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Glassforming Liquids


Introduction


In contrast to crystals this class of condensed matter is showing no long-range order when supercooled from the liquid state. Still the density and viscosity in the glassy state are high enough to speak of a solid, rigid body. Although the technology of vitrification is well known since archeological times and despite the fact that glass formation by viscous slow down is widely used for a large variety of technical applications, the microscopic mechanism that underlies the glass transition is still far from being understood.

Dielectric spectroscopy is ideally suited to investigate the huge change of the molecular dynamics at the glass transisiton. Recent experimental advances allow for the collection of dielectric spectra over an extremely wide frequency range of more than 18 decades. Those spectra reveal a rich variety of different dynamic processes that are present in glass-forming liquids as schematically shown in the following figure [1]. Typically two cases can be distinguished [2], depending on the occurrence of an excess wing or a β-relaxation, as shown in both frames of the following figure.
 
 

schema

 

 

[1] P. Lunkenheimer, U. Schneider, R. Brand, and A. Loidl, Contemporary Physics 41, 15 (2000); P. Lunkenheimer, U. Schneider, R. Brand und A. Loidl, Physikalische Blätter 56, 35 (2000).
[2] A. Kudlik, S. Benkhof, T. Blochowicz, C. Tschirwitz, and E. Rössler, J. Mol. Struct. 479, 201 (1999).

Examples:

 

 

We kindly encourage the scientific community to request the digital data of these and more experimental results from our group for analysis and testing of theoretical models!
 


Focus of our Investigations

(Click here for publications.)

Broadband dielectric measurements:
Glassformers reveal a rich "zoo" of dynamic processes. By collecting dielectric spectra of different glassformers in a frequency range of more than 18 decades all those processes can be investigated [1-4]. The understanding of those extreme broadband spectra is a challenge for every theory of glassy dynamics. Example...

Alpha-relaxation:
The α-relaxation shows up as a prominent peak in dielectric loss spectra. It mirrors the structural dynamics that shows a tremendeous, but continuous slowing down over many decades when the glass transition is approached. The α-relaxation reveals two hallmark features of glassy dynamics namely non-exponential and non-Arrhenius behavior. Both are investigated in our group (e.g., [3,5]). Due to the broad frequency range available in our experiments, the glassy freezing of molecular dynamics can be followed from the highest temperatures, deep in the liquid region, down to the structural arrest occurring at the glass temperature or even below. Part of those data are available for electronic download. More...

High-Frequency Dynamics:
In recent years the high-frequency response of glass forming materials has found increasing attention. This development was stimulated by the mode coupling theory (MCT) of the glass transition [6] which makes detailed predictions for the high-frequency susceptibility χ in the GHz to THz frequency range. Previous experimental results which were mainly obtained using neutron and light scattering techniques provided evidence for additional fast processes contributing in this regime and often showed good agreement with the theoretical predictions [7]. In addition, there exists a number of competing theoretical approaches and phenomenological descriptions (e.g., [8]). Concerning dielectric measurements there was a lack of data in the relevant high frequency range which is experimentally difficult to access. In comparison with the neutron and light scattering results, the frequency range was not sufficiently wide to investigate the region of the fast process, prevailing in the region of the loss minimum or the boson peak. Utilizing coaxial techniques, the Submillimeter Wave Spectrometer, and the Fourier Transform Infrared Spectrometer, our group is able to acquire dielectric data in a considerably enlarged temperature range and extending well into the THz region. In our broadband dielectric spectra, we found clear evidence for the fast process and also have detected the boson peak in several glassformers [2,9,10]. Example....

Excess Wing:
The occurence of the excess wing, i.e. a second power law at the high-frequency flank of the α-peak in some glassforming materials is a long-standing riddle of glass physics. We have performed time-dependent measurements of the excess-wing region at temperatures below the glass temperature ("aging"), with maximum aging times of up to five weeks. When thermodynamic equilibrium is approached, the excess wing is observed to develop into a shoulder (Examples...). This finding clearly indicates that the excess wing can be ascribed to a secondary relaxation. Most likely it is a manifestation of a β-relaxation that is deeply submerged under the α-peak [11]. This notion is supported by experiments at very high pressures [12].

Glassy Aging Dynamics:
When a glass is cooled below the glass temperature it "falls out of equilibrium". Keeping the glass at a constant temperature, then the so-called "physical aging" takes place, i.e. the physical quantities vary with time when the sample reapproaches equilibrium. We have performed aging experiments in a large variety of different glass formers and analyzed the results using a new approach that is much simpler and more straightforward to apply that those used so far [13]. More...

