Abstract
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 Peclet 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 sus...
Highlights
IntroductionThe interest and use of colloidal silica as a precursor in various industrial processes are due to its many advantageous properties including low toxicity, chemical stability, and high colloidal stability in various conditions.[1−3] It is used widely in applications such as postsynthesis surface modification,[4,5] drug carriers,[6,7] catalytic supports,[8,9] and antifouling coatings[10,11] and has factored significantly in nanoparticle research and particle formation from the drying of suspensions.[12−14]Understanding the drying of droplet suspensions is of great importance to a variety of processes such as production of catalyst, ceramic, and various pharmaceutical products.[15−17] Many of these products, such as paint pigments and milk powders, are manufactured in a complex industrial process typically through spray drying, whereby spray generation followed by solvent evaporation leads to the assembly of dried grains with different characteristics
The drying of a suspension and the associated grain morphology formed as a result of drying is a function of a number of parameters including, but not limited to, particle size, particle concentration, and droplet volume
The aim of the present work was to investigate the drying kinetics of droplet suspensions and the resulting morphology of grains at the end of drying, which is important to a variety of industrial applications
Summary
The interest and use of colloidal silica as a precursor in various industrial processes are due to its many advantageous properties including low toxicity, chemical stability, and high colloidal stability in various conditions.[1−3] It is used widely in applications such as postsynthesis surface modification,[4,5] drug carriers,[6,7] catalytic supports,[8,9] and antifouling coatings[10,11] and has factored significantly in nanoparticle research and particle formation from the drying of suspensions.[12−14]Understanding the drying of droplet suspensions is of great importance to a variety of processes such as production of catalyst, ceramic, and various pharmaceutical products.[15−17] Many of these products, such as paint pigments and milk powders, are manufactured in a complex industrial process typically through spray drying, whereby spray generation followed by solvent evaporation leads to the assembly of dried grains with different characteristics. Stage-2 drying, the so-called falling rate period, begins at the critical moisture content, Xcr, when the solvent from the interior of the droplet can no longer keep the entire surface saturated and a shell is formed as a result of particle deposition at the liquid−air interface. Evaporation continues in this stage through the pores of the shell, until the equilibrium moisture content, Xeq, is reached. At this point the resulting particles are typically both dry and rigid
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