The Effect of Solvent on Crystal Growth

3 Ikilor-Made Auxiliaries as Crystal Growth Promoters 

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Lahav, M. and Leiserowitz, L., 2001. The effect of solvent on crystal growth and morphology. Chemical Engineering Science, 56(7), 2245-2254. 

Some of the difficulties encountered in establishing the effect of solvent on crystal growth may be circumvented by focusing on polar crystals. This is because the difference in the rates of growth of opposite faces (hid) and (hkl) along a polar direction must arise primarily from differences in their solvent-surface interactions. Thus, one generally does not have to be concerned with faces other than the hemihedral ones in question. We illustrate below an approach to understanding solvent-surface interactions in the polar crystals of resorcinol (102). 

Growth of Hexamethykne Tetramine (HMT) from Various Solvents. Detailed studies of the effect of solvents on crystal growth have been conducted using the crystalline material HMT (Bourne and Davey 1976 Bourne 1980 Davey 1986). An analysis of HMT solubility data through the use of Eq. (3.33) indicates that HMT forms an approximately ideal solution with ethanol. By contrast, large negative deviations from ideal behavior are observed in water. 

Garti N, Leci CL, and Sarig S. The Effect of Solvents on Crystal Habit of 1,4-Di-Tert-Butylbenzene (DTB ). J Cryst Growth 1981 54 227-231. 

One of the most important results of theoretical investigations of crystal growth has been the quantification of the effect of solvents on crystal interface structure. In particular, a key parameter, called the a-factor, has been developed from fundamental theories that allows identification of likely growth mechanisms based only on solute and solution properties. 

The surface entropy factor, a, can be considered a relative measure of the degree of smoothness of a crystal face on the atomic level. In Section 3.9.3 it is shown how a correlates the effect of solvents on both growth rate and growth mechanism. 

The effects of a solvent on growth rates have been attributed to two sets of factors (28) one has to do with the effects of solvent on mass transfer of the solute through adjustments in viscosity, density, and diffusivity the second is concerned with the stmcture of the interface between crystal and solvent. The analysis (28) concludes that a solute-solvent system that has a high solubiUty is likely to produce a rough interface and, concomitandy, large crystal growth rates. 

As discussed in section 2.4.4 the coordinating ability of a solvent will often affect the rate of nucleation and crystal growth differently between two polymorphs. This can be used as an effective means of process control and information on solvent effects can often be obtained from polymorph screening experiments. There are no theoretical methods available at the present time which accurately predict the effect of solvents on nucleation rates in the industrial environment. 

A benchmark study on the effect of solvent on growth of polar crystals was carried out by Wells (42) in 1949. He found that in aqueous solution at room temperature the ot-form of resorcinol (space group Pna2t), 12a, grows unidi-rectionally along the polar c axis. The crystal exhibits benzene-rich 011 faces Sit one end of the c axis and O(hydroxyl)-rich OlT faces at the other end... 

Boochatum and co-workers [41] studied the effect of solvent on the crystallisation growth behaviour of crystals of l,4- r s-polyisoprene. 

The use of tailor made additives holds great promise in the area of crystal growth and morphology control. The routine selection and use of these type of additives will require a fundamental understanding of the mechanism which the additives work on a molecular basis. At the same time, the effect of solvent molecules on the crystal growth process is another related and important problem. In both instances, the relationship between internal aystal structure, aystal growth rate, solvent and impurities are needed to predict the habit of a crystal and thus allow seleaion of the proper conditions and components required to obtain a desired habit... 

Much of the literature information concerning the influence of solvent on polymorph crystallization is derived from the conventional crystallization system. The effect of solvent appears to be dictated by kinetics rather than by thermodynamics (30). The solvent may act by selective adsorption to certain crystallographic faces of the polymorphs, thereby inhibiting their nucleation or retarding their growth to the advantage of others. Similar solvent behavior... 

Bhat, M.N., Dharmaprakash, S.M. Effect of solvents on the growth morphology and physical characteristics of nonlinear optical y-glycine crystals, J. Crystal Growth 242 (1-2) (2002) 245-252. 

The polar crystalline properties of (/ ,S)-alanine and y-glycine have been used to probe the effect of solvent-surface interactions on crystal growth [33]. Both crystals grow unidirectionally at the CO end of the polar axis (see Figure 11.27) in aqueous solution. This was explained in terms of a preferred adsorption of H2O molecules at a subset of surface sites at the CO end of the crystal, leaving the other sites partially unsolvated, and so available for easy docking by solute molecules. 

A few years ago, a largely empirical approach was used to quantify the effect of admixtures and solvents. A theoretical description of the effect of admixtures has been developed only rather recently. Nevertheless, a consistent theory of the effect of admixtures on individual aspects of the process of crystallization is still missing. Various admixtures probably operate with different mechanisms. Some of them are selectively adsorbed on ciystal faces and deactivate individual growth centers, others can change the structural properties of the solution or of the interface they may be incorporated into the crystal lattice or pushed away by the growing crystal and sometimes there exists a chemical Interaction between the micro- and macrocomponents. It is obvious that this situation enables us to give subsequent explanations of individual effects but the prediction Is... 

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