Polyelectrolyte multilayer films built from poly(L-lysine) and a two-component anionic polysaccharide blend.

Area of Science:

• Materials Science
• Polymer Chemistry
• Surface Science

Background:

• Polyelectrolyte multilayer (PEM) films are built by sequential adsorption of oppositely charged polymers.
• Understanding the adsorption behavior of polymer blends in PEM formation is crucial for controlling film properties.

Purpose of the Study:

• Investigate the buildup of PEM films using poly(L-lysine) (PLL) and a blend of beta-1,3 glycan sulfate (GlyS) and alginate (Alg).
• Determine how the mass fraction of GlyS in the blend affects film thickness and composition.
• Elucidate the preferential adsorption mechanism of GlyS over Alg.

Main Methods:

• Fabrication of PEM films with varying GlyS/Alg ratios.
• Measurement of film thickness using ellipsometry or profilometry.
• Analysis of film composition using Infrared (IR) spectroscopy (Attenuated Total Reflection mode).
• Thermodynamic investigation of polymer interactions using Isothermal Titration Calorimetry (ITC).
• In-situ polymer exchange experiments within pre-formed PEM films.

Main Results:

• Film thickness reaches a minimum at low GlyS mass fractions (<0.1).
• GlyS is preferentially incorporated into PEM films, with its weight fraction in the film exceeding its fraction in the blend.
• Preferential adsorption of GlyS is attributed to stronger interactions with PLL compared to Alg, confirmed by ITC.
• GlyS can displace Alg from existing films, but Alg cannot displace GlyS.

Conclusions:

• Sulfated polysaccharides (GlyS) exhibit preferential interaction and adsorption over carboxylated polysaccharides (Alg) with polycations (PLL).
• This preferential adsorption mechanism provides a structural basis for controlling PEM film composition when using polymer blends.
• The findings offer insights into designing functional PEMs with tailored properties based on polysaccharide charge type.