Sat, 26 Jul 2008 04:35:40 BST CiteULike: Tag weitz http://www.citeulike.org/tag/weitz CiteULike.org en-gb Copyright © 2004-2008 citeulike.org http://www.citeulike.org/user/dchen/article/2730409 <i>Journal of Colloid and Interface Science, Vol. 179, No. 2. (10 May 1996), pp. 439-448.</i><br /><br />We have measured the yield transition of monodisperse emulsions as the volume fraction, [phi], and droplet radius,a, are varied. We study the crossover from the perturbative shear regime, which reflects the linear viscoelastic properties, to the steady shear regime, which reflects nonlinear, plastic flow. For small oscillatory strains of peak amplitude [gamma], the peak stress, [tau], is linearly proportional to [gamma]. As the strain is increased, the stress becomes nonlinear in [gamma] at the yield strain, [gamma]y. The [phi] dependence of [gamma]yis independent ofaand exhibits a minimum near the critical volume fraction, [phi]c[approximate] 0.635, associated with the random close packing of monodisperse spheres. We show that the yield stress, [tau]y, increases dramatically as the volume fraction increases above [phi]c; [tau]yalso scales with the Laplace pressure, [sigma]/a, where [sigma] is the interfacial tension. For comparison, we also determine the steady shear stress over a wide range of strain rates, [gamma]. Below [phi] [approximate] 0.70, the flow is homogeneous throughout the sample, while for higher [phi], the emulsion fractures resulting in highly inhomogeneous flow along the fracture plane. Above [phi] [approximate] 0.58, the steady shear stress exhibits a low strain rate plateau which corresponds with the yield stress measured with the oscillatory technique. Moreover, [tau]yexhibits a robust power law dependence on [gamma] with exponents decreasing with [phi], varying from to . Below [phi] [approximate] 0.58, associated with the colloidal glass transition, the plateau stress disappears entirely, suggesting that the equilibrium glassy dynamics are important in identifying the onset of the yield behavior. Yielding and Flow of Monodisperse Emulsions TG Mason J Bibette DA Weitz doi:10.1006/jcis.1996.0235 Journal of Colloid and Interface Science, Vol. 179, No. 2. (10 May 1996), pp. 439-448. 2008-04-28T16:14:56-00:00 1996 Journal of Colloid and Interface Science 179 2 439 448 emulsion mason weitz http://www.citeulike.org/user/dchen/article/2710365 <i>Science, Vol. 305, No. 5692. (24 September 2004), pp. 1944-1948.</i><br /><br />The dominant mechanism for creating large irreversible strain in atomic crystals is the motion of dislocations, a class of line defects in the crystalline lattice. Here we show that the motion of dislocations can also be observed in strained colloidal crystals, allowing detailed investigation of their topology and propagation. We describe a laser diffraction microscopy setup used to study the growth and structure of misfit dislocations in colloidal crystalline films. Complementary microscopic information at the single-particle level is obtained with a laser scanning confocal microscope. The combination of these two techniques enables us to study dislocations over a range of length scales, allowing us to determine important parameters of misfit dislocations such as critical film thickness, dislocation density, Burgers vector, and lattice resistance to dislocation motion. We identify the observed dislocations as Shockley partials that bound stacking faults of vanishing energy. Remarkably, we find that even on the scale of a few lattice vectors, the dislocation behavior is well described by the continuum approach commonly used to describe dislocations in atomic crystals. 10.1126/science.1102186 Visualization of Dislocation Dynamics in Colloidal Crystals Peter Schall Itai Cohen David Weitz Frans Spaepen doi:10.1126/science.1102186 Science, Vol. 305, No. 5692. (24 September 2004), pp. 1944-1948. 2008-04-23T22:01:50-00:00 2004 Science 305 5692 1944 1948 cohen schall science shear weitz http://www.citeulike.org/user/dchen/article/2709549 <i>Angewandte Chemie International Edition, Vol. 45, No. 16. (2006), pp. 2556-2560.</i><br /><br />No Abstract Electric Control of Droplets in Microfluidic Devices Darren Link Erwan Grasland-Mongrain Agnes Duri Flavie Sarrazin Zhengdong Cheng Galder Cristobal Manuel Marquez David Weitz doi:10.1002/anie.200503540 Angewandte Chemie International Edition, Vol. 45, No. 16. (2006), pp. 2556-2560. 2008-04-23T17:12:33-00:00 2006 Angewandte Chemie International Edition 45 16 2556 2560 2006 microrheology weitz http://www.citeulike.org/user/dchen/article/2713489 <i>Physical Review Letters, Vol. 93, No. 4. (23 July 2004), 046001.</i> Shear-Induced Configurations of Confined Colloidal Suspensions Itai Cohen Thomas Mason David Weitz doi:10.1103/PhysRevLett.93.046001 Physical Review Letters, Vol. 93, No. 4. (23 July 2004), 046001. 2008-04-24T16:40:15-00:00 2004 Physical Review Letters 93 4 046001 American Physical Society cohen shear weitz http://www.citeulike.org/user/dchen/article/2735614 <i>Journal of Physics: Condensed Matter, Vol. 14, No. 33. (2002), pp. 7581-7597.</i><br /><br />We present novel measurements of the structure of colloidal gels. Using confocal microscopy, we obtain the precise three-dimensional positions of a large number of particles. We develop quantitative descriptions of the topology of the gel, including the number of bonds per particle, the chemical or bond fractal dimension, the number of flexible pivot points and other topological parameters that describe the chainlike structure. We investigate the dependence of these parameters on the particle volume fraction and the strength of the attraction that holds the particles together. While all samples have approximately the same fractal and chemical dimensions, we find that gels formed with stronger attraction or larger volume fraction have fewer bonds per particle, more filamentous chains and a greater number of flexible pivot points. Finally, we discuss the topological results in the context of the gel's elasticity. Measurements of the elastic constants of individual chainlike segments are explained with a simple model. The distribution of elastic constants, however, has a general form that is not understood. Direct imaging of three-dimensional structure and topology of colloidal gels AD Dinsmore DA Weitz doi:10.1088/0953-8984/14/33/303 Journal of Physics: Condensed Matter, Vol. 14, No. 33. (2002), pp. 7581-7597. 