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Stabilised dense emulsions display a rich phenomenology connecting microstructure and rheology. In this work, we study how an emulsion with a finite yield stress can be built via large-scale stirring. By gradually increasing the volume fraction of the dispersed minority phase, under the constant action of a stirring force, we are able to achieve a volume fraction close to 80%. Despite the fact that our system is highly concentrated and not yet turbulent we observe a droplet size distribution consistent with the −10/3 scaling, often associated with inertial range droplets breakup. We report that the polydispersity of droplet sizes correlates with the dynamics of the emulsion formation process. Additionally, we quantify the visco-elastic properties of the dense emulsion finally obtained and we demonstrate the presence of a finite yield stress. The approach reported can pave the way to a quantitative understanding of the complex interplay between the dynamics of mesoscale constituents and the large-scale flow properties of yield stress fluids.

Viscoelastic (Maxwellian) slow, immiscible liquid-liquid displacement in a permeable medium is considered. The necessary and sufficient criteria for stability are that the displacing fluid is denser and less mobile than the displaced fluid. The instability criteria and critical wave length are found to be the same as those for ordinary viscous liquid-liquid displacements in permeable media.

We show that a viscous liquid confined between two low thermal conductive surfaces (Al2O3) emit a thermal response upon applying a low frequency (Hz) shear excitation. Hot and cold thermal waves are observed in situ at atmospheric pressure and room temperature, in polypropylene glycol layers of various thicknesses ranging from 100 microns up to 340 microns, upon applying a mechanical oscillatory shear strain. The observed thermal effects, synchronous with the mechanical excitation, are inconsistent with a homogeneous viscous flow. It indicates that mesoscopic liquids are able to (partly) convert mechanical shear energy in non-equilibrium thermodynamic states. This effect called thermoelasticity is well known in solid materials. The observation of a thermal coupling to the mechanical shear deformation reinforces the assumption of elastically correlated liquid molecules. The amplitude of the thermoelastic waves increases linearly by increasing the shear strain amplitude up to a transition to a non-linear thermal behavior, similar in strain behavior to an elastic to plastic regime. The thermo-elastic effects are not detectable via stress measurements and thus appear as a complementary liquid dynamic characterization., Comment: 10_pages

Glass formation is encountered in diverse materials. Experiments have revealed that dynamic relaxation spectra of supercooled liquids generically become asymmetric near the glass transition temperature, $T_g$, where an extended power law emerges at high frequencies. The microscopic origin of this "wing" remains unknown, and was so far inaccessible to simulations. Here, we develop a novel computational approach and study the equilibrium dynamics of model supercooled liquids near $T_g$. We demonstrate the emergence of a power law wing in numerical spectra, which originates from relaxation at rare, localised regions over broadly-distributed timescales. We rationalise the asymmetric shape of relaxation spectra by constructing an empirical model associating heterogeneous activated dynamics with dynamic facilitation, which are the two minimal physical ingredients revealed by our simulations. Our work offers a glimpse of the molecular motion responsible for glass formation at relevant experimental conditions., Comment: 5 pages, 4 figures, supplementary materials

A molecular-kinetic model of the processes of highly elastic deformation of amorphous polymers is proposed and, on its basis, nonlinear rheological equations are obtained; these latter make it possible to describe these processes under changes of deformation conditions in a wide range: temperature, deforming stress, and strain rate. A connection of the nonlinear micromechanical model of a polymer with the classical macromechanical model of a standard linear body is established. The transitions between the structural-deformation states of a warm and frozen elastomer, as well as the effects of low-temperature deformation melting and quantum elasticity of an amorphous polymer, are discussed.

The negative internal energetic contribution to the elastic modulus (negative energetic elasticity) has been recently observed in polymer gels. This finding challenges the conventional notion that the elastic moduli of rubberlike materials are determined mainly by entropic elasticity. However, the microscopic origin of negative energetic elasticity has not yet been clarified. Here, we consider the $n$-step interacting self-avoiding walk on a cubic lattice as a model of a single polymer chain (a subchain of a network in a polymer gel) in a solvent. We theoretically demonstrate the emergence of negative energetic elasticity based on an exact enumeration up to $n=20$ and analytic expressions for arbitrary $n$ in special cases. Furthermore, we demonstrate that the negative energetic elasticity of this model originates from the attractive polymer--solvent interaction, which locally stiffens the chain and conversely softens the stiffness of the entire chain. This model qualitatively reproduces the temperature dependence of negative energetic elasticity observed in the polymer-gel experiments, indicating that the analysis of a single chain can explain the properties of negative energetic elasticity in polymer gels., Comment: 6 pages, 5 figures (main text); 21 pages, 4 figures (Supplemental Material)

Continuum models of active nematic gels have proved successful to describe a number of biological systems consisting of a population of rod-like motile subunits in a fluid environment. However, to get a thorough understanding of the collective processes underlying the behaviour of active biosystems, the theoretical underpinnings of these models still need to be critically examined. To this end, we derive a minimal model based on a nematic elastomer energy, where the key parameters have a simple physical interpretation and the irreversible nature of activity emerges clearly. The interplay between viscoelastic material response and active dynamics of the microscopic constituents is accounted for by material remodelling. Partial degree of order and defect dynamics is included as a result of the kinematic coupling between the nematic elastomer shape-tensor and the orientational ordering tensor Q . In a simple one-dimensional channel geometry, we use linear stability analysis to show that even in the isotropic phase, the interaction between flow-induced local nematic order and activity results in a spontaneous flow of particles.

