Soft Matter最新文献

We theoretically determine the effective forces on hard disks near walls embedded inside active nematic liquid crystals. When the disks are sufficiently close to the wall and the flows are sufficiently slow, we can obtain exact expressions for the effective forces. We find these forces and the dynamics of disks near the wall depend both on the properties of the active nematic and on the anchoring conditions on the disks and the wall. Our results show that the presence of active stresses attract planar anchored disks to walls if the activity is extensile, and repel them if contractile. For normal anchored disks the reverse is true; they are attracted in contractile systems, and repelled in extensile ones. By choosing the activity and anchoring, these effects may be helpful in controlling the self assembly of active nematic colloids.

Cell polarization is crucial in most physiological functions. Living cells at the extracellular matrix (ECM) actively coordinate a polarized morphology to target the preferred signals. In particular, the initial heterogeneity of subcellular components, termed as structural polarity, has been discovered to mediate the early attachment and transmigration of cells in tumour metastasis. However, how heterogeneous cells initiate the early polarization remains incompletely discovered. Here, we establish a multiscale model of a cell to explore the chemo-mechanical mechanisms of cell polarization initiated by structural polarity. The two-dimensional vertex model of the cell is built with the main mechanical components of eukaryotic cells. The initial structural polarity of the modeled cell is introduced by seeding heterogeneous actin filaments at the cell cortex and quantified by the ratio of the filamentous forces at the vertices. Then, the structural polarity is integrated in the reaction-diffusion system of Rho GTPase (Cdc42) at the cell cortex to obtain the traction forces at the leading vertices. Finally, the modeled cell is actuated to spread under the traction forces and discovered to develop into a characteristic polarized morphology. The results indicate that the cell polarization is initiated and dynamically developed by structural polarity through the reaction-diffusion system of Cdc42. In addition, the bistability of Cdc42 activation at the cell cortex is defined and discovered to dominate the polarization status of the cell. Furthermore, biphasic (i.e., positive and negative) durotaxis of the cell is successfully modeled at an ECM with a stiffness gradient, and concluded to be codetermined by the chemo-mechanical coupling of the initial structural polarity and ECM stiffness gradient. The proposed multiscale model provides a quantitative way to probe cell polarization coupled with mechanical stimuli, biochemical reaction and cytoskeletal reorganization, and holds the potential to guide studies of cell polarization under multiple stimuli.

Supramolecular crystal gels, a subset of molecular gels, are formed through the self-assembly of low molecular weight gelators into interconnecting crystalline fibers, creating a three-dimensional soft solid network. This study focuses on the formation and properties of viologen-based supramolecular crystalline gels. It aims to answer key questions about the tunability of network properties and the origin of these properties through in-depth analyses of the gelation kinetics triggered by thermal quenching. Experimental investigations, including UV-Vis absorption spectroscopy, rheology, microscopy and scattering measurements, contribute to a comprehensive and self-consistent understanding of the system kinetics. We confirm that viologen-based gelators crystallize by forming nanometer radius hollow tubes that assemble into micro to millimetric spherulites. We then show that crystallization follows the Avrami theory and is based on pre-existing nuclei. We also establish that the growth is interface-controlled, leading the hollow tubes to branch into spherulites with fractal structures. Finally, we demonstrate that the gel properties can be tuned depending on the quenching temperature. Lowering the temperature results in the formation of denser and smaller spherulites. In contrast, the gel's elasticity is not significantly affected by the quench temperature, leading us to hypothesize that the densification of spherulites occurs at the expense of connectivity between spherulites.

Hybrid heterostructure materials have received considerable attention due to the integration of each component and abundant functional applications in micromotors, catalysis, photothermal therapy, drug delivery, and bioimaging. However, the preparation of organic/inorganic heterostructure nanoparticles (HSNPs) with high quality still remains a remarkable challenge since thermodynamically metastable structures usually coexist, resulting in a lack of organic scaffolds with extreme uniformity both in shape and size distribution. Here, we prepared polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer (BCP) core-shell spherical colloids driven by interfacial instability of soft and deformable emulsion droplets. Ultra-low interfacial tension was achieved through the co-adsorption of BCP segments and sodium dodecyl sulfate (SDS) surfactant, which had a strong affinity with the P4VP segment at the interface of the emulsified droplets. The excellent and homogeneous BCP colloids were further utilized as organic scaffolds to selectively grow a functional SiO₂ layer on the surface of the BCP spherical colloids, producing BCP/SiO₂ HSNPs with highly uniform shape and size distribution originating from the PS-b-P4VP scaffolds, thus providing an efficient and general strategy to construct and design organic/inorganic HSNPs with diverse applications.

Common neutral polymer microgels exhibit an inhomogeneous density profile with a gradual decay that is commonly described using the fuzzy sphere model. The model is based on the idea of convolving the collapsed solid sphere profile with a Gaussian to describe inhomogeneous swelling of the microgel in a good solvent. Here we show that the corresponding density profile in real space used in several recent works - such as in super-resolution microscopy - is different from the fuzzy sphere model, and we explain how to correctly transition between reciprocal space modelling to real space. Our work aims to clarify the application of the model so that errors can be avoided in the future. Our discussion is also crucial when comparing alternative real-space models for the density profile with the established fuzzy sphere model.

