Direct Visualization of Colloidal Rod Assembly by Confocal Microscopy

Mohraz, Ali; Solomon, Michael J.

doi:10.1021/la046908a

Cited by 141 publications

(188 citation statements)

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“…The method described here offers a powerful tool for fabricating particles of various shapes. It can be adopted to prepare particles from polymers other than PS, for example, biodegradable poly(lacticco-glycolic acid) (data not shown) and poly(methyl methacrylate) (16). The method is also amenable to scale up through increased particle loading in films, increased film thickness, parallel processing, and automation.…”

Section: Discussionmentioning

confidence: 99%

Making polymeric micro- and nanoparticles of complex shapes

Champion

Katare

Mitragotri³

2007

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

665

580

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Polymeric micro-and nanoparticles play a central role in varied applications such as drug delivery, medical imaging, and advanced materials, as well as in fundamental studies in fields such as microfluidics and nanotechnology. Functional behavior of polymeric particles in these fields is strongly influenced by their shape. However, the availability of precisely shaped polymeric particles has been a major bottleneck in understanding and capitalizing on the role of shape in particle function. Here we report a method that directly addresses this need. Our method uses routine laboratory chemicals and equipment to make particles with >20 distinct shapes and characteristic features ranging in size from 60 nm to 30 m. This method offers independent control over important particle properties such as size and shape, which is crucial to the development of nonspherical particles both as tools and products for a variety of fields.morphology ͉ nanotechnology ͉ geometry ͉ drug delivery ͉ nonspherical P olymeric particles are used in a diverse array of applications including drug delivery (1), advanced materials (2), personal care (3), and medical imaging (4). They also are used in fundamental studies in fields such as microfluidics (5) and nanotechnology (6). Particle shape is a critical parameter that can significantly influence particle function. The vast potential of shape, however, has not been fully explored due to difficulties in creating polymer particles with controlled shapes. Several reports exist on fabrication of polymeric particles with nonspherical geometries. These approaches make use of self-assembly (7-9), photolithography (10), nonwetting template molding (11), microfluidics (12, 13), and stretching of spherical particles (14,15). Collectively, these methods have produced particles of several distinct shapes. Some of these methods provide advantages such as scalability, high throughput, and precise control over particle shape. However, they also suffer from drawbacks including cost, particle size limitations, low throughput, and limited ability to sculpt particles in three dimensions. Accordingly, simple, versatile, inexpensive, and high-throughput methods of fabricating nonspherical particles still remain a bottleneck of future discoveries in a diverse array of fields. Here, we report a simple method that generates particles of Ͼ20 distinct shapes in large, reproducible quantities. ResultsSpherical polystyrene (PS) particles of diameters between 60 nm and 10 m are used here as a starting material for preparing particles of complex shapes. These particles are suspended in an aqueous solution of polyvinyl alcohol (PVA) and cast into films (14), which are then manipulated to engineer particle shape. The method for engineering shape can be classified into two general approaches (Fig. 1). In the first approach, termed scheme A, PS particles are liquefied by using solvent or by heating above the glass transition temperature (T g ) of PS and then stretched in one or two dimensions. In the second approach, scheme B...

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Section: Discussionmentioning

confidence: 99%

Making polymeric micro- and nanoparticles of complex shapes

Champion

Katare

Mitragotri³

2007

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

665

580

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“…It then becomes possible to study the changes in V 0 and A 0 upon increasing polymer concentration or to measure the insertion probability of a polymer and use the concept of free volume theory (31). Another possible extension lies in the use of nonspherical hard colloids, for example, fluorescent rods (32), where exactly the same concepts can be applied. Constructing the available volume and its surface area then become more cumbersome, but in principle possible.…”

