Electrodynamic-contact-line-lithography with nematic liquid crystals for template-less E-writing of mesopatterns on soft surfaces

We report the development of a single-step, template-less and fast pathway, namely, Electrodynamic-Contact-Line-Lithography (ECLL), to write micro to nanopatterns on the surface of a soft polymer film. As a model system, a layer of nematic liquid crystals (NLC), resting on a polymer thin film, was sandwiched between a pair of electrodes emulating the electrowetting on a dielectric (EWOD) setup. Upon the application of electric field, the Maxwell stresses thus generated at the NLC-polymer interface due to the high dielectric contrast stimulated an unprecedented fingering instability at the advancing NLC-polymer-air contact line. In the process, the advancing electrospreading front of NLC left the footprint of an array of micro to nanoscale wells on the polymer surface with a long-range ordering thus unveiling a pathway for maskless patterning of a soft elastic film. Unlike the conventional electric field induced lithography (EFL), the meso-scale morphology was found to follow the short wavelength-scales as the periodicity of the patterns (λ_c) varied linearly with the thickness of the film (h), (λ_c∝h). The high dielectric contrast at the NLC-polymer interface and the local fluctuation of the NLC directors ensured a time scale much faster than the same observed for the polymer-air systems.