Supersaturated solution dynamics

In the unsaturated solution, the added crystal dissolved and the solution appeared homogenous, as it did before the crystal was added. In the saturated solution, the added crystal remained and the solution became heterogeneous. Since the solution process is dynamic, the added crystal should become more uniform as time passes. In this dynamic process, dissolved solute particles are precipitating out onto the crystal surface at the same rate as crystal surface particles are dissolving. In the supersaturated solution, excess solute precipitated out of the solution, which was then a heterogeneous mixture. 

Preferential Enrichment is a secondary phenomenon caused by a polymorphic transition occurring during crystallization from a highly supersaturated solution. This unique dynamic enantiomeric resolution phenomenon has proved to be observable for a fairly ordered racemic mixed crystal showing a polymorphism a solvent-assisted solid-to-sohd type of polymorphic transition from the kinetically-formed metastable crystalline phase comprising homochiral R and S chains into the thermodynamically stable crystalline phase consisting of a heterochiral 2D sheet structure during crystallization is responsible for this phenomenon. That is, it is essential that homochiral R and S ID chain structures are stable in solution while a heterochiral 2D sheet structure is stable in the crystal. 

When a solution contains all the solute that can be dissolved at a particular temperature, it is saturated. Excess solute falls to the bottom of the container as a precipitate. Occasionally, on cooling, the excess solute may remain in solution for a time before precipitation. Such a solution is a supersaturated solution. When excess solute, the precipitate, contacts solvent, the dissolution process reaches a state of dynamic equilibrium. Colloidal suspensions have particle sizes between those of true solutions and precipitates. A suspension is a heterogeneous mixture that contains particles much larger than a colloidal suspension. Over time, these particles may settle, forming a second phase. 

Consider the initial stage of growth of a spherical gas bubble with initial radius Ro in a multicomponent supersaturated solution due to the diffusion of components with low concentration that dissolved in the liquid. Assume that the process is isothermal, and the factors Du, B, and Z are constants. The bubble is small enough to ignore its lifting inside the liquid. The dynamics of bubble growth is described by Eqs. (22.1)-(22.5), in which we must set uy = 0. 

Explain dynamic equihhrium with respect to solution formation. What is a saturated solution An unsaturated solution A supersaturated solution ... 

Each stage of particle formation is controlled variously by the type of reactor, i.e. gas-liquid contacting apparatus. Gas-liquid mass transfer phenomena determine the level of solute supersaturation and its spatial distribution in the liquid phase the counterpart role in liquid-liquid reaction systems may be played by micromixing phenomena. The agglomeration and subsequent ageing processes are likely to be affected by the flow dynamics such as motion of the suspension of solids and the fluid shear stress distribution. Thus, the choice of reactor is of substantial importance for the tailoring of product quality as well as for production efficiency. 

Gels are obtained for concentrations shown in the temperature-concentration phase diagram (Figure 1). Electron spin resonance (ESR) shows (10) that for a given temperature only a fraction (p) of the initial steroid concentration is transferred from the solution to the gel network. The picture of this gel is thus of a supersaturation gel there is a dynamic equilibrium between free molecules in solution and aggregated steroid molecules included in the long objects which constitute the gel network. The free steroid molecules concentration at a temperature where the gel state is stable is (1-p), while C p is the steroid concentration within the solid-iike gel aggregates. 

The perplexing difficulties that arise in the crystallization of macromolecules, in comparison with conventional small molecules, stem from the greater complexity, lability, and dynamic properties of proteins and nucleic acids. The description offered above of labile and metastable regions of supersaturation are still applicable to macromolecules, but it must now be borne in mind that as conditions are adjusted to transport the solution away from equilibrium by alteration of its physical and chemical properties, the very nature of the solute molecules is changing as well. As temperature, pH, pressure, or solvation are changed, so may be the conformation, charge state, or size of the solute macromolecules. 

Nancollas [1983] considers it important to establish not only the dependence of the rate of crystal growth on supersaturation, but also the influence of the ratio of solid to solution, the dynamics of stirring (agitation) and the temperature. He... 

The principal variables that must be controlled in crystallization are the solution supersaturation, the crystal surface area available for growth, and the nucleation rate. These are affected by multiple interacting secondary variables, which may be divided into two categories—equipment design variables and dynamic variables affecting the crystallization. It is the secondary dynamic variables, such as those listed in Table 9.1, to which automatic process control is applied in a typical crystallizer for these vari-... 

If a bubble of radius Ro was initially placed into a supersaturated (at the given pressure and temperature) mixture, then, due to the concentration difference Ap = pi — pi between the gas dissolved in the liquid far away from the bubble and the appropriate equilibrium value at the bubble surface, there arises a directional diffusion flux of the dissolved substance toward the surface. At the interface, the transition of substance from the liquid to the gaseous state takes place. The result is the increase in the bubble volume. The growth of the bubble, in its turn, results in the increase of its lift velocity, as well as the increase of convective diffusion flux. The statement of the problem and the basic dynamic equations for a bubble in a solution were described in Section 6.8. 

SECTION 13w2 The equilibrium between a saturated solution and undissolved solute is dynamic the process of solution and the reverse process, crystalizadon, occur simultaneously. In a solution in equilih-rium with undissohred solute, the two processes occur at equal rates, ing a saturated solution. If there is less solute present than is needed to saturate the solution, the solution is unsatairated. When solute concentration is greater than the equilihrium concentration ralue, the solution is supersaturated. This is an unstable condition, and separation of some solute from the solution will occur if the process is initiated with a solute seed crystaL The amount of solute needed to form a saturated solution at any particular temperature is the solubility of that solute at that temperature. 

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