A Variable Mass Meso-Model for the Mechanical and Water-Expelled Behaviors of PVA Hydrogel in Compression

Abstract

Static uniaxial compressive experiments were conducted to study the mechanical behaviors of polyvinyl alcohol (PVA) hydrogels in ambient conditions. It was found that water is expelled during the compression of hydrogels that have high water contents. It means hydrogels may be a mass variable under the compression. In order to depict the mechanical properties intrinsically, a variable mass model with meso-scale cells was proposed to simulate PVA hydrogels. In the model, there are uniform cells with frames of polymer fibers and water, and a virtue membrane designed to wrap up the boundary of the model. The model not only depicts the behaviors of the compressive mechanics and the expelled water, but also explains the nonlinear stress–strain relation of PVA hydrogels and why the hydrogels with high water content demonstrate a modulus considerably lower than the bulk modulus of water.

Water Harvesting from Air: Current Passive Approaches and Outlook

“…Inspired by the plant, another unique thought is that the water in hydrogels can be recovered by a moderate osmotic mechanical pressure. , As shown in Figure b, the osmotic pressure exerted by plant roots in the presence of soil water, on the order of 0.1–1.2 MPa, can also be sufficient to extract water from the gel mixed with soil and so provide water to the plant roots. , Actually, a related study that placing plant roots in the soil modified by the super moisture absorbent gels (SMAG) has been reported, as shown in Figure c . The plant can directly take advantage of the water harvested by the SMAG soil, whose water uptake is up to 1.1 L kg sorb –1 at 20 °C and 90% RH, almost 2 orders of magnitude higher than that of the sandy soil .…”

Gel-induced dew condensation

“…Water in hydrogels can be recovered by a moderate ( 1 bar) osmotic mechanical pressure (Milimouk et al, 2001;Zhang et al, 2017). The osmotic pressure exerted by plant roots in presence of soil water, on the order of 0.1 -1.2 MPa, can be high enough to extract water from the gel mixed with soil and so provide water to the plant roots (Rudzinski et al, 2002;Puoci et al, 2008).…”

Side Chains and the Insufficient Lubrication of Water in Polyacrylamide Hydrogel—A New Insight

“…Originating from the vast potential applications of hydrogels on biomedicine [2,3] and soft robotics [4,5], the swelling-deswelling process and mechanical behavior of hydrogels have been intensively studied in recent years because of their superior biocompatibility [6] and flexibility [7]. Researchers have proposed a series of constitutive models [8] based on the free energy change resulting from polymer stretching, mixture [9,10], temperature [11,12,13], light [14], ionic concentration [15,16,17,18], and magnetic field [19] to characterize the mechanical behavior and multi-stimuli response of hydrogels [20,21,22,23]. Although the swelling-deswelling deformation of hydrogels has been expounded in many research texts, the change of mechanical properties along with the swelling-deswelling process hardly obtains attention.…”