Time-dependent Phase Transitions Research Articles

Engineering Multiscale Coupled Electron/Ion Transport in Battery Electrodes.

Coupled electron/ion transport is a defining characteristic of electrochemical processes, for example, battery charge/discharge. Analytical models that represent the complex transport and electrochemical processes in an electrode in terms of equivalent electrical circuits provide a simple, but successful framework for understanding the kinetics of these coupled transport phenomena. The premise of this review is that the nature of the time-dependent phase transitions in dynamic electrochemical environments serves as an important design parameter, orthogonal to the intrinsic mixed conducting properties of the active materials in battery electrodes. A growing body of literature suggests that such phase transitions can produce divergent extrinsic resistances in a circuit model (e.g., Re, describing electron transport from an active electrode material to the current collector of an electrode, and/or Rion, describing ion transport from a bulk electrolyte to the active material surface). It is found that extrinsic resistances of this type play a determinant role in both the electrochemical performance and long-term stability of most battery electrodes. Additionally, successful suppression of the tendency of extrinsic resistances to accumulate over time is a requirement for practical rechargeable batteries and an important target for rational design. We highlight the need for battery electrode and cell designs, which explicitly address the specific nature of the structural phase transition in active materials, and for advanced fabrication techniques that enable precise manipulations of matter at multiple length scales: (i) meso-to-macroscopic conductive frameworks that provide contiguous electronic/ion pathways; (ii) nanoscale uniform interphases formed on active materials; and (iii) molecular-level structures that promote fast electron and/or ion conduction and mechanical resilience.

Detection and Stabilization of a Previously Unknown Two-Dimensional (Pseudo)polymorph using Lateral Nanoconfinement.

We report on the detection and stabilization of a previously unknown two-dimensional (2D) pseudopolymorph of an alkoxy isophthalic acid using lateral nanoconfinement. The self-assembled molecular networks formed by the isophthalic acid derivative were studied at the interface between covalently modified graphite and an organic solvent. When self-assembled on graphite with moderate surface coverage of covalently bound aryl groups, a previously unknown metastable pseudopolymorph was detected. This pseudopolymorph, which was presumably "trapped" in between the surface bound aryl groups, underwent a time-dependent phase transition to the stable polymorph typically observed on pristine graphite. The stabilization of the pseudopolymorph was then achieved by using an alternative nanoconfinement strategy, where the domains of the pseudopolymorph could be formed and stabilized by restricting the self-assembly in nanometer-sized shallow compartments produced by STM-based nanolithography carried out on a graphite surface with a high density of covalently bound aryl groups. These experimental results are supported by molecular mechanics and molecular dynamics simulations, which not only provide important insight into the relative stabilities of the different structures, but also shed light onto the mechanism of the formation and stabilization of the pseudopolymorph under nanoscopic lateral confinement.

Asymmetric Lipid Transfer between Zwitterionic Vesicles by Nanoviscosity Measurements.

The interest in nano-sized lipid vesicles in nano-biotechnology relies on their use as mimics for endosomes, exosomes, and nanocarriers for drug delivery. The interactions between nanoscale size lipid vesicles and cell membranes involve spontaneous interbilayer lipid transfer by several mechanisms, such as monomer transfer or hemifusion. Experimental approaches toward monitoring lipid transfer between nanoscale-sized vesicles typically consist of transfer assays by fluorescence microscopy requiring the use of labels or calorimetric measurements, which in turn require a large amount of sample. Here, the capability of a label-free surface-sensitive method, quartz crystal microbalance with dissipation monitoring (QCM-D), was used to monitor lipid transfer kinetics at minimal concentrations and to elucidate how lipid physicochemical properties influence the nature of the transfer mechanism and dictate its dynamics. By studying time-dependent phase transitions obtained from nanoviscosity measurements, the transfer rates (unidirectional or bidirectional) between two vesicle populations consisting of lipids with the same head group and differing alkyl chain length can be estimated. Lipid transfer is asymmetric and unidirectional from shorter-chain lipid donor vesicles to longer-chain lipid acceptor vesicles. The transfer is dramatically reduced when the vesicle populations are incubated at temperatures below the melting of one of the vesicle populations.

Progresses on topological phenomena, time-driven phase transitions, and unconventional superconductivity (a)Contribution to the Focus Issue Progress on Statistical Physics and Complexity edited by Roberta Citro, Giorgio Kaniadakis, Claudio Guarcello, Antonio Maria Scarfone and Davide Valenti.

