Colloid chemistry
The colloid chemistry is a branch of chemistry in which the preparation, characterization and modification of dispersed colloidal systems is paramount. Such systems consist of colloids , finely divided solid materials with particles in the size range from a few thousandths to a millionth of a millimeter . The particles are distributed as a disperse phase ( dispersion ).
Colloidal solutions stand between real solutions and suspensions ; they show no osmotic pressure , no increase in boiling point and no lowering of the freezing point (so-called colligative properties ).
In colloidal solutions, flocculation (coagulation) of the many small particles into energetically more favorable, larger particles would be expected. This mutual absorption of the colloid particles counteracts the electrostatic repulsion ( hydrophobic colloids ) or the presence of large hydration shells ( hydrophilic colloids ).
Hydrophobic colloids carry adsorbed charges, which is why they can be separated electrolytically ( electrophoresis ). The addition of salts reduces the electrostatic repulsion of the colloid particles and they settle as a precipitate or gel (coagulation, flocculation).
Hydrophilic colloids have large hydration shells. Here coagulation can be achieved by means of water-drawing agents.
Colloids that prevent others from flocculating are called protective colloids , such as dextrin . There are many active ingredients in colloidal solutions in the plant and animal bodies.
literature
- Gerhard Lagaly , Oliver Schulz, Ralf Zimehl: Dispersions and emulsions . An introduction to the colloidics of finely divided substances including clay minerals . Steinkopff, Darmstadt 1997, ISBN 3-7985-1087-3 .
Individual evidence
- ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 168.
- ↑ Attached: Klaus Beneke: Biographical Data of Important Colloid Scientists, pp. 519–548.