Macromolecular motion is reduced in crowded polymer nanocomposites. Tracer diffusion is measured for deuterated polystyrene (dPS) into a polystyrene (PS):silica nanoparticle (NP) matrix using elastic recoil detection. This nanocomposite is ideal for studying diffusion in a crowded system because the interparticle distance (ID) that defines confinement can be varied from much greater than to much less than the size of the dPS chain, which is described by 2R g, the radius of gyration, and varies from 10 to 40 nm in this study. Diffusion is observed to be significantly slower than that predicted by the Maxwell model. The tracer diffusion coefficient of dPS in the nanocomposite relative to the pure PS matrix (D/D 0) plotted against the NP separation relative to probe size (i.e., ID/2R g) falls on a master curve, indicating that crowding is a property of both the dPS size and confinement in the nanocomposite. Moreover, the normalized diffusion coefficient decreases more rapidly when ID/2R g is less than ∼1, suggesting strong confinement conditions. The scaling of the diffusion coefficient with chain length is in excellent agreement with the entropic barrier model that accounts for the slowing down associated with the loss of chain entropy due to constrictive bottlenecks.

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The tracer diffusion of deuterated polystyrene (dPS) is measured in a polystyrene nanocomposite containing silica nanoparticles (NPs), with number average diameters d n of 28.8 nm and 12.8 nm, using elastic recoil detection. The volume fractions of the large and small NPs (f NP ) range from 0 to 0.5, and 0 to 0.1, respectively. At the same volume fraction of NPs, the tracer diffusion of dPS is reduced as NP size decreases because the interparticle distance between NPs (ID) decreases. The reduced diffusion coefficient, defined as the tracer diffusion coefficient in the nanocomposite relative to pure PS (D/D 0 ), plotted against the confinement parameter, namely ID(d n ) relative to tracer size, ID(d n )/2R g , nearly collapses onto a master curve, although D/D 0 is slightly greater for the more polydisperse, smaller NPs. Using a log normal distribution of NP size from SAXS, the average ID of the smaller NPs is shown to increase by 25% at f NP ¼ 0.1 as polydispersity (s) increases from 1 to 1.39. By accounting for polydispersity, the confinement parameter better represents the effect of NP spacing on polymer diffusion. These experiments demonstrate that polymer tracer diffusion in polymer nanocomposites is empirically captured by the confinement parameter and that an increase in the average ID due to NP polydispersity has a secondary effect on model NP systems with a narrow distribution of sizes. However, for commercial systems, where polydispersity can be quite large, the effect of size distribution can significantly increase ID which in turn will influence polymer dynamics.1=3 À1 !(1)

Continuous crystallization has gained interest in the pharmaceutical sector as part of the drive toward the transition from exclusive batch manufacturing to integrated continuous manufacturing in this industry. As a result, the design and operation of continuous crystallization processes for the preparation of pharmaceutical materials has been featured strongly in recent scientific literature. This review is an effort to gather together all of the published understanding on continuous crystallization with a pharmaceutical focus and to benchmark progress to date in realizing the potential benefits of transitioning this stalwart pharmaceutical unit operation from batch to continuous configurations.

The realization of the full potential for polymeric nanocomposites to manifest their entitled property improvements relies, for some properties, on the ability to achieve maximum particle–matrix interfacial area. Well-dispersed nanocomposites incorporating colloidal silica as the filler can be realized in both polystyrene and poly(methyl methacrylate) matrices by exploiting the charge stabilized nature of silica in nonaqueous solvents which act as Bronsted bases. We demonstrate that dispersions of colloidal silica in dimethylformamide are charge stabilized, regardless of organosilyl surface functionalization. When formulated with polymer solutions, the charge stabilized structure is maintained during drying until the charged double layer collapses. Although particles are free to diffuse and cluster after this neutralization, increased matrix viscosity retards the kinetics. We demonstrate how high molecular weight polymers assist in immobilizing the structure of the silica to produce well-dispersed composites. The glass transition temperatures of these composites do not vary, even at loadings up to 50 vol %.

The effect of nanoparticles (NP) on chain dimensions in polymer melts has been the source of considerable theoretical and experimental controversy. We exploit our ability to ensure a spatially uniform dispersion of 13 nm silica NPs miscible in polystyrene melts, together with neutron scattering, x-ray scattering, and transmission electron microscopy, to show that there is no measurable change in the polymer size in miscible mixtures, regardless of the relative sizes of the chains and the nanoparticles, and for NP loadings as high as 32.7 vol%. Our results provide a firm basis from which to understand the properties of polymer nanocomposites.

Heterogeneity of porous structures is an important material property involved during the design of adsorbents, catalysts and molecular recognition materials. This review discusses the mathematical methods that can characterize adsorption site energies and surface heterogeneity from the adsorption isotherms.

The use of in situ tools to monitor the transformation of a polymorphic material has the potential to provide unique information about the mechanism and rate of transformation of the polymorphs. In this paper, the solution mediated transformation between α and β form p-aminobenzoic acid (PABA) was investigated in detail. Solubility of α and β form PABA in pure ethanol was also reported for the first time, allowing the accurate determination of the transition temperature of 13.8 °C. For the transformation experiments, Raman spectroscopy and Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy were used to in situ monitor the solid phase concentration and liquid concentration, respectively; Focused Beam Reflectance Measurement (FBRM) was used to in situ track the changes in the size and morphology of the particles. The observed changes were confirmed using PVM in-process imaging. It was proved by solubility data and transformation experiments that the relationship between α and β form is enantiotropic.