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As a glass-forming liquid is cooled, the dynamics of its constituent particles changes from being liquid-like to more solid-like. The solidity of the resulting glassy material is believed to be due to a cage-formation process, whereby the motion of individual particles is increasingly constrained by neighbouring particles. This process begins at the temperature (or particle density) at which the glass-forming liquid first shows signs of glassy dynamics; however, the details of how the cages form remain unclear.sup.1-4. Here we study cage formation at the particle level in a two-dimensional colloidal suspension (a glass-forming liquid). We use focused lasers to perturb the suspension at the particle level and monitor the nonlinear dynamic response of the system using video microscopy. All observables that we consider respond non-monotonically as a function of the particle density, peaking at the density at which glassy dynamics is first observed. We identify this maximum response as being due to cage formation, quantified by the appearance of domains in which particles move in a cooperative manner. As the particle density increases further, these local domains become increasingly rigid and dominate the macroscale particle dynamics. This microscale rheological deformation approach demonstrates that cage formation in glass-forming liquids is directly related to the merging of such domains, and reveals the first step in the transformation of liquids to glassy materials.sup.1,5. The onset of rigidity in a two-dimensional colloidal glass-forming system is identified by the formation and merging of locally rigid domains in which particles move in a cooperative manner., Author(s): Bo Li [sup.1] , Kai Lou [sup.1] , Walter Kob [sup.2] [sup.3] , Steve Granick [sup.1] [sup.4] [sup.5] Author Affiliations: (1) Center for Soft and Living Matter, Institute of [...]

The usual basis to analyze heat transfer within materials is the equation formulated 200 years ago, Fourier's law, which is identical mathematically to the mass diffusion equation, Fick's law. Revisiting this assumption regarding heat transport within translucent materials, performing the experiments in vacuum to avoid air convection, we compare the model predictions to infrared-based measurements with nearly mK temperature resolution. After heat pulses, we find macroscale non-Gaussian tails in the surface temperature profile. At steady state, we find macroscale anomalous hot spots when the sample is topographically rough, and this is validated by using two additional independent methods to measure surface temperature. These discrepancies from Fourier's law for translucent materials suggest that internal radiation whose mean-free-path is millimeters interacts with defects to produce small heat sources that by secondary emission afford an additional, non-local mode of heat transport. For these polymer and inorganic glass materials, this suggests unique strategies of heat management design. [ABSTRACT FROM AUTHOR]

Assessing the ergodicity of graphene liquid cell electron microscope measurements, we report that loop states of circular DNA interconvert reversibly and that loop numbers follow the Boltzmann distribution expected for this molecule in bulk solution, provided that the electron dose is low (80-keV electron energy and electron dose rate 1-20 e- Å-2 s-1). This imaging technique appears to act as a "slow motion" camera that reveals equilibrated distributions by imaging the time average of a few molecules without the need to image a spatial ensemble. [ABSTRACT FROM AUTHOR]

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. 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 t0.25 to t0.6 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. [ABSTRACT FROM AUTHOR]

Synchronization occurs widely in the natural and technological worlds, from the rhythm of applause and neuron firing (1) to the quantum mechanics of coupled Josephson junctions (2), but has not [...]

A challenging goal in materials chemistry and physics is spontaneously to form intended superstructures from designed building blocks. In fields such as crystal engineering (1) and the design of porous materials (2-4), this typically involves building blocks of organic molecules, sometimes operating together with metallic ions or clusters. The translation of such ideas to nanoparticles and colloidal-sized building blocks would potentially open doors to new materials and new properties (5-7), but the pathways to achieve this goal are still undetermined. Here we show how colloidal spheres can be induced to self-assemble into a complex predetermined colloidal crystal--in this case a colloidal kagome lattice (8-12)--through decoration of their surfaces with a simple pattern of hydrophobic domains. The building blocks are simple micrometre-sized spheres with interactions (electrostatic repulsion in the middle, hydrophobic attraction at the poles, which we call 'triblock Janus') that are also simple, but the self-assembly of the spheres into an open kagome structure contrasts with previously known close-packed periodic arrangements of spheres (13-15). This open network is of interest for several theoretical reasons (8-10). With a view to possible enhanced functionality, the resulting lattice structure possesses two families of pores, one that is hydrophobic on the rims of the pores and another that is hydrophilic. This strategy of 'convergent' self-assembly from easily fabricated (16) colloidal building blocks encodes the target supracolloidal architecture, not in localized attractive spots but instead in large redundantly attractive regions, and can be extended to form other supracolloidal networks., Colloidal crystals are important for their proposed applications in photonics, biomaterials, catalytic supports and lightweight structural materials. They also serve as model systems in which to study the phase behaviour [...]

A study of static and shear interactions between smooth surfaces separated by molecularly thin films of Fomblin-Z oligomers is presented. Results demonstrate the effect of polar end groups of fluorinated chain nonpolar environment on the films.

Polarized infrared spectroscopy in attenuated total reflection was used to investigate the orientation and adsorption of an aqueous organic ion having an anisotropic shape at an oxidized silicon surface with an opposite charge. The organic ion considered is the 1,4-dimethylpyridinium cation. The sticking behavior of the organic ion was found to be slightly greater than that of small inorganic ions of the same charge. Results also suggested that the organic ion at the surface act as an embryonic amphiphile.

A study was conducted to measure adhesion between opposed molecularly thin layers of perfluoropoly(alkyl ether)s on mica, with emphasis on the dependence of the adhesion on chain-end functionality and chain length of the polymer. Experimental results indicated that increases in the adhesion between thin, adsorbed layers of perfluoropoly(alkyl ether) with different chain-end functionality correlated with the logarithmic unloading rate.