Experimental Soft Matter Research:

All data images below are videos. For example, see labyrinth video and crystal melting video

Images are Experimental Data of Geometrical Frustration in Colloids

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Text Box: Penrose triangle

Text Box: Escher’s art

 

 

 

 

 

 

 

Text Box: Frustration ?Degeneracy ? non-zero entropy at zero temperature (contradict to the 3rd law of         thermodynamics?) ?no energy scale ?all perturbations are strong ?many instabilities, very rich behavior

 

 

A 20-sec Brownian motion trajectory of a 2.4 x 0.3 x 0.3 micrometer ellipsoid in quasi-two-dimensional confinement. Background: simulated Brownian motion trajectories of a sphere (grey) and of an ellipsoid (blue).
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Image made by Yilong Han and Felice Macera
self-organized 2D colloidal quasicrystal(??) under microscope (50 micrometer x 80 micrometer)
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self-organized free-floating colloidal crystal blobs by introducing attractions between NIPA spheres.
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Crystal blobs can be melted and re-crystallized by tuning the temperature (the diameters of small NIPA spheres change with temperature). At appropriate temperature, microcrystals do not sediment much overnight due to good density match. These tunable blobs of several to thousands of colloidal spheres exhibit crystal, liquid, glass and gas phases.
Two-layer colloidal crystal
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I measured the melting of two-layer square lattice for the first time and observed a middle phase between crystal and liquid phases. It could be the square analogy of the hexatic phase.
Prefreezing stage of liquid phase
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Heterogeneous nucleation
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More than 100 years ago, Ostwald asked the question: What is the smallest amount of solid to crystallize a supercooled liquid? Simulation in Nature 428, 404, 2005 answered this question for the first time. My experiment showed that if the diameter of the "dust" particle (big polystyrene sphere) is more than 10 times larger than "atoms" (small NIPA spheres), it is a nucleation promoter (see the crystal nucleated at the left surface of the big sphere in the figure). If the curvature ratio is less than 10, the big sphere acts like a defect and suppresses the nucleation near it.
A monolayer of 3x0.6 micrometer ellipsoids suspended in water. Overlaid red ellipses are the results of image analysis.
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dimers
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melting of two dimensional crystals:
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The hexatic phase between solid and liquid phases was observed. I proposed a new analysis method to avoid some ambiguities in previous analyses. By this method, we observed a novel premelting stage in solid phase. Traditional analysis methods can incorrectly associate the premelting stage with the hexatic phase. For example, it is not the presence of dislocations, but the total net dipole moment of dislocations determines the symmetry breaking point. ppt
Self-organized patterns of bidispersed colloidal spheres in electric fields.
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Optical artifacts in a monolayer of 3.0 micron silica spheres
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some of my Ph.D. work:


Configurational temperatures: thermodynamic temperature can be calculated from the positions and interactions of particles without knowledge of kinetic information. It has a profound connection with the HyperVirial Theorem, see J. Chem. Phys.122, 064907, Yilong Han & David Grier.

self-organized patterns of colloidal spheres in electric fields