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Direct Visualization of the Hydration Layer on Alumina Nanoparticles with the Fluid Cell STEM in situ.

Firlar E, Çınar S, Kashyap S, Akinc M, Prozorov T - Sci Rep (2015)

Bottom Line: Unusually high viscosities observed for suspensions of nanoparticles compared to those of micron size powders cannot be explained by current viscosity models.We observe the hydration layer formed over the particle aggregates and show that such hydrated aggregates constitute new particle assemblies and affect the flow behavior of the suspensions.We discuss how these hydrated nanoclusters alter the effective solid content and the viscosity of nanostructured suspensions.

View Article: PubMed Central - PubMed

Affiliation: Division of Materials Science and Engineering, US DOE Ames Laboratory, Ames, IA, 50011, USA.

ABSTRACT
Rheological behavior of aqueous suspensions containing nanometer-sized powders is of relevance to many branches of industry. Unusually high viscosities observed for suspensions of nanoparticles compared to those of micron size powders cannot be explained by current viscosity models. Formation of so-called hydration layer on alumina nanoparticles in water was hypothesized, but never observed experimentally. We report here on the direct visualization of aqueous suspensions of alumina with the fluid cell in situ. We observe the hydration layer formed over the particle aggregates and show that such hydrated aggregates constitute new particle assemblies and affect the flow behavior of the suspensions. We discuss how these hydrated nanoclusters alter the effective solid content and the viscosity of nanostructured suspensions. Our findings elucidate the source of high viscosity observed for nanoparticle suspensions and are of direct relevance to many industrial sectors including materials, food, cosmetics, pharmaceutical among others employing colloidal slurries with nanometer-scale particles.

No MeSH data available.


(A) BF-TEM ex situ images of as received alumina nanospheres with the diameter of the particle of measured as of 50 ± 26 nm (inset) (n = 132).Here the aggregation of nanoparticles is likely induced by the solvent evaporation during the TEM sample preparation. Inset shows particles size distribution. Scale bar: 50 nm. (B) A thin deposit on a surface of neighboring nanoparticles can be seen at higher magnification. Scale bar: 20 nm.
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f1: (A) BF-TEM ex situ images of as received alumina nanospheres with the diameter of the particle of measured as of 50 ± 26 nm (inset) (n = 132).Here the aggregation of nanoparticles is likely induced by the solvent evaporation during the TEM sample preparation. Inset shows particles size distribution. Scale bar: 50 nm. (B) A thin deposit on a surface of neighboring nanoparticles can be seen at higher magnification. Scale bar: 20 nm.

Mentions: As-received powders were characterized by means of Bright Field TEM (BF-TEM). Figure 1 (A, B) shows the BF-TEM images of as received Al2O3 nanoparticles on a standard EM grid, with the mean diameter of the particle of measured as 50 ± 26 nm (n = 132), in good agreement with the equivalent spherical diameter calculated from the measured surface area of 38.8 m2/g24. Significant fraction (25−40%) of nanoparticles was found to exhibit a surface-localized deposit shown in Fig. 1(B).


Direct Visualization of the Hydration Layer on Alumina Nanoparticles with the Fluid Cell STEM in situ.

Firlar E, Çınar S, Kashyap S, Akinc M, Prozorov T - Sci Rep (2015)

(A) BF-TEM ex situ images of as received alumina nanospheres with the diameter of the particle of measured as of 50 ± 26 nm (inset) (n = 132).Here the aggregation of nanoparticles is likely induced by the solvent evaporation during the TEM sample preparation. Inset shows particles size distribution. Scale bar: 50 nm. (B) A thin deposit on a surface of neighboring nanoparticles can be seen at higher magnification. Scale bar: 20 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4440531&req=5

f1: (A) BF-TEM ex situ images of as received alumina nanospheres with the diameter of the particle of measured as of 50 ± 26 nm (inset) (n = 132).Here the aggregation of nanoparticles is likely induced by the solvent evaporation during the TEM sample preparation. Inset shows particles size distribution. Scale bar: 50 nm. (B) A thin deposit on a surface of neighboring nanoparticles can be seen at higher magnification. Scale bar: 20 nm.
Mentions: As-received powders were characterized by means of Bright Field TEM (BF-TEM). Figure 1 (A, B) shows the BF-TEM images of as received Al2O3 nanoparticles on a standard EM grid, with the mean diameter of the particle of measured as 50 ± 26 nm (n = 132), in good agreement with the equivalent spherical diameter calculated from the measured surface area of 38.8 m2/g24. Significant fraction (25−40%) of nanoparticles was found to exhibit a surface-localized deposit shown in Fig. 1(B).

Bottom Line: Unusually high viscosities observed for suspensions of nanoparticles compared to those of micron size powders cannot be explained by current viscosity models.We observe the hydration layer formed over the particle aggregates and show that such hydrated aggregates constitute new particle assemblies and affect the flow behavior of the suspensions.We discuss how these hydrated nanoclusters alter the effective solid content and the viscosity of nanostructured suspensions.

View Article: PubMed Central - PubMed

Affiliation: Division of Materials Science and Engineering, US DOE Ames Laboratory, Ames, IA, 50011, USA.

ABSTRACT
Rheological behavior of aqueous suspensions containing nanometer-sized powders is of relevance to many branches of industry. Unusually high viscosities observed for suspensions of nanoparticles compared to those of micron size powders cannot be explained by current viscosity models. Formation of so-called hydration layer on alumina nanoparticles in water was hypothesized, but never observed experimentally. We report here on the direct visualization of aqueous suspensions of alumina with the fluid cell in situ. We observe the hydration layer formed over the particle aggregates and show that such hydrated aggregates constitute new particle assemblies and affect the flow behavior of the suspensions. We discuss how these hydrated nanoclusters alter the effective solid content and the viscosity of nanostructured suspensions. Our findings elucidate the source of high viscosity observed for nanoparticle suspensions and are of direct relevance to many industrial sectors including materials, food, cosmetics, pharmaceutical among others employing colloidal slurries with nanometer-scale particles.

No MeSH data available.