Preparation of micron-sized monodispersed thermoresponsive core-shell microcapsules

We have successfully prepared monodispersed thermoresponsive core-shell microcapsules with a mean diameter of about 4 Aim with a porous membrane and with linear-grafted poly(N-isopropylacrylamide) (PNIPAM) chains in the membrane pores acting as thermoresponsive gates. The preparation was carried out by using a Shirasu porous glass (SPG) membrane emulsification technique to prepare small-sized monodispersed oil-in-water emulsions and using interfacial polymerization to prepare the core-shell microcapsules with porous membranes. Plasma-graft pore-filling polymerization was used to graft linear PNIPAM chains into the pores of the. microcapsule membranes. In the SPG membrane emulsification process, the optimum surfactant sodium dodecyl sulfate (SDS) concentration and poly(vinyl alcohol) stabilizer concentration could be selected by solely considering the monodispersity of the emulsion droplets. However, before the interfacial polymerization process was started, these two concentrations needed to be monitored to avoid any aggregation of the microcapsules and, if necessary, the appropriate quantity of SDS or Tween 80 needed to be added to prevent the microcapsules from aggregating in the interfacial polymerization stage. The prepared PNIPAM-grafted monodispersed microcapsules with a mean diameter of about 4 pm showed satisfactory reversible and reproducible thermoresponsive release characteristics. The release of both NaCI and vitamin B-12(VB12) from the PNIPAM-grafted microcapsules was slow at 25 degreesC and fast at 40 degreesC, which is due to the closed/open state of the grafted "gates". The "on/off" ratio of the release rate of VB12 from the PNIPAM-grafted microcapsules was much larger than that of NaCl.