Polyelectrolyte adsorption on solid surfaces: theoretical predictions and experimental measurements.

Area of Science:

• Surface Science
• Polymer Science
• Physical Chemistry

Background:

• Cationic polyelectrolytes like poly(diallyldimethylammonium chloride) (PDADMAC) and poly(4-vinyl N-methylpyridinium iodide) (PVNP) are highly charged and soluble.
• Silica surfaces exhibit high negative charge density at pH 9, favoring electrostatic interactions.

Purpose of the Study:

• To explore the adsorption behavior of PDADMAC and PVNP on silica surfaces.
• To investigate the influence of simple salt concentration on polyelectrolyte adsorption.
• To compare experimental adsorption data with theoretical predictions from a novel density functional theory.

Main Methods:

• Ellipsometry was used to obtain quantitative experimental data on polyelectrolyte adsorption.
• Correlation-corrected classical density functional theory was employed for theoretical modeling.
• Experimental and theoretical adsorption curves were compared across varying salt concentrations.

Main Results:

• Polyelectrolyte adsorption initially increases with ionic strength, peaking at approximately 200 mM salt.
• Adsorption decreases at higher salt concentrations but remains significant, indicating nonelectrostatic contributions.
• Theoretical predictions, incorporating estimated nonelectrostatic affinities, accurately matched experimental adsorption data.

Conclusions:

• Electrostatic interactions dominate polyelectrolyte adsorption at low salt concentrations.
• Nonelectrostatic forces play a role in adsorption, particularly at high ionic strengths.
• The developed classical density functional theory provides a quantitatively accurate description of polyelectrolyte adsorption on charged surfaces.