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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.


Disordered overlayer formation on neighboring nanoparticles.(A) BF-TEM image of the baked-in overlayer. Scale bar: 50 nm. (B) Higher-magnification image reveals amorphous nature of the formed overlayer. Scale bar: 10nm.
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f2: Disordered overlayer formation on neighboring nanoparticles.(A) BF-TEM image of the baked-in overlayer. Scale bar: 50 nm. (B) Higher-magnification image reveals amorphous nature of the formed overlayer. Scale bar: 10nm.

Mentions: Figure 2 shows the disordered overlayer formed on a surface of neighboring nanoparticles of hydrated alumina powder dried at 125°C overnight. In Fig. 2 (A), individual nanoparticles appear to be linked together by such an overlayer. Figure 2 (B) shows a higher magnification image taken from a random sample area, with the amorphous overlayer of roughly 4 nm thickness encapsulating several crystalline particles at once. We attempted resetting the specimen history through the modification of the nanoparticles, described in experimental section. The result of the surface modification of the alumina nanopowder with ethanol, leading to removal of the overlayer formed on the powder surfaces, can be seen in the BF-TEM image in Fig. 3. Here the particle aggregation was attributed to the evaporation of solvent. Additional surface characterization was carried out by using the X-ray photoelectron Spectroscopy (XPS). Supp. Figure S1 shows the XPS spectra acquired on alumina powder exposed to different conditions.


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)

Disordered overlayer formation on neighboring nanoparticles.(A) BF-TEM image of the baked-in overlayer. Scale bar: 50 nm. (B) Higher-magnification image reveals amorphous nature of the formed overlayer. Scale bar: 10nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Disordered overlayer formation on neighboring nanoparticles.(A) BF-TEM image of the baked-in overlayer. Scale bar: 50 nm. (B) Higher-magnification image reveals amorphous nature of the formed overlayer. Scale bar: 10nm.
Mentions: Figure 2 shows the disordered overlayer formed on a surface of neighboring nanoparticles of hydrated alumina powder dried at 125°C overnight. In Fig. 2 (A), individual nanoparticles appear to be linked together by such an overlayer. Figure 2 (B) shows a higher magnification image taken from a random sample area, with the amorphous overlayer of roughly 4 nm thickness encapsulating several crystalline particles at once. We attempted resetting the specimen history through the modification of the nanoparticles, described in experimental section. The result of the surface modification of the alumina nanopowder with ethanol, leading to removal of the overlayer formed on the powder surfaces, can be seen in the BF-TEM image in Fig. 3. Here the particle aggregation was attributed to the evaporation of solvent. Additional surface characterization was carried out by using the X-ray photoelectron Spectroscopy (XPS). Supp. Figure S1 shows the XPS spectra acquired on alumina powder exposed to different conditions.

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.