Ring polymer dynamics in dilute and concentrated solutions with advances in automated flow control

Tu, Michael Quang

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https://hdl.handle.net/2142/115524 Copy

Description

Title

Ring polymer dynamics in dilute and concentrated solutions with advances in automated flow control

Author(s)

Tu, Michael Quang

Issue Date

2022-04-05

Director of Research (if dissertation) or Advisor (if thesis)

Schroeder, Charles M

Doctoral Committee Chair(s)

Schroeder, Charles M

Committee Member(s)

• Sing, Charles E
• Rogers, Simon A
• Schweizer, Kenneth S

Department of Study

Chemical & Biomolecular Engr

Discipline

Chemical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• ring polymers
• physics
• rheology

Abstract

The bulk mechanical properties of polymeric materials are ultimately governed by their chemical composition, structure, and molecular-scale motions of individual polymer chains over distributed timescales. Nearly all common classes of polymeric materials encountered in commercial applications have molecular architectures that include free ends (e.g. linear, branched, comb, star, H-polymers). In general, polymer chain ends give rise to distinct molecular phenomena that results in observable material properties (e.g. stress and viscosity). Ring polymers lack free ends, and therefore exhibit unique dynamics compared to the majority of most well-studied polymer architectures such as linear and branched polymer chains. Despite recent progress, we lack a complete understanding of the mechanical and rheological properties of ring polymers in dilute and concentrated solutions. In this dissertation, I experimentally interrogate the dynamics of ring polymers using a combination of single-molecule experiments of DNA-based rings and bulk rheological experiments of concentrated melt-like synthetic ring polymers. In Chapters 2 and 3, I describe the dynamics of single ring polymers in steady shear flow in dilute solution. In this work, I designed and built custom flow cells amenable to single-molecule visualization of fluorescently-labeled linear and ring DNA polymers in the flow-gradient and flow-vorticity planes of shear flow. Our results show similar average fractional extensional behavior as well as average orientational angles in the flow-gradient plane between linear and ring polymer topologies as functions of the dimensionless flow strength. However, we observe unexpected differences in the fractional extension distribution between the linear and ring topologies, which is attributed to the presence of a ring-polymer-specific tumbling motion in shear flow. Single molecule experiments were directly complemented by Brownian dynamics simulations of coarse-grained bead-spring polymers, which revealed similar phenomena in terms of the average conformational responses and fractional extension distributions for rings in shear flow. We further quantified the dynamics of linear and ring polymers in steady shear by analyzing cross-correlations of the polymer stretching in different directions relative to the shear motion along all three axes of shear. These studies provide molecular-level insight into the conformations and dynamics of dilute ring polymers in steady shear. In Chapter 4, I describe the dynamics and rheology of ultra-high molecular weight pure synthetic rings in concentrated solutions. This work focuses on understanding the role of intermolecular interactions in concentrated ring polymer systems using cyclic poly(phthalaldehyde) (cPPA), which is a metastable synthetic ring polymer chemistry enabling pure ring polymer samples in the absence of linear chain contaminants. At ambient temperatures, cPPA ring polymers are kinetically-trapped in the ring topology, there enabling the study of linear viscoelastic rheology of pure, concentrated ring polymers with unprecedented molecular weights and topological purity. Interestingly, our results show unexpected and clear deviations from predictions of prevailing theoretical models for ring polymer melts, which suggests new underlying physics that are not yet fully understood. The results from these studies will guide process development of ring-polymer-based systems of high molecular weight, and can be immediately applied to cPPA-based systems currently being studied for sustainability materials applications due to its properties as a depolymerizable-on-demand polymer. In Chapter 5, we extend the capabilities of a hydrodynamic-based trapping technique for freely suspended particles known as the Stokes Trap to fully three-dimensional (3D) flow fields. Here, we generated model uniaxial and biaxial extensional flow fields using 3D-printed devices with a 3D six-arm cross-slot geometry amenable to optical microscopy. In all cases, 3D flow fields are analyzed and validated using particle tracking velocimetry experiments and computational modeling. Remarkably, we use 3D trapping methods to demonstrate long-time confinement and manipulation (≥ 10 minutes) of fluorescent colloidal particles near the stagnation point of the 3D flows by employing active feedback control to localize particle positions. We further quantified trap performance by determining power spectral density of particle position fluctuations and trap stiffness. Finally, we demonstrated full 3D control over the particle center-of-mass position by manipulating and translating particles along user-defined trajectories in 3D space. Taken together, these results in this dissertation will aid in the development of new materials and processes that leverage the unique material properties conferred by ring polymer systems and automated manipulation and characterization of polymer and colloidal particle systems.

Graduation Semester

2022-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Michael Tu

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