Validity of the scaling functional approach for polymer interfaces as a variational theory

We discuss the soundness of the scaling functional (SF) approach proposed by Aubouy Guiselin and Raphael (Macromolecules 29, 7261 (1996)) to describe polymeric interfaces. In particular, we demonstrate that this approach is a variational theory. We emphasis the role of SF theory as an important link between ground-state theories suitable to describe adsorbed layers, and "classical" theories for polymer brushes.Comment: 8 pages, 1 figure, to be published in Phys. Rev.

Effective interactions and phase behaviour for a model clay suspension in an electrolyte

Since the early observation of nematic phases of disc-like clay colloids by Langmuir in 1938, the phase behaviour of such systems has resisted theoretical understanding. The main reason is that there is no satisfactory generalization for charged discs of the isotropic DLVO potential describing the effective interactions between a pair of spherical colloids in an electrolyte. In this contribution, we show how to construct such a pair potential, incorporating approximately both the non-linear effects of counter-ion condensation (charge renormalization) and the anisotropy of the charged platelets. The consequences on the phase behaviour of Laponite dispersions (thin discs of 30 nm diameter and 1 nm thickness) are discussed, and investigation into the mesostructure via Monte Carlo simulations are presented.Comment: LaTeX, 12 pages, 11 figure

Evidence of environmental strains on charge injection in silole based organic light emitting diodes

Using d. functional theory (DFT) computations, the authors demonstrated a substantial skeletal relaxation when the structure of 2,5-bis-[4-anthracene-9-yl-phenyl]-1,1-dimethyl-3,4-diphenyl-silole (BAS) is optimized in the gas-phase comparing with the mol. structure detd. from monocrystal x-ray diffraction. The origin of such a relaxation is explained by a strong environmental strains induced by the presence of anthracene entities. Also, the estn. of the frontier orbital levels showed that this structural relaxation affects mainly the LUMO that is lowered of 190 meV in the gas phase. To check if these theor. findings would be confirmed for thin films of BAS, the authors turned to UV photoemission spectroscopy and/or inverse photoemission spectroscopy and electrooptical measurements. The study of the c.d. or voltage and luminance or voltage characteristics of an ITO/PEDOT/BAS/Au device clearly demonstrated a very unusual temp.-dependent behavior. Using a thermally assisted tunnel transfer model, this behavior likely originated from the variation of the electronic affinity of the silole deriv. with the temp. The thermal agitation relaxes the mol. strains in thin films as it is shown when passing from the cryst. to the gas phase. The relaxation of the intramol. thus induces an increase of the electronic affinity and, as a consequence, the more efficient electron injection in org. light-emitting diodes

Exact asymptotic expansions for the cylindrical Poisson-Boltzmann equation

The mathematical theory of integrable Painleve/Toda type systems sheds new light on the behavior of solutions to the Poisson-Boltzmann equation for the potential due to a long rod-like macroion. We investigate here the case of symmetric electrolytes together with that of 1:2 and 2:1 salts. Short and large scale features are analyzed, with a particular emphasis on the low salinity regime. Analytical expansions are derived for several quantities relevant for polyelectrolytes theory, such as the Manning radius. In addition, accurate and practical expressions are worked out for the electrostatic potential, which improve upon previous work and cover the full range of radial distances

Arsenate removal with 3-mercaptopropanoic acid-coated superparamagnetic iron oxide nanoparticles

In the present work, superparamagnetic iron oxide nanoparticles (SPION) surface-coated with 3-mercaptopropanoic acid (3-MPA) were prepared and their feasibility for the removal of arsenate from dilute aqueous solutions was demonstrated. The synthesized 3-MPA-coated SPION was characterized using transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and Fourier transform infra-red spectrometry (FTIR). Separation efficiency of the coated nanoparticles and the equilibrium isotherm of arsenate adsorption were investigated. The obtained results reveal the arsenate adsorption to be highly pH-dependent, and the maximum adsorption was attained in less than 60 min. The resulting increase of 3-MPA-coated SPION adsorption capacity to twice the adsorption capacity of SPION alone under the same conditions is attributed to the increase of active adsorption sites. An adsorption reaction is proposed. On the other hand, efficient recovery of arsenate from the loaded nanoparticles was achieved using nitric acid (HNO3) solution, which also provides a concentration over the original arsenate solutio

The interplay between screening properties and colloid anisotropy: towards a reliable pair potential for disc-like charged particles

