Sat, 26 Jul 2008 08:39:26 BST CiteULike: dchen Frisken http://www.citeulike.org/user/dchen/author/Frisken CiteULike.org en-gb Copyright © 2004-2008 citeulike.org 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/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/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