197,000 research outputs found
"Effect of Temperature on High Shear-Induced Gelation of Charge-Stabilized Colloids without Adding Electrolytes"
No full textWe demonstrated previously (Wu, H.; Zaccone, A.; Tsoutsoura, A.; Lattuada, M.; Morbidelli, M. Langmuir 2009,25, 4715) that, for a colloid stabilized by charges from both polymer chain-end groups and adsorbed sulfonate surfactants, when the surfactant surface density reaches a certain critical value, the shear-induced gelation becomes unachievable at room temperature, even at an extremely large Peclet number, Pe = 4.6 x 10(4). This is due to the presence of the short-range, repulsive hydration force generated by the adsorbed surfactant. In this work, we investigate how such hydration force affects the shear-induced gelation at higher temperatures, in the range between 303 and 338 K. It is found that a colloidal system, which does not gel at room temperature in a microchannel at a fixed Pe = 3.7 x 10(4), does gel when temperature increases to a certain value. The critical initial particle volume fraction for the gelation to occur decreases as temperature increases. These results indicate that the effect of the hydration force oil the gelation decreases as temperature increases. Moreover, we have observed that at the criticality only part of the primary particles is converted to the gel network and the effective particle volume fraction forming the gel network does not change significantly with temperature. The effective particle volume fraction is also independent of the surfactant surface coverage. Since the effective particle volume fraction corresponds to space filling requirement of a standing gel network, which is mainly related to the clusters structure, this result indicates that at a given shear rate the Cluster structure does not change significantly with the surfactant Surface coverage. Oil the other hand, since the cluster morphology is a strong function of the shear rate, we have observed that when the Peclet number is lowered from Pe = 3.7 x 10(4) to 1.7 x 10(4), the effective particle Volume fraction reduces from 0.19 to 0.12 at 3 13 K
Patchy Colloidal Particles Via Surfactant Adsorption: Interactions and Gels of Tunable Structure
No full textThe presence of charged molecules attached on the surface of Brownian particles can dramatically affect their mutual interaction as well as their interactions with foreign surfaces. With respect to aggregation, the coexistence of domains of charged adsorbed molecules and hydrophobic domains on polymer colloids opens up the possibility of tuning the interactions in a wide range from homogeneously hydrophobic surfaces to completely hydrophilic repulsive surfaces with strong hydration forces. In a well characterized system made of styrene-acrylate copolymer particles and two different ionic surfactants, aliphatic C-18 carboxylate and aliphatic C-15 sulfonate, we have shown experimentally by means of laser light scattering that an initial, gas-like state of noninteracting adsorbed molecules laying down to the particle surface is followed, with increasing surfactant concentration, by the formation of condensed domains prior to reaching full coverage of the particle surface. In the low salt limit, by shearing the dispersion at very high shear-rate in a microchannel, it is shown that the surfactant domains on two particles can fuse/adhere leading to aggregation as long as an even small-sized uncovered polymer patch is present and aggregation is always possible on the free hydrophobic polymer patches. In the case of fully developed films, by analyzing the mechanism of shear aggregation in the low-salt limit theoretically, we show that short-range hydration repulsive forces dominate over DLVO forces and adhesion/aggregation can never be achieved even upon application of extremely high collision energies. We can also provide evidence that gels obtained by shearing the dispersion at high-shear rate at low-salt exhibit a structure that is strongly affected by the degree of coverage of surfactant, i.e. by the relative extension of charged-hydrophilic to hydrophobic patches. The fractal dimension of the gel can indeed vary from 2.1 at high surfactant coverage where only a few small patches are available for aggregation (valence-limited case) to 2.8 at low surfactant coverage where the gel is made of very compact clusters. This finding unfolds new possibilities for making engineered mesoscopic disordered materials by tuning the surface properties at microscopic level.
Zaccone, Wu, Lattuada and Morbidelli, Journal of Physical Chemistry B, 112, 1976 (2008)
Zaccone, Wu, Lattuada and Morbidelli, Journal of Physical Chemistry B, in pres
Riccardo Lattuada. Mattia Preti, ‘Abramo e i tre angeli’; attribuito a M. Preti, ‘Fumatore orientale’; Mattia e Gregorio Preti, ‘Cristo guarisce l’idropico’.
No full textMechanism of Adsorption of Anionic Surfactants on the Surface of Functionalized Nanoparticles
No full textThe mechanism of adsorption of amphiphillic molecules on the surface of Brownian particles is essential for understanding and controlling the stability of functionalized nanoparticles, which are nowadays used in a broad range of fields, such as semiconductor, drug delivery system and catalysis. In this work, we have used light scattering (LS) techniques combined with determination of adsorption isotherms, as developed previously in our lab1, to study the adsorption mechanism of anionic surfactants on the heterogeneous surface of particles consisting of a rubber core surrounded by a plastic shell. Particles with the same mass of the core but different masses of the shell have been used. The adsorption isotherms for the different particles have been obtained by surface tension measurements both before and after removal of the particles by centrifugation. At the same time, the shell thickness and the related change of the particle radius during the surfactant adsorption have been evaluated by LS. The evaluation of the radius of the particle, of the hydrodynamic radius, and of the gyration radius by LS (both static and dynamic) provided significant indications about the particle shape. Cryo-SEM images of the particles gave further evidence about their morphology. For pure rubber spheres, the information on the change of the particle radius obtained from LS confirmed the two-stage adsorption mechanism previously proposed for the adsorption on larger particles1 : at the beginning the surfactant molecules adsorb in a ?head to tail? way in order to maximize the hydrophobic interactions between the surface and the hydrocarbon tail; with the increase of the surfactant concentration on the surface, the molecules assume a ?tails on? disposition. However, for the particles with a partial polymeric shell surrounding the rubber core, the adsorption mechanism becomes more complicated. From the experimental data, the ratio of exposed surface of the rubber core to the total external surface has been calculated. A model has been developed, which is based on combining information about the adsorption of the same surfactant on the pure rubber core and pure shell materials measured indipendently, to describe the partitioning of the surfactant on different material surfaces. Starting from this clear picture of the adsorption mechanism, the colloidal stability of these particles both under shear and stagnant conditions has been investigated. For all the particles the turbulent coagulation was studied by shearing the dispersions in a micro channel at very high shear-rate and varying temperature and particle concentration. The conversion of the primary particles as well as the cluster size of the obtained gel were evaluated by Small Angle Light Scattering. The gel samples were also characterized in terms of rheological properties and by taking SEM pictures. Combination of several techniques allowed the understanding of the influence of the surface morphology on the particles interactions.
