Connecting the Wetting and Rheological Behaviors of Poly(dimethylsiloxane)-Grafted Silica Spheres in Poly(dimethylsiloxane) Melts
Using dynamic light scattering, mechanical rheometry, and visual observation, the static wetting behavior of PDMS-grafted silica spheres (PDMS-g-silica) in PDMS melts is related to their rheology. A phase diagram is mapped out for a constant grafted chain length as a function of grafting density and...
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Veröffentlicht in: | Langmuir 2006-11, Vol.22 (23), p.9546-9553 |
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Format: | Artikel |
Sprache: | eng |
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Zusammenfassung: | Using dynamic light scattering, mechanical rheometry, and visual observation, the static wetting behavior of PDMS-grafted silica spheres (PDMS-g-silica) in PDMS melts is related to their rheology. A phase diagram is mapped out for a constant grafted chain length as a function of grafting density and free polymer chain length. The transition between stable and aggregated regions is determined optically and with dynamic light scattering. It is associated with a first-order wetting transition. In the stable region Newtonian behavior is observed for semidilute suspensions. The hydrodynamic brush thicknesses, deduced from viscosity measurements, correspond closely to values obtained from self-consistent field calculations for the various parameter values. At the transition, the brush collapses suddenly and shear-thinning and thixotropy appear. The rheology indicates a degree of aggregation that increases with increasing length of the free polymer, as suggested by the theory. |
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ISSN: | 0743-7463 1520-5827 |
DOI: | 10.1021/la061136z |