Funder: Dutch Research Council (NWO), Colloidal molecules are designed to mimic their molecular analogues through their anisotropic shape and interactions. However, current experimental realizations are missing the structural flexibility present in real molecules thereby restricting their use as model systems. We overcome this limitation by assembling reconfigurable colloidal molecules from silica particles functionalized with mobile DNA linkers in high yields. We achieve this by steering the self-assembly pathway toward the formation of finite-sized clusters by employing high number ratios of particles functionalized with complementary DNA strands. The size ratio of the two species of particles provides control over the overall cluster size, i.e., the number of bound particles N, as well as the degree of reconfigurability. The bond flexibility provided by the mobile linkers allows the successful assembly of colloidal clusters with the geometrically expected maximum number of bound particles and shape. We quantitatively examine the self-assembly dynamics of these flexible colloidal molecules by a combination of experiments, agent-based simulations, and an analytical model. Our "flexible colloidal molecules" are exciting building blocks for investigating and exploiting the self-assembly of complex hierarchical structures, photonic crystals, and colloidal metamaterials.

Aqueous dispersions of geometrically anisometric nano sized sodium-montmorillonite (Na-Mt) display a sol–gel transition at very low solids concentrations. The microstructure of the gel formed at very low ionic strengths is considered electrostatically repulsive with a nematic character, and the gel state at ionic strengths where Debye length is of the order of particle size is conjectured to be physical aging free. Here, we investigate the true nature of osmotically prepared Na-Mt dispersions at low ionic strength (~10-5 M), below and above the gel point. The sol phase exhibited very low yield stress than the gel state, without any sign of physical aging, thus behaving as a equilibrium state. In contrast, the gel exhibited signatures of physical aging, that is, an evolving microstructure which consolidates with time when left undisturbed thus behaving as out of equilibrium state. The physical aging behaviour becomes more pronounced at Na-Mt concentrations far above the gel point. A critical shear rate existed, below which no stable flows were possible in the gel state representing the microstructural reorganization timescale. Overall, Na-Mt dispersions in the gel state behaves as out of equilibrium systems with an ever-evolving microstructure, in opposition to the assumption that low ionic strength Na-Mt gels are an equilibrium phase. The possible origin of physical aging such as reversible orientation of Brownian anisotropic particles, stiffening of an existing microstructure or reorganization of microstructure towards minimal energy configuration has been discussed in detail.

11 pags., 6 figs., We have assessed the performance and accuracy of different wavefunction-based electronic structure methods, such as DFMP2 and domain-based local pair-natural orbital (DLPNO-CCSD(T)), as well as a variety of density functional theory (DFT) approaches on He@(H2O)N cage systems. We have selected representative clathrate-like structures corresponding to the building blocks present in each of the sI, sII and sH natural gas clathrate hydrates, and we have carefully studied the interaction between a He atom with each of their individual cages. We reported well-converged DFMP2 and DLPNO-CCSD(T) reference data, together with interaction and cohesive energies of four different density functionals (two GGA, revPBE and PW86PBE, and two hybrids, B3LYP and PBE0), including diverse dispersion correction schemes (D3(0), D3(BJ), D4 and XDM) for both He-filled and empty clathrate-like cages. After the analysis of the results, we came to the conclusion that the PW86PBE functional, with both XDM and D4 corrections, and the PBE0-D4 functional present reasonably adequate approaches to describe the guest-host noncovalent interactions that take place in such He clathrate hydrates. Taking into account that the He@sII is the only helium clathrate that scientists have been able to synthesize recently, we have performed a thermodynamic study on the individual 512 and 51264 cages present in the sII crystal. We determined the change in enthalpy, ΔH, and in Gibbs free energy, ΔG, at various temperatures and pressures, and we found out that in the range of experimental conditions the reactions associated with the encapsulation of the He atom inside the cages are exothermic and spontaneous. Finally, we highlighted the importance of an accurate description of the interaction in He@water mixtures, as a crucial component in construction of reliable data-driven models. This journal is, The authors thank to Centro de Calculo del IFF, SGAI (CSIC) and CESGA for allocation of computer time. This work has been supported by MINECO grant No. FIS2017-83157-P, MICINN grant No, PID2020-114654GB-I00, Comunidad de Madrid grant No. IND2018/TIC-9467, and COST Action CA18212(MD-GAS).

The dynamics of polymer-grafted nanoparticles (PGNPs) in melts of unentangled linear chains were investigated by means of coarse-grained molecular dynamics simulations. The results demonstrated that the graft monomers closer to the particle surface relax more slowly than those farther away due to the constraint of the grafted surface and the confinement of the neighboring chains. Such heterogeneous relaxations of the surrounding environment would perturb the particle motion, making them fluctuating around their centers before they can diffuse through the melt. During such intermediate-time stage, the dynamics is subdiffusive while the distribution of particle displacements is Gaussian, which can be described by the popular fractional Brownian motion model. For the long-time Fickian diffusion, we found that the diffusivity

The fundamental relationships between the structure and properties of liquids are far from being well understood. For instance, the structural origins of many liquid anomalies still remain unclear, but liquid-liquid transitions (LLT) are believed to hold a key. However, experimental demonstrations of LLTs have been rather challenging. Here, we report experimental and theoretical evidence of a second-order-like LLT in molten tin, one which favors a percolating covalent bond network at high temperatures. The observed structural transition originates from the fluctuating metallic/covalent behavior of atomic bonding, and consequently a new paradigm of liquid structure emerges. The liquid structure, described in the form of a folded network, bridges two well-established structural models for disordered systems, i.e., the random packing of hard-spheres and a continuous random network, offering a large structural midground for liquids and glasses. Our findings provide an unparalleled physical picture of the atomic arrangement for a plethora of liquids, shedding light on the thermodynamic and dynamic anomalies of liquids but also entailing far-reaching implications for studying liquid polyamorphism and dynamical transitions in liquids., Unraveling the structural origin of liquid anomalies remains a challenging topic. Xu et al. propose a folded-network structural model for molten tin and provide insights into the observed second-order-like structural transition.

