higher chain length means higher hydrophobicity. so one can increase the pH (leads to deprotonation of carboxyl groups) to overcome the strong hydrophobic part.

Huang, Xu, et al. "Controllable organization of a carboxylic acid type gemini surfactant at different pH values by adding copper (II) ions." The Journal of Physical Chemistry B 110.39 (2006): 19479-19486.

Dear Marjan,

first you should get familiar with the Krafft point (temperature - only above this you can obtain an aqueous solution at meaningful concentration). Only for lauryl soaps (maybe myristyl too) this is below room temperature. Soaps with longer alkyl chain need higher temperature to be dissolved.

Further soaps are composed mostly of strong alkali and weak acid, so they hydrolyse. Natural pH of soap solutions is therefore always more or less alkaline. The lower the pH the higher the content of insoluble acids (solubilized in micelles).

increasing the size of the chain also increases the hydrophobic part of the molecule and the size of the micelle. As pH increases, also increases also anionic surfactants of this type and therefore its affinity to water