Droplet breakup driven by shear thinning solutions in a microfluidic T-Junction

Droplet-based microfluidics turned out to be an efficient and adjustable platform for digital analysis, encapsulation of cells, drug formulation, and polymerase chain reaction. Typically, for most biomedical applications, the handling of complex, non-Newtonian fluids is involved, e.g. synovial and salivary fluids, collagen, and gel scaffolds. In this study we investigate the problem of droplet formation occurring in a microfluidic T-shaped junction, when the continuous phase is made of shear thinning liquids. At first, we review in detail the breakup process providing extensive, side-by-side comparisons between Newtonian and non-Newtonian liquids over unexplored ranges of flow conditions and viscous responses. The non-Newtonian liquid carrying the droplets is made of Xanthan solutions, a stiff rod-like polysaccharide displaying a marked shear thinning rheology. By defining an effective Capillary number, a simple yet effective methodology is used to account for the shear-dependent viscous response occurring at the breakup. The droplet size can be predicted over a wide range of flow conditions simply by knowing the rheology of the bulk continuous phase. Experimental results are complemented with numerical simulations of purely shear thinning fluids using Lattice Boltzmann models. The good agreement between the experimental and numerical data confirm the validity of the proposed rescaling with the effective Capillary number.Comment: Manuscript: 11 pages 5 figures, 65 References. Textual Supplemental Material: 6 pages 3 figure. Video Supplemental Materials: 2 movie

Drop mobility on chemically heterogeneous and lubricant-impregnated surfaces

Controlling the motion of liquid drops in contact with a solid surface has broad technological implications in many different areas ranging from textiles to microfluidics and heat exchangers. The wettability of a surface is determined by specifying the apparent contact angle and contact angle hysteresis (CAH) that depend on the surface chemistry and morphology. The presence of chemical inhomogeneity and morphological disorder usually increases CAH. A liquid substrate, whose surface is atomically flat and homogenous, is then expected to exhibit a very low CAH. Low CAH determines high drop mobility, while high CAH favours drop pinning. Very slippery surfaces with exceptional omniphobicity are obtained by impregnating a textured solid with a lubricant. To guide and control the motion of drops, the solid surface can be decorated with suitable chemical patterns. In this review, we briefly outline the main results obtained in the past few years to passively control drop motion and produce robust omniphobic surfaces, highlighting some of the most promising applications of these novel functional surfaces

Brambilla et al. Reply to a Comment by J. Reinhardt et al. on "Probing the equilibrium dynamics of colloidal hard spheres above the mode-coupling glass transition"

G. Brambilla et al. Reply to a Comment by J. Reinhardt et al. questioning the existence of equilibrium dynamics above the critical volume fraction of colloidal hard spheres predicted by mode coupling theory.Comment: To appear in Phys. Rev. Lett. Reply to a Comment by J. Reinhardt et al. (see arXiv:1010.2891), which questions the existence of equilibrium dynamics above the critical volume fraction of glassy colloidal hard spheres predicted by mode coupling theor

Single-file escape of colloidal particles from microfluidic channels

Single-file diffusion is a ubiquitous physical process exploited by living and synthetic systems to exchange molecules with their environment. It is paramount quantifying the escape time needed for single files of particles to exit from constraining synthetic channels and biological pores. This quantity depends on complex cooperative effects, whose predominance can only be established through a strict comparison between theory and experiments. By using colloidal particles, optical manipulation, microfluidics, digital microscopy and theoretical analysis we uncover the self-similar character of the escape process and provide closed-formula evaluations of the escape time. We find that the escape time scales inversely with the diffusion coefficient of the last particle to leave the channel. Importantly, we find that at the investigated {\bf microscale}, bias forces as tiny as $10^{-15}\;{\rm N}$ determine the magnitude of the escape time by drastically reducing interparticle collisions. Our findings provide crucial guidelines to optimize the design of micro- and nano-devices for a variety of applications including drug delivery, particle filtering and transport in geometrical constrictions.Comment: 6 pages, 3 figure

Direct experimental evidence of a growing length scale accompanying the glass transition

Understanding glass formation is a challenge because the existence of a true glass state, distinct from liquid and solid, remains elusive: Glasses are liquids that have become too viscous to flow. An old idea, as yet unproven experimentally, is that the dynamics becomes sluggish as the glass transition approaches because increasingly larger regions of the material have to move simultaneously to allow flow. We introduce new multipoint dynamical susceptibilities to estimate quantitatively the size of these regions and provide direct experimental evidence that the glass formation of molecular liquids and colloidal suspensions is accompanied by growing dynamic correlation length scales.Comment: 5 pages, 2 figure

Un capitolo minore della narrativa cinquecentesca: gli Apologi di Bernardino Ochino (Ginevra, 1554). Appunti in vista di un’edizione

In quest’articolo viene fornita una prima descrizione degli Apologi di Bernardino Ochino, pubblicati a Ginevra nel 1554. Gli Apologi sono una raccolta di 100 brevi prose che, sul modello della facezia e del motto arguto, ricostruiscono quadretti comici ambientati in genere nella curia romana. I vizi, le cattive abitudini del clero, ma anche certe posizioni dottrinali come l’infallibilità papale ex cathedra sono il principale bersaglio degli Apologi. Allo scopo di allestire un’edizione critica e commentata, lo studio presenta un primo approccio agli aspetti principali di quest’opera: contenuti teologici, il genere letterario e le sue possibili fonti, e l’importanza della lingua comica ochiniana, nel contesto specifico della produzione in italiano all’estero durante l’epoca della Riforma.Dans cette étude on fournit une première description des Apologi de Bernardino Ochino. Cet ouvrage, publié à Genève en 1554, consiste en un recueil de 100 brèves nouvelles qui, à l’instar de la facétie et du mot d’esprit, esquissent des scènes comiques se déroulant principalement à la Curie Romaine. Les vices, les mœurs du clergé, mais aussi certaines positions doctrinales telle que l’infaillibilité papale ex cathedra, sont la cible des petites histoires et des courts dialogues des Apologi. Dans le but d’en fournir une édition critique et commentée, cet article présente une première approche pour l’étude des principaux aspects de cet ouvrage : les thématiques théologiques, le genre littéraire et ses sources éventuelles, ainsi que l’importance du langage comique d’Ochino, considéré dans le contexte de la production en langue italienne à l’étranger pendant les années de la Réforme

Il modello linguistico decameroniano e il suo rapporto con il volgare nel pensiero di Antonio Brucioli

Introduzione Circa vent’anni fa, Paolo Trovato, in uno studio che avrebbe contribuito a rinnovare l’approccio metodologico della cinquecentesca questione della lingua italiana, si chiedeva (e chiedeva ai suoi lettori): «Cosa possono insegnarci, in concreto, le Prefazioni?». Trovato, attraverso un’acuta analisi delle prefazioni di testi appartenenti a una letteratura cosiddetta “minore” (bibbie, trattati poco celebri, libri mercantili, ecc.), rispondeva mettendo in evidenza la fragilità delle ..