Vesicle-micelle transition in aqueous mixtures of the cationic dioctadecyldimethylammonium and octadecyltrimethylammonium bromide surfactants Fernanda Rosa Alves, 1 Maria Elisabete D. Zaniquelli, 2 Watson Loh, 3 Elisabete M.S. Castanheira, 4 M. Elisabete C.D. Real Oliveira, 4 and Eloi Feitosa 1,* 1 Physics Department, São Paulo State University, São José do Rio Preto - SP, Brazil 2 Instituto de Química, Universidade de São Paulo, Ribeirão Preto – SP, Brazil 3 Instituto de Química, Universidade Estadual de Campinas, Campinas – SP, Brazil 4 Physics Department, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal *To whom correspondence should be addressed: Eloi Feitosa Physics Department, IBILCE/UNESP Rua Cristóvão Colombo, 2265 São José do Rio Preto, SP - Brazil CEP: 15054-000 Voice: +55 17 3221 22 40 Telefax: +55 17 3221 22 47 e-mail: eloi@ibilce.unesp.br