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Initial Film Thickness (initial + film_thickness)

Distribution by Scientific Domains

Polymers and Materials Science	100%

Selected Abstracts

Swelling-Induced Surface Patterns in Hydrogels with Gradient Crosslinking Density

ADVANCED FUNCTIONAL MATERIALS, Issue 19 2009
Murat Guvendiren
Abstract Hydrogels with controlled surface patterns are useful for a range of applications, including in microdevices, sensors, coatings, and adhesives. In this work, a simple and robust method to generate a wide range of osmotically driven surface patterns, including random, lamellar, peanut, and hexagonal structures is developed. This method does not require the use of organic solvents for swelling, pre-patterning of the film surface, or coating of a second layer on the gel. The patterns are fabricated by exposing a photocurable formulation to light while open to air and then swelling, using oxygen inhibition of the radical polymerization at the surface to create a gradient of crosslinking with depth, which was confirmed by measuring the double bond conversion at the surface, surface mechanics, and molecule diffusion into the network. The modulus gradient, and hence osmotic pressure, is controlled by the crosslinker concentration, and the characteristic size of the patterns is determined by the initial film thickness. The patterns are stable in both swollen and dry states, creating a versatile approach that is useful for diverse polymers to create complex patterns with long-range order. [source]

Spontaneous Formation of Complex Periodic Superstructures under High Interferential Illumination of Small-Molecule-Based Photochromic Materials

ADVANCED FUNCTIONAL MATERIALS, Issue 5 2009
Eléna Ishow
Abstract A series of push-pull azo compounds containing bulky substituents are synthesized, yielding fully amorphous materials with glass-transition temperatures above 200,°C. Thin films are subjected to holographic illumination and show superior bulk photomigration in terms of speed and efficiency compared to materials exhibiting similar electronic and photochromic properties in the solid state. The reported results give evidence that a microscopic consideration of the free volume rather than macroscopic parameters like the glass-transition temperature should to be adopted to interpret the matrix stiffness and its deformation ability. Irradiation performed at higher laser intensity produces periodic superstructures whose height is five to six times as high as the initial film thickness. The surface tension and instability effects are put forward to interpret the growth of such superstructures. [source]

Numerical analysis of surface-tension-driven coating flow

POLYMER ENGINEERING & SCIENCE, Issue 2 2002
Richard H. J. Blunk
Bondline readout (BLRO) is a coating defect frequently exhibited on adhesively bonded, polymeric automotive body panels painted with high-glamour/flow clearcoats. BLRO or telegraphing results from Marangoni - type, surface-tension-driven flows. The goal of this study is to use an efficient one-dimensional numerical code (based on the lubrication approximation) to obtain further insight into the mechanism of temperature- and concentration-induced BLRO flows in order to validate a proposed BRLO mechanism and ultimately to help eliminate the highly undesirable BLRO coating defect. Further insight is realized by investigating numerically the effects on BLRO of gravity and five parameters,initial film thickness, heating rate, viscosity, solvent volatility, and solvent-to-resin surface-tension ratio. Possible solutions to the BLRO problem are discussed. [source]

Grafting CVD of Poly(vinyl pyrrolidone) for Durable Scleral Lens Coatings,

CHEMICAL VAPOR DEPOSITION, Issue 1-3 2010
Kyra L. Sedransk
Abstract Grafting (g)CVD from the monomer 1-vinyl-2-pyrrolidone (VP) and the Type II initiator benzophenone (BP) under 254,nm UV irradiation yields durable hydrophilic coatings on substrates of poly(methacrylic acid) (PMA) derivatives, desirable for scleral lens applications. The gCVD polymerization of the VP monomer is essentially complete, and little excess BP remains in the film. Process optimization, through single variable and two fractional factorial experiments, result in retention of >90% of the as-deposited film thickness after rinsing. Increasing the initiator dosing time beyond 10,min, or the UV exposure time beyond 5,min, has little effect on the as-deposited thickness, or percentage of film retained after rinsing. This suggests that UV irradiation rapidly transforms most of the BP absorbed on the surface to initiating radicals. Once sufficient initiator dosage and UV exposure have been achieved, the initial deposition thickness is controlled primarily by the total flux of monomer to the surface, which is consistent with previous studies. For all samples, thickness loss occurs primarily during the first 30 days of saline soak-testing with no statistically significant loss (p,>,0.25) during the next 90 days of soak testing. While the additional UV exposure time has a limited effect on initial film thickness, it does increase long term thickness retention, most likely by forming crosslinked and branched structures within the film. All samples tested retain sufficient gCVD coating thickness to impart improved hydrophilicity at the surface throughout the entire 120 day saline soak-testing period. The fractional factorial experiments correlate improved hydrophilicity with an interaction between initiator dosage time and UV exposure time. Indeed, decreasing these two process variables in tandem provides the greatest reduction in contact angle. While the uncoated PMA displayed 92.3°,±,2.1° advancing and 86.7°,±,3.0° receding contact angles with water, the most hydrophilic gCVD coating lowers the advancing and receding contact angles to 39.5°,±,2.6° and 36.2°,±,1.6°, respectively. [source]