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Soft Matter

Vladimir Toshchevikov, Tatiana Petrova, Marina Saphiannikova
Azobenzene-containing smart materials are able to transform the energy of light into directional mechanical stress. We develop a theory of time-dependent light-induced ordering and deformation in azobenzene materials starting from the kinetic equations of photoisomerization. The liquid crystalline (LC) interactions between rod-like trans-isomers are taken into account. Angular selectivity of the photoisomerization known as an "angular hole burning" or the Weigert effect leads to the light-induced ordering and deformation of the azobenzene materials...
March 27, 2017: Soft Matter
Rajeev Dattani, Enrico F Semeraro, Theyencheri Narayanan
The enhanced motion of dispersed particles driven by a concentration gradient is the basis for diffusiophoresis. Here we present the dynamics of colloids in a phase separating medium probed by X-Ray Photon Correlation Spectroscopy (XPCS) in the ultra-small angle scattering range. Charge stabilized silica colloids suspended in a binary mixture of 3-methylpyridine and water/heavy water are preferentially wetted by 3-methylpyridine and consequently display a phoretic motion towards that phase upon demixing. This activity lasts for hundreds of seconds before the phase separation is complete and the enhanced motion is arrested as the colloids return to normal diffusive dynamics...
March 27, 2017: Soft Matter
Nayoung Park, Jacinta C Conrad
Adding depletants to a colloidal suspension induces an attractive interparticle interaction that can be tuned to obtain desired structures or to probe phase behavior. When the depletant is not uniform in size, however, both the range and strength of the attraction become difficult to predict and hence control. We investigated the effects of depletant bidispersity on the non-equilibrium phase behavior of colloid-polymer mixtures. We added unary or binary mixtures of polystyrene as the depletant to suspensions of charged poly(methyl methacrylate) particles...
March 27, 2017: Soft Matter
Suwon Bae, Or Galant, Charles E Diesendruck, Meredith N Silberstein
Single chain polymer nanoparticles (SCPNs) are formed from intrachain cross-linking of a single polymer chain, making SCPN distinct from other polymer nanoparticles for which the shape is predefined before polymerization. The degree of cross-linking in large part determines the internal architecture of the SCPNs and therefore their mechanical and thermomechanical properties. Here, we use molecular dynamics (MD) simulations to study thermomechanical behavior of individual SCPNs with different underlying structures by varying the ratio of cross-linking and the degree of polymerization...
March 27, 2017: Soft Matter
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March 27, 2017: Soft Matter
Tanwi Debnath, Pulak K Ghosh, Franco Nori, Yunyun Li, Fabio Marchesoni, Baowen Li
We study the 3D dynamics of an elastic dimer consisting of an active swimmer bound to a passive cargo, both suspended in a Couette flow. Using numerical simulations, we determine the diffusivity of such an active dimer in the presence of long-range hydrodynamic interactions for different values of its self-propulsion speed and the Couette flow. We observe that the effect of hydrodynamic interactions is greatly enhanced under the condition that self-propulsion is strong enough to contrast the shear flow. The magnitude of the effect grows with the size of the dimer's constituents relative to their distance, which makes it appreciable under experimental conditions...
March 27, 2017: Soft Matter
Lyanne Valdez, Henry Shum, Isamar Ortiz-Rivera, Anna C Balazs, Ayusman Sen
Immobilized enzymes generate net fluid flow when exposed to specific reagents in solution. Thus, they function as self-powered platforms that combine sensing and on-demand fluid pumping. To uncover the mechanism of pumping, we examine the effects of solutal and thermal buoyancy on the behavior of phosphatase-based micropumps, using a series of reactants with known thermodynamic and kinetic parameters. By combining modeling and experiments, we perform the first quantitative comparison of thermal and solutal effects in an enzyme micropump system...
March 27, 2017: Soft Matter
Tyler N Shendruk, Amin Doostmohammadi, Kristian Thijssen, Julia M Yeomans
The spontaneous emergence of collective flows is a generic property of active fluids and often leads to chaotic flow patterns characterised by swirls, jets, and topological disclinations in their orientation field. However, the ability to achieve structured flows and ordered disclinations is of particular importance in the design and control of active systems. By confining an active nematic fluid within a channel, we find a regular motion of disclinations, in conjunction with a well defined and dynamic vortex lattice...