The complex relaxation dynamics in the identified thermodynamic states of a chiral smectogenic glass-former was studied.

We introduce a model for particles that are extremely polydisperse in size compared to monodisperse and bidisperse systems. In two dimensions (2D), size polydispersity inhibits crystallization and increases packing fraction at jamming points. However, no packing pattern common to diverse polydisperse particles has been reported. We focused on polydisperse particles with a power size distribution $r^{-a}$ as a ubiquitous system that can be expected to be scale-invariant. We experimentally and numerically constructed 2D random packing for various polydisperse particles with different size exponents, $a$. Analysis of the packing pattern revealed a common contact number distribution for $a, Comment: 8 pages, 5 figures

Smectic materials represent a unique state between fluids and solids, characterized by orientational and partial positional order, making them notoriously difficult to model, particularly in confining geometries. We propose a complex order parameter tensor to describe the local degree of lamellar ordering, layer displacement and orientation. The theory accounts for both dislocations and disclinations, as well as arrested configurations and colloid-induced local ordering. It considerably simplifies numerics, facilitating studies on the dynamics of topologically complex lamellar systems., Comment: 6 pages, 3 figures

A general theory has been developed for a polydisperse semi-flexible multi-block copolymer melt. Using the Bawendi-Freed approach to model semi-flexible chains an expression for the Landau free energy is derived in the weak segregation regime which includes the density and orientation order-parameters. The orientation order-parameter is described in the smectic phase and in more complicated structures such as the hexagonal phase. The Landau free energy contains contributions of two kinds of interactions. The first kind is the Flory- Huggins interaction which describes the incompatibility of chemically different blocks and may induce microphase separation. The second kind is the Maier- Saupe interaction which may induce nematic ordening. In the framework of the weak segragation limit the Landau theory allows to predict phase structures in the melt as a function of the composition, persistence length and the strength of the Flory-Huggins and Maier-Saupe interaction. The general theory is applied to a simple system of monodisperse semi-flexible diblock copolymers. In several phase diagrams a number of possible phase structures is predicted such as the bcc, hexagonal, smectic-A, smectic-C and nematic phase. The infuence of the Maier-Saupe interaction on the microphase structure is thoroughly discussed., 63 pages, 6 figures, to be published in The Journal of Chemical Physics

In Nucleation and Growth, the process by which most heterogeneous systems form, thermodynamics sets the asymptotic boundaries toward which the system must evolve, while kinetics tries to cope with it by imposing the transport rates. In all heterogeneous colloidal systems observed in nature, composition, shape, structure and physical properties result from the trade-off between thermodynamics and kinetics. Here we show, by carefully selecting colloidal systems and controlling phase separation in microfluidic devices, that it becomes possible to disentangle kinetics effects from thermodynamics. Using amyloids and nanocellulose filamentous colloids, we demonstrate that decoupling kinetics from thermodynamics in the phase separation process unveils new physical phenomena, such as orders of magnitude shorter timescales, a wider phase diagram, and structures that are not observable via conventional liquid-liquid phase separation. Our approach enables on-demand fabrication of multicomponent heterogeneous liquid crystals, enhancing their potential, and introducing original fundamental and technological directions in multicomponent structured fluids., Nature Communications, 14 (1), ISSN:2041-1723

We combine the swap Monte Carlo algorithm to long multi-CPU molecular dynamics simulations to analyse the equilibrium relaxation dynamics of model supercooled liquids over a time window covering ten orders of magnitude for temperatures down to the experimental glass transition temperature $T_g$. The analysis of \rev{several} time correlation functions coupled to spatio-temporal resolution of particle motion allow us to elucidate the nature of the equilibrium dynamics in deeply supercooled liquids. We find that structural relaxation starts at early times in rare localised regions characterised by a waiting time distribution that develops a power law near $T_g$. At longer times, relaxation events accumulate with increasing probability in these regions as $T_g$ is approached. This accumulation leads to a power-law growth of the linear extension of relaxed domains with time with a large, temperature-dependent dynamic exponent. Past the average relaxation time, unrelaxed domains slowly shrink with time due to relaxation events happening at their boundaries. Our results provide a complete microscopic description of the particle motion responsible for key experimental signatures of glassy dynamics, from the shape and temperature evolution of relaxation spectra to the core features of dynamic heterogeneity. They also provide a microscopic basis to understand the emergence of dynamic facilitation in deeply supercooled liquids and allow us to critically reassess theoretical descriptions of the glass transition., Comment: 22 pages, 21 figures

We propose a class of tangled vortex structures, tied from non-Abelian topological vortices, which are immune against decaying through local reconnections and strand crossings that are allowed by the system. We refer to such structures as being topologically protected. We then turn our attention to topological vortices classified by the quaternion group $Q_8$ ($Q_8$-colored links), which are realizable in systems consisting either of the biaxial nematic or the cyclic phase of a spin-2 Bose--Einstein condensate, or of biaxial nematic liquid crystal, and prove the existence of topologically protected $Q_8$-colored links. Remarkably, the strongest invariant we construct, the $Q$-invariant of $Q_8$-colored links, can be used to classify $Q_8$-colored links up to allowed local surgeries on the vortex cores., 29 pages, 12 figures. Comments welcome!

