Soft Matter最新文献

We study a multi-body finite element model of a packing of hydrogel particles using the Flory–Rehner constitutive law to model the deformation of the swollen polymer network. We show that while the dependence of the pressure, Π, on the effective volume fraction, ϕ, is virtually identical to a monolithic Flory material, the shear modulus, μ, behaves in a non-trivial way. μ increases monotonically with Π from zero and remains below about 80% of the monolithic Flory value at the largest Π we study here. The local shear strain in the particles has a large spatial variation. Local strains near the centers of the particles are all roughly equal to the applied shear strain, but the local strains near the contact facets are much smaller and depend on the orientation of the facet. We show that the slip between particles at the facets depends strongly on the orientation of the facet and is, on average, proportional to the component of the applied shear strain resolved onto the facet orientation. This slip screens the stress transmission and results in a reduction of the shear modulus relative to what one would obtain if the particles were welded together at the facet. Surprisingly, given the reduction in the shear modulus arising from the facet slip, and the spatial variations in the local shear strain inside the particles themselves, the deformation of the particle centroids is rather homogeneous with the strains of the Delaunay triangles having fluctuations of only order ±5%. These results should open the way to construction of quantitative estimates of the shear modulus in highly compressed packings via mean-field, effective-medium type approaches.

Biomolecules usually adopt ubiquitous circular structures which are important for their functionality. Based on three-dimensional Langevin dynamics simulations, we investigate the conformational change of a polymer confined in a spherical cavity. Both passive and active polymers with either homogeneous or heterogeneous stiffness are analyzed in a comparative manner. For a homogeneous chain, continuous rigidity along the backbone promotes a flat spiral expanding along the cavity surface, while activity-induced softening results in a less-ordered spiral structure. Stiffness heterogeneity basically plays a destructive role in spiral formation. However, as the chain is endowed with activity, the heterogeneity effect depends on the stiffness of the front edge of the chain. As the head is rigid, the flat spiral largely holds, whereas such a structure easily loses as the head is flexible. More intriguingly, a short flexible head induces a distinct compact helix in the interior of the cavity. Under low friction conditions, the prominent inertial effect leads to the break-up of both spiral and helix. In the presence of crowding, the flat spiral close to the surface keeps its stability, while the compact helix inside tends to be dissolved. Our results decipher the significant effects of activity, rigidity, confinement and crowding on modulating polymer conformations, which provides a deeper insight about mechanisms for circular structure formation of biopolymers in crowded environments.

We report an experimental study on how topological defects induced by cylindrical air inclusions in the ferroelectric nematic liquid crystal RM734 are influenced by ionic doping, including an ionic surfactant and ionic polymer. Our results show that subtle differences in molecular structure can lead to distinct surface alignments and topological defects. The ionic surfactant induces a planar alignment, with two −1/2 line defects adhering to the cylindrical bubble surface. In contrast, the ionic polymer promotes homeotropic alignment, resulting in a −1 polar disclination around the cylindrical bubble. By numerical simulations, we verify that these topological defects are vertical lines with two dimensional polarization fields. These configurations differ from the boojums and hedgehog defects induced by air inclusions in nematic liquid crystals, highlighting the significant role of broken inversion symmetry.

This study introduces a method for synthesizing electrically conductive hydrogels by incorporating a self-assembled, percolating graphene network. Our approach differs from previous approaches in two crucial aspects: using pristine graphene rather than graphene oxide and self-assembling the percolation network rather than creating random networks by blending. We use pristine graphene at an oil–water interface to stabilize a water-in-oil emulsion, successfully creating hydrogel foams with conductivities up to 15 mS m⁻¹ and tunable porosity. Our approach avoids the need for the conductivity-degrading oxidation process to form GO and decreases the amount of graphitic filler needed for percolation, leading to superior mechanical properties. The concentration of monomer and graphite in the emulsion was optimized to control the cell size, stability, and swelling behavior of the final hydrogels, offering versatility in structure and functionality. Electrical conductivity and thermogravimetric analysis (TGA) confirmed the stability and conductive properties imparted by the graphene network. This method demonstrates a cost-effective route to conductive hydrogels, making them promising candidates for applications in sensors, energy storage, bioelectronics, and other advanced technologies.

In the field of chiral smectic liquid crystals, orthoconic antiferroelectric liquid crystals (OAFLCs) have attracted the interest of the scientific community due to the very high tilt angle, close to 45°, and the consequent optical properties. In the present study, the first ²H NMR investigation is reported on two samples, namely 3F5HPhF9 and 3F7HPhF8, showing the phase sequence isotropic–SmC*–SmC_A* and the phase sequence isotropic–SmA–SmC*–SmC_A*, respectively, when cooling from the isotropic to the crystalline phases. To this aim, the liquid crystals were doped with a small amount of deuterated probe biphenyl-4,4′-diol-d₄. The trend of ²H NMR spectra versus temperature indicates the presence of very high values of the tilt of the deuterated probe in the antiferroelectric phase for both samples. The trend of the local order parameters and that of the tilt angle were compared with the results obtained for the same samples by means of different experimental techniques, namely X-ray diffraction and electrooptical measurements. Moreover, a computational study was performed on the sample labelled 3F5HPhF9 using fully atomistic classical molecular dynamics simulation of the orthoconic phase. The results obtained from the MD simulations show a very large molecular tilt of the molecules (about 42°) when packed in layers and this value is in very good agreement with experimental results. The present research aims to give additional clues about the molecular origin of the very peculiar high tilt angle of orthoconic liquid crystals in the antiferroelectric phase.

