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Granick, Steve

Publications and source records attributed to Granick, Steve.

14 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

DNA molecules deviate from shortest trajectory when driven through hydrogel

Dynamic fluorescence-based single-molecule imaging of $λ$-DNA molecules driven through agarose hydrogels by DC electric fields reveals that passage through the hydrogel (98.5% water content) induces mobility orthogonal to the external field. Tortuous paths followed by the DNA molecules, which are heavily entangled in the hydrogel mesh as their contour length is nearly 100 times the hydrogel mesh size of 200 nm, cause them to appear to diffuse orthogonal to the driving force. The higher the driving field, from 2 to 16 V/cm, the higher the off-axis dispersion is, over the same time interval. In this work we measure the off-axis displacement distribution over 3 orders of magnitude of probability density and find a master curve after normalizing for time (t) elapsed, but the power of time for normalizing increases with the external field, from t 0.25 to t 0.6 with increasing field. Comparing trajectories over the same distance traveled in the electric field direction, we observe whereas for the highest field strengths DNA molecules come closest to taking the shortest trajectory between two points in space, deviations from the shortest trajectory grow larger and larger (up to 40% larger) as one approaches the case of small yet finite external field strength.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Effective temperature concept evaluated in an active colloid mixture

Significance In the long-standing debate on whether the insights of statistical thermodynamics could apply to nonequilibrium systems, a key unsolved problem is whether it is useful to postulate an emergent effective temperature, different from the thermal temperature. Here, we introduce a two-component system of driven Janus colloids such that collisions induced by external energy sources play the role of temperature. We find that this nonequilibrium system quantitatively behaves as if at equilibrium, with collisions caused by differential rhythmic motion between the two components acting as a strict analog to thermal motion. We demonstrate that the effective temperature can serve as a common control parameter for both kinetics and phase behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Natural selection in the colloid world: active chiral spirals

We present a model system in which to study natural selection in the colloid world. In the assembly of active Janus particles into rotating pinwheels when mixed with trace amounts of homogeneous colloids in the presence of an AC electric field, broken symmetry in the rotation direction produces spiral, chiral shapes. Locked into a central rotation point by the centre particle, the spiral arms are found to trail rotation of the overall cluster. To achieve a steady state, the spiral arms undergo an evolutionary process to coordinate their motion. Because all the particles as segments of the pinwheel arms are self-propelled, asymmetric arm lengths are tolerated. Reconfiguration of these structures can happen in various ways and various mechanisms of this directed structural change are analyzed in detail. Here, we introduce the concept of VIP (very important particles) to express that sustainability of active structures is most sensitive to only a few particles at strategic locations in the moving self-assembled structures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Operating organic light-emitting diodes imaged by super-resolution spectroscopy

Super-resolution stimulated emission depletion microscopy is adapted here for materials characterization that would not otherwise be possible. With the example of organic lightemitting diodes (OLEDs), spectral imaging with pixel-by-pixel wavelength discrimination allows us to resolve local-chain environment encoded in the spectral response of the semiconducting polymer, and correlate chain packing with local electroluminescence by using externally applied current as the excitation source. We observe nanoscopic defects that would be unresolvable by traditional microscopy. They are revealed in electroluminescence maps in operating OLEDs with 50 nm spatial resolution. We find that brightest emission comes from regions with more densely packed chains. Conventional microscopy of an operating OLED would lack the resolution needed to discriminate these features, while traditional methods to resolve nanoscale features generally cannot be performed when the device is operating. Furthermore, this points the way towards real-time analysis of materials design principles in devices as they actually operate.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2016

Phospholipid Vesicles in Materials Science

The objective of this research was to develop the science basis needed to deploy phospholipid vesicles as functional materials in energy contexts. Specifically, we sought to: (1) Develop an integrated molecular-level understanding of what determines their dynamical shape, spatial organization, and responsiveness to complex, time-varying environments; and (2) Develop understanding of their active transportation in crowded environments, which our preliminary measurements in cells suggest may hold design principles for targeting improved energy efficiency in new materials systems. The methods to do this largely involved fluorescence imaging and other spectroscopy involving single particles, vesicles, particles, DNA, and endosomes. An unexpected importance outcome was a new method to image light-emitting diodes during actual operation using super-resolution spectroscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Directed Self‐Assembly Pathways of Active Colloidal Clusters

Abstract Despite the mounting interest in synthetic active particles, too little is known about their assembly into higher‐order clusters. Here, mixing bare silica particles with Janus particles that are self‐propelled in electric fields, we assemble rotating chiral clusters of various sorts, their structures consisting of active particles wrapped around central “hub” particles. These clusters self‐assemble from the competition between standard energetic interactions and the need to be stable as the clusters rotate when the energy source is turned on, and fall apart when the energy input is off. This allows one to guide the formation of intended clusters, as the final structure depends notably on the sequence of steps in which the clusters form.