In this perspective we discuss three emerging fields of condensed matter physics which in recent years have attracted considerable attention. In particular, we consider the recent challenging topics on time-dependent phase transitions, topological phenomena, and unconventional superconductivity, with the aim to foster the community towards new applications and technological advancements. As for the time-dependent phase transitions, in recent years the experiments have shown light-induced phase transitions and new fields of application are emerging, including material design. Regarding topological materials, new challenges have arisen to detect the Majorana origin of quantized conductance in superconducting hybrid structures, as well as the effect of interaction on edge channels. Finally, concerning superconductivity, non-conventional pairing and correlation effects dominate the physics of a vast class of two-dimensional materials and novel devices were recently conceived. This work offers a comprehensive overview on these topics for promoting new ideas in these fertile fields of research.

Restructuring of Porphyrin Networks Driven by Self-Assembled Octanoic Acid Monolayer on Au(111).

We report time-dependent surface restructuring of bicomponent domain structures of 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine (H2OEP) and cobalt(II) 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine (CoOEP) (H2/Co OEP) driven by self-assembled octanoic acid on the surface of Au(111). Scanning tunneling microscopy (STM) visualized molecular adsorption/desorption and rearrangement of supramolecular architectures in real-time in a solution of octanoic acid. We found that unique domain structures emerged at an initial state guided by adsorbed octanoic acid on the Au surface. Moreover, the desorption of octanoic acid occurred in solution, leading to the surface restructuring of porphyrin molecular networks. This molecular evidence is well-manifested in the time-dependent phase transitions, monitored by in situ STM.

Emergent large mechanical damping in ferroelastic-martensitic systems driven by disorder

Disorders and point defects strongly interplay with the phase transition and alter the properties of ferroelastic-martensitic systems. Unusual static and quasistatic behaviors, such as time-dependent phase transitions, are discovered when disorders are introduced. However, the role of disorders on the ferroelastic system in vibrational environments at moderate frequency is rarely known, investigation of which could further shed light on their application as mechanical damping materials. Here we present the emergence of large damping capacity in ferroelastic-martensitic systems [including both the $\mathrm{T}{\mathrm{i}}_{50\ensuremath{-}x}\mathrm{N}{\mathrm{i}}_{50+x}$ alloy and $(\mathrm{C}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{S}{\mathrm{r}}_{x})\mathrm{Ti}{\mathrm{O}}_{3}$ ceramics] by introducing disorder (i.e., substitutional Ni and Sr, respectively). As the level disorder increases, the damping capacity of both systems raises and eventually reaches a maximum when long-range-ordered martensite tends to vanish. Moreover, near the disorder-induced phase boundary, we observe a large mechanical damping in ferroelastic ceramics $(\mathrm{C}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{S}{\mathrm{r}}_{x})\mathrm{Ti}{\mathrm{O}}_{3}$ with a figure of merit $\ensuremath{\sim}2\phantom{\rule{0.16em}{0ex}}\mathrm{GP}{\mathrm{a}}^{1/2}$. Microscopic and dynamic investigations indicate that such damping plateau could result from the competing evolution of density and mobility of domain boundaries when disorder is introduced. Our work provides a degree of freedom to develop ferroelastic damping materials and a potential way to tune domain-boundary-mediated functionalities for other ferroic materials.

A tale of two timescales: Mixing, mass generation, and phase transitions in the early universe

Light scalar fields such as axions and string moduli can play an important role in early-universe cosmology. However, many factors can significantly impact their late-time cosmological abundances. For example, in cases where the potentials for these fields are generated dynamically --- such as during cosmological mass-generating phase transitions --- the duration of the time interval required for these potentials to fully develop can have significant repercussions. Likewise, in scenarios with multiple scalars, mixing amongst the fields can also give rise to an effective timescale that modifies the resulting late-time abundances. Previous studies have focused on the effects of either the first or the second timescale in isolation. In this paper, by contrast, we examine the new features that arise from the interplay between these two timescales when both mixing and time-dependent phase transitions are introduced together. First, we find that the effects of these timescales can conspire to alter not only the total late-time abundance of the system --- often by many orders of magnitude --- but also its distribution across the different fields. Second, we find that these effects can produce large parametric resonances which render the energy densities of the fields highly sensitive to the degree of mixing as well as the duration of the time interval over which the phase transition unfolds. Finally, we find that these effects can even give rise to a "re-overdamping" phenomenon which causes the total energy density of the system to behave in novel ways that differ from those exhibited by pure dark matter or vacuum energy. All of these features therefore give rise to new possibilities for early-universe phenomenology and cosmological evolution. They also highlight the importance of taking into account the time dependence associated with phase transitions in cosmological settings.

