Counterbalance between Surface and Confinement Effects As Studied for Amino-Terminated Poly(propylene glycol) Constraint in Silica Nanopores
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Altres documents de l'autoria: Kiprop Kipnusu, Wycliffe; M. Elmahdy, Mahdy; Elsayed, Mohamed; Krause-Rehberg, Reinhard; Kremer, Friedrich
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http://dx.doi.org/10.1021/acs.macromol.8b02687 |
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Títol
Counterbalance between Surface and Confinement Effects As Studied for Amino-Terminated Poly(propylene glycol) Constraint in Silica NanoporesAutoria
Data de publicació
2019Editor
American Chemical SocietyISSN
0024-9297; 1520-5835Cita bibliogràfica
Counterbalance between Surface and Confinement Effects As Studied for Amino-Terminated Poly(propylene glycol) Constraint in Silica Nanopores Wycliffe K. Kipnusu, Mahdy M. Elmahdy, Mohamed Elsayed, Reinhard Krause-Rehberg, and Friedrich Kremer Macromolecules 2019 52 (4), 1864-1873 DOI: 10.1021/acs.macromol.8b02687Tipus de document
info:eu-repo/semantics/articleVersió de l'editorial
https://pubs.acs.org/doi/10.1021/acs.macromol.8b02687Versió
info:eu-repo/semantics/publishedVersionResum
Broadband dielectric spectroscopy (BDS) and orthopositronium annihilation lifetime spectroscopy (PALS) are combined to study the
molecular dynamics and the free volume of poly(propylene glycol) terminated
with amino ... [+]
Broadband dielectric spectroscopy (BDS) and orthopositronium annihilation lifetime spectroscopy (PALS) are combined to study the
molecular dynamics and the free volume of poly(propylene glycol) terminated
with amino end groups (PPG-NH2) in the bulk state and when confined in
native and silanized unidirectional silica nanopores with average diameters of
4, 6, and 8 nm. In the bulk state, three dielectric relaxation processes are
observed: (i) the fast β-relaxation assigned to the librational fluctuations of
the −O−NH2 moiety, (ii) the α-process corresponding to the dynamic glass
transition, and (iii) the (slower) chain dynamics or normal mode (NM)
relaxation. Under confinement in native nanopores, the β-process becomes
slower, while the α and the normal mode relaxation processes become faster and broader and demonstrate a lower dielectric
strength with decreasing pore diameter. In silanized nanopores the normal and β-processes are nearly bulklike, but the α-process
still remains faster than bulk closer to the Tg. All these findings can be comprehended as controlled by the counterbalance
between surface and confinement effects. The former are caused by attractive interactions with the solid walls of the nanopores
(resulting in an additional slower process which is removed after silanization), and the latter are caused by an increase of the f ree
volume of the polymer segments due to a less efficient packing as proven by orthopositronium annihilation lifetime
spectroscopy. These results conform to the cooperative free volume model (CFV). [-]
Publicat a
Macromolecules 2019, 52.Proyecto de investigación
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