Time-dependent dynamical properties of a fluid can not be estimated from a single configuration without performing a simulation. Here we show, however, that the scaling properties of both structure and dynamics can be predicted from a single configuration. The new method is demonstrated to work very well for equilibrium dynamics of the Kob-Andersen Binary Lennard-Jones mixture. Furthermore, the method is applied to isobaric cooling where the liquid falls out of equilibrium and forms a glass, demonstrating that the method requires neither equilibrium nor constant volume conditions to work, in contrast to existing methods., 11 pages, 5 figures

The evolution of the microstructure due to spinodal decomposition in phase separated mixtures has a strong impact on the final material properties. In the late stage of coarsening, the system is characterized by the growth of a single characteristic length scale L ∼ Ctα. To understand the structure–property relationship, the knowledge of the coarsening exponent α and the coarsening rate constant C is mandatory. Since the existing literature is not entirely consistent, we perform phase field simulations based on the Cahn–Hilliard equation. We restrict ourselves to binary mixtures using a symmetric Flory–Huggins free energy and a constant composition-independent mobility term and show that the coarsening for off-critical mixtures is slower than the expected t1/3-growth. Instead, we find α to be dependent on the mixture composition and associate this with the observed morphologies. Finally, we propose a model to describe the complete coarsening kinetics including the rate constant C.

Substitutional metal doping is a powerful strategy for manipulating the emission spectra and excited state dynamics of semiconductor nanomaterials. Here, we demonstrate the synthesis of colloidal manganese (Mn

For iron-based superconductors, the phase diagrams under pressure or strain exhibit emergent phenomena between unconventional superconductivity and other electronic orders, varying in different systems. As a stoichiometric superconductor, LiFeAs has no structure phase transitions or entangled electronic states, which manifests an ideal platform to explore the pressure or strain effect on unconventional superconductivity. Here, we observe two types of superconducting states controlled by orientations of local wrinkles on the surface of LiFeAs. Using scanning tunneling microscopy/spectroscopy, we find type-I wrinkles enlarge the superconducting gaps and enhance the transition temperature, whereas type-II wrinkles significantly suppress the superconducting gaps. The vortices on wrinkles show a C2 symmetry, indicating the strain effects on the wrinkles. By statistics, we find that the two types of wrinkles are categorized by their orientations. Our results demonstrate that the local strain effect with different directions can tune the superconducting order parameter of LiFeAs very differently, suggesting that the band shifting induced by directional pressure may play an important role in iron-based superconductivity., The evolution of superconductivity in LiFeAs with respect to pressure or strain remains elusive. Here, the authors observe different response of superconducting states due to different orientations of local wrinkles on the surface of LiFeAs.

Liquid-liquid phase separation of multivalent proteins and RNAs drives the formation of biomolecular condensates that facilitate membrane-free compartmentalization of subcellular processes. With recent advances, it is becoming increasingly clear that biomolecular condensates are network fluids with time-dependent material properties. Here, employing microrheology with optical tweezers, we reveal molecular determinants that govern the viscoelastic behavior of condensates formed by multivalent Arg/Gly-rich sticker-spacer polypeptides and RNA. These condensates behave as Maxwell fluids with an elastically-dominant rheological response at shorter timescales and a liquid-like behavior at longer timescales. The viscous and elastic regimes of these condensates can be tuned by the polypeptide and RNA sequences as well as their mixture compositions. Our results establish a quantitative link between the sequence- and structure-encoded biomolecular interactions at the microscopic scale and the rheological properties of the resulting condensates at the mesoscale, enabling a route to systematically probe and rationally engineer biomolecular condensates with programmable mechanics., Here the authors show that disordered polypeptide-RNA condensates exhibit rheological properties similar to that of a viscoelastic Maxwell fluid, and use simple polypeptide design rules to create microcondensates with tunable viscoelasticity.

Liquid-phase exfoliation can be developed for the large-scale production of two-dimensional materials for photonic applications. Although atomically thin 2D transition metal dichalcogenides (TMDs) ...

The electron dynamics of atomically thin 2-D polar metal heterostructures, which consisted of a few crystalline metal atomic layers intercalated between hexagonal silicon carbide and graphene grown from the silicon carbide, were studied using nearly degenerate transient absorption spectroscopy. Optical pumping created charge carriers in both the 2-D metals and graphene components. Wavelength-dependent probing suggests that graphene-to-metal carrier transfer occurred on a sub-picosecond time scale. Following rapid (300 fs) carrier-carrier scattering, charge carriers monitored through the metal interband transition relaxed through several consecutive cooling mechanisms that included sub-picosecond carrier-phonon scattering and dissipation to the silicon carbide substrate over tens of picoseconds. By studying 2-D In, 2-D Ga, and a Ga/In alloy, we resolved accelerated electron-phonon scattering rates upon alloy formation as well as structural influences on the excitation of in-plane phonon shear modes. More rapid cooling in alloys is attributed to increased lattice disorder, which was observed through correlative polarization-resolved second harmonic generation and electron microscopy. This connection between the electronic relaxation rates, far-field optical responses, and metal lattice disorder is made possible by the intimate relation between nonlinear optical properties and atomic-level structure in these materials. These studies provided insights into electronic carrier dynamics in 2-D crystalline elemental metals, including resolving contributions from specific components of a 2-D metal-containing heterojunction. The correlative ultrafast spectroscopy and nonlinear microscopy results suggest that the energy dissipation rates can be tuned through atomic-level structures.

