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SUMMARY:New understanding of liquid thermodynamics and supercritical state
  - Kostya Trachenko\, Queen Mary\, University of London
DTSTART:20160512T131500Z
DTEND:20160512T141500Z
UID:TALK65386@talks.cam.ac.uk
CONTACT:Gareth Conduit
DESCRIPTION:Physics textbooks commonly derive and discuss equations for en
 ergy and heat capacity for gases and solids but not for liquids. Landau & 
 Lifshitz Statistical Physics textbook states (twice) that liquid energy ca
 n not be calculated in general form\, in contrast to solids and gases. The
  reason for this was summarized by Landau as "liquids have no small parame
 ter". Here\, based on the old idea of J Frenkel\, I formulate the problem 
 in the language of phonons\, and calculate liquid energy and heat capacity
  for both classical and quantum cases. The resulting equation relates heat
  capacity of the liquid to its relaxation time with no fitting parameters\
 , and is compared with the experimental data of several liquids\, includin
 g metallic\, noble\, molecular and network liquids [1]. I subsequently dis
 cuss how thermodynamic properties of the liquid change above the critical 
 point using the recent idea that the mean-free path defines the minimal wa
 velength of longitudinal phonons in the system and our recent finding of t
 he crossover of liquid specific heat in the supercritical state [2]. I fin
 ally discuss the new Frenkel line recently proposed to exist in the superc
 ritical state of matter [2]. Contrary to the existing view\, we have shown
  that the supercritical state is not physically homogeneous in terms of it
 s properties\, but exists in two distinct states: ‘rigid’ liquids and 
 ‘non-rigid’ gas-like fluids separated by a dynamic transition across t
 he Frenkel line on the phase diagram. All major properties of the system\,
  including diffusion\, viscosity\, thermal conductivity\, speed of sound a
 nd heat capacity as well as structure all undergo qualitative changes at t
 he Frenkel line\, from the liquid-like to gas-like.\n\n[1] K. Trachenko an
 d V.V Brazhkin\, Collective modes and thermodynamics of the liquid state\,
  Rep. Prog. Phys. 79\,  016502 (2016)\n\n[2] V.V. Brazhkin and K. Trachenk
 o\, Physics Today 65\, 68 (2012)\; Phys. Rev. Lett. 111\, 145901 (2013)\; 
 Nat. Comm. 4\, 2331 (2013)
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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