Liquids with high compressibility: experimental demonstration Beibei Lai 1 , John Cahir 1 , Barry Murrer 1 , Siyuan Liu 1 , Tristan Youngs 2 , Jin-Chong Tan 3 , Yueting Sun 4 , Haixia Yin 4 , Mario Del Pòpolo 5 , Sergio Fonrouge 5 , Jose Luis Borioni 5 , Deborah E. Crawford, 1 Francesca M. Alexander 1 , Chunchun Li 1 , Steven E. J. Bell 1 and Stuart L. James 1* 1 School of Chemistry and Chemical Engineering, Queen’s University Belfast, UK, 2 ISIS Pulsed Neutron and Muon Source, STFC Rutherford Appleton Laboratory, UK, 3 Department of Engineering Science, University of Oxford, UK, 4 School of Engineering, University of Birmingham, UK, 5 CONICET and Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Cuyo, Argentina The compressibility of each state of matter differs because there are different particle arrangements in gas, liquid and solid states. Gases are highly compressible because there are large spaces between their constituent molecules. There are only small voids between particles in liquid states, referred to as “extrinsic porosity”. Therefore, conventional liquids can be only compressed to a certain degree, much less than of gases. For example, the volume reduction of water between 1 to 500 bar is only 2-3%. If liquids could be engineered to have greater compressibility, new ways to control the mechanical behavior of hydraulic systems would be possible. Therefore, we have designed aqueous liquids systems to exhibit higher compressibility. Specifically, ZIF-8, a porous material with empty hydrophobic pores, has been dispersed into water to form milk-like dispersions. Due to the hydrophobic nature, water molecules do not enter the pores of the dispersed ZIF-8 particles at low pressures. However, water can be forced into dispersed ZIF-8 particles by applying mechanical pressure which results in an overall volume reduction of the dispersion of 7% over the pressure range 1 to 500 bar. In addition, the compression process is reversible by reducing the applied pressure. The compressibility of these aqueous dispersions is greater than for any conventional liquids. The compression pressure range can be also tuned, for example, by replacing some of the water with methanol the compression occurring at lower pressures. References 1. E. Sann, Y. Pan, Z. Gao, S. Zhan and F. Xia, Sep. Purif. Technol. , 2018, 206 , 186–191 2. O’Reilly, N. Giri and S. L. James, Chemistry , 2007, 13 , 3020–3025. 3. S. Kell, J. Chem. Eng. Data , 1970, 15 , 119–122. 4. Sun, S. M. J. Rogge, A. Lamaire, S. Vandenbrande, J. Wieme, C. R. Siviour, V. Van Speybroeck and J.-C. Tan, Nat. Mater. , 2021, 20 , 1015–1023. 5. Sun, Y. Li and J.-C. Tan, Phys. Chem. Chem. Phys. , 2018, 20 , 10108–10113.
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