Further investigation was carried out into the mechanism underlying the changes in electric resistance in an aqueous solution of poly(sodium acrylate) induced by a vigorous flow, as we had previously observed. The change in resistance increased with concentration and showed a broad peak at a NaPAA concentration of approximately 2 × 10-3 wt%, which was close to the entanglement concentration (1.2 × 10-3 wt%). The change in resistance of the NaPAA solution increased with increasing frequency and tended to reach a plateau above approximately 3 × 103 Hz. The absolute value of the change in resistance due to the flow could be quantitatively explained by the decrease in the polymer concentration.
Correction for 'Droplet breakup against an isolated obstacle' by David J. Meer et al., Soft Matter, 2026, 22, 2809-2822, https://doi.org/10.1039/d5sm01266j.
This research addresses the challenge of controlling complex director fields in confined chiral liquid crystal (CLC) geometries. CLC droplets were inkjet-printed onto high-resolution photoalignment patterns to study the competition among...
Conductive hydrogels have great potential as sensing materials for wearable flexible electronics; however, their practical applications are often limited by low mechanical strength, poor adhesion, and low self-healing efficiency. To meet the requirements of flexible wearable sensors, in this study we introduced zinc trifluoromethanesulfonate (Zn(CF3SO3)2) into the network structure of polyacrylic acid (PAA) and prepared a polyacrylic acid/zinc trifluoromethanesulfonate (PAA/Zn(CF3SO3)2) conductive hydrogel via free radical polymerization. The addition of Zn(CF3SO3)2 not only improves the ionic conductivity but also enhances the crosslinking density through metal coordination. The PAA/Zn(CF3SO3)2(6 wt%) conductive hydrogel exhibits excellent mechanical properties, with a tensile strength of 1.628 MPa, an elongation at break of 670%, and a high electrical conductivity of 1.212 S m-1. Furthermore, this hydrogel exhibits good moisture retention, anti-swelling, self-healing, and adhesive properties. Importantly, the wearable sensor based on the PAA/Zn(CF3SO3)2(6 wt%) hydrogel exhibits a wide detection range, fast response time, negligible hysteresis, and high sensitivity (GF = 4.56 at 400-600% strain), enabling accurate capture of large-scale human motions as well as movements such as mouth opening and swallowing. This study demonstrates a multifunctional, high-performance conductive hydrogel, showing promise for applications in wearable health monitoring.
Adjusting the formulations of aqueous solutions to maximize their power to clean oil soils from solid substrates, often called detergency, is mostly based on empirical knowledge. Here, we quantitatively describe the removal of a single oil droplet attached to a solid wall under the action of a flow of surfactant solutions. To do so, we design a microfluidic set-up allowing control of the flow and monitoring of the droplet volume, shape, contact area and its detachment. We work with surfactant solutions whose varied composition allows us to span a wide range of both oil solubility and interfacial tension: the system forms microemulsions. Two detergency regimes are identified and described. (i) At large flow rates, the viscous shear forces the droplet to detach which is well accounted for by a single-valued capillary number. As a result, the detachment threshold depends on the antagonistic effects of the detergent composition on the wetting of oil on the solid and the interfacial tension that we describe. (ii) Below the threshold for detachment, the oil from the droplet is solubilized into the detergent according to the advection-diffusion model for transport. This allows us to predict the optimum composition. In both cases we release quantitative predictions, provided that independent characterization studies, using conventional methods, of the oil solubility, micelle size and concentration, interfacial tension and wetting angles are available.
Peptide-based supramolecular assemblies provide experimentally accessible model systems for probing structure-property relationships in soft molecular materials. Here, three short β-sheet-forming peptides with graded histidine substitution were designed as minimal supramolecular networks to systematically examine how sequence-level variation regulates supramolecular organization, viscoelastic response, and pH-modulated molecular transport in aqueous environments. All peptides spontaneously assembled into β-sheet-rich nanofibrous networks, as confirmed by spectroscopic and microscopic characterization, and exhibited stable viscoelastic behavior with pronounced reversible self-recovery. Using doxorubicin as a representative small-molecule probe, the assemblies displayed distinct pH-dependent transport regimes, and kinetic analysis based on the Korsmeyer-Peppas model revealed sequence- and pH-dependent differences in release behavior. Rather than focusing on detailed molecular-level mechanisms, this work emphasizes experimentally accessible correlations between supramolecular network structure, mechanical response, and transport behavior. These results highlight histidine-substituted β-sheet peptide assemblies as adaptable soft-matter model systems for investigating pH-regulated transport phenomena in supramolecular networks.
