Record 1 of 6. Record 2 of 6

Transcription

1 Record 1 of 6 Furukawa T; Ishizu K Lattice formation of peripherally charged star polymers in aqueous solution Source: MACROMOLECULES 2003, Vol 36, Iss 2, pp Functionalized poly(ethylene oxide) (PEO) stars (arm number f = ) possessing peripheral tertiary amino groups were prepared by organized polymerization using macromonomers. Subsequently, positive charges were introduced into such peripheral tertiary amino groups by quaternization with methyl iodide. The structural ordering of these functionalized and peripherally charged stars was investigated through small-angle X-ray scattering in aqueous solution. PEO stars without charges (f > 72) formed a bodycentered-cubic (bcc) structure near the overlap threshold (C*). On the other hand, peripherally charged PEO stars (f > 37) formed a lattice of bcc even below C*. The results indicate that ionization (electric double layer) of stars results in interparticle interactions giving rise to ordering. These interactions were screened by adding inorganic salt (KI). Source item page count: 6 Publication Date: JAN YW 29-char source abbrev: MACROMOLECULES Record 2 of 6 Lowen H Density functional theory of inhomogeneous classical fluids: recent developments and new perspectives Source: JOURNAL OF PHYSICS-CONDENSED MATTER 2002, Vol 14, Iss 46, pp An introduction is given to this special issue which focuses on recent developments and future perspectives in density functional theory of inhomogeneous. classical fluids. Different and applications of classical density functional theory are discussed.. The topics briefly treated-are different approximation schemes for different interparticle interactions, binary mixtures and polydisperse systems, application to interfaces, wetting, confined geometries and porous media and also dynamical problems treated by density functional theory. Particular emphasis is placed on recent applications of Rosenfeld's fundamental measure approach. Finally a guide is presented to the subsequent articles in this Special Issue. Source item page count: 9 Publication Date: NOV GB 29-char source abbrev: J PHYS-CONDENS MATTER Page 1 of 5

2 Record 3 of 6 Riley T; Stolnik S; Garnett MC; Illum L; Davis SS; Taylor P; Tadros TF Use of viscoelastic measurements for investigating interparticle interactions in dispersions of micellar-like poly(lactic acid)-poly(ethylene glycol) nanoparticles Source: LANGMUIR 2002, Vol 18, Iss 20, pp A series of poly(lactic acid)-poly(ethylene oxide) (PIA-PEG) AB block copolymers have been synthesized and used to produce aqueous dispersions of micellar-like nanoparticles. The hydrodynamic radius of the PLA core plus the stabilizing 5 kda PEG layer, as determined by photon correlation spectroscopy, increased with the molecular weight of the PIA block. PLA-PEG particles have possible application as drug carriers for targeted drug delivery. In addition to particle size, the layer thickness and mobility of the hydrated PEG chains will be important in determining the particle's ability to avoid uptake by the defense system of the body, the phagocytic cells of the reticuloendothelial system. Viscoelastic measurements were used to investigate interparticle interactions in concentrated dispersions of the PLA-PEG nanoparticles. This approach has not previously been used to study how the interactions in dispersions of micellar-like assemblies depend on the copolymer geometry. When the volume fraction of the dispersions, phi(core) was increased, the storage modulus, G', became greater than the loss modulus, G", indicating steric interaction between the PEG chains. At higher phi(core) values, compression of the grafted polymer chains was observed. The critical volume fraction at which overlap of the PEG chains commences, phi(core)(crit) (i.e., G' = G"), was used in conjunction with the overall hydrodynamic radius to determine the grafted PEG chain layer thickness. Micellar-like nanoparticles assembled from a PLA-PEG copolymer with a 5 kda PEG block and a relatively low molecular weight 3 kda PLA chain had an appreciable steric layer thickness of 6.3 nm. Hence, interparticle interactions in the concentrated dispersion were "soft" in nature as a result of the long-range interactions, as shown by the weak scaling dependence of the storage modulus on the volume fraction. The layer became more extended as the molecular weight of the PLA block was increased from 3 to 6 kda, and as a consequence the PEG chains became less compressible. By using this method to characterize the PEG layer, it should be possible to rationalize the in vivo performance of the PLA-PEG nanoparticles and therefore aid the design of particulate drug carriers. Source item page count: 6 Publication Date: OCT 1 598WV 29-char source abbrev: LANGMUIR Page 2 of 5

