Metastable liquid dispersions

The presence of excess surface energy in such gas-liquid disperse system predetermines its nonequilibrium. However, by virtue of the stabilizing effect of surfactants, foam possesses a metastable structure and has a certain lifetime [118], Its properties slowly relax under the action of external factors provided that the latter do not exceed some threshold values beyond which the foam structure is destroyed. 

There is much evidence to suggest that the metastable liquid-liquid region of a protein solution is responsible for cataract formation. As the eye ages, its protein concentration changes and one (or more) proteins may achieve a concentration that exceeds the saturation concentration as indicated in the figiue. Following phase separation, the highly concentrated liquid phase does not set-tie but remains in the eye as a fine dispersion whose optical properties seriously interfere with vision. The experimental data show that when the concentration of native y-crystaUin exceeds about 100 mg cm at body temperature (310 K, 37 °C), a second liquid phase is formed whose concentration is about 700 mg cm. It is this... 

Stability may be inherent or induced. In the latter case, the original system is in a condition of metastable or neutral eouilibrium. External influences which induce instability in a dispersion on standing are changes in temperature, volume, concentration, chemical composition, and sediment volume. Applied external influences consist of shear, introduction of a third component, and compaction of the sediment. Interfacial energy between solid and liquid must be minimized, if a dispersion is to be truly stable. Two complementary stabilizing techniques are ionic and steric protection of the dispersed phase. The most fruitful approach to the prediction of physical stability is by electrical methods. Sediment volumes bear a close relation to repulsion of particles for each other. 

Similar considerations apply to chemical or physicochemical equilibria such as encountered in phase transitions. A chilled salt solution may be stable (at or below saturation), metastable (supercooled to an extent not allowing nucle-ation), or unstable (cooled sufficiently to nucleate spontaneously). In the case of a solid, S, dispersed in a binary liquid, Li + L2, instability at the instant of formation gives way to a neutral or metastable condition wherein three types of contacts are established ... 

The thin liquid films bounded by gas on one side and by oil on the other, denoted air/water/oil are referred to as pseudoemulsion films [301], They are important because the pseudoemulsion film can be metastable in a dynamic system even when the thermodynamic entering coefficient is greater than zero. Several groups [301,331,342] have interpreted foam destabilization by oils in terms of pseudoemulsion film stabilities [114]. This is done based on disjoining pressures in the films, which may be measured experimentally [330] or calculated from electrostatic and dispersion forces [331], The pseudoemulsion model has been applied to both bulk foams and to foams flowing in porous media. 

Wan] Electrolytic Co (99.99%), Fe (99.99%), Mo (99.5%). Melting in alumina crucibles in a high induction furnace under an Ag atmosphere. Hot-rolling at 800 °C. Optical microscopy, SEM/energy dispersive X-ray analysis. Thermodynamic calculations with the Redlich-Kister model and thermodynamic parameters evaluated with the PARROT software. The alloys of the compositions near Cu/ Fe 50/50 with Mo from 0 to 6 mass%. Annealing at 800 to 1300°C for 3 to 1680 h. Experimentally determined compositions of the phases in equilibrium at 1300, 1200, 1100, 1000, 900, 800°C. Calculated isothermal sections at 1500, 1300, 1100, 900°C vertical sections at 5 and 10 mass% Mo and up to 30 mass% Cu metastable miscibility gap of the liquid phase. 

In this lecture we characterize the effect of absence of unconstrained thermodynamic equilibrium and onset of a metastable state on the adiabatic flow of a mixture of liquid and its vapor through a convergent-divergent nozzle. We study steady-state flows and emphasize the relations that are present when the flow is choked. In such cases, there exists a cross-section in which the flow is critical and in which the adiabatic wave of small amplitude is stationary. More precisely, the relaxation process which results from the lack of equilibrium causes the system to be dispersive. In such circumstances, the critical velocity is equal to the frozen speed of sound, a corresponding to... 

In several papers [1,2,3], the present authors and their collaborators have made a systematic study of adiabatic one-dimensional flows of single substances present in the stream in a liquid and a gaseous phase, with emphasis on critical flow as a cause of choking. The study fell naturally under two headings. First, we explored the general qualitative features of such flows as they are described by a wide class of mathematical models [1]. Given that flows of this kind invariably start from rest with a liquid which expands into a metastable state, we have, secondly [2,3], undertaken an analytic study of the effect of the realxation mechanism which drives the local state to one of unconstrained equilibrium. Clearly such flows are dispersive and the attainment of a critical velocity at... 

It appears that the phase diagram for very small q <0.3) is much simpler than for larger q [144—145, 213, 214]. For small q the only effect of adding polymer chains to the pure hard-sphere dispersion is the widening of the fluid-solid coexistence region. A gas-liquid phase transition occurs at larger polymer concentrations above the fluid-solid phase line and is metastable, see Sect. 3.3.4. Only above a certain range of attraction, the (colloidal) gas-liquid phase transition shifts below the fluid-solid coexistence curve. For q close to 1/3 the critical point hits the fluid-solid coexistence curve. This critical point is the critical endpoint, which is rather insensitive to the shape of the interaction potential used [215]. 

An emulsion is a dispersion of one liquid in another where each liquid is immiscible, or poorly miscible in the other [1]. Emulsions exhibit all classical behaviors of metastable colloids Brownian motion, reversible phase transitions as a result of droplet interactions that may be strongly nradified and irreversible transitions that generally involve their destruction. They are obtained by shearing two immiscible fluids to the fragmentation of one phase into the other. From diluted to highly concentrated, emulsions exhibit very different internal dynamics and mechanical properties. Emulsifiers are usually added to oU/water mixture to enhance the formation of stable monomer emulsions. The molecules of emulsifier adsorb to the surface of oil droplets during homogenization and provide a protective membrane... 

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