We report a molecular engineered random terpolymer platform comprising 1D photonic cholesteric mesophases (half pitch length: 150-200 nm) in conjunction with microphase segregated PEG domains. Furthermore, we report for the first time, bulk material consisting of entrapped helical 1D photonic domains with the coexistence of microphase segregated domains retaining photonic reflection and improved mechanical features provided by dual level networks: a) optimal interchain UV-crosslinking with thiol-ene chemistry (b) physical junction points provided by microphase segregated domains. To this end, we synthesize poly(norbornene) based LCRTP architecture bearing side chains containing cholesteryl mesogens (NBCh9), cyanobiphenyl mesogens (NBCB12/NBCB6) and semicrystalline PEG (Mn = 2000 g/mol) (NBPEG) by Ring Opening Metathesis Polymerization (ROMP). Compression molding of LCRTP material at 90 °C and subsequent quenching yields the film with stabilized cholesteric mesophase capable of reflecting visible light. Judicious selection of amounts of cholesteric and smectogenic/nematogenic monomers lead to molecular level interaction between liquid crystalline domains to obtain a change in pitch length of cholesteric helices exhibiting red-shift in the reflection wavelength as compared to random copolymer control sample of NBCh9 and NBPEG (processed at 90 °C). For the retention of optical reflection after crosslinking, it is very important to optimize the extent of crosslinking so that delicate helical mesophases are not disrupted. Sample with optimized crosslinker content (1.75 wt %, 1.75 XL) exhibited retention of optical reflection along with improved mechanical features studied by Dynamic Mechanical Analysis. Interestingly, 1.75 XL sample exhibited one way shape memory properties based on Tcl (liquid crystalline clearing temperature) due to dual networking sites. The combination of structural control by molecular level design and mechanical integrity by physical and chemical crosslinking offers a versatile platform for development of functional stimuli responsive materials, optical sensors and actuators.

Stable entrapment of cholesteric 1D photonic domains in Liquid Crystalline Random Terpolymer (LCRTP) architecture with dual covalent and physical networking sites: A platform towards elastomeric 1D photonic material

253rd National Meeting (2017)

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