Silica gels are colloidal hydrogels that can be used in drug delivery techniques, and the introduction of proteins into the system would be of interest in cases where the protein is the element to be delivered. In this study repulsive colloids (silica particle) are mixed with ionic species to form a fractal gel. We then study the impact of adding a protein (bovine serum albumin (BSA)), whose overall charge is the same sign as silica, on the structural and mechanical properties of the gel. Thanks to SAXS and rheology measurements, we can deduce some micro and macro parameters such as, the interaction potential between beads, the gelation time, the elastic modulus and the critical strain of the gel and their variation with the volume fraction in BSA. The protein allows to form gels with very low ionic strength compared to the case without proteins; BSA acts as a binding agent between the silica particles. Thanks to a power-law model, hypotheses are proposed about the gel structure, to make a link between the structure and the mechanical properties.
The material properties of connective tissues are often considered to be dominated by the extracellular matrix. However, cells within tissues contribute significantly to the mechanics, particularly when considering volume-changing deformations such as axial compression. Recent studies have considered the compression response of model tissues at long times, where the role of the interstitial fluid is negligible. Here, we experimentally study the interplay of matrix, cell and fluid mechanics in the short time response of model tissues based on fibrous networks with embedded microgel inclusions as passive cell-like mimics. By simultaneously applying compression at a fixed strain rate while measuring the shear modulus via small strain shear oscillations, we show that at long times fibrous networks transition from compression-softening behaviour to compression-stiffening behaviour upon incorporation of microgel particles. At short times, however, we show that fluid pressure build-up leads to significant compression-stiffening, regardless of the inclusion of microgels. Our findings demonstrate that the role of fluid pressurisation is key to understanding the response of tissues to deformations on timescales on the order of a few seconds, common in many tissues subject to physiological deformations.
The ethylene oxide (EO)/propylene oxide (PO) triblock copolymers (EO)m-(PO)n-(EO)m, also known as poloxamers, self-assemble in aqueous solution due to the differences in hydrophobicity between EO and PO. Both the overall length of the blocks and their relative lengths in the copolymer impact self-assembly. Even though poloxamers lack charge, they respond to the presence of salts, including ionic liquids (ILs). Here, the response of poloxamer 188 to 1-alkyl-3-methylimidazolium chlorides having long and short alkyl chains was studied by small-angle neutron scattering. The dilute state of both the polymer and ILs was studied, with the IL concentrations being below published critical micelle concentrations. The goal was to probe initial stages of self-assembly. The results demonstrate a clear interaction between the long chain imidazolium chloride and the poloxamer that is surfactant-like, which is not observed for the short alkyl chain salt.
Molecular dynamics simulations were performed to investigate the structural evolution and frictional behaviors of breaking polymer brushes subjected to shear imposed by a moving wall with systematic comparisons to non-breaking systems. Our results show that the structural and dynamical properties of breakable brushes are strongly coupled with the shear velocity. At low wall velocities, bond cleavage is rare, and the two systems exhibit nearly identical structural and frictional responses. With increasing wall velocity, brush chains become progressively stretched and oriented along the shear direction, leading to bond rupture. Bonds with the highest degree of shear-induced orientation are more susceptible to breaking, while the location of maximum orientation shifts with wall velocity, i.e., the polydispersity of free and brush chains are altered by the velocity. When the wall velocity exceeds a critical value, a large number of free chains accumulate near the moving wall and form a mobile interfacial lubricating layer, resulting in a pronounced self-lubrication effect. In this high-velocity regime, the friction coefficient decreases by approximately one order of magnitude relative to the corresponding non-breaking system. Moreover, this critical velocity decreases with increasing chain length. Further analysis reveals that, compared with the contact number, which is conventionally used to estimate the strength of friction, chain orientation maintains a robust linear relation with the friction coefficient over a much broader shear range, therefore serves as a more reliable descriptor for the interfacial frictional response. This study elucidates the molecular mechanism of bond-breaking-induced self-lubrication in polymer brushes and provides physical insights for the design of polymer-brush interfaces with tunable frictional properties.
