Sat, 19 Jul 2008 03:08:04 BST CiteULike: dchen's Poon http://www.citeulike.org/user/dchen/author/Poon CiteULike.org en-gb Copyright © 2004-2008 citeulike.org http://www.citeulike.org/user/dchen/article/2801926 <i>Fungal Genetics and Biology, Vol. 44, No. 1. (January 2007), pp. 1-13.</i><br /><br />Optical tweezers have been little used in experimental studies on filamentous fungi. We have built a simple, compact, easy-to-use, safe and robust optical tweezer system that can be used with brightfield, phase contrast, differential interference contrast and fluorescence optics on a standard research grade light microscope. We have used this optical tweezer system in a range of cell biology applications to trap and micromanipulate whole fungal cells, organelles within cells, and beads. We have demonstrated how optical tweezers can be used to: unambiguously determine whether hyphae are actively homing towards each other; move the Spitzenkörper and change the pattern of hyphal morphogenesis; make piconewton force measurements; mechanically stimulate hyphal tips; and deliver chemicals to localized regions of hyphae. Significant novel experimental findings from our study were that germ tubes generated significantly smaller growth forces than leading hyphae, and that both hyphal types exhibited growth responses to mechanical stimulation with optically trapped polystyrene beads. Germinated spores that had been optically trapped for 25 min exhibited no deleterious effects with regard to conidial anastomosis tube growth, homing or fusion. Optical tweezer micromanipulation of filamentous fungi Graham Wright Jochen Arlt Wilson Poon Nick Read doi:10.1016/j.fgb.2006.07.002 Fungal Genetics and Biology, Vol. 44, No. 1. (January 2007), pp. 1-13. 2008-05-15T14:58:07-00:00 2007 Fungal Genetics and Biology 44 1 1 13 2006 biology opticaltweezer poon tracer http://www.citeulike.org/user/dchen/article/2800338 <i>Langmuir, Vol. 23, No. 11. (22 May 2007), pp. 5984-5994.</i><br /><br />Abstract: We present microscopy studies of particle-stabilized emulsions with unconventional morphologies. The emulsions comprise pairs of partially miscible fluids and are stabilized by colloids. Alcohol-oil mixtures are employed; silica colloids are chemically modified so that they have partial wettability. We create our morphologies by two distinct routes: starting with a conventional colloid-stabilized emulsion or starting in the single-fluid phase with the colloids dispersed. In the first case temperature cycling leads to the creation of extended fluid domains built around some of the initial fluid droplets. In the second case quenching into the demixed region leads to the formation of domains which reflect the demixing kinetics. The structures are stable due to a jammed, semisolid, multilayer of colloids on the liquid-liquid interface. The differing morphologies reflect the roles in formation of the arrested state of heterogeneous and homogeneous nucleation and spinodal decomposition. The latter results in metastable, bicontinuous emulsions with frozen interfaces, at least for the thin-slab samples, investigated here. Emulsification of Partially Miscible Liquids Using Colloidal Particles: Nonspherical and Extended Domain Structures PS Clegg EM Herzig AB Schofield SU Egelhaaf TS Horozov BP Binks ME Cates WCK Poon doi:10.1021/la063707t Langmuir, Vol. 23, No. 11. (22 May 2007), pp. 5984-5994. 2008-05-15T00:03:54-00:00 2007 Langmuir 23 11 5984 5994 colloids cool emulsion phase poon system http://www.citeulike.org/user/dchen/article/2735404 <i>Nature materials, Vol. 6, No. 12. (December 2007), pp. 966-971.</i><br /><br />Recent large-scale computer simulations suggest that it may be possible to create a new class of soft solids, called 'bijels', by stabilizing and arresting the bicontinuous interface in a binary liquid demixing via spinodal decomposition using particles that are neutrally wetted by both liquids. The interfacial layer of particles is expected to be semi-permeable; hence, if realized, these new materials would have many potential applications, for example, as micro-reaction media. However, the creation of bijels in the laboratory faces serious obstacles. In general, fast quench rates are necessary to bypass nucleation, so that only samples with limited thickness can be produced, which destroys the three-dimensionality of the putative bicontinuous network. Moreover, even a small degree of unequal wettability of the particles by the two liquids can lead to ill-characterized, 'lumpy' interfacial layers and therefore irreproducible material properties. Here, we report a reproducible protocol for creating three-dimensional samples of bijel in which the interfaces are stabilized by essentially a single layer of particles. We demonstrate how to tune the mean interfacial separation in these bijels, and show that mechanically, they indeed behave as soft solids. These characteristics and their tunability will be of great value for microfluidic applications. Bicontinuous emulsions stabilized solely by colloidal particles. EM Herzig KA White AB Schofield WC Poon PS Clegg doi:10.1038/nmat2055 Nature materials, Vol. 6, No. 12. (December 2007), pp. 966-971. 