Hydrophobic core/shell particles via miniemulsion polymerization

[摘要] Hydrophobic core/shell latex particles were synthesized for use in barrier coatings using theminiemulsion polymerization process. Particles with liquid or with hard cores weresuccessfully synthesized using miniemulsion as a one-step nanoencapsulation technique.Different materials, including an oil (hexadecane, HD) and two different waxes (paraffin andmicrocrystalline wax), were used as the core of the particles. The shell of the particles wasmainly made from a copolymer containing three relatively hydrophobic monomers, namelymethyl methacrylate (MMA), butyl acrylate (BA) and vinyl neodecanoate (Veova-10).Before any further investigations could be carried out, it was important to determine themorphology of the synthesized core/shell particles at the nanometer level. Particlemorphology was mainly determined by two different techniques: transmission electronmicroscopy (TEM) and atomic force microscopy (AFM). TEM was used to directly visualizethe morphology of the investigated core/shell particles at the nanometer level, while AFMwas used to confirm the formation of these core/shell particles. AFM was a powerfultechnique with which to study the particle morphology of the core/shell latices during thefilm formation process.As a second part of the study, the effect of various factors on the hydrophobicity and barrierproperties of the resulting films produced from the synthesized core/shell latices to water andwater vapour was investigated. This included the effect of: (i) the surfactant concentration,(ii) the wax/polymer ratio for both waxes, (iii) the molecular weight of the polymeric shell,(iv) the amount of the most hydrophobic monomer used (Veova-10), and (v) the degree ofcrosslinking in the polymeric shell.Results showed that all the above-mentioned factors had a significant impact on the watersensitivity of the resultant films prepared from the synthesized core/shell latices. It wasfound that the presence of wax materials as the cosurfactant, instead of HD, in theminiemulsion formulation could significantly improve the hydrophobicity and barrierproperties of the final films to water and water vapour. In addition, increasing the amount ofwax, Veova-10, and the molecular weight of the resultant polymeric shell, led to a significantincrease in the hydrophobicity and barrier properties of the resultant latex films. In contrast,hydrophobicity and water barrier properties decreased drastically as the quantity of surfactantand degree of crosslinking increased in the final latex films.

[发布机构] Stellenbosch University