Supercooled O-terphenyl Research Articles

Response to “Comment on ‘On the dielectric susceptibility spectra of supercooled o-terphenyl’” [J. Chem. Phys. 123, 154502 (2005)

The recent claim of time-temperature superposition (TTS) for o-terphenyl (OTP) in its viscous regime is revisited in order to clarify whether peak versus area normalization of the dielectric loss profiles impacts the results derived from the master plot. In the case of OTP, noise is the main source of differences between the two options. Using synthetic noisy data, it is shown that an area normalized master plot is more sensitive to deviations from TTS than the peak normalized counterpart. As a result, OTP is characterized by a stretching exponent β=0.50±0.03 in the 248–284K temperature range.

Isothermal desorption measurements of self-diffusion in supercooled o-terphenyl

Isothermal desorption of o-terphenyl thin-film bilayers was used to measure self-diffusion coefficients of supercooled o-terphenyl near the glass transition temperature (Tg=243 K). Diffusion coefficients from 10(-15.5) to 10(-12) cm2 s(-1) were obtained between 246 and 265 K. Protio and deuterio o-terphenyl were sequentially vapor deposited, then annealed to simultaneously diffuse and desorb the sample in a vacuum chamber. During the desorption of the bilayer, the concentration of each isotope was detected by a mass spectrometer, which revealed the extent of interfacial broadening. In these experiments, isotopic interdiffusion is indistinguishable from self-diffusion and the measured interfacial broadening is consistent with Fickian diffusion. The samples prepared under several different deposition conditions yielded the same self-diffusion coefficients, indicating that the experiments were conducted in the equilibrium supercooled liquid state.

On the dielectric susceptibility spectra of supercooled o-terphenyl

Supercooled o-terphenyl has been the subject of many investigations including dielectric relaxation spectroscopy. Due to the low dielectric strength and the tendency to crystallize at elevated temperatures, a detailed shape analysis of the loss profile from the glass transition temperature Tg to approximately 1.2 Tg is not available for the neat glass former. Assessing the origin of the different temperature dependencies of translational and rotational motions in supercooled liquids and its possible connection to heterogeneity requires this knowledge regarding the possible changes in the relaxation-time distribution across the 100 s-100 ns relaxation-time range. This note provides this information for o-terphenyl on the basis of a master curve representation: time-temperature superposition applies with a constant stretching exponent of beta=0.5 in the range of interest.

Scaling the $\alpha $ -relaxation time of supercooled fragile organic liquids

It was shown recently that the structural alpha-relaxation time tau of supercooled o-terphenyl depends on a single control parameter Gamma, which is the product of a function of density E(ro), by the inverse temperature T -1. We extend this finding to other fragile glassforming liquids using light-scattering data. Available experimental results do not allow to discriminate between several analytical forms of the function E(ro), the scaling arising from the separation of density and temperature in Gamma. We also propose a simple form for tau(Gamma), which depends only on three material-dependent parameters, reproducing relaxation times over 12 orders of magnitude.

Heterogeneous Dynamics and Domains in Supercooledo-Terphenyl: A Single Molecule Study

Single molecule spectroscopy was used to characterize the rotation of fluorescent probe molecules in supercooled o-terphenyl (OTP) just above the glass transition. Rotational motions of spatially i...

Time Domain Optical Studies of Dynamics in Supercooled o-Terphenyl: Comparison to Mode Coupling Theory on Fast and Slow Time Scales

Orientational relaxation of supercooled o-terphenyl (OTP) is studied over a wide range of temperatures and time scales using optical heterodyne detected optical Kerr effect techniques. A combination of experimental setups made it possible to study the dynamics for greater than six decades of time (100 fs to hundreds of nanoseconds). The complex shape of the data is analyzed in terms of power laws at intermediate times and an approximately exponential decay at long times. Most features of the relaxation curves are in accord with predictions of mode-coupling theory (MCT) for supercooled liquids. In particular, at long times the relaxation data show a temperature independent shape in the temperature regime 361−290 K. When plotted vs temperature, the long time decay constants scaled by a relationship given by MCT fall on a line as predicted and give a value of the MCT critical temperature, Tc = 285 K, in accord with literature values. On a faster time scale, the slowest of the power law decays has a temperatu...

Lifetime of spatially heterogeneous dynamic domains in polystyrene melts

A photobleaching method is used to measure the rotational dynamics of tetracene and rubrene in polystyrene, and to determine the lifetime of spatially heterogeneous dynamic domains in the polystyrene matrix. It is possible to selectively photobleach subsets of probe molecules in more mobile environments and to measure the time required for the remaining slower-than-average probes to be redistributed into an equilibrium set of environments. For polystyrene, this exchange time is much longer than the α-relaxation time at temperatures very near Tg and exhibits a strong temperature dependence. These results are qualitatively consistent with previous studies on tetracene in supercooled o-terphenyl and indicate that the observation of long-lived heterogeneous dynamic domains at temperatures very near Tg is neither matrix nor probe specific.

