Structural Characterization of Amphiphilic Star-Polymer Co-Networks

The structure of amphiphilic star-polymer model co-networks is simulated in a selective solvent for one polymer. For sufficiently large repulsive interactions, dense clusters form with an increasing asphericity and connectivity to the surrounding domains for increasing polymer content at network preparation. We test different types of labeling the network or the solvent regarding the information that is accessible from the network. A labeling with maximum contrast between both types of polymers is most suitable for determining the onset of the nano-phase separation. Labeling only the phase separated domains provides the clearest information on the statistics of the clusters, leading to a pronounced peak in the scattering intensity. For nearly spherical domains, analyzing peak height and domain spacing allows to determine the aggregation number of the domains. Our analysis shows that the nano-phase separated star polymer co-networks can be understood as a set of connected micelles where the statistics of the micelles and their connections encodes the different elastic properties. This explains why the equilibrium swelling degrees in a selective solvent can decouple from network modulus, which is qualitatively different from randomly cross-linked polymer blends or solutions.