March 27, 2017: Soft Matter
Brian Morgan, Mark D Dadmun
Device efficiency in key organic electronic devices such as organic photovoltaics, field transistors, and light emitting diodes has long been known to be closely tied to the conformation of the conjugated polymer chains which make up the active layers. Our previous results show that light exposure can have a profound effect on the structure and assembly of these optoelectronic materials in solution. In order to advance our understanding of the role which solvent quality plays in this phenomenon, we have further studied the modulation of these illumination dependent structural changes on the key benchmark conjugated polymers P3HT and MEH-PPV as a function of solvent quality over a wide range of polymer solubilities...
March 27, 2017: Soft Matter
Shifan Mao, Quinn MacPherson, Jian Qin, Andrew J Spakowitz
Copolymers play an important role in a range of soft-materials applications and biological phenomena. Prevalent works on block copolymer phase behavior use flexible chain models and incorporate interactions using a mean-field approximation. However, when phase separation takes place on length scales comparable to a few monomers, the structural rigidity of the monomers becomes important. In addition, concentration fluctuations become significant at short length scales, rendering the mean-field approximation invalid...
March 24, 2017: Soft Matter
K Sato, I Kunita, Y Takikawa, D Takeuchi, Y Tanaka, T Nakagaki, H Orihara
Shear banding is frequently observed in complex fluids. However, the configuration of macromolecules in solutions undergoing shear banding has not yet been directly observed. In this study, by using the fact that F-actin solutions exhibit shear banding and actin filaments are visualized by fluorescent labels, we directly observed the intrinsic states of an actin solution undergoing shear banding. By combining the 3D imaging of labeled actin filaments and particle image velocimetry (PIV), we obtained orientation distributions of actin filaments in both high and low shear rate regions, whose quantitative differences are indicated...
March 24, 2017: Soft Matter
Amy Y Xu, Laurence D Melton, Timothy M Ryan, Jitendra P Mata, Geoffrey B Jameson, Agata Rekas, Martin A K Williams, Duncan J McGillivray
We have simplified the structural heterogeneity of protein-polysaccharide binding by investigating protein binding to oligosaccharides. The interactions between bovine beta-lactoglobulin A (βLgA) and oligo-galacturonic acids (OGAs) with various numbers of sugar residues have been investigated with a range of biophysical techniques. We show that the βLgA-OGA interaction is critically dependent on the length of the oligosaccharide. Isothermal titration calorimetry results suggest that a minimum length of 7 or 8 sugar residues is required in order to exhibit appreciable exothermic interactions with βLgA - shorter oligosaccharides show no enthalpic interactions at any concentration ratio...
March 24, 2017: Soft Matter
Man Yang, Chunyan Liu, Yiwei Lian, Kongshuang Zhao, Dan Zhu, Jianfeng Zhou
The dielectric behavior of a thermo-sensitive poly-(N-isopropylacrylamide) (PNIPAM) microgel suspension with a dense concentration was investigated over the frequency range of 40 Hz to 110 MHz in a wide temperature window of 10-60 °C. By successfully removing the electrode polarization effect from the original data, two remarkable and temperature-dependent relaxation processes were observed. Both of the two-phase transition processes, i.e., the colloidal crystal-to-liquid transition, which has not yet been detected by dielectric spectroscopy before, as well as the volume phase transition, were detected by the relaxation parameters...
March 23, 2017: Soft Matter
Keshvad Shahrivar, Elizabeth Carreón-González, Jose R Morillas, Juan de Vicente
We investigate the (irreversible) two-dimensional aggregation kinetics of dilute non-Brownian magnetic suspensions in rectangular microchannels using video-microscopy, image analysis and particle-level dynamics simulations. Special emphasis is given to carbonyl iron suspensions that are of interest in the formulation of magnetorheological fluids. The results are compared to non-Brownian suspensions of magnetic latexes. We demonstrate that both suspensions follow a deterministic aggregation process. Furthermore, experimental and simulation aggregation curves can be collapsed onto a master curve when using the appropriate scaling time (∝λ(-1)ϕ2D(-2...
