Conformations of Isolated Macromolecules in Solution and on the Surface Public Deposited

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  • March 20, 2019
Creator
  • Shirvanyants, David
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • This dissertation studies different aspects of conformational properties of polymers. Two specific topics include (i) the deviations of single macromolecule conformations in the q-solution from the classical description, and (ii) conformations, order and flow of molecular brushes on solid surfaces. In solution we studied the deviations of single macromolecule conformations at the q-conditions from the predictions of classical theories. The previously unknown long range correlations in the conformations of linear polymers in a q-solvent were found using analytical calculations and molecular dynamics simulations. Long range power law decay of the bond vector correlation function hcosfi ¡« s.3/2 dominate the standard exponential decay hcosfi = e.s/lp , where f is the angle between the two bonds, s is their separation along the chain contour and lp is the persistence length. These long-range correlations lead to significant deviations of polymer size from ideal with mean square end-to-end distance hR2i.b2N ¡« ¡ÌN, where N is the number of Kuhn segments of size b. These findings are explained by a fine interplay of polymer connectivity and the non-zero range of monomer interactions. Moreover, this effect is not specific for dilute q-solutions and exists in semidilute solutions and melts of polymers. Our theory is in good agreement with the experimental data on Flory characteristic ratio, as well as with results of computer simulations. On surfaces, brush-like macromolecules were visualized by the atomic force microscopy (AFM). In order to quantitatively analyze conformations of visualized molecules we developed the corresponding algorithms and software. This software enables detection of the molecular contour, measurement of molecule size, area, orientational and nematic order parameters, etc. In addition, the automated procedure of molecular detection reduced the time and improved the quality of analysis of image series. Using our method we have studied the molecular weight and polydispersity of linear and multi-arm molecular brushes, the spontaneous curvature of grafted molecules, which is caused by competition of conformational entropy of side chains and elasticity of backbone, behavior of brushes in a matrix of linear polymer, the effect of structure of multi-armed brushes on their 2d orientational order, the dynamics and conformational transitions of individual molecules in the precursor layer of spreading droplet, the spontaneous scission of grafted molecules with long side-chains.
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  • Sheiko, Sergei
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