force p(during shear and tensile testing, respectively) at the point contacts between the individual fibers of cellulose, viscose, and cellulose acetate was studied. The comparison of these data with the results of ζ-potential and adsorption measurements enabled us to relate the nonmonotonic dependence of parameters μ and pon the surfactant concentration to the changes in electrosurface properties and the hydrophilicity or hydrophobicity of the fibers. The specific free energy of interaction U[mJ/m2] was estimated for cellulose acetate fibers.

The Lyophilic Structure-Mechanical Barrier as a Factor of Dispersion Strong Stabilization

The lyophilic structure-mechanical barrier formed by the interfacial adsorption layer is considered as a factor of strong stabilization of disperse systems with respect to high concentrations of disperse phase and electrolyte. Such barrier must possess two principal features: intrinsic mechanical strength of the layer — preventing coalescence, and high affinity of the external side of the layer and dispersion medium — opposing coagulation; independent experimental approaches for their quantitative characterization are presented.

Interactions between Nonpolar Surfaces in Mixed Solutions of Cationic and Nonionic Surfactants

The interaction energy between hydrophobic SiO2 particles in aqueous solutions of a cationic surfactant (dodecylpyridinium bromide, DDPB), a nonionic surfactant (Triton X-100, TX-100), and their mixed solutions was measured as a function of concentration. Synergism has been observed in mixed surfactant solutions: the surfactant concentration required for achieving the set interaction energy in the mixed solutions was lower than in the solutions of the individual surfactants. The molecular interaction parameters in surfactant mixtures were calculated using the Rosen model. Chain-chain interactions between nonionic and cationic surfactants were suggested as the main reason for the synergism.

V – Transfer Processes in Disperse Systems

Publisher Summary Structural features of disperse systems, particularly, the existence of the electrical double layer (EDL), are responsible for a number of peculiar phenomena related to heat and mass transfer, and electric current propagation in such systems. The methods used to study disperse systems include particle size distribution analysis, studies of the surface structure and of near-surface layers, and the structure of the EDL. Most transfer phenomena are described by the laws of irreversible thermodynamics, which allow carrying out a systematic investigation of different fluxes that originate as a result of the action of various generalized forces. One model example of a transfer process that takes place in a structured disperse system is the transfer of the dispersion medium through a single capillary of radius r c that occurs during filtration or in the processes involving various types of osmosis. The proportionality coefficient between the acting force and the resulting flux is referred to as the conductivity (or permeability) of the capillary, while the reciprocal value is known as the capillary resistance.

VIII - Structure, stability and degradation of various lyophobic disperse systems

Publisher Summary This chapter describes the preparation, structure, and properties of different colloidal systems. The chapter reviews the connection among particular properties of disperse systems and the aggregate states of both the dispersed matter and dispersion medium. Among all disperse systems, the aerosols, in which the dispersion medium is a gas, are unique. These systems are principally lyophobic and their stabilization—by introduced surfactants—is ineffective. Aerosols also reveal some specific electric properties. In systems with liquid dispersion medium, that is, in foams, emulsions, sols, and suspensions, there is a broad variety of means to control colloid stability. In these systems, the nature of colloid stability depends to a great extent on the aggregate state of dispersed phase. Similar to aerosols, foams are lyophobic, but in contrast to them, foam can be effectively stabilized by surfactants. Properties of emulsions, and, to some extent, those of sols are quite close to the properties of thermodynamically stable lyophilic colloidal systems. In such systems, a high degree of stability may be achieved with the help of surfactants.

Interfaces between condensed phases. Wetting

Publisher Summary The laws governing the interfacial phenomena between condensed phases and their vapor (or air) in single- and two-component systems are largely applicable to the interfaces between two condensed phases, which is between two liquids, two solids, or between a solid and a liquid. At the same time, these interfaces have some important peculiarities, primarily related to the partial compensation of the intermolecular interactions. The degree of saturation of the surface forces is determined by the similarity in the molecular nature of the phases in contact. When adsorption of surfactants takes place at such interfaces, it may substantially enhance the decrease in the interfacial energy. The latter is of great importance as surfactants play a major role in the formation and degradation of disperse systems. The intensity of intermolecular interactions at the interfaces between condensed phases is one of the critical factors determining the conditions for wetting and spreading. A large number of important technological processes, such as mineral processing (flotational enrichment and separation), are based on these phenomena.