Cellulose nanocrystal-grafted multi-responsive copolymers containing cleavable o-nitrobenzyl ester units for stimuli-stabilization of oil-in-water droplets

Abstract

• Synthesis of multi-responsive CNC-grafted copolymers by SI-RAFT, • Using the PDMAEMA and poly( o -nitrobenzyl acrylate) as the responsive blocks, • Stabilization of the oil-in-water emulsions by the CNC-grafted copolymers, • Application of the CNC-grafted copolymers in Pickering emulsion polymerization of styrene, • Excellent performance of the CNC-grafted copolymers in photolithography. Hybrid smart surfactants are highly applicable in stabilization of oil-in-water droplets and also Pickering polymerizations. Temperature-, photo-, and pH-responsive cellulose nanocrystal (CNC)-grafted copolymers of N , N ′-dimethylaminoethyl methacrylate (DMAEMA) and o -nitrobenzyl acrylate (NBA) were synthesized in different molar ratio of NBA to DMAEMA via surface-initiated reversible addition-fragmentation chain transfer polymerization. Temperature-, pH-, and light-responsivity of the CNC-grafted polymers were evaluated by Fourier-transform infrared spectroscopy, dynamic light scattering (DLS), zeta potential, and ultraviolet–visible (UV–vis) spectroscopy. Critical flocculation temperature (CFT) of the CNC-grafted polymers was decreased by increasing pH and length of the PNBA block. Photo-cleavage mechanism and kinetics of the o -nitrobenzyl ester groups upon UV light irradiation were experimentally investigated in solutions with different pH values using UV–vis spectroscopy. The CNC-grafted polymers were used to stabilize n -hexane droplets in water and also prepare polystyrene latex by Pickering polymerization before and after exposure to UV light, respectively. Stability of the n -hexane-in-water suspensions was investigated as a function of light irradiation, temperature, pH, and CO 2 by optical microscopy and DLS. The scanning electron microscopy and transmission electron microscopy images showed spherical morphology of the colloidal polystyrene latex samples with particle size in the range of 500–600 nm. Consequently, these hybrid smart surfactants could be highly applicable in the preparation of colloidal polymer particles and oil-in water droplets with switchable stability upon different stimuli.