Wetting enhanced by water adsorption in hygroscopic plantlike materials

Abstract

Water inside hygroscopic porous media such as plantlike systems can be found either freely penetrating in capillaries or absorbed into the solid phase (bound water). Here we demonstrate that the wetting properties (contact angle) of liquid along cell walls significantly depend on the amount of bound water absorbed: a change from poor to good wetting is observed when cell walls are saturated with bound water, which allows liquid displacement. We further show that this process is operative in hydrogels, suggesting that this might be a general property of porous hygroscopic systems. As a consequence, imbibition dynamics is controlled by water adsorption and diffusion in the walls, and even if the dynamics of capillary imbibition is strongly damped (by several orders of magnitude), water can freely climb over significant heights as long as sufficient water has been adsorbed into cell walls or in other hygroscopic walls. Under these conditions, the imbibition process in such systems is not described by the standard model but is analogous to the propagation of a front of solidification in a liquid. This process might contribute to the regulation of water absorption in unsaturated wood, allowing it to store available bound water in progressively higher depths, instead of leaving free water rapidly flow through it. Such a mechanism may be explored to design porous materials with tunable liquid adsorption timings for pharmaceutical or chemical engineering applications.

Enhanced water uptake in the longitudinal direction by shiitake mycelium in shiitake cultivation logs: increase in effective diffusion coefficient based on mass of liquid water uptake

“…The effective diffusion coefficient of liquid calculates water using a one-dimensional unsteady-state diffusion equation called Fick's laws of diffusion (Burr and Stamm 1956;Hunter 1993;Krus and Kunzel 1993;Kumaran 1999). On the other hand, the water penetration mechanism into a log in the longitudinal direction due to capillary force has been demonstrated in several papers (Zhou et al 2018(Zhou et al , 2019. Zhou et al (2019) used X-ray microcomputed tomography imaging to visualize water rising in vessels of a hornbeam sample.…”

“…On the other hand, the water penetration mechanism into a log in the longitudinal direction due to capillary force has been demonstrated in several papers (Zhou et al 2018(Zhou et al , 2019. Zhou et al (2019) used X-ray microcomputed tomography imaging to visualize water rising in vessels of a hornbeam sample. On the other hand, in the present study, optical microscope was used to observe the water rising to the top surface of the log disk from the bottom.…”

Progress in rheology and hydrodynamics allowed by NMR or MRI techniques

“…More precisely bound water appears to progress far beyond the front of free water, and the free water penetration along the sample axis apparently coincides with the development of a region saturated with bound water (see Figure 12 a) (Zhou et al 2018). This likely explains that water imbibition is about three orders of magnitude slower than expected from standard Washburn imbibition process (Zhou et al 2019). The inverse effect seems to occur during drying (Gezici-Koç et al 2017): bound water is extracted only when all free water has been extracted (see Figure 12 b), even from pores (such as fibers) in which the liquid is not connected to the free surface through a hydraulic network, which suggests that bound water is the vector of this extraction.…”

“…In recent years it appeared possible to follow the evolution in time of the distributions of bound and free water individually along the sample (van Meel et al 2011, Dvinskikh et al 2011, Kekkonen et al 2013, Gezici-Koç et al 2017, Zhou et al 2018, which provided a critical insight in the understanding of the processes. It was thus found that during spontaneous imbibition, in contrast to porous media with an impermeable solid structure, the water imbibition in the hydraulic conduits of hardwood is not simply driven by the standard capillary effects associated with a good wetting of the solid surface, but it is in fact strongly affected by the adsorption of bound water in cell walls (Zhou et al 2019). More precisely bound water appears to progress far beyond the front of free water, and the free water penetration along the sample axis apparently coincides with the development of a region saturated with bound water (see Figure 12 a) (Zhou et al 2018).…”

Investigating the impact of exit effects on solute transport in macroporous media

“…A multi-spin multiecho (MSME) sequence, schematized in Fig. 2, based on a succession of 16 echoes was used with an echo time T E = 7.4 ms and a recycle delay T R = 1.2 s. To produce a twodimensional image, the measured 16 echoes were added in order to improve the signal-to-noise ratio without increasing the measurement time (Zhou et al, 2019), thus preventing direct concentration quantification. Moreover, due to the short recycle delay used to keep the measurement time below 4 min, the resulting signal depends simultaneously on the spin-lattice relaxation time T 1 and the spin-spin relaxation time T 2 , thus complicating quantification.…”