Potential flow of 3He through a nematic aerogel of spherical shape is considered. A characteristic feature of the system under consideration is that the superfluid phases inside and outside the aerogel may be different. In particular, the cases are considered when the polar phase of superfluid 3He is implemented inside the aerogel, while, outside the aerogel, there exists either the B or the A phase of superfluid 3He. Under the condition that the order parameter of the system is a continuous function of the spatial coordinate without singular points and lines on the aerogel surface, as well as that there are no Josephson currents through the aerogel surface, boundary conditions needed for the hydrodynamic description of the flow are obtained for the phase of the order parameter on the aerogel surface. With the use of these boundary conditions, the added mass tensor of the potential flow of a fluid is found in the cases under consideration. A comparison with available experimental data is made.

In order to deepen the fundamental knowledge between the structure of ring diblock copolymers and their physico-chemical properties in bulk and in solution, this paper is devoted to a theoretical approach of the structural properties of such polymeric system. This study based on the equation of Benoit, which is a generalization of the relation of Zimm written in its matrix form. We mainly discuss the case of binary mixtures consisting of a diblock copolymer A-B in solution and in the bulk state. To this end, we have investigated the variations of the partial structure factor Saa(Q) as a function of the normalized wave-vector for various parameters. In particular, we have emphasized on the position of the scattering peak Qmax, its amplitude Saa(Qmax) and zero angle signal Saa(Q=0). The main conclusion is that, the circularity of cyclic chains affects drastically the structural properties of the system under consideration.

Phase-separated biomolecular condensates must respond agilely to biochemical and environmental cues in performing their wide-ranging cellular functions, but our understanding of condensate dynamics is lagging. Ample evidence now indicates biomolecular condensates as viscoelastic fluids, where shear stress relaxes at a finite rate, not instantaneously as in viscous liquids. Yet the fusion dynamics of condensate droplets has only been modeled based on viscous liquids, with fusion time given by the viscocapillary ratio (viscosity over interfacial tension). Here we used optically trapped polystyrene beads to measure the viscous and elastic moduli and the interfacial tensions of four types of droplets. Our results challenge the viscocapillary model, and reveal that the relaxation of shear stress governs fusion dynamics. These findings likely have implications for other dynamic processes such as multiphase organization, assembly and disassembly, and aging., Phase-separated biomolecular condensates are implicated in a myriad of biological processes. Here the authors apply optical tweezers to characterize the viscoelasticity and interfacial tension of a range of condensates, finding that condensates can deviate from simple fluids in opposite directions; and identify shear relaxation as a governing measure of condensate dynamics.

In this work, it is shown that the advantage of using matrix-stabilized magnetic nanoparticles to obtain polymer nanocomposites based on them is that such nanoparticles retain their dispersion and stability of size and shape in the technological modes of obtaining polymer nanocomposite materials, and thus ensured stable ferro- and superparamagnetic properties of the obtained target products. For the production of films by the method of hot pressing from blanks obtained in an injection molding machine or a mechanochemical mixture, a manual electrically heated hydraulic press was used. The magnetic properties of nanocomposite samples (about 50 mg on average) were studied using a vibration magnetometer. The character of the dependence of the magnetization on the magnitude of the magnetic field confirms the ferromagnetic character of the behavior of the obtained nanocomposites. The resulting film nanocomposites exhibit ferromagnetic properties at room temperature.

When compound jets are covered with surfactant on both interfaces, the property of those interfaces will be viscoelastic, unlike the Newtonian fluid interface. In this paper, the effects of surface viscoelasticity are principally studied through linear stability analysis and calculated using the Chebyshev spectral collocation method. Both surface elasticity and viscosity have properties to make the jet more stable, but the physical effects behind the two influencing mechanisms are different. When the inner and outer interfaces are separately covered with surfactant, the variations of surface viscoelastic parameters affect the growth rate and dominant wavenumber differently. In addition, the sensitivity of the maximum growth rate to the surface viscoelastic parameters depends on which interface the surfactant covers. A significant increase in the surface shear viscosity reduces the influence of surface elasticity on the maximum growth rate. The long-wave assumption was adopted to derive a one-dimensional dispersion equation in an algebraic form. The comparison between the simplified expression and the numerical results validated the applicability of the one-dimensional model in the vicinity of small wavenumber.

A novel type of Marangoni convection was predicted theoretically a decade ago. The thin liquid film atop a substrate of low thermal conductivity was considered. In the case of heating from below, the Marangoni convection emerges not only in a conventional stationary regime, but also as oscillatory flows. Specifically, the oscillatory Marangoni convection emerges if (1) the heat flux from the free surface is small, and (2) the large-scale deformation of the free surface is allowed. During the past decade, this novel Marangoni convection was detected and investigated in several other theoretical works. The review discusses the recent achievements in studying the oscillatory Marangoni convection in a thin film heated from below. The guiding data for observation of the oscillatory regime are also provided. Several recent theoretical works reveal the oscillatory Marangoni instability in thin liquid film atop a heated substrate. The oscillatory regime of convection can be observed in ultrathin films (~ 0.01 mm for water) or under microgravity conditions. The surface tension should allow interface deformations, and the heat transfer from the liquid to the ambient gas should be small.

