Tuning The Phase Separation Structure And Luminescence Behavior Of Aggregation-Induced Emission Polymer/Liquid Crystal Composites

Polymer/liquid crystal composites exhibit good mechanical properties and processability of polymers and unique response capability of liquid crystals to external forces,and thus have been widely applied in smart windows,flat panel displays and other fields.Aggregation-induced emission(AIE)polymers show strong luminescence at aggregation which enriches the functions of polymers.Therefore,it is of great significance to construct AIE polymer/liquid crystal composites and study the relations of luminescence behaviors to the phase separation structure,which would be beneficial for developing new functional polymer composites and enabling multiple functions in polymer/liquid crystal composites.First,an AIE molecule named tetra-(4-(7-octenyloxy)phenyl)ethylene(TPE-4NOE)was synthesized,based on which AIE polymer/liquid crystal composites with disordered phase separation structure were prepared via thiol-ene click reaction and the influences of liquid crystal content on the phase separation structure and luminescence behavior of composites were studied.Results show that when the liquid crystal content increases from 30 wt% to 70 wt%,the size of the liquid crystal droplets in the composites increases from 7.9 ± 1.4 to 30.9 ± 25.7 μm.In addition,the fluorescence emission intensity is more sensitive to temperature changes and the photocyclization rate upon UV light irradiation becomes faster.However,when the liquid crystal content is fixed,the variation of the liquid crystal droplet size displays negligible effects on the fluorescence emission spectrum,the relationship between fluorescence emission intensity and temperature,and the photocyclization kinetics of the TPE unit.Second,holographic photopolymer/liquid crystal composites were constructed based on acrylate/acrylamide monomers,and TPE-4NOE was immobilized in the polymer network through thiol-ene click reaction.The effect of functional group number of thiols on the phase separation structure and grating diffraction efficiency,along with the relationship between diffraction efficiency and composite luminescence behavior were investigated.Results show that when fixing the contents of TPE-4NOE and liquid crystal while increasing the thiol functional group number,the phase separation of the composites is boosted,leading to an increase of diffraction efficiency from 82% to 98%.However,the fluorescence emission spectrum,the relationship between fluorescence emission intensity and temperature,and photocyclization kinetics of the TPE unite almost does not change when varying the diffraction efficiency.This research would provide theoretical basis to optimiz the performances of AIE polymer/liquid crystal composites.