Abstract:When a sessile droplet of a complex fluid dries, a stain forms on the solid surface. The structure and pattern of the stain can be used to detect the presence of a specific chemical compound in the sessile droplet. In the present work, we investigate what parameters of the stain or its formation can be used to characterize the specific interaction between an aqueous dispersion of beads and its receptor immobilized on the surface. We use the biotin-streptavidin system as an experimental model. Clear dissimilari… Show more
“…Hurth et al . 23 conducted evaporation of sessile droplet containing streptavidin- or biotin-coated fluorescent polystyrene (PS) particles and found that both the biological binding force and the capillary force play significant roles in particle deposition and that the viscous drag, van der Waals forces, and solid-solid friction forces are negligible. Recently, using particle tracking velocimetry technique, Yu et al .…”
Evaporation of water and ethanol/water droplets containing large polystyrene (PS) microparticles on polydimethylsiloxane (PDMS) surface was experimentally investigated. It is found that no matter with or without small addition of ethanol, a compact monolayer deposition is formed for lower microparticle concentration while mountain-like deposition for higher concentration. Since the more volatile compound (ethanol) evaporates more quickly than the less volatile compound (water), evaporation of ethanol/water mixture droplet exhibits different characteristics from pure water. When the concentration of microparticle is low, the contact radius of ethanol/water mixture droplet decreases throughout the whole process, while the contact angle increases at first to a maximum, then keeps almost constant, and finally decreases sharply. However, the evaporation of ethanol/water mixture droplet with higher concentration of microparticle behaviors more complex. The settling time of microparticles was estimated and its theoretical value agrees well with the experimental one. Moreover, a mechanism of self-pinning of microparticles was used to elucidate the deposition behavior of microparticles, indicating that as the contact line is depinning, the liquid film covering the outmost microparticle becomes thicker and thicker, and the microparticles have to move spontaneously with the depinning contact line under the action of capillary force.
“…Hurth et al . 23 conducted evaporation of sessile droplet containing streptavidin- or biotin-coated fluorescent polystyrene (PS) particles and found that both the biological binding force and the capillary force play significant roles in particle deposition and that the viscous drag, van der Waals forces, and solid-solid friction forces are negligible. Recently, using particle tracking velocimetry technique, Yu et al .…”
Evaporation of water and ethanol/water droplets containing large polystyrene (PS) microparticles on polydimethylsiloxane (PDMS) surface was experimentally investigated. It is found that no matter with or without small addition of ethanol, a compact monolayer deposition is formed for lower microparticle concentration while mountain-like deposition for higher concentration. Since the more volatile compound (ethanol) evaporates more quickly than the less volatile compound (water), evaporation of ethanol/water mixture droplet exhibits different characteristics from pure water. When the concentration of microparticle is low, the contact radius of ethanol/water mixture droplet decreases throughout the whole process, while the contact angle increases at first to a maximum, then keeps almost constant, and finally decreases sharply. However, the evaporation of ethanol/water mixture droplet with higher concentration of microparticle behaviors more complex. The settling time of microparticles was estimated and its theoretical value agrees well with the experimental one. Moreover, a mechanism of self-pinning of microparticles was used to elucidate the deposition behavior of microparticles, indicating that as the contact line is depinning, the liquid film covering the outmost microparticle becomes thicker and thicker, and the microparticles have to move spontaneously with the depinning contact line under the action of capillary force.
“…For instance, this knowledge base will help to explain deposit obtained from the drying of blood droplets which could be useful in forensics [45], biomarkers [46] and fingerprint residues in blood pattern analysis [6]. In biology, the bio-molecular interaction between the particles and substrate is important to understand the formation of bio-assays [47]. In this review, we tried to put recent studies that considered the effect of substrate heating, particle size and substrate wettability, however, the combined or coupled effect of each of these parameters over another for wider range is still lacking in the literature.…”
Section: Concluding Remarks and Future Outlookmentioning
Understanding flow patterns and coupled transport phenomena during evaporation of droplets loaded with colloidal particles is central to design technical applications such as organizing proteins/DNA on a solid surface. We review recent reports on evaporating sessile droplets of colloidal suspensions on a solid surface. Starting from the classical mechanism of formation of a ring-like deposit, we discuss the influence of several problem parameters. Notably, thermal or solutal Marangoni effect, particle size, particle concentration, particle shape, substrate wettability, pH of the suspension etc have been found important in controlling the deposition pattern. The deposit pattern complexity and shape have been attributed to the underlying coupled transport phenomena during the evaporation. We discuss important regimes maps reported for different types of deposit, which allow us to classify the deposits and coupled physics. We also present studies that have demonstrated particles sorting in an evaporating bi-dispersed colloidal suspensions on a solid surface. Finally, some remarks for the future research opportunities in this arena are presented.
“…In addition, other effects which were found significant in controlling the shape of the deposit are the particle shape, 6 surfactant concentration, 15 substrate elasticity, 16 ambient pressure, 17 particle size, 18 and bio-molecular interaction between the particles and the substrate. 19 In the context of evaporation on a hydrophobic surface, the direction of the characteristic evaporation-driven flow velocity inside the droplet on a superhydrophobic surface is opposite to that on a hydrophilic surface. The colloidal particles move upward due to a larger mass loss at the apex of the droplet as compared to near the contact line.…”
Evaporating
droplets of colloidal suspensions leave behind particle
deposits which could be effectively controlled via manipulating the
surrounding conditions and particles and liquid properties. While
previous studies extensively focused on sessile and pendant droplets,
the present work investigates the evaporation dynamics of capillary
bridges of colloidal suspensions formed between two parallel plates.
We vary the wettability of the plates and the particle size and composition
of the colloidal suspensions, keeping the same spacing between the
plates. We employ side visualization, optical microscopy, fluorescence
microscopy, and scanning electron microscopy and develop computational
and theoretical models to collect the data. A computational model
based on diffusion-limited evaporation is used to characterize the
timescale of the evaporation of the capillary bridge. The model predictions
are in good agreement with the present and prior experimental measurements.
We discuss about the deposits of monodispersed particle suspension
formed by the interplay of pinning of the contact line and evaporation
dynamics. Multiple rings on the plates are observed due to the stick–slip
motion of the contact line. The larger particles tend to form asymmetric
deposits, with most particles concentrated on the bottom plates due
to a considerably stronger gravitational pull than the hydrodynamic
drag. This deposition is explained by estimating the competing forces
on the particles during the evaporation. A regime map is proposed
for classifying deposits on the particle size wettability plane. Lastly,
we demonstrate size-based particle sorting of bidispersed colloidal
suspensions in this framework. We describe two mechanisms: gravity-assisted
and geometry-assisted sorting, which can be designed to sort particles
efficiently. A regime map depicting the regions of influence of each
mechanism is presented.
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