A Photochemical Approach to Directing Flow and Stabilizing Topography in Polymer Films

Abstract

Coatings and substrates with topographically patterned features will play an important role in efficient technologies for harvesting and transmitting light energy. In order to address these applications, a methodology for prescribing height profiles in polymer films is presented here. This is accomplished by photochemcially patterning a solid-state, sensitized polymer film. After heating the film above its glass transition temperature, melt-state flow is triggered and directed by the chemical pattern. A second light exposure was applied to fully activate a heat-stable photo-crosslinking additive. The features formed here are thermochemically stable and can act as an underlayer in a multilayered film. To exemplify this capability, these films were also used to direct the macroscopic film morphology of a block copolymer overlayer.

Marangoni Instability Driven Surface Relief Grating in an Azobenzene-Containing Polymer Film

“…Hence, the flow directionality shown in Figure goes against a viscosity gradient driven flow. , In another example, Seki and co-workers have demonstrated that a polymer phase change from crystalline to amorphous upon light exposure can drive flow. , Since our polymer is completely amorphous (as confirmed by DSC Figure S4 and cross-polarized optical microscopy), the polymer flow in this study was clearly not driven by a phase transition. Although some studies suggest phase change, viscosity, and/or surface tension gradients can be combinatorial and synergistic to drive even more flow, , here, careful selection of our model polymer allowed elimination of these alternative mechanisms.…”

“…30,46 Since our polymer is completely amorphous (as confirmed by DSC Figure S4 and cross-polarized optical microscopy), the polymer flow in this study was clearly not driven by a phase transition. Although some studies suggest phase change, viscosity, and/or surface tension gradients can be combinatorial and synergistic to drive even more flow, 47,48 here, careful selection of our model polymer allowed elimination of these alternative mechanisms.…”

Symmetry plays a key role in the erasing of patterned surface features

“…Perturbations can be created atop a polymer film, on a mesoscopic length-scale in a variety of ways. Unfavourable wetting properties [33][34][35][36][37], electrohydrodynamic instability [38][39][40], Marangoni flow [41][42][43][44], and thermocapillary forces [45][46][47][48][49] can all drive a flat film away from a uniform film thickness. The film viscosity η, surface tension γ, and unperturbed film thickness h 0 , are three parameters that influence the effective mobility of a film, which affects the relaxation of an applied surface perturbation.…”

Modulating Solubility and Enhancing Reactivity of Photo-Cross-Linkable Poly(styrene sulfonyl azide-alt-maleic anhydride) Thin Films

“…In polymer applications the ability to easily tailor the physical state and properties of a material is often more desirable than precisely defining its molecular structure. With this perspective in mind, highly active chemistries which indiscriminately form covalent adducts with preformed, inert polymers are potentially useful as universal cross-linkers, surface modifiers, , and coating stabilizers . Benzophenone, − nitrene, and ketene chemistries have recently been employed to these ends.…”

“…With this perspective in mind, highly active chemistries which indiscriminately form covalent adducts with preformed, inert polymers are potentially useful as universal cross-linkers, surface modifiers, , and coating stabilizers . Benzophenone, − nitrene, and ketene chemistries have recently been employed to these ends. To realize the full potential of indiscriminate grafting chemistries, a quantitative understanding of how various factors affect network outcomes is needed, in addition to simple validation.…”