On the Crucial Role of Surfaces and Interfaces in Polymer Thin Films, Coatings and Adhesives

Polymeric materials are increasingly used as thin films or coatings with end-use dimensions approaching those of individual polymer molecules. As they become smaller, the surface-to-volume ratio increases, emphasizing the crucial role of polymer surfaces and interfaces [1]. Research in this field investigates phenomena such as wettability, surface energy, surface structuration, chain dynamics in confined conditions, adhesion, and friction, which are important for applications in coatings; paints; adhesives; polymer hybrids and composites; multilayer polymer films for electronics; and biomaterials [2].

To successfully incorporate polymer thin films and coatings into functional devices, several prerequisites must be met, including dedicated surface chemical functions, controlled surface energy, micro- and/or nano-scale topography, porosity, adapted stiffness or flexibility, and improved durability and sustainability [3]. Tuning these properties necessitates knowing and controlling the polymer chains characteristics at interfaces [4]. However, the complexity of interfaces, as well as the difficulties of studying hidden structures, make it difficult to unravel the relationships between the interface properties, enhanced performance and final applications of polymer thin films and coatings. Therefore, fundamental knowledge of surface science associated with multi-scale advanced microscopic and spectroscopic surface characterization techniques [5] is necessary to investigate these pathways.

Thus, even though broad generalization is challenging, important concepts have to be addressed regarding the crucial role of surfaces and interfaces in polymer thin films, coatings and adhesives. These are based on the control of wetting phenomena at surfaces and/or interfaces by amending the surface chemistry and/or roughness and porosity—considering that interfacial forces act per the “actual” contact area and require close molecular contact—and on the gradient of properties at surfaces and interfaces such as polymer chain-selective adsorption, diffusion across interfaces and/or formation of an interphase/weak boundary layer that will control interfacial strength and energy dissipation mechanisms during the separation process. Considering that high-dissipation mechanisms depend on bonding chemistry, mechanical properties, temperature and speed [6], these factors must be targeted, as they mitigate crack propagation and increase resistance to failure and, thus, final properties, durability and sustainability.

Understanding these concepts substantially aids in determining the relationship between surfaces and interface characteristics, and in improving the properties of polymer thin films, coatings or adhesives. This is because these concepts are interrelated and constitute practical and efficient guidelines to promote interdisciplinary, multi-technique and multi-scale approaches in the field of polymer surface science.

Considering these guidelines, the Reprint of the Special Issue of Surfaces “Surface science: polymer thin films, coatings and adhesive” presents cutting-edge original research articles discussing surface and interface properties and phenomena, contributing to the development of new polymer-based thin films, coatings and adhesives. The presented articles address new chemical (nanoimprinting coupled with controlled graft polymerization) and physical (plasma activation) surface treatments to prepare surface-functionalized polymer-based films and fibers or to enhance corrosion protection. Wettability challenges are also highlighted in this Reprint, demonstrating how Marangoni flow drives self-assembly of hydrogels. The core focus of the Reprint is on the development of advanced coatings, with original articles discussing new polyurethane preventive coatings, functional polyacrylate textile coatings and waterborne acrylic coatings. Finally, some of the published articles discuss enhancement of the properties (fracture toughness, wear), performance and sustainability of polymer films and coatings.