Condensed Matter

The flexibility and the extension along the direction of the force are shown to be related to the bubble number fluctuation and the average number of bubbles respectively, when the strands of the DNA are subjected to a force along the same direction, here we call a stretching force. The force-temperature phase diagram shows the existence of a tricritical point (TCP), where the first-order force induced zipping transition becomes continuous. On the other hand, when the forces are being applied in opposite directions, here we call an unzipping force, the transition remains first-order,with the possibility of vanishing of the low-temperature re-entrant phase for a semiflexible DNA. Moreover, we found that the bulk elasticity changes only if an external force penetrates the bound phase and affect the bubble states

We provide an extension to previous analysis of the localised beading instability of soft slender tubes under surface tension and axial stretching. The primary questions pondered here are: under what loading conditions, if any, can bifurcation into circumferential buckling modes occur, and do such solutions dominate localisation and periodic axial modes? Three distinct boundary conditions are considered; in case 1 the tube's curved surfaces are traction free and under surface tension, whilst in cases 2 and 3 the inner and outer surfaces (respectively) are fixed to prevent radial displacement and surface tension. A linear bifurcation analysis is conducted to determine numerically the existence of circumferential mode solutions. In case 1 we focus on the tensile stress regime given the preference of slender compressed tubes towards Euler buckling over axial wrinkling. We show that tubes under several loading paths are highly sensitive to circumferential modes; in contrast, localised and periodic axial modes are absent, suggesting that the circumferential buckling is dominant by default. In case 2, circumferential mode solutions are associated with negative surface tension values and thus are physically implausible. Circumferential buckling solutions are shown to exist in case 3 for tensile and compressive axial loads, and we demonstrate for multiple loading scenarios their dominance over localisation and periodic axial modes within specific parameter regimes.

In this paper we investigate the possibility of elastodynamic transformation cloaking in bodies made of non-centrosymmetric gradient solids. The goal of transformation cloaking is to hide a hole from elastic disturbances in the sense that the mechanical response of a homogeneous and isotropic body with a hole covered by a cloak would be identical to that of the corresponding homogeneous and isotropic body outside the cloak. It is known that in the case of centrosymmetric gradient solids the balance of angular momentum is the obstruction to transformation cloaking. We will show that this is the case for non-centrosymmetric gradient solids as well.

Control of physical behaviors of nematic colloids and colloidal crystals has been demonstrated by tuning particle shape, topology, chirality and surface charging. However, the capability of altering physical behaviors of such soft matter systems by changing particle shape and the ensuing responses to external stimuli has remained elusive. We fabricated genus-one nematic elastomeric colloidal ring-shaped particles and various microstructures using two-photon photopolymerization. Nematic ordering within both the nano-printed particle and the surrounding medium leads to anisotropic responses and actuation when heated. With the thermal control, elastomeric microstructures are capable of changing from genus-one to genus-zero surface topology. Using these particles as building blocks, we investigated elastomeric colloidal crystals immersed within a liquid crystal fluid, which exhibit crystallographic symmetry transformations. Our findings may lead to colloidal crystals responsive to a large variety of external stimuli, including electric fields and light. Pre-designed response of elastomeric nematic colloids, including changes of colloidal surface topology and lattice symmetry, are of interest for both fundamental research and applications.

By using the generalized version of the Shell Theorem analytical equations are derived to calculate the electric energy of a charged sphere and the field energy of the electrolyte inside and around the sphere. These electric energies are calculated as a function of the ion concentration of the electrolyte. The work needed to build up the charged sphere (i.e. the total charge-charge interaction energy) decreases with increasing ion concentration of the electrolyte because of the screening effect of the electrolyte on the charge-charge interaction. The energy needed to build up the charged sphere appears as sum of the field energy of the electrolyte and the polarization energy of the electrolyte ions. At zero ion concentration the field energy of the electrolyte is equal with the charge-charge interaction energy, while the polarization energy is zero. At high ion concentrations 50% of the charge-charge interaction energy appears as the polarization energy of ions, 25% as the field energy of the electrolyte inside the sphere and 25% as the field energy of the electrolyte around the sphere.

