Polypeptoid Monomer Sequence and Chemical Composition as Independent Controls of Interfacial Tension and Elasticity at Air/Fluid Interfaces.

We use sequence-specific polypeptoids to characterize the impact of the monomer sequence on the adsorption of surface-active polymers at fluid/fluid interfaces. Sets of 36 repeat unit polypeptoids with identical chemical composition, but different sequences of hydrophobic moieties along the oligomer chain (taper, inverse taper, blocky, and evenly distributed), are designed and characterized at air/water interfaces. Polypeptoids are driven to the interfaces by decreasing the solvent quality of the aqueous solution.

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 adsorption rates, evaluating equilibrium surface tensions as a function of bulk surfactant concentration, and relating how surface tension changes with changes in the interfacial area following equilibration. Simultaneous visualization of the interface using fluorescence imaging with a high-speed confocal microscope allows the direct evaluation of structure-function relationships.

Inflammation product effects on dilatational mechanics can trigger the Laplace instability and acute respiratory distress syndrome.

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.

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

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

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.