doi:10.1016/S0022-3093(98)00777-7 
Copyright © 1998 Elsevier Science B.V. All rights reserved.
Spatial uniformity of the β-relaxation in 
-sorbitol
Hermann Wagner and Ranko Richert*
Max-Planck-Institut für Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany
Received 13 April 1998;
revised 22 June 1998.
Available online 25 February 2000.
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Abstract
Signatures of the slow β-relaxation of
-sorbitol as observed by macroscopic dielectric relaxation and solvation dynamics over a wide range of temperatures are compared. The latter technique senses the local dielectric relaxation in the immediate vicinity of a chromophore, which is present only at very low concentrations. The conformity of locally sensitized and macroscopically averaged results for the glassy state indicates that the secondary relaxation is a spatially uniform feature. If the β-process were spatially confined it should not be detectable by solvation probes.
PACS classification codes: 78.47.+p; 64.70.Pf; 77.22.GmSubject-index terms:
R170; D185; M280
Fig. 1.
Dielectric loss curves 
″(ω) of
-sorbitol as a function of temperature in the range 136 K
T302 K. The curves are plotted in steps of 4 K for 136 K
T264 K and in steps of 2 K for 266 K
T302 K. The low frequency wings due to dc-conductivity are drawn as dotted lines.
Fig. 2.
Dielectric properties of
-sorbitol,
′(
ωo) and
″(
ωo), as a function of temperature in the range 120 K
T310 K. The data refer to a fixed frequency
fo=14.7 Hz, corresponding to
ωo ≈ 100 s
−1 and
τo=1/
ωo ≈ 10 ms. The loss curve
″(
T) displays the broad β-process between 150 and 250 K, the α-relaxation near 275 K, and dc-conductivity effects above 290 K (
Tg=268 K). The relative errors are below the symbol size level.
Fig. 3.
Temperature dependence of the S0 ← T1 (0-0) emission energy (symbols, error bars) of QX in
-sorbitol for the time delay
τo=10 ms. The solid line marks
ν(
T) as expected on the basis of the
′(
ωo) data for a dielectrically homogeneous material. The dashed line refers to
ν(
T) expected for the islands of mobility picture as regards the β-relaxation. The inset displays normalized emission spectra for the temperatures
T=170, 265, 280, and 285 K, in the order from high to low emission energy.
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10.0% w/w water. The sub-
= 800 conform to the Kohlrausch-Williams-Watts relaxation law with stretching parameter β decreasing from 0.48 – 0.37 as temperature T decreases from 329 – 283 K. Results of coupling model analysis confirm that existence of an additional dielectric loss maximum (secondary relaxation) is caused by simple activated cooperative conformational transitions of the same type of molecular units in regions of lower density.
