in Wiley InterScience (www.interscience.wiley.com).Hydrate inbibition in natural gas production by antiagglomeration is promising because of effectiveness at high subcoolings encountered in many offshore operations. There are various mechanisms that are believed to contribute to the repulsion and attraction of hydrate particles. These include: (1) steric, (2) dispersion, (3) capillary, and (4) shear forces. Some of the expressions derived, and some formulas are used from the literature to provide a theoretical analysis of the forces between two hydrate particles to examine antiagglomeration using surfactants. Results show that hydrate particle size has the most important effect on antiagglomeration. Results also show that the contact angle increase and the oil-water interfacial tension decrease will either reduce capillary forces significantly or eliminate it. Effective antiagglomerants reduce the size, decrease interfacial tension, and increase contact angle through the water phase.

The expression for driving force is presented for multicomponent gas hydrate nucleation in an aqueous phase. The derivation includes working equations for predicting the composition of a hydrate nucleus. The results for driving force in multicomponent systems show a significant effect of the composition of the hydrate nucleus. All past work assume a fixed composition based on the three-phase equilibrium point independent of subcooling and supersaturation.

The effect of water on the flow behavior of glass microspheres dispersed in mineral oil was investigated for various levels of water, particle volume fractions, and particle sizes. The addition of small amounts of water leads to large increases in viscosity due to the formation of water bridges between particles that give rise to capillary forces between the particles. The capillary forces between the particles also make the flow profile highly shear-thinning across the range of particle volume fractions that were studied (0.10 to 0.25). The presence of water leads to a significant effect of particle size, and the viscosity of dispersion goes through a maximum as the amount of water is increased. Two hydrophobic surfactants, Span 80 and Arquad 2HT, were found to reduce the viscosity of the dispersions with added water, but the mechanism and extent of viscosity reduction differed.

We present a unified model for complete crystal-growth inhibition based on the thermodynamics of interfaces. The premise for our model is that the adsorption of inhibitor leads to a reduction in interfacial tension or edge energy for the crystal surface or step, respectively. In our formulation, the work to add a layer or grow a step increases due to the difference in interfacial tensions or edge energies for surfaces with and without an adsorbed inhibitor. For a large enough difference in interfacial tensions or edge energies, complete inhibition of growth is realized when the total work does not decrease as more crystals are formed. We demonstrate that our model can provide a theoretical description of critical subcooling data for ice with antifreeze proteins and glycoproteins, critical subcooling data for hydrates and ionic crystals, and critical supersaturation data for various crystal systems.

Thin, supported decane films stabilized with comb−graft copolymers were studied as models of polymeric surfactant stabilized water-in-oil emulsions. The stabilizing polymeric surfactant (“polysoap”) was composed of a poly(dimethylsiloxane) backbone with hydrophobic alkyl and hydrophilic ethylene/propylene oxide grafts with a total molecular weight of 62 000. Electrical compressive stresses were imposed on the films, and their thicknesses were determined from measurements of capacitance and optical interference. The theory for the interpretation of capacitance versus applied electric field in terms of disjoining pressure was developed. Sessile drop measurements of interfacial tension were used to infer a polymer coverage of 1.7 nm2/molecule. Dynamic light scattering measurements showed hydrodynamic diameters of 6 nm at 5.2 wt % of the polymer in decane. The measured film thicknesses ranged from 32 to 62 nm over a compressive force range of 0−1400 Pa. The films were remarkably thick and compressible compared to films formed from simple surfactant or lipid systems. The films displayed compressive moduli ranging from 1000 to 6400 Pa. The film properties were relatively insensitive to the surfactant concentration and moderately sensitive to polymeric surfactant purity. The observed thicknesses are shown not to arise from interfacial electrostatic effects or van der Waals forces but from steric interactions. The observed thicknesses are consistent either with strongly stretched chains adsorbed at the interface or with multichain aggregate structures at the interface.