Condensed Phase Materials Research Articles

Microfluidic mid-infrared spectroscopy via microresonator-based dual-comb source.

Over the past decade, microresonator-based soliton combs based on photonic integration have broadened the scope of applications in sensing, ranging, and imaging. The large comb line spacing on the order of hundreds of gigahertz allows for rapid acquisition of absorption spectra in the condensed matter phase without aliasing via a dual-comb interferometer. We present a proof-of-principle demonstration of high-throughput label-free microresonator-based dual-comb spectroscopy in a microfluidic chip that dynamically probes the linear absorption of liquid acetone in the mid-infrared wavelength regime. We measure the flow dynamics of an acetone droplet with a spectral acquisition rate of 25kHz (40μs per spectrum) covering a spectral range from 2900 to 2990nm. Combining microfluidics and silicon-photonic technology would potentially enable a compact time-resolved spectroscopy system for a wide range of applications such as chemical synthesis, biological cell-sorting, and lab-on-a-chip.

Fluorescence microscopy of biophysical protein dynamics in nanoporous hydrogels

Proteins within nanoporous hydrogels have important biotechnological applications in pharmaceutical purification, tissue engineering, water treatment, biosensors, and medical implants. Yet, oftentimes proteins that are functional in solution lose activity when in contact with soft, nanostructured, condensed phase materials due to perturbations in the folded state, conformation, diffusion, and adsorption dynamics of the protein by the material. Fluorescence microscopy experimentally measures the biophysical dynamics of proteins within hydrogels at the nanoscale and can overcome the limitations of conventional ensemble techniques. An explanation of the benefits of fluorescence is provided, and principles of fluorescence microscope instrumentation and analysis are discussed. Then several nanoscale fluorescence microscopies that image nanoscale protein dynamics within hydrogels are introduced. First, location-based super-resolution imaging resolves the adsorption kinetics of proteins to charged ligands within hydrogels used in pharmaceutical separations. Next, correlation-based super-resolution techniques image the heterogeneity of the nanoscale pore size of the hydrogels and the diffusion of analytes within the pores simultaneously. Finally, fluorescence resonance energy transfer imaging combined with temperature jump perturbations determines the folding and stability of a protein within hydrogels. A common finding with all three fluorescence microscopies is that heterogeneous nanoporous hydrogel materials cause variability of protein behavior dependent on gel sterics and/or interfacial electrostatic forces. Overall, in situ observations of proteins in hydrogels using fluorescence microscopies can inform and inspire soft nanomaterial design to improve the performance, shelf life, and cost of biomaterials.

Numerical tests of coherence-corrected surface hopping methods using a donor-bridge-acceptor model system.

Surface hopping (SH) is a popular mixed quantum-classical method for modeling nonadiabatic excited state processes in molecules and condensed phase materials. The method is simple, efficient, and easy to implement, but the use of classical and independent nuclear trajectories introduces an overcoherence in the electronic density matrix which, if ignored, often leads to spurious results, such as overestimated reaction rates. Several methods have been proposed to incorporate decoherence into SH simulations, but a lack of insightful benchmarks makes their relative accuracy unknown. Herein, we run numerical simulations of common coherence-corrected SH methods including Truhlar's decay-of-mixing (DOM) and Subotnik's augmented SH using a Donor-bridge-Acceptor (DbA) model system. Numerical simulations are carried out in the superexchange regime, where charge transfer proceeds from a donor to an acceptor as a result of donor-bridge and bridge-acceptor couplings. The computed donor-to-acceptor reaction rates are compared to the reference Marcus theory results. For the DbA model under consideration, augmented SH recovers Marcus theory with quantitative accuracy, whereas DOM is only qualitatively accurate depending on whether predefined parameters in the decoherence rate are chosen wisely. We propose a general method for parameterizing the decoherence rate in the DOM method, which improves the method's reaction rates and presumably increases its transferability. Overall, the decoherence method of choice must be chosen with great care and this work provides insight using an exactly solvable model.

High harmonic generation tomography of impurities in solids: Conceptual analysis

A three step model for high harmonic generation from impurities in solids is developed. The process is found to be similar to high harmonic generation in atomic and molecular gases with the main difference coming from the non-parabolic nature of the bands. This opens a new avenue for strong field atomic and molecular physics in the condensed matter phase. As a first application, our conceptual study demonstrates the feasibility of tomographic measurement of impurity orbitals.

Modeling the effects of molecular disorder on the properties of Frenkel excitons in organic molecular semiconductors.

