Dynamic mechanical analysis of confined glass-forming liquids

Abstract

Acoustic spectroscopy is a valuable tool, when the degrees of freedom of a material couple to strain. Since this is the case for molecular glass-forming liquids the dynamic mechanical response is a quantity of primary interest here. Dynamic mechanical analysis measurements (0.1–100 Hz) have been performed for salol, toluene and ortho-terphenyl confined in mesoporous (2.5–10 nm) silica matrices. Important parameters (relaxation times τ of the slow α-relaxation, change of T _g with pore size, number and size of dynamically correlated molecules, etc.) characterizing the glass freezing in the three glass-forming liquids have been extracted from the measurements for various confining pore sizes. A comparison with literature data shows excellent agreement and demonstrates that mechanical measurements provide a very sensitive tool to probe the dynamics of molecular glass forming liquids in confined systems.

Keywords:

• glasses
• confinement
• dynamic mechanical analysis
• dynamic heterogeneities
• relaxors

Acknowledgements

This study was supported by the Austrian FWF project (P19284-N20). We also thank Irena Drevensek-Olenik and Miha Devetak from the Jozef-Stefan Institute in Ljubljana for help concerning silanation, which was done within the ÖAD-WTZ project SI 19/2009.

Notes

1. Philip W. Anderson, a Nobel Prize-winning physicist at Princeton, wrote in 1995: “The deepest and most interesting unsolved problem in solid state physics is probably the theory of the nature of glass and the glass transition.” In New York Times, 29 July 2008.