Memory, congruence, and avalanche events in hysteretic capillary condensation

We report measurements of the hysteretic capillary condensation of helium in the porous material Nuclepore which display a hierarchy of return point memory effects and near congruence of closed internal hysteresis loops. Deviations from predictions based on the Preisach model of independent elementary hysteresis domains, originally developed to understand magnetic phenomena, are observed and are attributed to the appearance of additional domains on draining induced by the internal structure of the porous material. Pore intersections result in weak interactions among the pores which lead to avalanches.