Effects of surfactant head group modification on vertically oriented mesoporous silica produced by the electrochemically assisted surfactant assembly method

Production of mesoporous silica films with vertically oriented pores has been a challenge since interest in such systems developed in the 1990s. Vertical orientation can be achieved by the electrochemically assisted surfactant assembly (EASA) method using cationic surfactants such as cetyltrimethylammonium bromide (C(16)TAB). The synthesis of porous silicas using a series of surfactants with increasing head sizes is described, from octadecyltrimethylammonium bromide (C(18)TAB) to octadecyltriethylammonium bromide (C(18)TEAB). These increase pore size, but the degree of hexagonal order in the vertically aligned pores reduces as the number of ethyl groups increases. Pore accessibility is also reduced with the larger head groups.