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Topic: Polydispersity

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	Polydispersity (Site not responding. Last check: 2007-10-19)
		The influence of this polydispersity on the phase behavior of colloidal dispersions is not well understood.
		In the next chapter we discuss the effect of polydispersity on the freezing of hard spheres.
		In this section we combine the methods of this and the next chapter to assess the influence of polydispersity on the solid-solid transition.
	www.science.uva.nl /~bolhuis/ths/pages/node33.html (279 words)

	A novel hplc assay for pentamidine: comparative effects of creatinine and inulin on gfr estimation and pentamidine ... (Site not responding. Last check: 2007-10-19)
		The aim of the present study is to investigate the effect of powder polydispersity on the aerosol generation in vitro.
		The polydispersity of the powder was expressed by the span.
		The present study investigated the role of the primary powder polydispersity on the generation of dry powder aerosols, using mannitol and BSA as model compounds.
	www.ualberta.ca /~csps/JPPS5(2)/N.Chew/aerosol.htm (2786 words)

	Introduction
		The influence of polydispersity on the solid-fluid transition in colloidal suspensions was first examined by Dickinson and Parker [78,79,80].
		For a triangular distribution, Dickinson and Parker extrapolated the change in volume upon melting to zero, and estimated the terminal polydispersity at 11% (we define the polydispersity as the standard deviation of the particle size distribution, divided by the mean).
		The purpose of the present work is to determine rigorously the phase diagram of polydisperse hard spheres by molecular simulation, establish the terminal polydispersity and test the validity of the constrained eutectic assumption made explicit in ref. [83].
	www.science.uva.nl /~bolhuis/ths/pages/node36.html (793 words)

	The phase behavior of polydisperse multiblock copolymer melts : (a theoretical study)
		The main theme of this thesis is the influence of polydispersity on the phase behavior of copolymer melts.
		Study of the influence of polydispersity is important because synthesizing purely monodisperse copolymers is very difficult, and for most polymerization techniques the occurrence of a certain degree of polydispersity is inevitable.
		By changing continuously the degree of polydispersity, it is possible to study its influence on the phase behavior.
	dissertations.ub.rug.nl /faculties/science/1998/h.j.angerman (954 words)

	Encapsulation of Protein Nanoparticles Into Uniform-sized Microspheres Formed in a Spinning Oil Film
		In contrast, large burst release was observed for polydisperse microspheres produced by a conventional emulsification technique, particularly for microspheres smaller than 25 μm in diameter, which gave 93% burst at 15% loading.
		Polydispersity was calculated as the standard deviation of all measured microsphere radii divided by the average radius.
		Microspheres from a single polydisperse emulsion were separated with sieves into (A) 0 to 25 μm, (B) 25 to 50 μm, (C) 50 to 100 μm, and (D) 100 to 150 μm size classes.
	www.aapspharmscitech.org /view.asp?art=pt060475 (7087 words)

	Patent 6,126,919
		This surprising effect is accomplished by limiting the polydispersity (i.e., the ratio of weight-average to number-average molecular weight) of the polymer to a relatively narrow range as compared to the normally occurring distribution (i.e., the molecular weight distribution that occurs normally from the conventional polymerization methods).
		It is hypothesized that this unexpected improvement is the result of several factors: reducing the amount of the slowly degrading high molecular weight component of the polymer reduces the polymer's overall biological half-life; while reducing the amount of the plasticizing low molecular weight component of the polymer raises the Tg of the material.
		Additionally, normal polydispersity poly-L-lactic acids with molecular weights greater than about 800 may exhibit partial insolubility (depending on the weight percentage, propellant used, and the presence of co-solvents or other excipients) of the highest molecular weight fraction of the polymer.
	www.pharmcast.com /Patents/October2000/100300OG/6126919_Biocompatible1003000.htm (2771 words)

	Research (Site not responding. Last check: 2007-10-19)
		Polydispersity in particular has applications in the thermodynamic aspect of enhanced recovery of oil and gas reserves and mitigating fouling and scale formation due to wax and asphaltene precipitation as well as in the polymer industry where the phase behavior is qualitatively modified due to the presence of polydispersity.
		Fundamental contributions have been made to elucidate the effect of chain length and compositional polydispersity on the phase behavior of copolymer solutions.
		The methodologies developed during my research at Rice are characterized by the invariance of the size of the system of equations with increasing number of pseudocomponents used to represent the molecular weight or compositional distribution.
	www.owlnet.rice.edu /~aghosh/Research.html (336 words)

	Akhremitchev Research - AFM force spectroscopy experiments
		In order to be able to discriminate single- and double- tether events, the polydispersity of tether lengths he as to be known.
		These expected values are indicated wih vertical bars in the figure to the right and for PEG with average molecular weight of 3350 the double-tether range is from ~37 nm up to 75 nm.
		The range is so large in part due to polydispersity of commercial PEG linkers and in part due to conformational transition of PEG from helical to stretched (planar) monomer conformation.
	www.chem.duke.edu /~boris/research/force_spectroscopy/force_experiments.htm (2391 words)

