Study of dynamics of drying processes in FE2O3 and SIO2 nanocolloid droplets (original) (raw)
Related papers
On liquid evaporation from droplets of colloidal solutions of SiO2 and Fe2O3 nanoparticles
Colloid Journal, 2015
Liquid evaporation from Fe 2 O 3 and SiO 2 nanocolloid droplets has been studied. The geometry of the droplets has been juxtaposed with the intensity of light transmitted through them. It has been established that the droplet evaporation process may be divided into a number of stages, with each of them being distin guished by a certain type of the behavior of suspended nanoparticles. The regularities of the formation of ring shaped deposits, which are referred to as coffee rings in the literature, have been investigated. The main fea tures of the structures of the ring shaped deposits resulting from evaporation of different dispersions are the same. The time of complete liquid evaporation determined by spectrometry has appeared to be longer than the time determined by visual monitoring of droplet geometry. A model has been proposed for the evaporation of droplets of colloidal solutions of nanoparticles.
Amplifying and attenuating the coffee-ring effect in drying sessile nanofluid droplets
Physical Review E, 2013
Experiments and simulations to promote or attenuate the "coffee-ring effect" for pinned sessile nanofluid droplets are presented. The addition of surfactant inside a water suspension of aluminum oxide nanoparticles results in coffee-ring formation after the pinned sessile droplets are fully dried on a substrate, while droplets of the same suspension without the surfactant produce a fine uniform coverage. A mathematical model based on diffusion-limited cluster-cluster aggregation has been developed to explain the observed difference in the experiments. The simulations show that the particle sticking probability is a crucial factor on the morphology of finally dried structures.
Fundamental Investigation of the Drying of Solid Suspensions
Industrial & Engineering Chemistry Research
In this work, a comprehensive series of experiments is conducted to investigate the drying behavior of micro-and nanosized particle dispersions. To this end, an acoustic levitator was used to study the drying kinetics of single droplets. The temporal evolution of the actual droplets was recorded using a complementary metal oxide semiconductor (CMOS) camera, and the solid grains produced at the end of drying were investigated by scanning electron microscopy (SEM) imaging. At the end of drying, the grains show different morphologies as a function of the particle size, concentration, and initial droplet volume. We combine these experimental data to show the drying behavior is dependent on all the parameters and that the data all collapse when plotted against the Pećlet number. This resulted in a novel characteristic diagram which allows one to predict the shape of the dried colloidal droplet based on Pe. Our results extend the fundamental understanding of the mechanisms controlling the drying of droplet suspensions.
Some physics inside drying droplets
Resonance, 2014
Netherlands. His research interests include micronanofluidics and nanoscale electrochemistry. Spreading of a droplet placed on a solid surface (sessile droplet) depends on the wetting properties of the liquid on that surface. Droplets are of great scientific interest because studying their formation and dynamics is important in many technologies such as in microfluidics [1, 2]. Evaporation of droplets is another interesting aspect that has caught much scientific attention. An example of an evaporating droplet is a coffee droplet spilled on a table. After evaporation the coffee droplet leaves a ring-like stain called a coffee ring or coffee stain [3]. This phenomenon, known as the 'coffee ring effect', occurs not only with coffee droplets but also with all droplets containing non-volatile solutes. There are a number of interesting physical processes going on within the droplets during evaporation to form the 'coffee stains'. In this article, we will see what they are.
2015
Ring-stains are seen when droplets of liquid containing particles are left to dry on a surface: a pinned contact line leads to outward radial flow, which is enhanced by the diverging evaporative flux at the contact line. As a result, suspended particles in the drops are transported to the edge of the droplet, and deposited in a circular stain. In the first section of this study, we investigated how the width and height of ring in water droplets containing suspensions of polystyrene microparticles with diameters ≤0.5μm vary with experimentally controlled parameters, including particle size, contact angle, concentration, evaporation rate and orientation of the droplets. Our studies found, for the first time, that the drying rate plays an important role in determining the shape of the final deposit which may contribute to a better understanding of a coffee ring effect. At low drying rates, nearly all the particles are deposited in the ring and the width and height of the ring follow a ...
