Probing particle structure in waterborne pressure-sensitive adhesives with atomic force microscopy

Area of Science:

• Materials Science
• Polymer Science
• Surface Science

Background:

• Understanding the nanostructure of pressure-sensitive adhesive (PSA) films is essential for correlating structure with material properties.
• Waterborne polymer colloids are widely used in PSA formulations, necessitating detailed characterization of their morphology.

Purpose of the Study:

• To investigate the nanostructure of acrylic waterborne PSA films using intermittent-contact atomic force microscopy (AFM).
• To correlate the observed nanostructure with the film's properties by analyzing component interactions under varying AFM tapping conditions.

Main Methods:

• Intermittent-contact atomic force microscopy (AFM) was employed to image the surface topography and phase behavior of acrylic waterborne PSA films.
• AFM tapping force (F(av)) and tapping amplitude were systematically varied to assess their impact on image formation and component differentiation.

Main Results:

• AFM height images showed apparent shape changes (concave to convex) of polymer particles with increasing F(av), attributed to a height artifact caused by differential indentation.
• Phase contrast images provided reliable differentiation of polymer and serum components based on viscoelastic properties, independent of tapping conditions.
• The serum component was observed in localized depressions on films dried at room temperature.

Conclusions:

• Optimizing AFM tapping parameters, specifically F(av), is critical for accurate nanostructural analysis and maximizing contrast between PSA components.
• AFM phase imaging offers a robust method for distinguishing PSA components based on viscoelasticity, overcoming height-related artifacts.
• The study provides insights into the surface morphology of waterborne PSA films, aiding in the design of advanced adhesive materials.