3 Record 4 of 6 Vattulainen I; Karttunen M; Besold G; Polson JM Integration schemes for dissipative particle dynamics simulations: From softly interacting systems towards hybrid models Source: JOURNAL OF CHEMICAL PHYSICS 2002, Vol 116, Iss 10, pp We examine the performance of various commonly used integration schemes in dissipative particle dynamics simulations. We consider this issue using three different model systems, which characterize a variety of different conditions often studied in simulations. Specifically, we clarify the performance of integration schemes in hybrid models, which combine microscopic and mesoscale descriptions of different particles using both soft and hard interactions. We find that in all three model systems many commonly used integrators may give rise to surprisingly pronounced artifacts in physical observables such as the radial distribution function, the compressibility, and the tracer diffusion coefficient. The artifacts are found to be strongest in systems, where interparticle interactions are soft and predominated by random and dissipative forces, while in systems governed by conservative interactions the artifacts are weaker. Our results suggest that the quality of any integration scheme employed is crucial in all cases where the role of random and dissipative forces is important, including hybrid models where the solvent is described in terms of soft potentials. Regarding the integration schemes, the best overall performance is found for integrators in which the velocity dependence of dissipative forces is taken into account, and particularly good performance is found for an approach in which velocities and dissipative forces are determined self-consistently. Remaining temperature deviations from the desired limit can be corrected by carrying out the self-consistent integration in conjunction with an auxiliary thermostat, in a manner that is similar in spirit to the well-known Nose-Hoover thermostat. Further, we show that conservative interactions can play a significant role in describing the transport properties of simple fluids, in contrast to approximations often made in deriving analytical theories. In general, our results illustrate the main problems associated with simulation methods in which dissipative forces are velocity dependent, and point to the need to develop new techniques to resolve these issues. (C) 2002 American Institute of Physics. Source item page count: 13 Publication Date: MAR 8 525TL 29-char source abbrev: J CHEM PHYS Page 3 of 5

4 Record 5 of 6 Louis AA; Roth R Generalized depletion potentials Source: JOURNAL OF PHYSICS-CONDENSED MATTER 2001, Vol 13, Iss 33, pp L777- L784 We propose that the behaviour of asymmetric binary fluid mixtures with a large class of attractive or repulsive interparticle interactions can be understood by mapping onto effective non-additive hard-sphere models. The latter are best analysed in terms of their underlying depletion potentials which can be exactly scaled onto known additive ones. By tuning the non-additivity, a wide variety of attractive or repulsive generalized depletion potential shapes and associated phase behaviour can be 'engineered', leading, for example, to two ways to stabilize colloidal suspensions by adding smaller particles. Source item page count: 8 Publication Date: AUG YM 29-char source abbrev: J PHYS-CONDENS MATTER Record 6 of 6 Dubois E; Perzynski R; Boue F; Cabuil V Liquid-gas transitions in charged colloidal dispersions: Small-angle neutron scattering coupled with phase diagrams of magnetic fluids Source: LANGMUIR 2000, Vol 16, Iss 13, pp We study here the phase behavior of colloidal dispersions, which are constituted of almost monodisperse gamma-fe2o3 magnetic nanoparticles dispersed in water at ph 7. Those electrostatically stabilized dispersions present, if the interparticle repulsion is decreased, gas-liquid transitions, a phase behavior scarcely reported for such charged nanoparticles. Small-angle neutron scattering experiments prove that there is no chaining of the particles and that, from the point of view of interparticle interactions, increasing ionic strength (through addition of NaCl) is equivalent to decreasing temperature. A phenomenological expression of the osmotic pressure pi is determined and shown to be in agreement with direct pi measurements. The scattering experiments associated to optical microscopy determinations of phase diagrams lead to a general pi- Phi diagram. Gas-solid transitions may exist even if their observation is disturbed by metastability phenomena. The results are in qualitative agreement with theoretical predictions on charged colloids and in agreement with theoretical works on weak dipolar systems. Source item page count: 9 Publication Date: JUN NQ 29-char source abbrev: LANGMUIR Acceptable Use Policy Copyright 2003 Thomson ISI Page 4 of 5

5 Page 5 of 5