Niels Boye Olsen

Time-Temperature Superposition in Viscous Liquids

Dielectric relaxation measurements on supercooled triphenyl phosphite show that time-temperature superposition (TTS) is obeyed for the primary relaxation process at low temperatures. Measurements on other molecular liquids close to the calorimetric glass transition indicate that TTS is linked to an omega(-1/2) high-frequency decay of the loss, while the loss peak width is nonuniversal.

Scaling of β-relaxation in the equilibrium liquid state of sorbitol

Abstract The Johari–Goldstein dielectric β-relaxation has been studied in the molecular liquid, sorbitol. In the narrow temperature interval in which α- and β-relaxation are separated (still being in the equilibrium liquid state), it is shown that β-relaxation has a temperature-dependence of loss peak frequency and magnitude, which differs from what is found in the glassy state. Within experimental error the β-peak is “time–temperature invariant” (i.e., shape and loss peak frequency are temperature-independent), while the magnitude increases with temperature following an Arrhenius equation. Finally, for non-equilibrium states we find that loss peak frequency and magnitude show a simple isothermal correlation, which is independent of thermal history.

Minimal model for beta relaxation in viscous liquids

Contrasts between beta relaxation in equilibrium viscous liquids and glasses are rationalized in terms of a double-well potential model with structure-dependent asymmetry, assuming structure is described by a single order parameter. The model is tested for tripropylene glycol where it accounts for the hysteresis of the dielectric beta loss peak frequency and magnitude during cooling and reheating through the glass transition.

beta relaxation of nonpolymeric liquids close to the glass transition

Dielectric beta relaxation in a pyridine-toluene solution is studied close to the glass transition. Loss peak frequency and maximum loss both exhibit thermal hysteresis. An annealing-state-independent parameter involving loss and loss peak frequency is identified. This parameter has a simple Arrhenius temperature dependence. The same behavior is found for four other viscous liquids, indicating that the phenomenon is possibly general.

A rheometer for the measurement of a high shear modulus covering more than seven decades of frequency below 50 kHz

A new rheometer is described. It consists of a transducer unit supplied with an electric impedance analyzing unit. The transducer unit converts a mechanical impedance into an electrical impedance by the piezoelectric effect. A detailed quantitative analysis of the interaction between the sample and the transducer is given. The real and imaginary parts of the shear modulus of a viscoelastic sample can be found in the frequency range of 1 mHz–50 kHz, modulus range of 0.1 MPa–10 GPa, and the temperature range of 150–300 K. The sample volume is 0.3 cm3 and the strain amplitude is exceedingly small. The small size of the transducer allows for good temperature control and equilibration. It has a simple construction based on inexpensive components. Results on the supercooled liquid 2‐metyl‐2,4‐pentandiol at the glass transition obtained by the method are included.

Supercooled Liquid Dynamics Studied via Shear-Mechanical Spectroscopy

We report dynamical shear-modulus measurements for five glass-forming liquids (pentaphenyltrimethyltrisiloxane, diethyl phthalate, dibutyl phthalate, 1,2-propanediol, and m-touluidine). The shear-mechanical spectra are obtained by the piezoelectric shear-modulus gauge (PSG) method. This technique allows one to measure the shear modulus (10(5)-10(10) Pa) of the liquid within a frequency range from 1 mHz to 10 kHz. We analyze the frequency-dependent response functions to investigate whether time-temperature superposition (TTS) is obeyed. We also study the shear-modulus loss-peak position and its high-frequency part. It has been suggested that when TTS applies, the high-frequency side of the imaginary part of the dielectric response decreases like a power law of the frequency with an exponent -1/2. This conjecture is analyzed on the basis of the shear mechanical data. We find that TTS is obeyed for pentaphenyltrimethyltrisiloxane and in 1,2-propanediol while in the remaining liquids evidence of a mechanical beta process is found. Although the high-frequency power law behavior w(-alpha) of the shear loss may approach a limiting value of alpha = 0.5 when lowering the temperature, we find that the exponent lies systematically above this value (around 0.4). For the two liquids without beta relaxation (pentaphenyltrimethyltrisiloxane and 1,2-propanediol) we also test the shoving model prediction, according to which the relaxation time activation energy is proportional to the instantaneous shear modulus. We find that the data are well described by this model.

Single-order-parameter description of glass-forming liquids: a one-frequency test.

A master equation description of the inherent dynamics is used to calculate the frequency-dependent linear thermo-visco-elastic response functions of a glass-forming liquid. From the imaginary parts of the isobaric specific heat, isothermal bulk modulus, and isobaric thermal expansion coefficient, we define a quantity

Communication: Identical temperature dependence of the time scales of several linear-response functions of two glass-forming liquids

\Lambda_{Tp}(\omega)

Mechanical spectra of glass-forming liquids. I. Low-frequency bulk and shear moduli of DC704 and 5-PPE measured by piezoceramic transducers

with the property that

A cryostat and temperature control system optimized for measuring relaxations of glass-forming liquids

\Lambda_{Tp}(\omega)=1