Synthesis and Investigation of Stimuli-Responsive Amphiphilic Latex Nanoparticles by the Seeded Emulsion Polymerization

Stimuli-responsive amphiphilic core-shell polymer nanoparticles are important categories of smart materials which have been studied due to their advantages of changing physical or chemical properties in response to stimuli. In this study, poly[2(dimethylamino)ethyl methacrylate] (PDMAEMA) as the hydrophilic core with hydrophobic layer polystyrene (PS) as shell were synthesized by the seeded emulsion polymerization to achieve dual-sensitive core-shell nanoparticles (CSNP). Temperature and CO2 dually-responsive CSNPs were investigated as two important smart behaviors. The CSNPs were characterized by dynamic light scattering (DLS) and scanning electron microscopy (SEM). In addition, two essential parameters including the polymerization conversion and stability of latex polymers were investigated. Obtained results showed that the hydrophilicity-hydrophobicity balance of the latex nanoparticles could be changed by the variation of temperature and the induction of CO2 gas flow, as a result of temperature and CO2 dual-responsivities of the PDMAEMA core. The particle size of the CSNP was increased when the temperature rised above the lower critical solution temperature (LCST) of the PDMAEMA. It is due to the formation of hydrogen bonds between water molecules and the tertiary amine group which leads to swelling in PDMAEMA below the LCST, and deswelling by losing water above the LCST of the PDMAEMA. Furthermore, the size of the latex nanoparticles was increased from 696 nm to 853 nm after CO2-bubbling which led to increasing hydrophilicity or swelling of PDMAEMA by absorbing water in latex nanoparticle.