Properties of surface layers of polyethylene naphthalate substrates modified by ultraviolet light irradiation for their electroless deposition

The properties of thin surface layers of polymer substrates should be investigated and controlled for their application in electroless deposition. In this paper, polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) substrates were modified by plasma treatment, ultraviolet (UV)/ozone treatment, or UV (254 nm) irradiation. The chemical and physical properties of the modified layer were studied by measuring contact angle and zeta potential, field-emission scanning electron microscope (FE-SEM) imaging, and infrared spectroscopy. The condition of the surface modification affected oxygenation of the polymer chains. The oxygenation formed hydrophilic surface functional groups and relatively polar low-molecular-weight fragments resulting from the scission of the polymer chains. The surface functional groups and the fragments governed the properties of the modified layer. Adhesive metal films were electrolessly deposited on the thinner modified layer having the hydrophilic functional groups. In contrast, the thicker modified layer containing the fragments decreased the adhesion of the metal films. For example, UV/ozone treatment of the PEN substrate formed the thicker modified layer, on which no adhesive metal films were deposited. These findings illustrate that optimizing the condition of the surface modification thoroughly is feasible to form the modified layer having the chemical and physical properties appropriate for depositing adhesive metal films.