Modulating the Swelling Behavior of Polymer Brushes via Interfacial Chemistry

Area of Science:

• Polymer Science
• Surface Chemistry
• Materials Science

Background:

• Polymer brushes are used as surface coatings and lubricants in a swollen state.
• Grafting density and molecular weight are key parameters controlling brush swelling.
• The role of substrate surface chemistry in brush swelling is less understood.

Purpose of the Study:

• To investigate substrate surface chemistry as a parameter for controlling polymer brush swelling.
• To explore the impact of initiator-presenting substrates on brush behavior.
• To compare swelling in different solvent conditions for various polymer brushes.

Main Methods:

• Synthesized hydrophobic poly(tert-butyl methacrylate) (PtBMA) and hydrophilic poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes using surface-initiated atom transfer radical polymerization (SI-ATRP).
• Grafted brushes from substrates with dipeptide and alkyl spacer tethered ATRP initiators.
• Analyzed brush swelling in different solvent systems (good solvent, mixed solvents, water).

Main Results:

• For PtBMA brushes in a good solvent (THF), swelling is dominated by polymer-solvent interactions, with negligible substrate effects.
• In mixed solvents, PtBMA brush swelling is influenced by substrate surface chemistry, correlating with initiator polarity.
• Swelling of hydrophilic PDMAEMA brushes in water also indicates an impact of substrate surface chemistry.

Conclusions:

• Substrate surface chemistry is an additional tunable parameter for controlling polymer brush swelling.
• The influence of substrate chemistry is more pronounced in mixed solvents and for hydrophilic brushes in water.
• This work expands the understanding of factors governing polymer brush behavior in solution.