Themed collection Soft Matter Lectureship Winners
Solid capillarity: when and how does surface tension deform soft solids?
This Opinion highlights important outstanding questions in the deformation of soft solid interfaces.
Microrheology of biomaterial hydrogelators
Small sample volumes, a large dynamic response and short acquisition times make microrheology important for characterizing emerging biomaterial hydrogelators.
Nanoemulsions: formation, properties and applications
Nanoemulsions are kinetically stable liquid-in-liquid dispersions with droplet sizes on the order of 100 nm.
Multi-scale multi-mechanism design of tough hydrogels: building dissipation into stretchy networks
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.
DNA compaction: fundamentals and applications
We describe the physico-chemical aspects of reversible DNA compaction and its applications in gene regulation, DNA protection and nanostructure fabrication.
Traction force microscopy in physics and biology
We review diverse applications of traction force microscopy and provide detailed instructions, including computer code, for performing it.
Avoiding the pull-in instability of a dielectric elastomer film and the potential for increased actuation and energy harvesting
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.
3D printing of self-assembling thermoresponsive nanoemulsions into hierarchical mesostructured hydrogels
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.
An extreme toughening mechanism for soft materials
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.
Supramolecular hydrogels from unprotected dipeptides: a comparative study on stereoisomers and structural isomers
Unprotected dipeptides are studied for self-assembly into hydrogels and single-crystal XRD data reveal key insights in the supramolecular interactions.
Localizing genesis in polydomain liquid crystal elastomers
Programming genesis in polydomain liquid crystal elastomers (LCEs) is a differentiated approach to prepare monolithic material compositions with localized, omnidirectional deformation.
Polymer nanocomposite capsules formed by droplet extraction: spontaneous stratification and tailored dissolution
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.
Surface forces generated by the action of electric fields across liquid films
Oscillating electric fields across electrolyte cause anomalously large forces between the electrodes.
Ideal reversible polymer networks
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
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.
Effects of polymer–nanoparticle interactions on the viscosity of unentangled polymers under extreme nanoconfinement during capillary rise infiltration
Extreme nanoconfinement increases polymer viscosity and glass transition temperature significantly, whereas polymer–nanoparticle interactions have little influence.
Multiple particle tracking study of thermally-gelling nanoemulsions
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.
Nanoconfinement greatly speeds up the nucleation and the annealing in single-DNA collapse
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.
Blue-shifting tuning of the selective reflection of polymer stabilized cholesteric liquid crystals
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.
Voxel resolution in the directed self-assembly of liquid crystal polymer networks and elastomers
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 through sequential capillary assembly
Hybrid colloidal microswimmers of programmable shape and composition are prepared by sequential capillary assembly and their modes of motion and functionality are characterized.
High-frequency linear rheology of hydrogels probed by ultrasound-driven microbubble dynamics
Ultrasound-driven microbubble oscillations can probe the linear viscoelastic properties of hydrogels. The bubble resonance frequency increases with shear modulus.
High-density equilibrium phases of colloidal ellipsoids by application of optically enhanced, direct current electric fields
Highly dense equilibrium assemblies of colloidal ellipsoids having three-dimensional order and packing fraction upto 67%.
Tracking particles with large displacements using energy minimization
We describe a method to track particles undergoing large displacements.
Maximum likelihood estimations of force and mobility from single short Brownian trajectories
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.
Effect of internal architecture on microgel deformation in microfluidic constrictions
Through experiments and simulations, we show how microparticle internal structure controls particle deformation during flow through microfluidic constrictions.
Shape oscillations of particle-coated bubbles and directional particle expulsion
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.
Compression of hard core–soft shell nanoparticles at liquid–liquid interfaces: influence of the shell thickness
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.
Fringe instability in constrained soft elastic layers
A constrained soft elastic layer with comparable thickness and width can undergo a new mode of mechanical instability: fringe instability.
Particle detachment from fluid interfaces: theory vs. experiments
Theory and experiments show that the contact angles of microspheres at oil–water interfaces can be accurately extracted from AFM force–distance curves.
Mechanical properties of the superficial biofilm layer determine the architecture of biofilms
Cells in biofilms sense and interact with their environment through the extracellular matrix.
Translocation dynamics of knotted polymers under a constant or periodic external field
Knotted polymers can ratchet through pores under a periodic force if the cycle time and knot relaxation time are comparable.
Surface waves on a soft viscoelastic layer produced by an oscillating microbubble
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.
Isostructural solid–solid phase transition in monolayers of soft core–shell particles at fluid interfaces: structure and mechanics
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.
Controlling and predicting droplet size of nanoemulsions: scaling relations with experimental validation
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.
Photosensitivity of reflection notch tuning and broadening in polymer stabilized cholesteric liquid crystals
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.
Celebrating Soft Matter's 10th Anniversary: Sequential phase transitions in thermoresponsive nanoemulsions
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.
Kinetics of colloidal deposition, assembly, and crystallization in steady electric fields
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.
Stretching self-entangled DNA molecules in elongational fields
Initially self-entangled DNA molecules exhibit drastically different stretching behavior compared to identical molecules without self-entanglements.
Surface tension and the mechanics of liquid inclusions in compliant solids
We reformulate Eshelby's theory of composites to account for interfacial tension.
A multiscale approach to the adsorption of core–shell nanoparticles at fluid interfaces
Multiscale characterisation highlights the unique behaviour of soft, core–shell nanoparticles at fluid interfaces.
