Researchers using the DND-CAT 5-ID-D beamline at the APS are performing combined scattering and deformation experiments to find a more complete picture of the toughening mechanisms in block copolymer modified epoxies.
The team used in situ small-angle X-ray scattering (SAXS) to describe the deformation of block copolymer micelles with either rubbery or glassy cores that serve as modifiers for epoxies with different cross-link densities.
One of the most common toughening strategies for epoxies is modification with second phase rubber particles. Additions of well-designed block copolymers to the uncured matrix have proven to be a particularly effective method to incorporate rubbery domains into the resulting material. This strategy provides significant toughness enhancement over the unmodified material upon addition of small amounts of block copolymer (ca. 5 wt %), while still retaining important properties of the network such as stiffness and glass transition temperature
Real-time deformation events in epoxies with different cross-link density, modified with rubbery and glassy core block copolymer micelles, were captured by collecting small-angle X-ray scattering patterns while simultaneously straining the sample. Analysis and interpretation of the scattering patterns provide quantitative information about deformation processes leading to toughness in these materials. These experiments yielded direct evidence of cavitation in 30 nm rubber particles as anticipated by theory. We found that the extent of void growth after cavitation is strongly affected by the cross-link density of the matrix and is directly correlated to the toughness enhancement of the material. Our findings imply that the combination of micelle and matrix properties strongly affects the processes leading to toughness in block copolymer modified epoxies.
Carmelo Declet-Perez, Lorraine F. Francis and Frank S. Bates, “Deformation Processes in Block Copolymer Toughened Epoxies,” Macromolecules, Article ASAP. DOI: 10.1021/acs.macromol.5b00243, Published May 19, 2015.