Properties of micellar solutions: Part 3. - Spin lattice relaxation times of water protons in solutions of sodium alkyl sulphates

The nuclear magnetic resonance spin lattice relaxation times of water protons in aqueous solutions of sodium alkyl sulphates have been measured. The hydrocarbon chains in solution increase the relaxation rates of adjacent water molecules to an extent proportional to the chain length. This is because of dipole/dipole interaction between the alkyl chain protons and water protons, and because of the effect of the alkyl chains on the mobility of water molecules. When a number of single alkyl sulphate ions aggregate to form a micelle there is a resultant reduction of the effect of solute on the water molecules. However a micelle still increases the relaxation rate of water molecules more than equivalent number of isolated head groups, because of electrostriction of the water molecules near the micelle.