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Evolution of the dynamic susceptibility in molecular glass formers: Results from light scattering, dielectric spectroscopy, and NMR
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10.1063/1.4770055
/content/aip/journal/jcp/138/12/10.1063/1.4770055
http://aip.metastore.ingenta.com/content/aip/journal/jcp/138/12/10.1063/1.4770055
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

(a) Dynamic susceptibility of o-terphenyl (normalized by relaxation strength of the α-process) as a function of frequency obtained from depolarized light scattering (tandem-Fabry-Perot interferometry and double monochromator); 90 relaxation regimes are indicated; dashed lines: “hybrid model” including α- and fast relaxation contribution, dotted lines: corresponding Cole-Davidson fit of α-peak with stretching parameter = 0.64. (b) Spectra of glycerol; 73 different colors signal different relaxation regimes (cf. text); flattening of the low-frequency side of the susceptibility minimum is described by a power-law with exponent γ = 0.19 (dotted line).

Image of FIG. 2.
FIG. 2.

The correlation function, (t), obtained from photon correlation spectroscopy (PCS) as well as from tandem-Fabry-Perot interferometry (DM/TFPI) data after Fourier transformation; dash-dotted line: fit by Kohlrausch law including excess wing contribution, solid blue line: correlation function at = 290 K shifted to coincide with that at T = 207 K; dotted line: amplitude of slow dynamics. 108

Image of FIG. 3.
FIG. 3.

Time constants (T) for o-terphenyl (OTP), 90,113,116 m-tricresyl phosphate (m-TCP), 5,95,114 picoline, 70 and glycerol 3,5,49,73,115 as obtained by different techniques. Solid lines are fits by Eq. (2) .

Image of FIG. 4.
FIG. 4.

Minimum scaling (data from Fig. 1 ): reduced susceptibility vs. reduced frequency; below some temperature the scaling fails. (a) o-terphenyl; envelope of high-temperature data interpolated by a sum of two power-laws with exponent = 0.65 and = 0.33 in agreement with prediction of MCT. (b) Glycerol, colors correspond to those in Fig. 1(b) ; dotted line: interpolation with sum of two power-laws (adapted from Ref. 73 and 90 ).

Image of FIG. 5.
FIG. 5.

(a) Dielectric loss of glycerol, 3 and propylene carbonate 84 (scaled by static susceptibility). Emergence of the excess wing contribution (arrow) is recognized; dashed line: phenomenological interpolation. 122 (b) Dynamic susceptibility (normalized by relaxation strength of α-process) of m-tricresyl phosphate as obtained by light scattering: 108 DM/TFPI spectra and PCS data transformed into the frequency domain; numbers indicate temperature; dashed lines: full interpolation of α-peak, excess wing and fast dynamics with temperature independent parameters , , and , respectively.

Image of FIG. 6.
FIG. 6.

Rescaled OKE data vs. reduced time t/τ of benzophenone (BZP), 77 pulse-response representation of the dielectric data of glycerol 51 and PCS data of m-tricresyl phosphate (m-TCP); 108 dashed lines indicate intermediate power-law/excess wing, dotted lines von-Schweidler law and α-process, respectively.

Image of FIG. 7.
FIG. 7.

(a) Susceptibility spectra of the fast dynamics after subtracting -peak and excess wing contributions from the overall susceptibility; dashed line: power-law ν0.33 of the fast dynamics; shaded area: relaxation strength 1 – of the fast dynamics (adapted from Ref. 90 ). (b) 1 – for α-picoline and o-terphenyl (LS), and glycerol (DS) as a function of temperature. 90,121

Image of FIG. 8.
FIG. 8.

(a) Comparing susceptibilities of m-tricresyl phosphate as obtained from PCS (circles), from 31P NMR 95 (pentagons) and dielectric spectroscopy (diamonds); (b) susceptibility master curves of glycerol compiled from field-cycling 1H NMR (pentagons), 134 dielectric spectroscopy (circles; DS) 135 and DM/TFPI (crosses) 73,135 and PCS (solid circles); 108 dashed (blue) lines: interpolations assuming a relaxation described by a Cole-Davidson function (β = 0.64) together with a power-law contribution with exponent = 0.2; arrow indicates factor 3 between the amplitudes of the excess wing.

Image of FIG. 9.
FIG. 9.

Data of m-tricresyl phosphate from dielectric spectroscopy (DS), photon correlation spectroscopy (PCS) and NMR in the step-response representation normalized by the relaxation strength of α-process and excess wing (data from Fig. 8(a) , see text). 108

Image of FIG. 10.
FIG. 10.

(a) Dielectric spectra of dimethyl phthalate (DMP) disclosing two secondary processes in addition to an α-peak. (b) Corresponding relaxation times. 141

Image of FIG. 11.
FIG. 11.

Comparison of the susceptibilities of dimethyl phthalate (DMP) from photon correlation spectroscopy (PCS) 108 and dielectric spectroscopy (DS); 141 the β-process is not probed by PCS, instead an excess wing is observed.

Image of FIG. 12.
FIG. 12.

(a) 2H NMR solid-echo spectra at different inter-pulse distances (see inset) for type-B glass formers; plastic crystal cyano cyclohexane (CCH), structural glasses toluene (TOL) and ethanol (ETH); spectra shown for comparable correlation times = 10 μs ( < ). (b) Corresponding spectra of the type-A glass former glycerol not displaying changes. (c) NMR spectra of cyano cyclohexane at > ( = 20 μs) revealing line-shape changes due to a loss of spatial hindrance of the β-process. 92,96,152

Image of FIG. 13.
FIG. 13.

(a) Spin-lattice relaxation time T as a function of the time constant of the β-process: plastic crystal cyano cyclohexane, neat structural glass formers toluene and ethanol, and binary structural glass chlorobenzene-d/decalin (b) corresponding dielectric relaxation strength Δɛ/Δɛ data from Refs. 49, 92, and 96 , and 152 .

Image of FIG. 14.
FIG. 14.

(a) Susceptibility spectra of ethyl benzene obtained by applying DM/TFPI; blue curves: reflect glassy dynamics; red curves: “simple liquid” dynamics approaching the boiling point ; green dashed line: interpolation with hybrid model assuming MCT relations for the exponents and (b) Corresponding time domain representation of the data. 154

Image of FIG. 15.
FIG. 15.

Reorientational correlation times of molecular liquids obtained by dielectric spectroscopy (open symbols) and light scattering (full symbols); for trinaphthylbenzene (TNB) and o-terphenyl viscosity data are included; 155,156 numbers in K: ; straight dashed lines: high-temperature Arrhenius behavior; solid lines: full fit by Eq. (2) (adapted from Ref. 112 ).

Image of FIG. 16.
FIG. 16.

Reduced activation energy (T)/ plotted vs. a reduced temperature scale in order to provide a master curve for all investigated molecular liquids; color code like in Fig. 15 (adapted from Ref. 112 ).

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/content/aip/journal/jcp/138/12/10.1063/1.4770055
2013-01-03
2014-04-17
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Evolution of the dynamic susceptibility in molecular glass formers: Results from light scattering, dielectric spectroscopy, and NMR
http://aip.metastore.ingenta.com/content/aip/journal/jcp/138/12/10.1063/1.4770055
10.1063/1.4770055
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