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In this Perspective article, we introduce a new framework for the global non-equilibrium thermodynamics of stationary states. This theory uses the spatial distributions of temperature, density, velocity, and other variables in stationary states as its input. It outputs the global state parameters to describe the system's energy exchange with the environment. The number of state parameters is determined solely by the type of substance in the system and external potentials, regardless of the number of boundary conditions, fluxes within the system, or its specific geometry. The theory offers a second law of non-equilibrium thermodynamics for stationary states, predicting the direction of spontaneous processes between them. When all macroscopic fluxes reach zero, the theory reduces to equilibrium thermodynamics. [ABSTRACT FROM AUTHOR]

The tendency of relative motion via rolling between contacting objects exists in various aspects of industry and nature because, in many practical situations, forces and moments may be simultaneously induced at the contacting interfaces. Due to the presence of adhesion, which may be prominent on small scales, research on contacts with the tendency to roll, termed herein as rolling adhesion, is very limited. In the present work, a novel double-Hertz model is developed for adhesive contact between spherical objects subjected to the combined action of normal forces and moments. The results from the new model agree well with available numerical simulations and experimental results. It has been demonstrated that the contact behavior with the effect of rolling adhesion seemingly resembles that of conventional adhesive contact, but the applied moment may impact the pull-off force and may even induce novel contact instability if large enough. The resistance moment at the interface has also been obtained analytically, which is proportional to adhesion hysteresis and contact area. Given the applicability to the full range of the Tabor parameter and nonsingular stresses involved, these results might shed light on adhesive contacts with rolling adhesion and help to characterize them better than existent models. [ABSTRACT FROM AUTHOR]

Electric double layers (EDL) with counterions only, say electrons with the elementary charge âˆ' e, in thermal equilibrium at the inverse temperature β are considered. In particular, we study the effect of the surface charge modulation on the particle number density profile and the pressure. The mobile particles are constrained to the surface of a 2D cylinder and immersed in vacuum (no dielectric image charges). An EDL corresponds to the end-circle of the cylinder which carries a (fixed) position-dependent line charge density. The geometries of one single EDL and two EDLs at distance d are considered; the particle density profile is studied for both geometries, the effective interaction of two EDLs is given by the particle pressure on either of the line walls. For any coupling constant Î" ≡ βe 2 = 2 Ă— integer, there exists a mapping of the 2D one-component Coulomb system onto the 1D interacting anticommuting-field theory defined on a chain of sites. Using specific transformation symmetries of anticommuting variables, the contact value theorem is generalized to the EDL with modulated line charge density. For the free-fermion coupling Î" = 2 it is shown that, under certain conditions, the matrix of interaction strengths between anticommuting variables diagonalizes itself which permits one to obtain exact formulas for the particle density profile as well as the pressure. The obtained results confirm the previous indications of weak-coupling and Monte Carlo observations that the surface charge inhomogeneity implies an enhancement of the counterion density at the contact with the charged line and a diminution of the pressure between two parallel lines in comparison with the uniformly charged ones (with the same mean charge densities). [ABSTRACT FROM AUTHOR]

Introductory mechanics courses use the bouncing ball model to familiarize students with the principles of binary inelastic collisions. Nonetheless, in undergraduate courses, the modeling of binary systems typically disregards the time of contact and the effects of gravity, which yields to a constant coefficient of restitution (COR) and, as a consequence, prevents students from elucidating the real dependence of COR with impact speed. In this work, we proposed a simple experimental setup to investigate the impact dynamics of a spring-mass body that bounces on a rigid plate as well as a theoretical framework that captures the velocity dependence of the COR for low-impact speeds. Our analytical expression for the COR highlights the role-played by gravity, impact speed and collision time on the collision dynamics. Our results suggest that the inclusion of gravity force allows an adequate estimation of the critical impact speed and maximum deformation distance, crucial parameters to differentiate between repulsive and attractive interaction regimes. Our experimental setup enables the clarification of several key concepts of mechanics while it is easy to be performed in most undergraduate laboratories. [ABSTRACT FROM AUTHOR]