References:
[1] A. Zaccone, H. Wu, M. Lattuada and M. Morbidelli, Journal of Physical Chemistry B; 2008, 112, 197
Note sull’attribuzione come abduzione, a cura di M. Bonfantini e M. Lombardi, Napoli, Edizioni Scientifiche Italiane
No full textRationally designed Magnetic Particles enable Capturing and Detection of Bacterial Pathogens
No full textIn this work we highlight magnetic blood purification as possible therapy for blood stream infections [1-2], where circulating pathogens are at first removed from the bodily fluid and subsequently recovered and analyzed. (Fig. 1) This process would result in an immediate therapeutic benefit for the patient, while also considerably shortening the diagnosis process, a critical step which heavily affects the final outcome of the treatment. Finally, the use of a newly developed human IgG1 monoclonal antibody against poly-N-acetylglucosamine (PNAG) as targeting moiety extends this therapy to the majority of the pathogens responsible for the most frequent nosocomial infections. We show an experimental proof-of-concept study along with an optimization of carrier-pathogen interactions based on a mathematical model and an investigations on the process safety [3].
[1] I. K. Herrmann, M. Urner, F. M. Koehler, M. Hasler, B. Roth-Z’Graggen, R. N. Grass, U. Ziegler, B. Beck-Schimmer, and W. J. Stark, Small, 2010, 6, 1388
[2] I. K. Herrmann , M. Urner, S. Graf , C. M. Schumacher , B. Roth-Z’graggen , M. Hasler , W. J. Stark , and B. Beck-Schimmer, Adv. Healthcare Mater., 2013, 2, 829–835
[3] M. Lattuada, Q. Ren, F. Zuber, M. Galli, N. Bohmer, A. Wichser, S. Bertazzo, G. B. Pier and I. K. Herrmann, J. Mater Chem. B, under review
Filogenesi di alcune popolazioni di cinghiali (Sus scrofa) in Italia
No full textFilogenesi di alcune popolazioni di cinghiali (Sus Scrofa) in Italia
Laura Lattuada, Federica Quaglia, Renato Bacchetta, Michele Polli
La consistenza e l’attuale diffusione del cinghiale (Sus Scrofa) in Italia sono il risultato di una vera e propria esplosione demografica avvenuta, come in altri paesi europei, a partire dal secondo dopoguerra; un ruolo fondamentale in questo processo è stato svolto anche dall’importazione di animali da alcuni paesi dell’Europa centro-orientale che hanno potuto incrociarsi con nuclei di cinghiali autoctoni e con locali popolazioni di maiali viventi in regime di semilibertà. Lo scopo di questo lavoro è quello di analizzare le relazioni filogenetiche tra diverse popolazioni di cinghiali italiane e verificare l’esistenza di eventuali ibridazioni con i maiali domestici. Sono state così sequenziate 466 bp, dalla posizione 15619 alla posizione 16085 rispetto alla sequenza di riferimento GenBank AJ002189 del DNA mitocondriale, di 59 esemplari provenienti da tre regioni italiane: Lombardia (provincia di Bergamo), Toscana (provincia di Arezzo) ed Emilia Romagna (provincia di Parma). Le analisi hanno individuato13 SNPs definendo 9 differenti aplotipi che sono stati confrontati con 53 sequenze di maiali e cinghiali europei ed asiatici. Le analisi sono state condotte utilizzando i software PHYLIP e TREEPUZZLE per la costruzione degli alberi filogenetici con il metodo Neighbour-Joining e Maximum Likelihood; come outgroup è stato considerato il facocero (Phacochoerus aethiopicus). I risultati delle analisi filogenetiche indicano che le 3 popolazioni studiate, posizionandosi principalmente nel clade che include linee selvatiche e razze domestiche europee, mostrano chiari segni di introgressione dei geni alloctoni. Solo gli esemplari della Maremma Toscana, presenti in GeneBank, sembrerebbero presentare una linea mitocondriale esclusiva dei cinghiali italiani
Attribuzioni a Christian Berentz, Rosa da Tivoli, Luciano Borzone, Charles Mellin e Luca Giordano per dipinti della Pinacoteca Comunale di Macerata
No full textAlessandro Farnese, un grande condottiero in miniatura. Il Duca di Parma e Piacenza ritratto da Jean de Saive
No full textEstimation of Fractal Dimension of Colloidal Gels in the Presence of Multiple Scattering
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