Particulate polymer microdevices are fabricated using protocols based on a transfer‐molding process that allows the controlled assembly of multiple materials to produce functional devices. Specifically, protocols for reservoir‐containing (see image; scale bar=100 μm), capsulelike, and self‐folding polymer microdevices are presented. The encapsulated materials are not exposed to high temperatures or caustic solutions, which is important in drug‐delivery applications.
In this paper, a fractal in‐plane permeability model for various fabrics is developed. The model is based on the fractal characteristics of pores in fiber preforms. Four different glass fabrics are considered in the modeling: plain woven, 4‐harness, bidirectional stitched, and continuous strand random mats. The fractal in‐plane permeability model can be expressed as a function of the pore area fractal dimension and architectural parameters of the fiber preform. This model also relates the permeability to porosity changes of fiber preforms under compression, which usually occurs in the molding processes. To verify the applicability of the model, the results from the present fractal model are compared with those from the one‐dimensional analysis model and with a set of permeability measurements. Good agreement is found between the two models and the permeability measurements in the general porosity ranges of interest.
It is found that the pore microstructures of textile fabrics, widely used in the manufacture of fiber-reinforced composites, exhibit the fractal characters. The fractal behaviors are described by the proposed analytical method and measured by the box-counting method for the three different types of textile fabrics: plain woven, four-harness, bidirectional-stitched fiberglass mats. The pore area fractal dimension is derived analytically and found to be the function of the porosity and architectural parameters of fabrics. The results indicate that the fractal characters are isotropic although the fabrics are rothotropic in structures. The theoretical predictions by the proposed analytical model are in good agreement with those from the box-counting method, and this verifies the proposed fractal dimension model. The present fractal analysis may have the potential and significance on fractal analysis of transport properties (such as the permeability, dispersion, thermal and mechanical properties) in porous media.
Thermoplastic additives tend to promote the phase separation during the reaction of unsaturated polyester resins. Consequently, they reduce the amount of shrinkage during curing. Several thermoplastic additives which resulted in significant different microstructure of cured resins were investigated. The effects of microstructure formation on the sol-gel transition, reaction kinetics, and gelation time were studied. The mechanism of microstructure formation and causes of macro-gelation were explained by the influence of thermoplastic additives on the particle formation rate and inter-particle reaction rate during curing.
A colloidal processing technique based on the heterocoagulation of selected ceramic oxide systems, and analogous to reaction injection molding of polymers, is described. Commercial colloidal silica and boehmite sols, which have oppositely charged particles in the pH range 2.0-9.0, and mixtures of these suspensions with micron sized oxide powders, have been used to determine whether a liquid to solid transformation could be induced when the two materials are simultaneously injected at high velocities into a mold cavity. Rheological changes have been measured as a function of relative flow rates of the two suspensions, solids loading and oscillatory frequency. Viscosity is observed to increase by as much as six orders of magnitude under optimized conditions.
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