Chem 5395J. Rusling

Fall 2009

Introductory Materials

“interfacial properties differ from bulk properties”

Phase 1 Phase 2

Colloidal Materialsdimensions ~1 nm to 1 m

nanoparticlesspheres

rods

proteins

DNA

TEM of 5 nm AuNPs

2 nm

(A) (B)

Carbon Nanotubes

0.7-2 nm diameter

Single wall (SWNT)Multiwall CNT

5-40 nm diameter

Surfaces of nanoparticles can be derivatized

AFM, AuNP on PDDA Antibodies on AuNP surface

> 98% coverage of surface with AuNPs

Molecular aggregates can be particles or present complex interfaces: micelles and microemulsions:

Oil

Water

WaterWater

Water

O/W

Oil

Oil

Water

Oil

Bicontinuous

Detergent molecule

Many practical applications of colloids/nanoparticles:• sensors, chromatography, electrophoresis• membranes, catalysis, water treatment, detergency, ceramics• adhesion, aerosols, smog, oil recovery• soaps, drugs, paints, lubricants, beer

Common Factors: small particles - high surf. Arealarge molecules - polymers, proteins,

DNA

Size range between m and approaching atomic scale

Surf. Area of colloids is much larger than bulk systems of same mass: Subdivide sphere of radius (r) = 1 cm into equal spheres:

Molecular limits if subdivisions, e.g. water, 1 molecule Fraction of molecules on surface and surface free energy increases:

r, cm f, H2O,s Gs, J

1 9x10-8 9x10-5

10-4 9x10-4 9x10-1

10-6 9x10-2 9x101

10-7 0.91 9x103

Specific Surface Area = Total Area/mass = Atot/mtot Perfect Sphere of radius R Asp = 3/ R

= density

# subdivides r, cm # spheres A/sphere, cm2 Total A, cm2

1 1 1 4.2 12.6

2 0.5 8 3.1 25.1

5 3.1 x 10-2 3.3 x 104 0.0123 402

20 10-6 1018 1.3 x 10-11 1.3 x 107

Colloids are classed as:

Lyophobic “solvent fearing” in water, hydrophobic

Lyophilic “solvent loving” in water, hydrophilic

Colloidal suspension (dispersion) has continuous (solvent)And dispersed (particulate) phases

Lyophilic dispersions - usually true solutions, e.g. polymerprotein solution

Lyophobic dispersion - 2 or more phases, see examples