We propose a microscopic picture for understanding the nonlinear rheology of supercooled liquids with soft-repulsive potentials. Based on Brownian dynamics simulations of supercooled charge-stabilized colloidal suspensions, our analysis shows that the shear thinning of viscosity (eta) at large enough shear rates (sr), expressed as eta~sr^(-lambda), originates from the evolution of the localized elastic region (LER). An LER is a transient region composed of the first several coordination shells of a reference particle. In response to the external shear, particles within LER undergo nearly affine displacement before the yielding of LER. The characteristic strain (gamma) and size (xi) of LER respectively depend on the shear rate by gamma~sr^epsilon and xi~sr^(-nu). Three exponents, lambda, epsilon, and nu, are related by lambda=1-epsilon=4*nu. This simple relation connects the nonlinear rheology to the elastic properties and the microscopic configurational distortion of the system. The relaxation of the LER is promoted by the large-step nonaffine particle displacement along the extensional direction of the shear geometry with the step length of 0.4 particle diameter. The elastic deformation and the relaxation of the LER are ubiquitous and succesive in the flow, which compose the fundamental process governing the bulk nonlinear viscoelasticity. We apply this model to analyze the Rheo-Small Angle Neutron Scattering data of sheared charge-stabilized colloidal suspensions. It is seen that our model well explains the neutron spectra and the rheological data., 21 pages,15 figures

Despite the extensive research that has been conducted for decades on the behavior of confined liquids, detailed knowledge of this phenomenon, particularly in the mixed/boundary lubrication regime, remains limited. This can be attributed to several factors including the difficulty of direct experimental observations of the behavior of lubricant molecules under non-equilibrium conditions, the high computational cost of molecular simulations to reach steady state, and the low signal-to-noise ratio at extremely low shear rates corresponding to actual operating conditions. To this end, we studied the correlation between the structure formation and shear viscosity of octamethylcyclotetrasiloxane confined between two mica surfaces in a mixed/boundary lubrication regime. Three different surface separations corresponding to two-, three-, and five-layered structures were considered to analyze the effect of confinement. The orientational distributions with one specific peak for $n=2$ and two distributions, including a parallel orientation with the surface normal for $n>2$, were observed at rest. The confined liquids exhibited a distinct shear-thinning behavior independent of surface separations for a relatively low sliding velocity, $V_{\rm x}\lesssim 10^{-1}\,{\rm m/s}$. However, the shear viscosities at $V_{\rm x}\lesssim 10^{-1}\,{\rm m/s}$ depended on the number of layered structures. Newtonian behavior was observed with a further increase in the sliding velocity. Furthermore, we found a strong correlation between the degree of molecular orientation and the shear viscosity of the confined liquids. The magnitude of the shear viscosity of the confined liquids can primarily be determined by the degree of molecular orientation, and shear-thinning originates from the vanishing of specific orientational distributions with increasing sliding velocity., 8 pages, 5 figures

Colloidal patchy particles with divalent attractive interaction can self-assemble into linear polymer chains. Their equilibrium properties in 2D and 3D are well described by Wertheim's thermodynamic perturbation theory which predicts a well-defined exponentially decaying equilibrium chain length distribution. In experimental realizations, due to gravity, particles sediment to the bottom of the suspension forming a monolayer of particles with a gravitational height smaller than the particle diameter. In accordance with experiments, an anomalously high monomer concentration is observed in simulations which is not well understood. To account for this observation, we interpret the polymerization as taking place in a highly confined quasi-2D plane and extend the Wertheim thermodynamic perturbation theory by defining addition reactions constants as functions of the chain length. We derive the theory, test it on simple square well potentials, and apply it to the experimental case of synthetic colloidal patchy particles immersed in a binary liquid mixture that are described by an accurate effective critical Casimir patchy particle potential. The important interaction parameters entering the theory are explicitly computed using the integral method in combination with Monte Carlo sampling. Without any adjustable parameter, the predictions of the chain length distribution are in excellent agreement with explicit simulations of self-assembling particles. We discuss generality of the approach, and its application range., Comment: The following article has been submitted to The Journal of Chemical Physics

Similar to cells, bacteria, and other microorganisms, synthetic chemically-active colloids can harness the energy from their environment through a surface chemical reaction and use its energy to self-propel in fluidic environments. In this paper, we study the chemo-mechanical coupling that leads to the self-propulsion of chemically active colloids. The coupling between chemical reactions and momentum transport is a consequence of the Onsager reciprocal relations. They state that the velocity and the surface reaction rate are related to the mechanical and chemical affinities through a symmetric matrix. A consequence of the Onsager reciprocal relations is that, if a chemical reaction drives the motion of the colloid, then an external force generates a reaction rate. Here, we investigate the Onsager reciprocal relations for a spherical active colloid that catalyzes a reversible surface chemical reaction between two species. We solve the relevant transport equations using a perturbation expansion and numerical simulations to demonstrate the validity of the reciprocal relations around the equilibrium. Our results are consistent with previous studies and highlight the key role of solute advection in preserving the symmetry of the Onsager matrix. Finally, we show that the Onsager reciprocal relations break down around a nonequilibrium steady state, which has implications for the thermal fluctuations of the active colloids used in experiments.

The blue phases are observed in highly chiral liquid crystalline compositions that nascently organize into a three-dimensional, crystalline nanostructure. The periodicity of the unit cell lattice spacing is on the order of the wavelength of visible light and accordingly, the blue phases exhibit a selective reflection as a photonic crystal. Here, we detail the synthesis of liquid crystalline elastomers that retain blue phase I, blue phase II, and blue phase III. The mechanical properties and optical reconfiguration via deformation of retained blue phases are contrasted to the cholesteric phase in fully solid elastomers with glass transition temperatures below room temperature. Mechanical deformation and chemical swelling of the lightly crosslinked polymer networks induces lattice asymmetry in the blue phase evident in the tuning of the selective reflection. The lattice periodicity of the blue phase elastomer is minimally affected by temperature. The oblique lattice planes of the blue phase tilt and red-shift in response to mechanical deformation. The retention of the blue phases in fully solid, elastomeric films could enable functional implementations in photonics, sensing, and energy applications., Permanently retaining liquid crystalline blue phases in a solid matrix warrants many prospective applications in photonics. Schlafmann and White are able to make a blue phase rubber that retains a crystalline structure upon deformation and responds with angle-dependent color changes.

