Anomalous Front Broadening During Spontaneous Imbibition in a Matrix with Elongated Pores

TL;DR

This study reveals that in porous media with elongated pores, water imbibition exhibits anomalously rapid front roughening due to uncorrelated menisci movements, indicating a new universality class of imbibition behavior.

Contribution

The paper introduces a theoretical model and experimental evidence showing that elongated pore structures lead to uncorrelated menisci and faster front roughening, differing from traditional models.

Findings

Experimental neutron imaging shows rapid imbibition front roughening.

Theoretical model predicts uncorrelated menisci movements.

Results suggest a new universality class of imbibition behavior.

Abstract

During spontaneous imbibition a wetting liquid is drawn into a porous medium by capillary forces. In systems with comparable pore length and diameter, such as paper and sand, the front of the propagating liquid forms a continuous interface. Sections of this interface advance in a highly correlated manner due to an effective surface tension, which restricts front broadening. Here we investigate water imbibition in a nanoporous glass (Vycor) in which the pores are much longer than they are wide. In this case, no continuous liquid-vapor interface with coalesced menisci can form. Anomalously fast imbibition front roughening is experimentally observed by neutron imaging.We propose a theoretical pore network model, whose structural details are adapted to the microscopic pore structure of Vycor glass, and show that it displays the same large scale roughening characteristics as observed in the experiment. The model predicts that menisci movements are uncorrelated. This indicates that despite the connectivity of the network the smoothening effect of surface tension on the imbibition front roughening is negligible. These results suggest a new universality class of imbibition behavior which is expected to occur in any matrix with elongated, interconnected pores of random radii.