Novel synthesis and luminescence properties of t-LaVO4:Eu3+micro cube

Well-defined t-LaVO4:Eu3+ microcrystals have been synthesized through a facile hydrothermal route using La0.95Eu0.05(1,3,5-BTC)(H2O)6 as a precursor for the first time. It was found that the pH value and temperature have a remarkable influence on the morphology determination. By tuning the initial pH value, uniform micro cubes and cuboid rods can be obtained. The possible growth mechanism has been discussed, underlying the systematic time-dependent phase transition and morphological evolution. In addition, the luminescence properties showed that the cuboid rod-shaped LaVO4:Eu3+ sample shows a slightly stronger red emission than the cube-shape one. Our novel synthetic route may provide some new guidance in the design and controlled synthesis of inorganic nano/micromaterials.

Universal frozen spectra after time-dependent symmetry restoring phase transitions

For a general O(N) model, we study the time-dependent phase transition from a state with broken symmetry to the symmetric phase . During this non-equilibrium process, the primordial quantum (or thermal) fluctuations of the initial Goldstone modes are frozen and result in a deviation from the final ground (or thermal) state. For very slow transitions, we find that these fluctuations display a universal scaling behaviour. Their spectra are universal functions of a single parameter, which combines the initial frequency of the Goldstone modes and the sweep rate. As a result, the final two-point function is not exponentially suppressed at large distances Δr = r − r′ (as it would be in the ground state) but decays polynomially in 1/|Δr|. Finally, we exemplify this universal behaviour for the transition from the super-fluid phase to the Mott state in the Bose–Hubbard model.

Gold-embedded photosensitive liposomes for drug delivery: Triggering mechanism and intracellular release

Liposomes embedded with gold nanoparticles show light-triggered contents release. We investigated the mechanism of the light-induced changes and functionality of the light-induced release in the cells. The real time small angle X-ray scattering (SAXS) analysis revealed time-dependent phase transitions in distearoylphosphatidylcholine (DSPC)/dipalmitoylphosphatidylcholine (DPPC) liposomes upon heating. Similar changes were observed when gold nanoparticle-embedded liposomes were exposed to the UV light: gold nanoparticles absorb light energy and transfer it to heat, thereby causing lipid phase transition from gel phase to rippled phase, and further to fluid phase. Without UV light exposure the gold nanoparticles did not affect the liposomal bilayer periodicity. The light-triggered release of hydrophilic fluorescent probe (calcein) from the gold nanoparticle-loaded liposomes was demonstrated with fluorescence-activated cell sorting after liposome internalization into the ARPE-19 cells. The liposome formulations did not decrease the cell viability in vitro. In conclusion, the light-triggered release from the liposomes is functional in the cells, and the release is triggered by thermal phase changes in the lipid bilayers.

Simulation of non-equilibrium phase transition in a random magnetic system

The time-dependent phase transition of a random magnetic system is investigated using a dynamic Monte Carlo simulation. The present random system is a simple dilution of magnetic atoms with Ising spins in a square lattice. The time-dependent order parameters are calculated as a function of temperature for several concentrations of magnetic atoms. The results indicate that as the averaging time becomes shorter, the phase transition becomes more gradual. This tendency is most pronounced around the percolation concentration. These results are compared to results of a recent NMR spin echo experiment on MnxCd1-x(HCOO)2·2(NH2)2CO reported by Kubo et al. (2007). Although the present simulation includes essentially no adjustable parameter, the results are in satisfactory agreement.

Time-Dependent Phase Transition of Self-Assembled Monolayers Formed by Thioacetyl-Terminated Tolanes on Au(111)

The binding conditions and time-dependent phase transition of self-assembled monolayers (SAMs) formed by thioacetyl-terminated tolane molecules on Au(111) were examined by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). XPS measurements revealed that two S 2p3/2 XPS peaks of the tolanethioacetate (TTA) SAMs on Au(111) were observed at 162 eV (bound sulfur) and 163.4 eV (unbound sulfur). On the other hand, an additional strong S 2p3/2 XPS peak for the SAMs of tolane methylthioacetate (TMTA) that contained a methylene spacer between the tolane group and the sulfur atom was observed at 161.2 eV (bound sulfur). This suggested that the adsorption conditions of the tolane SAMs were strongly influenced by the difference in the chemical structure of the tolanes. It was found that TTA and TMTA molecules did not form ordered SAMs after the immersion of the Au(111) substrate in a 0.5 mM N,N'-dimethylformamide solution for 1 day. However, we observed a time-dependent phase transition of the TTA and TMTA SAMs from the disordered phase to the ordered phase as a result of a long-term structural rearrangement after incubation at room temperature for 10 days. These results will be very useful in understanding the formation and binding conditions of thioacetyl-terminated SAMs on Au(111) and in controlling the two-dimensional SAM structure.

