Search results for "Dimple"
showing 4 items of 4 documents
Phase diagram of a mixed polymer brush
2001
We investigate the structure and phase behavior of a two-component (binary) polymer brush in a solvent within self-consistent field theory as a function of the chains' stretching, the composition, and the incompatibility. Grafting the chains irreversibly prevents macrophase separation and the chains assemble into three-dimensional structures with lateral periodicity. At small incompatibilities a "ripple" phase is formed where different species aggregate into an array of parallel cylinders. At larger incompatibilities or asymmetric composition two "dimple" phases become stable, where different species form clusters which arrange on a quadratic (checkerboard structure) or hexagonal lattice.
Impurity analysis of JET DiMPle pulses
2021
Divertor monitoring pulses (DiMPle) have been run in JET from the C35 campaign onwards. They provide an opportunity to study the impurity contamination of the plasma when it is limited by different surfaces within the machine, as well as the longer term behaviour of the impurities. In these discharges the plasma is first limited on the outer wall, then on the inner wall and, subsequently, in the X-point configuration the outer strike point is positioned on the horizontal tile 5 of the machine followed by tile 6 and then the vertical tile 7. The present study details the impurity behaviour in the DiMPle pulses from JET-ILW campaigns C35 to C38, which ran from 2015 to 2019. The impurities can…
Scaling concepts for polymer brushes and their test with computer simulation
2004
After a brief review of the scaling concepts for static and dynamic properties of polymer brushes in good solvents and Theta solvents, the Monte Carlo evidence is discussed. It is shown that under typical conditions the diameter of the last blob is of the order of 10-20% of the brush height, and therefore pronounced deviations from the self-consistent field predictions occur. In bad solvents, lateral microphase separation occurs leading to an irregular pattern of "dimples". Particularly interesting is the response of brushes to shear deformation, and the interaction between two interpenetrating brushes. Recent attempts to understand the resulting shear forces via molecular-dynamics simulati…
Lateral versus perpendicular segregation in mixed polymer brushes.
2002
Grafting of incompatible polymers on a substrate prevents macrophase separation and the chains self-assemble laterally. Mixed brushes are exposed to different solvents and the morphology is observed via atomic force and x-ray photoemission microscopy. In a nonselective solvent the different species segregate into parallel cylinders ("ripple structure"). Upon exposure to a selective solvent, we encounter a transition to a "dimple" structure, in which the unfavored component forms clusters. Simultaneously, we observe an enhanced perpendicular segregation. The experimental observations are compared to self-consistent field calculations, where qualitative agreement is found.