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Cross‐Linking Density and Temperature Effects on the Self‐Assembly of SiO 2 —PNIPAAm Core–Shell Particles at Interfaces
Author(s) -
Özlem Nazli Kadriye,
Pester Christian W.,
Konradi Artjom,
Böker Alexander,
van Rijn Patrick
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201203900
Subject(s) - materials science , pickering emulsion , scanning electron microscope , particle (ecology) , polymer , shell (structure) , silicon dioxide , polymerization , self assembly , chemical engineering , emulsion polymerization , chemical physics , adsorption , nanotechnology , nanoparticle , composite material , chemistry , oceanography , geology , engineering
SiO 2 –PNIPAAm core–shell microgels (PNIPAAm=poly( N ‐isopropylacrylamide)) with various internal cross‐linking densities and different degrees of polymerization were prepared in order to investigate the effects of stability, packing, and temperature responsiveness at polar–apolar interfaces. The effects were investigated using interfacial tensiometry, and the particles were visualized by cryo‐scanning electron microscopy (SEM) and scanning force microscopy (SFM). The core–shell particles display different interfacial behaviors depending on the polymer shell thickness and degree of internal cross‐linking. A thicker polymer shell and reduced internal cross‐linking density are more favorable for the stabilization and packing of the particles at oil–water (o/w) interfaces. This was shown qualitatively by SFM of deposited, stabilized emulsion droplets and quantitatively by SFM of particles adsorbed onto a hydrophobic planar silicon dioxide surface, which acted as a model interface system. The temperature responsiveness, which also influences particle–interface interactions, was investigated by dynamic temperature protocols with varied heating rates. These measurements not only showed that the particles had an unusual but very regular and reversible interface stabilization behavior, but also made it possible to assess the nonlinear response of PNIPAAm microgels to external thermal stimuli.