2023 AIChE Annual Meeting

(454d) Soluble Surfactant Adsorption Above and below the Critical Micelle Concentration

Authors

Steven Iasella, University of Minnesota
Meenal Rathi, University of Minnesota
David Morse, University of Minnesota
Joseph Zasadzinski, University of Minnesota
Acute respiratory distress syndrome (ARDS) is a pulmonary disease that affects over 300,000 people in the US each year and has a 40% mortality rate. A major barrier for the effective treatment of ARDS is that the underlying causes of the disease are poorly understood. We believe that the root cause may be a change in the interfacial properties of the lung surfactant due to blood components, in particular phospholipase A2, entering the lungs as a result of inflammation. PLA2 catalyzes the formation of soluble lysophosphatidylcholine (LysoPC) from the membranes phospholipids of bacteria or viruses. Understanding how LysoPC adsorbs onto an air-water interface is essential to improving our understanding of its role in ARDS. A capillary pressure microtensiometer enables us to create a curved bubble at a size similar to lung alveoli and measures the dynamic surface tension as LysoPC adsorbs onto the interface.

Here we present a study of LysoPC adsorption phenomena onto a clean curved air-water interface using the microtensiometer below and above the critical micelle concentration (CMC). We fit equilibrium surface tension data to the equation of state based on Langmuir isotherms to obtain the value of kL and Ⲅ∞. These two parameters then were used to fit Ward-Tordai theory to experimental surface tension adsorption. We show that at concentrations below CMC, the diffusion-controlled Ward-Tordai theory fits the experimental data well, and the monomer diffusivity of LysoPC can be obtained from the fitting. The diffusivity of best fit decreases from 5e-10 to 2.5e-10 m2/s as concentration increases from 1/10 of CMC to CMC. This decrease in diffusivity of similar surfactants is observed by NMR measurements. We also show that at concentrations above CMC, the Ward-Tordai equation does not fit the data well, due to its lack of accounting for the distribution of surfactant between micelles and monomers. We present a two-zone model theory, where the maximum monomer concentration is the CMC, and the remainder of the surfactant is present in the form of micelles. Diffusion and adsorption cause an expanding micelle-free zone in the vicinity of the interface.