Mapping Substrate Surface Field Propagation in Block Polymer Thin Films

We isolated the key substrate polymer interactions responsible for the propagation of substrate surface field effects in block polymer (BP) thin films through a modified approach to the Owens and Wendt interfacial energy formalism. This modification captured the influence of long-range surface energy components on through-film nanostructure orientation in BP thin films, and it provides a framework for manipulating BP thin film behavior without the need for extensive parameter space exploration. Optical microscopy (OM) of gradient thickness films on chlorosilane-modified substrates provided a high-throughput approach for identifying the critical propagation depth of substrate polymer interfacial energy effects. Atomic force microscopy (AFM) was combined with OM to verify changes in free surface nanostructure as a function of film thickness. Using a model poly(methyl methacrylate-b-n-butyl acrylate) BP thin films system, we mapped the critical propagation depth as a function of interfacial energy difference and found a nearly linear increase in propagation depth at low interfacial energy differences followed by the onset of a plateau at high interfacial energy differences. Our results connect seemingly disparate trends found in the substrate surface field propagation literature and demonstrate a more translatable approach for improving BP thin film through-film orientation via appropriate chemical tailoring of substrate surfaces.