Depletion-driven antiferromagnetic, paramagnetic, and ferromagnetic behavior in quasi-two-dimensional buckled colloidal solids.

We investigate quasi-two-dimensional buckled colloidal monolayers on a triangular lattice with tunable depletion interactions. Without depletion attraction, the experimental system provides a colloidal analog of the well-known geometrically frustrated Ising antiferromagnet [Y. Han et al.

Classification of Aggregates Using Multispectral Two-Dimensional Angular Light Scattering Simulations.

Airborne particulate matter plays an important role in climate change and health impacts, and is generally irregularly shaped and/or forms agglomerates. These particles may be characterized through their light scattering signals. Two-dimensional angular scattering from such particles produce a speckle pattern that is influenced by their morphology (shape and material composition).

Correlations between short- and long-time relaxation in colloidal supercooled liquids and glasses.

Spatiotemporal dynamics of short- and long-time structural relaxation are measured experimentally as a function of packing fraction, ϕ, in quasi-two-dimensional colloidal supercooled liquids and glasses. The relaxation times associated with long-time dynamic heterogeneity and short-time intracage motion are found to be strongly correlated and to grow by orders of magnitude with increasing ϕ toward dynamic arrest. We find that clusters of fast particles on the two timescales often overlap, and, interestingly, the distribution of minimum-spatial-separation between closest nonoverlapping clusters across the two timescales is revealed to be exponential with a decay length that increases with ϕ.

Vibrational and structural signatures of the crossover between dense glassy and sparse gel-like attractive colloidal packings.

We investigate the vibrational modes of quasi-two-dimensional disordered colloidal packings of hard colloidal spheres with short-range attractions as a function of packing fraction. Certain properties of the vibrational density of states (vDOS) are shown to correlate with the density and structure of the samples (i.e.

Phonons in two-dimensional soft colloidal crystals.

The vibrational modes of pristine and polycrystalline monolayer colloidal crystals composed of thermosensitive microgel particles are measured using video microscopy and covariance matrix analysis. At low frequencies, the Debye relation for two-dimensional harmonic crystals is observed in both crystal types; at higher frequencies, evidence for van Hove singularities in the phonon density of states is significantly smeared out by experimental noise and measurement statistics. The effects of these errors are analyzed using numerical simulations.

Synthesis of micrometer-size poly(N-isopropylacrylamide) microgel particles with homogeneous crosslinker density and diameter control.

Poly(N-isopropylacrylamide) microgel particles are synthesized using a semi-batch surfactant-free emulsion polymerization method. Particle diameter can be precisely adjusted by controlling the initial conditions, the electrolyte concentration, and the monomer feeding rate and duration. Larger particles are obtained in the presence of small amounts of co-monomer with cationic amino groups that compete against the negative charges arising from the initiator.

Phonons in two-dimensional colloidal crystals with bond-strength disorder.

We study phonon modes in two-dimensional colloidal crystals composed of soft microgel particles with hard polystyrene particle dopants distributed randomly on the triangular lattice. This experimental approach produces close-packed lattices of spheres with random bond strength disorder, i.e.

Irreversible rearrangements, correlated domains, and local structure in aging glasses.

Bidisperse colloidal suspensions of temperature-sensitive microgel spheres were quenched from liquid to glass states by a rapid temperature drop, and then the glass was permitted to age. Irreversible rearrangements, events that dramatically change a particle's local environment, were observed to be closely related to dynamic heterogeneity. The rate of these irreversible events decreased during aging and the the number of particles required to move as part of these irreversible rearrangements increased.

Thermal vestige of the zero-temperature jamming transition.

When the packing fraction is increased sufficiently, loose particulates jam to form a rigid solid in which the constituents are no longer free to move. In typical granular materials and foams, the thermal energy is too small to produce structural rearrangements. In this zero-temperature (T = 0) limit, multiple diverging and vanishing length scales characterize the approach to a sharp jamming transition.

Angularly resolved light scattering from aerosolized spores: observations and calculations.

Angularly resolved elastic light scattering patterns from individual aerosolized Bacillus subtilis spores were qualitatively compared with simulations. Two-dimensional angular optical scattering patterns of the spores were collected for polar scattering angles varying from approximately 77 degrees to 130 degrees and azimuthal angles varying from 0 degrees to 360 degrees . Computations were performed with single T-matrix formalism by simulating a spore with three different particle shapes: (1) a finite-length cylinder with spherical end caps, (2) a spheroid, and (3) two spheres in contact.

Two-dimensional angular optical scattering patterns of microdroplets in the mid infrared with strong and weak absorption.

Two-dimensional angular optical scattering (TAOS) patterns of droplets composed of a mixture of H2O and D2O are detected in the mid infrared. First, a lens is used in the Abbé sine condition to collect a small solid angle of light, where the scattering pattern matches well numerical simulations based on Mie theory. Next, TAOS patterns from droplets spanning a large (approximately 27pi sr) solid angle are captured simultaneously at two wavelengths.

Characterizing and monitoring respiratory aerosols by light scattering.

The elastic-scattering intensity pattern from a single particle as a function of spherical coordinate angles theta and phi provides detailed information on the pattern's morphology. By use of an ellipsoidal reflector and a CCD camera, a single-laser-shot intensity pattern from a large angular range (theta from 90 degrees to 168 degrees and phi from 0 degrees to 360 degrees) was detected from a single aerosol (e.g.