	U.S. Patent: 6143820 - Preparation of a low polydisperse water-soluble polymeric composition - November 7, 2000
		A water-soluble polymer having a low polydispersity index and controlled molecular weight can be prepared by oxidative degradation and shearing of a water-swellable crosslinked polymer or by hydrolysis of the crosslinked polymer to a high molecular weight soluble polymer, followed by oxidative degradation of the high molecular weight polymer.
		Although the theoretical limit for polydispersity (M.sub.w /M.sub.n) in radical chain polymerizations is 1.5 or less, in practice the distribution is greater than 2.
		Another method for preparing low molecular weight low polydisperse acid polymers is to oxidatively degrade a soluble higher molecular weight polymer to a lower molecular weight lower polydisperse polymer, as described in EP 0404377 A1, which teachings are incorporated herein by reference.
	www.everypatent.com /comp/pat6143820.html (3111 words)

	Process for polymerizing vinyl chloride polymers with iodinated chain transfer agents - Patent 5455319
		The resin obtained has reduced molecular weight and polydispersity, good thermal stability, and enhanced mechanical properties, compared to poly(vinyl halide) conventionally formed by free radical methods at higher temperatures and/or with the use of conventional chain transfer agents for vinyl halide polymer.
		The polydispersity of the poly(vinyl halide) resin is the ratio of the weight average molecular weight to the number average molecular weight.
		A lower polydispersity enhances the mechanical properties of the resulting poly(vinyl chloride) resin by eliminating the low molecular weight fraction that has chains shorter than the critical chain entanglement length.
	www.freepatentsonline.com /5455319.html (6144 words)

	Shea Research Group (Site not responding. Last check: 2007-10-19)
		The reaction offers a degree of control of molecular weight, linearity, polydispersity, functionality and topology that is difficult to achieve by other means.
		The very low polydispersity and molecular weight control of the polyhomologation reaction provides material for testing some of the most fundamental assumptions concerning solution behavior of branched polymers.
		The sp3-sp3 carbon-carbon bond-forming step is common to a number of synthetically important reactions in chemistry so we have initiated a detailed mechanistic investigation of this reaction.
	chem.ps.uci.edu /~kjshea/research/webpolysynth.htm (328 words)

	CHARACTERIZATION THE HYDROLYTIC DEGRADATION OF PLA AND ITS COPOLYMERS
		The major factors, affecting the rate and the mechanism (mode) of the degradation of these polymers, are copolymer composition, hydrophilicity, molecular weight, polydispersity, polymer morphology, size and the shape of the sample, end groups and the conditions of the degradation.
		Whereas, a non-random chain scission in the vicinity of the branching points of the backbone was found for the graft polyester with dextran sodium sulphate (DSS) as a backbone.
		Transparency of PLLA films, measured by a spectrophotometer at 570 nm, was ascribed to the increased density of spherulites.
	www.angelfire.com /pa5/parag/Report01.htm (5648 words)

	Research Projects \| The O'Hern Group
		As long as the magnitude of the charge polydispersity is small, the freezing transition will not be altered significantly.
		With strong charge polydispersity, the system can become trapped in a metastable disordered glassy state characterized by anomalously large viscosities and relaxation times that exceed experimental time scales.
		For large polydispersity and the same temperature, the crystal structure no longer exists, but there are mesoscopic regions that seem to be denser than their surroundings.
	research.yale.edu /jamming/?q=research/projects (3592 words)

	COLL 177 - Effect of of polydispersity on adsorption of poly(vinyl caprolactam)s and correlation with their phase ... (Site not responding. Last check: 2007-10-19)
		Effect of of polydispersity on adsorption of poly(vinyl caprolactam)s and correlation with their phase behavior
		The lower critical solution temperature (LCST) of these polymers was in qualitative agreement with Flory-Huggins°¦ polymer theory, with the adsorption density at the silica/water interface correlating with molecular weight as MW 0.16p0.04.
		Clearly the properties of PVCAP are not only affected by the apparent molecular weight of the polymer, but also its polydispersity and the reasons for this are explored with the help of electrokinetic and flocculation/dispersion results for the system.
	membership.acs.org /c/coll/neworleans/P629456.HTM (265 words)

	Polymer Applications of SCF - Phasex Corporation
		It is possible to tailor the performance of polymers by modifying certain properties such as molecular weight, polydispersity, or crystallinity via supercritical fluid extraction or fractionation.
		An example is presented to demonstrate the effectiveness of SCF fractionation in preparing narrow polydispersity polymer fractions which are useful in characterizing structure-property relations, elucidating reaction kinetics, and even as calibration standards.
		The polydispersity of the parent polymer shown is 1.87.
	www.phasex4scf.com /supercritical_markets/supercritical_fluids_polymers.htm (1421 words)

