arXiv subjects

Guido Bolognesi

Publications and source records attributed to Guido Bolognesi.

4 recordsLinked to original sources

arXiv2025

Surface Chemistry-based Continuous Separation of Colloidal Particles via Diffusiophoresis and Diffusioosmosis

The separation of colloidal particles based solely on their surface properties is a highly challenging task. This study demonstrates that diffusiophoresis and diffusioosmosis enable the continuous separation of carboxylate polystyrene particles with similar sizes and zeta potentials but distinct surface concentrations of carboxyl groups. The particles are exposed to salt concentration gradients generated in a double-junction microfluidic device. Through experimental and theoretical analyses, we demonstrate how the particle dynamics are influenced by their zeta potential sensitivity to the local salt concentration, which in turn is affected by surface conductance effects induced by the surface carboxyl groups. Consequently, colloids with comparable zeta potentials but differing surface concentrations of carboxyl groups can be separated with 100% efficiency. This approach, which employs a simple, easy-to-operate device, has discipline-spanning potential for the continuous separation of colloids distinguished solely by surface properties that influence their zeta potential sensitivities, like roughness, permeability, heterogeneity, and chemical composition.

cond-mat.soft↗

arXiv2023

Continuous manipulation and characterization of colloidal beads and liposomes via diffusiophoresis in single- and double-junction microchannels

We reveal an unreported physical mechanism that enables the pre-concentration, sorting and characterization of charged polystyrene nanobeads and liposomes dispersed in a continuous flow within a straight micron-sized channel. Initially, a single $Ψ$-junction microfluidic chip is used to generate a steady-state salt concentration gradient in the direction perpendicular to the flow. As a result, fluorescent nanobeas dispersed in the electrolyte solutions accumulate into symmetric regions of the channel, appearing as two distinct symmetric stripes when the channel is observed from top via epi-fluorescence microscopy. Depending on the electrolyte flow configuration and, thus, the direction of the salt gradient field, the fluorescent stripes get closer to or apart from each other as the distance from the inlet increases. Our numerical and experimental analysis shows that, although diffusiophoresis and hydrodynamic effects are involved in the accumulation process, diffusioosmosis plays a crucial role in the observed particles dynamics. In addition, we developed a proof-of-concept double $Ψ$-junction microfluidic device which exploits this new accumulation mechanism for the size-based separation and size detection of nanobeads as well as for the measurement of zeta potential and charged lipid composition of liposomes under continuous flow settings. This device is also used to investigate the effect of fluid-like or gel-like states of the lipid membranes on the liposome diffusiophoretic response. The proposed strategies for solute-driven manipulation of colloids have great potential for microfluidic bio-analytical testing applications, including bioparticle pre-concentration, sorting, sensing and analysis.

cond-mat.soft↗

arXiv2020

Reversible Trapping of Colloids in Microgrooved Channels via Diffusiophoresis under Steady-State Solute Gradients

The controlled transport of colloids in dead-end structures is a key capability that can enable a wide range of applications, such as bio-chemical analysis, drug delivery and underground oil recovery. This letter presents a new trapping mechanism that allows the fast (i.e., within a few minutes) and reversible accumulation of sub-micron particles within dead-end micro-grooves by means of parallel streams with different salinity level. For the first time, particle focusing in dead-end structures is achieved under steady-state gradients. Confocal microscopy analysis and numerical investigations show that the particles are trapped at a flow recirculation region within the grooves due to a combination of diffusiophoresis transport and hydrodynamic effects. Counterintuitively, the particle velocity at the focusing point is not vanishing and, hence, the particles are continuously transported in and out of the focusing point. The accumulation process is also reversible and one can cyclically trap and release the colloids by controlling the salt concentration of the streams via a flow switching valve.

cond-mat.soft↗

arXiv2014

Experimental evidence of slippage breakdown for a superhydrophobic surface in a microfluidic device

A full characterization of the water flow past a silicon superhydrophobic surface with longitudinal micro-grooves enclosed in a microfluidic device is presented. Fluorescence microscopy images of the flow seeded with fluorescent passive tracers were digitally processed to measure both the velocity field and the position and shape of the liquid-air interfaces at the superhydrophobic surface. The simultaneous access to the meniscus and velocity profiles allows us to put under a strict test the no-shear boundary condition at the liquid-air interface. Surprisingly, our measurements show that air pockets in the surface cavities can sustain non-zero interfacial shear stresses, thereby hampering the friction reduction capabilities of the surface. The effects of the meniscus position and shape as well as of the liquid-air interfacial friction on the surface performances are separately assessed and quantified.

physics.flu-dyn↗