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MODELING THE PHYSICAL BEHAVIOR OF HELICAL POLYMERS

Varshney, Vikas
http://rave.ohiolink.edu/etdc/view?acc_num=akron1153774229

Abstract Details

2006, Doctor of Philosophy, University of Akron, Polymer Science.
The main objective of this dissertation is to develop a minimal model for helical conformations present in semi-flexible polymers and to study their consequences on the physical behavior of such polymers subjected to various external stimuli. The polymer chain is modeled with the Freely Rotating Chain model while the helical structure is realized using the geometrical concept of torsion of a curve. Thereafter, the changes in the conformations of polymer chain under various kinds of external stimuli such as long-range interactions and external mechanical forces are investigated using Monte Carlo simulations based on the Wang-Landau sampling algorithm. The modeling approach is shown to successfully capture the phyiscal properties of the helix-coil transition in a semi-flexible polymer chain as a function of temperature and provides an opportunity to explore real-space characteristics of the transition, in addition to its thermodynamic properties. Furthermore, the model successfully captures the characteristic cooperativity of the transition and is shown to be in accordance with many experimental observations and theoretical predictions for helical polymers such as homopolypeptides. The minimal model is extended further to include long range attractive interactions among beads which lead to the collapse of the polymer chain. However, such collapse interferes with the presence of helical structure due to torsional energy, leading to a rich phase behavior of chain configurations where both interactions are significant. This phase behavior for various chain lengths is investigated in terms of temperature and strength of attractive interactions and the results suggest that the emergence of many stable chain configurations is the consequence of the coupling between the helix-coil and coil-globule transitions. The original model is also extended to include the effect of an external mechanical force to study the force-elongation characteristics of helical, semi-flexible polymers. The analysis suggests a non-monotonic behavior of helix-coil transition temperature as a function of force which is attributed to the change in the nature of the helix-coil transition which becomes a helix-extended coil transition for strong forces. Moreover, force-elongation curves at constant temperature display three different behaviors depending on the temperature of the system. At temperatures below or slightly above the helix-coil transition temperature, the force-elongation curve shows one or two coexistence regions, respectively. In these regions, helical sequences and random coil domains coexist while the strength of the force and temperature determine the fraction of the polymer adopting each conformation. At high temperatures, our model recovers the elastic behavior of a random coil.
Gustavo Carri (Advisor)
163 p.
HELICAL; ¿¿¿¿; ¿¿¿¿¿¿gure; beads; con¿¿¿¿¿¿gurations; helix-coil

Recommended Citations

Citations

  • Varshney, V. (2006). MODELING THE PHYSICAL BEHAVIOR OF HELICAL POLYMERS [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1153774229

    APA Style (7th edition)

  • Varshney, Vikas. MODELING THE PHYSICAL BEHAVIOR OF HELICAL POLYMERS. 2006. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1153774229.

    MLA Style (8th edition)

  • Varshney, Vikas. "MODELING THE PHYSICAL BEHAVIOR OF HELICAL POLYMERS." Doctoral dissertation, University of Akron, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1153774229

    Chicago Manual of Style (17th edition)

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© 2006, all rights reserved.
This open access ETD is published by University of Akron and OhioLINK.
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