2008-04-29T22:57:53-00:00 2002 Journal of Physics: Condensed Matter 14 33 7581 7597 colloids dinsmore gel structure weitz http://www.citeulike.org/user/dchen/article/2553079 <i>Physical Review Letters, Vol. 99, No. 2. (2007)</i><br /><br />Colloidal suspensions are susceptible to gravitationally induced phase separation. This can be mitigated by the formation of a particle network caused by depletion attraction. The effectiveness of this network in supporting the buoyant weight of the suspension can be characterized by its compressional modulus. We measure the compressional modulus for emulsion networks induced by depletion attraction and present a model that quantitatively predicts their gravitational stability. We also determine the relationship between the strength of the depletion attraction and the magnitude of the compressional modulus. Gravitational Stability of Suspensions of Attractive Colloidal Particles Chanjoong Kim Yaqian Liu Angelika Kühnle Stephan Hess Sonja Viereck Thomas Danner L Mahadevan David Weitz doi:10.1103/PhysRevLett.99.028303 Physical Review Letters, Vol. 99, No. 2. (2007) 2008-03-18T22:07:07-00:00 2007 Physical Review Letters 99 2 APS 2007 colloids gel weitz http://www.citeulike.org/user/dchen/article/2683405 <i>Physical Review Letters, Vol. 99, No. 9. (2007)</i><br /><br />A liquid forced through an orifice into an immiscible fluid ultimately breaks into drops due to surface tension. Drop formation can occur right at the orifice in a dripping process. Alternatively, the inner fluid can form a jet, which breaks into drops further downstream. The transition from dripping to jetting is not understood for coflowing fluid streams, unlike the case of drop formation in air. We show that in a coflowing stream this transition can be characterized by a state diagram that depends on the capillary number of the outer fluid and the Weber number of the inner fluid. Dripping to Jetting Transitions in Coflowing Liquid Streams Andrew Utada Alberto Nieves Howard Stone David Weitz doi:10.1103/PhysRevLett.99.094502 Physical Review Letters, Vol. 99, No. 9. (2007) 2008-04-17T20:17:14-00:00 2007 Physical Review Letters 99 9 APS 2007 microrheology weitz http://www.citeulike.org/user/dchen/article/1429816 <i>Trends Biochem Sci, Vol. 29, No. 7. (July 2004), pp. 364-370.</i> Dealing with mechanics: mechanisms of force transduction in cells. PA Janmey DA Weitz doi:10.1016/j.tibs.2004.05.003 Trends Biochem Sci, Vol. 29, No. 7. (July 2004), pp. 364-370. 2007-07-03T03:53:26-00:00 2004 Trends Biochem Sci 0968-0004 29 7 364 370 biology review weitz http://www.citeulike.org/user/dchen/article/2683399 <i>Applied Physics Letters, Vol. 91, No. 9. (2007)</i><br /><br />View this record in Web of Science Optical manipulation and rotation of liquid crystal drops using high-index fiber-optic tweezers Kazi Abedin Charles Kerbage Alberto Nieves David Weitz Applied Physics Letters, Vol. 91, No. 9. (2007) 2008-04-17T20:15:01-00:00 2007 Applied Physics Letters 91 9 AIP 2007 liquidcrystal opticaltweezer weitz http://www.citeulike.org/user/dchen/article/1605887 <i>Journal of Physics: Condensed Matter, Vol. 19, No. 20. (2007)</i><br /><br />We use a confocal microscope to examine the motion of individual particles in a dense colloidal suspension. Close to the glass transition, particle motion is strongly spatially correlated. The correlations decay exponentially with particle separation, yielding a dynamic length scale of O(2-3s) (in terms of particle diameter s). This length scale grows modestly as the glass transition is approached. Further, the correlated motion exhibits a strong spatial dependence on the pair correlation function g(r). Motion within glassy samples is weakly correlated, but with a larger spatial scale for this correlation. Short-~and long-range correlated motion observed in colloidal glasses and liquids John DA Weitz doi:10.1088/0953-8984/19/20/205131 Journal of Physics: Condensed Matter, Vol. 19, No. 20. (2007) 2007-08-29T17:41:41-00:00 2007 Journal of Physics: Condensed Matter 19 20 2007 weeks weitz http://www.citeulike.org/user/dchen/article/2711079 <i>Physics of Fluids, Vol. 16, No. 8. (2004), pp. 2828-2834.</i><br /><br />View This Record in Scopus A new device for the generation of microbubbles José Gordillo Zhengdong Cheng Alfonso M Márquez DA Weitz Physics of Fluids, Vol. 16, No. 8. (2004), pp. 2828-2834. 2008-04-24T00:28:26-00:00 2004 Physics of Fluids 16 8 2828 2834 AIP bubbles microrheology weitz http://www.citeulike.org/user/dchen/article/2710107 <i>Applied Physics Letters, Vol. 88, No. 2. (2006)</i><br /><br />View This Record in Scopus Dielectrophoretic manipulation of drops for high-speed microfluidic sorting devices Keunho Ahn Charles Kerbage Tom Hunt RM Westervelt Darren Link DA Weitz Applied Physics Letters, Vol. 88, No. 2. (2006) 2008-04-23T20:17:36-00:00 2006 Applied Physics Letters 88 2 AIP microrheology weitz http://www.citeulike.org/user/dchen/article/2683388 <i>Nano Lett., Vol. 7, No. 9. (12 September 2007), pp. 2876-2880.</i><br /><br />Abstract: We present a robust and straightforward approach for fabricating a novel colloidosome system where colloidal particles are assembled to form colloidal shells on the surface of stimuli-responsive microgel scaffolds. We demonstrate that the structural properties of the colloidal shells can be controlled through the colloidal particle size and modulus, and the state of supporting microgel particles. This technique offers a new way to engineer colloidosomes, enabling fine control over their permeability over a wide range of length scales. Colloidal Assembly Route for Responsive Colloidosomes with Tunable Permeability JW Kim A Fernandez-Nieves N Dan AS Utada M Marquez DA Weitz doi:10.1021/nl0715948 Nano Lett., Vol. 7, No. 9. (12 September 2007), pp. 2876-2880. 