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- High fraction of atoms at or near the surface.
- Surface Tension: liquids surfaces
behave as though they are an elastic film.
- Kelvin Effect: higher vapor
pressure over smaller droplets
- Ostwald Ripening: large particles
grow at the expense of smaller particles
- Adsorption: impurities tend to
stick to surfaces
- Surface charge: adsorption of
ions can leave the nanoparticle electrically charged
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2
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3
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- A sphere of radius R is composed of atoms of radius a. Make the assumption that the surface
atoms occupy a spherical shell 2a thick.
Use the packing fraction to correct for the interstitial
volume. You do not need to
consider the granular nature of the particle any further (ignore
packing, stacking, surface corrugations, etc.).
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4
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- Fluids behave as though they have a surface composed of an elastic skin
which is always in tension. There
are many manifestations of surface tension you can observe
everyday. Here are some
fundamental properties of surface tension.
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5
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- Forces on a liquid sphere of radius r
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6
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- Contact Angle for a Sessile Drop
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7
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- The surface tension causes an increased chemical potential for a
molecule inside a droplet. This
is manifested as an increase in the vapor pressure P of the liquid
droplet compared to that of the bulk liquid P0. The is
described by the Kelvin equation.
Two radii of curvature appear in the result, r1 and r2. For a sphere both terms are equal, but
for a cylindrical surface one term vanishes because one radius is
infinite (flat).
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8
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9
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10
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- catalysis (high surface area, controlled crystal surfaces)
- optical properties (sun screen, hyperthermic cancer treatment,
fluorescent tags)
- light scattering (smoke./fog screens)
- drug delivery (inhalation asthma, timed drug release.
- pesticide delivery (fogging and fumigation)
- magnetic recording (orient magnetic domain axis, important for hard
drives, video & audio tapes)
- pigments, inks, paints (coloring and opacity)
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