All ETDs from UAB

Advisory Committee Chair

Eugenia Kharlampieva

Advisory Committee Members

Aaron Lucius

Tracy Hamilton

Pengfei Wang

Shane A Catledge

Subramaniam Ananthan

Document Type

Dissertation

Date of Award

2020

Degree Name by School

Doctor of Philosophy (PhD) College of Arts and Sciences

Abstract

The behavior of stimuli-responsive polymers is often inspired by the desire to mimic nature. Over the years, the development of polymeric systems, which respond to the environment by changing their physical and/or chemical properties, has been increased in biomedical and environmental applications. The demand for fresh water is also growing dramatically. This long-term development in the global water situation is closely connected to the growth of the world population and global climate change. In recent years, the use of nanomaterials in water remediation has increased considerably. In addition, shape and stimuli-responsiveness to size and surface chemistry of micro-engineered delivery carriers play an important role in functional responses of polymeric particulates. The research presented in this dissertation is to study and understand the structural property relationship of two different stimuli responsive polymers: Poly (methacrylic acid) (PMAA) and Poly (L-lactic acid) (PLA). In the presented dissertation, Chapter 1 serves as the overall introduction of stimuli responsive polymers and their effect on mechanical properties and dye degradation. Chapter 2 describes the details of experimental methods and characterization techniques for validation of overall hypothesis and results. In Chapter 3, we report on the effect of shell thickness on mechanical properties of two component poly (methacrylic acid) (PMAA) and poly N-vinylpyrrolidone (PVPON) multilayer hydrogen bonded capsules and crosslinked (PVPON/PMAA)10 hydrogel capsules at pH=3 and pH=8, respectively. We also explore the effect of the PMAA hydrogel capsule wall thickness and hydrogel cross-link density on the ability of these spherical capsules to retain their non-spherical shape in pH range from 3 to 7.5 after dissolution of a sacrificial silica core. The two component (PVPON/PMAA)n hydrogen bonded capsules were obtained from layer by layer deposition of PMAA layers and PVPON chains to obtain hydrogen-bonded (PVPON/PMAA)n multilayer capsules. We explore the effect of the PVPON/PMAA hydrogen bonded capsule wall thickness and number of bilayers on the ability of spherical micro-capsules to retain their spherical shape in pH=3 after dissolution of solid silica cores. Also, we investigate mechanical stability of spherical (PVPON/PMAA)n hydrogen bonded capsules and crosslinked (PVPON/PMAA)10 hydrogel capsules against deformation in solution under various osmotic pressures induced by increased concentrations of polystyrene sulfonate chains in exterior solution. We have found that increasing the number of bilayers can improve their mechanical stability against pressure-induced deformations. The elasticity modulus of hydrogen bonded spherical (PVPON/PMAA)n microcapsules was approximately 97 + 8 MPa. Our findings indicate that increasing the number of bilayers can improve mechanical stability of cross-linked hydrogel microcapsules around 22% against pressure-induced deformations. We believe that the findings of this study on shape- and shell thickness regulated mechanical stability of spherical multilayer hydrogen bonded capsules can give new insights for developing advanced hydrogen bonded materials with controllable shape. In Chapter 4, We have developed a novel type of photocatalytic polymer microsponges composed of porous polylactic acid (PLA) microparticles with incorporated titanium oxide nanoparticles (TiO2) capable of absorption of organic compounds and their degradation under UV irradiation. Titania nanoparticles are integrated into PLA microsponges using two approaches where PLA/TiO2 mixed microsponges are obtained by oil/water emulsion method with directly mixing of TiO2 anatase nanoparticles with PLA in the presence of 2-methylpentane while PLA/TiO2 grown microsponges, PLA was mixed with TiO2 precursor, titanium (IV) isopropoxide in the presence of 2-methylpentane resulting in PLA/TiO2 microsponges with amorphous TiO2. The amorphous TiO2 was mineralized to crystalline TiO2 by treatment with methanol for 24 h with a subsequent methanol evaporation at 60 °C. The Raman spectroscopy, X-ray diffraction spectrometry, scanning electron microscopy, and confocal laser scanning fluorescence microscopy were used to confirm the presence of crystalline titania nanoparticles and analyze the PLA/TiO2 microsponges. We found that both PLA/TiO2 composite systems effectively absorbed organic dye Rhodamine 6G from water which could be degraded by the UV-light exposure. We also demonstrated that after the dye degradation the PLA matrix can be disintegrated under UV-light due to the present crystalline titania. The composite biodegradable microsponges developed and studied in this work can be applied as non-toxic photocatalytic materials for environmental cleanup of contaminated water.

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