Materials with continuous dissipation can exhibit responses and functionalities that are not possible in thermodynamic equilibrium. While this concept is well-known, a major challenge has been the implementation: how to rationally design materials with functional non-equilibrium states and quantify the dissipation? Here we address these questions for the widely used colloidal nanoparticles that convey several functionalities. We propose that useful non-equilibrium states can be realised by creating and maintaining steady-state nanoparticle concentration gradients by continuous injection and dissipation of energy. We experimentally demonstrate this with superparamagnetic iron oxide nanoparticles that in thermodynamic equilibrium form a homogeneous functional fluid with a strong magnetic response (a ferrofluid). To create non-equilibrium functionalities, we charge the nanoparticles with anionic charge control agents to create electroferrofluids where nanoparticles act as charge carriers that can be driven with electric fields and current to non-homogeneous dissipative steady-states. The dissipative steady-states exhibit voltage-controlled magnetic properties and emergent diffuse interfaces. The diffuse interfaces respond strongly to external magnetic fields, leading to dissipative patterns that are not possible in the equilibrium state. We identify the closest non-dissipative analogues of these dissipative patterns, discuss the differences, and highlight how pattern formation in electroferrofluids is linked to dissipation that can be directly quantified. Beyond electrically controlled ferrofluids and patterns, we foresee that the concept can be generalized to other functional nanoparticles to create various scientifically and technologically relevant non-equilibrium states with optical, electrical, catalytic, and mechanical responses that are not possible in thermodynamic equilibrium.

In the present work, we study an electrolyte solution confined between planar surfaces with nonopatterned charged domains, which has been connected to a bulk ionic reservoir. The system is investigated through an improved Monte Carlo (MC) simulation method, suitable for simulation of electrolytes in the presence of modulated surface charge distributions. We also employ a linear approach in the spirit of the classical Debye-Hückel approximation, which allows one to obtain explicit expressions for the averaged potentials, ionic profiles, effective surface interactions and the net ionic charge confined between the walls. Emphasis is placed in the limit of strongly confined electrolytes, in which case local electroneutrality in the inter-surface space might not be fulfilled. In order to access the effects of such lack of local charge neutrality on the ionic-induced interactions between surfaces with modulated charge domains, we consider two distinct model systems for the confined electrolyte: one in which a salt reservoir is explicitly taken into account {\it via} the osmotic equilibrium with an electrolyte of fixed bulk concentration, and a second one in which the equilibrium with a charge neutral ionic reservoir is implicitly considered. While in the former case the osmotic ionic exchange might lead to non-vanishing net charges, in the latter model charge neutrality is enforced through the appearance of an implicit Donnan potential across the charged interfaces. A strong dependence of the ionic-induced surface interactions in the employed model system is observed at all particle separations. These findings strongly suggest that due care is to be taken while choosing among different scenarios to describe the ionic exchanging in electrolytes confined between charged surfaces, even in cases when the monopole (non zero net charge) surface contributions are absent.

Polyvinylidene difluoride (PVDF) is a ferroelectric polymer characterized by negative strain along the direction of the applied electric field. However, the electromechanical response mechanism of PVDF remains unclear due to the complexity of the hierarchical structure across the length scales. As described in this letter, we employ the Finsler geometry model as a new solution to the aforementioned problem and demonstrate that the deformations observed through Monte Carlo simulations on 3D tetrahedral lattices are nearly identical to those of real PVDF. Specifically, the simulated mechanical deformation and polarization are similar to those observed experimentally.

Due to their unique electromechanical coupling properties, soft electro-active (SEA) resonators are actively tunable, extremely suitable, and practically important for designing the next-generation acoustic and vibration treatment devices. In this paper, we investigate the electrostatically tunable axisymmetric vibrations of SEA tubes with different geometric sizes. We consider both axisymmetric torsional and longitudinal vibrations for an incompressible SEA cylindrical tube under inhomogeneous biasing fields induced by radial electric voltage and axial pre-stretch. We then employ the state-space method, which combines the state-space formalism in cylindrical coordinates with the approximate laminate technique, to derive the frequency equations for two separate classes of axisymmetric vibration of the tube subjected to appropriate boundary conditions. We perform numerical calculations to validate the convergence and accuracy of the state-space method and to illuminate that the axisymmetric vibration characteristics of SEA tubes may be tuned significantly by adjusting the electromechanical biasing fields as well as altering the tube geometry. The reported results provide a solid guidance for the proper design of tunable resonant devices composed of SEA tubes

In its original formulation, the seminal Deryaguin-Landau-Verwey-Overbeek (DLVO) theory of colloidal stability seemed like a simple but realistic description of the world of colloid interactions in electrolyte solutions. It is based on a straightforward superposition of the mean-field Poisson-Boltzmann (PB) electrostatics with the electrodynamic van der Waals (vdW) interactions driven by thermal and quantum fluctuations. However, subsequent developments continued to reveal a much richer and deeper structure of fundamental interactions on the nano- and micro-scale: the granularity and structure of the solvent, charging equilibria of dissociable charge groups, inhomogeneous charge distributions, the finite size of the ions, non-mean-field electrostatics, ion-ion correlations, and more. Today, the original simplicity is gone and we are left with an embarrassingly rich variety of interactions that defy simple classification and reduction to a few fundamental mechanisms. In this mini-review, we comment on the contemporary state-of-the-art picture of colloidal interactions, in view of some recent progress in experiments.