[1] U. Schneider, P. Lunkenheimer, R. Brand, and A. Loidl, J. Non-Cryst. Solids 235-237 (1998) 173.
[2] U. Schneider, P. Lunkenheimer, R. Brand, and A. Loidl, Phys. Rev. E 59 (1999) 6924.
[3] P. Lunkenheimer, U. Schneider, R. Brand, and A. Loidl, Contemporary Physics 41 (2000) 15.
[4] P. Lunkenheimer, U. Schneider, R. Brand und A. Loidl, Physikalische Blätter 56 (2000) 35.
[5] P. Lunkenheimer, S. Kastner, M. Köhler, and A. Loidl, Phys. Rev. E 81 (2010) 051504.
[6] U. Bengtzelius et al., J. Phys. C 17 (1984) 5915; W. Götze and L. Sjögren, Rep. Progr. Phys. 55 (1992) 241.
[7] for review, see: W. Petry et al., Transp. Theory Statist. Phys. 24 (1995) 1075; H.Z. Cummins, Gen Li, Y.H. Hwang, G.Q. Shen, W.M. Du, J. Hernandez, N.J. Tao, Z. Phys. B 103 (1997) 501.
[8] K.L. Ngai, J Non-Cryst. Solids 274 (2000) 155; D. Kivelson et al., Physica A 219 (1995) 27; V.N. Novikov, Phys. Rev. B 55 (1997) 14685; P.K. Dixon et al., Phys. Rev. Lett. 65 (1990) 1108; R.V. Chamberlin, Phys. Rev. Lett 82 (1999) 2520.
[9] P. Lunkenheimer, A. Pimenov, M. Dressel, Yu. G. Goncharov, and A. Loidl, Phys. Rev. Lett. 77 (1996) 318.
[10] P. Lunkenheimer, A. Pimenov, and A. Loidl, Phys. Rev. Lett. 78 (1997) 2995.
[11] U. Schneider, R. Brand, P. Lunkenheimer, and A. Loidl, Phys. Rev. Lett. 84, (2000) 5560; P. Lunkenheimer, R. Wehn, Th. Riegger, and A. Loidl; J. Non-Cryst. Solids. 307-310 (2002) 336.
[12] A.A. Pronin, M.V. Kondrin, A.G. Lyapin, V.V. Brazhkin, A.A. Volkov, P. Lunkenheimer, and A. Loidl, Phys. Rev. E 81 (2010) 041503.
[13] P. Lunkenheimer, R. Wehn, U. Schneider, and A. Loidl, Phys. Rev. Lett. 95 (2005) 055702.


Materials

The investigations in our group include the following glass formers:

 

Some relevant publications from our group:

