Transition from spin dewetted droplets to continuous film in a semi-crystalline Polyethylene Oxide thin film

Polymeric thin films are increasingly being utilized for technological applications, such as coatings, functional surfaces, etc. Dewetting and crystallization both play a significant role in determining the film morphology and ultimate film properties. When polyethylene oxide (PEO) is spin coated from a nonpolar solvent (chloroform), crystallization proceeds via formation of spherulites, which correlate well with Avrami kinetics. Spontaneous rupture of the dispensed solution layer during spin coating results in isolated periodic morphologies of the solute at low concentrations (C_n). Here, the morphology of PEO thin films coated on pre-patterned PDMS substrate transforms from spin-dewetted droplets to elongated threads to continuous films with an increase in C_n. We investigated the effects of RPM variation during spin coating on the transition of spin-dewetted morphologies from droplets at lower RPM to continuous film at higher RPM. We further show that within the spin-dewetted regime, with a decrease in solute concentration and increase in RPM, droplet periodicity (λ_D) reduces and number density of droplets increases. Spherulite structures were observed in both spin-dewetted aligned droplets and continuous films; however, lamellar structures were observed in elongated threads.