HYPOTHESIS: The surface dilatational and shear moduli of surfactant and protein interfacial layers can be derived from surface pressures measured with a Wilhelmy plate parallel, ΔΠ par and perpendicular ΔΠ perp to the barriers in a Langmuir trough.
EXPERIMENTAL: Applying area oscillations, A 0+ ΔAe iωt, in a rectangular Langmuir trough induces changes in surface pressure, ΔΠ par and ΔΠ perp for monolayers of soluble palmitoyl-lysophosphatidylcholine (LysoPC), insoluble dipalmitoylphosphatidylcholine (DPPC), and the protein β-lactoglobulin to evaluate E s∗+G s∗=A 0ΔΠ parΔA and E s∗-G s∗=A 0ΔΠ perpΔA. G s∗ was independently measured with a double-wall ring apparatus (DWR) and E s∗ by area oscillations of hemispherical bubbles in a capillary pressure microtensiometer (CPM) and the results were compared to the trough measurements.
FINDINGS: For LysoPC and DPPC, A 0ΔΠ parΔA≅A 0ΔΠ perpΔA meaning E s∗≫G s∗ and E s∗≅A 0ΔΠ parΔA≅A 0ΔΠ perpΔA. Trough values for E s∗ were quantitatively similar to CPM when corrected for interfacial curvature. DWR showed G ∗ was 4 orders of magnitude smaller than E s∗ for both LysoPC and DPPC. For β-lactoglobulin films, A 0ΔΠ parΔA>A 0ΔΠ perpΔA and E s∗ and G s∗ were in qualitative agreement with independent CPM and DWR measurements. For β-lactoglobulin, both E s∗ and G s∗ varied with film age and history on the trough, suggesting the evolution of the protein structure.
Bibliographical noteFunding Information:
This project was supported by National Institutes of Health Grant HL 51177 and NSF Grant CBET 170378. SI was supported by a Ruth L. Kirschstein NRSA Institutional Research Training Grant F32 HL151128. We acknowledge the guidance and assistance of the support staff, especially Guillermo Marques, at the University Imaging Center at the University of Minnesota.
© 2022 Elsevier Inc.
- Dilatational modulus
- Interfacial dilatational rheology
- Interfacial rheology
- Interfacial shear rheology
- Soluble surfactant
PubMed: MeSH publication types
- Journal Article