Themed collection Soft Matter Lectureship Winners

This Opinion highlights important outstanding questions in the deformation of soft solid interfaces.

Small sample volumes, a large dynamic response and short acquisition times make microrheology important for characterizing emerging biomaterial hydrogelators.

Nanoemulsions are kinetically stable liquid-in-liquid dispersions with droplet sizes on the order of 100 nm.

The general principle for the design of tough hydrogels is to implement mechanisms for dissipating mechanical energy and maintaining high elasticity into hydrogels. A particularly promising strategy for the design is to implement multiple mechanisms across multiple length scales, for example, integrating fiber-reinforcement, high-functionality crosslinkers, and hybrid crosslinkers from macro-scale to nano-scale.

We describe the physico-chemical aspects of reversible DNA compaction and its applications in gene regulation, DNA protection and nanostructure fabrication.

We review diverse applications of traction force microscopy and provide detailed instructions, including computer code, for performing it.

Pull-in instability often occurs when a film of a dielectric elastomer is subjected to an electric field. In this work, we concoct a set of simple, experimentally implementable, conditions that render the dielectric elastomer film impervious to pull-in instability for all practical loading conditions.

Spinodal decomposition and phase transitions are viable methods to generate a variety of bicontinuous materials. Here, we use 3D printing in conjunction with colloidal self-assembly to create mesostructured hydrogels with tunable micron-sized networks. The rheological properties of the ink and appropriate choice of the photoinitiator are key to printing high fidelity structures.

This work utilizes a combined effort of experiment and theory to report a new mechanism and scaling law to account for extreme toughening of diverse soft materials.

Unprotected dipeptides are studied for self-assembly into hydrogels and single-crystal XRD data reveal key insights in the supramolecular interactions.

Programming genesis in polydomain liquid crystal elastomers (LCEs) is a differentiated approach to prepare monolithic material compositions with localized, omnidirectional deformation.

We report the formation of polymeric and nanocomposite capsules via droplet solvent extraction, elucidating the interplay between solvent exchange and removal, demixing and directional solidification kinetics.

Oscillating electric fields across electrolyte cause anomalously large forces between the electrodes.

This work introduces ideal reversible polymer networks, describes and validates experimentally a theory to relate the network mechanical behavior to the crosslink dynamics.

Kirigami enhances film adhesion due to (i) the shear-lag effect of the film segments; (ii) partial debonding at the film segments’ edges; and (iii) compatibility of kirigami films with inhomogeneous deformation of substrates.

Extreme nanoconfinement increases polymer viscosity and glass transition temperature significantly, whereas polymer–nanoparticle interactions have little influence.

We demonstrate that, by tailoring the MPT probe surface chemistry, we can control the residence of probes in each domain in thermally-gelling nanoemulsions, thus allowing us to independently probe each phase at rising temperatures.

Manipulating and measuring single-molecule dynamics and reactions in nanofluidics is a rapidly growing field with broad applications in developing new biotechnologies, understanding nanoconfinement effects in vivo, and exploring new phenomena in confinement.

We report on electrically-induced, large magnitude (>300 nm), and reversible tuning of the selective reflection in polymer stabilized cholesteric liquid crystals (PSCLCs) prepared from negative dielectric anisotropy nematic liquid crystal hosts.

Monomeric mixtures formulated to prepare a liquid crystal polymer network (LCN) or elastomer (LCE) can be “programmed” by surface alignment to retain complex and arbitrary spatial distributions of the director orientation upon polymerization.

Hybrid colloidal microswimmers of programmable shape and composition are prepared by sequential capillary assembly and their modes of motion and functionality are characterized.

Ultrasound-driven microbubble oscillations can probe the linear viscoelastic properties of hydrogels. The bubble resonance frequency increases with shear modulus.

Highly dense equilibrium assemblies of colloidal ellipsoids having three-dimensional order and packing fraction upto 67%.

We describe a method to track particles undergoing large displacements.

We introduce a new method to extract force and diffusion profiles from short, single trajectories of Brownian particles, even when the dynamical parameters vary spatially.

Through experiments and simulations, we show how microparticle internal structure controls particle deformation during flow through microfluidic constrictions.

Ultrasound waves drive shape oscillations of particle-coated microbubbles. During the ultrafast, non-uniform deformation of the interface, particles are expelled from the antinodes of the shape oscillations.

Hard core-soft shell nanoparticles show a rich structural behavior under compression when confined at a fluid interface and present crucial differences to fully deformable hydrogel particles.

A constrained soft elastic layer with comparable thickness and width can undergo a new mode of mechanical instability: fringe instability.

Theory and experiments show that the contact angles of microspheres at oil–water interfaces can be accurately extracted from AFM force–distance curves.

Cells in biofilms sense and interact with their environment through the extracellular matrix.

Knotted polymers can ratchet through pores under a periodic force if the cycle time and knot relaxation time are comparable.

An ultrasound-driven microbubble undergoing volumetric oscillations deforms a soft viscoelastic layer causing propagation of a surface elastic wave. High-speed video microscopy reveals characteristics of the elliptical particle trajectories that depend on the rheological properties of the layer.

We investigated the 2D phase diagram of core–shell microgels by simultaneous compression and deposition from a fluid interface and discovered a solid–solid isostructural transition between two hexagonal phases.

