A confocal microscopy study of micron-sized poly(N-isopropylacrylamide) microgel particles at the oil–water interface and anisotopic flattening of highly swollen microgel

• Published in: Journal of colloid and interface science 2016-01, Vol.461, p.409-418
• Main Authors: Kwok, Man-hin, Ngai, To
• Format: Article
• Language: English
• Subjects: Acrylic Resins - chemistry; Anisotropy; Confocal laser scanning microscopy; Emulsions - chemistry; Gels - chemistry; Hydrogen-Ion Concentration; Micron-sized microgel; Microscopy, Confocal; Oils - chemistry; Particle Size; PNIPAM; Surface Properties; Water - chemistry
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2015.09.049

Confocal laser scanning microscopy (CLSM) was applied to examine the structure of responsive soft PNIPAM microgel particles at decane/water interface in a microgel-stabilized emulsion. The deformation of ordinary, micron-sized microgel samples was not significant if they were not at pH-swollen state. However, the soft, pH-swollen microgel particles showed anisotropic deformation at the decane–water interface. [Display omitted] 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. 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. 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.