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Register a new userDynamic mechanical analysis of supercooled water in nanoporous confinement
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Wilfried Schranz WS
Publication date
2020
fields
Physics
and research's language is
English
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Dynamical mechanical analysis (DMA)(f=0.2 - 100 Hz) 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 T=80 K 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 waters so called no mans land, in parts of the pores. Two distinct relaxation peaks are observed around T1 = 145 K (P1) and T2 = 205 K (P2) 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 Ea=0.47 eV, in good agreement with literature values. It is suggested that P1 corresponds to the glass transition of supercooled water far from pore walls, whereas P2 reflects the dynamics of water molecules near the surface of the pores. The observation of a pronounced softening of the Youngs modulus around 165 K (for Gelsil 2.6 nm at 0.2 Hz) is in agreement with 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 Tg(1/d=0)=136 K, i.e. the traditional value of water.
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Water shapes and defines the properties of biological systems. Therefore, understanding the nature of the mutual interaction between water and biological systems is of primary importance for a proper assessment of biological activity and the development of new drugs and vaccines. A handy way to characterize the interactions between biological systems and water is to analyze their impact on water density and dynamics in the proximity of the interfaces. It is well established that water bulk density and dynamical properties are recovered at distances in the order of $sim1$~nm from the surface of biological systems. Such evidence led to the definition of emph{hydration} water as the thin layer of water covering the surface of biological systems and affecting-defining their properties and functionality. Here, we review some of our latest contributions showing that phospholipid membranes affect the structural properties and the hydrogen bond network of water at greater distances than the commonly evoked $sim1$~nm from the membrane surface. Our results imply that the concept of hydration water should be revised or extended, and pave the way to a deeper understanding of the mutual interactions between water and biological systems.
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