Short-time rotational relaxation in supercooled and glassy o-terphenyl: a nonlinear electron spin resonance study by using molecular probes with different symmetries

Short-time rotational relaxation in supercooled and glassy o-terphenyl: a nonlinear electron spin resonance study by using molecular probes with different symmetries

How Long Do Regions of Different Dynamics Persist in Supercooled o-Terphenyl?

In supercooled o-terphenyl (OTP), subsets of probe molecules in more mobile environments can be selectively photobleached. The time required for the remaining slower-than-average probes to be redis...

Comment on “A 250 GHz ESR study of o-terphenyl: Dynamic cage effects above Tc” [J. Chem. Phys 106, 9996 (1997)

In a recent ESR study Earle, Moscicki, Polimeno and Freed investigated the rotational dynamics of tracers in supercooled o-terphenyl (OTP). Their claims were (1) the correct analysis of the ESR data must account for the possible nonexponential decay of the the rotational correlation function; (2) the average rotational correlation time, 〈τ〉 follows the Stokes–Einstein–Debye law (SED); (3) there are substantial voids in OTP. We show that (i) claims #1 and #2 become very questionable after having corrected inconsistencies between the data and the related plot; (ii) the claim #3 is not supported by additional experimental data.

Linear and non-linear electron spin resonance study of the rotational diffusion of a molecular tracer in supercooled o-terphenyl

The long-time and the short-time rotational relaxation of a molecular tracer in supercooled o-terphenyl (OTP) have been studied by linear and non linear electron spin resonance (ESR) spectroscopy, respectively. At higher temperatures the related correlation times, τ l and τ s, are equal within the experimental errors, i.e. the relaxation is exponential, and well coupled to the viscosity, η. On cooling, τ s, and, at lower temperatures, τ l, are partially coupled to the viscosity in agreement with the fractional Debye–Stokes–Einstein (DSE) law τ i ∝( η/ T) ξ i , i=l,s with ξ i constant. For T < 330 K the rotational correlation function is not exponential.

A study of the Debye - Stokes - Einstein law in supercooled fluids

The reorientation of a nearly spherical paramagnetic tracer dissolved in supercooled o-terphenyl is studied by electron spin resonance in the range 200 K < T < 370 K. For T > 300 K the rotational correlation time follows the Debye - Stokes - Einstein law. On decreasing the temperature, the rotational motion of the probe and the viscosity decouple. In particular, in the region around T = 290 K it is found that with .

Enhanced translation of probe molecules in supercooled o-terphenyl: Signature of spatially heterogeneous dynamics?

A holographic fluorescence recovery after photobleaching technique has been used to measure translational diffusion coefficients DT for four probes in supercooled o-terphenyl (OTP). DT values from 10−6 to 10−14 cm2/s were observed in the temperature range from Tg+8 K to Tg+90 K (Tg=243 K). In agreement with previous reports, the translational diffusion of probe molecules which are the same size as OTP molecules has a significantly weaker temperature dependence than T/η. However, as the size of the probe molecule is increased the temperature dependence of DT tracks T/η increasingly well. The transition between a weak temperature dependence to that of T/η occurs over only a factor of 3 in probe size. Previous work established that the rotational correlation times τc of these four probes in OTP tracks η/T. The product DTτc is independent of temperature for the largest probe but increases almost 2 orders of magnitude for the smaller probes as Tg is approached. A strong correlation is observed between this enhancement of translational diffusion and the KWW β values obtained from rotation measurements; probes with small β values show enhanced translation. These observations are qualitatively explained by spatially heterogeneous dynamics. The probes studied are rubrene, 9,10-bis(phenylethynyl)anthracene, tetracene, and anthracene.

Relaxation of spatially heterogeneous dynamic domains in supercooled ortho-terphenyl

A photobleaching technique has been used to observe rotational dynamics of dilute probe molecules in supercooled o-terphenyl (OTP). The nonexponential rotational relaxation of the probe molecules is shown to be due, at least in part, to the presence of spatial heterogeneity in the host dynamics. Under appropriate photobleaching conditions, a nonequilibrium distribution of probe molecule mobilities can be created by preferentially bleaching the more mobile probe molecules in a sample. Near Tg this nonequilibrium distribution is observed to return to an equilibrium distribution of relaxation times over times on the order of 103 τc, where τc is the average rotational correlation time of a probe molecule. The time required to return to equilibrium is interpreted as a structural relaxation time for dynamic heterogeneities in OTP.

β-process of supercooled o-terphenyl: a comparison of dielectrical and NMR data guided by mode-coupling theory

According to predictions of mode-coupling theory of the liquid-glass transition, a Cole-Cole dynamical susceptibility is applied to the β-relaxation of supercooled o-terphenyl as studied by 2H NMR spin-lattice relaxation and by dielectrical relaxation. A temperature-dependent amplitude (1-f) is assumed for the β-process which yields a description of the NMR data consistent with the dielectrical data. The plateau value f separating the α- and β-processes in the two-step correlation function reveals a similar temperature dependence as compared to the Debye-Waller factor.

