13 research outputs found
Hydrogen bonding exchange and supramolecular dynamics of monohydroxy alcohols
This Letter unravels hydrogen bonding dynamics and their relationship with
supramolecular relaxations of monohydroxy alcohols (MAs) at intermediate times.
Rheological modulus of MAs exhibit Rouse scaling relaxation of G(t) ~ t^(-1/2)
switching to G(t) ~ t^(-1) at time tau_m before their terminal time. Meanwhile,
dielectric spectroscopy reveals clear signatures of new supramolecular dynamics
matching with tau_m from rheology. Interestingly, the characteristic time,
tau_m, follows an Arrhenius-like temperature dependence over exceptionally wide
temperatures and agrees well with the hydrogen bonding exchange time from
nuclear magnetic resonance measurements. These observations demonstrate the
presence of collective Rouse-like sub-chain motions and the active
chain-swapping of MAs at intermediate times. Moreover, detailed theoretical
analyses point out explicitly that the hydrogen bonding exchange truncates the
Rouse-type supramolecular dynamics and triggers the chain-swapping processes,
supporting a recently proposed living polymer model.Comment: 15 pages, 4 figure
Magnitude of Dynamically Correlated Molecules as an Indicator for a Dynamical Crossover in Ionic Liquids
In this work, we show how the structure and intermolecular interactions affect the dynamic heterogeneity of aprotic ionic liquids. Using calorimetric data for 30 ionic samples, we examine the influence of the strength of van der Waals and Coulombic interactions on dynamic heterogeneity. We show that the dynamic length scale of spatially heterogeneous dynamics decreases significantly with decreasing intermolecular distances. Additionally, we assume that the magnitude of the number of dynamically correlated molecules at the liquid−glass transition temperature can be treated as an indicator for a dynamical crossover
Complex reorientation dynamics of sizable glass-formers with polar rotors revealed by dielectric spectroscopy
We present the results of dielectric measurements for three sizable glass-formers
with identical nonpolar cores linked to various dipole-labeled rotors that shed new light on the
picture of reorientation of anisotropic systems with significant moment of inertia revealed by
broadband dielectric spectroscopy. The dynamics of sizable glass-formers formed by partially
rigid molecular cores linked to small polar rotors in many respects differs from that of typical
glass-formers. For instance, the extraordinarily large prefactors (τ0 > 10−12 s) in the Vogel−
Fulcher−Tammann equation were found. The rich and highly diverse relaxation pattern was
governed by the location of a dipole, its ability to rotate freely, and the degree of coupling to the
motion of the entire sizable system
Revealing fast proton transport in condensed matter by means of density scaling concept
Herein, we investigate the charge transport and structural dynamics in
the supercooled and glassy state of protic ionic material with an efficient interionic
Grotthuss mechanism. We found that superprotonic properties of studied acebutolol
hydrochloride (ACB-HCl) depend on thermodynamic conditions with the most
favorable regions being close to the glass-transition temperature (Tg) and glasstransition
pressure (Pg). To quantify the contribution of fast proton hopping to overall
charge transport over a broad T−P space, we employed the density scaling concept,
one of the most important experimental findings in the field of condensed matter
physics. We found that isothermal and isobaric dc-conductivity (σdc) and dynamic
light scattering (τα) data of ACB-HCl plotted as a function of (TVγ)−1 satisfy the
thermodynamic scaling criterion with the ratio γσ/γα appearing as a new measure of
fast charge transport in protic ionic glass-formers in the T−P plane. Such a universal
factor becomes an alternative to the well-known Walden rule being limited to ambient
pressure conditions
Surface Equilibration Mechanism Controls the Stability of a Model Codeposited Glass Mixture of Organic Semiconductors
While previous work has identified the conditions for preparing ultrastable singlecomponent organic glasses by physical vapor deposition (PVD), little is known about the stability of
codeposited mixtures. Here, we prepared binary PVD glasses of organic semiconductors, TPD (N,N′-
Bis(3-methylphenyl)-N,N′-diphenylbenzidine) and m-MTDATA (4,4′,4″-Tris[phenyl(m-tolyl)-
amino]triphenylamine), with a 50:50 mass concentration over a wide range of substrate temperatures
(Tsub). The enthalpy and kinetic stability are evaluated with differential scanning calorimetry and
spectroscopic ellipsometry. Binary organic semiconductor glasses with exceptional thermodynamic and
kinetic stability comparable to the most stable single-component organic glasses are obtained when
deposited at Tsub = 0.78−0.90Tg (where Tg is the conventional glass transition temperature). When
deposited at 0.94Tg, the enthalpy of the m-MTDATA/TPD glass equals that expected for the
equilibrium liquid at that temperature. Thus, the surface equilibration mechanism previously advanced
for single-component PVD glasses is also applicable for these codeposited glasses. These results
provide an avenue for designing high-performance organic electronic devices
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Revealing Fast Proton Transport in Condensed Matter by Means of Density Scaling Concept
Herein, we investigate the charge transport and structural dynamics in the supercooled and glassy state of protic ionic material with an efficient interionic Grotthuss mechanism. We found that superprotonic properties of studied acebutolol hydrochloride (ACB-HCl) depend on thermodynamic conditions with the most favorable regions being close to the glass-transition temperature (Tg) and glass-transition pressure (Pg). To quantify the contribution of fast proton hopping to overall charge transport over a broad T–P space, we employed the density scaling concept, one of the most important experimental findings in the field of condensed matter physics. We found that isothermal and isobaric dc-conductivity (σdc) and dynamic light scattering (τα) data of ACB-HCl plotted as a function of (TVγ)−1 satisfy the thermodynamic scaling criterion with the ratio γσ/γα appearing as a new measure of fast charge transport in protic ionic glass-formers in the T–P plane. Such a universal factor becomes an alternative to the well-known Walden rule being limited to ambient pressure conditions
Pressure-induced liquid-liquid transition in a family of ionic materials
Liquid−liquid transition (LLT) between two disordered phases of single-component material
remains one of the most intriguing physical phenomena. Here, we report a first-order LLT in a
series of ionic liquids containing trihexyl(tetradecyl)phosphonium cation [P666,14]+ and
anions of different sizes and shapes, providing an insight into the structure-property relationships
governing LLT. In addition to calorimetric proof of LLT, we report that ion dynamics
exhibit anomalous behavior during the LLT, i.e., the conductivity relaxation times (τσ) are
dramatically elongated, and their distribution becomes broader. This peculiar behavior is
induced by isobaric cooling and isothermal compression, with the τσ(TLL,PLL) constant for a
given system. The latter observation proves that LLT, in analogy to liquid-glass transition, has
an isochronal character. Finally, the magnitude of discontinuity in a specific volume at LLT
was estimated using the Clausius-Clapeyron equation
The Compact Pulsed Hadron Source Construction Status
This paper reports the design and construction status, technical challenges, and future perspectives of the proton-linac based Compact Pulsed Hadron Source (CPHS) at the Tsinghua University, Beijing, Chin