Noncovalent charge repulsion

The alternative noncovalent functionalization does not rely on chemical bonds but on weaker Coulomb, van der Waals or n-n interactions to connect CNTs to surface-active molecules such as surfactants, aromatics, biomolecules (e.g. DNA), polyelectrolytes and polymers. In most cases, this approach is used to improve the dispersion properties of CNTs [116], for example via charge repulsion between micelles of sodium dodecylsulfate [65] adsorbed on the CNT surface or a large solvation shell formed by neutral molecule (e.g. polyvinylpyrrolidone) [117] around the CNTs. 

Porphyrin bolaamphiphiles have been shown to form platelets with a thickness of 8 A in bulk water. Well-defined monolayers have been obtained with bolaamphiphilic porphyrins with two positive charges on each edge. Charge repulsion obviously first prevents crystallization and second unlimited growth of the isolated sheets. Their surface area is a few [ixn. In aqueous solution lecithin bilayers of unlimited extension (myelin figures) are known to have erne s below 10" M and can thus be considered as noncovalent polymers. ... 

Figure 5 Illustration of ion formation in an electrospray ion source (16). When the size of the charged droplet decreases due to evaporation of the solvent, the charge density on its surface increases. Then strong mutual coulombic repulsions cause ions to be ejected from the droplet until the droplet is small enough that the surface charge density field can desorb ions from the droplet into the ambient gas. The molecular ions desorb with noncovalently associated solvent. After the ions form at atmospheric pressure, they are electrostatically directed into the mass analyzer.

---