Theory and Simulation of Polymer and Polyelectrolyte Self-Assembly

Public Deposited

Polymers and polyelectrolytes are ideal tools for the development of novel self-assembled materials. The ability to control the length-scales of self-assembly, and thus the properties, for soft materials lies in the understanding and subsequent manipulation of competing intermolecular interactions, such as hydrophobicity, hydrogen bonding, van der Waals, electrostatics. In this thesis, computer simulation and theory describe two separate phenomena in soft condensed matter---polymer gelation, as well as pattern formation at interfaces by charged macromolecules. A mean field theory of thermoreversible gelation is outlined, that incorporates a chemical approach to intermolecular interactions. For example, gels that form due to hydrogen bonding between polymer chains. Using Monte Carlo, the processes of chemical interactions, as well as physical interactions are used to describe gelation. Physical interactions refer to hydrogels, or gels that are formed through hydrophobic interactions. It is found that the mean field theory can be extended to describe physical gelation, by incorporating a concentration dependent association constant. The self-assembly of oppositely charged, immiscible molecular components at interfaces is introduced. The theoretical behavior is outlined at low temperatures, by assuming the formation of finite, strongly segregated lamellar or hexagonal domains. At high temperatures, density fluctuations are examined to determine the transition from the disordered to microphase region. Molecular dynamics simulations are designed to explore the phase behavior of this model at intermediate temperatures. The formation of lamellar and hexagonal domains are characterized. It is shown that the strength of the electrostatic interactions in competition with short range interactions determines the degree of interfacial ordering between the domains, and the periodicity, illustrating the transition between low and high temperatures. In addition, it is shown that for asymmetrically charged molecular components, increased electrostatic interactions can decrease the fluctuations in the local inter-domain structure. Molecular dynamics results are then be used in complement to theory, to describe the possibility of phase coexistence of the previous phases with a low charge density gas phase. It is found that the periodicity of the structure at intermediate temperatures can be well described, by accounting for the solid phase swelling at low densities.

Last modified
  • 07/25/2018
Date created
Resource type
Rights statement