(Poly) NIPAm On The Preparation And Properties Of N-oct / PMMA Microcapsules

Microcapsules are a kind of new polymeric functional materials, which has some excellent performance, such as thermal energy storage and release, drug control release, excellent protection performance, and so on, and it has great potential values in many fields. Hitherto, there are various technologies for preparing microcapsules, including in situ polymerization, suspension-like polymerization, and interfacial polymerization, internal phase separation, sol-gel method, and spray drying, among others. In this paper, we introduced N-isopropylacrylamide (NIPAm) or N-isopropylacrylamide polymer (PNIPAm) as thermosensitive additive agent into the system for the synthesis of core-shell microcapsules. Microcapsules containing n-octadecane (n-oct) were synthesized by internal phase separation in an emulsion polymerization system, using cross-linked poly methylmethacrylate (PMMA) as the shell, and the sodium salt of styrene-maleic anhydride copolymer (SMA) as emulsifier. The effect of NIPAm or PNIPAm on the formation mechanism, surface morphologies, crystallization properties, and thermal stabilities of the microcapsules was studied using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-Ray diffraction (XRD), and thermogravimetric analysis (TGA), respectively. The results indicate that adding NIPAm into the system conducive to the synthesis of microencapsulated phase change materials (MicroPCMs). And causes a significant increase in the enthalpy of the heterogeneous nucleation (approximately 2 to 4 times more than without its addition), effectively improving the supercooled crystallization behavior of the MicroPCMs. The addition of NIPAm causes a decrease in the particle size of the MicroPCMs and the size distribution becomes narrower (the polydispersity index (PDI) has a minimum of 0.073). In addition, the encapsulation ratio and the encapsulation efficiency increase. On the other hand, if we added PNIPAm into the system, PNIPAm as thermosensitive pore-foaming agent for the synthesis of porous core-shell microcapsules containing n-oct by internal phase separation. The results indicate that adding PNIPAm into the system the resulting microcapsules containing n-oct have some irregular holes on the capsule shell. The number of holes increased with the addition of PNIPAm. At the same time, the number of the holes decreases with the increase of the molecular weight of PNIPAm and the content of MMA, so only the PNIPAm with small molecular weight conducive to the synthesis of porous microcapsules. Lastly, we investigated the particle morphology by thermodynamic analysis according to Torza and Mason’s spreading coefficients theory. The contact angles, interfacial tensions, and spreading coefficients have been calculated for the various systems under the experimental conditions. The results indicate that the addition of NIP Am effectively improved the behavior of core-shell structure forming, and PNIPAm tends to be allocated on the oil-water interface as a pore-foaming agent.