Introduction into the world of colloids Joachim Koetz, Universität Potsdam History of Colloid Chemistry • Alchemy Alchemist • Elexier of life ? • drinking gold-solution (aurum potabile) + reducing agent + 3 HAuCl 4 What you would expect is elementary gold • What you find is an optically clear, red solution !! + 3 HAuCl 4 Optically clear, red solution History of Colloid Chemistry 1857 Faraday: Light scattering studies of colloidal gold sols What is the reason for the red colour ? • If the particle dimensions are well defined a part of the visible light (blue light) will be absorbed (surface plasmon resonance) and the colour of the solution becomes red ! History of Colloid Chemistry • 1871 Rayleigh: Theory of light scattering History of Colloid Chemistry • 1861 Graham: Diffusion behaviour Definition ( Graham ) • Colloids are glue-like substances, diffuse very slowly, and do not dialyse What is a Colloid ? DEFINITION: κολλα = glue Thomas Graham History of Colloid Chemistry • 1907 Wolfgang Ostwald: Different types of colloidal systems DIE WELT DER VERNACHLÄSSIGTEN DIMENSIONEN (The world of neglected dimensions) EINE EINFÜHRUNG IN DIE KOLLOIDCHEMIE MIT BESONDERER BERÜCKSICHTIGUNG IHRER ANWENDUNGEN VON WOLFGANG OSTWALD PROF. DER KOLLOIDCHEMIE a. d. UNIVERSITÄT LEIPZIG 1927 Types of disperse systems (W. Ostwald ) Disperse systems suspensions colloidal dispersions solutions > 1000 nm 1 bis 1000 nm < 1 nm Definition Any particle that has some linear dimension between 1 nm and 1 µm is considered a colloid! However, the limits are rather arbitrary. Definition: • A state of subdivision in which the particles, droplets, or bubbles dispersed in another phase have at least one dimension between 1 – 1000 nm • All combinations are possible between gas, liquid, and solid W. Ostwald Colloidal Systems (according to Wolfgang Ostwald) Medium Particle Colloidal system Gas Liquid Aerosol Gas Solid Aerosol Liquid Gas Foam Liquid Liquid Emulsion Liquid Solid Suspension Solid Gas Solid Foam Solid Liquid Porous Material Solid Solid Solid Suspension History of Colloid Chemistry • 1927 Burry, Ekwall: Associating Colloids Associating Colloids • Amphiphilic self-organizing systems • Colloids are associated physically, not chemically • Size and shape of the associates can change History of Colloid Chemistry • 1929 Staudinger: Macromolecules Macromolecules as colloidal systems • Any macromolecule consisting of 10 3 up to 10 9 atoms • Any dispersed macromolecular coil having colloidal dimensions History of Colloid Chemistry • 1923 Svedberg: Ultracentrifugation • 1932 Ruska: First electron microscope The Colloidal Domain • One dimension between 1 and 1000 nm • All combinations of dispersed matter • Classification: - colloidal dispersions - associating colloids - macromolecules Log (size in Meter) Matterial 20 Science 18 16 14 12 10 Sun →→→ 8 Earth →→→ Macrocosmos 6 4 Life Science TV tower →→→ 2 House →→→ ← Whale brick →→→ 0 ←←← Human ←←← Mouse -2 ←←← Flea Hair →→→ -4 ←←← Bacterium Nanosized particles -6 ← Virus or macromolecules -8 Molecule →→→ -10 Atom →→→ -12 Colloidal region -14 Microcosmos Electron →→→ -16 Ultra -high Resolution Scanning ElectronREM deutsch Microscope S- 4800 (Hitachi) Specifications : Image resolution : 1.0 nm / 15 kV 1.4 nm / 1 kV EDX - System : Thermo - NORAN system SIX Cryo preparation system : Gatan – Alto 2500-S STEM Imaging Colloidal systems in Nature Biomineralization Inorganic Organic Organism component component composite of SiO 2 * x H2O Diatomeen hydrocarbon and protein Aragonite, composite of Pearl hydrocarbon CaCO 3 and protein Hydroxylapatit, composite of Bone and teeth collagenfilament Ca 10 (PO 4)6(OH) 2 and protein Colloidal systems • A state of subdivision in which the particles, droplets, or bubbles dispersed in another phase have at least one dimension between 1 and 1000 nm • all combinations are possible between : gas, liquid, and solid W. Ostwald Fields of Application for nanostructured systems Disciplines and Topics for which Colloids and colloidal phenomena are important • Adsorption phenomena, • Analytical chemistry chromatography • Physical chemistry • Nucleation, supersaturation, liquid crystals • Biochemistry • Electrophoresis, osmosis, • Material Science ultrafiltration • Petroleum Science • Ceramics, fibres, powder metallurgy • Household products • Oil recovery, • Imaging technology • Milk, beer, cosmetics • Emulsions, printing inks, paper coating Colloids and Surfaces • Special features of colloidal systems Surface area of colloidal systems • Cube (1cm; 1cm; 1cm) after size reduction to an edge length of 500 nm: surface area of 60 m 2 • Spinning dope (1 cm 3) after spinning to a fibre with diameter of 1000 nm: fiber length of 1273 km • 1 liter of a 0.1 M surfactant solution: interfacial area of 40000 m 2 Colloidal systems • have very large surface areas Surface atoms [in %] in dependence on the particle size [in nm] 100 90 80 70 60 % 50 part of surface 40 atoms in % 30 20 10 0 20 10 5 2 1 nm Colloidal systems • surface atoms become dominant Surface tension Increase in Gibbs free energy per unit increment in area Surface Tension Phenomena • Droplet formation • Coalescence • Bubble formation • Wetting Marangoni-Effect Processes induced by a change of surface tension „Wine Tears “ • Alcohol is evaporated from the liquid film at the glass wall • Surface tension is increased • Wine is absorbed at the glass wall • Droplets are flowing back into the glas.