Soft Matter最新文献

Micellization is commonly described as a collective response driven by the hydrophobic effect. Here we propose and study a topological Ising model that abstracts this effect as a solvent-exclusion constraint defined purely by local connectivity. On a square lattice with binary occupancy (amphiphiles/water), we characterize neighborhood by a topological kernel of radius R and metric (Chebyshev or Manhattan). A water site becomes “restricted” when the local overlap with amphiphiles, computed via convolution with the kernel, exceeds a fixed threshold. The system energy is F = N_restr; we set α = 1 by design, working in dimensionless units that prevent interpreting α as carrying any metric information. Dynamics are explored with Metropolis updates at temperature T. Control parameters are amphiphile density ρ, temperature T, the metric, and R. As an order parameter we use S_max/N_a, the fraction of amphiphiles in the largest connected cluster. In the surveyed ranges we observe, for more connective kernels (e.g., Chebyshev with R ≥ 3), the emergence of a giant component in finite regions of (ρ, T), while less connective configurations (e.g., Manhattan with R = 1) do not aggregate in the same window. These results support the view that micellization, in this framework, is a connectivity transition governed by the topology of local interactions rather than by explicit metric scales. We discuss implications and routes for quantitative comparisons with experiments and more detailed simulations.

A numerical modeling of the field-induced electrization in a magnetoelectric composite filament of polyvinylidene fluoride (PVDF) filled with cobalt ferrite (CFO) nanoparticles is performed. The filament is considered in the framework of the representative volume element (RVE) scheme, and two configurations of the particle magnetic moments are taken as examples: parallel (structure I) and anti-parallel (structure II). Under an applied magnetic field, the magnetostrictive and magnetorotational effects in the CFO particles induce mechanical stresses in the PVDF matrix, which, due to its piezoelectric properties, generate electric polarization. The resulting electric potential distributions on the filament surface and in the surrounding space are obtained with the aid of the finite element method. Key findings reveal that structure I exhibits a transverse polarization with higher electric potential, while structure II shows a helical charge distribution with more tightly localized fields. The results provide insights into the design of magnetoelectric filaments intended for regenerative medicine and flexible electronics, detailing the interplay between the electromagnetic properties and structure of the composites under study.

The linear viscoelastic response of single semiflexible polymer chains in the infinite-dilution limit is studied using Brownian dynamics simulations of coarse-grained bead–spring chains. The springs obey the FENE–Fraenkel force law, a bending potential is used to capture chain stiffness and hydrodynamic interactions are included through the Rotne–Prager–Yamakawa tensor. By calculating the relaxation modulus following a step strain, we demonstrate that the bead–spring chain behaves like an inextensible semiflexible rod over a wide time window with an appropriate choice of spring stiffness and chain extensibility. In the absence of hydrodynamic interactions, our results agree with the existing theoretical predictions for the linear viscoelastic response of free-draining, inextensible, semiflexible rods in the limit of infinite dilution. It is shown that at intermediate times, the stress relaxation modulus exhibits power law behaviour, with the exponent ranging from (−1/2) for flexible chains to (−5/4) for highly rigid chains. At long times, rigid chains undergo orientational relaxation, while flexible chains exhibit Rouse relaxation. Hydrodynamic interactions are found to affect the behaviour at intermediate and long times, with the difference in free-draining behaviour increasing with increasing chain flexibility. Computations of the frequency dependence of loss and storage moduli are found to be in good agreement with experimental data for a wide variety of systems involving semiflexible polymers of varying stiffness across a broad frequency range.

The stiffness and the volume of human platelets change under various conditions, affecting their function and viability. Although the influence of platelet volume on platelet function in health and disease has been extensively studied, the relationship between volume and stiffness - in contrast to many other cell types - remains unexplored for platelets, probably due to the difficulty in measuring platelet mechanics as platelets tend to activate under stress. Here, we investigate the relationship between platelet volume and stiffness using scanning ion conductance microscopy (SICM). SICM can image the topography and therefore quantify the volume as well as measure the mechanical properties of living cells under physiological conditions with submicrometer resolution. We found a link between platelet stiffness and volume changes caused by water efflux/influx due to osmotic compression/expansion at the single cell level. With increasing platelet volume, the stiffness decreased and vice versa. We then confirmed this inverse relationship by measurements of platelets during two additional, physiologically highly relevant situations: The dynamic spreading of platelets on a surface and platelets subjected to a spatial confinement, where a decrease in volume was also accompanied by an increase in stiffness and platelets subjected to spatial confinement showed a significantly larger volume compared to unconfined platelets, with a correspondingly lower stiffness, respectively. In conclusion, our SICM analysis revealed a universal, inverse correlation between platelet stiffness and volume change, opening up new perspectives in platelet research.

