Capillary rise of non-aqueous liquids in cellulose sponges

Abstract

A cellulose sponge is a mundane porous medium composed of numerous microporous cellulose sheets surrounding macroscale voids. Here, we quantify the capillary rise dynamics of non-aqueous liquids in a sponge using a combination of experiment and theory. Although the classical law of Washburn is obeyed in the early stages, the wet front propagation is no longer diffusive in the late stages and follows a power law, $h\sim t^{1/4}$, with $h$ and $t$ being the capillary rise height and time respectively. The transition of the power law is a consequence of the peculiar heterogeneous pore structure of cellulose sponges. The permeability and driving pressure change at the rise height above which the macro voids can no longer be filled completely due to significant effects of gravity. We rationalize the $t^{1/4}$ law by considering liquid flows along the corners of macro voids driven by capillary pressure of microscale wall pores.

Poro-elasto-capillary wicking of cellulose sponges

“…As shown in the scanning electron microscopy (SEM) images ( Fig. 2 , A to C), it consists of numerous cellulose sheets with two-dimensional microscale pores surrounding macro voids ( 13 ). The sheets approximately 10 nm in thickness are randomly stacked with nanometric spacings.…”

Wetting enhanced by water adsorption in hygroscopic plantlike materials

“…On the one hand, to explain these results, structures made of a network of channels with connections with a probability of passage [28,29], or with a double permeability [14], were suggested, which are nevertheless not fully consistent with the effective structure of hardwood. On the other hand, a dynamics differing from that expected from the standard Washburn process has been observed for bi-porous systems [30][31][32][33] and other peculiar effects were observed with specific pore shapes [25,34,35]. Among these materials were cellulose sponges [31,32] made of macropores (few millimeters) connected by micropores (few micrometers), and a solid structure formed of sheets able to adsorb water so that the structure swells when in contact with water.…”

“…On the other hand, a dynamics differing from that expected from the standard Washburn process has been observed for bi-porous systems [30][31][32][33] and other peculiar effects were observed with specific pore shapes [25,34,35]. Among these materials were cellulose sponges [31,32] made of macropores (few millimeters) connected by micropores (few micrometers), and a solid structure formed of sheets able to adsorb water so that the structure swells when in contact with water. The late stage of water imbibition dynamics is slowed down by micropore deformation and merging, resulting from deformations of the hygroscopic structure [32].…”

“…Among these materials were cellulose sponges [31,32] made of macropores (few millimeters) connected by micropores (few micrometers), and a solid structure formed of sheets able to adsorb water so that the structure swells when in contact with water. The late stage of water imbibition dynamics is slowed down by micropore deformation and merging, resulting from deformations of the hygroscopic structure [32]. However, this effect is much weaker (less than one order of magnitude) than that observed here, and hardwoods are a priori simpler systems (straight continuous vessels).…”

Imbibition in plant seeds

“…Multi-scale pores are common in biological materials [12]; either due to variations in the particle/cell size or due to the presence of cracks. It is thus unclear if the imbibition process in plant seeds is homogenous, or if spatial variations could lead to heterogeneous flow patterns [13][14][15][16].…”