Experimental evidence of ultrathin polymer film stratification by AFM force spectroscopy

• Published in: The European physical journal. E, Soft matter and biological physics Vol. 38; no. 6; p. 56
• Main Authors: Delorme, Nicolas, Chebil, Mohamed Souheib, Vignaud, Guillaume, Le Houerou, Vincent, Bardeau, Jean-François, Busselez, Rémi, Gibaud, Alain, Grohens, Yves
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-06-2015; EDP Sciences: EPJ
• Subjects: Biological and Medical Physics; Biophysics; Complex Fluids and Microfluidics; Complex Systems; Condensed Matter; Materials Science; Nanotechnology; Physics; Physics and Astronomy; Polymer Sciences; Regular Article; Soft and Granular Matter; Surfaces and Interfaces; Thin Films; Soft Matter: Polymers and Polyelectrolytes; Soft Matter : Polymers and Polyelectrolytes
• ISSN: 1292-8941; 1292-895X
• DOI: 10.1140/epje/i2015-15056-9

By performing Atomic Force Microscopy measurements of pull-off force as a function of the temperature, we were able to probe the dynamic of supported thin polystyrene (PS) films. Thermal transitions induce modifications in the surface energy, roughness and surface modulus that are clearly detected by AFM and related to PS chain relaxation mechanisms. We demonstrated the existence of three transition temperatures that can be associated to the relaxation of polymer chains located at different depth regions within the polymer film. Independently of the film thickness, we have confirmed the presence of a region of high mobility for the polymer chains at the free interface. The thickness of this region is estimated to be above 7nm. The detection of a transition only present for film thicker than the gyration radius R
g
is linked to the dynamics of polymer chains in a bulk conformation (
i.e.
not in contact with the free interface). We claim here that our results demonstrate, in agreement with other techniques, the stratification of thin polymer film depth profile in terms of relaxation behavior.
Graphical abstract