The melt-state linear and nonlinear shear rheological properties of hybrid materials of polypropylene and amine-exchanged montmorillonite were studied. The materials were prepared by melt mixing with maleic anhydride functionalized polypropylene as the compatibilizer. The clay interlayer spacing (as determined by wide-angle X-ray scattering) increased upon melt mixing; however, the short-range ordering of the clay layers was preserved. Above inorganic loadings of 2.0 wt % the hybrid materials exhibited apparent low-frequency plateaus in the linear viscoelastic moduli. The hybrid storage modulus was sensitive to the chemistry of the amine exchanged into the clay. The amount of stress overshoot observed in flow reversal experiments was found to be a function of the rest time allowed between the reversal. The transient stress in start-up of steady shear scaled with the applied strain. These observations allow features of the polypropylene/montmorillonite hybrid structure to be deduced. The transient nonlinear rheology is consistent with an anisometric, non-Brownian structure. These anisometric particulate domains are mesoscopic, and internally, they contain multiple, ordered platelets. This mesoscopic structure is itself thermodynamically unstable, because the rheology indicates that quiescent structural evolution whose origin is not Brownian relaxation is observed. The demonstration of the sensitivity of melt-state rheological measurements to interparticle structure and chemistry of the hybrid materials indicates the potential usefulness of such studies for the development of new nanocomposite materials.

A mechanism for cocrystal synthesis is reported whereby nucleation and growth of cocrystals are directed by the effect of the cocrystal components on reducing the solubility of the molecular complex to be crystallized. The carbamazepine:nicotinamide cocrystal (CBZ:NCT) was chosen as a model system to study the reaction cocrystallization pathways and kinetics in aqueous and organic solvents. Fiber optic Raman spectroscopy and Raman microscopy were used for in situ monitoring of the cocrystallization in macroscopic and microscopic scales in solutions, suspensions, slurries, and wet solid phases of cocrystal components. This study demonstrates the advantages of reaction cocrystallization methods to develop rational approaches for high-throughput screening of cocrystals that can be transferable to control batch and continuous cocrystallization processes.

The work presented here was motivated by the premise that the amorphous state serves as a medium to study cocrystal formation. The molecular mobility inherent to amorphous phases can lead to molecular associations between different components such that a single crystalline phase of multiple components or cocrystal is formed. Cocrystallization pathways and kinetics were investigated from amorphous equimolar phases of carbamazepine and nicotinamide using hot-stage polarized microscopy (HSPM), hot-stage Raman microscopy (HSRM), differential scanning calorimetry (DSC), and X-ray powder diffraction (XRPD). Nonisothermal studies revealed that amorphous phases generate cocrystals and that thermal history affects crystallization pathways in significant ways. Two different pathways to cocrystal formation from the amorphous phase were identified: (1) at low heating rates (3 degrees C/min) a metastable cocrystalline phase initially nucleates and transforms to the more stable cocrystalline phase of CBZ-NCT, and (2) at higher heating rates (10 degrees C/min) individual components crystallize, then melt and the stable cocrystalline phase nucleates and grows from the melt. Isothermal studies above the T(g) of the amorphous equimolar phase also confirm the nucleation of a metastable cocrystalline phase from the amorphous state followed by a solid phase mediated transformation to the stable cocrystalline phase. Cocrystallization kinetics were measured by image analysis and by thermal analysis from small samples and are described by the Avrami-Erofeev model. These findings have important implications for the use of amorphous phases in the discovery of cocrystals and to determine the propensity of cocrystallization from process-induced amorphization.

A general, quantitative relationship between the photon-transport mean free path ͑l * ͒ and resin sensitivity ͑D P ͒ in multiple-scattering alumina/monomer suspensions formulated for ceramic stereolithography is presented and experimentally demonstrated. A Mie-theory-based computational method with structure factor contributions to determine l * was developed. Planar-source diffuse transmittance experiments were performed on monodisperse and bimodal polystyrene/water and alumina/monomer systems to validate this computational tool. The experimental data support the application of this l * calculation method to concentrated suspensions composed of nonaggregating particles of moderately aspherical shape and log-normal size distribution. The values of D P are shown to be approximately five times that of l * in the tested ceramic stereolithography suspensions.

The colloidal short-time self-diffusivity D(s)(s)(phi) is significantly retarded relative to hard sphere suspensions for the case of interparticle potential interactions induced by a nonadsorbing polymer. A comparison of diffusing wave spectroscopy measurements with direct calculations of D(s)(s)(phi) demonstrates that depletion effects on structure explain the observed retardation. We show that coexistence boundaries place unexpectedly severe constraints on the amount of D(s)(s)(phi) retardation possible for stable suspensions. The measured retardation is demonstrated to be an indicator of suspension metastability.