2008-04-17T20:10:58-00:00 2007 Nano Lett. 7 9 2876 2880 2007 colloid emulsion weitz http://www.citeulike.org/user/dchen/article/733339 <i>J. Phys. Chem. B, Vol. 109, No. 45. (17 November 2005), pp. 21235-21240.</i> Weak Correlations between Local Density and Dynamics near the Glass Transition JC Conrad FW Starr DA Weitz doi:10.1021/jp0514168 J. Phys. Chem. B, Vol. 109, No. 45. (17 November 2005), pp. 21235-21240. 2006-07-03T19:08:55-00:00 2005 J. Phys. Chem. B 109 45 21235 21240 dynamics freevolume structure weitz http://www.citeulike.org/user/dchen/article/2714010 <i>Nature, Vol. 420, No. 6913. (21 November 2002), pp. 299-301.</i> Electric-field-induced capillary attraction between like-charged particles at liquid interfaces MG Nikolaides AR Bausch MF Hsu AD Dinsmore MP Brenner C Gay DA Weitz doi:10.1038/nature01113 Nature, Vol. 420, No. 6913. (21 November 2002), pp. 299-301. 2008-04-24T19:25:39-00:00 2002 Nature 420 6913 299 301 colloids interaction interface nature weitz http://www.citeulike.org/user/dchen/article/2711055 <i>Physical Review Letters, Vol. 93, No. 10. (2004), 108302.</i> Limits to Gelation in Colloidal Aggregation S Manley L Cipelletti V Trappe AE Bailey RJ Christianson U Gasser V Prasad PN Segre MP Doherty S Sankaran AL Jankovsky B Shiley J Bowen J Eggers C Kurta T Lorik DA Weitz doi:10.1103/PhysRevLett.93.108302 Physical Review Letters, Vol. 93, No. 10. (2004), 108302. 2008-04-23T23:55:21-00:00 2004 Physical Review Letters 93 10 108302 American Physical Society clusters colloids gel weitz http://www.citeulike.org/user/dchen/article/822252 <i>Physical Review E, Vol. 65, No. 5. (20 May 2002), 051505.</i><br /><br />Experiments investigating the local viscoelastic properties of a simple uncross-linked flexible polymer are performed on polyethylene oxide solutions in the semidilute regime using polystyrene beads of varying sizes and surface chemistry as probes. We measure the thermal motions of the beads to obtain the elastic and viscous moduli of our sample. Two different dynamic light scattering techniques; diffusing wave spectroscopy and quasielastic light scattering (QELS); are used to determine the dynamics of the probe particles. Diffusing wave spectroscopy probes the short time dynamics of the scatterers while QELS or single scattering measures the dynamics at larger times. This results in a larger frequency overlap of the data obtained from the microrheological techniques with the data obtained from the conventional bulk measurements. The moduli are estimated using a modified algebraic form of the generalized Stokes-Einstein equation. Comparison of microrheology with bulk measurements shows excellent similarity confirming the applicability of this method for simple; uncross-linked polymeric systems. Microrheology of polyethylene oxide using diffusing wave spectroscopy and single scattering Bivash Dasgupta Shang-You Tee John Crocker BJ Frisken DA Weitz doi:10.1103/PhysRevE.65.051505 Physical Review E, Vol. 65, No. 5. (20 May 2002), 051505. 2006-08-30T16:29:17-00:00 2002 Physical Review E 65 5 051505 American Physical Society dws microrheology weitz http://www.citeulike.org/user/dchen/article/2683180 <i>Angewandte Chemie International Edition, Vol. 46, No. 47. (2007), pp. 8970-8974.</i><br /><br />No Abstract Controllable Monodisperse Multiple Emulsions Liang-Yin Chu Andrew s Rhutesh k Jin-Woong Kim David a doi:10.1002/anie.200701358 Angewandte Chemie International Edition, Vol. 46, No. 47. (2007), pp. 8970-8974. 2008-04-17T18:59:41-00:00 2007 Angewandte Chemie International Edition 46 47 8970 8974 2008 emulsion people weitz http://www.citeulike.org/user/dchen/article/2709840 <i>Physical Review Letters, Vol. 96, No. 8. (2006)</i><br /><br />Networks of filamentous actin cross-linked with the actin-binding protein filamin A exhibit remarkable strain stiffening leading to an increase in differential elastic modulus by several orders of magnitude over the linear value. The variation of the frequency dependence of the differential elastic and loss moduli as a function of prestress is consistent with that observed in living cells, suggesting that cell elasticity is always measured in the nonlinear regime, and that prestress is an essential control parameter. Stress-Dependent Elasticity of Composite Actin Networks as a Model for Cell Behavior ML Gardel F Nakamura J Hartwig JC Crocker TP Stossel DA Weitz doi:10.1103/PhysRevLett.96.088102 Physical Review Letters, Vol. 96, No. 8. (2006) 2008-04-23T19:30:02-00:00 2006 Physical Review Letters 96 8 APS biology elasticity weitz http://www.citeulike.org/user/dchen/article/954119 <i>J. Cell Biol., Vol. 173, No. 5. (5 June 2006), pp. 733-741.</i><br /><br />Cytoskeletal microtubules have been proposed to influence cell shape and mechanics based on their ability to resist large-scale compressive forces exerted by the surrounding contractile cytoskeleton. Consistent with this, cytoplasmic microtubules are often highly curved and appear buckled because of compressive loads. However, the results of in vitro studies suggest that microtubules should buckle at much larger length scales, withstanding only exceedingly small compressive forces. This discrepancy calls into question the structural role of microtubules, and highlights our lack of quantitative knowledge of the magnitude of the forces they experience and can withstand in living cells. We show that intracellular microtubules do bear large-scale compressive loads from a variety of physiological forces, but their buckling wavelength is reduced significantly because of mechanical coupling to the surrounding elastic cytoskeleton. We quantitatively explain this behavior, and show that this coupling dramatically increases the compressive forces that microtubules can sustain, suggesting they can make a more significant structural contribution to the mechanical behavior of the cell than previously thought possible. 