March 23, 2017: Soft Matter
Prerna Dahiya, Andrew DeBenedictis, Timothy J Atherton, Marco Caggioni, Stuart W Prescott, Richard W Hartel, Patrick T Spicer
The stability of shapes formed by three viscoelastic droplets during their arrested coalescence has been investigated using micromanipulation experiments. Addition of a third droplet to arrested droplet doublets is shown to be controlled by the balance between interfacial pressures driving coalescence and internal elasticity that resists total consolidation. The free fluid available within the droplets controls the transmission of stress during droplet combination and allows connections to occur via formation of a neck between the droplets...
March 23, 2017: Soft Matter
Brice Saint-Michel, Thomas Gibaud, Sébastien Manneville
Soft materials may break irreversibly upon applying sufficiently large shear oscillations, a process whose physical mechanism remains largely elusive. In this work, the rupture of protein gels made of sodium caseinate under an oscillatory stress is shown to occur in an abrupt, brittle-like manner. Upon increasing the stress amplitude, the build-up of harmonic modes in the strain response can be rescaled for all gel concentrations. This rescaling yields an empirical criterion to predict the rupture point way before the samples are significantly damaged...
March 22, 2017: Soft Matter
A Ciach, J Pękalski
A generic model for self-assembly of a monolayer of hybrid core-shell particles at an interface is developed. We assume that for distances larger than the size of the incompressible core a soft repulsion appears, and the repulsion is followed by an attraction at larger separations. The model is solved exactly in a one-dimensional lattice version. One, two or three periodic structures and variety of shapes of the pressure-density isotherms may occur in different versions of the model. For strong interactions the isotherm consists of nearly vertical segments at densities optimal for the periodic structures that are connected by segments with a small slope...
March 22, 2017: Soft Matter
Sivaramakrishnan Ramadurai, Marco Werner, Nigel K H Slater, Aaron Martin, Vladimir A Baulin, Tia E Keyes
Deeper understanding of the molecular interactions between polymeric materials and the lipid membrane is important across a range of applications from permeation for drug delivery to encapsulation for immuno-evasion. Using highly fluidic microcavity supported lipid bilayers, we studied the interactions between amphiphilic polymer PP50 and a DOPC lipid bilayer. As the PP50 polymer is pH responsive the studies were carried out at pH 6.5, 7.05 and 7.5, corresponding to fully, partly protonated (pH = pKa = 7.05) and fully ionized states of the polymer, respectively...
March 22, 2017: Soft Matter
Sarit Dutta, Michael D Graham
We study the dynamics of piecewise rigid sheets containing predefined crease lines in shear flow. The crease lines act like hinge joints along which the sheet may fold rigidly, i.e. without bending any other crease line. We choose the crease lines such that they tessellate the sheet into a two-dimensional array of parallelograms. Specifically, we focus on a particular arrangement of crease lines known as a Miura-pattern in the origami community. When all the hinges are fully open the sheet is planar, whereas when all are closed the sheet folds over itself to form a compact flat structure...
March 22, 2017: Soft Matter
I C Bellettini, S J Fayad, V G Machado, E Minatti
Polycationic polymers and DNA form soluble complexes in aqueous solution, which allows the transfer of genetic material into cells. Therefore, these chemically-modified polymers are of interest for use in studies aimed at better transfection efficiency and gene expression along with reduced cytotoxicity. In this study, branched poly(ethylene imine) (PEI) was modified by alkylation with n-alkyl groups (n = 4, 6, 8 and 12 carbons). The polyplexes formed through interaction of the modified PEIs and calf thymus DNA (ctDNA) were investigated using UV-Vis spectrophotometry, ethidium bromide fluorescence emission, circular dichroism spectroscopy, dynamic light scattering, and small-angle X-ray scattering techniques along with the determination of the zeta potential and viscosity...
March 22, 2017: Soft Matter
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