Probing pH-responsive interactions between polymer brushes and hydrogels by neutron reflectivity.

Area of Science:

• Polymer Science
• Materials Science
• Surface Chemistry

Background:

• Understanding polymer brush and hydrogel interface structure is crucial for designing advanced materials.
• Switchable interactions offer tunable control over material properties at the nanoscale.

Purpose of the Study:

• To investigate how specific interactions influence the structure of polymer brush-hydrogel interfaces.
• To quantify the effect of switchable interactions on polymer chain conformation and swelling.

Main Methods:

• Synthesis of weak polyelectrolyte brushes (poly(acrylic acid)) and hydrogels (polyacrylamide, poly(N,N-dimethylacrylamide)).
• Utilized neutron reflectivity to determine monomer density profiles of brushes in deuterium oxide (D2O) and in contact with D2O-swollen gels.
• Investigated interactions at different pH levels (pH 2 and pH 9) to control brush charge and interaction strength.

Main Results:

• At pH 2, poly(acrylic acid) brushes (neutral form) interact with the hydrogel via hydrogen bonds.
• At pH 9, poly(acrylic acid) brushes (polyelectrolyte form) exhibit no significant interaction with the hydrogel.
• The presence of hydrogen bonding interactions at pH 2 increased the brush swelling ratio compared to pure D2O, indicating more extended polymer chain conformations.

Conclusions:

• Switchable interactions, specifically hydrogen bonding, significantly impact polymer brush structure at interfaces.
• Controlling inter-chain interactions allows for tunable extension and swelling of polymer brushes.
• Findings provide insights into designing responsive materials with controlled interfacial properties.