10.1083/jcb.200601060 Microtubules can bear enhanced compressive loads in living cells because of lateral reinforcement Clifford Brangwynne Frederick Mackintosh Sanjay Kumar Nicholas Geisse Jennifer Talbot L Mahadevan Kevin Parker Donald Ingber David Weitz doi:10.1083/jcb.200601060 J. Cell Biol., Vol. 173, No. 5. (5 June 2006), pp. 733-741. 2006-11-20T22:19:20-00:00 2006 J. Cell Biol. 173 5 733 741 biology microrheology weitz http://www.citeulike.org/user/dchen/article/2710298 <i>Physical Review Letters, Vol. 94, No. 1. (2005)</i><br /><br />Minute concentrations of suspended particles can dramatically alter the behavior of a drying droplet. After a period of isotropic shrinkage, similar to droplets of a pure liquid, these droplets suddenly buckle like an elastic shell. While linear elasticity is able to describe the morphology of the buckled droplets, it fails to predict the onset of buckling. Instead, we find that buckling is coincident with a stress-induced fluid to solid transition in a shell of particles at a droplet's surface, occurring when attractive capillary forces overcome stabilizing electrostatic forces between particles. Onset of Buckling in Drying Droplets of Colloidal Suspensions N Tsapis ER Dufresne SS Sinha CS Riera JW Hutchinson L Mahadevan DA Weitz doi:10.1103/PhysRevLett.94.018302 Physical Review Letters, Vol. 94, No. 1. (2005) 2008-04-23T21:45:07-00:00 2005 Physical Review Letters 94 1 APS colloids drying weitz http://www.citeulike.org/user/dchen/article/2713987 <i>Nature, Vol. 424, No. 6952. (2003), pp. 1014-1014.</i> Capillary attraction (communication arising): Like-charged particles at liquid interfaces MG Nikolaides AR Bausch MF Hsu AD Dinsmore MP Brenner C Gay DA Weitz doi:10.1038/4241014b Nature, Vol. 424, No. 6952. (2003), pp. 1014-1014. 2008-04-24T19:16:11-00:00 2003 Nature 424 6952 1014 1014 interaction interface microrheology nature weitz http://www.citeulike.org/user/dchen/article/2710294 <i>Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 71, No. 2. (2005)</i><br /><br />Experiments investigating the local viscoelastic properties of a chemically cross-linked polymer are performed on polyacrylamide solutions in the sol and the gel regimes using polystyrene beads of varying sizes and surface chemistry as probes. The thermal motions of the probes are measured to obtain the elastic and viscous moduli of the sample. Probe dynamics are measured using two different dynamic light scattering techniques, diffusing wave spectroscopy (DWS) and quasielastic light scattering (QELS) as well as video-based particle tracking. Diffusing wave spectroscopy probes the short-time dynamics of the scatterers while QELS measures the dynamics at larger times. Video-based particle tracking provides a way to investigate the local environment of the individual probe particles. A combination of all the techniques results in a larger range of frequencies that can be probed compared to conventional bulk measurements while providing local information at the level of individual probes. A modified algebraic form of the generalized Stokes-Einstein equation is used to calculate the frequency-dependent moduli. A comparison of microrheological measurements with bulk rheology exhibits striking similarity, confirming the applicability of microrheology for chemically cross-linked polymeric systems. Microrheology of cross-linked polyacrylamide networks Bivash Dasgupta DA Weitz doi:10.1103/PhysRevE.71.021504 Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 71, No. 2. (2005) 2008-04-23T21:44:04-00:00 2005 Physical Review E (Statistical, Nonlinear, and Soft Matter Physics) 71 2 APS microrheology polymer weitz http://www.citeulike.org/user/dchen/article/1234789 <i>Science, Vol. 252, No. 5006. (3 May 1991), pp. 686-688.</i><br /><br />The structure and dynamics of three-dimensional foams are probed quantitatively by exploiting the strong multiple scattering of light that gives foams their familiar white color. Approximating the propagation of light as a diffusion process, transmission measurements provide a direct probe of the average bubble size. A model for dynamic light scattering is developed that can be used to interpret temporal fluctuations in the intensity of multiply scattered light. The results identify previously unrecognized internal dynamics of the foam bubbles. These light-scattering techniques are direct, noninvasive probes of bulk foams and therefore should find wide use in the study of their properties. 10.1126/science.252.5006.686 Multiple Light-Scattering Probes of Foam Structure and Dynamics DJ Durian DA Weitz DJ Pine doi:10.1126/science.252.5006.686 Science, Vol. 252, No. 5006. (3 May 1991), pp. 686-688. 2007-04-18T19:27:19-00:00 1991 Science 252 5006 686 688 durian foam mls pine science weitz http://www.citeulike.org/user/dchen/article/2709608 <i>Langmuir, Vol. 22, No. 21. (10 October 2006), pp. 8618-8622.</i><br /><br />Abstract: The microfluidic assembly of colloid-filled hydrogel granules of varying shape and composition is described. First, drops are formed by shearing a concentrated colloidal microsphere-acrylamide suspension in a continuous oil phase using a sheath-flow device. Both homogeneous and Janus (hemispherically distinct) spheres and disks are produced by confining the assembled drops in microchannels of varying geometry. Next, photopolymerization is carried out shortly after drop breakup to preserve their morphology. Representative wet and dried granules are characterized using fluorescence and scanning electron microscopy, respectively. Our approach offers a facile route for assembling colloid-filled hydrogel granules with controlled shape and composition. Microfluidic Assembly of Homogeneous and Janus Colloid-Filled Hydrogel Granules RF Shepherd JC Conrad SK Rhodes DR Link M Marquez DA Weitz JA Lewis doi:10.1021/la060759+ Langmuir, Vol. 22, No. 21. (10 October 2006), pp. 8618-8622. 2008-04-23T17:33:28-00:00 2006 Langmuir 22 21 8618 8622 2006 colloids weitz http://www.citeulike.org/user/dchen/article/2710279 <i>Advanced Materials, Vol. 17, No. 6. (2005), pp. 680-684.</i><br /><br />No abstract. Optically Anisotropic Colloids of Controllable Shape A Fernández-Nieves G Cristobal V Garcés-Chávez G C Spalding K Dholakia D A Weitz doi:10.1002/adma.200401462 Advanced Materials, Vol. 17, No. 6. (2005), pp. 680-684. 