Abstract
Studies of the evaporation of aqueous nanoparticle solutions have been limited due to lack of homogeneity of the solution, difficulties in obtaining reproducible samples and stability of substrates, as well as the effect of other volatile components or contaminants such as surfactants. Colloidal unimolecular polymer (CUP) is a spheroidal nanoparticle with charged hydrophilic groups on the surface, and the particle size ranges from 3 to 9 nm. The large amount of surface water on the CUP surface provides the opportunity to evaluate the evaporation of surface water, which may contribute to the investigation the factors that affect the evaporation rate in solutions of ultra-small particles, like protein, micelle, colloidal, etc. Six CUP systems were evaluated by thermogravimetric analysis (TGA) with respect to time and solids content. The evaporation rate of water was initially enhanced due to the deformation of the air-water interface at low to moderate concentration due to particle charge repulsive forces. At higher concentrations, above 20%, surface charge condensation and increasing viscosity began to dominate. At higher concentration where the CUP reached the gel point the rate of diffusion controlled the evaporation. The final drying point was the loss of three waters of hydration for each carboxylate on the CUP surface.
Highlights
The evaporation of aqueous nanoparticle solutions has been a topic of interest, and it is one of the most important, fundamental kinetic and thermodynamic characteristics, which offers an opportunity to investigate the basic concept in diffusion, surface behavior, polymer properties and solution dynamics [1,2]
The polymers selected for this study were based on particle size and surface charge density issues which have been shown to dominate the properties of surface water, viscosity, and density
The results showed thatthat evaporation raterate sharply decreased whenwhen the percent solidssolids passes passes the hexagonal close packing (HCP), due to the highly limited mobility of particles and water molecules
Summary
The evaporation of aqueous nanoparticle solutions has been a topic of interest, and it is one of the most important, fundamental kinetic and thermodynamic characteristics, which offers an opportunity to investigate the basic concept in diffusion, surface behavior, polymer properties and solution dynamics [1,2]. The investigation of the water evaporation of aqueous nanoparticles solutions provide a great study model for DNA packing, protein drying processes and drug delivery, its potential application in the drying of water borne coatings, water borne pesticides and biocides, herbicide, cosmetics, and many others [3,4,5,6,7]. Boukherroub et al [8] reported an increase in the evaporation rate of water-based graphene nanofluids. It was proposed that graphene oxide functionalization with polyethylene glycol promoted the dispersion of graphene nanoparticles and increased the evaporation rate at constant temperature. The potential agglomeration and poor dispersion of graphene nanoparticles at high concentration could cause a decrease in the evaporation rate. Kim et al [9] found that the evaporation rate of nanofluid aqueous droplet was higher than deinoized water with the presence of 80 nm sized CuO powder under
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