In this work, a theoretical approach is developed to investigate the structural properties of ionic microgels induced by a circularly polarized (CP) electric field. Following a similar study on chain formation in the presence of linearly polarized fields [T. Colla et al., ACS Nano, 2018, 12, 4321–4337], we propose an effective potential between microgels which incorporates the field-induced interactions via a static, time averaged polarizing charge at the particle surface. In such a coarse-graining framework, the induced dipole interactions are controlled by external parameters such as the field strength and frequency, ionic strength, as well as microgel charge and concentration, thus providing a convenient route to induce different self-assembly scenarios through experimentally adjustable quantities. In contrast to the case of linearly polarized fields, dipole interactions in the case of CP light are purely repulsive in the direction perpendicular to the polarization plane, while featuring an in-plane attractive well. As a result, the CP field induces layering of planar sheets arranged perpendicularly to the field direction, in strong contrast to the chain formation observed in the case of linear polarizations. Depending on the field strength and particle concentration, in-plane crystallization can also take place. Combining molecular dynamics (MD) simulations and the liquid-state hypernetted-chain (HNC) formalism, we herein investigate the emergence of layering formation and in-plane crystal ordering as the dipole strength and microgel concentration are changed over a wide region of parameter space.

The adsorption of charged clay nanoplatelets plays an important role in stabilizing emulsions by forming a barrier around the emulsion droplets and preventing coalescence. In this work, the adsorption of charged clay nanoplatelets on a preformed Latex microsphere in an aqueous medium is investigated at high temporal resolution using optical tweezer-based single-colloid electrophoresis. Above a critical clay concentration, charged clay nanoplatelets in an aqueous medium self-assemble gradually to form gel-like networks that become denser with increasing medium salinity. In a previous publication [R. Biswas et. al., Soft Matter, 2023, 19, 24007-2416], some of us had demonstrated that a Latex microsphere, optically trapped in a clay gel medium, is expected to attach to the network strands of the gel. In the present contribution, we show that for different ionic conditions of the suspending medium, the adsorption of clay nanoplatelets increases the effective surface charge on an optically trapped Latex microsphere while also enhancing the drag experienced by the latter. Besides the ubiquitous contribution of non-electrostatic dispersion forces in driving the adsorption process, we demonstrate the presence of an electrostatically-driven adsorption mechanism when the microsphere was optically trapped in a clay gel. These observations are qualitatively verified via cryogenic field emission scanning electron microscopy and are useful in achieving colloidal stabilisation, for example, during the preparation of clay-armoured Latex particles in Pickering emulsion polymerisation.

The theoretical study of instabilities, thermal fluctuations, and topological defects in the crystal–rotator-I–rotator-II (X–R_I–R_II) phase transitions of n-alkanes has been conducted. First, we examine the nature of the R_I–R_II phase transition in nanoconfined alkanes. We propose that under confined conditions, the presence of quenched random orientational disorder makes the R_I phase unstable. This disorder-mediated transition falls within the Imry-Ma universality class. Next, we discuss the role of thermal fluctuations in certain rotator phases, as well as the influence of dislocations on the X–R_I phase transition. Our findings indicate that the herringbone order in the X-phase and the hexatic order in the R_II-phase exhibit quasi-long-range characteristics. Furthermore, we find that in two dimensions, the unbinding of dislocations does not result in a disordered liquid state.

Understanding photodegradation of nanogels is critical for dynamic control of their properties and functionalities. We focus on nanogels formed by end-linking of four-arm polyethylene glycol precursors with photolabile groups and characterize dynamic heterogeneities in these systems during degradation. We use our recently developed dissipative particle dynamics framework that captures the controlled scission of bonds between the precursors and diffusion of degraded fragments at the mesoscale. To quantify spatiotemporal fluctuations in the local dynamic behavior, we calculate the self-part of the van-Hove correlation function for the reactive beads for nanogels degrading in various environments. We demonstrate strong deviations from the Gaussian behavior during the degradation and quantify variations in the non-Gaussian parameter as a function of the relative extent of degradation. We show that for the nanogels degrading in a good solvent, the peak values in the non-Gaussian parameter are observed significantly earlier than the reverse gel point, and earlier than the peak values in the dispersity of the broken off fragments. Further, our study shows that a systematic decrease in solvent quality significantly affects the behavior of the non-Gaussian parameter as a function of the relative extent of degradation. The findings of this study allow one to quantify the dynamic heterogeneities during degradation in various environments and can potentially provide guidelines for designing controllably degrading nanocarriers.

Identical, inelastic spheres crystallize when sheared between two parallel, bumpy planes under a constant load larger than a minimum value. We investigate the effect of the inter-particle friction coefficient of the sheared particles on the flow dynamics and the crystallization process with discrete element simulations. If the imposed load is about the minimum value to observe crystallization in frictionless spheres, adding small friction to the granular assembly results in a shear band adjacent to one of the planes and one crystallized region, where a plug flow is observed. The ordered particles are arranged in both face-centered cubic and hexagonal-closed packed phases. The particles in the shear band are in between the crystalline state and the fluid state, but the latter is never reached, which results in a large shear resistance. As the particle friction increases, the shear band disappears, and the ordering in the core region is destroyed. A significant portion of the particles are in a fluid state with a zero shear rate, leading to a substantial and unexpected reduction in the shear resistance with respect to the frictionless case. If the imposed load is increased well above the minimum from the onset of crystallization, we observe the formation of one shear band in the core, where the particles are again between the crystalline state and the fluid state, surrounded by two crystallized regions near the boundaries, in which most of the particles are in the face-centered cubic phase and translate as a rigid body with the boundaries themselves. In this case, the macroscopic shear resistance is independent of the particle friction.