Han Goossens

Self-healing systems based on disulfide–thiol exchange reactions

New thermoset systems based on disulfide bonds were synthesized with self-healing capabilities. The self-healing mechanism is not related to disulfide–disulfide exchange reactions, but to thiol–disulfide exchange reactions that are pH-dependent. Stress relaxation experiments showed large relaxation for systems having PTM2 as a curing agent, which indicates that the system can rearrange its molecular structure as a mechanism to release stress. However, relaxation rates decreased for samples tested longer after production. This indicates the disappearance of thiol-groups probably caused by thiol–thiol oxidation.

Influence of drying procedure on glass transition temperature of PMMA based nanocomposites

Abstract A literature review of poly(methyl methacrylate) (PMMA) nanocomposites shows inconsistent results regarding the influence of the addition of nanofillers on the mobility of the system. In academic research, solvent based preparation methods are often used to prepare nanocomposites with the aim to obtain a good and controlled dispersion. However, little attention is paid to the influence of the used solvent on the properties of the nanocomposites. We show that in PMMA nanocomposites prepared via solution casting from different solvents, the apparent decrease in glass transition temperature is caused by insufficient drying and that when an adequate drying procedure is used, an increase in glass transition temperature is always observed.

Submicrometer thermoplastic vulcanizates obtained by reaction-induced phase separation of miscible poly(ε-caprolactone)/dimethacrylate systems

Abstract Reaction-induced phase separation of initially miscible mixtures of poly(E-caprolactone) (PCL) and elastomer precursors based on difunctional methacrylate resins was applied to prepare thermoplastic vulcanizates (TPVs) with rubber particle sizes ranging from 80 to 900 nm. The radicals formed by the peroxide decomposition initiate the formation of a cross-linked rubber network with gel contents exceeding 90%, but also abstract hydrogen atoms from the aliphatic moieties in PCL. This leads to the formation of PCL-grafted rubber particles, which show a high nucleating efficiency for crystallization of the PCL matrix. It is demonstrated that the tensile and elastic properties of these TPVs are determined by a complex interplay of the morphology, the type of elastomer precursor, the extent of PCL grafting, the crystallinity, and the lamellar thickness. The materials showed a rheological behavior that is typical for TPVs, for which the melt changes from an elastic to a viscous behavior above a critical ...

Co-extruded multilayer polymer films for photonic applications

Co-extrusion through a series of layer-multiplying die elements enables the production of polymer films containing tens to thousands of layers with individual layer thicknesses from the micro- to the nanoscale. The use of polymers with different refractive indexes allows to fabricate, with a simple and inexpensive process, narrowband one-dimensional photonic crystals. Tunability of the photonic gap can be achieved by proper choice of the materials or of the dies, varying the contrast in refractive indexes or the number and thickness of the individual layers. The use of elastomeric polymers offers the opportunity to modify the UV–VIS spectral response of the 1-D photonic crystals simply by deformation of the film. Finally, co-extrusion of multi-layer polymeric films revealed to be an enabling technology, which allows the realization of new polymeric optical devices, going from flexible lasers to gradient refractive index lenses.