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Void Structures (void + structure)

Distribution by Scientific Domains
Polymers and Materials Science75%

Selected Abstracts

Random discontinuous carbon fiber preforms: Experimental permeability characterization and local modeling

POLYMER COMPOSITES, Issue 4 2010
A. Endruweit
Injection experiments indicate that for random discontinuous carbon fiber preforms, increasingly uneven flow fronts develop with increasing fiber bundle length and filament count. While at high propensity for fiber bundle splitting, the preform permeability increases continuously with increasing fiber length, no trend can be identified at low propensity. No clear influence of the virgin bundle filament count on the preform permeability was observed. Types of sizing used on the fibers and bundle cross-sectional shapes may vary and affect the intrinsic filamentization behavior, thus dominating the preform permeability. In a model for local preform permeability, interbundle voids, distributed randomly across the preform thickness, are approximated via a regular void structure. Simulated filling patterns are qualitatively similar to those observed experimentally, showing more pronounced features than those derived from a model based on local through-thickness homogenization of the filament distribution. A model based on an alternating arrangement of fiber bundles and voids allows prediction of global preform permeability values from series of injection simulations, showing quantitatively better agreement with corresponding experimental results than the homogenization model. For global permeability, agreement between simulated and experimental mean values improves with increasing fiber volume fraction, whereas calculated coefficients of variation show no strong dependence on the fiber volume fraction. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers [source]

Dynamic, 3D-Pattern Formation Within Enzyme-Responsive Hydrogels

ADVANCED MATERIALS, Issue 41 2009
Karin S. Straley
Dynamic, 3D hydrogel patterns emerge over time in response to cell-secreted enzymes (see image). Composite hydrogels fabricated from engineered proteins exhibit customized half-lives ranging across two orders of magnitude due to slight changes in the primary amino acid sequence. The evolution of internal 3D void structures within these polymeric materials is used to release multiple payload molecules with distinct spatial and temporal delivery profiles. [source]

Solvent Resistant Honeycomb Films from Photo-Crosslinkable Polycinnamate

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 8 2007
Olaf Karthaus
Abstract Microporous films consisting of two-dimensionally ordered void structures - so-called honeycomb films - were produced by evaporation of polymer solutions under high humidity. Two types of poly(vinyl cinnamate)s were used: A newly synthesized amphiphilic poly(vinyl cinnamate) and a mixture of a commercial poly(vinyl cinnamate) and an amphiphilic polyion complex. Photo-crosslinking of the honeycomb structure could be achieved by UV irradiation while completely retaining the film morphology. The crosslinked films showed excellent stability against organic solvents. [source]

Femtosecond laser-assisted formation of channels in sapphire using KOH solution

PHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 6 2008
Saulius Juodkazis
Abstract We report on wet etching of photomodified regions in crystalline sapphire using KOH solution. Tightly focused femtosecond laser pulses (150 fs at 800 nm wavelength) were used to create void structures enclosed in an amorphised sapphire shell inside the bulk of a crystalline host. The diameter of the amorphous regions can be controlled by pulse energy and was typically 0.5,1.5 µm. The etching rate depends on the distance between adjacent irradiation spots, pulse energy, concentration of etchant and ultrasonic agitation. Amorphised sapphire is etched out in KOH solution. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]