The formation of liquid crystals (LCs) is the most viable approach to produce macroscopic, periodic self-assembled materials from oriented graphene sheets. Herein, we have discovered that ...well-soluble and single-layered graphene oxide (GO) sheets can exhibit nematic liquid crystallinity in water and first established their isotropic−nematic solid phase diagram versus mass fraction and salt concentration. The zeta potential of GO dispersion is around −64 mV, and its absolute value decreases with increasing salt concentration, implying that the electrostatic repulsive force between negatively charged GO sheets is the dominant interaction in the system of GO LCs and also explaining the salt-dependent phase behavior. For single-layer GO sheets with average diameter of 2.1 μm and polydispersity index of 83%, the isotropic−nematic phase transition occurs at a mass concentration of ∼0.025%, and a stable nematic phase forms at ∼0.5%. Rheological measurements showed that GO aqueous dispersions performed as typical shear flows and confirmed the isotropic−nematic transition. The ordering of GO sheets in aqueous dispersions and the solid state is demonstrated by the characterizations of polarized-light optical microscopy, small-angle X-ray scattering, scanning electron microscopy, and transmission electron microscopy. The direct, real-time fluorescent inspections by confocal laser microscopy further reveal that the individually dispersed fluorescent GO sheets align with orientational directions along their long axes. These novel findings shed light on the phase behaviors of diversely topological graphenes and lay the foundation for fabrication of long-range, ordered nano-objects and macroscopically assembled graphene-based functional materials.
The Cover Feature illustrates the distribution of the different components of aqueous choline chloride solution around the hydrophobe methane. The hydrogen bonds formed between water molecules, ...choline cations, and chloride ions are shown using light yellow dots. The preferred orientations of water with respect to methane at different distances from the latter are quantified in a 2D histogram. More information can be found in the Research Article by Rajarshi Chakrabarti and co‐workers.
We investigate the degree of local structural similarity between the parent-liquid and children-crystal states for a model soft-matter system of particles interacting through the harmonic-repulsive ...pair potential. At different pressures, this simple system crystallizes into several significantly different crystal structures. Therefore, the model is well suited for addressing the question under consideration. In our studies, we carefully analyze the developments of the pair and triple correlation functions for the parent-liquid as the pressure increases. In particular, these considerations allow us to address the similarities in the orientational orderings of the corresponding liquid and solid phases. It is demonstrated that the similarities in the orientational ordering between the two states extend beyond the first and second neighbors. Currently, it is widely accepted that orientational ordering is important for understanding the behaviors of liquids, supercooled liquids, and the development of detailed theories of the crystallization process. Our results suggest that, up to a certain degree, it might be possible to predict the structures of the children-solids from studies of the parent-liquids. Our results raise anew a general question of how much insight into the properties of the liquid-state can be gained from drawing a parallel with the solid-state.
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•Structural similarity between the parent-liquids and children-crystals states studied.•Similarity in the orientational ordering extends well beyond the second neighbors.•Changes in the corresponding liquid and crystal structures are correlated.•Suggested methods to measure the degree of the structural similarity.•Suggested applications of the observed structural similarity between the two states.
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•A new DEM method is introduced to simulate any convex particle shape.•The method uses a new contact point detection scheme.•Mechanical stability is achieved, even for tall towers of ...particles.•Packings of cuboids, cylinders and ellipsoids are investigated in detail.•More complex sand and woodchip particles are also investigated.
A novel granular discrete element method (DEM) is introduced to simulate mixtures of particles of any convex shape. To quickly identify pairs of particles in contact, the method first uses a broad-phase and a narrow-phase contact detection strategy. After this, a contact resolution phase finds the contact normal and penetration depth. A new algorithm is introduced to effectively locate the contact point in the geometric center of flat faces in partial contact. This is important for a correct evaluation of the torque on each particle, leading to a much higher stability of stacks of particles than with previous algorithms. The granular DEM is used to generate random packings in a cylindrical vessel. The simulated shapes include non-spherical particles with different aspect ratio cuboids, cylinders and ellipsoids. More complex polyhedral shapes representing sand and woodchip particles are also used. The latter particles all have a unique shape and size, resembling real granular particle packings. All packings are analyzed extensively by investigating positional and orientational ordering.