Evaporation of multicomponent drops can induce liquid-liquid phase separation and spatial reconfiguration of phases. Here, we unveil several novel dynamics near the contact line of evaporating multicomponent drops containing polyethylene glycol and dextran. The interplay between background Marangoni flow and self-migration of nucleated microdroplets creates both unstable and stable equilibrium points. This leads to either continuous migration or stepwise advancement of microdroplets, influenced by random coalescence events. Tiny dextran microdroplets nucleating at the contact line can migrate toward the bulk only by growing in size with coalescence events. Our findings offer new insights into the fundamental understanding of evaporating multicomponent drops and factors influencing the spatial segregation of phases in evaporative liquid-liquid phase separation with implications in prebiotic biomolecular reactions to industrial applications.

We numerically examine the impacts of particle-wall alignment interactions on active species diffusion through a structureless narrow two-dimensional channel. We consider particle-wall interaction to depend on the self-propulsion velocity direction whereby some specific particle's alignments with respect to the boundary walls are stabilized more. Further, the alignment interaction is meaningful as long as particles are close to the confining boundaries. Unbiased diffusion of active particles for various possible stable velocity alignments against the walls has been examined. We show that for the most stable configuration leading to the self-propulsion velocity direction perpendicular to the wall, diffusivity becomes inversely proportional to the square of the alignment interaction torque. On the other hand, when the self-propulsion velocity direction making an acute angle to the channel walls is the most stable configuration, diffusion exponentially grows with strengthening alignment interaction. Hence, particle-wall interaction plays a pivotal role in the transport control of active particles through narrow channels. Moreover, the impacts of the alignment interactions on diffusion largely depend on the particle's self-propulsion properties and its chirality. Our simulation results can potentially be used to understand unbiased diffusion of artificial or living micro/nano-objects (such as virus, bacteria, Janus particles, etc.) though narrow confined structures.

Active nematic fluids exhibit complex dynamics in both bulk and in simple confining geometries. However, complex confining geometries could have substantial impact on active spontaneous flows. Using multiparticle collision dynamics simulations adapted for active nematic particles, we study the dynamic behaviour of an active nematic fluid confined in a corrugated channel. The transition from a quiescent state to a spontaneous flow state occurs from a weak swirling flow to a strong coherent flow due to the presence of curved-wall induced active flows. We show that the active nematic fluid flows in corrugated channels can be understood in two different ways: (i) as the result of an early or delayed flow transition when compared with that in a flat-walled channel of appropriate width and (ii) boundary-induced active flows in the corrugations providing an effective slip velocity to the coherent flows in the bulk. Thus, our work illustrates the crucial role of corrugations of the confining boundary in dictating the flow transition and flow states of active fluids.

Tailoring polymers for target applications often involves selecting candidates from a large design parameter space including polymer chemistry, molar mass, sequence, and architecture, and linking each candidate to their assembled structures and in turn their properties. To accelerate this process, there is a critical need for inverse design of polymers and fast exploration of the structures they can form. This need has been particularly challenging to fulfill due to the multiple length scales and time scales of structural arrangements found in polymers that together give rise to the materials' properties. In this work, we tackle this challenge by introducing a computational framework called RAPSIDY - Rapid Analysis of Polymer Structure and Inverse Design strategY. RAPSIDY enables inverse design of polymers by accelerating the evaluation of stability of multiscale structure for any given polymer design (sequence, composition, length). We use molecular dynamics simulations as the base method and apply a guiding potential to initialize polymers chains of a selected design within target morphologies. After initialization, the guiding potential is turned off, and we allow the chains and structure to relax. By evaluating similarity between the target morphology and the relaxed morphology for that polymer design, we can screen many polymer designs in a highly parallelized manner to rank designs that are likely to remain in that target morphology. We demonstrate how this method works using an example of a symmetric, linear pentablock, A_xB_yA_zB_yA_x, copolymer system for which we determine polymer sequences that exhibit stable double gyroid morphology. Rather than trying to identify the global free-energy minimum morphology for a specific polymer design, we aim to identify candidates of polymer design parameter space that are more stable in the desired morphology than others. Our approach reduces computational costs for design parameter exploration by up to two orders-of-magnitude compared to traditional MD methods, thus accelerating design and engineering of novel polymer materials for target applications.

Milk foams are fragile objects, readily prepared for frothy cappuccinos and lattes using bovine milk. However, evolving consumer preferences driven by health, climate change, veganism, and sustainability have created a substantial demand for creating frothy beverages using plant-based milk alternatives or plant milks. In this contribution, we characterize maximum foam volume and half-lifetime as metrics for foamability and foam stability and drainage kinetics of two animal milks (cow and goat) and compared them to those of the six most popular, commercially available plant milks: almond, oat, soy, pea, coconut, and rice. We used three set-ups: an electric frother with cold (10 °C) and hot (65 °C) settings to emulate the real-life application of creating foam for cappuccinos, a commercial device called a dynamic foam analyzer or DFA and fizzics-scope, a bespoke device we built. Fizzics-scope visualizes foam creation, evolution, and destruction using an extended prism-based imaging system facilitating the capture of spatiotemporal variation in foam microstructure over a broader range of heights and liquid fractions. Among the chosen eight milks, oat produces the longest-lasting foams, and rice has the lowest amount and stability of foam. Using the hot settings, animal milks produce more foam volume using an electric frother than the top three plant milks in terms of foamability (oat, pea, and soy). Using the cold settings, oat, soy, and almond outperform cow milk in terms of foam volume and lifetime for foams made with the frother and sparging. Most plant milks have higher viscosity due to added polysaccharide thickeners, and in some, lecithin and saponin can supplement globular proteins as emulsifiers. Our studies combining foam creation by frothing or sparging with imaging protocols to track global foam volume and local bubble size changes present opportunities for contrasting the physicochemical properties and functional attributes of animal and plant-based milk and ingredients for engineering better alternatives.