The Frenkel exciton model provides a convenient framework for simulating electronic excitations in organic conjugated systems that are too large to address with atomistic level electronic structure methods. Parameterization of this model is typically based on analytical expressions that incompletely describe the spatial and temporal correlations that are inherent to many condensed phase molecular systems. In this manuscript, we present a general procedure for including these correlations in the Frenkel exciton model, by mapping them directly from all-atom molecular configurations, for instance from classical molecular dynamics. Regardless of system morphology, this mapping automatically captures the spatial and temporal molecular correlations that are otherwise difficult or impossible to represent in terms of low-dimensional correlation functions. We apply this procedure to study the excited state properties of condensed phase materials made up of thiophene oligomers. We show that Frenkel model parameters can be mapped from a series of single molecule electronic structure calculations, and that for these materials efficient semi-empirical methods are sufficient to accurately reproduce experimental spectral measurements. By analyzing the statistics of model parameters derived from materials with different characteristic morphologies, we highlight failures in some assumptions that are commonly applied when generating model parameters. Finally, by simulating exciton dynamics on a mapped Frenekel exciton model, we demonstrate the ability to quantify the effect of material morphology on the dynamic properties of excitons.

Templated Assembly of a Functional Ordered Protein Macromolecular Framework from P22 Virus-like Particles.

Bottom-up construction of mesoscale materials using biologically derived nanoscale building blocks enables engineering of desired physical properties using green production methods. Virus-like particles (VLPs) are exceptional building blocks due to their monodispersed sizes, geometric shapes, production ease, proteinaceous composition, and our ability to independently functionalize the interior and exterior interfaces. Here a VLP, derived from bacteriophage P22, is used as a building block for the fabrication of a protein macromolecular framework (PMF), a tightly linked 3D network of functional protein cages that exhibit long-range order and catalytic activity. Assembly of PMFs was electrostatically templated, using amine-terminated dendrimers, then locked into place with a ditopic cementing protein that binds to P22. Long-range order is preserved on removal of the dendrimer, leaving a framework material composed completely of protein. Encapsulation of β-glucosidase enzymes inside of P22 VLPs results in formation of stable, condensed-phase materials with high local concentration of enzymes generating catalytically active PMFs.

Emergent phases of fractonic matter

Fractons are emergent particles which are immobile in isolation, but which can move together in dipolar pairs or other small clusters. These exotic excitations naturally occur in certain quantum phases of matter described by tensor gauge theories. Previous research has focused on the properties of small numbers of fractons and their interactions, effectively mapping out the "Standard Model" of fractons. In the present work, however, we consider systems with a finite density of either fractons or their dipolar bound states, with a focus on the $U(1)$ fracton models. We study some of the phases in which emergent fractonic matter can exist, thereby initiating the study of the "condensed matter" of fractons. We begin by considering a system with a finite density of fractons, which we show can exhibit microemulsion physics, in which fractons form small-scale clusters emulsed in a phase dominated by long-range repulsion. We then move on to study systems with a finite density of mobile dipoles, which have phases analogous to many conventional condensed matter phases. We focus on two major examples: Fermi liquids and quantum Hall phases. A finite density of fermionic dipoles will form a Fermi surface and enter a Fermi liquid phase. Interestingly, this dipolar Fermi liquid exhibits a finite-temperature phase transition, corresponding to an unbinding transition of fractons. Finally, we study chiral two-dimensional phases corresponding to dipoles in "quantum Hall" states of their emergent magnetic field. We study numerous aspects of these generalized quantum Hall systems, such as their edge theories and ground state degeneracies.

Scaling of the detonation product state with reactant kinetic energy

Chemical explosives provide one of the most high-power and energy-dense storage materials available. During detonation, transfer of this energy to adjacent materials is governed by the detonation product equation of state. No accurate methodology exists for prediction of this thermodynamic relationship and equation-of-state data continues to be experimentally characterized for each new formulation or charge density. Here we present a universal detonation product equation of state derived from several newly discovered empirical correlations in prior condensed-phase detonation product measurements. This model depends only on initial charge density and detonation velocity as inputs, dramatically simplifying the calibration process relative to existing models, which require measurement of up to seven formulation-specific parameters. This new result implies the product energy density scales with reactant kinetic energy density, which is the product of the explosive initial density and detonation velocity squared, for all condensed-phase energetic materials and that explosive microstructural or chemical details only influence the product energy density though these two parameters.

Perturbed path integrals in imaginary time: Efficiently modeling nuclear quantum effects in molecules and materials.

