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Soft Matter

Simeng Chen, Volfango Bertola
The impact of viscoplastic drops onto viscoplastic substrates characterized by different magnitudes of the yield stress is investigated experimentally. The interaction between viscoplastic drops and surfaces has an important application in additive manufacturing, where a fresh layer of material is deposited on a partially cured or dried layer of the same material. So far, no systematic studies on this subject have been reported in literature. The impact morphology of different drop/substrate combinations, with yield stresses ranging from 1...
December 5, 2016: Soft Matter
N V Lukasheva, D A Tolmachev, V M Nazarychev, J M Kenny, S V Lyulin
Specific intermolecular interactions, in particular H-bonding, have a strong influence on the structural, thermal and relaxation characteristics of polymers. We report here the results of molecular dynamics simulations of Nylon 6 which provides an excellent example for the investigation of such an influence. To demonstrate the effect of proper accounting for H-bonding on bulk polymer properties, the AMBER99sb force field is used with two different parametrization approaches leading to two different sets of partial atomic charges...
December 2, 2016: Soft Matter
Mehmet Can Uçar, Reinhard Lipowsky
Intracellular transport is performed by molecular motors that pull cargos along cytoskeletal filaments. Many cellular cargos are observed to move bidirectionally, with fast transport in both directions. This behaviour can be understood as a stochastic tug-of-war between two teams of antagonistic motors. The first theoretical model for such a tug-of-war, the Müller-Klumpp-Lipowsky (MKL) model, was based on two simplifying assumptions: (i) both motor teams move with the same velocity in the direction of the stronger team, and (ii) this velocity matching and the associated force balance arise immediately after the rebinding of an unbound motor to the filament...
December 2, 2016: Soft Matter
Arman Boromand, Safa Jamali, João M Maia
Core-Modified Dissipative Particle Dynamics (CM-DPD) with a modified depletion potential and full hydrodynamics description is used to study non-equilibrium properties of colloidal gels with short range attraction potentials at an intermediate volume fraction (ϕ = 0.2) under start-up shear deformation. Full structural and rheological analysis using the stress fabric tensor complemented by bond number and bond distribution evolution under flow reveals that similarly to dilute colloidal gels, flow-induced anisotropy and strain-induced stretching of bonds are present during the first yielding transition...
December 2, 2016: Soft Matter
Maxime Theillard, Roberto Alonso-Matilla, David Saintillan
Recent experimental studies have shown that confinement can profoundly affect self-organization in semi-dilute active suspensions, leading to striking features such as the formation of steady and spontaneous vortices in circular domains and the emergence of unidirectional pumping motions in periodic racetrack geometries. Motivated by these findings, we analyze the two-dimensional dynamics in confined suspensions of active self-propelled swimmers using a mean-field kinetic theory where conservation equations for the particle configurations are coupled to the forced Navier-Stokes equations for the self-generated fluid flow...
December 1, 2016: Soft Matter
Jochen Schneider, Malte Wiemann, Anna Rabe, Eckhard Bartsch
Polystyrene (PS) microgel colloids have often been used successfully to model hard sphere behaviour even though the term "gel" invokes inevitably the notion of a more or less soft, deformable object. Here we systematically study the effect of reducing the cross-link density from 1 : 10 (1 cross-link per 10 monomers) to 1 : 100 on particle interactions and "softness". We report on the synthesis and purification of 1 : 10, 1 : 25, 1 : 50, 1 : 75 and 1 : 100 cross-linked PS particles and their characterization in terms of single particle properties, as well as the behaviour of concentrated dispersions...
December 1, 2016: Soft Matter
Massimo Mastrangeli, Quan Zhou, Veikko Sariola, Pierre Lambert
Surface tension-driven self-alignment is a passive and highly-accurate positioning mechanism that can significantly simplify and enhance the construction of advanced microsystems. After years of research, demonstrations and developments, the surface engineering and manufacturing technology enabling capillary self-alignment has achieved a degree of maturity conducive to a successful transfer to industrial practice. In view of this transition, a broad and accessible review of the physics, material science and applications of capillary self-alignment is presented...
