Revealing the pure confinement effect in glass-forming liquids by dynamic mechanical analysis

Autor(en)

Johannes Koppensteiner, Wilfried Schranz, Michael Allan Carpenter

Abstrakt

The dynamic mechanical response of mesoporous silica with coated inner surfaces confining the glass-forming liquid salol is measured as a function of temperature and frequency (1–100 Hz) for various pore sizes (2.4–7.3 nm). Compared to former results on natural pores, a distinct acceleration of dynamics due to the removal of surface-related retardation of molecular dynamics is found now, which can be fitted by a homogeneous relaxation using an unmodified Vogel-Fulcher-Tammann relation. This lubrication effect leads to a stronger decrease in the glass transition temperature Tg with decreasing pore size. The present data allow to quantify and separate competing side effects as surface bondings and negative pressure from the pure confinement induced acceleration of molecular dynamics with decreasing pore size. We analyze the dynamic elastic susceptibility data in terms of a recently proposed procedure [C. Dalle-Ferrier et al., Phys. Rev. E 76, 041510 (2007)], which relates the number Ncorr,T of molecules, whose dynamics is correlated with a local enthalpy fluctuation, to the three-point dynamic susceptibility chi T. The observed increase of Ncorr,T with decreasing temperature strongly indicates that the size xi of dynamic heterogeneities increases when approaching the glass transition.

Organisation(en)

Physik Funktioneller Materialien

Externe Organisation(en)

University of Cambridge

Journal

Physical Review B

Band

81

Anzahl der Seiten

8

ISSN

1098-0121

DOI

https://doi.org/10.1103/PhysRevB.81.024202

Publikationsdatum

2010

Peer-reviewed

Ja

ÖFOS 2012

1030 Physik, Astronomie

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/7b458dbb-da63-4a41-86e5-44b282356a07