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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) In situ fluid cell HAADF STEM image of diluted aqueous alumina slurry.The hydration layer is manifested as a cloud enveloping aggregated nanopsheres. These hydrated aggregates and surrounding liquid represent the new nanoparticles in the slurries. Scale bar: 100 nm. Inset shows schematics of the formed aggregate with the size and aspect ratio different from that of initial spherical particles. (B) Size distribution of long axis, X, of the hydrated aggregates measured 133 ± 100 nm (n = 100). (C) Size distribution of short axis of the hydrated aggregates, Y, measured 87 ± 61 nm (n = 100).
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f6: (A) In situ fluid cell HAADF STEM image of diluted aqueous alumina slurry.The hydration layer is manifested as a cloud enveloping aggregated nanopsheres. These hydrated aggregates and surrounding liquid represent the new nanoparticles in the slurries. Scale bar: 100 nm. Inset shows schematics of the formed aggregate with the size and aspect ratio different from that of initial spherical particles. (B) Size distribution of long axis, X, of the hydrated aggregates measured 133 ± 100 nm (n = 100). (C) Size distribution of short axis of the hydrated aggregates, Y, measured 87 ± 61 nm (n = 100).

Mentions: Figure 6 (A) reveals the alumina nanoparticles in water, with the hydration layer manifested as a cloud enveloping several nanopsheres at once, as schematically shown in the inset. The aggregate is considered an ellipsoid with the mean values of the long and short axes of the aggregates formed in the liquid were reported in Fig. 6 (B, C) as 133 ± 100 nm and 87 ± 61.2 nm (n = 100), respectively. Here a relatively low image contrast had likely led to a larger error in the size measurements, contributing to a wider size distribution. Liquid cell holder allowed for limited tilting (± 22 degrees), and we have employed imaging of the tilted cell specifically to evaluate the third (thickness) dimension of the specimen. Based on the data obtained in this manner, the aggregation in Z-direction could be viewed as very similar to that in the direction of short (Y) axis.


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) In situ fluid cell HAADF STEM image of diluted aqueous alumina slurry.The hydration layer is manifested as a cloud enveloping aggregated nanopsheres. These hydrated aggregates and surrounding liquid represent the new nanoparticles in the slurries. Scale bar: 100 nm. Inset shows schematics of the formed aggregate with the size and aspect ratio different from that of initial spherical particles. (B) Size distribution of long axis, X, of the hydrated aggregates measured 133 ± 100 nm (n = 100). (C) Size distribution of short axis of the hydrated aggregates, Y, measured 87 ± 61 nm (n = 100).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f6: (A) In situ fluid cell HAADF STEM image of diluted aqueous alumina slurry.The hydration layer is manifested as a cloud enveloping aggregated nanopsheres. These hydrated aggregates and surrounding liquid represent the new nanoparticles in the slurries. Scale bar: 100 nm. Inset shows schematics of the formed aggregate with the size and aspect ratio different from that of initial spherical particles. (B) Size distribution of long axis, X, of the hydrated aggregates measured 133 ± 100 nm (n = 100). (C) Size distribution of short axis of the hydrated aggregates, Y, measured 87 ± 61 nm (n = 100).
Mentions: Figure 6 (A) reveals the alumina nanoparticles in water, with the hydration layer manifested as a cloud enveloping several nanopsheres at once, as schematically shown in the inset. The aggregate is considered an ellipsoid with the mean values of the long and short axes of the aggregates formed in the liquid were reported in Fig. 6 (B, C) as 133 ± 100 nm and 87 ± 61.2 nm (n = 100), respectively. Here a relatively low image contrast had likely led to a larger error in the size measurements, contributing to a wider size distribution. Liquid cell holder allowed for limited tilting (± 22 degrees), and we have employed imaging of the tilted cell specifically to evaluate the third (thickness) dimension of the specimen. Based on the data obtained in this manner, the aggregation in Z-direction could be viewed as very similar to that in the direction of short (Y) axis.

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.