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Polystyrene microgels, small network particles with an overall size in the region of 100 nm, are synthesized via radical copolymerization of styrene and m-diisopropenylbenzene in microemulsion. The resulting structures are characterized by viscosimetry, static and dynamic light scattering (LS), and dynamic mechanical experiments. These microgels represent strictly spherical particles with a moderate polydispersity where the size of the microemulsion droplets can only be adjusted in the restricted range 60 nm < d < 200 nm. This is possibly due to the polymeric surfactant used. The intrinsic viscosity data are related to molecular swelling where the internal density of the particles in dependence of the cross-linking density obeys the rules of rubber elasticity. From LS experiments it is concluded that the swelling occurs heterogeneously even on the size scale given by the microgel dimensions. The application of microgels as a model for macroscopic networks is extended to the examination of the influence of dilution during the crosslinking reaction. The efficiency of cross-linking decreases with increasing amount of solvent. Dynamic mechanical shear experiments of microgels result in a typical rubbery plateau at high frequencies and small strains known also from macroscopic networks. The absolute plateau value indicates a large amount of defects reducing the cycle rank of the network. Dilution during cross-linking causes a qualitative change of the complete spectrum, which exhibits a continuous loss of the moduli toward lower frequencies, a behavior known for systems close to gel transition.ABSTRACT: Conformational dynamics of short probes dispersed in a matrix is investigated. The matrix can be in two states, fast or slow, depending on the amount of free volume. Following the work of Anderson and Ullman,4 the amount of free volume is assumed to fluctuate in time, thus modifying the states of the matrix. The probe undergoes transitions between two states resembling trans-cis isomeric transitions. Correlation times of the probe-matrix system exhibit a clear transition as the free-volume fluctuations of the matrix become faster. In a fast matrix, the temperature dependence of correlation times for probes reflects both the intramolecular conformational barrier in the probe and the energy change of viscous origin in the matrix, while in a slow matrix only the activation energy of the matrix is observed. This is in agreement with the results from recent experiments with fluorescent probes dissolved in small-molecule solvents and in bulk polymer.

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The final step in the supramolecular buildup of eumelanin particles is investigated regarding the involved species and mechanism. Time-resolved in situ light scattering and scanning electron microscopy reveal an aggregation of particles with a narrow size distribution around 40 nm, previously only observed as substructures. These form larger particles with again very uniform size and diameters around 200 nm. Aggregation of each single particle takes only a few minutes to complete, whereas the entire process goes on for at least 3 h, partly due to the kinetics of the precursors. The individual particles also undergo an additional consolidation step toward their final form, which takes up to 24 h. Atomic force microscopy shows that the size before consolidation is around twice the size of the final particles, due to free space between the substructures. Light scattering also reveals that the aggregation is random with respect to where the particles attach, as the shape of aggregates changes from sphere to coil, before it returns to a spherical shape at the end. Application of enzyme mediated autodeposition finally shows the potential to stop the supramolecular buildup at each level, and therefore enables isolation of the respective eumelanin particles at will. This may enable the full potential for melanin materials in nanotechnology deriving from its unique (for biological polymers) properties like paramagnetism, electrical conductivity, and many more.