The structure and dynamics of microparticles at pickering emulsion interfaces

We have employed a laser scanning confocal microscope (LSCM) to study the structure and dynamics of microparticles at Pickering emulsion interfaces. The microparticles can have rich morphology at the emulsion interfaces, ranging from an aggregated structure to colloidal lattices, with a possibility of involving heterogeneous particles. With a specific interest in colloidal lattices, we find that although the enhanced electrostatic repulsion explains the formation of colloidal lattices by sulfate-treated polystyrene (S-PS) particles, it fails to interpret the unsuccessfulness of assembling lattices containing single-species carboxylate-treated polystyrene (C-PS) particles. A small percentage of C-PS particles in the colloidal mixture does not disturb the formation of lattices made of S-PS particles. The LSCM also provides a meaningful way to probe dynamic information. The diffusion of single particles at the emulsion interfaces depends strongly on the oil phase viscosity, particle size, and particle wettability. A highly curved emulsion interface slows the motion of microparticles at oil-water interfaces but the interface curvature effect decreases with increasing oil phase viscosity. Although the confocal microscope was originally used as an imaging tool, we find that the thermodynamic equilibrium of colloidal lattices can be disturbed and even destroyed when increasing the output laser intensity.     

Thermal and mechanical properties of poly(N‐isopropylacrylamide)‐based hydrogels as a function of porosity and medium change

Poly(N‐isopropylacrylamide) (PNIPAAm) has been a well‐known stimuli–responsive material and has been used in multiple novel applications. One of the key attributes to make the hydrogel more attractive is to control the response time and temperature. This work focused on comparing the physical properties, such as response time, transition temperature, heat of fusion, and mechanical strength, of macroporous and microporous PNIPAAm hydrogels, respectively. It was found that the macroporous hydrogels synthesized from a low‐temperature polymerization with addition of tetramethyl orthosilicate exhibited a faster response time and superior mechanical strength. Furthermore, to modulate the transition temperature, both the macroporous and microporous hydrogels were subjected to different qualities of media by introducing a cosolvent (methanol) or an anionic surfactant (sodium dodecyl sulfate). Interestingly, addition of a cosolvent demonstrated a more pronounced effect on the macroporous hydrogel, whereas the surfactant resulted in a more pronounced effect on the microporous hydrogel. Such results revealed that based on their porosity; there were appreciable differences when the PNIPAAm hydrogels interacted with media molecules. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42776.