Nuclear quantum effects (NQE), which include both zero-point motion and tunneling, exhibit quite an impressive range of influence over the equilibrium and dynamical properties of molecules and materials. In this work, we extend our recently proposed perturbed path-integral (PPI) approach for modeling NQE in molecular systems [I. Poltavsky and A. Tkatchenko, Chem. Sci. 7, 1368 (2016)], which successfully combines the advantages of thermodynamic perturbation theory with path-integral molecular dynamics (PIMD), in a number of important directions. First, we demonstrate the accuracy, performance, and general applicability of the PPI approach to both molecules and extended (condensed-phase) materials. Second, we derive a series of estimators within the PPI approach to enable calculations of structural properties such as radial distribution functions (RDFs) that exhibit rapid convergence with respect to the number of beads in the PIMD simulation. Finally, we introduce an effective nuclear temperature formalism within the framework of the PPI approach and demonstrate that such effective temperatures can be an extremely useful tool in quantitatively estimating the "quantumness" associated with different degrees of freedom in the system as well as providing a reliable quantitative assessment of the convergence of PIMD simulations. Since the PPI approach only requires the use of standard second-order imaginary-time PIMD simulations, these developments enable one to include a treatment of NQE in equilibrium thermodynamic properties (such as energies, heat capacities, and RDFs) with the accuracy of higher-order methods but at a fraction of the computational cost, thereby enabling first-principles modeling that simultaneously accounts for the quantum mechanical nature of both electrons and nuclei in large-scale molecules and materials.

Fractionalized quantum excitations in correlated two-dimensional topological phases

The research field of topological phases and materials is one of the most exciting frontiers in modern condensed matter physics [1]; [2]; [3]; [4]; [5]; [6] ; [7]. In contrast to the classification of conventional condensed matter phases according to their symmetries, different topological states of matter generally do not involve broken symmetries. Rather, they are associated with certain fundamental physical properties that are insensitive to smooth changes in materials parameters. Therefore, a topological state cannot change into another unless the system undergoes a quantum phase transition [6] ; [7].

Incoherent population mixing contributions to phase-modulation two-dimensional coherent excitation spectra.

We present theoretical and experimental results showing the effects of incoherent population mixing on two-dimensional (2D) coherent excitation spectra that are measured via a time-integrated population and phase-sensitive detection. The technique uses four collinear ultrashort pulses and phase modulation to acquire two-dimensional spectra by isolating specific nonlinear contributions to the photoluminescence or photocurrent excitation signal. We demonstrate that an incoherent contribution to the measured line shape, arising from nonlinear population dynamics over the entire photoexcitation lifetime, generates a similar line shape to the expected 2D coherent spectra in condensed-phase systems. In those systems, photoexcitations are mobile such that inter-particle interactions are important on any time scale, including those long compared with the 2D coherent experiment. Measurements on a semicrystalline polymeric semiconductor film at low temperatures show that, in some conditions in which multi-exciton interactions are suppressed, the technique predominantly detects coherent signals and can be used, in our example, to extract homogeneous line widths. The same method used on a lead-halide perovskite photovoltaic cell shows that incoherent population mixing of mobile photocarriers can dominate the measured signal since carrier-carrier bimolecular scattering is active even at low excitation densities, which hides the coherent contribution to the spectral line shape. In this example, the intensity dependence of the signal matches the theoretical predictions over more than two orders of magnitude, confirming the incoherent nature of the signal. While these effects are typically not significant in dilute solution environments, we demonstrate the necessity to characterize, in condensed-phase materials systems, the extent of nonlinear population dynamics of photoexcitations (excitons, charge carriers, etc.) in the execution of this powerful population-detected coherent spectroscopy technique.

Geometrical shock dynamics applied to condensed phase materials

Taylor blast wave (TBW) theory and geometrical shock dynamics (GSD) theory describe a radially expanding shock wave front through an inert material, typically an ideal gas, in the strong blast wave limit and weak acoustic limit respectively. We simulate a radially expanding blast shock in air using a hydrodynamic simulation code and numerically describe the intermediate region between these two limits. We test our description of the intermediate shock phase through a two-dimensional simulation of the Bryson and Gross experiment. We then apply the principles of GSD to materials that follow the Mie–Gruneisen equation of state, such as plastics and metals, and derive an equation that accurately relates the acceleration, velocity and curvature of the shock through these materials. Along with detonation shock dynamics (DSD), which describes detonation shock propagation through high explosive fluids, we develop a hybrid DSD/GSD model for the simulation of heterogeneous explosives. This model enables computationally efficient simulation of the shock front in high explosive/inert mixtures consisting of simple or complex geometric configurations. We simulate an infinite two-dimensional slab consisting of one half explosive, PBXN-9, and one half aluminium and model the boundary angle conditions using shock polar analysis. We also simulate a series of high explosive unit cells embedded with aluminium spherical particles, and we compare the propagation of the detonation shock front with a direct numerical simulation performed with the ALE3D code.

