Sol-Gel Transition of a Thermo-Responsive Polymer at the Closest Solid Interface

Area of Science:

• Materials Science
• Polymer Chemistry
• Surface Science

Background:

• Thermo-responsive polymers are utilized for surface modifications, enabling temperature-controlled switching of surface properties.
• Understanding the influence of surface-bound polymer chains on the transition behavior of these polymers remains limited.
• Methylcellulose (MC) is a thermo-responsive polymer exhibiting sol-gel transitions in aqueous solutions.

Purpose of the Study:

• To investigate the effect of bound polymer chains at the solid-liquid interface on the thermo-responsive sol-gel transition of methylcellulose.
• To elucidate the role of interfacial interactions and chain mobility in modulating thermo-responsive behavior.

Main Methods:

• Utilized Quartz Crystal Microbalance (QCM) to evaluate shear modulus and probe behavior near the solid interface.
• Employed a simple analytical model for QCM to control analytical depth and assess physical properties at the interface.
• Investigated aqueous methylcellulose solutions with varying proximity to solid substrates.

Main Results:

• At millimeter scales, reduced sample thickness and MC condensation near the interface lowered the sol-gel transition temperature.
• At nanometer scales (QCM interface), increased sol-gel transition temperature was observed due to reduced chain mobility.
• Adsorption and interfacial interactions restrained MC chain aggregation, thereby hindering the sol-gel transition.

Conclusions:

• Interfacial interactions significantly influence the thermo-responsive sol-gel transition of methylcellulose.
• Reduced chain mobility at the solid interface must be considered for applications of thermo-responsive polymers in thin films or adsorbed states.
• QCM combined with analytical modeling provides a method for evaluating polymer behavior at the solid-polymer interface.