Bacterial swarming is a phenomenon characterized by the rapid migration of microorganisms on a surface powered by flagella. While extensive studies have explored various factors influencing swarming dynamics, the impact of length variation within a single strain on swarming remains to be elucidated. Here, we investigate the effect of length variants within a single strain, Vibrio alginolyticus, as an ideal model to explore the cooperative mechanisms driven by a heterogeneous, flexible population. Through individual cell tracking, we found that cell length directly impacts collective organization. Long, flexible cells move faster and more persistently than shorter cells, promoting the emergence of large-scale, coordinated flow. In contrast, shorter cells slow down due to frequent reverse movements, which create spaces and prevent jamming within the dense colony. This division of labor, where longer cells act as leaders and shorter cells serve as buffers, facilitates efficient collective movement and demonstrates the significant advantage of phenotypic heterogeneity within a single strain for robust swarming. Our findings suggest that the diversity in length of active matter may facilitate efficient spreading across soft interfaces.

New di-chain anionic surfactants containing silicon (Si) atoms in the hydrophobic chain-tips (trimethylsilyl (TMS) hedgehog surfactants) are able to reduce air–water (A–W) surface tension γ_cmc to as low as ≈22 mN m⁻¹ (A. Czajka, C. Hill, J. Peach, J. C. Pegg, I. Grillo, F. Guittard, S. E. Rogers, M. Sagisaka and J. Eastoe, Phys. Chem. Chem. Phys., 2017, 19, 23869). However, the extent to which these surfactants stabilize alkane oil–water (O–W) interfaces is unexplored. Here, it is shown that such TMS surfactants are able to stabilize water-in-oil microemulsions (W/O-µEs). The O–W interfacial tensions γ_o/w in these µEs are ultra-low, in the range of 10⁻² to 10⁻⁴ mN m⁻¹, and µE-stability can be optimized by varying surfactant and solvent chemical structures. For example, with aliphatic n-alkanes and cycloalkanes, the surfactant AOT–SiC alone stabilizes W/O-µEs over a wide temperature window, but not with the aromatic solvent toluene. Likewise, AOT–SiB forms W/O-µEs, but preferably in aromatic solvents, such as toluene. Contrast-variation small-angle neutron scattering (SANS) measurements indicate that the water droplets in these W/O-µEs are stabilized by surfactant-monolayers. In all of these systems, the droplet morphologies and shapes are correlated with the proximity to (from) the µE-phase stability boundaries. The results show that Si-containing TMS surfactants are effective at O–W interfaces, promoting the ultra-low interfacial tensions necessary for stabilization of µEs. These TMS surfactants offer credible alternatives to environmentally damaging and health-hazardous fluorinated surfactants (FSURFs).

The growing energy crisis has intensified the focus on green energy, sparking widespread interest in aqueous zinc-ion batteries. However, their development has been hindered by issues in the zinc anode. Here, Ca²⁺/Zn²⁺ alginate hydrogel electrolyte was designed to effectively suppress dendritic growth and parasitic side reactions. The Ca²⁺ primary cross-linking provides a regular “egg-box” network framework for fast ion transport, whereas secondary cross-linking with Zn²⁺ creates a denser, interpenetrating network with calcium, thereby enhancing the hydrogel's mechanical strength. Furthermore, the abundant –OH and –COO⁻ groups on the alginate chains formed hydrogen bonds with H₂O, which reduced water activity. Meanwhile, the abundant –OH and –COOH groups on the alginate chains formed hydrogen bonds/coordination with H₂O/Zn²⁺, reducing the activity of H₂O and strengthening the ion confinement effect. Therefore, the Zn/SCZ/Zn symmetric cell achieved stable cycling for over 900 hours at 2 mA cm⁻² and 2 mAh cm⁻², while the Zn/SCZ/MnO₂ battery retained 62.03% of its capacity after 700 cycles. This Ca²⁺/Zn²⁺ dual-ion crosslinking strategy for the alginate hydrogel electrolyte offers a novel approach to address the limitations of conventional aqueous electrolytes.

