Crystal formation modeling systems

M. lijima, H. Tohda, Y. Moriwaki, Growth and structure of lamellar mixed crystals of octacalcium phosphate and apatite in model system of enamel formation, J. Cryst. Growth 116 (1992) 319-326. 

As will be shown, model systems for cells employing lipids or composed of polymers have been in existence for some time. Model systems for coccolith-type structures are well known on the nanoscale in inorganic and materials chemistry. Indeed, many complex metal oxides crystallize into approximations of spherical networks. Often, though, the spherical motif interpenetrates other spheres making the formation of discrete spheres rare. Inorganic clusters such as quantum dots may appear as microscopic spheres, particularly when visualized by scanning electron microscopy, but they are not hollow, nor do they contain voids that would be of value as sites for molecular recognition. All these examples have the outward appearance of cells but not all function as capsules for host molecules. 

The destabilization of the premlcellar aggregates at high water content may give rise to a) separation of liquid water, b) formation of Inverse micelles, or c) separation of a lamellar liquid crystal. Approximate calculations using the Tanford-Nlnham approach gave correct Information for a model system, but the critical ratio appeared too Insensitive to the alcohol/soap ratio to be useful. 

Like crystallization, US also successfully assists the formation of extremely finely divided and uniform particles, which can be termed sonoprecipitation. This effect, which has not yet been used in analytical chemistry and might facilitate sample preparation in nephelometric or turbidimetric methods, has been widely exploited by the pharmaceutical industry to prepare liquid dispersions of drugs for oral or subcutaneous administration where extremely small particle sizes ensure stable suspensions of the drug and faster assimilation into the body. On a laboratory scale, US-assisted precipitation of magnesium carbonate in a model system has been studied [65]. 

The formation of colloidal silver halide dispersions (photographic emulsions) was reviewed as a model system of colloids which are formed by precipitation of sparingly soluble salts. For such systems, models for crystal nucleation and growth were derived which were verified for the AgBr system. These models can probably be extended to the study of nucleation and growth of other highly insoluble colloidal systems. 

The study of colloidal crystals was initiated as part of research into the determination of phase diagrams for colloids, which itself was perceived as a means to model phase behaviour in molecular systems [22]. Extensive literature is available on the dynamics of colloidal crystal formation, as a function of several parameters, such as the nature of the solvent, surface charge, particle size and concentration. The results described here refer to the formation of colloidal crystals from dispersions of silica-coated gold nanoparticles in ethanol, after silica surface functionalization with 3-(trimethoxysilyl)propyl methacrylate (TPM). Earlier studies by Philipse and Vrij [23] showed that TPM adsorption leads to a reduction in surface charge, so that the particles are stable in organic solvents with low polarity, such as ethanol, toluene or DMF. This means that the particle be-... 

The pseudolocal phonon approach to dephasing, in the field of micro-wave and electronic spectroscopy rests on the assumption that insertion of a guest in a host crystal leads to formation of phonons which are substantially localized at the guest sites. There seems to be an urgent need for a model system where the pseudolocal phonons themselves are accessible for a direct relaxation study. Specifically the lifetime of this phonon and its temperature dependence are crucial quantities in a test of the dephasing... 

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