We present a method by which multi-harmonic signals acquired during a normal tapping mode (amplitude modulated) AFM scan of a sample in air or vacuum with standard microcantilevers can be used to map quantitatively the local mechanical properties of the sample such as elastic modulus, adhesion, and indentation. The approach is based on the observation that during the tapping mode operation in air or vacuum, the 0th and 2nd harmonic signals of microcantilever vibration are encountered under most operating conditions and can be mapped with sufficient signal to noise ratio. By measuring the amplitude and phase of the driven harmonic as well as the 0th and 2nd harmonic observables, we find analytical/semi-analytical formulas that relate these multi-harmonic observables to local mechanical properties for several classical tip-sample interaction models. Least squares estimation of the local mechanical properties is performed pixel by pixel. The method is validated through computations as well as experimental data acquired on a polymer blend made of Polystyrene and Polyolefin elastomer. [ABSTRACT FROM AUTHOR]

Atomic force microscopy (AFM) quantitatively maps viscoelastic parameters of polymers on the nanoscale by several methods. The loss tangent, the ratio between dissipated and stored energy, was measured on a blend of thermoplastic polymer materials by a dynamic contact method, contact resonance, and by a recently developed loss tangent measurement by amplitude modulation AFM. Contact resonance measurements were performed both with dual AC resonance tracking and band excitation (BE), allowing for a reference-free measurement of the loss tangent. Amplitude modulation AFM was performed where a recent interpretation of the phase signal under certain operating conditions allows for the loss tangent to be calculated. The loss tangent measurements were compared with values expected from time–temperature superposed frequency-dependent dynamical mechanical curves of materials and reveal that the loss tangents determined from the BE contact resonance method provide the most accurate values. [ABSTRACT FROM AUTHOR]

Present atomic force microscopes are capable of acquiring large data volumes by point using point force–distance spectroscopic measurements. Even if different trade names and different technical implementations are used, for most of these techniques a force–distance curve in every image pixel is measured, this curve is immediately fitted by some theoretical dependence and results are displayed as a mechanical properties channel (Young modulus, adhesion, etc). Results are processed during the measurement directly in the scanning probe microscopy controller or, after it, by manufacturer provided software. In this paper, we present a software tool for independent numerical processing of such data, including more numerical models for the force–distance curve evaluation and including a simple estimate of uncertainties related to the fitting procedure. This can improve the reliability and the analytical possibilities of mechanical properties mapping methods in an atomic force microscopy. [ABSTRACT FROM AUTHOR]

We study the surface tension of electrolyte solutions at the air/water and oil/water interfaces. Employing field-theoretical methods and considering short-range interactions of anions with the surface, we expand the Helmholtz free energy to first order in a loop expansion and calculate the excess surface tension. Our approach is self-consistent and yields an analytical prediction that reunites the Onsager-Samaras pioneering result (which does not agree with experimental data), with the ionic specificity of the Hofmeister series. We obtain analytically the surface-tension dependence on the ionic strength, ionic size and ion-surface interaction, and show consequently that the Onsager-Samaras result is consistent with the one-loop correction beyond the mean-field result. Our theory fits well a wide range of concentrations for different salts using one fit parameter, reproducing the reverse Hofmeister series for anions at the air/water and oil/water interfaces. [ABSTRACT FROM AUTHOR]

We develop a multiscale hybrid scheme for simulations of soft condensed matter systems, which allows one to treat the system at the particle level in selected regions of space, and at the continuum level elsewhere. It is derived systematically from an underlying particle-based model by field theoretic methods. Particles in different representation regions can switch representations on the fly, controlled by a spatially varying tuning function. As a test case, the hybrid scheme is applied to simulate colloid–polymer composites with high resolution regions close to the colloids. The hybrid simulations are significantly faster than reference simulations of a pure particle-based model, and the results are in good agreement. [ABSTRACT FROM AUTHOR]