2008-04-29T20:39:54-00:00 2007 Nature materials 1476-1122 6 12 966 971 2007 binary colloids edinburgh emulsion interface nature poon http://www.citeulike.org/user/dchen/article/2719797 <i>Physical Review E, Vol. 57, No. 6. (1 June 1998), 6859.</i> Direct observation of oscillatory-shear-induced order in colloidal suspensions MD Haw WCK Poon PN Pusey doi:10.1103/PhysRevE.57.6859 Physical Review E, Vol. 57, No. 6. (1 June 1998), 6859. 2008-04-25T23:58:33-00:00 1998 Physical Review E 57 6 6859 American Physical Society crystallization edinburgh poon shear http://www.citeulike.org/user/dchen/article/688326 <i>Journal of Physics: Conference Series, Vol. 40, No. 1. (2006), 124.</i> Experimental studies of the flow of concentrated hard sphere suspensions into a constriction L Isa R Besseling ER Weeks WCK Poon doi:10.1088/1742-6596/40/1/016 Journal of Physics: Conference Series, Vol. 40, No. 1. (2006), 124. 2006-06-07T11:46:33-00:00 2006 Journal of Physics: Conference Series 1742-6596 40 1 124 Institute of Physics Publishing flow poon weeks http://www.citeulike.org/user/dchen/article/2713611 <i>Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 76, No. 4. (2007)</i><br /><br />We have studied the behavior of a colloidal gel under oscillatory shear. The quiescent gel was an arrested structure formed by a 40% volume fraction hard-sphere suspension in which a “depletion” interparticle attraction was induced by adding nonadsorbing polymer. We applied progressively larger amplitude oscillatory shear to the sample, and observed its behavior using conventional and confocal microscopy as well as dynamic light scattering echo spectroscopy. We find that, to within experimental uncertainties, the point at which irreversible particle rearrangements (or yielding) occur coincides with the observation of crystallization. We summarize our findings in a “shear state diagram.” The strain amplitude required for yielding/crystallization increases with decreasing oscillation frequency. We can quantitatively account for our observations by estimating the effect of shear on the probability for a particle to escape from the attractive potential of its neighbor using a Kramers approach. Yielding and crystallization of colloidal gels under oscillatory shear PA Smith G Petekidis SU Egelhaaf WCK Poon doi:10.1103/PhysRevE.76.041402 Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 76, No. 4. (2007) 2008-04-24T17:45:46-00:00 2007 Physical Review E (Statistical, Nonlinear, and Soft Matter Physics) 76 4 APS 2007 colloids gel poon pre shear http://www.citeulike.org/user/dchen/article/2670772 <i>Nature, Vol. 367, No. 6463. (10 February 1994), pp. 541-543.</i> Deformation-induced nanocrystal formation in shear bands of amorphous alloys H Chen Y He GJ Shiflet SJ Poon doi:10.1038/367541a0 Nature, Vol. 367, No. 6463. (10 February 1994), pp. 541-543. 2008-04-14T22:43:53-00:00 1994 Nature 367 6463 541 543 application shear shearband http://www.citeulike.org/user/dchen/article/2453919 <i>Physical Review E, Vol. 69, No. 1. (28 January 2004), 011503.</i><br /><br />We report a detailed experimental study of the structure and dynamics of glassy states in hard spheres with short-range attraction. The system is a suspension of nearly hard-sphere colloidal particles and nonadsorbing linear polymer which induces a depletion attraction between the particles. Observation of crystallization reveals a reentrant glass transition. Static light scattering shows a continuous change in the static structure factors upon increasing attraction. Dynamic light scattering results; which cover 11 orders of magnitude in time; are consistent with the existence of two distinct kinds of glasses; those dominated by interparticle repulsion and caging; and those dominated by attraction. Samples close to the “ A 3 point” predicted by mode coupling theory for such systems show very slow; logarithmic dynamics. Glasses in hard spheres with short-range attraction KN Pham SU Egelhaaf PN Pusey WCK Poon doi:10.1103/PhysRevE.69.011503 Physical Review E, Vol. 69, No. 1. (28 January 2004), 011503. 2008-03-01T22:40:03-00:00 2004 Physical Review E 69 1 011503 American Physical Society depletion glass poon