Pore decoration on microcapsule surface using nonionic surfactant micelles as template: Temperature effect and encapsulation mechanism investigation

In the present work, in situ polymerization method was used to prepare nearly monodispersed microcapsules with long chain normal alkanes as core and melamine–formaldehyde (M–F) resin as shell at reaction temperature both above and below the cloud point of nonionic surfactant. A previously neglected point has been clarified, i.e., changing the reaction temperature is proved to be an effective way to tune the microcapsule size, surface pore size and density. Nano-scaled pores (from 5 to 200 nm) on the microcapsule surface were formed by the self-assembly template of nonionic surfactant micelles at different reaction temperatures. The dynamic morphological evolution in the encapsulation process was illustrated, for the first time, by scanning electron microscopy (SEM) at different reaction time. It is the alteration of the hydrophilic–lipophilic balance of crosslinked M–F preploymer in the polymerization process that leads the micelle droplets to migrate inside out, and consequently forms nano- or submicron-pores on the microcapsule surface. The prepared microcapsules have close inner space, providing a good 3-dimensional environment for the confined crystallization of alkanes within the polymeric shell. This methodology is versatile and effective for the synthesis of other porous microspheres, which can be applied potentially for encapsulating lipophilic functional materials.