Understanding organization of soft materials on mesoscopic and nanoscopic scales is importantfor materials design. In this regard, non-van der Waals interactions such as hydrogen bonding and electrostatic interactions offer great opportunities due to the richness and diversity in morphological structures they produce. The primary reason for this is that these interactions often couple with van der Waals interactions in a non-additive way and also the fact that the strength of these interactions can be tuned by varying external physical and chemical conditions such as pH, temperature and salt concentration. While experimental studies on these systems are quite abundant, theoretical efforts on them are still an active and evolving area of research due to inadequacy of different theoretical models in different contexts and also due to the improvement in computing power, which is allowing for relaxing assumptions inherent in simplified theories. This dissertation is an attempt to contribute to this ongoing endeavor by extending some of the existing theories to various soft matter systems such as hydrogen-bonding polymers, polyelectrolytes and dissociable monolayers. The dissertation is organized as follows. It starts with an introduction (Chapter 1), which surveys the current state of theoretical research in hydrogen bonding and polyelectrolyte systems. The rest of the thesis examines specific interactions in the context of specific material systems, each in a separate chapter. In Chapter 2, we study the phase behavior of a blend of polymers containing hydrogen bonding groups. Herein, we deviate from the existing treatment of capturing hydrogen bonding through a van der Waals like interaction parameter and instead, introduce a function that does enumeration of all possible combinations of hydrogen bond pairs. We find that our model produces closed-loop as well as eutectic miscibility phase diagrams. In chapter 3, we study phase behavior of a weak polyampholyte brush, which is again a multicomponent system containing two types of functional groups, namely acid and base, on the chains. Here, we find that due to the presence of both acid and base groups on it, the polymer chain responds to salt addition very differently from a single component weak polyelectrolyte. In the latter case, salt addition always increases the degree of dissociation across the whole pH spectrum while in polyampholyte brushes, salt addition increases the charging of base groups and decreases the charging of acid groups at low pHs and vice versa at high pHs. This is accompanied by conformational changes of the chains. In chapter 4, the role of acid and base dissociation behavior has been studied in absorption of oppositely charged polymers into a charged brush. Herein, a low salt concentration results in enhanced absorption. Going a step further, we also incorporate the effect of short-range correlation into the analysis through classical density functional theory for strong polyelectrolytes. It is seen that inclusion of correlation can bring about dramatic changes in absorption behavior, even predicting desorption of chains in situations that a mean-field treatment predicts absorption. We also look at the effect of chain sequence on the absorption and link the results to the counterion release in these architectures. In chapter 5, to incorporate short-range correlation effects into charge regulation of dissociable surfaces, a liquid state theory based technique has been proposed.

Creator

• Prusty, Debadutta

DOI

• https://doi.org/10.21985/n2-xwqk-xg47

Subject

• Molecular physics
• Materials Science

Language

• en

Alternate Identifier

• http://dissertations.umi.com/northwestern:16315
• etdadmin_upload_938426

Date created

• 2022-01-01

Resource type

• Dissertation

Rights statement

• In Copyright