The liquid crystalline ferroelectric nematic (NF) phase is well known for its distinctive physical and electrical properties, namely the bulk polarity. It is therefore important to consider whether the nematic bulk properties are affected by very highly polar molecules and underlying polar phases. In this paper, we present a detailed temperature-dependence of the splay (K11) and bend (K33) elastic constants, and the Fréedericksz threshold voltage for a positive dielectric anisotropy LC mixture exhibiting both non-polar (N) and polar (NF) nematic phases, and include theoretical discussions. Such properties are compared to those of two conventional nematic liquid crystals (NLCs). In the NF LC mixture, we show a marked reduction in the splay elastic constant (1.8-0.5 pN) and the threshold voltage (150-35 mV), across the nematic phase, at temperatures much lower than the nematic to isotropic transition. The values for K11 and Vth linearly extrapolate to 0 pN and 0 V respectively, at the nematic to the intermediate nematic (NX) phase transition. Such reduction in the splay elastic constant, which is a deviation from conventional nematic behaviour, is attributed to flexoelectric coupling becoming significant at these temperatures. Corrections with temperature dependent flexoelectric coupling for the elastic constants, dielectric permittivity, and Fréedericksz threshold voltage, are discussed in detail.
The equilibrium shear modulus of some swollen polymer networks decreases with increasing temperature, even when the corresponding dry network shows the classical positive temperature coefficient of entropic elasticity. This sign reversal cannot be explained by the conventional Frenkel-Flory-Rehner framework, in which the mixing free energy is assumed independent of deformation. We show that allowing the Flory-Huggins parameter χ to depend on isochoric strain invariants, a thermodynamically general but previously unexplored possibility, resolves this inconsistency. Within continuum thermodynamics, this yields, to leading order under commonly encountered conditions, an affine modulus-temperature relation, Geq = θ(X - Y) +ΘY, which separates the dry-network contribution X from a solvent-mediated contribution Y. The resulting structure defines an experimental strategy: measure dry and swollen networks over temperature and concentration, then test the consistency of Y inferred from slope and intercept, or directly when Θ is known independently. We apply this framework to poly(n-butyl acrylate) swollen in butyl benzoate and poly(ethylene glycol) swollen in dimethylformamide, obtaining Y < 0 and Y > 0, respectively. For the latter system, the fitted Θ agrees with the known crystallization temperature of poly(ethylene glycol) in dimethylformamide. The present work establishes a thermodynamic framework and validation strategy for solvent-deformation coupling in swollen networks, while leaving molecular identification to future study.
A strategy for the fabrication of porous polymeric micro-/nanomaterials via reversible addition-fragmentation chain transfer (RAFT) polymerization-induced self-assembly (PISA) has been proposed. The process is regulated by tuning the stepwise addition strategy of the macromolecular chain transfer agent (macro-CTA). A systematic study was carried out on three types of polymerization-induced self-assembly (PISA) systems, including redox-initiated and photo-initiated aqueous emulsion polymerization of glycidyl methacrylate (GlyMA), as well as thermally initiated dispersion polymerization of styrene (St) in methanol. All systems were mediated by the same poly(ethylene glycol) methacrylate (PPEGMA) macro-CTA. Experimental results show that all three polymerization-induced self-assembly systems can successfully prepare porous polymer micro-/nanomaterials with regular morphology, tunable pore size, and abundant pores, namely PPEGMA9.1-b-PGlyMAn and PPEGMA9.1-b-PSn. It should be noted that the redox and thermal systems are comprehensively characterized by kinetic and GPC tests, while the photoinitiated system only acts as a supporting demonstration based on TEM images in the supplementary information. Moreover, the process conditions for achieving porous morphologies were explored by adjusting the molar ratio of the macro-CTA added in batches, the time intervals between additions, and the monomer concentration.
Most coarse-grained models of the nanoscale self-assembly process employ rigid building blocks that do not exhibit shape adaptation, limiting our understanding of the role of elasticity in altering self-assembly pathways....
Topological defects in liquid crystals (LCs) emerge from elastic distortions of the director field under confinement, but the influence of geometric confinement in open microstructured systems remains poorly understood. Here...
Hydrogel spheres, which undergo large deformations under external forcing, are widely used in applications ranging from soil conservation to biomedicine, soft robotics, and wearable devices. These large deformations induce strong...
Granular hydrogels resulting from the dense packing of hydrogel microparticles have recently attracted a lot of attention, both from a fundamental perspective and for application as biomaterials. However, comparisons between the properties of bulk and granular hydrogels of similar compositions remain scarce. Here we have prepared chitosan-collagen I granular hydrogels via fragmentation of bulk hydrogels and centrifugation of the resulting microparticle suspension. Microparticles exhibited a fibrillated collagen I core embedded in a chitosan shell, suggesting that the fragmentation process is controlled by the protein microstructures dispersed in the polysaccharide matrix. Rheological studies indicated that the granular hydrogels were less elastic (lower storage modulus) but more ductile (higher critical shear strain) than the corresponding bulk hydrogels. Moreover, their rheological properties were more sensitive to collagen content and collagen fiber organization, which impacted both particle compressibility and inter-particle interactions. Extension of the herein-described approach should allow us to improve our understanding of existing correlations between the mechanical properties of bulk hydrogels, hydrogel microparticles and granular hydrogels.
