Solvent-rich polyelectrolyte complexes display a wide range of rheological properties, when different environmental parameters are applied. Due to the low energy barrier of the complexation (~10 kT), these materials possess tunable properties, with the states of these materials varying from Newtonian liquids to very tough hydrogels. This thesis aims to elucidate the mechanism of polyelectrolyte complexation in a model system, and further to extend that fundamental understanding to applications in soft materials, including thermo-thickening fluids and tough hydrogels. The fracture of highly deformable (hydro-)gels is an extreme case of non-linear viscoelasticity of these materials. This thesis connects the fracture behavior of (hydro-)gels with network structures, and provides one of the first few experimental data sets of fatigue failure of gels in this area. The model material system throughout this thesis consists of partially quaternized poly (4-vinyl pyridine) (QVP) and poly (methacrylic acid) (PMAA). Hydrogen bonding interaction is the primary interaction that drives the formation of viscoelastic liquids/solids when dimethyl sulfoxide (DMSO)/water or DMSO/ethylene glycol (EG) mixed solvents are utilized. The addition of protic solvents (water or EG), leads to a well-defined sol-gel transition, characterized by the increase of viscosity and the decrease of phase angle. The effect of solvent composition is analogous to that of temperature, and both of them alter the relaxation times of associating groups in the mixture. By introducing a solvent shift factor and a temperature shift factor, a mastercurve is obtained. The validation of time-temperature-solvent superposition (TTSS) rule provides a simple way for quantifying the effects of environmental factors. QVP-PMAA model system is a good platform for designing functional materials. Examples include using QVP-PMAA mixtures as thermo-thickening materials, and doping QVP into PMMA-PMAA-PMMA [PMMA: poly (methyl methacrylate)] triblock copolymer hydrogels. The thermo-thickening colloidal suspensions are self-stabilized, exhibiting an increase of viscosity by 1000 times with an increase of temperature by ~20 ^{\circ}C. This is a novel thermo-thickening mechanism driven by the swelling of colloids, and the thickening/thinning transition temperature could be tailored in a facile manner. In PMMA-PMAA-PMMA/QVP hydrogels, the introduction of QVP-PMAA interaction strengthens and toughens the pure triblock copolymer network, giving material responses similar to traditional double network (DN) gels. In the applications of solvent-rich materials, they might be subjected to repeated pressures (or stresses). This thesis examines the fatigue failure of nearly elastic triblock copolymer [PMMA-PnBA-PMMA (PnBA: poly n-butyl acrylate)] gels. When being exposed to a repeated load, a gel is ruptured at much lower energy level compared with the required energy for typical fast fracture. The fatigue failure threshold is in the order of a few J/m^{2}. This sets a lower energy limit under which these materials are safe for long term applications.

Creator

• Chen, Yaoyao

DOI

• https://doi.org/10.21985/n2-gcx0-mj55

Subject

• Materials Science

Language

• en

Alternate Identifier

• etdadmin_upload_662844
• http://dissertations.umi.com/northwestern:14666

Keyword

• polyelectrolyte
• thermo-thickening
• fracture
• gels
• viscoelasticity

Date created

• 2019-01-01

Resource type

• Dissertation

Rights statement

• In Copyright