Osmotic Pressure versus Swelling Pressure: Comment on “Bifunctional Polymer Hydrogel Layers As Forward Osmosis Draw Agents for Continuous Production of Fresh Water Using Solar Energy”

Abstract

The authors thought that the principle ofabsorbing water of the hydrogels was based on forwardosmosis, that is, the hydrogel particles (2−25 μm) provided theosmotic pressure. The authors may misunderstand the swellingpressure of hydrogels as the osmotic pressure. The followingdiscussion aims to clarify two confused concepts (i.e., osmoticpressure and swelling pressure) and to differentiate theprinciples of forward osmosis and of hydrogel absorbingwater for both readers and the authors. It is believed that theclarification is very necessary because a number of publishedpapers