A.M. Parfenova

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.

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.

Transport of the colloid matter of riverine runoff through estuaries

A procedure for separating the colloid component of natural waters is proposed. It was shown that this component is the main form of matter transfer in Ob River runoff, because the mass of colloid substance is two orders of magnitude higher than that of particulate matter in the outer part of the estuary. Simulation and field experiments revealed the influence of nature and concentration of organic matter on their ability to stabilize or flocculate clay particles with an increase in salinity, thus affecting the range of transfer of riverine runoff matter. It was shown that the interaction of humic acids and clay particles, as well as the increase in hydrophobic properties of a flocculant, improve flocculation efficiency. Criteria are proposed to recognize in the estuarine region areas of pronounced contribution of flocculation processes to sedimentation of fine particles. It is shown that the newly formed organic matter produced by biota under saline stress might be flocculants of fine particulate matter.

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.

Morphology and Hydrophobicity of Humic Coatings on Glass as Studied by Atomic Force Microscopy (AFM) and Contact Angle Measurements

In nature, many functional nanoarchitectures are self-assembled due to supramolecular interactions of natural organic matter and surfaces of mineral particles. However, direct evidence for molecular mechanisms responsible for these interactions is still missing. Here, we developed silanol derivatives of humic substances capable of self-assembling onto hydroxylated surfaces. By using humic substances from peat and coal and DNA array glass slides, we show that humic adlayers were homogeneous on macroscale, but separated into domains of nanosize in coal HS and submicro size in peat HS. The peat adlayers were characterized with larger roughness of 11 nm versus 5 nm for coal. Measurement of the contact angle showed that application of humic coatings leads to an increase in hydrophobicity of glass. It was shown that treatment of soil aggregates with silanol derivatives of humic acids increases water stability of the aggregates.

Estimation of the Molecular Component of the Friction Force between Fibers in Surfactant Solutions

The molecular component F0 of the friction force (by Derjaguin) between fibers in solutions of cationic surfactants–tetrabutylammonium iodide and poly(ethylene imine)—was estimated from adhesion forces and the friction coefficient measured in point contacts between individual fibers. The nonmonotonic character of the dependence of F0 on the surfactant concentration was explained on the basis of a comparison of these data with experimental data on the ζ potential and the adsorption.