Microparticles size reduction

Microparticles. Size matters release rates depend on surface area, ie, a function of the square of the radius of a spherical particle, and thus larger particles release for longer and are able to manipulate the external availability of the pesticide. Small microparticles are therefore limited in their scope for controlling release but can be used in traditional spraying of dispersions onto soils and crops as well as for seed dressing. Suspension concentrate formulations of matrix microparticles have been developed based on various rosins, phenoUc resins, waxes, and bitumens. These have focused on lipophilic pesticides such as trifluralin and chlorpyrifos and reductions in volatility have been demonstrated (43). 

Researchers at the University of Illinois utilize a small-gauge needle that vibrates at an ultrasonic frequency for this purpose. A jet of a polymer solution passing the needle breaks up into uniform droplets, which becomes solidified micromatrices after solvent removal. The droplet size can be precisely controlled as a function of orifice size, solution flow rate, and vibration frequency. An optional carrier stream enables further reduction of the particle size. In vitro release studies using microparticles of different mean diameters demonstrated the dependence of the diffusion-dependent release profiles on the particle size. ... 

The reduction in particle size (c.g., by micronization) increattes ihe surface area and consequently Ihe dissolution velocity dc/dt), according to the Noyes-Whitney equation. However, transfer of the drug microparticles to nanoparticlcs not only increases the solution velocity but also the saturation solubility C,. 

Crystalline silicon is a strong but brittle material. The introduction of porosity often lowers hardness, stiffiiess, and fracture strength (see handbook chapter Mechanical Properties of Porous Silicon ), and if the stmcture becomes too weak, it cannot often survive common material processing techniques without alteration. Examples include air drying (see handbook chapter Drying Techniques Applied to Porous Silicon ), reduction of particle size via communition (see handbook chapter Milling of Porous Silicon Microparticles ), and oxidation of layers (see handbook chapter Oxidation of Mesoporous Silicon ). The properties of electrochemically etched layers can depend not only on etch parameters but how the material was dried. The properties of microparticles can be sensitive to how they were milled. 

Even using a combination of supercritical N2 and CO2 in the SEDS process improved the dispersion of pol5mier solutions compared with CO2 alone. This resulted in a reduction of the particle size of discrete microparticles produced from amorphous biodegradable pol5nners [41]. 

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