2008-04-23T21:34:08-00:00 2005 Advanced Materials 17 6 680 684 colloids liquidcrystal optical technique weitz http://www.citeulike.org/user/dchen/article/2713983 <i>Proceedings of the National Academy of Sciences, Vol. 100, No. 19. (16 September 2003), pp. 10718-10721.</i><br /><br />Vesicles are bilayers of lipid molecules enclosing a fixed volume of aqueous solution. Ubiquitous in cells, they can be produced in vitro to study the physical properties of biological membranes and for use in drug delivery and cosmetics. Biological membranes are, in fact, a fluid mosaic of lipids and other molecules; the richness of their chemical and mechanical properties in vivo is often dictated by an asymmetric distribution of these molecules. Techniques for vesicle preparation have been based on the spontaneous assembly of lipid bilayers, precluding the formation of such asymmetric structures. Partial asymmetry has been achieved only with chemical methods greatly restricting the study of the physical and chemical properties of asymmetric vesicles and their use in potential applications for drug delivery. Here we describe the systematic engineering of unilamellar vesicles assembled with two independently prepared monolayers; this process produces asymmetries as high as 95%. We demonstrate the versatility of our method by investigating the stability of the asymmetry. We also use it to engineer hybrid structures comprised of an inner leaflet of diblock copolymer and an independent lipid outer leaflet. 10.1073/pnas.1931005100 Engineering asymmetric vesicles Sophie Pautot Barbara Frisken DA Weitz doi:10.1073/pnas.1931005100 Proceedings of the National Academy of Sciences, Vol. 100, No. 19. (16 September 2003), pp. 10718-10721. 2008-04-24T19:14:13-00:00 2003 Proceedings of the National Academy of Sciences 100 19 10718 10721 emulsion technique weitz http://www.citeulike.org/user/dchen/article/2683174 <i>Physical Review Letters, Vol. 100, No. 1. (2008)</i><br /><br />Cylindrical liquid jets are inherently unstable and eventually break into drops due to the Rayleigh-Plateau instability, characterized by the growth of disturbances that are either convective or absolute in nature. Convective instabilities grow in amplitude as they are swept along by the flow, while absolute instabilities are disturbances that grow at a fixed spatial location. Liquid jets are nearly always convectively unstable. Here we show that two-phase jets can breakup due to an absolute instability that depends on the capillary number of the outer liquid, provided the Weber number of the inner liquid is >O(1). We verify our experimental observations with a linear stability analysis. Absolute Instability of a Liquid Jet in a Coflowing Stream Andrew Utada Alberto Nieves Jose Gordillo David Weitz doi:10.1103/PhysRevLett.100.014502 Physical Review Letters, Vol. 100, No. 1. (2008) 2008-04-17T18:57:14-00:00 2008 Physical Review Letters 100 1 APS 2008 atlanta flow weitz http://www.citeulike.org/user/dchen/article/1685995 <i>Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 74, No. 6. (2006)</i><br /><br />We investigate clogging of microchannels at the single-pore level using microfluidic devices as model porous media. The process of clogging is studied at low volume fractions and high flow rates, a technologically important regime. We show that clogging is independent of particle flow rate and volume fraction, indicating that collective effects do not play an important role. Instead, the average number of particles that can pass through a pore before it clogs scales with the ratio of pore to particle size. We present a simple model that accounts for the data. Mechanism for clogging of microchannels Hans Wyss Daniel Blair Jeffrey Morris Howard Stone David Weitz doi:10.1103/PhysRevE.74.061402 Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 74, No. 6. (2006) 2007-09-22T19:57:03-00:00 2006 Physical Review E (Statistical, Nonlinear, and Soft Matter Physics) 74 6 APS microrheology weitz http://www.citeulike.org/user/dchen/article/2713647 <i>Science, Vol. 303, No. 5660. (13 February 2004), pp. 968-969.</i><br /><br />10.1126/science.1094581 PHYSICS: Packing in the Spheres David Weitz doi:10.1126/science.1094581 Science, Vol. 303, No. 5660. (13 February 2004), pp. 968-969. 2008-04-24T18:10:33-00:00 2004 Science 303 5660 968 969 review science weitz http://www.citeulike.org/user/dchen/article/2714497 <i>Science, Vol. 299, No. 5613. (14 March 2003), pp. 1716-1718.</i><br /><br />10.1126/science.1081160 Grain Boundary Scars and Spherical Crystallography AR Bausch MJ Bowick A Cacciuto AD Dinsmore MF Hsu DR Nelson MG Nikolaides A Travesset DA Weitz doi:10.1126/science.1081160 Science, Vol. 299, No. 5613. (14 March 2003), pp. 1716-1718. 2008-04-24T22:18:23-00:00 2003 Science 299 5613 1716 1718 2d crystal surface weitz http://www.citeulike.org/user/dchen/article/2709655 <i>Applied Physics Letters, Vol. 88, No. 26. (2006)</i><br /><br />View This Record in Scopus Electrocoalescence of drops synchronized by size-dependent flow in microfluidic channels Keunho Ahn Jeremy Agresti Henry Chong Manuel Marquez DA Weitz Applied Physics Letters, Vol. 88, No. 26. (2006) 2008-04-23T17:54:25-00:00 2006 Applied Physics Letters 88 26 AIP emulsion microrheology weitz http://www.citeulike.org/user/dchen/article/2679268 <i>Physical review letters, Vol. 96, No. 2. (20 January 2006)</i><br /><br />We show that colloidal particles with attractive interactions induced by a nonadsorbing polymer exhibit a stable phase consisting of a fluid of clusters of particles. This phase persists even in the absence of any long-range repulsion due to charge, contrary to expectations based on simulation and theory. Cluster morphology depends strongly on the range of the interparticle attraction: With a shorter range, clusters are tenuous and branched; with a longer range, they are more compact. Fluids of clusters in attractive colloids. PJ Lu JC Conrad HM Wyss AB Schofield DA Weitz Physical review letters, Vol. 96, No. 2. (20 January 2006) 