Ergodic to nonergodic transition in liquids with a local order: the case of m-toluidine.

The dynamic structure factor of m-toluidine has been measured by inelastic x-ray scattering in the mesoscopic Q range between 1 and 10 nm(-1), where a prepeak is revealed in the static structure factor resulting from the existence of hydrogen bonded, nanometer size clusters. Evidence is given of (i) a square-root cusp in the nonergodicity factor and of (ii) critical nonergodicity parameters which oscillate in phase with the static structure factor. These results demonstrate that local order in a liquid can coexist with the signatures of the ergodic to nonergodic transition predicted by the mode coupling theory for simple, dense liquids.