Visualisation and characterisation of heterogeneous bimodal PDMS networks

The existence of short-chain domains in heterogeneous bimodal PDMS networks has been confirmed
visually, for the first time, through confocal fluorescence microscopy. The networks were prepared using
a controlled reaction scheme where short PDMS chains were reacted below the gelation point into
hyperbranched structures using a fluorescent silicone compatible cross-linker. The formation of the
hyperbranched structures was confirmed by FTIR, 1H-NMR and size exclusion chromatography (SEC).
The short-chain hyperbranched structures were thereafter mixed with long-chain hyperbranched
structures to form bimodal networks with short-chain domains within a long-chain network. The
average sizes of the short-chain domains were found to vary from 2.1 to 5.7 mm depending on the
short-chain content. The visualised network structure could be correlated thereafter to the elastic
properties, which were determined by rheology. All heterogeneous bimodal networks displayed
significantly lower moduli than mono-modal PDMS elastomers prepared from the long polymer chains.
Low-loss moduli as well as low-sol fractions indicate that low-elastic moduli can be obtained without
compromising the network's structure