Design of Thermally Responsive Polymeric Hydrogels for Brackish Water Desalination: Effect of Architecture on Swelling, Deswelling, and Salt Rejection

Abstract

In this work, we explore the ability of utilizing hydrogels synthesized from a temperature-sensitive polymer and a polyelectrolyte to desalinate salt water by means of reversible thermally induced absorption and desorption. Thus, the influence of the macromolecular architecture on the swelling/deswelling behavior for such hydrogels was investigated by tailor-made network structures. To this end, a series of chemically cross-linked polymeric hydrogels were synthesized via free radical-initiated copolymerization of sodium acrylate (SA) with the thermoresponsive comonomer N-isopropylacrylamide (NIPAAm) by realizing different structural types. In particular, two different polyNIPAAm macromonomers, either with one acrylate function at the chain end or with additional acrylate functions as side groups were synthesized by controlled polymerization and subsequent polymer-analogous reaction and then used as building blocks. The rheological behaviors of hydrogels and their estimated mesh sizes are discussed. The performance of the hydrogels in terms of swelling and deswelling in both deionized water (DI) and brackish water (2 g/L NaCl) was measured as a function of cross-linking degree and particle size. The salt content could be reduced by 23% in one cycle by using the best performing material.

Energy Consumption for the Desalination of Salt Water Using Polyelectrolyte Hydrogels as the Separation Agent

“…The κ-value as a function of pressure for a 1 mol% crosslinked poly(acrylic acid) using a 10 g L −1 NaCl solution. The data are fitted with an empirical hyperbola function as described in the text and Equation(11).…”

Durability and Self-healing Effects of Hydrogel Coatings with respect to Contact Condition

“…Figure 5b shows the main mechanism and process of self-healing of the hydrogel coating. The swelling of each fiber, which occurred by osmosis, filled the compressed fibers 35 . In other words, when the hydrogel fibers come into contact with water molecules, they expand through osmosis as per the Gibbs–Donnan effect, and the pores between the fibers shrink through the capillary process, and thus the hydrogel coating structure becomes more compact 30 , 35 , 36 .…”

Poly(sodium acrylate) hydrogels: synthesis of various network architectures, local molecular dynamics, salt partitioning, desalination and simulation

“…The crosslinker efficiency varies over a broad range for the present system (e.g., 15-78%) 65 and depends besides the monomer and crosslinker on many synthetic parameters, such as the charge density, the polymer concentration during the crosslinking and DC itself. 58,66 Assuming a crosslinker efficiency of 50% simplifies eqn (18) to N = 1/DC. However, this assumption would result in elastic chain lengths of 333, 100 and 20 for the samples plotted with a DC of 0.3, 1 and 5 mol%, respectively.…”

“…The best value found so far has been 8.9 kW h m À3 , when fully charged poly(sodium acrylate) (PSA) with a high degree of crosslinking of 5 mol% was used. 12 Other groups, such as Fan et al and Ali et al, experimentally investigated PSA copolymer hydrogels, where further monomers like 2-hydroxyethyl methacrylate 17 or thermally responsive N-isopropylacrylamide 18 were incorporated into the polyelectrolyte network. With the latter example, the partially desalinated water inside the hydrogel could be recovered by applying a temperature of 50 1C instead of pressure as an external stimulus.…”