Adsorption of Small Cationic Nanoparticles onto Large Anionic Particles from Aqueous Solution: A Model System for Understanding Pigment Dispersion and the Problem of Effective Particle Density

The present study focuses on the use of copolymer nanoparticles as a dispersant for a model pigment (silica). Reversible addition-fragmentation chain transfer (RAFT) alcoholic dispersion polymerization was used to synthesize sterically stabilized diblock copolymer nanoparticles. The steric stabilizer block was poly(2-(dimethylamino)ethyl methacrylate) (PDMA) and the core-forming block was poly(benzyl methacrylate) (PBzMA). The mean degrees of polymerization for the PDMA and PBzMA blocks were 71 and 100, respectively. Transmission electron microscopy (TEM) studies confirmed a near-monodisperse spherical morphology, while dynamic light scattering (DLS) studies indicated an intensity-average diameter of 30 nm. Small-angle X-ray scattering (SAXS) reported a volume-average diameter of 29 ± 0.5 nm and a mean aggregation number of 154. Aqueous electrophoresis measurements confirmed that these PDMA71-PBzMA100 nanoparticles acquired cationic character when transferred from ethanol to water as a result of protonation of the weakly basic PDMA chains. Electrostatic adsorption of these nanoparticles from aqueous solution onto 470 nm silica particles led to either flocculation at submonolayer coverage or steric stabilization at or above monolayer coverage, as judged by DLS. This technique indicated that saturation coverage was achieved on addition of approximately 465 copolymer nanoparticles per silica particle, which corresponds to a fractional surface coverage of around 0.42. These adsorption data were corroborated using thermogravimetry, UV spectroscopy and X-ray photoelectron spectroscopy. TEM studies indicated that the cationic nanoparticles remained intact on the silica surface after electrostatic adsorption, while aqueous electrophoresis confirmed that surface charge reversal occurred below pH 7. The relatively thick layer of adsorbed nanoparticles led to a significant reduction in the effective particle density of the silica particles from 1.99 g cm(-3) to approximately 1.74 g cm(-3), as judged by disk centrifuge photosedimentometry (DCP). Combining the DCP and SAXS data suggests that essentially no deformation of the PBzMA cores occurs during nanoparticle adsorption onto the silica particles

First-order phase transition during displacement of amphiphilic biomacromolecules from interfaces by surfactant molecules

The adsorption of surfactants onto a hydrophobic interface, already laden with a fixed number of amphiphilic macromolecules, is studied using the self consistent field calculation method of Scheutjens and Fleer. For biopolymers having unfavourable interactions with the surfactant molecules, the adsorption isotherms show an abrupt jump at a certain value of surfactant bulk concentration. Alternatively, the same behaviour is exhibited when the number of amphiphilic chains on the interface is decreased. We show that this sudden jump is associated with a first-order phase transition, by calculating the free energy values for the stable and the metastable states at both sides of the transition point. We also observe that the transition can occur for two approaching surfaces, from a high surfactant coverage phase to a low surfactant coverage one, at sufficiently close separation distances. The consequence of this finding for the steric colloidal interactions, induced by the overlap of two biopolymer + surfactant films, is explored. In particular, a significantly different interaction, in terms of its magnitude and range, is predicted for these two phases. We also consider the relevance of the current study to problems involving the competitive displacement of proteins by surfactants in food colloid systems

Structure and rheological properties of model microemulsion networks filled with nanoparticles

Model microemulsion networks of oil droplets stabilized by non ionic surfactant and telechelic polymer C18-PEO(10k)-C18 have been studied for two droplet-to-polymer size ratios. The rheological properties of the networks have been measured as a function of network connectivity and can be described in terms of simple percolation laws. The network structure has been characterised by Small Angle Neutron Scattering. A Reverse Monte Carlo approach is used to demonstrate the interplay of attraction and repulsion induced by the copolymer. These model networks are then used as matrix for the incorporation of silica nanoparticles (R=10nm), individual dispersion being checked by scattering. A strong impact on the rheological properties is found for silica volume fractions up to 9%

Unstable Flow and Non-Monotonic Constitutive Equation of Transient Networks

We have measured the nonlinear rheological response of a model transient network over a large range of steady shear rates. The system is built up from an oil in water droplet microemulsion into which a telechelic polymer is incorporated. The phase behaviour is characterized which comprises a liquid-gas phase separation and a percolation threshold. The rheological measurements are performed in the one phase region above the percolation line. Shear thinning is observed for all samples, leading in most cases to an unstable stress response at intermediate shear rates. We built up a very simple mean field model which involves the reduction of the residence time of the stickers in the droplets due to the chain tensions at high shear. The computed constitutive equation is non-monotonic with a range where the stress is a decreasing function of the rate, a feature that indeed makes homogeneous flows unstable. The computed the flow curves compare well to the experiments.Comment: mai 200

‘Sons of athelings given to the earth’: Infant Mortality within Anglo-Saxon Mortuary Geography

