Langmuir films of N-alkylpyridinium alkylsulphates

It is well known that the molecular amphiphilic properties, which lead to t he appearance of liquid crystalline phases. are also responsible for the tw o dimensional molecular self-organisation on the water-air interface. Havin g this in mind, we prepared Langmuir films with mixtures and pure homologue s of the mesogenic series of N-alkylpyridinium alkylsulphates. Using the st andard compression technique we obtained isotherm curves which were analyse d considering the variation, at constant pressure, of the 2D packing as a f unction of the molecular properties. This analysis, carried out for differe nt surface pressure values, allows us to examine how the variation of the m olecular hydrophilic or hydrophobic character reflects on the main structur al characteristics of the two-dimensional phases of the film.