Dear Kamal,

of course this depends on definition of 'highly insoluble'.

Certainly dialkyl dimethyl ammonium halides (traditional fabric softener) belong into this group. They usually form vesicles. To obtain equilibrium adsorption at air-water interface extremely long times are necessary due to their extremely low monomer concentration.

Further all cationics with a Krafft point temperature below room temperature, e.g. hexadecyl amine hydrochloride.

Hope that this is a suitable starting point. What is the starting point of your question?

Simply, due to two main reasons:

1- The cationic surfactants are generally derived from very weak organic base which increases the association constant and therefore decreases the solubility in water in contrast to that of anionic surfactants.

2- The presence of relatively long hydrophobic chain also makes a bad effect towards solubility in water. So you have to enhance the solubility by breaking the hydrogen bonds between water molecules through heating due to the hydrophobic effect that resulted from this chain.