In nanotechnology and semiconductor fabrication geometry parameters of nanostructures such as curvatures and side wall angles are of increasing relevance with decreasing feature sizes. The atomic force microscope (AFM) is still one of the main measurement tools employed to investigate topographical parameters. It is generally operated in oscillation mode in order to avoid wear or damage of the probe. As imaging instruments deliver data that are influenced by the probing process, appropriate reconstruction processes are needed. This paper shows a significant contrast of the phase lag of the probe of an amplitude-modulated AFM (AM-AFM) and its driving force at the edge transition of nanostructures with a high aspect ratio. A simulation model reveals the relation between interaction forces and the observed phase behavior. It illustrates how the equilibrium positions of an oscillating probe differ from those of a sample geometry that is purely dilated by static probe tip contact. We show that AFM measurements in oscillation mode deliver a distorted topography image and that the greater the distortion the more energy dissipation is involved. An understanding of the distortion mechanism forms the basis for the development of reconstruction strategies. [ABSTRACT FROM AUTHOR]

A novel method for quantitative lateral force measurement (LFM) calibration has been developed. Using a single-molecule spectroscopy approach it is possible to calibrate the AFM levers for both lateral and normal spring constants with a single image scan. Moreover, our method does not involve tip modifications. Dextran molecules were chosen for testing our calibration procedure due to their characteristic plateau feature in the force-elongation curve which enables an easy identification of single-molecule stretching events. Using a non-standard (tilted) geometry of AFM scanning, it is possible to observe different components of the stretching force on both normal and lateral force signals. These signals can be further compared to the values obtained by standard (normal) spectroscopic measurements. The values of the normal spring constant obtained with our method are in good agreement with the results obtained from the method exploiting the energy equipartition theorem. The statistical analysis shows that the approach proposed in our paper gives reproducible results of the lateral sensitivity with a relative standard deviation less than 15%. [ABSTRACT FROM AUTHOR]

The discrete element method (DEM) was used to model calcium-silicatehydrate (C-S-H) at the nanoscale. The C-S-H nanoparticles were modeled as spherical particles with diameters of approximately 5 nm. Interparticle forces included traditional mechanical contact forces, van der Waals forces and ionic correlation forces due to negatively charged C-S-H nanoparticles and ion species in the nanopores. Previous work by the authors demonstrated the DEM method was feasible in studying the properties of the C-S-H nanostructures. In this work, the simulations were performed to look into the effects of nanoparticle packing, nanoparticle morphology, interparticle forces and nanoparticle properties on the deformation mechanisms and mechanical properties of the C-S-H matrix. This work will provide insights into possible ways to improve the properties of the C-S-H matrix. [ABSTRACT FROM AUTHOR]

Nanotechnology is touted as the next logical sequence in technological evolution. This has led to a substantial surge in research activities pertaining to the development and fundamental understanding of processes and assembly at the nanoscale. Both top-down and bottom-up fabrication approaches may be used to realize a range of well-defined nanostructured materials with desirable physical and chemical attributes. Among these, the bottom-up self-assembly process offers the most realistic solution toward the fabrication of next-generation functional materials and devices. Here, we present a comprehensive review on the physical basis behind self-assembly and the processes reported in recent years to direct the assembly of nanoscale functional blocks into hierarchically ordered structures. This paper emphasizes assembly in the synthetic domain as well in the biological domain, underscoring the importance of biomimetic approaches toward novel materials. In particular, two important classes of directed self-assembly, namely, (i) self-assembly among nanoparticle-polymer systems and (ii) external field-guided assembly are highlighted. The spontaneous self-assembling behavior observed in nature that leads to complex, multifunctional, hierarchical structures within biological systems is also discussed in this review. Recent research undertaken to synthesize hierarchically assembled functional materials have underscored the need as well as the benefits harvested in synergistically combining top-down fabrication methods with bottom-up self-assembly. [ABSTRACT FROM AUTHOR]

