Dissertation
Quantifying competitive surfactant adsorption to the silica-water interface by continuous-flow FTIR
Doctor of Philosophy (Ph.D.), Drexel University
Aug 2026
DOI:
https://doi.org/10.17918/00011574
Abstract
Surfactant adsorption at charged solid-liquid interfaces affects surface modification, cleaning, formulation, and transport through porous materials. In mixed surfactant systems, the retention or release of one component can depend on another component and on the prior state of the surface. This dissertation examines these effects for sodium dodecyl sulfate (SDS) and Laureth-23 (L23) on silica using a component-resolved continuous-flow approach. A packed silica column was coupled with inline transmission Fourier transform infrared spectroscopy (FTIR). Characteristic absorption bands allowed SDS and L23 concentrations to be monitored independently over time during single-component, sequential, and competitive adsorption, including in binary mixtures. Methanol tracer measurements and tracer-assisted mass balances accounted for nonadsorbing transport. A finite-volume transport-adsorption model was developed to describe axial transport, mobile-immobile exchange, Langmuir adsorption, and finite adsorption kinetics. Single-component experiments established the uncoupled adsorption behavior of SDS and L23. Static equilibrium adsorption did not fully describe their continuous-flow responses. SDS breakthrough depended on concentration, flow rate, pore structure, and prior surface exposure. For L23, tracer-corrected apparent surface excesses at 9.2 and 21.2 mM were similar, consistent with adsorption in a high-concentration plateau region. The dynamic response remained lower than predicted from the static isotherm. In the binary system, introducing SDS to L23-modified silica released preadsorbed L23 and substantially enhanced SDS retention relative to pristine silica. Increasing SDS concentration from 2 to 15 mM at a fixed L23 concentration of 10 mM raised the fraction of the initial L23 inventory released from approximately 5.70% to 31.4%. Reverse-sequence experiments showed that L23 retention could accompany renewed SDS retention. Simultaneous introduction onto pristine silica produced a different response from sequential exposure. Mixture composition and surface history thus strongly influenced dynamic adsorption. Nonionic-surfactant release and enhanced SDS retention can occur concurrently. Their dependence on concentration, mixture composition, and surface history supports a coupled, concentration-dependent partitioning process. In this interpretation, the L23-modified interfacial layer is progressively eroded and reorganized while enabling additional SDS retention. The composition and molecular arrangement of the retained layer were not measured directly. The component-resolved measurements link surfactant release and interfacial retention over time, a relationship that total-concentration measurements alone cannot resolve. Together, the experiments and model provide a framework for studying dynamic competitive adsorption in multicomponent surfactant systems.
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Details
- Title
- Quantifying competitive surfactant adsorption to the silica-water interface by continuous-flow FTIR
- Creators
- Yao Zhou
- Contributors
- Nicolas J. Alvarez (Advisor)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University
- Number of pages
- xx, 214 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- Nick Howley College of Engineering and Computing; Chemical and Biological Engineering; School of Engineering; Drexel University
- Other Identifier
- 991022234045404721