In this article, we propose and validate a scaling relation to predict the dependence of nanoemulsion droplet size with physical properties such as viscosity of the droplet phase and continuous phase, and process parameters such as input power density.

The position or bandwidth of the selective reflection of polymer stabilized cholesteric liquid crystals (PSCLCs) prepared from negative dielectric anisotropy (“−Δε”) liquid crystalline hosts can be shifted by applying a DC voltage.

We combine confocal microscopy and rheological characterization to show that both percolation and liquid–gas phase separation are dynamically arrested states that support elastic stresses in a colloidal gel.

We quantify and model the deposition and crystallization kinetics of initially dilute colloidal spheres due to application of a steady, direct current electric field in the thin gap between parallel electrodes.

Initially self-entangled DNA molecules exhibit drastically different stretching behavior compared to identical molecules without self-entanglements.

We reformulate Eshelby's theory of composites to account for interfacial tension.

Multiscale characterisation highlights the unique behaviour of soft, core–shell nanoparticles at fluid interfaces.

Atomic force microscopy studies show that binding of YOYO-1 to DNA increases the contour length of DNA without affecting the persistence length due to the underwinding of DNA.

We report the effect of flow-induced dynamical heterogeneity on the nonlinear elastic modulus of weakly aggregated colloidal gels that have undergone yielding by an imposed step strain deformation.

A microgel monolayer at the oil–water interface is prepared using two adsorption methods and visualized by cryo-SEM and AFM methods. Hexagonal microgel arrays of different degrees of ordering are gained.

We report the synthesis of non-spherical, Brownian microparticles with sub-micron height using a modified flow lithography technique.

Here we report multi-scale and multi-mechanism design of a new hydrogel composite that contains around 80% water but can achieve an extremely high toughness (>30 kJ m⁻²), high modulus (>6 MPa), and can be stretched over 2.8 times even in the presence of large structural defects.

We use particle shape and confinement to design a suspension that self-organizes into a flowing crystal when driven by pressure.

Suspensions of paramagnetic colloids are driven to phase separate and self-assemble by a toggled magnetic field.

Soft materials capable of both planar and flexural–torsional responses could enable the development of soft robotic elements that emulate the dexterity and functionality of a multitude of creatures in the animal kingdom.

The metallization of DNA–protein nanostar templates leads to branched silver nanostructures with controllable branch sizes and degrees of branching.

High-energy X-ray reflectivity (HE-XR) sheds light on the microstructure of core–shell oxide–polymer nanoparticles adsorbed at planar liquid–liquid interfaces.

The article is the first to demonstrate near field capillary repulsion between microparticles with sinusoidal contact lines.

We develop a novel technique to grow and characterize Staphylococcus epidermidis bacterial biofilms in a continuously fed bioreactor incorporated into a parallel plate rheometer.

In collections of flowing particles, ordered states can arise from viscous hydrodynamic interactions. Via theory and simulations, we investigate new collective hydrodynamic behaviors that require a thin channel geometry: strong confinement in one spatial direction and weak confinement in another.

Young's law breaks down for small droplets on soft substrates, depending strongly on the interplay between elasticity and surface tension.

Out-of-equilibrium microstructure and consequent depletion forces are measured between two probe particles held in a strongly driven colloidal suspension.

Various regimes for DNA confined in a slit.

A simple magnetic tweezer technique for probing nonlinear microrheology is described. Micro-scale yield stress measurements are demonstrated on aqueous dispersions of Laponite^® clay, and comparisons are made to bulk properties.

We investigate the adsorption of core-shell nanoparticles at liquid–liquid interfaces. Experiments on the time evolution of the interfacial tension are accompanied by numerical simulations to investigate the structure of the assembly and theoretical modeling aimed at shedding light on the thermodynamics of individual composite nanoparticles at liquid interfaces.

Micromechanics of colloidal aggregates formed at oil–water interfaces are quantitatively measured using optical tweezers. Micromechanical properties link the interfacial rheology with underlying particle interactions.

Attractive and repulsive interaction forces between charged spherical latex colloids are directly measured using optical tweezers.

Electro-creasing instability occurs in a polymer film under a high enough voltage. Biaxially pre-stretching the film greatly increases the critical voltage for the instability.

We report that negatively charged nanoparticles enhance the ability of cationic surfactants to induce genomic DNA compaction and apply it for reversible photocontrol of DNA higher-order structure.

This paper reports that centrifugation can be used to induce bulk nematic order in suspensions of micron-sized colloidal rods.

The interactions between colloids at a decane-water interface is measured by optical tweezers. Monte Carlo simulations are used to understand the effect of heterogeneity on the equilibrium suspension structure.

The integration of a soft, polymeric microbristle with a patterned hydrogel muscle enables the fabrication of responsive, reversibly actuated surface structures that easily reconfigure into intricate geometries upon hydrogel's swelling/contraction.

A nonlinear field theory is described for pH-sensitive hydrogels undergoing inhomogeneous deformation. The theory is implemented as a finite element method in the commercial software ABAQUS.

Polymer stabilization of an azobenzene-based cholesteric liquid crystal reduces the temporal restoration of the original reflection characteristics by two orders of magnitude.