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Author Gulati, H. S. ♦ Hall, C. K. ♦ Jones, R. L. ♦ Spontak, R. J.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword CHEMISTRY ♦ GRAFT POLYMERS ♦ CONFORMATIONAL CHANGES ♦ CHAINS ♦ SELF-CONSISTENT FIELD ♦ RELAXATION TIME ♦ CORRELATION FUNCTIONS ♦ EQUILIBRIUM ♦ MOLECULAR DYNAMICS CALCULATIONS ♦ AUTOCORRELATIONS ♦ DIFFUSIVITY
Abstract In this work, the static conformational properties and dynamic relaxation behavior of monolayers of chain molecules grafted at both ends (polymer {open_quote}{open_quote}loops{close_quote}{close_quote}) to an impenetrable plane are investigated utilizing off-lattice discontinuous molecular dynamics (DMD) simulations. The conformational properties observed from DMD simulation are compared to the results of a previous on-lattice bond fluctuation (BF) study. This provides a unique opportunity to decouple the effects of excluded volume, chain flexibility and interparticle interactions, since these effects are treated differently in the two simulation methods. Static equilibrium properties of the looped chain layers determined from the DMD and BF models are in qualitative agreement with each other and with self-consistent field (SCF) predictions for brushes of {ital N}/2 repeat units. By allowing the chain anchors to move laterally along the interfacial plane, the effect of annealing on layer properties is also investigated. The characteristic relaxation time of the annealed looped chains, discerned from radius of gyration autocorrelation functions, obeys a scaling relationship of the form {tau}{approximately}{ital N}{sup 3}{sigma}{sup 4/3}, where {sigma} is the surface density of the tethered chain ends. The lateral self-diffusion coefficient of the chains during annealing is also measured, with lateral diffusivity scaling as {ital N}{sup {alpha}}{sigma}{sup {beta}}. The exponents {alpha} and {beta} undergo a smooth transition from {alpha}{approx_equal}{minus}4/3, {beta}{approx_equal}{minus}4/3 at low densities to {alpha}{approx_equal}{minus}2, {beta}{approx_equal}{minus}2 at high densities. Both relaxation times and lateral diffusivity exhibit different density scaling than brushes with {ital N}/2 repeat units. {copyright} {ital 1996 American Institute of Physics.}
ISSN 00219606
Educational Use Research
Learning Resource Type Article
Publisher Date 1996-11-01
Publisher Place United States
Journal Journal of Chemical Physics
Volume Number 105
Issue Number 17


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