Man-Hin Kwok1, To Ngai2. 1. Department of Chemistry, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong. 2. Department of Chemistry, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong; Shenzhen Municipal Key Laboratory of Chemical Synthesis of Medicinal Organic Molecules, Shenzhen Research Institute, The Chinese University of Hong Kong, Shenzhen 518057, China. Electronic address: tongai@cuhk.edu.hk.
Abstract
HYPOTHESIS: Responsive poly(N-isopropylacrylamide) microgel (PNIPAM microgel) stabilized Pickering emulsions were investigated in this study. A recent theoretical study of other researchers has suggested that large soft particles at the oil/water interface are less deformable than their small counterparts. Therefore, we expected that our micron-sized microgel particles might not significantly deform at the oil/water interface. EXPERIMENTS: We applied confocal laser scanning microscopy (CLSM) to examine the structure of soft PNIPAM-based microgel particles at the decane-water interface in a microgel-stabilized emulsion. Using micron-sized microgel particles with better labelling techniques, we could compensate the weakness in resolution of using CLSM. Seven PNIPAM-based microgel samples with various softness values and morphologies were examined at different pH values. FINDINGS: Our results demonstrate that the deformation of ordinary micron-sized microgel samples was not significant if they were not in the pH-swollen state. Nevertheless, the soft, pH-swollen microgel particles exhibited anisotropic deformation at the decane-water interface. Such flattening was not reported in previous studies. The studies of microgel particles at the oil-water interface with different imaging techniques and their comparison are valuable to help to elucidate the particles' roles in stabilizing the Pickering emulsions.
HYPOTHESIS: Responsive poly(N-isopropylacrylamide) microgel (PNIPAM microgel) stabilized Pickering emulsions were investigated in this study. A recent theoretical study of other researchers has suggested that large soft particles at the oil/water interface are less deformable than their small counterparts. Therefore, we expected that our micron-sized microgel particles might not significantly deform at the oil/water interface. EXPERIMENTS: We applied confocal laser scanning microscopy (CLSM) to examine the structure of soft PNIPAM-based microgel particles at the decane-water interface in a microgel-stabilized emulsion. Using micron-sized microgel particles with better labelling techniques, we could compensate the weakness in resolution of using CLSM. Seven PNIPAM-based microgel samples with various softness values and morphologies were examined at different pH values. FINDINGS: Our results demonstrate that the deformation of ordinary micron-sized microgel samples was not significant if they were not in the pH-swollen state. Nevertheless, the soft, pH-swollen microgel particles exhibited anisotropic deformation at the decane-water interface. Such flattening was not reported in previous studies. The studies of microgel particles at the oil-water interface with different imaging techniques and their comparison are valuable to help to elucidate the particles' roles in stabilizing the Pickering emulsions.