Competition Between Chemical Network Formation and Physical Adsorption and Desorption Processes in a Silica-Filled Silicone Rubber: Calorimetry versus Refractometry Studies

in Journal of Adhesion (2012), 88(7), 649-663

Calorimetry and high-performance refractometry are applied to study the network formation and accompanying morphological changes in reactive polydimethylsiloxane systems filled with silica nanoparticles ... [more ▼]

Calorimetry and high-performance refractometry are applied to study the network formation and accompanying morphological changes in reactive polydimethylsiloxane systems filled with silica nanoparticles. Both methods give insight into the structure formation during the polymerization of silica-filled silicone nanocomposites in an impressively complementary way. It will be shown that the specific heat flow as determined by calorimetry does not allow for estimating the chemical conversion whereas the refractive index does, which results from the different perspectives of both techniques on the relevant polymerization, adsorption, and desorption processes occurring in the nanocomposites. Finally, the interphase formation in the polymeric matrix in the vicinity of the nanoparticles and the network formation within the silicone rubber are demonstrated to be strongly correlated processes. [less ▲]

Interactions between silica nanoparticles and an epoxy resin before and during network formation.

in Polymer (2009), 50(14), 3211-3219

In polymer nanocomposites, interactions between filler particles and matrix material play a crucial role for their macroscopic properties. Nanocomposites consisting of varying amounts of silica ... [more ▼]

In polymer nanocomposites, interactions between filler particles and matrix material play a crucial role for their macroscopic properties. Nanocomposites consisting of varying amounts of silica nanoparticles and an epoxy resin based on diglycidyl ether of bisphenol A (DGEBA) have been studied before and during network formation (curing). Rheology and mainly temperature modulated differential scanning calorimetry (TMDSC) have been used to investigate interactions between the silica nanoparticles and molecules of the epoxy oligomer or molecules of the growing epoxy network. Measurements of the complex specific heat capacity before curing showed that interactions between the nanoparticles and DGEBA molecules are very weak. An expression for an effective specific heat capacity of the silica nanoparticles could be deduced. Examination of the isothermal curing process after addition of an amine hardener yielded evidences for a restricted molecular mobility of the reactants in the cause of network formation. These restrictions could be overcome by increasing the curing temperature. No evidences for an incorporation of the silica nanoparticles into the epoxy network, i.e. for a strong chemical bonding to the network, were found. Interactions between the silica nanoparticles and the epoxy resins under study are assumed to be of a physical nature at all stages of network formation. [less ▲]

Acoustic Profilometry Of Interphases In An Epoxy Due To Segregation and Diffusion Using Brillouin Microscopy.

in New Journal of Physics (2008), 10(2), 023-031

Reactive network forming polymer systems like epoxies are of huge technological interest because of their adhesive properties based on specific interactions with a large variety of materials. These ... [more ▼]

Reactive network forming polymer systems like epoxies are of huge technological interest because of their adhesive properties based on specific interactions with a large variety of materials. These specific interactions alter the morphology of the epoxy within areas determined by the correlation length of these interactions. The changed morphology leads to interphases with altered (mechanical) properties. Besides these surface-induced interphases, bulk interphases do occur due to segregation, crystallization, diffusion, etc. A new experimental technique to characterize such mechanical interphases is μ-Brillouin spectroscopy (μ-BS). With μ-BS, we studied interphases and their formation in epoxies due to segregation of the constituent components and due to selective diffusion of one component. In the latter case, we will demonstrate the influence of changing the boundary conditions of the diffusion process on the shape of the interphase. [less ▲]

Temperature modulated Differential Scanning Calorimetry: The Dynamic Aspect of the Specific Heat Capacity and its Relation to Entropy Production

in Beiträge zur Experimentalphysik, Didaktik und computergestützten Physik (2007)