Mechanism of the temperature-responsive material regulating porous morphology on epoxy phenolic novolac resin microcapsule surface

Abstract Porous microcapsules (MCs) with tailorable surface morphology are indispensable in practical applications because of their large surface area and controlled release. In this study, epoxy phenolic novolac resin MCs were prepared with temperature-responsive 2,4,6-tris(dimethylaminomethyl)phenol (DMP) as crosslinker. Reaction temperature was proved to generate distinct effects on MC porous morphology, shell thickness, mechanical strength and release behavior. The MC surface varied from nonporous to dense small pores (ca. 237 nm in diameter) with increasing temperature from 40 °C to 70 °C, but they showed decreasing tendency at higher temperature (＞70 °C). The encapsulation process illuminated that DMP aggregates formed and deposited on the loose shells at 60 °C and 70 °C (close to the so-called cloud point (Tscp) of DMP), leading to porous morphology. Nevertheless, at temperature far below or above the Tscp of DMP (＜50 °C or ＞70 °C), DMP kept its solubility in water or insufficiently deposited on the shells, which resulted in no pores existed. Higher temperature promoted the reactivity to generate thicker shells and larger mechanical strength, further leading to prolong payload release. The present work provided an insight about the reaction temperature to prepare tunable MCs, which can be employed to encapsulate lipophilic components in agriculture field.