Observation of a re-entrant kinetic glass transition in a micellar system with temperature-dependent attractive interaction
ABSTRACT We detect in a tri-block co-polymer micellar system an ergodic-to-nonergodic-to-ergodic transition, as a function of temperature, in a range of concentrations, by photon correlation measurements. The shear viscosity is also shown to jump two order of magnitude at these transition temperatures. Surprisingly, the structure factor as measured by small angle neutron scattering shows a marked narrowing at the structural arrest state. Rationalization of these results with the existence of an attractive branch in the phase diagram of an attractive colloid system predicted by mode coupling theory is made.
SourceAvailable from: Domenico Lombardo[Show abstract] [Hide abstract]
ABSTRACT: We describe the hydrothermal synthesis of zeolite Linde type A (LTA) submicrometer particles using a water-soluble amphiphilic block copolymer of poly(dimethylsiloxane)-b-poly(ethylene oxide) as a template. The formation and growth of the intermediate aggregates in the presence of the diblock copolymer have been monitored by small-angle X-ray scattering (SAXS) above the critical micellar concentration at a constant temperature of 45 °C. The early stage of the growth process was characterized by the incorporation of the zeolite LTA components into the surface of the block copolymer micellar aggregates with the formation of primary units of 4.8 nm with a core–shell morphology. During this period, restricted to an initial time of 1–3 h, the core–shell structure of the particles does not show significant changes, while a subsequent aggregation process among these primary units takes place. A shape transition of the SAXS profile at the late stage of the synthesis has been connected with an aggregation process among primary units that leads to the formation of large clusters with fractal characteristics. The formation of large supramolecular assemblies was finally verified by scanning electron microscopy, which evidenced the presence of submicrometer aggregates with size ranging between 100 and 300 nm, while X-ray diffraction confirmed the presence of crystalline zeolite LTA. The main finding of our results gives novel insight into the mechanism of formation of organic–inorganic mesoporous materials based on the use of a soft interacting nanotemplate as well as stimulates the investigation of alternative protocols for the synthesis of novel hybrid materials with new characteristics and properties.Langmuir 05/2013; 29(23):7079–7086. DOI:10.1021/la400951s · 4.38 Impact Factor
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ABSTRACT: We present a study which illustrates the modeling of the Particle Scattering Structure Factor of an hyperbranched biopolymer in water solution using the Small Angle X-ray Scattering (SAXS) data. The studied sample was a sodium carboxilate terminated poly(amidoamine) dendrimer (generation 2.5) dispersed in water medium. The experimental inter-dendrimer structure factor S(q) has been analyzed in the framework of liquid integral equation theory for charged systems in solution. From that, we derive an effective interparticle interaction composed of a screened Coulombic plus hard-sphere repulsion potential, which allows the estimation of the dendrimer effective charge Zeff. The present analysis strongly supports the finding that structures and interaction of dendrimer are strongly influenced by charge effects. As a result, this quantity can be considered as a crucial parameter for the modulation of the degree of structural organization in solution, suitable for a number of potential applications. We conclude our form factor analysis with the investigation of the long-range assembly conditions during the growth of the intermediate nanoaggregates generated by the inclusion of aluminosilicate components of zeolite 13X on the surface of dendrimers.Journal of Quantitative Spectroscopy and Radiative Transfer 12/2012; 113(18):2536–2541. DOI:10.1016/j.jqsrt.2012.06.015 · 2.29 Impact Factor
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ABSTRACT: Active matter, whose motion is driven, and glasses, whose dynamics are arrested, seem to lie at opposite ends of the spectrum in nonequilibrium systems. In spite of this, both classes of systems exhibit a multitude of stable states that are dynamically isolated from one another. While this defining characteristic is held in common, its origin is different in each case: for active systems, the irreversible driving forces can produce dynamically frozen states, while glassy systems vitrify when they get kinetically trapped on a rugged free energy landscape. In a mixture of active and glassy particles, the interplay between these two tendencies leads to novel phenomenology. We demonstrate this with a spin glass model that we generalize to include an active component. In the absence of a ferromagnetic bias, we find that the spin glass transition temperature depresses with the active fraction, consistent with what has been observed for fully active glassy systems. When a bias does exist, however, a new type of transition becomes possible: the system can be cooled out of the glassy phase. This unusual phenomenon, known as reentrance, has been observed before in a limited number of colloidal and micellar systems, but it has not yet been observed in active glass mixtures. Using low order perturbation theory, we study the origin of this reentrance and, based on the physical picture that results, suggest how our predictions might be measured experimentally.Soft Matter 08/2014; 10(38). DOI:10.1039/C4SM01177E · 4.15 Impact Factor