Surface alignment of a recently discovered ferroelectric nematic liquid crystal (N_F) is usually achieved using buffed polymer films, which produce a unidirectional polar alignment of the spontaneous electric polarization. We demonstrate that photosensitive polymer substrates could provide a broader variety of alignment modes. Namely, a polyvinyl cinnamate polymer film irradiated by linearly polarized ultraviolet (UV) light yields two modes of surface orientation of the N_F polarization: (1) a planar apolar mode, in which the equilibrium N_F polarization aligns perpendicularly to the polarization of normally impinging UV light; the N_F polarization adopts either of the two antiparallel states; (2) a planar polar mode, produced by an additional irradiation with obliquely impinging UV light; in this mode, there is only one stable azimuthal direction of polarization in the plane of the substrate. The two modes differ in their response to an electric field. In the planar apolar mode, the polarization can be switched back and forth between two states of equal surface energy. In the planar polar mode, the field-perturbed polarization relaxes back to the single photoinduced “easy axis” once the field is switched off. The versatility of modes and absence of mechanical contact make the photoalignment of N_F attractive for practical applications.

A major challenge hampering the industrial and biological exploitation of lipases is the self-limiting effect of the lipolytic reaction. Defying sustained attention throughout history, the influence of lipase catalysed lipolysis on the internal structure of thin triglyceride films has proved elusive. An in-depth understanding of the lipolysis process at the triglycerides/aqueous interface will assist in creating innovative methods to enhance yields. This study furthers our understanding of the influence of solution pD (pH equivalent for aqueous solutions prepared with D₂O) on the effect of lipolysis on the structure of thin triolein films. All experiments were performed at pD 7.0 or pD 8.5, either side of the apparent pK_a of the primary product of the hydrolysis (oleic acid/oleate). Spectroscopic ellipsometry measurements were employed to kinetically track the changes in thickness of the triolein film after the introduction of 2 ppm Thermomyces lanuginosus lipase (TLL). Neutron reflectometry experiments revealed the internal structure of the thin films before and after TLL digestion, while fast kinetic measurements capturing changes to the reflectivity profile throughout lipolysis. Both techniques revealed significant variations in the physical properties and enzymatic conversion of the triolein films between pD 7.0 and pD 8.5.

Incorporating hydrophobic associations into hydrophilic networks as energy dissipation units is an efficient strategy to toughen hydrogels. However, the micro-segregated structures often lead to turbid hydrogels with poor optical properties. Here, we report the synthesis of transparent, tough, and fluorescent hydrogels in which tetraphenylethylene (TPE) fluorogens are linked to the network by a polymethylene spacer. The TPE motif and polymethylene spacer form hydrophobic associations, affording the transparent hydrogels with excellent mechanical properties and strong fluorescence. The mechanical properties of the hydrogels can be tuned by the fraction of hydrophobic units, the length of the polymethylene spacer, and the presence of the TPE motif. A rubbery-to-glassy transition is found in poly(12-(4-(1,2,2-triphenylvinyl)phenoxy)dodecyl acrylate-co-acrylic acid) hydrogels and poly(4-(1,2,2-triphenylvinyl)phenoxy)hexyl acrylate-co-acrylic acid) hydrogels as the fraction of hydrophobic units increases. The increased glass transition temperatures and apparent activation energies of the hydrogels with longer spacers and the TPE motif indicate a synergistic effect between the hydrophobic polymethylene and TPE motifs. Small- and wide-angle X-ray scattering results show that these tough and fluorescent hydrogels have compact hydrophobic domains with a quasi-lamellar structure. The hydrophobic domains are disrupted during stretching to dissipate energy, accounting for the high toughness of the hydrogels. This study presents a novel strategy to construct tough and fluorescent hydrogels by forming synergistic associations, which should be informative for designing other tough materials with specific functions and applications.