Evaluation of the interactions between polymeric chains and surfaces with different structures performed by an atomic force microscope

Abstract

Interactions between polymers and inorganic surfaces are present in a series of phenomena involving processes such as coagulation and deffloculation of ceramic powder and adsorption of organic macromolecules on the surface of implants, among others. In this work, Atomic Force Microscopy (AFM) was modified to allow the evaluation of interactions between polymeric chains and inorganic surfaces (silica) with different structures. Polymers (sulfonated polysulfone) were grafted onto AFM cantilevers. AFM force-distance curves were obtained for this modified tip against a series of substrates produced by depositing silica films on silicon wafers. The structure of the silica layer was modified by employing heat treatments at different temperatures. The results showed that the interactions between polymer and surfaces are dependent on the structure of the surfaces. Penetration of the polymeric chains can occur through a soft gel layer (substrates treated at low temperature, 110 °C). For surfaces with dense silica layers, the results showed that not only the concentration of hydroxy groups but also their spatial distribution along the surfaces are important in defining the magnitude of interactions between polymers and surfaces. A model involving a molecular recognition process, in which interactions are maximized for inorganic surfaces with structures that can match the chemical architecture of the polymer, was then used to explain the obtained results

An Atomic Force Microscopy Study of the Interactions Involving Polymers and Silane Networks

“…Finally the grafted spheres were washed extensively with dimethylformamide, to remove any non-bonded polymer. The success of the grafting technique was confirmed with XPS results [15] . The modified silica spheres were then attached onto AFM silicon nitride cantilevers.…”

“…In Figure 2, a drawing representing the whole technique developed to measure interactions between surfaces and polymeric entities grafted on modified AFM tips (glass sphere with polymer grafts) is shown [15] . In this scenario, the polymer chains are being brought continuously in and out of contact with the surface.…”

“…The polymer chosen was a sulfonated polysulfone (SPSF), because this polymer can readily interact with functional groups present in the amino silane networks, such as amine groups, through hydrogen bond formation, and eventually through the formation of primary sulfonamide bonds. This same procedure involving the modification of AFM tips with SPSF grafts was successfully employed in another work to study the interactions between polymers and inorganic surfaces [15] .…”

Sulfonation of Poly(arylene Ethers) and ABA Triblock Copolymers With a Mild Sulfonation Agent

“…The infrared spectra of sPEES samples do not show a clear presence of characteristic bands of sulfonic groups due to the overlapping of sulfone groups on backbone chain with signals from sulfonic acid. Nonetheless, it is possible to identify in Figure the presence of a shoulder around 1025 cm −1 associated with SO 3 stretching of sulfonic groups …”

Atomic Force Microscopy

“…Treatment of the aminosilane with boiling water, which destroys the silane network, was shown to significantly reduce silane-polymer adhesive forces (155). Similarly, the authors showed correlation between maximum adhesive forces and silanol and sulfonic acid groups as well as mechanical entanglements (156). Adhesion between glass and HDPE or LDPE (low density polyethylene) was measured using afm.…”