The effect of magnetic field of 0.3 T on the concentration, distribution of sizes in suspension and zeta potential of colloidal gold and colloidal silver nanoparticles, obtained by considering the pulsed laser ablation in double distilled water was studied. The magnetic field was transverse to the direction of incidence of the laser radiation and parallel to the surface of a submerged target. An Nd: YAG laser was used (1064 nm in wavelength, 10 ns in duration, repetition rate of 10 Hz and 37 mJ of energy) to ablate targets. The colloids were characterized by inductively coupled plasma optical emission spectroscopy, ultraviolet-visible spectroscopy, dynamic light scattering and zeta potential. Concentration analysis suggested that applying magnetic field of 0.3 T during nanoparticle synthesis leads to higher concentration. Applying magnetic field led to an eleven percent increase in the concentration of the colloid with gold nanoparticles and a five percent increase in the concentration of the colloidal silver nanoparticles. The absorption spectra suggested the presence of spherical nanoparticles. When analyzing the effect of the magnetic field on the hydrodynamic size distribution of the nanoparticles and the zeta potential of the colloids, no significant changes were evidenced. The magnetic confinement of the plasma induced by laser ablation caused changes in the characteristics of the colloids.

The development of appropriate methods to correlate the structure and optical properties of colloidal photonic structures is still a challenge. Structural information is mostly obtained by electron, X-ray, or optical microscopy methods and X-ray diffraction, while bulk spectroscopic methods and low resolution bright-field microscopy are used for optical characterization. Here, we describe the use of reflectance confocal microscopy as a simple and intuitive technique to provide a direct correlation between the ordered/disordered structural morphology of colloidal crystals and glasses, and their corresponding optical properties.

Laser-induced hydrodynamic (LIH) motions in nematic liquid crystal (NLC) which is an initially oriented hybrid have been studied theoretically. For the direction when the flow velocity is directed out of the “flexible ribbon’s” curvature, it brings an increase of the curvature. But when the velocity has the opposite direction, we have two different cases depending on the surface anchoring energies. When there is a strong boundary condition (anchoring energy >10–1 erg/cm2) on the planar oriented wall, and there is a week boundary condition (anchoring energy ≈10–3 erg/cm2) on the homeotropic oriented wall, the molecules of a liquid crystal (LC) take the direction of the flow. “Flexible ribbon’s” curvature is reversed when is given a week boundary condition on the planar oriented wall and on the homeotropic oriented wall is given strong boundary condition.

The theory of thermoelasticity with three-phase-lag is used to study the phase lag effects on wave propagation in granular medium. A two-dimensional thick granular plate with axisymmetric temperatu...

A stochastic theoretical analysis of electromagnetic wave propagation inside a planar slab waveguide filled with a cholesteric material, whose azimuthal angular component on its director n is rando...

The dynamics near the surface of glasses can be much faster than in the bulk. We studied the surface dynamics of a Pt-based metallic glass using electron correlation microscopy with sub-nanometer resolution. Our studies show an ∼20 K suppression of the glass transition temperature at the surface. The enhancement in surface dynamics is suppressed by coating the metallic glass with a thin layer of amorphous carbon. Parallel molecular dynamics simulations on Ni80P20 show a similar temperature suppression of the surface glass transition temperature and that the enhanced surface dynamics are arrested by a capping layer that chemically binds to the glass surface. Mobility in the near-surface region occurs via atomic caging and hopping, with a strong correlation between slow dynamics and high cage-breaking barriers and stringlike cooperative motion. Surface and bulk dynamics collapse together as a function of temperature rescaled by their respective glass transition temperatures.

The interplay of different electronic phases underlies the physics of unconventional superconductors. One of the most intriguing examples is a high-temperature superconductor, FeTe1 – xSex (refs. 1–11). This superconductor undergoes both a topological transition3,4, linked to the electronic band inversion, and an electronic nematic phase transition, associated with rotation symmetry breaking, around the same Se composition where the superconducting transition temperature peaks12,13. In this regime, nematic fluctuations and symmetry-breaking strain could be important, but this is yet to be fully explored. Using spectroscopic-imaging scanning tunnelling microscopy, we study the electronic nematic transition in FeTe1 – xSex as a function of composition. Near the critical Se composition, we find electronic nematicity in nanoscale regions. The superconducting coherence peaks are suppressed in areas where static nematic order is the strongest. By analysing atomic displacement in scanning tunnelling microscopy topographs, we find that small anisotropic strain can give rise to these strongly nematic localized regions. Our experiments reveal a tendency of FeTe1 – xSex, near x ≈ 0.45, to form puddles hosting static nematic order, suggestive of nematic fluctuations pinned by structural inhomogeneity, and demonstrate the effect of anisotropic strain on superconductivity in this regime. The interplay of superconductivity and nematicity of electrons remains unclear in a wide range of materials. Now, more evidence emerges that nematic fluctuations can be pinned into a static phase by disorder, which hinders the superconductivity.