Concentrated surfactant pastes often form lamellar liquid-crystalline phases whose processing depends on alignment, confinement, temperature, and defect topology. Here, we investigate temperature-driven lamellar contraction and parabolic focal conic defect (pFCD) formation in 70 wt% sodium lauryl ether sulfate (SLEnS) lamellar pastes using small-angle X-ray scattering (SAXS), confined cross-polarized microscopy, and confined oscillatory rheometry. SAXS measurements show that the lamellar repeat spacing decreases with increasing temperature in both SLE1S and SLE3S, corresponding to one-dimensional, bilayer-normal negative thermal expansion. This contraction was observed in both bulk-thickness and confined SAXS geometries, indicating that the nanoscale thermal response is not specific to sample thickness, chemistry, or instrument configuration. Under confinement, squeeze-flow alignment appears to produce coherent lamellar stacks that cannot freely accommodate the temperature-dependent spacing decrease. Heating these aligned lamellae produces thermal undulations and optically resolved pFCD fleurettes. SLE3S forms pFCDs at a lower onset temperature and completes defect development over a lower temperature range, whereas SLE1S forms brighter and larger final pFCD textures. Confined rheometry shows non-monotonic changes in storage and loss moduli over the same temperature range as lamellar contraction and pFCD development, suggesting coupling between nanoscale contraction, mesoscale defect formation, and bulk viscoelasticity. Together, these results establish a confinement-mediated mechanism by which lamellar negative thermal expansion generates compressive strain, undulatory defect formation, and altered mechanics in industrially relevant concentrated surfactant pastes.
Elucidating the dynamic mechanisms of polymer translocation through nanochannels with channel oscillation characterized by periodic opening and closing is critical for advancing the understanding of polymer transport in confined environments and guiding the design of advanced nanofluidic systems. We employed coupled molecular dynamics and multi-particle collision dynamics simulations to investigate the influence of channel oscillation on polymer capture and translocation in varying dielectric environments. The capture probability and translocation time of polymers consistently exhibit a non-monotonic dependence on oscillation frequency. Translocation is accelerated within a certain range of the reduced oscillation frequency , with the translocation time reaching a minimum in the interval of 10-1 to 100, where is defined as the ratio of the translocation time through a static channel to the oscillation period. This interval corresponds to the regime where the oscillation period is commensurate with the timescale of polymer translocation. Analysis indicates that periodic opening and closing of the channel generates a microflow toward the trans side via hydrodynamic interactions, driving monomers into the channel during opening and facilitating their expulsion during channel closure, thereby accelerating capture and translocation. Furthermore, it modulates polymer conformation, enhancing the driving force on polymers and further promoting translocation. Conversely, electrostatic interactions impede these processes by altering polymer conformation and introducing steric hindrance from condensed counterions. These findings reveal fundamental mechanisms of polymer dynamics in oscillatory channels and may provide insights into systems where such dynamics are a key factor, from biological pores to the design of synthetic nanochannels.
Dynamic heterogeneity in complex fluids is often inferred from broad relaxation spectra or non-Gaussian probe motion, but these signatures do not by themselves identify the relevant spatial length scales or distinguish heterogeneity from inter-particle dynamic correlation. Here, we develop an analytical framework for multiparticle tracking microrheology that separates these two aspects of dynamics. The framework compares single-particle and multi-particle non-Gaussian parameters αsp2 and αmp2 to infer the accessible length-scale range of diffusivity heterogeneity, and introduces an overlap-based cross-covariance quantity, χcross, to quantify inter-particle dynamic correlation. Brownian-dynamics simulations validate the expected behavior of these estimators under simplified heterogeneous-diffusivity and correlated-motion models. The framework is then applied to two-component tetra-PEG hydrogels with symmetric and asymmetric stoichiometric ratios. In post-gel samples, αmp2 > 0 while αsp2 ≈ 0, indicating dynamic heterogeneity on length scales larger than the single-trajectory span and within the experimental field of view, on the order of tens of microns. The two gel systems exhibit distinct dynamical signatures: in the post-gel regime, the symmetric-ratio gel shows slightly smaller αmp2 and little detectable cross-correlation, whereas the asymmetric-ratio gel shows slightly larger αmp2 and significant cross-correlation. These results demonstrate that dynamic heterogeneity and dynamic correlation are not equivalent observables in particle-tracking experiments, and that their combined analysis provides a more resolved description of gelling complex fluids.
