A comparison of rheology, dielectric response, and calorimetry within indane-based glass-formers

Erwin, Brian M.; Masser, Kevin A.; Colby, Ralph H.

doi:10.1016/j.jnoncrysol.2005.12.059

Cited by 4 publications

(3 citation statements)

References 32 publications

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“…Two ways of accounting for the distance of the measurement T from T g were considered. The first was to consider the dimensionless temperature T / T g,bulk . − In Figure b, the data for both linear and cyclic architectures are seen to nearly collapse onto a single curve when plotted vs T / T g,bulk , suggesting that T g is the key parameter for understanding the surface dynamics of both cyclic and linear PS films in the molecular weight (below M c ) and temperature range (20–60 °C above T g,bulk ) studied here. The capillary wave dynamics for the polystyrene polymers with linear and cyclic architectures have very similar temperature dependences. , Guo and Simon suggest that plotting relaxation times as a function of the difference between the actual temperature and T g (i.e., T – T g ) may be helpful.…”

Section: Resultsmentioning

confidence: 88%

Dynamics of Surface Fluctuations on Macrocyclic Melts

et al. 2012

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A hydrodynamic continuum theory (HCT) of thermally stimulated capillary waves describing surface fluctuations of linear polystyrene melts is found to describe surface fluctuations of sufficiently thick films of unentangled cyclic polystyrene. However, for cyclic polystyrene (CPS) films thinner than 10R g , the surface fluctuations are slower than expected from the HCT universal scaling, revealing a confinement effect active over length scales much larger than R g . Surface fluctuations of CPS films can be slower than those of films of linear polystyrene analogues, due to differences between the glass transition temperatures, T g , of the linear and cyclic chains. The temperature dependences of the surface fluctuations match those of bulk viscosities, suggesting that whole chain dynamics dictate the surface height fluctuation dynamics at temperatures 25−60 °C above T g . When normalized surface relaxation rates of thicker films are plotted as a function of T/T g , a universal temperature behavior is observed for linear and cyclic chains.

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Section: Resultsmentioning

confidence: 88%

Dynamics of Surface Fluctuations on Macrocyclic Melts

et al. 2012

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“…Those sizes are believed to be dependent on temperature in the vicinity of T g . 35 In this paper we compare the rotational motion of 5CB in dynamically homogeneous 5CB/polymer mixtures with the viscoelastic glass mode as functions of temperature and the relevant length scale of the glass mode is determined from the length (long axis) of the rodlike LM molecule whose rotational relaxation time coincides with the segmental relaxation time of polymer components. 13,32 Concerning the LM motion in polymer/LM mixtures, one important finding in our previous studies 32 is the existence of two separated relaxation modes (slow and fast modes) both related to the LM motion.…”

Section: Introductionmentioning

confidence: 99%

“…Here, “glass segment” is a dynamical unit in a single chain determined by both the intra- and intermolecular interactions, while “CRR” is the dynamical unit including neighbor molecules with which cooperative motion takes place. − Therefore, the notions of “segment” and “CRR” are not necessarily the same even though they will have the similar length scales. Those sizes are believed to be dependent on temperature in the vicinity of T g . In this paper we compare the rotational motion of 5CB in dynamically homogeneous 5CB/polymer mixtures with the viscoelastic glass mode as functions of temperature and the relevant length scale of the glass mode is determined from the length (long axis) of the rodlike LM molecule whose rotational relaxation time coincides with the segmental relaxation time of polymer components. , …”

Section: Introductionmentioning

confidence: 99%

Dynamics of a Probe Molecule Dissolved in Several Polymer Matrices with Different Side-Chain Structures: Determination of Correlation Length Relevant to Glass Transition

et al. 2013

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Dynamics of 4-pentyl-4′-cyanobiphenyl (5CB) dissolved in several polymers at concentrations of 3−7 wt % was examined by dielectric relaxation measurement. Glassy (segmental) mode of the matrix polymer was also investigated by viscoelastic measurements for the same samples. Polystyrene (PS), poly(4-methylstyrene) (P4MS), and poly(4-tertbutylstyrene) (PtBS) were used as host polymers, considering that they have the same backbone structure but different sidechain bulkiness. Two dielectric relaxation modes (slow and fast modes) of 5CB component appeared in all the mixtures, and the relative intensity of the fast mode increased in the order of PS < P4MS < PtBS, corresponding to the order of the side-chain bulkiness and main-chain stiffness. The effects of such chemical structure differences on the two relaxation modes, particularly their temperature dependence, were examined in detail. Comparison of relaxation times for the fast mode and the segmental dynamics of the matrix polymer suggests that the fast mode was attributed to the restricted orientational fluctuation, which includes precession motion around the long axis, of 5CB molecule in a confined space formed by slow polymer chains. The dielectric intensity of the fast mode increased with increasing side-chain bulkiness of polymers. This means that the larger side chain decreases the spatial restriction for the movement of guest 5CB molecules in the glassy state. The slow mode was attributed to the rotational motion of 5CB molecule nearly cooperative with the segmental motion of matrix polymer. The relaxation times of dielectric slow mode and viscoelastic glass mode were compared. Temperature dependence of the slow mode was slightly different from that of the segmental motion of polymer corresponding to the glass mode. From the difference between these relaxation times, the correlation length relevant to the glass mode was determined as functions of temperature for the three polymers.

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Rheological complexity in simple chain models

Dotson

Heffernan

Budzien

et al. 2008

The Journal of Chemical Physics

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Dynamical properties of short freely jointed and freely rotating chains are studied using molecular dynamics simulations. These results are combined with those of previous studies, and the degree of rheological complexity of the two models is assessed. New results are based on an improved analysis procedure of the rotational relaxation of the second Legendre polynomials of the end-to-end vector in terms of the Kohlrausch-Williams-Watts (KWW) function. Increased accuracy permits the variation of the KWW stretching exponent beta to be tracked over a wide range of state points. The smoothness of beta as a function of packing fraction eta is a testimony both to the accuracy of the analytical methods and the appropriateness of (eta(0)-eta) as a measure of the distance to the ideal glass transition at eta(0). Relatively direct comparison is made with experiment by viewing beta as a function of the KWW relaxation time tau(KWW). The simulation results are found to be typical of small molecular glass formers. Several manifestations of rheological complexity are considered. First, the proportionality of alpha-relaxation times is explored by the comparison of translational to rotational motion (i.e., the Debye-Stokes-Einstein relation), of motion on different length scales (i.e., the Stokes-Einstein relation), and of rotational motion at intermediate times to that at long time. Second, the range of time-temperature superposition master curve behavior is assessed. Third, the variation of beta across state points is tracked. Although no particulate model of a liquid is rigorously rheologically simple, we find freely jointed chains closely approximated this idealization, while freely rotating chains display distinctly complex dynamical features.

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A comparison of rheology, dielectric response, and calorimetry within indane-based glass-formers

Cited by 4 publications

References 32 publications

Dynamics of Surface Fluctuations on Macrocyclic Melts

Dynamics of Surface Fluctuations on Macrocyclic Melts

Dynamics of a Probe Molecule Dissolved in Several Polymer Matrices with Different Side-Chain Structures: Determination of Correlation Length Relevant to Glass Transition

Rheological complexity in simple chain models

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