The electrostatic potential of a highly charged disc (clay platelet) in an electrolyte is investigated in detail. The corresponding non-linear Poisson-Boltzmann (PB) equation is solved numerically, and we show that the far-field behaviour (relevant for colloidal interactions in dilute suspensions) is exactly that obtained within linearized PB theory, with the surface boundary condition of a uniform potential. The latter linear problem is solved by a new semi-analytical procedure and both the potential amplitude (quantified by an effective charge) and potential anisotropy coincide closely within PB and linearized PB, provided the disc bare charge is high enough. This anisotropy remains at all scales; it is encoded in a function that may vary over several orders of magnitude depending on the azimuthal angle under which the disc is seen. The results allow to construct a pair potential for discs interaction, that is strongly orientation dependent.Comment: 13 pages, 19 figure

Nanofiber-based filters as novel barrier systems for nanomaterial exposure scenarios

In this article our latest advances in the development of efficient barrier systems against micro- and nano-particulate materials are presented. Nanofibrous polyamide 6 (PA6) mats were fabricated by electrospinning onto a nonwoven viscose substrate. The influence of electrospinning parameters including solution concentration, viscosity, and conductivity, were studied for the production of nonwovens with different fiber size distribution ranging from 74 to 261 nm in diameters. Moreover, the formation of nanowebs (30-40 nm) which are widely distributed among fibers was observed. By varying several process parameters, membranes with different thickness of the nanofiber layer and therefore air permeability and nanoparticle filtration efficiency were obtained.The financial support of this work was provided by MICINN (Spanish Ministry of Science and Innovation) and ERDF (European Regional Development Fund) (ref: PSE-420000-2008-003)

Superparamagnetic iron oxide nanoparticle-loaded polyacrylonitrile nanofibers with enhanced arsenate removal performance

Novel nanocomposite sorbents of superparamagnetic iron oxide nanoparticles (SPION) supported onto electrospun polyacrylonitrile nanofibers were synthesized by a simple and scalable method. The influence of both nanofiber size and SPION loading on As(V) adsorption capacity was studied and optimization was conducted. A maximum uptake capacity of 32.5 mmol As(V) per gram SPION in batch mode tests using an extremely low loading of only 2.9 mg of SPION per gram of adsorbent was achieved. This represents a remarkable improvement of 36 times compared with SPION in suspension. The optimal material was tested in continuous flow operation mode, reaching an adsorption capacity of 851.7 mg As(V) per gram of adsorbent at pH 3.8. It is also demonstrated that the new adsorbents can retain high performance when tested under real conditions using polluted wastewater from a lixiviation dump containing a large amount of competing anions (Cl- and F- ) and interfering cations (K+, Na+, Mg2+, and Ca2+). Furthermore, there was no release of nanoparticles observed during the operation and the spent porous material can be compressed, generating a small amount of solid waste that can be easily treated or stored

Two-dimensional flow of foam around an obstacle: force measurements

A Stokes experiment for foams is proposed. It consists in a two-dimensional flow of a foam, confined between a water subphase and a top plate, around a fixed circular obstacle. We present systematic measurements of the drag exerted by the flowing foam on the obstacle, \emph{versus} various separately controlled parameters: flow rate, bubble volume, bulk viscosity, obstacle size, shape and boundary conditions. We separate the drag into two contributions, an elastic one (yield drag) at vanishing flow rate, and a fluid one (viscous coefficient) increasing with flow rate. We quantify the influence of each control parameter on the drag. The results exhibit in particular a power-law dependence of the drag as a function of the bulk viscosity and the flow rate with two different exponents. Moreover, we show that the drag decreases with bubble size, and increases proportionally to the obstacle size. We quantify the effect of shape through a dimensioned drag coefficient, and we show that the effect of boundary conditions is small.Comment: 26 pages, 13 figures, resubmitted version to Phys. Rev.

Testing the relevance of effective interaction potentials between highly charged colloids in suspension

Combining cell and Jellium model mean-field approaches, Monte Carlo together with integral equation techniques, and finally more demanding many-colloid mean-field computations, we investigate the thermodynamic behavior, pressure and compressibility of highly charged colloidal dispersions, and at a more microscopic level, the force distribution acting on the colloids. The Kirkwood-Buff identity provides a useful probe to challenge the self-consistency of an approximate effective screened Coulomb (Yukawa) potential between colloids. Two effective parameter models are put to the test: cell against renormalized Jellium models