Domain purity and interface structure are known to be critical for fullerene‐based bulk heterojunction (BHJ) solar cells, yet have been very difficult to study. Using novel soft X‐ray tools, we ...delineate the importance of these parameters by comparing high performance cells based on a novel naphtha1,2‐c:5,6‐cbis1,2,5thiadiazole (NT) material to cells based on a 2,1,3‐benzothiadiazole (BT) analogue. BT‐based devices exhibit ∼15 nm, mixed domains that differ in composition by at most 22%, causing substantial bimolecular recombination. In contrast, NT‐based devices have more pure domains that are >80 nm in size, yet the polymer‐rich phase still contains at least 22% fullerene. Power conversion efficiency >6% is achieved for NT devices despite a domain size much larger than the nominal exciton diffusion length due to a favourable trade‐off in the mixed domain between exciton harvesting, charge transport, and bimolecular recombination. The miscibility of the fullerene with the NT and BT polymer is measured and correlated to the purity in devices. Importantly, polarized x‐ray scattering reveals preferential face‐on orientation of the NT polymer relative to the PCBM‐rich domains. Such ordering has previously not been observed in fullerene‐based solar cells and is shown here to be possibly a controlling or contributing factor to high performance.
The importance of domain purity and molecular orientation are investigated for solar cell devices based on naphtha1,2‐c:5,6‐cbis1,2,5thiadiazole (NT) or 2,1,3‐benzothiadiazole based conjugated polymers. The results show that purer domains reduce bimolecular recombination. Molecular ordering of the polymer at the donor/acceptor interface is also observed and could be a critical parameter to explain high performance in organic solar cells. Both molecular ordering and domain purity should be widely considered to reveal structure–performance relationships.
Water and other polar liquids exhibit nanoscale structuring near charged interfaces. When a polar liquid is confined between two charged surfaces, the interfacial solvent layers begin to overlap, ...resulting in solvation forces. Here, we perform molecular dynamics simulations of polar liquids with different dielectric constants and molecular shapes and sizes confined between charged surfaces, demonstrating strong orientational ordering in the nanoconfined liquids. To rationalize the observed structures, we apply a coarse-grained continuum theory that captures the orientational ordering and solvation forces of those liquids. Our findings reveal the subtle behavior of different nanoconfined polar liquids and establish a simple law for the decay length of the interfacial orientations of the solvents, which depends on their molecular size and polarity. These insights shed light on the nature of solvation forces, which are important in colloid and membrane science, scanning probe microscopy, and nano-electrochemistry.
The generation of polarity in the solid state necessitates ordered, polar basic-building units (BBUs). This paper examines the evolution of ordered BBUs of 1D chains constructed of early transition ...metals (ETMs) and late transition metals. The cause of polar distortion orientation is illustrated with subtle alterations in the heterotypic structures of one previously reported compound (CuNbOF5(H2O)2(pyz)3) and three new hybrid materials, presented here: CuNbOF5(H2O)4(pyz)2 (1), CuVOF5(H2O)4(pyz)2 (2) and CuVOF5(H2O)2(pyz)3 (3) (pyz=pyrazine). In contrast to the NbOF52− octahedra of CuNbOF5(H2O)2(pyz)3 and compound (1) that have oxide ligands within the 1D BBUs, the VOF52− octahedra of compounds (2) and (3) contain disordered oxide ligands perpendicular to the chains. To create polar 1D BBUs in the solid state, one must have an understanding of how to direct distortions. We demonstrate that the choice of specific polar BBUs within a distinct environment is necessary for orientational order of the ETM anions.
The orientational order of VOF52− and NbOF52− polar anions in chains and its influence on noncentrosymmetry are discussed on the basis of the three new hybrid compounds composed of linear chains: (CuVOF5(H2O)4(pyz)2, CuNbOF5(H2O)4(pyz)2 and CuVOF5(H2O)2(pyz)3). Orientational order of the distortion of the early transition metal can be achieved by subtle modifications of the anisotropy in the anionic environment and a proper choice of the polar anion. Display omitted
► Three new hybrid compounds were characterized by single-crystal XRD. ► VOF52− and NbOF52− anions differ in the nucleophilicities of the ligands. ► The order of the anion is controlled by increasing the anisotropy of its environment.
