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Diffusion Behavior (diffusion + behavior)

Distribution by Scientific Domains

Chemistry	60%
Polymers and Materials Science	40%

Selected Abstracts

Binding and release studies of a cationic drug from a star-shaped four-arm poly(ethylene oxide)- b -poly(methacrylic acid)

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2010
E. He
Abstract Star-shape polymers possess higher densities of terminal functional groups and three-dimensional tetrahedron structure that induce significantly different association and interactions with drug compared to linear structure of identical molecular weights. Four-arm poly(ethylene oxide)- b -poly(methacrylic acid) block copolymer was synthesized by atom transfer radical polymerization technique, and it self-assembled into core-shell micelles and extended unimers at low and high pH respectively. The negatively charged carboxylate groups on the polymer chains interacted with a cationic drug through electrostatic interaction forming polymer/drug complexes stabilized by biocompatible hydrophilic PEO segments. The hydrodynamic radius (Rh) of the polymeric aggregates and polymer/drug complexes ranged from 46 to 84,nm and 32 to 55,nm at pH of 4.6 and 8.0 respectively, making them suitable for drug delivery applications. The thermodynamic parameters and interactions between polymer and drug were determined by isothermal titration calorimetric technique. The electrostatic force, hydrogen bonding and hydrophobic interactions controlled the characteristics of polymer/drug formation and complexes when the molar ratios of drug and polymer were varied. Drug selective electrode system was used to measure the dynamic release of imipramine hydrochloride (IPH) from multi-arm PEO- b -PMAA star polymer. The release exponent n was greater than 0.5 indicating a non-Fickian type diffusion behavior, where the release behavior was dominated by chain relaxation induced by ion exchange that was dependent on pH. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:782,793, 2010 [source]

Diffusion Kinetics at Liquid-Glassy Polymer Interphases

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 8 2005
Luis Arzondo
Abstract Summary: We explored the diffusion mechanisms in a series of liquid/glassy polymer interphases. The diffusion experiments were performed in a unique way: the temperature range studied encompassed the glass transition temperature (Tg) of the glassy matrices. We observed that the diffusion behavior of the liquid polymer was remarkably continuous when passing through the matrix Tg, and that the diffusion modes at the liquid/glassy interphases were very similar to those observed in liquid/liquid polymer diffusion. Diffusion profiles of liquid PS in glassy PPO obtained by confocal Raman spectroscopy. The sample was held at 160,°C for the times indicated in the plot. [source]

Transport of aromatic solvents through nitrile rubber/epoxidized natural rubber blend membranes

POLYMER ENGINEERING & SCIENCE, Issue 3 2003
Asha Elizabeth Mathai
The sorption and diffusion behavior of a series of aromatic solvents through blends of nitrile rubber (NBR) and epoxidized natural rubber (ENR) have been studied in the temperature range of 28,70°C. The effect of blend ratio, penetrant size and temperature on the transport properties was investigated. The relationship between the diffusion behavior and the morphology of the system was examined. Different transport parameters such as diffusion coefficient, permeability coefficient and swelling ratio have been calculated. Experimental permeability coefficients were compared with various theoretical models. The van't Hoff relation was used to compute the thermodynamic parameters. [source]

Solid,Solid Phase Transitions: Interface Controlled Reactivity and Formation of Intermediate Structures

CHEMISTRY - A EUROPEAN JOURNAL, Issue 36 2007
Stefano Leoni Dr.
Abstract Finding new pathways to novel materials is an open challenge in modern solid-state chemistry. Among the reasons that still prevent a rational planning of synthetic routes is the lack of an atomistic understanding at the moment of phase formation. Metastable phases are, in this respect, powerful points of access to new materials. For the synthetic efforts to fully take advantage of such peculiar intermediates, a precise atomistic understanding of critical processes in the solid state in its many facets, that is, nucleation patterns, formation and propagation of interfaces, intermediate structures, and phase growth, is mandatory. Recently we have started a systematic theoretical study of phase transitions, especially of processes with first-order thermodynamics, to reach a firm understanding of the atomistic mechanisms governing polymorphism in the solid state. A clear picture is emerging of the interplay between nucleation patterns, the evolution of domain interfaces and final material morphology. Therein intermediate metastable structural motifs with distinct atomic patterns are identified, which become exciting targets for chemical synthesis. Accordingly, a new way of implementing simulation strategies as a powerful support to the chemical intuition is emerging. Simulations of real materials under conditions corresponding to the experiments are shedding light onto yet elusive aspects of solid,solid transformations. Particularly, sharp insights into local nucleation and growth events allow the formulation of new concepts for rationalizing interfaces formed during phase nucleation and growth. Structurally different and confined in space, metastable interfaces occurring during polymorph transformations bring about distinct diffusion behavior of the chemical species involved. More generally, stable structures emerge as a result of the concurrence of the transformation mechanism and of chemical reactions within the phase-growth fronts. [source]

Understanding Adsorption and Interactions of Alkane Isomer Mixtures in Isoreticular Metal,Organic Frameworks

CHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2007
Li Zhang Dr.
Abstract Novel metal,organic frameworks (MOFs) may lead to advances in adsorption and catalysis owing to their superior properties compared to traditional nanoporous materials. A combination of the grand canonical Monte Carlo method and configurational-bias Monte Carlo simulation was used to evaluate the adsorption isotherms of C4,C6 alkane isomer mixtures in IRMOF-1 and IRMOF-6. The amounts of adsorbed linear and branched alkanes increase with increasing pressure, and the amount of branched alkanes is larger than that of the linear ones. The locations of the alkane isomer reveal that the Zn4O clusters of the IRMOFs are the preferential adsorption sites for the adsorbate molecules. The interaction energy between the Zn4O cluster and the adsorbate is larger than that between the organic linker and the adsorbate. It was further confirmed that the Zn4O cluster plays a much more important role in adsorption by pushing a probe molecule into the pore at positions closer to the Zn4O cluster. It is difficult for branched alkane molecules to approach the Zn4O cluster of IRMOF-6 closely owing to strong spatial hindrance. In addition, the adsorption selectivity is discussed from the viewpoints of thermodynamics and kinetics, and the diffusion behavior of n -butane and 2-methylpropane were investigated to illustrate the relationship between diffusion and adsorption. [source]