Preparation of n-octadecane nanocapsules by using interfacial redox initiation in miniemulsion polymerization

Abstract

In recent years, various kinds of phase change material (PCM) as energy storage materials have been widely studied. Important features of PCM are high enthalpy change near temperature of use, high density, non-toxicity, low cost, and abundance. PCMs can be divided into organic and inorganic materials, and which are encapsulated as microor nano-size particular shapes with organic, inorganic, polymeric, and hybrid materials, in order to avoid leakage of PCM and enhance thermal responsibility. Therefore, encapsulation of PCM seems indispensable in applications of fibers, interior or exterior of buildings, heat exchangers, electronic materials, and optical materials. For this, several encapsulation techniques have been developed; for example, free-radical polymerization, interfacial polymerization, in-situ polymerization, coacervation, and so on. In free-radical polymerization, thermal initiators are generally used to initiate the vinyl or acryl monomers, and the representatives can be potassium persulfate (KPS) and 2,2'azobisisobutyronitrile (AIBN) for the preparation of PCM/ polymer capsules. However, the encapsulation efficiency in these systems varies significantly with polymerization conditions or ingredients. In addition, it is not easy to get high encapsulation efficiency in the encapsulation of PCM with less than 100 nm scale. This work aims to prepare PCM/polymer core/shell nanocapsules with having high encapsulation efficiency by using interfacial redox initiation system. With regard to initiation system, cumene hydroperoxide (CHP, oil-soluble oxidant) and tetraethylenepentamine (TEPA, water-soluble reductant) were used to encapsulate n-octadecane (as PCM) in the presence of styrene and methyl methacrylate monomers, respectively.