HILIC columns have zwitter ion (neutral molecule with a positive and negative charge) as a functional group in stationary phase. This zwitter ion can attract ionic compounds. Because of this function HILIC columns can be used for reverse phase and ion chromatography.
Because, HILIC stationary phases have polar fonctional groups and well interact with polar analytes by ion-dipl interaction, H-bondind and ion-ion interaction. Some anlytes are very polar and can not interact with apolar C18 stationary phase, therefore this polar analytes is eluated very fast wit C18 column. the attachet paper is be very useful for you.