Biswal, Sibani Lisa2021-04-132022-05-012021-052021-03-16May 2021Chen, Yi-Lin. "Characterization of switchable surfactant interactions with biomimetic surfaces." (2021) Diss., Rice University. <a href="https://hdl.handle.net/1911/110266">https://hdl.handle.net/1911/110266</a>.https://hdl.handle.net/1911/110266Amphiphiles are molecules that have both hydrophobic and hydrophilic chemical groups. Common examples of amphiphiles are surfactants, phospholipids, and block copolymers. Due to their dual chemical nature, amphiphiles readily partition to surfaces and interfaces. In the bulk phase, amphiphiles assemble into complex morphologies, such as micelles, vesicles, and lamella structures, to reduce the system free energy. They are widely utilized in different industries such as consumer products, detergents, pharmaceutical drug delivery agents, food science, and oil recovery. Several interfacial interactions have been studied, including amphiphile adsorption or desorption onto substrates, and amphiphile-amphiphile interactions. Recently, switchable surfactants have been reported as an interesting class of amphiphiles that could change their chemical or physical properties when triggered by stimuli, such as pH or light. These are utilized in a variety of applications such as cargo delivery and release and as viscoelastic rheological fluids. However, the underlying mechanism of the behavior of switchable surfactants with surfaces and interfaces remains unclear. Thus, this dissertation systematically investigates how switchable surfactants interact with interfaces by utilizing different surface characterization techniques, including quartz crystal microbalance with dissipation (QCM-D), zeta potential measurements and surface tension measurements. First, the interaction between the switchable surfactant, DTTM (N,N,N' trimethyl-N'-tallow-1,3- diaminopropane), and a silica substrate is investigated. Our results showed that the adsorption is the function of ionic strength and pH of the solution. A two-step adsorption model was applied to characterize DTTM adsorption when above its critical micelle concentration (CMC) while a Langmuir model was used to describe the adsorption when its concentration is below CMC. Next, another switchable surfactant, MSDH (O-methyl-serine dodecylamide hydrochloride), and its interaction with a biomimetic phospholipid membrane, is studied. Two morphologies of phospholipid membrane, liposomes and supported lipid bilayers, were used to understand the governing interactions between MSDH and lipid membranes. Our results suggest that the underlying mechanism for membrane lysis by MSDH differs from the commonly described three-step model used to describe membrane lysis by amphiphiles. Lastly, surface characterization platforms developed for these switchable surfactants are applied to study the interaction between exosomes and lipid bilayers. Exosomes are cell-derived vesicles, which contain protein, RNA, as well as other genetic material, and have been considered to assist with intracellular communication and cargo delivery. However, an understanding of how exosomes pass through the cell membrane remains unclear. From our characterization platform, our results suggest new insights into how cells uptake exosomes. When combined, this thesis provides a systematic platform to study the interactions between complex amphiphiles and interfaces. This dissertation also provides new insights and models to explain how solution conditions alter the interactions of switchable surfactants with interfaces.application/pdfengCopyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.switchable surfactantslipid membranesThesis2021-04-13