Photodissociation dynamics of organic molecules in condensed phase by femtosecond transient grating spectroscopy

In condensed phase, the dissociation mechanism of molecule is different from that of isolated molecule due to the effect of interaction between molecules. How to effectively trace the reaction process and products in condensed phase is a technical problem which needs to be solved urgently. In this paper, femtosecond transient grating spectroscopy is used to investigate dissociation dynamics in condensed phase. Transient grating spectroscopy, as a coherent spectral technique, has some advantages such as high signal-noise ratio and free background, thus it can identify trace numbers of reaction products in dissociation. The investigation about model molecules such as iodomethane and nitromethane demonstrates that the transient grating technique can observe relaxation in electronic excited state and also has ability to track reactants, products, and vibration of molecule or perssad. The dissociation dynamics in condensed phase material is significant for understanding the reaction mechanism in the fields of biochemistry and detonation. Thus the femtosecond transient grating has a wide application prospect in these fields. In addition, the transient grating technique, as a non-contact diagnostic approach, can be easily adapted to high temperature and high pressure conditions, etc. Thus, the transient grating technique also has a potential value in the fields of phase transform dynamics and high pressure synthesis, etc.

Static three-dimensional topological solitons in fluid chiral ferromagnets and colloids.

Three-dimensional (3D) topological solitons are continuous but topologically nontrivial field configurations localized in 3D space and embedded in a uniform far-field background, that behave like particles and cannot be transformed to a uniform state through smooth deformations. Many topologically nontrivial 3D solitonic fields have been proposed. Yet, according to the Hobart-Derrick theorem, physical systems cannot host them, except for nonlinear theories with higher-order derivatives such as the Skyrme-Faddeev model. Experimental discovery of such solitons is hindered by the need for spatial imaging of the 3D fields, which is difficult in high-energy physics and cosmology. Here we experimentally realize and numerically model stationary topological solitons in a fluid chiral ferromagnet formed by colloidal dispersions of magnetic nanoplates. Such solitons have closed-loop preimages-3D regions with a single orientation of the magnetization field. We discuss localized structures with different linking of preimages quantified by topological Hopf invariants. The chirality is found to help in overcoming the constraints of the Hobart-Derrick theorem, like in two-dimensional ferromagnetic solitons, dubbed 'baby skyrmions'. Our experimental platform may lead to solitonic condensed matter phases and technological applications.

Surface-Induced Energetics, Electronic Structure, and Vibrational Properties of β-HMX Nanoparticles: A Computational Study

Surface chemistry plays an prominent part in the behaviors of condensed phase materials and nanoparticles. A combinational strategy based on density-functional theory (DFT) and density-functional tight-binding (DFTB) methods was used to study the surface-induced effect on the energetics, electronic structure, and vibrational properties of a series of β-octatetramethylene tetranitramine nanoparticles (β-HMX NPs). A comparative analysis of the NPs, isolated constituent molecule, and periodic solid-state phase of β-HMX indicates that the NPs possess quite different characteristics from either the constituent molecule or the bulk crystal. The anitsotropy of surface energies, enthalpy of sublimation, and melting point for the NPs are predicted. The surface-induced surface states of the HMX NPs lead to a significant reduction of the energy gap and provide active sites at surfaces. The vibrational properties of the experimentally determined strong modes are compared and discussed among the NPs, gas phase, and so...

