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Abstract:In this work, we compare the properties of smart homopolymer microgels based on N-n-propylacrylamide (NNPAM), N-isopropylacrylamide (NIPAM) and N-isopropylmethacrylamide (NIPMAM) synthesized under identical conditions. The particles are studied with respect to size, morphology, and swelling behavior using scanning electron and scanning force microscopy. In addition, light scattering techniques and fluorescent probes are employed to follow the swelling/de-swelling of the particles. Significant differences are found and discussed. Poly(N-n-propylacrylamide) (PNNPAM) microgels stand out due to their very sharp volume phase transition, whereas Poly(N-isopropylmethacrylamide) (PNIPMAM) particles are found to exhibit a more homogeneous network structure compared to the other two systems.

Thermoresponsive copolymer microgels based on N-n-propylacrylamide (NNPAM) and N-isopropylmethacrylamide (NIPMAM) with varying compositions were synthesized via precipitation polymerization. Photon correlation spectroscopy (PCS) and turbidity measurements were used to investigate their volume phase transition. A linear correlation between the nominal composition and the volume phase transition temperature (VPTT) was observed. Furthermore, the hydrodynamic radii of the particles exhibit a linear dependency on the nominal composition. The presented system is suitable for the synthesis of thermoresponsive microgels with a well defined VPTT or size and gives access to tune these two crucial parameters in a systematic and controlled way by simply choosing the right composition of the monomer feed. Additionally, the first derivatives of the swelling curves obtained from turbidity measurements were analyzed in detail, allowing a quantitative comparison of the phase transition of different microgels.

We investigated the influence of two anionic surfactants, namely, sodium dodecyl sulfate and sodium decyl sulfate, on acrylamide-based microgels consisting of N - n -propylacrylamide. In this context, the main focus was on the influence of surfactant addition on the size of the microgels. The surfactant was added to the reaction mixture before or during the polymerization at different points in time. Microgels were characterized via photon correlation spectroscopy and atomic force microscopy. All results were compared to those for other more common acrylamide-based microgels consisting of N- isopropylacrylamide and N -isopropylmethacrylamide. A significant difference between the three microgels and a strong dependence on the surface activity of the surfactant was found.

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