	Project Summary
		In between attempts to add particles, the other attached particles on the surface are allowed to diffuse for a long-time to equilibrate on the surface.
		Figure 2: Polydispersity/tether length (non-dimensionalized by the particle radius) phase diagram for adsorption of polydisperse tethered particles.
		This computational study demonstrated the feasibility of using molecular tethers for controlling order-disorder in 2D nanoparticulate films and set targets for the tether-lengths and maximum polydispersity of the particles for order to help chemists and materials scientists synthesize these materials.
	www.che.utexas.edu /fluids-group/self-assembly.htm (817 words)

	Higher Order Liquid Crystalline Structure in Low-Polydispersity DEH-PPV
		Since optical and electrical properties of polymer electronics are closely related to the structure and morphology of the active layer, morphological control is important for the fabrication of PPV-based devices.
		The orientation of molecules within the aligned layers was characterized by polarization-dependent X-ray absorption spectroscopy, and the PPV molecular axis was found to align parallel to the shear direction while the layers aligned perpendicular to the shear direction.
		Low polydispersity is critical to forming these types of highly ordered structures, and an analogous PPV sample with polydispersity greater than 5 does not form smectic layers.
	pubs.acs.org /cgi-bin/abstract.cgi/mamobx/2006/39/i13/abs/ma060164l.html (276 words)

	The effects of size polydispersity in nearly hard sphere colloids
		We have investigated the effects of size polydispersity on glass transition in nearly hard sphere colloidal systems in non-equilibrium condition after rapid compression by the Brownian dynamics simulation method.
		The interparticle interaction is chosen as the Yukawa potential and the size distribution of colloidal particles is assumed to be Gaussian.
		We also mention the possibility that by performing Browian dynamics simulations on colloidal systems with a sufficiently reduced level of thermal noise, one can observe glass transition.
	www.edpsciences.org /articles/jp2/abs/1993/08/jp2v3p1179/jp2v3p1179.html (197 words)

	e-Polymers (Site not responding. Last check: 2007-10-19)
		By using an atom transfer process we are able to control the polydispersity and molecular weight of the parent polymer.
		We are then able to cleave this polymer from the resin and analyse it using NMR and GPC to assess its molecular weight and polydispersity.
		By washing with a good hydrogen bond donor solvent, trifluoroethanol we are then able to separate the daughter strand and analyse it using NMR and GPC to assess its polydispersity.
	www.e-polymers.org /abstract_shw.cfm?Abstract_id=315 (304 words)

	Effect of Polydispersity on the Formation of Vesicles from Amphiphilic Diblock Copolymers (Site not responding. Last check: 2007-10-19)
		Using a continuous chain length distribution, the effect of polydispersity on the structures of vesicles self-assembled by amphiphilic polydisperse diblock copolymers in dilute solutions is investigated by two-dimensional (2D) real-space self-consistent-field theory.
		This polydispersity effect can be attributed to the segregation of copolymers according to their chain lengths.
		Second, there is a separation of copolymers to the inner and outer monolayers of the bilayers, leading to a longer average chain length in outer monolayer.
	pubs.acs.org /cgi-bin/abstract.cgi/mamobx/2005/38/i15/abs/ma050424j.html (156 words)

	Polydispersity
		The word "polydispersity" uses 14 letters: D E I I L O P P R S S T Y Y.
		Words within polydispersity not shown as it has more than seven letters.
		Other words with the same letter pairs: po ol ly yd di is sp pe er rs si it ty
	www.morewords.com /word/polydispersity (197 words)

	Events at the Maths Dept. at KCL
		Polydispersity Working Group Meeting, Friday 18th June 1999.
		This one-day meeting was organized within the UK Soft Matter research network (funded by EPSRC) and brought together researchers interested in the effects of polydispersity (the presence of particles with a continuously varying attribute, such as particle radius or polymer chain length) on the equilibrium behaviour and dynamics of soft materials.
		Details of the postgraduate open day held on 18th February, 2000 The open day will be held on the 18th of February, 2000.
	www.mth.kcl.ac.uk /events (2025 words)

	Recent Publications by NIST Authors
		Furthermore, the bile salt cosurfactant was also shown to increase the activity of the enzyme chymotrypsin that is solubilized in the AOT reversed micelle.
		In the present work, small-angle neutron scattering (SANS) was used to determine the effects of NaTC on the size and polydispersity of AOT reversed micelles.
		Results indicate that the addition of 5 mM NaTC to AOT reversed micelles in heptane results in a decrease in the overall size and the size of the interior water pools and an increase in the polydispersity of the reversed micelles.
	ois.nist.gov /nistpubs/technipubs/recent/search.cfm?dbibid=4666 (319 words)

	Polydispersity
		Isotropic-nematic phase equilibria of polydisperse hard rods: The effect of fat tails in the length distribution.
		Effects of colloid polydispersity on the phase behaviour of colloid-polymer mixtures.
		Effects of polymer polydispersity on the phase behaviour of colloid-polymer mixtures.
	www.mth.kcl.ac.uk /~psollich/publications/node18.html (202 words)

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