Dynamic mechanical analysis of supercooled water in nanoporous confinement

¹ University of Vienna, Faculty of Physics, Physics of Functional Materials - Boltzmanngasse 5, A-1090 Wien, Austria
² Institute of Materials Physics and Technology, Hamburg University of Technology (TUHH) - Eißendorfer Str. 42, D-21073 Hamburg-Harburg, Germany

Received: 3 June 2016
Accepted: 25 August 2016

Abstract

Dynamical mechanical analysis is used to study the dynamics of confined water in mesoporous Gelsil (2.6 nm and 5 nm pores) and Vycor (10 nm) in the temperature range from to 300 K. Confining water into nanopores partly suppresses crystallization and allows us to perform measurements of supercooled water below 235 K, i.e., in water's so-called “no man's land”, in parts of the pores. Two distinct relaxation peaks are observed in tan δ around and for Gelsil 2.6 nm and Gelsil 5 nm at 0.2 Hz. Both peaks shift to higher T with increasing pore size d and change with f in a systematic way, typical of an Arrhenius behaviour of the corresponding relaxation times. For P₁ we obtain an average activation energy of , in good agreement with literature values, suggesting that P₁ corresponds to the glass transition of supercooled water. The observation of a pronounced softening of the Young's modulus around 165 K (for Gelsil 2.6 nm at 0.2 Hz) supports the conjecture of a glass-to-liquid transition in the vicinity of P₁. In addition we find a clear-cut (1/d)-dependence of the calculated glass transition temperatures which extrapolates to , in agreement with the traditional value of water.