Degree
Doctor of Philosophy (PhD)
Department
Chemistry
Document Type
Dissertation
Abstract
Colloidal interfaces play a critical role in drug delivery, environmental sensing, and nanomedicine, yet quantifying molecular interactions at these surfaces remains experimentally challenging. This dissertation uses second harmonic generation (SHG) and extinction spectroscopy to investigate the adsorption and transport behavior of charged molecules at the colloidal interface in aqueous environments, including polystyrene sulfate (PSS) microparticles (MPs), phospholipid liposomes, and live bacterial membranes. The adsorption of the cationic dye malachite green (MG) to PSS microparticles was studied across a range of pH conditions, with enhanced interfacial binding observed under acidic conditions and diminished adsorption at higher pH values due to altered electrostatic attraction and dye degradation. SHG adsorption isotherms were modeled using a modified Langmuir approach, yielding equilibrium constants, surface site densities, and free energies of adsorption. Extinction corrections and microparticle depletion models were applied to account for absorption and scattering at both the fundamental and second harmonic wavelengths. A separate microparticle dilution correction is introduced to account for changes in available surface area resulting from the addition of MG solution volume. Additionally, time-resolved SHG was applied to probe MG transport across the outer and cytoplasmic membranes of Pseudomonas aeruginosa bacteria in aqueous suspension. Numerical modeling using Euler’s method provided estimates of transport rates and supported a two-membrane system model. Overall, this work demonstrates a surface-specific method for probing adsorption and transport processes at colloidal interfaces. The combined use of SHG and extinction spectroscopy techniques provide new insights into interfacial thermodynamics, molecular permeability, and experimental strategies for future studies in surface chemistry, membrane biophysics, and nanomaterial-based drug delivery systems.
Date
8-22-2025
Recommended Citation
Ali, Rasidah O., "Investigating Molecular Adsorption and Transport at Colloidal and Biological Interfaces Using Second Harmonic Generation Spectroscopy" (2025). LSU Doctoral Dissertations. 6907.
https://repository.lsu.edu/gradschool_dissertations/6907
Committee Chair
Louis H. Haber
Included in
Biophysics Commons, Lipids Commons, Materials Chemistry Commons, Medicinal Chemistry and Pharmaceutics Commons, Physical Chemistry Commons