Particle morphology internal porosity

Perhaps the princ al area of ignorance in both the filtration and dewat g of precipitates is the effect of crystal morphology. Serious theoretical and practical problems arise in cases where the crystal in ct possesses internal porosity. Liquors bound inade a crystal will be iirposable to remove by normal dewatering methods. Agam, m process cakulaticms and correlations of e qrerimehtal results, uncertainties arise in the vabes of particle doisity fin these materials. 

The morphology of the matrix on which we wish to make a SFE can have an enormous influence on the efficiency of the extraction rate. Generally a rapid and complete extraction depends upon the relative size of the matrix particles, the smaller being the better. This is due principally to the short internal distance that the solute must cover in order to attain the core of the supercritical fluid solution. Some studies have shown that the geometrical form can also have an influence on the rate and efficacity of the extraction. As in the case of an extraction solid-liquid, an increase in the porosity of the matrix will lead to an efficient and rapid extraction. 

The porosity (ie, pore size and amount of pores) of microparticles is also an important characteristic to take into consideration when fabricating microparticles because it plays an essential role in controlling the release of payloads. The porosity and morphology of particles are usually determined by scanning electron microscopy (SEM). For the emulsification solvent extraction/evaporation method of fabrication, the rate of solvent extraction, which depends on the flow in the stirred vessel the droplet size the temperature and the dispersed phase hold-up in the 0/W emulsion have an effect on porosity [87]. The porosity usually increases with a decrease in solvent extraction rate. The porosity of microparticles results in initial burst release due to pore diffusion [78,88]. Mao et al. studied the influence of different W/O/W emulsification solvent extraction/evaporation process parameters on internal and external porosity of PLGA microparticles [78]. The surface morphology of the microparticles can be influenced by the type of polymer, internal aqueous phase voliune (Wi), volume of continuous phase (W2), polymer concentration, homogenization speed, and equipment used for the primary emulsion [78,79]. 

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