Photopolymerization

Glass substrates were cleaned by successive sonication in 2-propanol and acetone baths (20 min each), and dried under the flow of nitrogen gas. For planar alignment, two glass slides were spin coated with 1 wt% water solution of polyvinyl alcohol (PVA, Sigma Aldrich; 4000 RPM, 1 min) and rubbed unidirectionally using a satin cloth. After rubbing, the PVA substrates were blown with high-pressure nitrogen to remove dust particles from the surfaces. For splayed alignment, the glass slides were spin coated with PVA as before and a homeotropic alignment layer (JSR OPTMER, 5000 RPM, 1 min), and baked at 180 °C for 20 min. For cell preparation, two coated substrates were fixed together with UV glue (UVS 91, Norland Products Inc., Cranbury, NJ), using spacer particles (Thermo scientific, 10, 20, or 50 µm) to define the cell thickness. The mixture was then infiltrated into the cell on a heating stage at 90 °C and cooled down to 50 °C with a rate of 3 °C min⁻¹. An LED (Prior Scientific; 420 nm, 11 mW cm⁻², 30 min) was used to polymerize the LC mixture. A linear polarizer (Thorlabs, LPVISE100-A, extinction ratio >100) was placed in between the light source and the sample, with orientation perpendicular to the alignment direction in order to minimize the cis-isomer concentration induced by the polymerization. The polymerized film together with cross-polarized microscope images are shown in Supplementary Figure ¹⁰. The cell was opened, and strip-like LCNs were cut out from the film using a blade.