December 1, 2016: Soft Matter
Erik R Reale, Alison C Dunn
It is widely accepted that hydrogel surfaces are slippery, and have low friction, but dynamic applied stresses alter the hydrogel composition at the interface as water is displaced. The induced osmotic imbalance of compressed hydrogel which cannot swell to equilibrium should drive the resistance to slip against it. This paper demonstrates the driving role of poroelasticity in the friction of hydrogel-glass interfaces, specifically how poroelastic relaxation of hydrogels increases adhesion. We translate the work of adhesion into an effective surface energy density that increases with the duration of applied pressure from 10 to 50 mJ m(-2), as measured by micro-indentation...
November 30, 2016: Soft Matter
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November 30, 2016: Soft Matter
Kelley Lynch Heatley, Fuduo Ma, Ning Wu
Colloidal particles are envisioned as analogues of atoms and molecules, however they often lack the complexities present in their counterparts. In this work, we report the assembly of colloidal molecules from a binary mixture of polystyrene spheres (1, 1.6, 2, and 4 μm) under an alternating current electric field. The rich family of assembled oligomers typically consists of a large sphere that is closely surrounded by a number of smaller petal particles, driven by the dipolar attraction between large and small particles...
November 30, 2016: Soft Matter
Jiangjiang Duan, Xichao Liang, Kunkun Zhu, Jinhua Guo, Lina Zhang
Smart hydrogel actuators with excellent biocompatibility and biodegradation are extremely desired for biomedical applications. Herein, we have constructed bio-hydrogel actuators inspired by the bilayer structures of plant organs from chitosan and cellulose/carboxymethylcellulose (CMC) solution in an alkali/urea aqueous system containing epichlorohydrin (ECH) as a crosslinker, and demonstrated tight adhesion between two layers through strong electrostatic attraction and chemical crosslinking. The bilayer hydrogels with excellent mechanical properties could carry out rapid, reversible, and repeated self-rolling deformation actuated by pH-triggered swelling/deswelling, and transformed into rings, tubules, and flower-, helix-, bamboo-, and wave-like shapes by effectively designing the geometric shape and size...
November 30, 2016: Soft Matter
E Drolle, W F D Bennett, K Hammond, E Lyman, M Karttunen, Z Leonenko
The molecular arrangement of lipids and proteins within biomembranes and monolayers gives rise to complex film morphologies as well as regions of distinct electrical surface potential, topographical and electrostatic nanoscale domains. To probe these nanodomains in soft matter is a challenging task both experimentally and theoretically. This work addresses the effects of cholesterol, lipid composition, lipid charge, and lipid phase on the monolayer structure and the electrical surface potential distribution...
November 30, 2016: Soft Matter
Tongjie Sun, Ping Tang, Feng Qiu, An-Chang Shi
Applying the string method to the self-consistent field theory (SCFT) of ABC linear triblock copolymers, we developed a new strategy to design kinetic pathways for the formation of stable or metastable network mesophases in order-order transition (OOT) processes. The design principle regarding the kinetic pathways between distinct mesophases is based on the matching relationships of both domain spacing and dominant Fourier components of the density distributions. The results suggest that complex ordered network mesophases, such as alternating diamond (D(A)) and alternating plumber's nightmare (P(A)) could be obtained in kinetic pathways between simple phases covering lamellae, cylinders and spheres...
November 29, 2016: Soft Matter
Marzieh Ebrahimi, Vinod Kumar Konaganti, Sona Moradi, Antonios K Doufas, Savvas G Hatzikiriakos
The slip behavior of high-density polyethylenes (HDPEs) is studied over surfaces of different topology and surface energy. Laser ablation has been used to micro/nano-pattern the surface of dies in order to examine the effect of surface roughness on slip. In addition, fluoroalkyl silane-based coatings on smooth and patterned substrates were used to understand the effect of surface energy on slip. Surface roughness and surface energy effects were incorporated into the double reptation slip model (Ebrahimi et al...