ChemInform Abstract: RAYLEIGH‐BRILLOUIN SCATTERING STUDIES OF LIQUID AND SUPERCOOLED LIQUID O‐TERPHENYL

Chemischer InformationsdienstVolume 12, Issue 28 Physical Organic Chemistry ChemInform Abstract: RAYLEIGH-BRILLOUIN SCATTERING STUDIES OF LIQUID AND SUPERCOOLED LIQUID O-TERPHENYL Y. HIGASHIGAKI, Y. HIGASHIGAKISearch for more papers by this authorC. H. WANG, C. H. WANGSearch for more papers by this author Y. HIGASHIGAKI, Y. HIGASHIGAKISearch for more papers by this authorC. H. WANG, C. H. WANGSearch for more papers by this author First published: July 14, 1981 https://doi.org/10.1002/chin.198128040AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume12, Issue28July 14, 1981 RelatedInformation

Dielectric and NMR study of conformational dynamics in t r a n s-1,2-dichlorocyclohexane

The complex dielectric permittivity of trans-1,2-dichlorocyclohexane (DCCH) in supercooled o-terphenyl at audio frequencies is reported. These data are interpreted in terms of a dynamical model involving internal site exchange coupled to a cooperative solvent controlled molecular reorientation process. Fourier transform 13C lines shapes are reported for DCCH in mixed carbon tetrachloride–deuterochloroform solvent over a range of temperatures encompassing the coalescence region. Details of the site dynamics are extracted from these data via numerical line shape analysis. Reasonable agreement between the parameters common to both models is found.

Molecular dynamics of viscous liquids. A comparison of dielectric and Kerr-effect relaxation for tritolyl phosphate, ortho-terphenyl and their mixtures

Low frequency dielectric (10–2 to 105 Hz) and Kerr-effect (10–5 to 102 s) relaxation behaviour of pure liquid tritolylphosphate, super-cooled o-terphenyl and three tritolylphosphate +o-terphenyl mixtures have been examined. The Kerr-effect rise and decay transients for each of these systems at a given temperature, are characterized by the same relaxation time τK,r and τK,d respectively. For both pure liquids τK,r and τK,d are essentially the same as the dielectric relaxation time τD, and the dielectric loss curves and Kerr-effect transients are adequately described by the William–Watts empirical relaxation function. These results suggest that reorientational motions in highly viscous liquids do not occur by rotational diffusion, but that they are entirely consistent with a “fluctuation relaxation” mechanism, and they are discussed in terms of the Ivanov and Anderson models of rotational Brownian motion. For some o-terphenyl + tritolylphosphate mixtures τK,r=τK,d > τD and possible explanations of this result are considered.

Time-dependent orientation distribution function calculated from time-correlation functions by use of information theory

The information-theory method of Berne and coworkers for the orientational distribution function (Ω, t) has been extended by adding 〈P2[cos θ(t)]〉 to the quantities assumed to be known. The original theory and its extension have been applied to the case of rotational diffusion where 〈P1[cos θ(t)]〉, 〈P2[cos θ(t)]〉 and (Ω, t) are analytically related. The accuracy of the (Ω, t) deduced by the two information methods is discussed. In addition, (Ω, t) has been evaluated using the information theory method for the computer simulated results obtained by Berne for CO using a modified Stockmayer potential, for Gordon's results for liquid methane and for experimental dielectric data for two supercooled o-terphenyl solutions.

Molecular dynamics of the supercooled liquid state. A dielectric study of the low frequency motions of fluorenone in o-terphenyl and mixed solvents and of di-n-butyl phthalate in o-terphenyl

The low frequency dielectric relaxation (1 to 105 Hz) of dipolar systems has been studied in the supercooled liquid state. Studies were made on fluorenone/o-terphenyl, fluorenone/o-terphenyl/triphenylbenzene, fluorenone/o-terphenyl/decalin, and di-n-butyl phthalate/o-terphenyl systems, where the latter system was studied from dilute solution to pure di-n-butyl phthalate. The results show that the dipolar molecules move co-operatively with their environment in the supercooled liquid state, and the derived dipole moment autocorrelation function has a natural non-exponential dependence upon time. It was shown that the fluorenone reorientation rate in o-terphenyl could be made faster by addition of small amounts of decalin, and could be made slower by an addition of small amounts of triphenylbenzene. The concentration dependence of the shape of the relaxation of di-n-butyl phthalate is quite different from that of fluorenone in o-terphenyl, and is analyzed to yield the effective distribution of local concentration surrounding a dipolar molecule. The relationship between dielectric relaxation and other techniques which detect molecular motion is briefly discussed, and the dipole correlation function for dilute supercooled o-terphenyl solutions is used to predict [〈3 cos2θ(t)〉—1]/2 for these systems.