Fig. 1.

Computer simulation box of dry MCM41, along the c-axis (a) and at right angles to the c-axis (along the a-axis (b). The dimensions of the box are 66.2Å along each of the a and b axes, and 148Å along the c axis. The small red dots at the centre of each pore represent the Q-atoms mentioned in the text: these make no contribution to the scattering pattern, but are used simply to prevent silica and “silanol” water molecules from entering the pores. Silanol water molecules populate the surface of the pores, but some of these are seen to permeate the silica matrix as well.