All ETDs from UAB

Advisory Committee Chair

Sergey Vyazovkin

Advisory Committee Members

Renato Camata

Eugenia Kharlampieva

Aaron Lucius

Andrei Stanishevsky

Document Type

Dissertation

Date of Award

2017

Degree Name by School

Doctor of Philosophy (PhD) College of Arts and Sciences

Abstract

This research explores the effects of nanoconfinement and solid surfaces on gel-sol and liquid-liquid phase transitions through the changes in the thermodynamics and kinetics. The transitions that occur in the presence of solid surfaces were studied calorimetrically and compared to bulk. Two systems, gelatin gels and triethylamine/water (TEA/H2O) binary solution both undergo a phase transition on heating. Employing differential scanning calorimetry (DSC) and isoconversional kinetic analysis, the changes upon introducing a solid surface or nanoconfining were quantified. The first system probes the effect of the addition of laponite, montmorillonite, and chitosan particles on the structure of gelatin gels. It was found that adding particles increased the heat of melting while decreasing the temperature of melting, indicating that gels formed with added solid surfaces were less thermally stable. Examining the effective activation energy revealed that the barrier to melting increased. The lowered melting temperature is attributed to an increase in the pre-exponential factor, which increases the frequency of attempts to melt the gel. The second system examines the effect of nanoconfinement on the structure of gelatin gel through melting in silica pores of 4, 6, 15, and 30 nm diameters. With decreasing pore size, the heat of melting decreased from 3.5 J g-1 in bulk to 0.6 J g-1 in 6 nm silica pores, while increasing the temperature of melting by ~10ºC. In 4 nm silica pores, gel formation was suppressed. Analysis of the activation energy revealed a decrease. The increase in thermal stability is attributed to the decrease of the pre-exponential factor related to a diminished mobility of gelatin strands inside the pores, leading to broken bonds reforming. The third system examines the demixing of TEA/H2O in native and organically modified silica pores of 4, 6, 9, 15, and 30 nm diameter. The enthalpy and temperature of demixing both decrease upon nanoconfinement for both native and organically modified pores. Through isoconversional kinetic analysis it was revealed that the effective activation energy decreased upon nanoconfinement for both native and organically modified pores causing the decrease in demixing temperatures.

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