The aggregation of proteins is of fundamental relevance in a number of daily phenomena, as important and diverse as blood coagulation, medical diseases, or cooking an egg in the kitchen. Colloidal food systems, in particular, are examples that have great significance for protein aggregation, not only for their importance and implications, which touches on everyday life, but also because they allow the limits of the colloidal science analogy to be tested in a much broader window of conditions, such as pH, ionic strength, concentration and temperature. Thus, studying the aggregation and self-assembly of proteins in foods challenges our understanding of these complex systems from both the molecular and statistical physics perspectives. Last but not least, food offers a unique playground to study the aggregation of proteins in three, two and one dimensions, that is to say, in the bulk, at air/water and oil/water interfaces and in protein fibrillation phenomena. In this review we will tackle this very ambitious task in order to discuss the current understanding of protein aggregation in the framework of foods, which is possibly one of the broadest contexts, yet is of tremendous daily relevance. [ABSTRACT FROM AUTHOR]

Stochastic thermodynamics as reviewed here systematically provides a framework for extending the notions of classical thermodynamics such as work, heat and entropy production to the level of individual trajectories of well-defined non-equilibrium ensembles. It applies whenever a non-equilibrium process is still coupled to one (or several) heat bath(s) of constant temperature. Paradigmatic systems are single colloidal particles in time-dependent laser traps, polymers in external flow, enzymes and molecular motors in single molecule assays, small biochemical networks and thermoelectric devices involving single electron transport. For such systems, a first-law like energy balance can be identified along fluctuating trajectories. For a basic Markovian dynamics implemented either on the continuum level with Langevin equations or on a discrete set of states as a master equation, thermodynamic consistency imposes a local-detailed balance constraint on noise and rates, respectively. Various integral and detailed fluctuation theorems, which are derived here in a unifying approach from one master theorem, constrain the probability distributions for work, heat and entropy production depending on the nature of the system and the choice of non-equilibrium conditions. For non-equilibrium steady states, particularly strong results hold like a generalized fluctuation-dissipation theorem involving entropy production. Ramifications and applications of these concepts include optimal driving between specified states in finite time, the role of measurement-based feedback processes and the relation between dissipation and irreversibility. Efficiency and, in particular, efficiency at maximum power can be discussed systematically beyond the linear response regime for two classes of molecular machines, isothermal ones such as molecular motors, and heat engines such as thermoelectric devices, using a common framework based on a cycle decomposition of entropy production. [ABSTRACT FROM AUTHOR]

In a colloidal system confined by a small cylindric pipeline, the depletion interaction between two large spheres is different to the system confined by two plates, and the influence on depletion interaction from the pipeline is related to both the size and shape of it. In this paper, the depletion interactions in the systems confined by pipelines of different sizes or different shapes are studied by Monte Carlo simulations. The numerical results show that the influence on depletion force from the cylindric pipeline is stronger than that from two parallel plates, and the depletion force will be strengthened when the diameter of the cylinder is decreased. In addition, we also find that the depletion interaction is rather affected if the shape change of the pipeline is slightly changed, and the influence on depletion force from the shape change is stronger than that from the size change. [ABSTRACT FROM AUTHOR]

In this paper molecular dynamics simulations are performed to study the accumulation behaviour of N2 and H2 at water/graphite interface under ambient temperature and pressure. It finds that both N2 and H2 molecules can accumulate at the interface and form one of two states according to the ratio of gas molecules number to square of graphite surface from our simulation results: gas films (pancake-like) for a larger ratio and nanobubbles for a smaller ratio. In addition, we discuss the stabilities of nanobubbles at different environment temperatures. Surprisingly, it is found that the density of both kinds of gas states can be greatly increased, even comparable with that of the liquid N2 and liquid H2. The present results are expected to be helpful for the understanding of the stable existence of gas film (pancake-like) and nanobubbles. [ABSTRACT FROM AUTHOR]

A numerical method for determining the elliptical adhesive contact in rectangular coordinates is proposed. Using a fast Fourier transform (FFT), the matrix multiplication can be performed. Then, using the preconditioned inexact Newton-bi-CGSTAG (bi-conjugate stabilized) method and the path-following method, the adhesive contact can be found. The elliptical adhesive contact can then be investigated by this method. It is found that the pull-off force depends on the Tabor parameter and the ratio between the principal relative radii of curvature. It is also found that the contact area is approximately elliptical. [ABSTRACT FROM AUTHOR]