Structure factor for the periodic walls of mesoporous MCM-41 molecular sieves

A periodic wall model has been developed to calculate the structure factor of hexagonal MCM-41 molecular sieves. This is a discrete lattice version of the continuum periodic cylindrical shell model of Oster and Riley. Using t he periodic wall model we can explain the dramatic change in Bragg X-ray sc attering that occurs upon removal of the structure-directing surfactant fro m the pores of the as-synthesized mesostructure. The physical origin of thi s intensity change can be traced to the sensitive phase relationship betwee n the scattering from the pores and the walls constituting the open inorgan ic (silica) framework. The scattering intensity is affected only weakly by short-range disorder within the framework walls, provided that the long-ran ge order of the pores channels is maintained. A. similar periodic wall mode l may also be expected to explain the large Bragg intensity changes that oc cur upon surfactant removal from cubic MCM-48 mesostructures. (C) 1999 Else vier Science B.V. All rights reserved.