CONICET | Buscador de Institutos y Recursos Humanos

Self-assembly of amphiphilic molecules provides a fundamental mechanism for building complex soft materials. This report describes the preparation of thermoset materials containing self-assembled nanostructures of a low-molecular-weight poly(ethylene oxide)-poly(ethylene) (PEO-b-PE) diblock copolymer dispersed in a epoxy matrix. The preparation of these nanostructured materials involves firstly the dissolution of the block copolymer in an epoxy monomer of the type diglycidyl ether of bisphenol A (DGEBA) at 150 ºC for 5 min. The mixture was then allowed to cool to room temperature and exposed to visible-light in order to polymerize the DGEBA monomer via a cationic photopolymerization mechanism. DGEBA monomer undergoes slow photoinitiated polymerization allowing during this term the growth of block copolymer micelles. After the DGEBA cured, samples looked cloudy with the opacity increasing with the block copolymer content. Transmission electron microscopy (TEM) analysis of samples containing up to 20 wt% PEO-b-PE showed elongated micelles dispersed in the epoxy matrix without any macroscopic phase separation evidence. These micelles were typically on the order of 20 to 30 nm in width with variable lengths, comprised between 1 and greater than 10 microns, depending on block copolymer concentration. Figure 1a shows a TEM image of the sample modified with 10 wt% PEO-b-PE, whereas Figure 1b shows the same sample stained with RuO4. In this last image, PEO appears black, epoxy gray, and PE white. A micelle structure consisting in a semicrystalline PE core surrounded by a PEO shell is revealed. We were able to explore the growth mechanism of these micelles by following the evolution of the DRX (X-Ray Diffraction) pattern corresponding to semicrystalline PE moiety. Additional experiments are currently under study in order to understand the formation mechanism and structural features of this intriguing system.

enviar mensaje