[[The]] effect of grafted brush MW and matrix MW on viscoelastic and mechanical properties of polymer nanocomposites

Giovino, Marissa
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Schadler, L. S. (Linda S.)
Ozisik, Rahmi
Ryu, Chang Yeol
Ullal, Chaitanya
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Materials engineering
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The mechanical properties of polymer nanocomposites will also depend on the grafted brush-matrix interactions. Thin film fracture studies and uniaxial tensile testing on bulk samples were conducted. The materials system for thin film fracture studies was: low loading (1 vol.% SiO2 core) of modified nanoparticles dispersed in low MW matrix (N ~ P) and high MW matrices (N < P). Two surface modifications were used: PS grafted SiO2 and octylsilane grafted SiO2. The onset of crazing was unaffected by matrix MW and surface modification. All composites tested had lower fracture strain than pure matrix regardless of surface modification. Presence of nanoparticles likely destabilized the crazes resulting in earlier failure. Interestingly only the PS grafted SiO2 was incorporated into the craze fibrils. Mechanical testing via uniaxial tensile testing with DIC (digital image correlation) was done on PS grafted SiO2 in low MW (N ~ P) and high MW (2N = P) matrices at different loadings. Low matrix MW composites were predicted to have higher strength due to grafted brush-matrix interactions while high matrix MW composites were expected to have higher toughness due to weak grafted chain-matrix interactions. The low matrix MW composites had higher strength than high MW composites at high loading but lower strength than the pure matrix. The high matrix MW composites had higher toughness at low loadings. SEM images of fracture surfaces revealed voids in high toughness samples. The P/N ratio is important for viscoelastic and mechanical properties of polymer grafted nanoparticle composites.
December 2018
School of Engineering
Dept. of Materials Science and Engineering
Rensselaer Polytechnic Institute, Troy, NY
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