FOR 20 OR MORE YEARS early Anglo-Saxon archaeologists have believed children are underrepresented in the cemetery evidence. They conclude that excavation misses small bones, that previous attitudes to reporting overlook the very young, or that infants and children were buried elsewhere. This is all well and good, but we must be careful of oversimplifying compound social and cultural responses to childhood and infant mortality. Previous approaches have offered methodological quandaries in the face of this under-representation. However, proportionally more infants were placed in large cemeteries and sometimes in specific zones. This trend is statistically significant and is therefore unlikely to result entirely from preservation or excavation problems. Early medieval cemeteries were part of regional mortuary geographies and provided places to stage events that promoted social cohesion across kinship systems extending over tribal territories. This paper argues that patterns in early Anglo-Saxon infant burial were the result of female mobility. Many women probably travelled locally to marry in a union which reinforced existing social networks. For an expectant mother, however, the safest place to give birth was with experience women in her maternal home. Infant identities were affected by personal and legal association with their mother’s parental kindred, so when an infant died in childbirth or months and years later, it was their mother’s identity which dictated burial location. As a result, cemeteries central to tribal identities became places to bury the sons and daughters of a regional tribal aristocracy

KD5170, a novel mercaptoketone-based histone deacetylase inhibitor that exhibits broad spectrum antitumor activity in vitro and in vivo

Abstract Histone deacetylase (HDAC) inhibitors have garnered significant attention as cancer drugs. These therapeutic agents have recently been clinically validated with the market approval of vorinostat (SAHA, Zolinza) for treatment of cutaneous T-cell lymphoma. Like vorinostat, most of the small-molecule HDAC inhibitors in clinical development are hydroxamic acids, whose inhibitory activity stems from their ability to coordinate the catalytic Zn 2+ in the active site of HDACs. We sought to identify novel, nonhydroxamate-based HDAC inhibitors with potentially distinct pharmaceutical properties via an ultra-high throughput small molecule biochemical screen against the HDAC activity in a HeLa cell nuclear extract. An A-mercaptoketone series was identified and chemically optimized. The lead compound, KD5170, exhibits HDAC inhibitory activity with an IC 50 of 0.045 Mmol/L in the screening biochemical assay and an EC 50 of 0.025 Mmol/L in HeLa cell -based assays that monitor histone H3 acetylation. KD5170 also exhibits broad spectrum classe

Re-evaluating the Quoit Brooch Style: Economic and Cultural Transformations in the 5th Century ad, with an Updated Catalogue of Known Quoit Brooch Style Artefacts

Quoit Brooch Style material, produced from the early 5th century onwards, has previously been considered mostly from a stylistic point of view, leaving much scope for further investigation. In addition, the known corpus of material has been much expanded through newly excavated and metal-detected finds. In this article, I bring together the known extant material for the first time, and document important evidence relating to contextual dating, gender associations, manufacture (including new compositional analysis of c 75 objects), repair, and reuse. The article questions previous interpretations of Quoit Brooch Style material relating to Germanic mercenaries and/or post-Romano-British political entities. It interprets the earliest material as part of wider trends elsewhere, in Britain and in Continental northwestern Europe, for the production of material imitating late Roman symbols of power. It presents new evidence for connectivity with Continental Europe via the western Channel route in the 5th century. A detailed investigation of individual artefacts shows that many Quoit Brooch Style objects were reused, sometimes being subjected to extensive repair and modification. This provides new insights into the 5th century metal economy, for instance, acute problems in the availability of new metal objects in southeastern Britain in the middle years of the 5th century. Compositional analysis contributes further to our understanding of metal supply in the 5th century and relationships with the post-Roman West. Insights are provided into wider cultural transformations in the 5th century and the gradual loss of value that occurred for Roman-style objects

Effects of the association on the phase behaviour of mixed solutions of hydrophobically modified and similar unmodified polymers

Il est prévu théoriquement et démontré expérimentalement que lors du mélange de solutions de polymères associatifs obtenus par des substitutions hydrophobes et des homologues non modifiés hydrosolubles, il existe un domaine de composition où le système n'est pas compatible et se sépare en deux phases liquides. Les polymères modifiés utilisés, appelés polymères associatifs (AT) sont des dérivés du polyéthyléne-glycol (PEG) dont chaque extrémité prote un substituant alkyle. Des homopolymères de PEG de même taille sont utilisés comme homologues non associatifs. Sur toute la gamme de concentration ou le système démixte la composition de chaque phase reste constante. Toutefois la viscosité de deux phases en équilibre diffères de plusieurs orders de grandeur. Ceci suggère que l'une des phases contient surtout l'espèce AT et l'autre la polymère non modifié. La démixtion est observée quand la concentration totale en polymère est supérieure à 2 % et la fraction molaire en AT inférieure à 0.65. Il a été montré que les résultats pouvaient s'expliquer qualitativement en prenant en compte les effets d'association selon l'approche de Flory-Huggins. En particulier une fraction molaire critique en AT de 0.68 est prédite, en excellent accord avec les observations expérimentales. Les développements théoriques ont été étendus au cas ou les solutions mélangées contiennent des PEG portant un substituant alkyle à une seule extrémité ainsi qu'aux mélanges de polymères avec une structure en étoile avec leurs d'homologues hydrophobes. Dans ce dernier cas la tendance à la séparation de phases entre les deux espèces augmente rapidement avec le nombre de substituants hydrophobes fixés sur les polymères associatif