Mapping the coating failure modes of electroless plated metal on ABS polymer with micro-nano structured interface

Electroless plating is the default industrial process for depositing glossy metallic coatings on polymeric parts, most often made of acrylonitrile-butadiene-styrene (ABS) plastic. Unfortunately, the adhesion of plated metals on ABS requires harsh acid etching of the polymer, leaving hazardous chemical waste. We recently offered "Greener electrochemical plating of ABS polymer with unprecedented adhesion via hierarchical micro-nano texturing". Understanding of the coating failure mechanism at the micro-nano structured interface would allow programming the adhesion strength via the topographical design of the interface. This study develops a theoretical map of coating failure modes versus geometrical parameters of the metal-polymer interface and validate via precise nanofabrication experiments. The ABS polymer was hot embossed with 2-6 & mu;m wide, 2-6 & mu;m deep microtextures, then it was acid-etched for 1 min to superpose nano-texture over the micro-textures prior to the electroless Cu plating, coating peeling test, and microscopic characterization of the fractured interface. We observed four coating failure modes: (1) adhesive failure at interface, (2) mixed adhesive/cohesive failure, (3) cohesive failure of metal, and (4) cohesive failure of polymer; the last one demonstrated the highest peeling forces. Surprisingly, the proportionality of the adhesion force to the texture aspect ratio was valid only up to a certain threshold, beyond which the adhesion forces falls down due to the fail of metal. The results presented here allows one to control/program the adhesion strength at the metal-polymer interface and optimize the microtexture of ABS parts for greener electroless plating and durable coating adhesion.