Ultra-long range correlations of the dynamics of jammed soft matter

We use Photon Correlation Imaging, a recently introduced space-resolved dynamic light scattering method, to investigate the spatial correlation of the dynamics of a variety of jammed and glassy soft materials. Strikingly, we find that in deeply jammed soft materials spatial correlations of the dynamics are quite generally ultra-long ranged, extending up to the system size, orders of magnitude larger than any relevant structural length scale, such as the particle size, or the mesh size for colloidal gel systems. This has to be contrasted with the case of molecular, colloidal and granular ``supercooled'' fluids, where spatial correlations of the dynamics extend over a few particles at most. Our findings suggest that ultra long range spatial correlations in the dynamics of a system are directly related to the origin of elasticity. While solid-like systems with entropic elasticity exhibit very moderate correlations, systems with enthalpic elasticity exhibit ultra-long range correlations due to the effective transmission of strains throughout the contact network.Comment: To appear in Soft Matte

Hybrid magnetic iron oxide nanoparticles with tunable field-directed self-assembly

We describe the synthesis of hybrid magnetic ellipsoidal nanoparticles that consist of a mixture of two different iron oxide phases, hematite (α-Fe2O3) and maghemite (γ- Fe2O3), and characterize their magnetic field-driven self-assembly. We demonstrate that the relative amount of the two phases can be adjusted in a continuous way by varying the reaction time during the synthesis, leading to strongly varying magnetic properties of the particles. Not only does the saturation magnetization increase dramatically as the composition of the spindles changes from hematite to maghemite, but also the direction of the induced magnetic moment changes from being parallel to the short axis of the spindle to being perpendicular to it. The magnetic dipolar interaction between the particles can be further tuned by adding a screening silica shell. Small-angle X-ray scattering (SAXS) experiments reveal that at high magnetic field, magnetic dipole–dipole interaction forces the silica coated particles to self- assemble into a distorted hexagonal crystal structure at high maghemite content. However, in the case of uncoated maghemite particles, the crystal structure is not very prominent. We interpret this as a consequence of the strong dipolar interaction between uncoated spindles that then become arrested during field-induced self- assembly into a structure riddled with defects

The influences of the transfer method and particle surface chemistry on the dispersion of nanoparticles in nanocomposites

The synthesis via in situ polymerization and characterization of nanocomposites (NCs) made from silica (SiO2) nanoparticles in a methyl methacrylate (MMA) monomer matrix is reported. We first investigate the transfer of well-defined spherical silica nanoparticles (NPs) (average radius R = 24.2 +/- 3.2 nm) into the monomer solvent. We study the influence of two transfer methods and different surface chemistries on the resulting colloidal stability. The first transfer method consists of drying the silica particles into powder before dispersing them via ultrasonication in the MMA matrix. The second is based on repetitive centrifugations to exchange NPs from their synthetic milieu to pure MMA, avoiding the dried powder state. These transfer methods are compared for two kinds of NP surface chemistry, natural silanol (Si-OH) groups of the silica NPs and an additional silane coupling agent, namely 3-(trimethoxysilyl)propyl methacrylate (TPM), which mimics the monomeric group of the MMA dispersing milieu. We then characterize the morphology of the resulting nanocomposites prepared via in situ polymerization at a fixed amount of dispersed NPs (2.2 wt%; 1 vol%) using a combination of transmission electron microscopy (TEM) from ultramicrotomed nanocomposite films, thermogravimetry (TGA) and small angle X-ray scattering (SAXS)

Advanced multiresponsive comploids: from design to possible applications.

We extend the commonly used synthesis strategies for responsive microgels to the design of novel multiresponsive and multifunctional nanoparticles that combine inorganic magnetic, metallic/catalytic and thermoresponsive organic moieties. Magnetic responsiveness is implemented through the integration of silica-coated maghemite nanoparticles into fluorescently labeled crosslinked poly(N-isopropylmethacrylamide) microgels. These particles are then employed as templates for the in situ reduction of catalytically active gold nanoparticles. In order to tune the reactivity of the catalyst through a thermally controlled barrier, an additional layer of crosslinked poly(N-isopropylacrylamide) is added in the final step. We subsequently demonstrate that these particles can be employed as smart catalysts. We show that the thermoresponsive nature of the outer particle shell not only provides control over the catalytic activity, but when combined with a magnetic core allows for very efficient removal of the catalytic system through temperature-controlled reversible coagulation and subsequent magnetophoresis in an applied magnetic field gradient. We finally discuss the use of this design principle for the synthesis of complex hybrid particles for various applications that would all profit from their multiresponsive and multifunctional nature

Experiências de mulheres sem filhos: a mulher singular no plural

Este é um estudo exploratório das dimensões atribuídas à não maternidade, baseado na experiência de oito mulheres sem filhos, na faixa entre 40/50 anos. Através da análise qualitativa das narrativas e de um enfoque psicossocial, busca compreender e ultrapassar a abordagem tradicional e estigmatizada da não maternidade e evidencia a complexidade dessa experiência moldada na intersecção entre história, cultura, sociedade, família e personalidade. A não maternidade emerge como uma experiência multifacetada e com significados diversos, não apenas para as diferentes mulheres entrevistadas mas também para cada uma individualmente, em função da perspectiva e do momento em que foi avaliada ao longo do tempo