Effect of YOYO-1 on the mechanical properties of DNA
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.
Role of shear-induced dynamical heterogeneity in the nonlinear rheology of colloidal gels
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.
Highly ordered 2D microgel arrays: compression versus self-assembly
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.
Synthesis of colloidal microgels using oxygen-controlled flow lithography
We report the synthesis of non-spherical, Brownian microparticles with sub-micron height using a modified flow lithography technique.
Design of stiff, tough and stretchy hydrogel composites via nanoscale hybrid crosslinking and macroscale fiber reinforcement
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.
Self-organizing microfluidic crystals
We use particle shape and confinement to design a suspension that self-organizes into a flowing crystal when driven by pressure.
Directed colloidal self-assembly in toggled magnetic fields
Suspensions of paramagnetic colloids are driven to phase separate and self-assemble by a toggled magnetic field.
Torsional mechanical responses in
azobenzene functionalized liquid crystalline polymer networks
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.
Preparation of one- to four-branch silver
nanostructures of various sizes by metallization of hybrid DNA– protein assemblies
The metallization of DNA–protein nanostar templates leads to branched silver nanostructures with controllable branch sizes and degrees of branching.
nanoparticle monolayers at planar liquid–liquid interfaces: effects of polymer architecture on the interface microstructure
High-energy X-ray reflectivity (HE-XR) sheds light on the microstructure of core–shell oxide–polymer nanoparticles adsorbed at planar liquid–liquid interfaces.
Near field capillary repulsion
The article is the first to demonstrate near field capillary repulsion between microparticles with sinusoidal contact lines.
rheology of Staphylococcus epidermidis bacterial biofilms
We develop a novel technique to grow and characterize Staphylococcus epidermidis bacterial biofilms in a continuously fed bioreactor incorporated into a parallel plate rheometer.
Collective dynamics of small clusters of particles flowing in a quasi-two-dimensional microchannel
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.
Static wetting on deformable substrates, from liquids to soft solids
Young's law breaks down for small droplets on soft substrates, depending strongly on the interplay between elasticity and surface tension.
Out-of-equilibrium forces between colloids
Out-of-equilibrium microstructure and consequent depletion forces are measured between two probe particles held in a strongly driven colloidal suspension.
A systematic study of DNA conformation in slitlike confinement
Various regimes for DNA confined in a slit.
Nonlinear microrheology of an aging, yield stress fluid using magnetic tweezers
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.
Adsorption of core-shell nanoparticles at liquid–liquid interfaces
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 at the oil–water interface
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 interactions between colloids at the oil–water interface
Attractive and repulsive interaction forces between charged spherical latex colloids are directly measured using optical tweezers.
Electro-creasing instability in deformed
polymers: experiment and theory
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.
Enhancement of DNA compaction by negatively charged
nanoparticles. Application to reversible photocontrol of DNA higher-order structure
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.
Nematic order in suspensions of colloidal rods by application of a centrifugal field
This paper reports that centrifugation can be used to induce bulk nematic order in suspensions of micron-sized colloidal rods.
Heterogeneity of the electrostatic repulsion between colloids at the oil–
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.
Microbristle in gels: Toward all-
polymer reconfigurable hybrid surfaces
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 theory of constrained swelling of a pH-sensitive hydrogel
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 phototunable cholesteric liquid crystals
Polymer stabilization of an azobenzene-based cholesteric liquid crystal reduces the temporal restoration of the original reflection characteristics by two orders of magnitude.
About this collection
This collection highlights winners of the Soft Matter Lectureship. This annual award was established in 2009 to honour an early-stage career scientist who has made a significant contribution to the soft matter field.
The 2022 Soft Matter Lectureship was awarded to Xuanhe Zhao (MIT). Xuanhe Zhao is a Professor of Mechanical Engineering and Civil and Environmental Engineering at MIT. The mission of Zhao Lab is to advance science and technology on the interfaces between humans and machines for addressing grand societal challenges in health and sustainability. A major focus of Zhao Lab's current research is the study and development of soft materials and systems. Dr. Zhao is the recipient of the NSF CAREER Award, ONR Young Investigator Award, SES Young Investigator Medal, ASME Hughes Young Investigator Award, Adhesion Society’s Young Scientist Award, Materials Today Rising Star Award, and Clarivate Highly Cited Researcher. Six patents from Zhao Lab have been licensed by established and startup companies and contributed to widely used medical devices such as hydrogel-elastomer tissue phantoms.
This collection features articles published in Soft Matter from Professor Zhao, as well as previous lectureship winners:
2021 – Silvia Marchesan, University of Trieste, Italy
2020 – Valeria Garbin, Delft University of Technology, The Netherlands
2019 - Tim White, University of Colorado Boulder, USA
2018 – Susan Perkin, University of Oxford, UK
2017 - Daeyeon Lee, University of Pennsylvania, USA
2016 – Damien Baigl, Ecole Normale Supérieure, Paris, France
2015 – Lucio Isa, ETH Zürich, Switzerland
2014 – Eric Dufresne, Yale Univeristy, USA
2013 – Eric Furst, University of Delaware, USA
2012 – Patrick Doyle, MIT, USA
2011 – Michael J. Solomon, University of Michigan, USA
2010 – Bartosz Grzybowski, UNIST, Republic of Korea
2009 – Emanuela Zaccarelli, University of Rome, Italy