2008-04-17T00:53:44-00:00 2006 Physical review letters 0031-9007 96 2 cluster colloids weitz http://www.citeulike.org/user/dchen/article/2709851 <i>Physical Review Letters, Vol. 96, No. 2. (2006)</i><br /><br />We show that colloidal particles with attractive interactions induced by a nonadsorbing polymer exhibit a stable phase consisting of a fluid of clusters of particles. This phase persists even in the absence of any long-range repulsion due to charge, contrary to expectations based on simulation and theory. Cluster morphology depends strongly on the range of the interparticle attraction: With a shorter range, clusters are tenuous and branched; with a longer range, they are more compact. Fluids of Clusters in Attractive Colloids Peter Lu Jacinta Conrad Hans Wyss Andrew Schofield David Weitz doi:10.1103/PhysRevLett.96.028306 Physical Review Letters, Vol. 96, No. 2. (2006) 2008-04-23T19:32:58-00:00 2006 Physical Review Letters 96 2 APS cluster colloids weitz http://www.citeulike.org/user/dchen/article/2713643 <i>Journal of Fluid Mechanics, Vol. 501, No. -1. (2004), pp. 71-104.</i> A model for velocity fluctuations in sedimentation Peter Mucha Shang-You Tee David Weitz Boris Shraiman Michael Brenner Journal of Fluid Mechanics, Vol. 501, No. -1. (2004), pp. 71-104. 2008-04-24T18:08:14-00:00 2004 Journal of Fluid Mechanics 501 -1 71 104 flow gravity weitz http://www.citeulike.org/user/dchen/article/2714504 <i>Colloids and Surfaces A: Physicochemical and Engineering Aspects, Vol. 213, No. 2-3. (12 February 2003), pp. 189-197.</i><br /><br />Suspensions of clay particles (laponite), mixed with poly(ethylene oxide) (PEO) undergo a dramatic shear thickening when subjected to vigorous shaking, which transforms them from a low viscosity fluid into a [`]shake-gel', a solid with elasticity sufficient enough to support its own weight. The shake-gel is reversible, relaxing back to a fluid with a relaxation time that is strongly dependent on PEO concentration. Shake-gels are observed for PEO concentrations slightly below the threshold for complete saturation of the laponite particles by the polymer. Light scattering measurements confirm that the PEO is adsorbed on the surface of the laponite particles, and suggests that shear induces a bridging between the colloidal particles, resulting in a gel network which spans the system. Desorption of the polymer reduces the bridging and thus relaxes the network. Shake-gels: shear-induced gelation of laponite-PEO mixtures J Zebrowski V Prasad W Zhang LM Walker DA Weitz doi:10.1016/S0927-7757(02)00512-5 Colloids and Surfaces A: Physicochemical and Engineering Aspects, Vol. 213, No. 2-3. (12 February 2003), pp. 189-197. 2008-04-24T22:24:38-00:00 2003 Colloids and Surfaces A: Physicochemical and Engineering Aspects 213 2-3 189 197 gel shear weitz http://www.citeulike.org/user/dchen/article/553502 <i>Nature, Vol. 440, No. 7082., pp. 319-323.</i> Visualizing dislocation nucleation by indenting colloidal crystals Peter Schall Itai Cohen David Weitz Frans Spaepen doi:10.1038/nature04557 Nature, Vol. 440, No. 7082., pp. 319-323. 2006-03-15T23:36:35-00:00 Nature 0028-0836 440 7082 319 323 Nature Publishing Group defect schall shear weitz http://www.citeulike.org/user/dchen/article/2453811 <i>Science, Vol. 318, No. 5858. (21 December 2007), pp. 1895-1899.</i><br /><br />Structural rearrangements are an essential property of atomic and molecular glasses; they are critical in controlling resistance to flow and are central to the evolution of many properties of glasses, such as their heat capacity and dielectric constant. Despite their importance, these rearrangements cannot directly be visualized in atomic glasses. We used a colloidal glass to obtain direct three-dimensional images of thermally induced structural rearrangements in the presence of an applied shear. We identified localized irreversible shear transformation zones and determined their formation energy and topology. A transformation favored successive ones in its vicinity. Using continuum models, we elucidated the interplay between applied strain and thermal fluctuations that governs the formation of these zones in both colloidal and molecular glasses. 10.1126/science.1149308 Structural Rearrangements That Govern Flow in Colloidal Glasses Peter Schall David Weitz Frans Spaepen doi:10.1126/science.1149308 Science, Vol. 318, No. 5858. (21 December 2007), pp. 1895-1899. 2008-03-01T21:29:01-00:00 2007 Science 318 5858 1895 1899 colloids flow schall shear stz weitz http://www.citeulike.org/user/dchen/article/2710276 <i>Langmuir, Vol. 21, No. 7. (29 March 2005), pp. 2963-2970.</i><br /><br />Abstract: We construct shells with tunable morphology and mechanical response with colloidal particles that self-assemble at the interface of emulsion droplets. Particles self-assemble to minimize the total interfacial energy, spontaneously forming a particle layer that encapsulates the droplets. We stabilize these layers to form solid shells at the droplet interface by aggregating the particles, connecting the particles with adsorbed polymer, or fusing the particles. These techniques reproducibly yield shells with controllable properties such as elastic moduli and breaking forces. To enable diffusive exchange through the particle shells, we transfer them into solvents that are miscible with the encapsulant. We characterize the mechanical properties of the shells by measuring the response to deformation by calibrated microcantilevers. Self-assembled Shells Composed of Colloidal Particles: Fabrication and Characterization MF Hsu MG Nikolaides AD Dinsmore AR Bausch VD Gordon X Chen JW Hutchinson DA Weitz M Marquez doi:10.1021/la0472394 Langmuir, Vol. 21, No. 7. (29 March 2005), pp. 2963-2970. 2008-04-23T21:31:14-00:00 2005 Langmuir 21 7 2963 2970 colloids dinsmore emulsion technique weitz http://www.citeulike.org/user/dchen/article/2709589 <i>J. Am. Chem. Soc., Vol. 128, No. 44. (8 November 2006), pp. 14374-14377.