Surface Characterization of Oxyfluorinated Isotactic Polypropylene Films:  Scanning Force Microscopy with Chemically Modified Probes and Contact Angle Measurements

Abstract

The surface of isotactic polypropylene (iPP) films modified by oxyfluorination was studied by a combination of complementary techniques to elucidate the effect of the modification on the chemical composition, surface energy, and morphology. The elemental composition was measured by X-ray photoelectron spectroscopy (XPS), and the surface free energy was characterized by contact angle measurements with different liquids. Following the approach by Good and co-workers, the acid−base characteristics of the modified polymer surfaces were estimated. Subsequently, the modified iPP films were investigated by scanning force microscopy (SFM). In tapping mode SFM, the sample topography was imaged and the surface roughness was quantitatively determined. Gold-covered SFM probes modified with carboxylic acid and methyl terminated self-assembled monolayers of thiols were used to determine the pull-off force distributions in ethanol. The interaction of the treated polymer film surfaces with chemically functionalized SFM tips was shown to correlate with the surface tensions obtained by contact angle measurements. In particular, pull-off forces measured with carboxylic acid functionalized tips in ethanol depended approximately linearly on the basic part of the surface free energy of the polymer film surface.

Chemical force microscopy of chemical and biological interactions

“…we also note that this type of probe tip functionalization is also common in CFM studies of polymer surfaces. The topic of CFM of polymers deserves a separate consideration due to the complex of interactions that arise during these measurements; we will not consider it here and instead point the reader to work by Vancso group [17,18,19].…”

Chemical force microscopy: probing chemical origin of interfacial forces and adhesion

“…Applications of CFM to polymers also deserve a separate summary (e.g. see work by the Vancso group [14][15][16][17][18][19][20][21]). In addition, while CFM uses chemical sensitivity of friction forces to map the distribution of the chemical functionality on the surface [9], we will only mention relevant studies in the context of adhesive contact between functionalized tips and samples.…”

Modeling of Adhesion in Tablet Compression—I. Atomic Force Microscopy and Molecular Simulation

“…Numerous researchers have tried to test the JKR theory for AFM force measurements 13–16. The peak height and area of the “pull‐off” peak on the retracting curve in the force–displacement plot are the adhesion force and the total work of adhesion for a particular system, respectively, in a given environment 14,15,17–20. According to Israelachvili,21 the work of adhesion is defined as the work needed to separate the tip and the sample surface in a given medium per unit contact area.…”