The intercalation process of alpha-zirconium phosphate (alpha-ZrP) was investigated by using two alpha-ZrP samples with different levels of crystallinity and two structurally different intercalating molecules, i.e., linear hexylamine and non-planar cyclohexylamine. The results show that the intercalation energy barrier, which is affected by both host alpha-ZrP and guest intercalating molecules, has a significant effect on the intercalation process. When the intercalation energy barrier is relatively low, the interlayer distance of alpha-ZrP expands continuously with increasing amount of intercalating molecules. When the energy barrier reaches a certain level, the interlayer distance expansion becomes stepwise. The observed differences in the intercalation process correspond well with the geometric arrangement of the intercalated molecules inside the gallery of alpha-ZrP. (C) 2009 Elsevier Inc. All rights reserved.