microtensiometer-for-confocal-microscopy-visualization-dynamic

Microtensiometer for Confocal Microscopy Visualization of Dynamic Interfaces

Adsorption of surface-active molecules to fluid-fluid interfaces is ubiquitous in nature. Characterizing these interfaces requires measuring surfactant ...

Carnegie Mellon University

The transport, equilibrium properties, and mechanics of stable, rodlike surfactant-polyelectrolyte aggregates, poly(cetyltrimethylammonium vinyl benzoate) or pCTVB, are characterized at air/water interfaces for bulk concentrations near and below the critical aggregation concentration. The surfactant drives the transport to air/water interfaces, while the polyelectrolyte provides elasticity to the coated interfaces and appears to remain adsorbed after the bulk solution is exchanged with water. The processing of interfaces is shown to allow the interfacial tension of the interface to be changed significantly while maintaining a high dilatational elasticity. The results of this work provide a tool to control interfacial properties through design of polyelectrolyte-surfactant complexes.

Interfacial Properties of Polyelectrolyte-Surfactant Aggregates at Air/Water Interfaces.

The connection between block copolymer architecture and adsorption at fluid/fluid interfaces is poorly understood. We characterize the interfacial properties of a well-defined series of polyethylene oxide/polydimethyl siloxane (PDMS) diblock and BAB triblock copolymers at the dodecane/water interface. They are oil-soluble and quite flexible because of their hydrophobic PDMS block. Rather than relying on equilibrium interfacial measurements for which it is difficult to mitigate experimental uncertainty during adsorption, we combine measurements of steady-state adsorption, dilatational rheology, and adsorption/desorption dynamics. Steady-state interfacial pressure is insensitive to interfacial curvature and mostly agrees with theory. Adsorption does not occur in the diffusive limit as is the case for many aqueous, small-molecule surfactants. Dilatational rheology reveals differences in behavior between the diblocks and triblocks, and all interfaces possess elasticities below the thermodynamic limit. Desorption dynamics show that material exchange between the interface and the neighboring fluid occurs too slowly to relax dilatational stresses. The mechanism of relaxation occurs at the interface, likely from the reorientation of adsorbed chains.

Transport of Flexible, Oil-Soluble Diblock and BAB Triblock Copolymers to Oil/Water Interfaces.

In the lungs, the Laplace pressure, ΔP = 2γ/R, would be higher in smaller alveoli than larger alveoli unless the surface tension, γ decreases with alveolar interfacial area, A, such that 2ε > γ in which ε = A(dγ/dA) is the dilatational modulus. In Acute Respiratory Distress Syndrome (ARDS), lipase activity due to the immune response to an underlying trauma or disease causes single chain lysolipid concentrations to increase in the alveolar fluids via hydrolysis of double-chain phospholpids in bacterial, viral, and normal cell membranes. Increasing lysolipid concentrations decrease the dilatational modulus dramatically at breathing frequencies if the soluble lysolipid has sufficient time to diffuse off the interface, causing 2ε < γ, thereby potentially inducing the "Laplace Instability", in which larger alveoli have a lower internal pressure than smaller alveoli. This can lead to uneven lung inflation, alveolar flooding, and poor gas exchange, typical symptoms of ARDS. While the ARDS lung contains a number of lipid and protein species in the alveolar fluid in addition to lysolipids, the surface activity and frequency dependent dilatational modulus of lysolipid suggest how inflammation may lead to the lung instabilities associated with ARDS. At high frequencies, even at high lysolipid concentrations, 2ε - γ > 0, which may explain the benefits ARDS patients receive from high frequency oscillatory ventilation.

Article	Year
Interfacial Properties of Polyelectrolyte-Surfactant Aggregates at Air/Water Interfaces. Langmuir : the ACS journal of surfaces and colloids\| PubMed ID: 30274519	2018
Transport of Flexible, Oil-Soluble Diblock and BAB Triblock Copolymers to Oil/Water Interfaces. Langmuir : the ACS journal of surfaces and colloids\| PubMed ID: 32482075	2020
Inflammation product effects on dilatational mechanics can trigger the Laplace instability and acute respiratory distress syndrome. Soft matter\| PubMed ID: 32643749	2020

Michael L. Davidson

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