EFFECT OF CHEMICAL-STRUCTURE ON HYDROLYSIS OF SILOXANE ALKYL AMMONIUMBROMIDES

The influence of the chemical structure of siloxane alkyl ammonium bro mides on their long-term stability in aqueous solution has been invest igated by means of the change of the double layer capacity at the merc ury/electrolyte interface and by mass spectroscopic measurements. Gene rally, the degradation of the surfactants is caused by a hydrolytic cl eavage of the siloxane bonds, leading to a loss of surface activity. S uch a loss could be detected only in concentrated solutions (10(-1) M) , not in those less than or equal to 10(-4) M. In the case of branched trisiloxanes, the successive addition of a few methylene groups to on e alkyl chain at the nitrogen atom resulted in a dramatic decrease of the rate of hydrolysis. This effect is consistent with the assumption that polar groups, located at the surface of siloxane micelles, protec t the siloxane bonds against hydrolytic attack and that this protectio n increases significantly with increasing alkyl chain length. (C) 1998 Academic Press.