Confocal microscopy of colloids

Prasad, V.; Semwogerere, Denis; Weeks, Eric R.

doi:10.1088/0953-8984/19/11/113102

Cited by 261 publications

(237 citation statements)

References 169 publications

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“…The particles are dyed with rhodamine 6G so that they can be viewed with a laser-scanning confocal microscope (15,27). We acquire images of size 20 ϫ 55 ϫ 60 m 3 once every 25 s, where the long direction (z) is parallel to gravity.…”

Section: Methodsmentioning

confidence: 99%

The equilibrium intrinsic crystal–liquid interface of colloids

Hernandez-Guzman

Weeks

2009

Proc. Natl. Acad. Sci. U.S.A.

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We use confocal microscopy to study an equilibrated crystal-liquid interface in a colloidal suspension. Capillary waves roughen the surface, but locally the intrinsic interface is sharply defined. We use local measurements of the structure and dynamics to characterize the intrinsic interface, and different measurements find slightly different widths of this interface. In terms of the particle diameter d, this width is either 1.5d (based on structural information) or 2.4d (based on dynamics), both not much larger than the particle size. This work is the first direct experimental visualization of an equilibrated crystal-liquid interface.surface tension ͉ capillary waves ͉ confocal microscopy T he interface between crystal and liquid phases of a material governs phenomena such as wetting, lubrication, and crystal nucleation (1, 2). Interfaces are poorly defined at the atomic level: Capillary waves cause fluctuations in the interface position (3-6), and locally the structure varies in a smooth way from ordered to disordered (2). Existing literature makes a distinction between the intrinsic interface (presumed to be sharp) (3), and the observed surface blurred by capillary waves (4, 7). The standard equilibrium interface profile is well defined and contains fluctuations at all length and time scales, due to these capillary waves. Because of the rapid time scales of capillarywave fluctuations, along with the small length scales at the interface, it is difficult to study these interfaces directly (1). Thus, computer simulations provide useful information about model crystal-liquid interfaces, such as hard-sphere systems (2,8,9) and Lennard-Jones systems (10, 11).Recently, crystal-liquid interfaces were directly studied in colloidal suspensions by using confocal microscopy (6, 12). Colloids are systems of solid particles in a liquid and are a good model system for phase transitions (5,6,13,14). Microscopy allows direct observation of structure and dynamics of the colloidal particles (15). However, the previous experiments focused on nonequilibrium cases where samples were crystallizing and did not provide data on equilibrium interfaces, such as those studied by simulation (2,(8)(9)(10)16). Furthermore, these experiments did not examine the intrinsic interface, perhaps because they were nonequilibrium studies, and thus crystalline particles were present in the ''liquid'' side and vice versa, which confuse the structure near the interface.In this work, we present confocal microscope observations of an equilibrated colloidal crystal-liquid interface. By following the positions of several thousand colloidal particles on both sides of the interface, we directly visualize the interface. An example of our data is shown in Fig. 1A, where blue particles are crystalline and yellow/red particles are liquid-like. This interface has a low surface tension, and we see capillary waves. We are able to remove the influence of these capillary waves from the data and measure the intrinsic surface profile. In particular, we find that capill...

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Section: Methodsmentioning

confidence: 99%

The equilibrium intrinsic crystal–liquid interface of colloids

Hernandez-Guzman

Weeks

2009

Proc. Natl. Acad. Sci. U.S.A.

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“…This builds on extensive studies using light scattering techniques 12,13 , and, more recently, microscopy techniques [14][15][16] . The most widely studied system is that of particles which behave as hard spheres 17 .…”

Section: Introductionmentioning

confidence: 99%

Dynamics of hard sphere suspensions using dynamic light scattering and X-ray photon correlation spectroscopy: Dynamics and scaling of the intermediate scattering function

Martinez

Thijssen

Zontone

et al. 2011

The Journal of Chemical Physics

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Intermediate Scattering Functions (ISF's) are measured for colloidal hard sphere systems using both Dynamic Light Scattering (DLS) and X-ray Photon Correlation Spectroscopy (XPCS). We compare the techniques, and discuss the advantages and disadvantages of each. Both techniques agree in the overlapping range of scattering vectors. We investigate the scaling behaviour found by Segre and Pusey 1 but challenged by Lurio et al. 2 . We observe a scaling behaviour over several decades in time but not in the long time regime. Moreover, we do not observe long time diffusive regimes at scattering vectors away from the peak of the structure factor and so question the existence of a long time diffusion coefficients at these scattering vectors.

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“…The optical microscopy observations therefore reveal just a particular projection of the full 3D interaction map between the colloidal particles. The confocal microscopy (including fluorescent confocal polarizing microscopy, FCPM 18 ) provides truly 3D information about the investigated system and has been used successfully for fast imaging in water-based colloids 19 . However, this method is too slow for real-time 3D imaging and recovery of colloidal pair interactions in LCs because of the small amount of added fluorescent dye and low level of fluorescent light emission.…”

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confidence: 99%

Assembly and control of 3D nematic dipolar colloidal crystals

et al. 2013

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Topology has long been considered as an abstract mathematical discipline with little connection to material science. Here we demonstrate that control over spatial and temporal positioning of topological defects allows for the design and assembly of three-dimensional nematic colloidal crystals, giving some unexpected material properties, such as giant electrostriction and collective electro-rotation. Using laser tweezers, we have assembled threedimensional colloidal crystals made up of 4 mm microspheres in a bulk nematic liquid crystal, implementing a step-by-step protocol, dictated by the orientation of point defects. The threedimensional colloidal crystals have tetragonal symmetry with antiparallel topological dipoles and exhibit giant electrostriction, shrinking by 25-30% at 0.37 V mm À 1 . An external electric field induces a reversible and controllable electro-rotation of the crystal as a whole, with the angle of rotation being B30°at 0.14 V mm À 1 , when using liquid crystal with negative dielectric anisotropy. This demonstrates a new class of electrically highly responsive soft materials.

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Confocal microscopy of colloids

Cited by 261 publications

References 169 publications

The equilibrium intrinsic crystal–liquid interface of colloids

The equilibrium intrinsic crystal–liquid interface of colloids

Dynamics of hard sphere suspensions using dynamic light scattering and X-ray photon correlation spectroscopy: Dynamics and scaling of the intermediate scattering function

Assembly and control of 3D nematic dipolar colloidal crystals

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