Free Surface Energy of COANP Thin Films Doped with C70 Fullerene: A Study of Concentration Effects

Introduction. Tuning surface properties such as wettability and adhesion in thin-film organic systems is key to their use in optoelectronics and photonics. Surface modification via nanoparticle doping is a promising route for tailoring these properties. Specifically, studying the impact of fullerenes on the free surface energy (FSE) of organic films offer opportunities for engineering materials with targeted functionality, e. g., for use in optical limiters.
Aim. To investigate the effect of C70 fullerene on the FSE and its components (polar and dispersive) of 2-cyclooctylamino-5-nitropyridine (COANP) thin films. FSE was calculated for three samples using the OWRK method based on contact angle measurements.
Materials and methods. The study objects were COANP thin films sensitized with C70 fullerene, spin-coated onto glass substrates. Contact angles were measured using an OCA 15EC setup with distilled water (polar liquid) and liquid petrolatum LP-004836 (nonpolar liquid). Drop profile analysis was performed via ellipse approximation using the software of the setup. Results. Doping the organic film with C70 fullerenes significantly alters its surface: a substantial drop in total surface energy and a major shift in its structure due to a sharp decrease in the polar component. The dependence of surface properties on nanoparticle concentration was established. The contribution of surface modification to nonlinear optical mechanisms, such as laser beam reflection, is discussed, which is crucial for explaining the reduction in transmitted high-power radiation energy in sensitized systems.
Conclusion. The results demonstrate the feasibility of tailoring the surface energy and wettability of COANP thinfilm systems through fullerene sensitization. The established trends show promise for applying these materials in optoelectronic and photonic devices, including optical limiters, modulators, and display elements, where controlled adhesion and nonlinear optical properties are critical.

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