November 28, 2016: Soft Matter
Hassan Srour, Martien Duvall Deffo Ayagou, Thi Thanh-Tam Nguyen, Nicolas Taberlet, Sébastien Manneville, Chantal Andraud, Cyrille Monnereau, Mathieu Leocmach
We demonstrated recently that polyelectrolytes with cationic moieties along the chain and a single anionic head are able to form physical hydrogels due to the reversible nature of the head-to-body ionic bond. Here we generate a variety of such polyelectrolytes with various cationic moieties and counterion combinations starting from a common polymeric platform. We show that the rheological properties (shear modulus, critical strain) of the final hydrogels can be modulated over three orders of magnitude depending on the cation/anion pair...
November 25, 2016: Soft Matter
A Ashour, S Wegner, T Trittel, T Börzsönyi, R Stannarius
Outflow of granular material through a small orifice is a fundamental process in many industrial fields, for example in silo discharge, and in everyday's life. Most experimental studies of the dynamics have been performed so far with monodisperse disks in two-dimensional (2D) hoppers or spherical grains in 3D. We investigate this process for shape-anisotropic grains in 3D hoppers and discuss the role of size and shape parameters on avalanche statistics, clogging states, and mean flow velocities. It is shown that an increasing aspect ratio of the grains leads to lower flow rates and higher clogging probabilities compared to spherical grains...
November 23, 2016: Soft Matter
Alban Sauret, François Boulogne, Katarzyna Somszor, Emilie Dressaire, Howard A Stone
Various materials are made of long thin fibers that are randomly oriented to form a complex network in which drops of wetting liquid tend to accumulate at the nodes. The capillary force exerted by the liquid can bend flexible fibers, which in turn influences the morphology adopted by the liquid. In this paper, we investigate through a model situation the role of the fiber flexibility on the shape of a small volume of liquid on a pair of crossed flexible fibers. We characterize the liquid morphologies as we vary the volume of liquid, the angle between the fibers, and the length of the fibers...
November 22, 2016: Soft Matter
Hanumantha Rao Vutukuri, Zdeněk Preisler, Thijs H Besseling, Alfons van Blaaderen, Marjolein Dijkstra, Wilhelm T S Huck
In recent years, there is a growing interest in designing artificial analogues of living systems, fueled not only by potential applications as 'smart micro-machines', but also by the demand for simple models that can be used to study the behavior of their more complex natural counterparts. Here, we present a facile, internally driven, experimental system comprised of fluorescently labeled colloidal silica rods of which the self-propulsion is powered by the decomposition of H2O2 catalyzed by a length-wise half Pt coating of the particles in order to study how shape anisotropy and swimming direction affect the collective behavior...
November 21, 2016: Soft Matter
Nicoletta Gnan, Francesco Sciortino, Emanuela Zaccarelli
We report numerical results for the effective potential arising between two colloids immersed in a self-assembling cosolute which forms reversible clusters. The potential is evaluated at cosolute state points with different densities and temperatures but with the same connectivity properties. We find that the range of the resulting effective potential is controlled only by the cosolute thermal correlation length rather than by its connectivity length. We discuss the significant differences from previous results focusing on the cosolute forming irreversible clusters and we show that the irreversible bond case represents a singular limit which cannot be accessed in equilibrium by continuously increasing the bond lifetime...
November 21, 2016: Soft Matter
Johannes Blaschke, Maurice Maurer, Karthik Menon, Andreas Zöttl, Holger Stark
A striking feature of the collective behavior of spherical microswimmers is that for sufficiently strong self-propulsion they phase-separate into a dense cluster coexisting with a low-density disordered surrounding. Extending our previous work, we use the squirmer as a model swimmer and the particle-based simulation method of multi-particle collision dynamics to explore the influence of hydrodynamics on their phase behavior in a quasi-two-dimensional geometry. The coarsening dynamics towards the phase-separated state is diffusive in an intermediate time regime followed by a final ballistic compactification of the dense cluster...
November 21, 2016: Soft Matter
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