</i><br /><br />Abstract: We describe a promising and flexible technique for fabricating uniform nonspherical particles with anisotropic phase and surface properties. Our approach is based on the seeded polymerization technique in which monomer-swollen particles are polymerized. The polymerization causes a phase separation to occur, giving rise to two-phase nonspherical particles. We show that the elastic contraction of the swollen polymer particles induced by elevated polymerization temperatures plays an important role in the phase separation. Moreover, chemical anisotropy of nonspherical particles can be obtained by using immiscible polymer pairs and by employing surface treatments. Furthermore, we are able to produce amphiphilic dumbbell particles consisting of two different bulbs: hydrophilic poly (ethylene imine)-coated polystyrene and hydrophobic polystyrene. Controlled geometries of these amphiphilic nonspherical particles will allow a wide range of potential applications, such as engineered colloid surfactants. Synthesis of Nonspherical Colloidal Particles with Anisotropic Properties JW Kim RJ Larsen DA Weitz doi:10.1021/ja065032m J. Am. Chem. Soc., Vol. 128, No. 44. (8 November 2006), pp. 14374-14377. 2008-04-23T17:26:53-00:00 2006 J. Am. Chem. Soc. 128 44 14374 14377 2006 colloids weitz http://www.citeulike.org/user/dchen/article/2710273 <i>Science, Vol. 308, No. 5721. (22 April 2005), pp. 537-541.</i><br /><br />Double emulsions are highly structured fluids consisting of emulsion drops that contain smaller droplets inside. Although double emulsions are potentially of commercial value, traditional fabrication by means of two emulsification steps leads to very ill-controlled structuring. Using a microcapillary device, we fabricated double emulsions that contained a single internal droplet in a core-shell geometry. We show that the droplet size can be quantitatively predicted from the flow profiles of the fluids. The double emulsions were used to generate encapsulation structures by manipulating the properties of the fluid that makes up the shell. The high degree of control afforded by this method and the completely separate fluid streams make this a flexible and promising technique. 10.1126/science.1109164 Monodisperse Double Emulsions Generated from a Microcapillary Device AS Utada E Lorenceau DR Link PD Kaplan HA Stone DA Weitz doi:10.1126/science.1109164 Science, Vol. 308, No. 5721. (22 April 2005), pp. 537-541. 2008-04-23T21:28:11-00:00 2005 Science 308 5721 537 541 emulsion microrheology weitz http://www.citeulike.org/user/dchen/article/2713958 <i>Langmuir, Vol. 19, No. 24. (25 November 2003), pp. 10281-10287.</i><br /><br />Abstract: We report the spontaneous formation of emulsion droplets and multilamellar concentric onions when a water drop is immersed into dodecane containing phospholipids. We show that the origin of the spontaneous emulsification is the formation of a semicrystalline multilamellar film at the dodecane-water interface, which swells with water, shedding the emulsion and onion droplets. We use coherent anti-Stokes Raman scattering microscopy to determine that the shell of the onion structures is composed of partially hydrated concentric bilayers, and the core is composed of lipids, water, and dodecane. Spontaneous Formation of Lipid Structures at Oil/Water/Lipid Interfaces S Pautot BJ Frisken JX Cheng XS Xie DA Weitz doi:10.1021/la034532f Langmuir, Vol. 19, No. 24. (25 November 2003), pp. 10281-10287. 2008-04-24T19:05:39-00:00 2003 Langmuir 19 24 10281 10287 interface weitz http://www.citeulike.org/user/dchen/article/2730434 <i>Physical Review Letters, Vol. 69, No. 16. (19 October 1992), 2439.</i> Stability criteria for emulsions J Bibette DC Morse TA Witten DA Weitz doi:10.1103/PhysRevLett.69.2439 Physical Review Letters, Vol. 69, No. 16. (19 October 1992), 2439. 2008-04-28T16:23:12-00:00 1992 Physical Review Letters 69 16 2439 American Physical Society emulsion mason weitz http://www.citeulike.org/user/dchen/article/2722885 <i>Physical Review E, Vol. 52, No. 6. (1 December 1995), 6289.</i> Thermal fluctuations of the shapes of droplets in dense and compressed emulsions Hu Gang AH Krall DA Weitz doi:10.1103/PhysRevE.52.6289 Physical Review E, Vol. 52, No. 6. (1 December 1995), 6289. 2008-04-27T00:26:02-00:00 1995 Physical Review E 52 6 6289 American Physical Society emulsion fluctuation temperature weitz http://www.citeulike.org/user/dchen/article/2265040 <i>Proceedings of the National Academy of Sciences, Vol. 104, No. 41. (9 October 2007), pp. 16128-16133.</i><br /><br />Microtubules are highly dynamic biopolymer filaments involved in a wide variety of biological processes including cell division, migration, and intracellular transport. Microtubules are very rigid and form a stiff structural scaffold that resists deformation. However, despite their rigidity, inside of cells they typically exhibit significant bends on all length scales. Here, we investigate the origin of these bends using a Fourier analysis approach to quantify their length and time dependence. We show that, in cultured animal cells, bending is suppressed by the surrounding elastic cytoskeleton, and even large intracellular forces only cause significant bending fluctuations on short length scales. However, these lateral bending fluctuations also naturally cause fluctuations in the orientation of the microtubule tip. During growth, these tip fluctuations lead to microtubule bends that are frozen-in by the surrounding elastic network. This results in a persistent random walk of the microtubule, with a small apparent persistence length of approx30 microm, approx100 times smaller than that resulting from thermal fluctuations alone. Thus, large nonthermal forces govern the growth of microtubules and can explain the highly curved shapes observed in the microtubule cytoskeleton of living cells. 10.1073/pnas.0703094104 Force fluctuations and polymerization dynamics of intracellular microtubules Clifford Brangwynne FC Mackintosh David Weitz doi:10.1073/pnas.0703094104 Proceedings of the National Academy of Sciences, Vol. 104, No. 41. (9 October 2007), pp. 16128-16133. 