Large-scale solvent driven actuation of polyelectrolyte multilayers based on modulation of dynamic secondary...

Area of Science:

• Materials Science
• Polymer Science
• Chemical Engineering

Background:

• Polyelectrolyte multilayers (PEMs) assembled from weak polyelectrolytes are explored for smart material applications.
• Existing PEMs show limited response to chemical stimuli, primarily in aqueous solutions with varying ionic strength or pH.

Purpose of the Study:

• To achieve a large-magnitude, reversible transition in swelling/shrinking and viscoelastic behavior of PEMs in response to polar organic solvents.
• To investigate the underlying mechanisms responsible for these transitions.

Main Methods:

• Assembly of branched polyethylenimine/poly(acrylic acid) multilayers.
• Exposure of PEMs to various polar organic solvents (ethanol, DMSO, THF) and solvent/water mixtures.
• Characterization of swelling/shrinking behavior and viscoelastic properties (rheology).

Main Results:

• PEMs exhibited a large, reversible transition in swelling and viscoelasticity upon exposure to polar organic solvents.
• Swelling decreased with increasing organic solvent content, leading to film contraction without dissolution.
• A stepwise transition from liquid-like to rigid solid behavior was observed, enhancing elasticity.

Conclusions:

• The observed response is attributed to changes in the medium's dielectric constant and increased hydrophobic interactions within the PEM.
• This solvent-induced transition is significantly larger than responses to ionic strength or pH variations.
• The study presents a pathway for developing advanced smart artificial materials with large-scale actuation capabilities.