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R Richert

Publications and source records attributed to R Richert.

12 recordsLinked to original sources
PubMed2000

Heterogeneous relaxation patterns in supercooled liquids studied by solvation dynamics

We have measured the solvation dynamics of a dipolar supercooled liquid near its glass transition in a temperature range in which the average structural relaxation time varies more than four orders of magnitude. The analysis of the time dependent average emission energy and the inhomogeneous linewidth of the S0<--T1(0-0) transition reveals that the orientation correlation decay pattern intrinsic in each relaxing unit is associated with a stretching exponent beta(intr)=1.00+/-0.08 in the entire range T(g)</=T</=T(g)+6 K. Our analysis also allows one to detect fluctuations in terms of the resulting apparent homogeneity within the long time tail of the decay. Even at times significantly exceeding the average structural relaxation time, no sign of a transition towards purely exponential or otherwise homogeneous behavior could be observed. This implies that even at t approximately 50 (KWW) the individual time constants remain correlated to their initial values at t=0.

Journal Article↗
PubMed2000

Capacitive scanning dilatometry and frequency-dependent thermal expansion of polymer films

The dilatometric properties of polymer films near and above their glass-transition temperatures were explored using capacitive high-frequency detection in temperature ramping as well as in harmonic temperature cycling experiments. The broad applicability of capacitive scanning dilatometry is demonstrated by the investigation of macromolecular systems of vastly different polarity such as polystyrene, polybutadiene, and polyvinylacetate. From temperature cycling experiments the real and imaginary parts of the frequency-dependent thermal-expansion coefficient are determined in the sub-Hz regime.

Journal Article↗