Section: Discussionmentioning

confidence: 99%

Direct measurement of the free energy by optical microscopy

Dullens

Aarts

Kegel

2006

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

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We report the direct measurement of thermodynamic properties of colloidal hard spheres by optical microscopy. By using confocal microscopy, we obtain three-dimensional snapshots of a colloidal hard-sphere suspension over a wide range of densities. From these snapshots, the available volume to insert an additional sphere and the surface area of that volume are determined, which are directly related to the thermodynamics of the system. This procedure enables us to measure in a direct and noninterfering way, in principle, all thermodynamic properties, here demonstrated for the pressure, the chemical potential, and the free-energy density of a colloidal hard-sphere suspension. The ''visual'' determination of thermodynamic quantities opens up the possibility to experimentally study the relation between thermodynamics and geometry in real space beyond the hard-sphere potential.colloids ͉ statistical geometry ͉ thermodynamics T he intimate relation between colloids and statistical mechanics was pioneered by Perrin (1) in his determination of Boltzmann's constant k B from microscopy images of sedimenting colloids at low densities. At these densities, the equation of state is given by van 't Hoff's law for the ideal (osmotic) pressure P ϭ k B T, with as the colloid number density and T as the absolute temperature. The pressure in dense suspensions of interacting colloids can be measured by, for example, scattering experiments (2-4) or analysis of the sedimentation-diffusion density profile (5-8). In most interacting systems, the structure is dominated by the repulsive part of the potential (9, 10), and the simplest model liquid with a purely repulsive potential is a fluid consisting of hard spherical particles. Statistical geometry of hard spheres provides an elegant, microscopic, and direct route to the thermodynamics of such a system (11)(12)(13)(14). Here, we apply these concepts to hard-sphere configurations obtained by confocal microscopy and directly measure the pressure, chemical potential, and free energy of a colloidal hard-sphere suspension.The available volume to insert an additional sphere into the system, V 0 , and the surface area of that volume, A 0 , are the key geometrical quantities and are illustrated in Fig. 1. For hard spheres the pressure P and chemical potential can be exactly expressed in terms of V 0 and A 0 (11, 12) asHere, is the particle diameter, 0 is the ideal gas chemical potential, and V is the total system volume. Once the pressure and chemical potential are known, the free-energy density F͞V is directly given by F͞V ϭ ϪP ϩ . Results and DiscussionA typical fluorescence confocal microscopy image representing a two-dimensional (2D) slice of the colloidal hard-sphere system (see Experimental Methods) at a volume fraction of spheres ϵ v ϭ 0.25 is shown in Fig. 2A. Here, v is the particle's volume.The distribution of particles in the 2D slice is reminiscent of a homogeneous fluid. Because the particles consist of a fluorescent core and a nonfluorescent shell, only the fluorescent cores are vi...

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“…In Fig. 5a, for example, the oil was nucleated in the presence of elongated seeds obtained by stretching regular sulphonated PS spheres 26 . This resulted in spherical particles with identical ellipsoidal dimples.…”

Section: Spherical Seeds Discs Cavitiesmentioning

confidence: 99%

Shaping colloids for self-assembly

et al. 2013

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The creation of a new material often starts from the design of its constituent building blocks at a smaller scale. From macromolecules to colloidal architectures, to granular systems, the interactions between basic units of matter can dictate the macroscopic behaviour of the resulting engineered material and even regulate its genesis. Information can be imparted to the building units by altering their physical and chemical properties. In particular, the shape of building blocks has a fundamental role at the colloidal scale, as it can govern the self-organization of particles into hierarchical structures and ultimately into the desired material. Herein we report a simple and general approach to generate an entire zoo of new anisotropic colloids. Our method is based on a controlled deformation of multiphase colloidal particles that can be selectively liquified, polymerized, dissolved and functionalized in bulk. We further demonstrate control over the particle functionalization and coating by realizing patchy and Janus colloids.

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Direct Visualization of Colloidal Rod Assembly by Confocal Microscopy

Cited by 141 publications

References 50 publications

Making polymeric micro- and nanoparticles of complex shapes

Making polymeric micro- and nanoparticles of complex shapes

Direct measurement of the free energy by optical microscopy

Shaping colloids for self-assembly

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