Zhang, Jie↗
DOE OSTI2016

Directed Self–Assembly Pathways of Active Colloidal Clusters

Despite the mounting interest in synthetic active particles, too little is known about their assembly into higher-order clusters. Here, mixing bare silica particles with Janus particles that are self-propelled in electric fields, we assemble rotating chiral clusters of various sorts, their structures consisting of active particles wrapped around central “hub” particles. These clusters self-assemble from the competition between standard energetic interactions and the need to be stable as the clusters rotate when the energy source is turned on, and fall apart when the energy input is off. Furthermore, this allows one to guide the formation of intended clusters, as the final structure depends notably on the sequence of steps in which the clusters form.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Correlated two-particle diffusion in dense colloidal suspensions at early times: Theory and comparison to experiment

The spatially resolved diffusive dynamic cross correlations of a pair of colloids in dense quasi-two-dimensional monolayers of identical particles are studied experimentally and theoretically at early times where motion is Fickian. In very dense systems where strong oscillatory equilibrium packing correlations are present, we find an exponential decay of the dynamic cross correlations on small and intermediate length scales. At large separations where structure becomes random, an apparent power law decay with an exponent of approximately –2.2 is observed. For a moderately dense suspension where local structural correlations are essentially absent, this same apparent power law decay is observed over all probed interparticle separations. A microscopic nonhydrodynamic theory is constructed for the dynamic cross correlations which is based on interparticle frictional effects and effective structural forces. Hydrodynamics enters only via setting the very short-time single-particle self-diffusion constant. No-adjustable-parameter quantitative predictions of the theory for the dynamic cross correlations are in good agreement with experiment over all length scales. The origin of the long-range apparent power law is the influence of the constraint of fixed interparticle separation on the amplitude of the mean square force exerted on the two tagged particles by the surrounding fluid. The theory is extended to study high-packing-fraction 3D hard sphere fluids. Here, the same pattern of an oscillatory exponential form of the dynamic cross correlation function is predicted in the structural regime, but the long-range tail decays faster than in monolayers with an exponent of –3.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Ligand accessibility and bioactivity of a hormone–dendrimer conjugate depend on pH and pH history

Estrogen conjugates with a polyamidoamine (PAMAM) dendrimer have shown remarkably selective regulation of the nongenomic actions of estrogens in target cells in this paper. In response to pH changes, however, these estrogen–dendrimer conjugates (EDCs) display a major morphological transition that alters the accessibility of the estrogen ligands that compromises the bioactivity of the EDC. A sharp break in dynamic behavior near pH 7 occurs for three different ligands on the surface of a PAMAM-G6 dendrimer: a fluorophore (tetramethylrhodamine [TMR]) and two estrogens (17α-ethynylestradiol and diphenolic acid). Collisional quenching and time-resolved fluorescence anisotropy experiments with TMR–PAMAM revealed high ligand shielding above pH 7 and low shielding below pH 7. Furthermore, when the pH was cycled from 8.5 (conditions of ligand–PAMAM conjugation) to 4.5 (e.g., endosome/lysosome) and through 6.5 (e.g., hypoxic environment) back to pH 8.5, the 17α-ethynylestradiol– and diphenolic acid–PAMAM conjugates experienced a dramatic, irreversible loss in cell stimulatory activity; dynamic NMR studies indicated that the hormonal ligands had become occluded within the more hydrophobic core of the PAMAM dendrimer. Thus, the active state of these estrogen–dendrimer conjugates appears to be metastable. Finally, this pH-dependent irreversible masking of activity is of considerable relevance to the design of drug conjugates with amine-bearing PAMAM dendrimers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Memoryless self-reinforcing directionality in endosomal active transport within living cells

In contrast to Brownian transport, the active motility of microbes, cells, animals and even humans often follows another random process known as truncated Levy walk 1,2 . These stochastic motions are characterized by clustered small steps and intermittent longer jumps that often extend towards the size of the entire system. As there are repeated suggestions, although disagreement, that Levy walks have functional advantages over Brownian motion in random searching and transport kinetics 3-8 , their intentional engineering into active materials could be useful. Here, we show experimentally in the classic active matter system of intracellular trafficking 9-15 that Brownian-like steps self-organize into truncated Levy walks through an apparent time-independent positive feedback such that directional persistence increases with the distance traveled persistently. A molecular model that allows the maximum output of the active propelling forces to fluctuate slowly fits the experiments quantitatively. Furthermore, our findings offer design principles for programming efficient transport in active materials.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Colloidal Superstructures Programmed into Magnetic Janus Particles

By engineering thin magnetic films onto homogeneous colloidal particles, various crystalline lattices are induced from simple magnetic Janus spheres. In situ formation of dicolloids amplifies the diversity of achievable dynamic structures. The competition between shape anisotropy and dipole orientation generates mesoscopic isomerism. Furthermore, this opens design space for anisotropic building blocks for smart colloidal materials.

36 MATERIALS SCIENCE↗