This title appears in the Scientific Report :
2005
Please use the identifier:
http://dx.doi.org/10.1016/j.jnoncrysol.2005.03.062 in citations.
Polymers in nanocomposites: What can be learned from relaxation and scattering experiments?
Polymers in nanocomposites: What can be learned from relaxation and scattering experiments?
Dielectric spectroscopy in combination with temperature modulated differential scanning calorimetry and quasielastic/inelastic neutron scattering are employed to investigate the molecular (glassy) dynamics of poly(dimethyl siloxane) (PDMS) and poly(methyl phenyl siloxane) (PMPS) confined to random n...
Saved in:
Personal Name(s): | Schönhals, A. |
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Goering, H. / Schick, Ch. / Frick, K. H. / Zorn, R. | |
Contributing Institute: |
Neutronenstreuung; IFF-INS |
Published in: | Journal of non-crystalline solids, 351 (2005) S. 2668 - 2677 |
Imprint: |
Amsterdam [u.a.]
Elsevier Science
2005
|
Physical Description: |
2668 - 2677 |
DOI: |
10.1016/j.jnoncrysol.2005.03.062 |
Document Type: |
Journal Article |
Research Program: |
Kondensierte Materie |
Series Title: |
Journal of Non-Crystalline Solids
351 |
Subject (ZB): | |
Publikationsportal JuSER |
Dielectric spectroscopy in combination with temperature modulated differential scanning calorimetry and quasielastic/inelastic neutron scattering are employed to investigate the molecular (glassy) dynamics of poly(dimethyl siloxane) (PDMS) and poly(methyl phenyl siloxane) (PMPS) confined to random nanoporous glasses with nominal pore sizes between 2.5 nm and 20 nm. Inside the pores PDMS and PMPS have faster molecular dynamics than in the bulk state. Down to a pore size of 7.5 nm the temperature dependence of the relaxation times (or rates) obeys the Vogel/Fulcher/Tammann (VFT) equation where the data obtained from dielectric and thermal spectroscopy agree quantitatively. At a pore size of 5 nm this VFT-like temperature dependence changes to an Arrhenius behavior. At the same confining length scale the increment of the specific heat capacity at T-g normalized to the weight of the confined polymer vanishes. The results indicate that a minimal length scale seems to be relevant for glassy dynamics in both polymers although the estimated length scale of about 5 nm seems to a bit too large in comparison to other experimental results and theoretical approaches. Neutron scattering is employed to investigate methyl group reorientation and the fast segmental dynamics of both polymers in confinement. Although the methyl group rotation is a localized process these experiments show that a part of the methyl groups is immobilized by the confinement whereas the effects for PDMS are much more pronounced than for PMPS. With regard to the segmental dynamics, neutron scattering reveals a big difference in the behavior of both polymers. Whereas the data obtained for PMPS are in accord with a boundary layer formed at the surfaces of the nanopores, for PDMS a considerable amount of elastic scattering is observed. To explain this result it is assumed that some structure formation of PDMS takes place in the nanopores, although the thermal data show no crystallization or melting effects. (c) 2005 Elsevier B.V. All rights reserved. |