2008-01-21T00:56:00-00:00 2007 Proceedings of the National Academy of Sciences 104 41 16128 16133 2007 biology microfluid weitz http://www.citeulike.org/user/dchen/article/2710262 <i>Langmuir, Vol. 21, No. 11. (24 May 2005), pp. 4881-4887.</i><br /><br />Abstract: While the important role of electrostatic interactions in aqueous colloidal suspensions is widely known and reasonably well-understood, their relevance to nonpolar suspensions remains mysterious. We measure the interaction potentials of colloidal particles in a nonpolar solvent with reverse micelles. We find surprisingly strong electrostatic interactions characterized by surface potentials, e, from 2.0 to 4.4 kBT and screening lengths, -1, from 0.2 to 1.4 m. Interactions depend on the concentration of reverse micelles and the degree of confinement. Furthermore, when the particles are weakly confined, the values of e and extracted from interaction measurements are consistent with bulk measurements of conductivity and electrophoretic mobility. A simple thermodynamic model, relating the structure of the micelles to the equilibrium ionic strength, is in good agreement with both conductivity and interaction measurements. Since dissociated ions are solubilized by reverse micelles, the entropic incentive to charge a particle surface is qualitatively changed from aqueous systems, and surface entropy plays an important role. Charge Stabilization in Nonpolar Solvents MF Hsu ER Dufresne DA Weitz doi:10.1021/la046751m Langmuir, Vol. 21, No. 11. (24 May 2005), pp. 4881-4887. 2008-04-23T21:21:25-00:00 2005 Langmuir 21 11 4881 4887 micelle weitz http://www.citeulike.org/user/dchen/article/1203416 <i>Physical Review Letters, Vol. 89, No. 9. (2002), 095704.</i><br /><br />We use confocal microscopy to study particle motion in colloidal systems. Near the glass transition; motion is inhibited; as particles spend time trapped in transient “cages” formed by neighboring particles. We measure the cage sizes and lifetimes; which; respectively; shrink and grow as the glass transition approaches. Cage rearrangements are more prevalent in regions with lower concentrations and higher disorder. Neighboring rearranging particles typically move in parallel directions; although a nontrivial fraction moves in antiparallel directions; usually from particle pairs with initial separations corresponding to local maxima and minima of the pair correlation function g ( r ); respectively. Properties of Cage Rearrangements Observed near the Colloidal Glass Transition Eric Weeks DA Weitz doi:10.1103/PhysRevLett.89.095704 Physical Review Letters, Vol. 89, No. 9. (2002), 095704. 2007-04-02T22:33:06-00:00 2002 Physical Review Letters 89 9 095704 American Physical Society glass review weeks weitz http://www.citeulike.org/user/dchen/article/2683459 <i>Advanced Materials, Vol. 19, No. 15. (2007), pp. 2005-2009.</i><br /><br />No abstract. Uniform Nonspherical Colloidal Particles with Tunable Shapes JW Kim R J Larsen D A Weitz doi:10.1002/adma.200602345 Advanced Materials, Vol. 19, No. 15. (2007), pp. 2005-2009. 2008-04-17T20:35:27-00:00 2007 Advanced Materials 19 15 2005 2009 2007 colloids technique weitz http://www.citeulike.org/user/dchen/article/2688208 <i>Chemical Engineering Science, Vol. 62, No. 4. (February 2007), pp. 1042-1048.</i><br /><br />We use a microdevice where microdroplets of reagents are generated and coalesce in a carrier continuous phase. The work focuses on the characterization of the mixing step inside the droplets, in the perspective to use them for chemical kinetic data acquisition. A dye and water are used, and an acid-base instantaneous chemical reaction is monitored thanks to a colored indicator. Acquisitions are done with a high-speed camera coupled to a microscope and a mixing parameter is calculated by image analysis. Different angles of bended channels and different ways of coalescence are compared. It is shown that the homogenization of the droplets can be reached in less than 10 ms after coalescence. This is achieved by forcing the droplets to coalesce in a "shifted" way, and later by adding 45o angle bends along the channel. Mixing characterization inside microdroplets engineered on a microcoalescer F Sarrazin L Prat N Di Miceli G Cristobal DR Link DA Weitz doi:10.1016/j.ces.2006.10.013 Chemical Engineering Science, Vol. 62, No. 4. (February 2007), pp. 1042-1048. 2008-04-18T15:32:47-00:00 2007 Chemical Engineering Science 62 4 1042 1048 2007 microrheology weitz http://www.citeulike.org/user/dchen/article/2709644 <i>Langmuir, Vol. 22, No. 14. (4 July 2006), pp. 6024-6030.</i><br /><br />Abstract: Spray drying of complex liquids to form solid powders is important in many industrial applications. One of the challenges associated with spray drying is controlling the morphologies of the powders produced; this requires an understanding of how drying mechanics depend on the ingredients and conditions. We demonstrate that the morphology of powders produced by spray drying colloidal polystyrene (PS) suspensions can be significantly altered by changing the molecular weight of dissolved poly(ethylene oxide) (PEO). Samples containing high-molecular-weight PEO produce powders with more crumpled morphologies than those containing low-molecular-weight PEO. Observations of drying droplets suspended by a thin film of vapor suggest that this occurs because the samples with high-molecular-weight PEO buckle earlier in the drying process when the droplets are larger. Earlier buckling times are likely caused by the decreased stability, demonstrated by bulk rheology experiments, of PS particles in the presence of high-molecular-weight PEO at elevated temperatures. We present a consistent picture in which decreased particle stability hastens droplet buckling and leads to more crumpled powder morphologies; this underscores the importance of interparticle forces in determining the buckling of particle-laden droplets. Buckling and Crumpling of Drying Droplets of Colloid-Polymer Suspensions Y Sugiyama RJ Larsen JW Kim DA Weitz doi:10.1021/la053419h Langmuir, Vol. 22, No. 14. (4 July 2006), pp. 6024-6030. 2008-04-23T17:51:21-00:00 2006 Langmuir 22 14 6024 6030 colloids drying weitz