Much attention has been devoted to water’s metastable phase behavior, including polyamorphism (multiple amorphous solid phases), and the hypothesized liquid-liquid transition and associated critical point. However, the possible relationship between these phenomena remains incompletely understood. Using molecular dynamics simulations of the realistic TIP4P/2005 model, we found a striking signature of the liquid-liquid critical point in the structure of water glasses, manifested as a pronounced increase in long-range density fluctuations at pressures proximate to the critical pressure. By contrast, these signatures were absent in glasses of two model systems that lack a critical point. We also characterized the departure from equilibrium upon vitrification via the non-equilibrium index; water-like systems exhibited a strong pressure dependence in this metric, whereas simple liquids did not. These results reflect a surprising relationship between the metastable equilibrium phenomenon of liquid-liquid criticality and the non-equilibrium structure of glassy water, with implications for our understanding of water phase behavior and glass physics. Our calculations suggest a possible experimental route to probing the existence of the liquid-liquid transition in water and other fluids., The subtle connections between water’s supercooled liquid and glassy states are difficult to characterize. Gartner et al. suggest with MD simulations that the long-range structure of glassy water may reflect signatures of water’s debated second critical point in the supercooled liquid.

The complex shear modulus of silicon dioxide nanoparticle suspensions in a polyethylsiloxane liquid is determined via acoustic resonance using a piezoelectric crystal. The technique is based on studying effect additional coupling forces have on the resonance characteristics of an oscillating system. Specific features of the dependence of the shear modulus on the deformation amplitude are due to intermolecular interactions in suspensions, determined via IR spectrometry.

Glass transition is one of the unresolved critical issues in solid-state physics and materials science, during which a viscous liquid is frozen into a solid or structurally arrested state. On account of the uniform arrested mechanism, the calorimetric glass transition temperature (Tg) always follows the same trend as the dynamical glass transition (or α-relaxation) temperature (Tα) determined by dynamic mechanical analysis (DMA). Here, we explored the correlations between the calorimetric and dynamical glass transitions of three prototypical high-entropy metallic glasses (HEMGs) systems. We found that the HEMGs present a depressed dynamical glass transition phenomenon, i.e., HEMGs with moderate calorimetric Tg represent the highest Tα and the maximum activation energy of α-relaxation. These decoupled glass transitions from thermal and mechanical measurements reveal the effect of high configurational entropy on the structure and dynamics of supercooled liquids and metallic glasses, which are associated with sluggish diffusion and decreased dynamic and spatial heterogeneities from high mixing entropy. The results have important implications in understanding the entropy effect on the structure and properties of metallic glasses for designing new materials with plenteous physical and mechanical performances., Here the authors study thermodynamic and dynamic glass transition of high entropy metallic glasses. Results show retarded α-relaxation and distinct crystallization resistance attributed to their sluggish diffusion and high-entropy mixing that is different from the traditional metallic glasses.

The structure and properties of organic–inorganic hybrid perovskites are impacted by the order–disorder transition, whose driving forces from the organic cation and the inorganic framework cannot easily be disentangled. Herein, we report the design, synthesis and properties of a cage-in-framework perovskite AthMn(N3)3, where Ath+ is an organic cation 4-azatricyclo[2.2.1.02,6]heptanium. Ath+ features a rigid and spheroidal profile, such that its molecular reorientation does not alter the cubic lattice symmetry of the Mn(N3)3− host framework. This order–disorder transition is well characterized by NMR, crystallography, and calorimetry, and associated with the realignment of Ath+ dipole from antiferroelectric to paraelectric. As a result, an abrupt rise in the dielectric constant was observed during the transition. Our work introduces a family of perovskite structures and provides direct insights to the order–disorder transition of hybrid materials., In hybrid perovskites, the driving forces of an order–disorder transition that arise from the organic cation and inorganic framework cannot be easily untangled. Here, the authors introduce a cage-in-framework structure in which reorientation of the cage cation does not alter the cubic symmetry of the perovskite lattice.

Analyzing the atomic structure of glassy materials is a tremendous challenge both experimentally and computationally, and the lack of direct, detailed insights into glass structure hinders our ability to navigate structure-property relationships. For instance, the structural origin of the density anomaly in silica glasses - the negative thermal expansion coefficient - is still poorly understood. Simulations based on molecular dynamics (MD) produce atomically resolved structures, but quantifying the role of disorder in the density anomaly is challenging. Here, we propose to use a a graph-theoretical approach to assess topological differences between disordered structural arrangements from MD trajectories of silica glasses. A graph similarity metric quantifies the similarity between the covalent networks and can characterize the nature of the disordered solid, by comparing to reference crystalline solids, or with glasses in different thermodynamic states . This approach involves casting all-atom glass configurations as networks, and subsequently applying a graph-similarity metric (D-measure). Calculated D-measure values are then taken as the topological distances between two configurations. By measuring the topological distances of silica glass configurations across a range of temperatures, distinct structural features could be observed at temperatures higher than the fictive temperature. In addition, we compared topological distances between local atomic environments in the glass and crystalline silica phases. This approach suggests that more coesite-like and quartz-like local structures emerge in silica glasses when the density is at a minimum during the heating process., Comment: 12 pages, 7 figures, supporting information

Extending the tweezering range of the electromechanical nano-tweezers is of high interest. Herein, a pair of nano-tweezers with linearly varying width is designed to achieve higher tweezering rage. To this end, using the modified couple stress theory and considering the surface elasticity, the nonlinear equation of motion of tapered nano-tweezers is developed. The electrical field is simulated by incorporating the fringing field effect. Also, the impact of Casimir force is considered in the developed model. A finite element procedure is established based on Euler–Bernoulli beam theory to investigate the nano-tweezers’ pull-in behavior. The role of influential parameters, including the size dependency, the surface effect, Casimir force, and the width ratio on the tweezering range and instability voltage, are investigated. The outcomes demonstrate that the nano-tweezers with the converging geometry exhibit a higher tweezering range. Notably, the nano-tweezers with the needle configuration can extend the tweezering range up to 53% of the initial gap.