Final Phase of Alkanethiol Self-Assembled Monolayers on Au(111)

Time-dependent phase transitions of closely packed alkanethiol self-assembled monolayers (SAMs) on Au(111) were investigated by scanning tunneling microscopy (STM). We report a new phase, the 6 × √3 superlattice, that exhibits deviations from the hexagonal packing arrangement formed through long-term rearrangement of the usual c(4 × 2) superlattice of alkanethiol SAMs. Our STM images show clearly systematic phase transitions with molecular-scale images from the c(4 × 2) phase to the 6 × √3 phase. This result implies that the monolayers in the c(4 × 2) phase are still in the nonequilibrium state, although it has been regarded to be in the equilibrium state in a number of previous studies. The striking implication in this study is to provide new features for closely packed alkanethiol SAMs for the first time.

Nonequilibrium quantum dynamics of second order phase transitions

We use the so-called Liouville-von Neumann (LvN) approach to study the nonequilibrium quantum dynamics of time-dependent second order phase transitions. The LvN approach is a canonical method that unifies the functional Schr\"{o}dinger equation for the quantum evolution of pure states and the LvN equation for the quantum description of mixed states of either equilibrium or nonequilibrium. As nonequilibrium quantum mechanical systems we study a time-dependent harmonic and an anharmonic oscillator and find the exact Fock space and density operator for the harmonic oscillator and the nonperturbative Gaussian Fock space and density operator for the anharmonic oscillator. The density matrix and the coherent, thermal and coherent-thermal states are found in terms of their classical solutions, for which the effective Hamiltonians and equations of motion are derived. The LvN approach is further extended to quantum fields undergoing time-dependent second order phase transitions. We study an exactly solvable model with a finite smooth quench and find the two-point correlation functions. Due to the spinodal instability of long wavelength modes the two-point correlation functions lead to the $t^{1/4}$-scaling relation during the quench and the Cahn-Allen scaling relation $t^{1/2}$ after the completion of quench. Further, after the finite quench the domain formation shows a time-lag behavior at the cubic power of quench period. Finally we study the time-dependent phase transition of a self-interacting scalar field.

Effect of oligomeric or polymeric additives on glass transition, viscosity and crystallization of amorphous isomalt

The main purpose of this study was to further improve the stability of the amorphous state of isomalt by the addition of high molecular weight compounds. Differential scanning calorimetry (DSC) was used to determine the glass transition temperature T g of a series of polyol mixtures containing isomalt as a function of water content. As expected, for each mixture T g decreased with increasing moisture. Only with the addition of more than 75% of higher molecular weight compounds to isomalt an increase of T g could be achieved. Moisture content and time dependent phase transitions in the metastable amorphous state of the mixtures strongly affect the storage stability of isomalt hard candies. Storage tests indicated a markedly accelerated water absorption and crystallization when oligomeric or polymeric compounds were added to amorphous isomalt. Rheological experiments showed that in contrast to pure isomalt melts, the viscosity of melts containing oligomeric or polymeric additives deviated from the model curve predicted by the Williams–Landel–Ferry-kinetics (WLF) with increasing water content.

The Time-of-Flight Small-Angle Neutron Diffractometer (SAD) at IPNS, Argonne National Laboratory

The design, development and performance of the time-of-flight (TOF) small-angle diffractometer (SAD) at the Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory are described. Similar TOF-SANS instruments are in operation at the pulsed neutron sources at Los Alamos National Laboratory, USA, at Rutherford Appleton Laboratory, England, and at KEK, Japan. These instruments have an advantage by comparison with their steady-state counterparts in that a relatively wide range of momentum transfer (q) can be monitored in a single experiment without the need to alter the collimation or the sample-to-detector distance. This feature makes SANS experiments easy and very effective for studying systems such as those undergoing phase transitions under different conditions, samples that cannot be easily reproduced for repetitive experiments, and systems under high temperature, pressure or shear. Three standard samples are used to demonstrate that the quality of the SANS data from SAD is comparable with those from other established steady-state SANS facilities. Two examples are given to illustrate that the wide q region accessible in a single measurement at SAD is very effective for following the time-dependent phase transitions in paraffins and temperature- and pressure-dependent phase transitions in model biomembranes.