Detection of nanostructures and soot in laminar premixed flames

This paper presents both in-situ and ex-situ measurements of nanostructures (also loosely referred to as nanoparticles) in laminar flames with the purpose of providing an understanding of their evolution to soot. Two laminar flame burners are studied covering a range of C/O ratios and hence different sooting propensities. Ex-situ measurements, utilizing soot sampling and analysis using differential mobility analyzers, are performed to yield information on the particle size distribution (PSD). A broad range of in-situ measurement techniques are employed including laser-induced fluorescence (LIF), laser-induced incandescence (LII), and elastic laser scattering. In-situ measurements completed at the University of Sydney, utilise fast response photomultiplier tubes to monitor time-resolved emission signals simultaneously in four different spectral regions, whilst measurements performed at the University of Naples Federico II are spectrally resolved. The temporal lifetimes of the LIF signals are found to be much longer than that expected for molecules at the same temperature, yet much shorter and spectrally different than that of soot particles. The laser based measurements, combined with the PSD results, suggest that LIF is able to track nanostructures as condensed phase matter with sizes in the order of few nanometers and with internal structures exhibiting the spectroscopic behavior of small PAHs. Conversely, LII is more suited for the detection of solid state particles which are larger in size and have a more aromatic character. It is found that close to the burner exit plane in the early regions of the flames LIF is measured both in the visible and ultraviolet (UV) bands, but not LII, implying the existence of nanostructures rather than soot. Further downstream, these nanostructures continue to exist but now in the presence of soot as is evident by the persistence of the LIF–UV and LIF–visible in conjunction with LII and laser scattering. Collectively, these findings confirm the hybrid nature of nanostructures that dominate the early evolution of soot.

Spectral functions of the uniform electron gas via coupled-cluster theory and comparison to theGWand related approximations

We use, for the first time, ab initio coupled-cluster theory to compute the spectral function of the uniform electron gas at a Wigner-Seitz radius of $r_\mathrm{s}=4$. The coupled-cluster approximations we employ go significantly beyond the diagrammatic content of state-of-the-art $GW$ theory. We compare our calculations extensively to $GW$ and $GW$-plus-cumulant theory, illustrating the strengths and weaknesses of these methods in capturing the quasiparticle and satellite features of the electron gas. Our accurate calculations further allow us to address the long-standing debate over the occupied bandwidth of metallic sodium. Our findings indicate that the future application of coupled-cluster theory to condensed phase material spectra is highly promising.

Non-commutative odd Chern numbers and topological phases of disordered chiral systems

An index theorem for higher Chern characters of odd Fredholm modules over crossed product algebras is proved, together with a local formula for the associated cyclic cocycle. The result generalizes the classic Noether–Gohberg–Krein index theorem, which in its simplest form states that the winding number of a complex-valued function over the circle is equal to the index of the associated Toeplitz operator. When applied to the non-commutative Brillouin zone, this generalization allows to define topological invariants for all condensed matter phases from the chiral unitary (or AIII-symmetry) class in the presence of strong disorder and magnetic fields, whenever the Fermi level lies in a region of Anderson localized spectrum.

Quantifying the Heterogeneous Dynamics of a Simulated Dipalmitoylphosphatidylcholine (DPPC) Membrane.

Heterogeneity of dynamics plays a vital role in membrane function, but the methods for quantifying this heterogeneity are still being developed. Here we examine membrane dynamical heterogeneity via molecular simulations of a single-component dipalmitoylphosphatidylcholine (DPPC) lipid bilayer using the MARTINI force field. We draw upon well-established analysis methods developed in the study of glass-forming fluids and find significant changes in lipid dynamics between the fluid (Lα), and gel (Lβ) phases. In particular, we distinguish two mobility groups in the more ordered Lβ phase: (i) lipids that are transiently trapped by their neighbors and (ii) lipids with displacements on the scale of the intermolecular spacing. These distinct mobility groups spatially segregate, forming dynamic clusters that have characteristic time (1-2 μs) and length (1-10 nm) scales comparable to those of proteins and other biomolecules. We suggest that these dynamic clusters could couple to biomolecules within the membrane and thus may play a role in many membrane functions. In the equilibrium membrane, lipid molecules dynamically exchange between the mobility groups, and the resulting clusters are not associated with a thermodynamic phase separation. Dynamical clusters having similar characteristics arise in many other condensed phase materials, placing membranes in a broad class of materials with strong intermolecular interactions.

A universal preconditioner for simulating condensed phase materials.

We introduce a universal sparse preconditioner that accelerates geometry optimisation and saddle point search tasks that are common in the atomic scale simulation of materials. Our preconditioner is based on the neighbourhood structure and we demonstrate the gain in computational efficiency in a wide range of materials that include metals, insulators, and molecular solids. The simple structure of the preconditioner means that the gains can be realised in practice not only when using expensive electronic structure models but also for fast empirical potentials. Even for relatively small systems of a few hundred atoms, we observe speedups of a factor of two or more, and the gain grows with system size. An open source Python implementation within the Atomic Simulation Environment is available, offering interfaces to a wide range of atomistic codes.