Surface viscoelastic properties of floating polyelectrolyte multilayers films: a capillary wave study

Area of Science:

• Materials Science
• Surface Chemistry
• Physical Chemistry

Background:

• Polyelectrolyte multilayers (PEMs) are versatile materials with tunable properties.
• Understanding their behavior at interfaces is crucial for applications in coatings, sensors, and drug delivery.
• The viscoelastic properties of floating PEMs at the air-water interface remain less explored.

Purpose of the Study:

• To investigate the viscoelastic properties of floating polyelectrolyte multilayers, specifically (PSS/PAH)(n).
• To examine the influence of different Langmuir monolayers (lipid DODAB and block copolymer PS-b-PAA) on PEM behavior.
• To elucidate the structural and mechanical changes within the PEMs as layers accumulate.

Main Methods:

• Utilized a capillary wave technique to measure interfacial viscoelastic properties.
• Fabricated polyelectrolyte multilayers ((PSS/PAH)(n)) on pre-formed Langmuir monolayers.
• Characterized PEMs adsorbed onto dimethyldioctadecylammonium bromide (DODAB) and poly(styrene-b-sodium acrylate) (PS-b-PAA) monolayers.

Main Results:

• Observed an increase in elasticity with the formation of four polyelectrolyte layers.
• Detected an apparent negative viscosity, suggesting a complex mechanical response.
• Proposed a three-zone model (precursor, bulk, outer) for the multilayer structure.
• Reported Young's modulus for seven layers comparable to planar PEM films.

Conclusions:

• The observed increase in elasticity and negative viscosity indicates a shift in mechanical dominance from the precursor zone (Zone I) to the bulk zone (Zone II).
• The findings provide insights into the interfacial viscoelasticity of floating PEMs, relevant for understanding their behavior in complex environments.
• The study establishes a foundation for designing and controlling the properties of interfacial polyelectrolyte multilayer systems.