Polyelectrolyte multilayers of diblock copolymer micelles with temperature-responsive cores

Area of Science:

• Materials Science
• Polymer Chemistry
• Nanotechnology

Background:

• Layer-by-layer (LbL) assembly is a versatile technique for creating thin films.
• Stimuli-responsive polymers offer tunable properties for advanced applications.
• Cationic diblock copolymer micelles (BCMs) exhibit pH- and temperature-dependent behavior.

Purpose of the Study:

• To investigate the assembly and stimuli-response behavior of LbL films incorporating pH- and temperature-responsive BCMs.
• To understand the role of a polyanion (PSS) in stabilizing BCM morphology within LbL films.
• To explore the potential of these BCM/PSS assemblies for controlled release applications.

Main Methods:

• Synthesis of poly(2-(dimethylamino)ethyl methacrylate)-block-poly(N-isopropylacrylamide) (PDMA-b-PNIPAM) diblock copolymers.
• Formation of BCMs and their subsequent assembly with polystyrene sulfonate (PSS) via LbL technique.
• Characterization of film morphology and response using ellipsometry and atomic force microscopy (AFM).

Main Results:

• BCM/PSS assemblies preserved their dry-state morphology under pH and temperature variations, unlike BCM monolayers.
• Wet-state swelling of BCM/PSS multilayers was temperature-dependent but largely pH-independent.
• Reversible swelling transitions and controlled release of a hydrophobic dye were achieved by cycling temperature around the PNIPAM's LCST.

Conclusions:

• PSS coating effectively stabilizes BCMs within LbL films, preventing irreversible restructuring.
• The BCM/PSS system exhibits tunable swelling and controlled release properties based on temperature stimuli.
• These findings highlight the potential of stimuli-responsive BCM/PSS LbL films for smart material applications.