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Thickness Gradient (thickness + gradient)

Distribution by Scientific Domains
Polymers and Materials Science100%

Selected Abstracts

Spontaneous Lamellar Alignment in Thickness-Modulated Block Copolymer Films

ADVANCED FUNCTIONAL MATERIALS, Issue 16 2009
Bong Hoon Kim
Abstract Here, spontaneous lamellar alignment in a thickness-modulated block copolymer film is presented as a facile, scalable, and general approach for creating a highly aligned lamellar morphology. Thickness-modulated block copolymer films are prepared on neutral surfaces by various methods, such as solution dropping, dewetting-induced self-organized patterning, and thermal imprinting. Regardless of the film preparation method, the self-assembled lamellar domains become spontaneously aligned along the thickness gradient after sufficient thermal annealing. Real-time AFM imaging reveals that spontaneous alignment occurs through the directional growth of well-ordered domains along the thickness gradient, which is accompanied by defect dynamics, with vertical linear defects moving from thicker parts of the film towards the thinner ones, reducing their length and thus the associated energy. The mechanism underlying this interesting self-aligning behavior is provided by a ,geometric anchoring' phenomenon, originally envisioned to account for the liquid crystal alignment under a non-flat geometry of confinement. This novel self-aligning principle offers a valuable opportunity to control nanoscale alignment in block copolymer films by manipulating the, much larger, microscale morphology. [source]

Modeling and analysis of thickness gradient and variations in vacuum-assisted resin transfer molding process

POLYMER COMPOSITES, Issue 5 2008
Jing Li
As vacuum-assisted resin transfer molding (VARTM) is being increasingly used in aerospace applications, the thickness gradient and variation issues are gaining more attention. Typically, thickness gradient and variations result from the infusion pressure gradient during the process and material variations. Pressure gradient is the driving force for resin flow and the main source of thickness variation. After infusion, an amount of pressure gradient is frozen into the preform, which primarily contributes to the thickness variation. This study investigates the mechanism of the thickness variation dynamic change during the infusion and relaxing/curing processes. A numerical model was developed to track the thickness change of the bagging film free surface. A time-dependent permeability model as a function of compaction pressure was incorporated into an existing resin transfer molding (RTM) code for obtaining the initial conditions for relaxing/curing process. Control volume (CV) and volume of fluid (VOF) methods were combined to solve the free surface problem. Experiments were conducted to verify the simulation results. The proposed model was illustrated with a relatively complex part. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers [source]

Copolymer Film Alignment: Spontaneous Lamellar Alignment in Thickness-Modulated Block Copolymer Films (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 16 2009
Mater.
Self-alignment of lamellar nanodomains is accomplished by imposing thickness modulation to a block copolymer thin film. Real-time atomic-force microscopy imaging reveals that the self-alignment occurs through the directional growth of well-aligned domains along thickness gradients. This novel self-aligning principle, based on a "geometric anchoring" phenomenon, is reported by S. O. Kim, O. D. Lavrentovich and co-workers on page 2584. [source]