(click here for complete list of publications of our group)
  1. Fast dynamics of glass-forming glycerol studied by dielectric spectroscopy
    P. Lunkenheimer, A. Pimenov, M. Dressel, Yu. G. Goncharov, and A. Loidl
    Phys. Rev. Lett. 77, 318 (1996)
  2. Fast dynamics in CKN and CRN investigated by dielectric spectroscopy
    P. Lunkenheimer, A. Pimenov, and A. Loidl
    Phys. Rev. Lett. 78, 2995 (1997)
  3. Ionic transport and heat capacity of glass-forming metal-nitrate mixtures
    A. Pimenov, P. Lunkenheimer, M. Nicklas, R. Böhmer, A. Loidl, and C. A. Angell
    J. Non-Cryst. Solids 220, 93 (1997)
  4. Ionic conductivity and relaxations in ZrO2-Y2O3 solid solutions
    A. Pimenov, J. Ullrich, P. Lunkenheimer, A. Loidl, and C. H. Rüscher
    Solid State Ionics 109, 111 (1998)
  5. Dielectric and Far Infrared Spectroscopy on Glycerol
    U. Schneider, P. Lunkenheimer, R. Brand, and A. Loidl
    Journal of Non-Crystalline Solids 235-237, 173-179 (1998)
  6. Broadband dielectric spectroscopy on glass-forming propylene carbonate
    U. Schneider, P. Lunkenheimer, R. Brand, and A. Loidl
    Phys. Rev. E 59, 6924-6936 (1999); online: Abstract, PDF
  7. Dielectric spectroscopy of glassy dynamics
    P. Lunkenheimer
    Shaker Verlag, Aachen (1999)
  8. Glassy dynamics
    P. Lunkenheimer, U. Schneider, R. Brand and A. Loidl
    Contemp. Phys. 41, 15-36 (2000)
  9. Scaling of broadband dielectric data of glass-forming liquids and plastic crystals
    U. Schneider, R. Brand, P. Lunkenheimer, and A. Loidl
    Eur. Phys. J. E 2 (2000) 67-73; online cond-mat/9902318
  10. Excess wing in the dielectric loss of glass formers: A secondary relaxation?
    U. Schneider, R. Brand, P. Lunkenheimer, and A. Loidl
    Phys. Rev. Lett. 84, 5560 (2000)
  11. Relaxationsdynamik in Gläsern
    P. Lunkenheimer, U. Schneider, R. Brand and A. Loidl
    Phys. Blätter, Juni 2000, p. 35
  12. Excess wing in the dielectric loss of glass-forming ethanol: A relaxation process
    R. Brand, P. Lunkenheimer, U. Schneider, and A. Loidl
    Phys. Rev. B 62, 8878 (2000)
  13. Nature and properties of the Johari-Goldstein β-relaxation in the equilibrium liquid state of type A glass-formers
    K. L. Ngai, P. Lunkenheimer, C. León, U. Schneider, R. Brand, and A. Loidl
    J. Chem. Phys. 115, 1405 (2001)
  14. Dynamic processes at the glass transition
    P. Lunkenheimer and A. Loidl
    Advances in Solid State Physics, Vol. 41, edited by B. Kramer (Springer, Berlin 2001), p. 405
  15. Excess wing in the dielectric loss of glass formers: Further evidence for a β-relaxation
    P. Lunkenheimer, R. Wehn, Th. Riegger, and A. Loidl
    J. Non-Cryst. Solids 307-310, 336 (2002)
  16. Dielectric spectroscopy of glass-forming materials: α-relaxation and excess wing
    P. Lunkenheimer and A. Loidl
    Chem. Phys. 284, 205 (2002)
  17. Glassy dynamics beyond the α-relaxation
    P. Lunkenheimer and A. Loidl
    in Broadband Dielectric Spectroscopy, edited by F. Kremer and A. Schönhals (Springer, Berlin, 2002), chapter 5.
  18. Response of disordered matter to electromagnetic fields
    P. Lunkenheimer and A. Loidl
    Phys. Rev. Lett. 91, 207601 (2003)
  19. Glassy Aging Dynamics
    P. Lunkenheimer, R. Wehn, U. Schneider, and A. Loidl
    Phys. Rev. Lett. 95, 055702 (2005)
    online cond-mat/0503449
  20. Broadband dielectric spectroscopy and aging of glass formers
    R. Wehn, P. Lunkenheimer, and A. Loidl
    J. Non-Cryst. Solids 353, 3862 (2007)
  21. Dielectric spectroscopy in benzophenone: The α-relaxation and its relation to the mode-coupling Cole-Cole peak
    L. C. Pardo, P. Lunkenheimer, and A. Loidl
    Phys. Rev. E 76, 030502(R) (2007)
  22. Broadband dielectric spectroscopy on benzophenone: α relaxation, β relaxation, and mode coupling theory
    P. Lunkenheimer, L. C. Pardo, M. Köhler, and A. Loidl
    Phys. Rev. E 77, 031506 (2008)
  23. Dielectric and conductivity relaxation in mixtures of glycerol with LiCl
    M. Köhler, P. Lunkenheimer, and A. Loidl
    Euro. Phys. J. E 27, 115 (2008)
  24. Glassy dynamics in mono-, di-, and tri-propylene glycol: From the α- to the fast β-relaxation
    M. Köhler, P. Lunkenheimer, Y. Goncharov, R. Wehn, and A. Loidl
    J. Non-Cryst. Solids 356, 529 (2010)
  25. Temperature development of glassy α-relaxation dynamics determined by broadband dielectric spectroscopy
    P. Lunkenheimer, S. Kastner, M. Köhler, and A. Loidl
    Phys. Rev. E 81, 051504 (2010)
  26. High-frequency dynamics of type-B glass formers investigated by broadband dielectric spectroscopy
    S. Kastner, M. Köhler, Y. Goncharov, P. Lunkenheimer, and A. Loidl
    J. Non-Cryst. Solids 357, 510 (2011).
  27. Hydrogen-bond equilibria and lifetimes in a monohydroxy alcohol
    C. Gainaru, S. Kastner, F. Mayr, P. Lunkenheimer, S. Schildmann, H. J. Weber, W. Hiller, A. Loidl, and R. Böhmer
    Phys. Rev. Lett. 107, 118304 (2011).

For further information please contact:
peter.lunkenheimer@physik.uni-augsburg.de