title: The peculiar behavior of the molecular dynamics of a glass-forming liquid confined in native porous materials - the role of negative pressure.
abstract: In this paper, we combine Broadband Dielectric Spectroscopy (BDS) at ambient and high pressure, and positron annihilation lifetime spectroscopy (PALS) data of 2-ethylhexanol in the bulk state and when infiltrated in native silica nanopores to elucidate the relative role of surface effects on the Debye and structural relaxation processes under 2D spatial constraints. We show that the two processes have different sensitivities to (i) the changes in density as quantified by the EV/Hp ratio and (ii) the degree of confinement. Significant enhancement of the dynamics of the confined molecules at low temperatures is related to the vitrification of the interfacial molecules (Tg,int) affecting the packing density of the core molecules. This is corroborated by the PALS measurements, which demonstrated that the effective volume for the confined samples is slightly higher and seems to be temperature invariant below Tg,int. Consequently, negative pressure systematically develops with lowering temperature reaching values of -100 and -110 MPa (depending on the pore size) at the glass transition temperature. This result offers a better understanding of the counterbalance between surface and finite size effects as well as the role of negative pressure in controlling the dynamics and the glass transition of liquids under 2D spatial restrictions.
authors: Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice, Poland. magdalena.tarnacka@smcebi.edu.pl and Silesian Center for Education and Interdisciplinary Research, University of Silesia, 75 Pulku Piechoty 1A, 41-500 Chorzow, Poland.
authors: Magdalena
authors: M
authors: Tarnacka
authors: Institute of Experimental Physics I, University of Leipzig, Linnestrasse 5, 04103 Leipzig, Germany and Leibniz Institute of Surface Modification (IOM), Permoserstrasse 15, 04318 Leipzig, Germany.
authors: Wycliffe K
authors: WK
authors: Kipnusu
authors: Department of Pharmacognosy and Phytochemistry, Medical University of Silesia in Katowice, School of Pharmacy with the Division of Laboratory Medicine in Sosnowiec, Jagiellonska 4, 41-200 Sosnowiec, Poland.
authors: Ewa
authors: E
authors: Kaminska
authors: Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice, Poland. magdalena.tarnacka@smcebi.edu.pl and Silesian Center for Education and Interdisciplinary Research, University of Silesia, 75 Pulku Piechoty 1A, 41-500 Chorzow, Poland.
authors: Sebastian
authors: S
authors: Pawlus
authors: Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice, Poland. magdalena.tarnacka@smcebi.edu.pl and Silesian Center for Education and Interdisciplinary Research, University of Silesia, 75 Pulku Piechoty 1A, 41-500 Chorzow, Poland.
authors: Kamil
authors: K
authors: Kaminski
authors: Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice, Poland. magdalena.tarnacka@smcebi.edu.pl and Silesian Center for Education and Interdisciplinary Research, University of Silesia, 75 Pulku Piechoty 1A, 41-500 Chorzow, Poland.
authors: Marian
authors: M
authors: Paluch