Surface Forces of Asymmetrically Grown Polyelectrolyte Multilayers: Searching for the Charges

Area of Science:

• Polymer Science
• Surface Chemistry
• Materials Science

Background:

• Polyelectrolyte multilayers (PEMs) are versatile materials with tunable properties.
• Understanding PEM formation and surface characteristics is crucial for applications.

Purpose of the Study:

• Investigate polymer conformation and surface charge in PEMs.
• Elucidate the growth mechanisms and surface behavior of PEMs under varying conditions.

Main Methods:

• Surface force measurements
• Preparation of polyelectrolyte multilayers using poly(diallyldimethylammonium) (PDADMA) and poly(styrenesulfonate) (PSS)
• Varying ionic strength during characterization

Main Results:

• PEMs exhibit distinct growth regimes: initial charge neutrality followed by cationic excess (PDADMA).
• PSS-terminated films show surface charge reversal from negative to low positive in the linear growth regime.
• PDADMA-terminated films display steric forces, forming a pseudobrush structure.

Conclusions:

• Surface charge reversal in PSS-terminated films is attributed to excess PDADMA monomers.
• A model for PEM formation suggests weak adsorption of PDADMA and anion exchange.
• Surface properties are dictated by the terminal polyelectrolyte and internal composition.