Contraction of weak polyelectrolyte multilayers in response to organic solvents

Area of Science:

• Materials Science
• Polymer Chemistry
• Surface Science

Background:

• Weak polyelectrolyte multilayers (PEMs) exhibit unique solvent-dependent contraction.
• Understanding the correlation between solvent properties and PEM contraction is crucial.

Purpose of the Study:

• To analyze the contraction response of branched poly(ethylene imine)/poly(acrylic acid) (BPEI/PAA) multilayers in various organic solvents.
• To correlate contraction magnitude with solvent parameters like solubility and dielectric constant.

Main Methods:

• Layer-by-layer assembly of BPEI/PAA multilayers.
• Immersion of PEMs in 16 different organic solvents and mixtures.
• Analysis of film thickness, mechanical properties, and correlation with solubility parameters (Hansen, Kamlet-Taft) and dielectric constant.

Main Results:

• BPEI/PAA multilayers contracted upon exposure to organic solvents due to dehydration.
• Film thickness was a better predictor of swelling/contraction than assembly pH.
• Contraction correlated with Hansen and Kamlet-Taft solubility parameters and dielectric constant.
• Hydrogen bonding ability was the primary factor for contraction in most solvents.

Conclusions:

• Solvent's hydrogen bonding ability and dielectric constant are key determinants of PEM contraction.
• Both solvent quality and electrostatic interactions influence PEM behavior in organic solvents.
• Temperature effects on hydrogen bonding further elucidate dehydration mechanisms in PEMs.