EFFECT OF SALT CONCENTRATION (NaCl) ON DRYING PATTERN OF FERROFLUID DROPLETS
Journal of Flow Visualization and Image Processing, 2018
Droplets leave a coffee ring-like pattern on a solid surface after complete evaporation. This study reports evaporation and drying pattern of a ferrofluid droplet on a PDMS substrate at different concentrations of NaCl using goniometric imaging, confocal microscopy, and optical profilometry. The receding of the contact line of the droplet gets delayed with increase in the salt concentration. Width of the coffee ring pattern decreases with increase in the salt concentration. Crystals are formed at a higher NaCl concentration. The attraction force between a particle and substrate increases with increase in the salt concentration. Zeta potential and thickness of the double layer decrease due to addition of salt leading to reduction in the repulsion force between the particle and substrate surface. Deposition pattern formation gets affected by a combined effect of surface tension force, electrostatic force, and van der Waals force acting on the particle near the contact line.
The Journal of …, 2008
The method of formation of nanoparticle aggregates such as high-coverage spherical shells of microspheres or 3-D micro crystals grown in the geometry unaffected by a substrate is described. In the reported experiment, the evaporation of single levitated water droplet containing 200 nm diameter polystyrene spheres was studied. Successive stages of the drying process were discussed by analyzing the intensity of light elastically scattered by the evaporating droplet. The numerically simulated self-assembly coincides nicely with the observed morphologies resulting from transformation of a droplet of suspension into a solid microcrystal via kinetically driven self-assembly of nanostructures.
Langmuir, 2020
The present study experimentally and numerically investigates the evaporation and resultant patterns of dried deposits of aqueous colloidal sessile droplets, when the droplets are initially elevated to a high temperature before being placed on a substrate held at ambient temperature. The system is then released for natural evaporation without applying any external perturbation. We employed digital controlled heating and temperature measurement scheme of colloidal particle laden liquid, high-speed side visualization, high-speed infrared thermography, optical microscopy of fluorescent particle tracers and optical profilometry as essential tools for data acquisition. Initially, a significant temperature gradient exists along the liquid-gas interface as soon as the droplet is deposited on the substrate-the droplet remains the hottest at the top and the coolest near the contact line. The temperature gradient induces a Marangoni recirculation flow, which is directed from the top of the droplet towards the contact line along the liquidgas interface-thus, the flow is in reverse direction to that seen in conventional substrate heating case. Interestingly, this temperature gradient decays rapidly-within the first 10% of the total evaporation time and the droplet-substrate system reaches thermal equilibrium with ambient thereafter. Despite fast decay of the temperature gradient, the coffee-ring dimensions significantly diminish, leading to an inner deposit. The reproducibility of the observations has been confirmed by varying particle concentrations in the aqueous suspension. This suppression of the coffee-ring effect is attributed to the fact that the recirculation flow, generated by initial temperature gradient induced Marangoni stress, continues till the last stage of the evaporation, even after the interfacial temperature gradient vanishes. This is essentially a consequence of liquid inertia. Thus, the suspended colloidal particles are advected by this recirculating flow towards the inner region of the droplet, thereby suppressing the coffee-ring effect. Finally, a finite-element based twodimensional modeling in axisymmetric geometry has been developed and employed to verify the measurements. The modeling and measurements are in reasonable agreement and the hypothesis considered in the present study corroborates well with a first approximation qualitative scaling analysis. Overall, together with a new experimental condition, the present investigation discloses a distinct nature of Marangoni stress induced flow in the droplet and its role in influencing the associated colloidal deposits, which was not explored previously. The insights gained from this study are useful to advance technical applications such as spray cooling, ink-jet printing, bioassays, etc.
Morphological transformations during drying of surfactant-nanofluid droplets
Journal of Industrial and Engineering Chemistry
The effect of surfactants with different chain length on the drying dynamics of nanosized dispersion droplets and on the final morphology of the grains formed after water evaporation is investigated experimentally. An acoustic levitator was used to examine the drying dynamics of single droplets and SEM imaging was used to characterise the morphology of the final dried grains. Results show that the drying of drops with high molecular weight surfactants leads to more irregular grains and that the grain morphology is related to surface tension driven instability of the evaporating droplets which may lead to formation of hollow dried grains.