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We report a novel phenomenon of increasing the adherence of a poly­(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS/PEO) nanofilm for Si3N4 through cosolvent treatment by DMSO. By varying the w/w% ratio of DMSO, nanofilms with different conductivities were produced. Atomic force microscopy (AFM) analysis showed that the adhesive force between the AFM’s Si3N4 probe and the nanofilm increased by 35.8% as the conductivity of the nanofilm increased. The conductivity became saturated after the PEDOT:PSS-to-DMSO ratio reached a certain level. This study demonstrates that the variations in the adhesive force are determined by two factors: (1) the difference in EWF between the nanofilm and the counter-body Si3N4 and (2) the electrical conductivity of the materials involved. The former is used for establishing a dipole layer at the interface, while the latter determines the degree of ease to achieve the dipole layer. This study demonstrates an approach to tailor interfacial bonding for different types of materials without atomic diffusion, which is promising for applications in various fields such as control of biomedical films on implants and functional films for electronic devices.

In this article, we demonstrate the dependence of the adhesive force (F Ad) between two different substances on their electron work functions (EWF or φ) without atomic diffusion involved. The adhesive forces between Si3N4 and a number of metals were measured using an atomic force microscope. It is shown that the larger the difference in φ between the two substances in contact, the larger the F Ad. F Ad is also influenced by the electron freedom and density (related to the charge availability). An analytical model is proposed to elucidate the underlying mechanism and quantify the adhesive interaction.

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We propose a novel method to tune the interfacial adhesive force (Fad) between PEDOT:PSS/PEO organic electroconductive polymer and Si3N4 (a ceramic) by decreasing the electron work function (EWF) and the electrical resistivity of the PEDOT:PSS/PEO nanosheet. By using the known method of preferential solvation using polar aprotic solvent (DMSO), we were able rearrange the spatial orientation of PSSH backbone chain in the polymer and increase the Density of States (DOS) and the electron hopping length (ξ') of the polymer, thus increasing its conductivity. As the material becomes more conductive, the formation of a dipole layer between the Schottky Diode system of PEDOT:PSS/PEO and Si3N4 is facilitated. This leads to the increased interaction between the two materials, raising the adhesive force by 35.8% with only 5% w/w DMSO addition to the polymer. This relatively simple treatment of PEDOT:PSS results in an interfacial adhesion or bonding strength. This approach is general, which would be applicable for enhancing interfacial bonding between two different types of material without atomic diffusion involved.