Electro-rheology is the phenomenon in which the rheology of fluids is modified by the imposition of electric fields. In this Review the nature of the fluids active in this role are presented and the influence of important variables such as shear rate, field strength, field frequency, temperature and fluid composition are described. Also discussed are the dielectric behaviour of dispersions in flow since this is of direct bearing on the phenomenon of electro-rheology. Various models for electro-rheology are presented and assessed. The authors also describe how recent developments in new classes of electro-rheological fluids have resulted from a clearer understanding of the probable electrodynamic origins of the effect. The Review concludes with an overview of the practical applications that electro-rheology has and may have in the future.
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Orthogonally functionalized PEGs displaying alkenes and azides have been prepared and their dual-purpose scaffolding potential was exploited via click chemistry for controlled insertion of biorelevant moieties as well as facile fabrication of soft, non-toxic and degradable hydrogels.
The antibiotic resistance developed among several pathogenic bacterial strains has spurred interest in understanding bacterial adhesion down to a molecular level. Consequently, analytical methods that rely on bioactive and multivalent sensor surfaces are sought to detect and suppress infections. To deliver functional sensor surfaces with an optimized degree of molecular packaging, we explore a library of compact and monodisperse dendritic scaffolds based on the nontoxic 2,2-bis(methylol)propionic acid (bis-MPA). A self-assembled dendritic monolayer (SADM) methodology to gold surfaces capitalizes on the design of aqueous soluble dendritic structures that bear sulfur-containing core functionalities. The nature of sulfur (either disulfide or thiol), the size of the dendritic framework (generation 1-3), the distance between the sulfur and the dendritic wedge (4 or 14 Å), and the type of functional end group (hydroxyl or mannose) were key structural elements that were identified to affect the packaging densities assembled on the surfaces. Both surface plasmon resonance (SPR) and resonance-enhanced surface impedance (RESI) experiments revealed rapid formation of homogenously covered SADMs on gold surfaces. The array of dendritic structures enabled the fabrication of functional gold surfaces displaying molecular covering densities of 0.33-2.2 molecules·nm(-2) and functional availability of 0.95-5.5 groups·nm(-2). The cell scavenging ability of these sensor surfaces for Escherichia coli MS7fim+ bacteria revealed 2.5 times enhanced recognition for G3-mannosylated surfaces when compared to G3-hydroxylated SADM surfaces. This promising methodology delivers functional gold sensor surfaces and represents a facile route for probing surface interactions between multivalently presented motifs and cells in a controlled surface setting.
Engineered surfaces with nanoscale features of gold on silicon or glass have recently been used to improve the understanding of adhesion-mediated environmental sensing of cells.Often such surfaces present a cell-binding ligand, such as arginine-glycine-aspartic acid (RGD) peptide motifs, at controlled intramolecular distances on an inert background surface such as polyethylene glycol (PEG).[1] The adhesion mechanism of macromolecular ligands in which direct interaction with cells is nonspecific is not known and the cell response is dictated by the type and the concentration of proteins adsorbed from solution.[2] Dendrimers may increase the availability and multivalency of cell-interacting ligands as a consequence of their branched shape and inherently high concentration of end groups.[3] It is therefore interesting to examine the eventual effect of the macromolecular architecture on the cell viability by the controlled reduction of ligands on a surface. Herein, we demonstrate the fabrication of selfassembled macromolecular hybrid arrays in which the relative position of two anionic macromolecules of different architectures-a carboxy-functionalized dendrimer and a linear polymer-is straightforwardly controlled on a PEG surface. We also show how the interaction of primary human endothelial cells with these surfaces is modulated by the molecular spacing and how protein binding to the macromolecular arrays can be evaluated by using a standard surface plasmon resonance (SPR) technique.Self-assembled, short-range-ordered Au nanoparticle (NP) arrays were used as a versatile template to arrange polymeric entities at the nanometer scale (Figure 1 a). This Figure 1. a) The self-assembly protocol in which formation of the octanedithiol (1) monolayer is followed by immobilization of NPs 2 of a = 5 nm radius and reaction with malemide-functionalized PEG 3. The fabrication of the polymer hybrid array ends with modification of the NP template with cysteamine (4) and immobilization of the synthesized G4-COOH dendrimer 5. b) The interparticle distance as determined by SEM under two deposition conditions, ka = 1.84 and ka = 0.48, together with the radial distributions (scale bars = 500 nm).
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