Biological membranes are composed of isotropic and anisotropic curved nanodomains. Anisotropic membrane components, such as Bin/Amphiphysin/Rvs (BAR) superfamily protein domains, could ...trigger/facilitate the growth of membrane tubular protrusions, while isotropic curved nanodomains may induce undulated (necklace-like) membrane protrusions. We review the role of isotropic and anisotropic membrane nanodomains in stability of tubular and undulated membrane structures generated or stabilized by cyto- or membrane-skeleton. We also describe the theory of spontaneous self-assembly of isotropic curved membrane nanodomains and derive the critical concentration above which the spontaneous necklace-like membrane protrusion growth is favorable. We show that the actin cytoskeleton growth inside the vesicle or cell can change its equilibrium shape, induce higher degree of segregation of membrane nanodomains or even alter the average orientation angle of anisotropic nanodomains such as BAR domains. These effects may indicate whether the actin cytoskeleton role is only to stabilize membrane protrusions or to generate them by stretching the vesicle membrane. Furthermore, we demonstrate that by taking into account the in-plane orientational ordering of anisotropic membrane nanodomains, direct interactions between them and the extrinsic (deviatoric) curvature elasticity, it is possible to explain the experimentally observed stability of oblate (discocyte) shapes of red blood cells in a broad interval of cell reduced volume. Finally, we present results of numerical calculations and Monte-Carlo simulations which indicate that the active forces of membrane skeleton and cytoskeleton applied to plasma membrane may considerably influence cell shape and membrane budding.
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•Orientational ordering of finite sized water dipoles in electrolyte in saturation regime.•Analytical models of spatial variation of permittivity in electrolyte solution.•Differential ...capacitance of electric double layer and water ordering.•Osmotic pressure of the electrolyte solution between charged surfaces.•Attractive interactions between like-charged surfaces mediated by macroions.
The electrolyte-charged surface interface is described within the Langevin–Poisson–Boltzmann (LPB) and Langevin–Bikerman models. It is shown that in the saturation regime close to the charged surface, water dipole ordering and depletion of water molecules may result in a strong local decrease of permittivity. Analytical expressions for the space dependence of relative permittivity are derived for both models. The differential capacitance as a function of the surface potential is calculated within the modified Langevin–Bikerman model and compared to the prediction of the classical Gouy–Chapman theory. As an example of the application of the models described, a zwitterionic lipid surface with non-zero dipole moments in contact with an electrolyte solution of monovalent salt ions and water dipoles is studied within the LPB model. An analytical expression for the osmotic pressure of the electrolyte solution between the zwitterionic lipid surface and a charged particle (macroion) is derived. Some of the predictions of the described electric double layer mean-field theoretical considerations are evaluated using the results of a molecular dynamics simulation. At the end a theoretical description of the possible origin of the attractive interactions between like-charged surfaces mediated by charged macroions with distinctive internal charge distribution is given.
Recent studies have reported manifold industrial applications of aqueous choline chloride (ChCl) solution as an alternative to deep eutectic solvent. ChCl also serves as a protecting co‐solvent for ...proteins by restricting urea to approach the protein surface and thereby maintaining the water structure around the protein. However, a detailed molecular‐level picture of the ChCl and water, even in the absence of urea around a representative hydrophobe is largely lacking. This motivates us to probe the effect of varying wt % of ChCl on the occupancy and orientations of the constituents around a representative solute like methane using computer simulations. Accumulation of water molecules and preferential exclusion of ChCl from the surface of methane perturb the tetrahedral geometry of water around it. We find a tangential alignment of the polar part of the ChCl molecules that interact with water, whereas its hydrophobic part is preferentially facing the methane. With an increase in ChCl wt %, a disruption in the tetrahedrality is evident for water molecules accompanied by a reduction in hydrogen bonds between water pairs in the solution. In short, ChCl induces crowding and modifies the microscopic arrangement and hydrogen bonding structure of the water around the methane and beyond.
Denaturation inhibiting agent choline chloride forces solvent (water) towards methane, which gets reflected in the spatial distribution of water. This arrangement of solvent and the co‐solvent results in two populated orientations ‐ tangential and bulk, and affects the tetrahedral hydrogen bonding network of water.
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