(387r) Direct Measurement of Line Tension, Diffusivity, and Young’s Modulus in Lung Surfactant Monolayers Using a Customized Microtensiometer–Confocal Platform
2025 AIChE Annual Meeting
(387r) Direct Measurement of Line Tension, Diffusivity, and Young’s Modulus in Lung Surfactant Monolayers Using a Customized Microtensiometer–Confocal Platform
Quantitatively characterizing the mechanical and transport properties of monolayers is essential for understanding phase behavior in soft matter systems yet remains experimentally challenging. We present a newly developed bubble-based microtensiometer platform integrated with high-speed confocal fluorescence microscopy, enabling simultaneous measurement of surface tension and interfacial phase morphology on curved, micrometer-scale air bubbles. Using clinical lung surfactants as model systems, we observed phase-separated monolayers exhibiting coexisting liquid-ordered (LO) and liquid-disordered (LD) phases at low surface pressures (π ≈ 2 mN/m). As adsorption progresses, a critical mixing point is reached, beyond which the two immiscible liquid phases merge into a single homogeneous phase. The line tension, λO-D between coexisting domains is extracted from the force balance between interfacial contraction and viscous drag acting on domain boundaries. At higher surface pressure (π > 10 mN/m), coexisting liquid-condensed (LC) and liquid-expanded (LE) domains form. The diffusivity of LC domains within the LE matrix is quantified by tracking their Brownian motion. Furthermore, the monolayer’s Young’s modulus (Y) is estimated from a curvature-induced circle-to-stripe morphological transition of LC domains—consistent with theoretical predictions after accounting for anisotropic bending energy on curved surfaces (R < 150 µm), where the average stripe width, w, at equilibrium surface pressure (πeq) relates to bubble radius R, line tension λC-E between LC and LE domains, and Y, which follows w ~ R4/5 (λC-E/Y)1/5. This platform enables the first such measurements of monolayers on curved interfaces using tools we developed and validates a generalizable approach for probing interfacial mechanics in biologically and industrially relevant systems.
Research Interests: Interfacial science; surfactant-laden systems; colloidal interactions; transport phenomena in soft matter
