Temperature responsive microgels undergo a volume phase transition at a certain temperature. Such kind of materials are interesting for various applications, such as drug delivery systems or in catalysis. An optimal performance of microgels requires a method for an adjustment of the application-specific properties. Especially the particle size and the volume phase transition temperature (VPTT) are a matter of particular interest.
In this study we present experimental results regarding the influence of the feed composition, the chemical structure of the incorporated monomers and the amount of surfactant in the synthesis procedure on the properties of copolymer microgels. Therefore, we prepared microgels based on two of the following temperature responsive alkylacrylamides in the presence of different surfactant amounts under equal reaction conditions. The used monomers are N-n-propylacrylamide (NNPAM), N-isopropylacrylamide (NIPAM) and N-isopropylmethacrylamide (NIPMAM) with VPTTs of 22°C, 32°C and 43°C, respectively. For the characterization scanning electron microscopy, dynamic light scattering, small angle neutron scattering, light attenuance measurements and pyrene probe fluorescence measurements were used.
All monomer combinations and feed compositions yielded spherically shaped particles exhibiting a low polydispersity. Adding surfactant in the synthesis reduces the particle size, whereby the strength of the effect is depending on the monomer structure. Interestingly, a linear correlation between size and composition is observed for all systems synthesized in presence of surfactant and the limits of the microgel dimensions are predetermined by the homopolymer systems. Because of that, a precise tuning of the particle size is achievable. Additionally, the VPTT depends also linearly on the composition and this interdependence is not affected by the surfactant. Due to that, a simultaneous tuning of the particle size and the VPTT is possible, which constitutes an important result concerning the usage of microgels for various applications.
bastian.wedel1@uni-bielefeld.de
