All ETDs from UAB

Advisory Committee Chair

Sergey Vyazovkin

Advisory Committee Members

Tracy P Hamilton

Haibin Ning

Vinoy Thomas

Gayan B Wijeratne

Document Type

Dissertation

Date of Award

2021

Degree Name by School

Doctor of Philosophy (PhD) College of Arts and Sciences

Abstract

THERMODYNAMICS AND KINETICS OF SOL-GEL PHASE TRANSITION: EFFECTS OF NANOCONFINEMENT MARIA ALEJANDRA ESPINOSA DZIB CHEMISTRY ABSTRACT This research applies differential scanning calorimetry (DSC) to explore the effects of nanoconfinement on the kinetics and thermodynamics of gelation. The effects are quantified by evaluating the enthalpies, temperatures and the activation energies of gelation in the bulk and nanoconfined systems, Isoconversional kinetic analysis is employed to determine the temperature dependencies of the activation energies of gelation that are further interpreted in the frameworks of the nucleation model of Turnbull and Fisher.The first chapter highlights the surface and size effects of the nanopores on the thermodynamics and kinetics of gelation of poly(vinylidene fluoride) solutions in tetraethylene glycol dimethyl ether and γ-butyrolactone. Nanoconfinement has been accomplished by introducing gels into native and organically modified silica nanopores. The second chapter examines the effect of nanoconfined gelation of the solutions of polyacrylonitrile in propylene carbonate, poly(vinyl alcohol) in ethylene glycol, and isotactic polypropylene in o-dichlorobenzene and decalin in silica nanopores. All systems demonstrate similar effects under nanoconfinement. These are lowering of the heat of gelation and increase of temperature of gelation. The effects are respectively interpreted as the formation of fewer ordered crosslinks and acceleration of gelation due to heterogeneous nucleation at the confining surface. Kinetic analysis suggests that nanoconfinement lowers the free energy of nucleation. The third chapter examines the effect of nanoconfinement on gelation of mineral oil (MO), soybean oil (SO), ethylene glycol (EG), polyethylene glycol (PEG), and polypropylene glycol (PPG) by stearic and 12-hydroxystearic acids inside the silica nanopores. A new effect discovered in this work is a decrease in the gelation temperature of the nanoconfined MO and SO systems. By combining Isoconversional method with the Turnbull-Fisher nucleation model it has been possible to link this effect to deceleration of gelation that originates from an increase in the nucleation energy barrier. It has been proposed that whether nanoconfinement causes a decrease or an increase in the gelation temperature can depend on polarity of a liquid. The systems with polar liquids (EG, PEG, PPG) have indeed demonstrated an increase in the gelation temperature under nanoconfinement. Keywords: Differential scanning calorimetry, nanoconfinement, isoconversional kinetic analysis, Turnbull-Fisher, kinetics, gelation.

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