Shear modulation force microscopy study of near surface glass transition temperatures

Area of Science:

• Materials Science
• Polymer Science
• Surface Science

Background:

• Understanding the glass transition temperature (T(g)) of polymer thin films is crucial for their application in various technologies.
• Previous studies have indicated potential thickness-dependent T(g) behavior in polymer films, but experimental evidence remains debated.
• Atomic Force Microscopy (AFM) offers high-resolution surface analysis capabilities.

Purpose of the Study:

• To accurately measure the surface glass transition temperature (T(g)) of polymer thin films.
• To investigate the influence of film thickness, substrate interactions, and substrate presence on the measured T(g).
• To validate the utility of shear modulation force microscopy (SMFM) for T(g) determination.

Main Methods:

• Utilized Atomic Force Microscopy (AFM) in shear modulation force microscopy (SMFM) mode.
• Measured the temperature-dependent shear force exerted on an AFM tip modulated parallel to the polymer film surface.
• Analyzed thin polymer films with thicknesses ranging from 17 to 500 nm.

Main Results:

• The surface glass transition temperature (T(g)) was successfully measured for polymer thin films.
• T(g) was found to be independent of film thickness for films thicker than 17 nm.
• No significant influence of substrate interaction strength or the presence of a substrate was observed on the T(g).

Conclusions:

• The surface T(g) of polymer thin films is robust and not affected by film thickness above 17 nm.
• Shear modulation force microscopy (SMFM) is a reliable technique for determining the surface T(g) of polymer films.
• The findings suggest that surface T(g) is an intrinsic property of the polymer film material itself under these experimental conditions.