Osmosis, from molecular insights to large-scale applications

Abstract

Osmosis is a universal phenomenon occurring in a broad variety of processes and fields. It is the archetype of entropic forces, both trivial in its fundamental expression -the van 't Hoff perfect gas law -and highly subtle in its physical roots. While osmosis is intimately linked with transport across membranes, it also manifests itself as an interfacial transport phenomenon: the so-called diffusio-osmosis and -phoresis, whose consequences are presently actively explored for example for the manipulation of colloidal suspensions or the development of active colloidal swimmers. Here we give a global and unifying view of the phenomenon of osmosis and its consequences with a multi-disciplinary perspective. Pushing the fundamental understanding of osmosis allows one to propose new perspectives for different fields and we highlight a number of examples along these lines, for example introducing the concepts of osmotic diodes, active separation and far from equilibrium osmosis, raising in turn fundamental questions in the thermodynamics of separation. The applications of osmosis are also obviously considerable and span very diverse fields. Here we discuss a selection of phenomena and applications where osmosis shows great promises: osmotic phenomena in membrane science (with recent developments in separation, desalination, reverse osmosis for water purification thanks in particular to the emergence of new nanomaterials); applications in biology and health (in particular discussing the kidney filtration process); osmosis and energy harvesting (in particular, osmotic power and blue energy as well as capacitive mixing); applications in detergency and cleaning, as well as for oil recovery in porous media.to counteract the flow: the applied pressure is then equal to the osmotic pressure. solute semi-permeable membrane hydrostatic pressure drop relaxation Fig. 1 : Key manifestation of osmosis. A semi-permeable membrane allows transport of water upon a solute concentration difference (in red). The flow of water is directed from the fresh water reservoir to the concentrated reservoir.Osmosis is therefore extremely simple in its expression. Yet it is one of the most subtle physics phenomenon in its roots -it resulted in many debates over years 1,2 . Osmosis also implies subtle J o u r n a l N a me , [ y e a r ] , [ v o l . ] , 1-43 | 1 arXiv:1902.06219v2 [cond-mat.soft] 6 May 2019 2 | 1-43 J o u r n a l N a me , [ y e a r ] , [ v o l . ] , .Noting then that for small pressure drops, µ w (T, p (r) , 0)0) the molec-J o u r n a l N a me , [ y e a r ] , [ v o l . ] , 1-43 | 3where L hyd = κ hyd A /(ηL) is the solvent permeance through the 4 | 1-43 J o u r n a l N a me , [ y e a r ] , [ v o l . ] , 6 | 1-43 J o u r n a l N a me , [ y e a r ] , [ v o l . ] ,

Local and global force balance for diffusiophoretic transport

“…Phoresis corresponds to the motion of a particle induced by an external field, say Θ ∞ : typically an electric potential for electrophoresis, a solute concentration gradient for diffusiophoresis, or a temperature gradient for thermophoresis (Anderson 1989;Marbach & Bocquet 2019). The particle velocity is accordingly proportional to the gradient of the applied field, writing in the general form v P = µ P × (−∇Θ ∞ ) (1.1)…”

“…total force acting on the system of the particle and its ionic diffuse layer experiences a vanishing total force. Both electro-and diffusio-phoresis and correspondingly electroand diffusio-osmosis can all be interpreted as a single osmotic phenomena, since the two are related via a unique driving field, the electro-chemical potential (Marbach & Bocquet 2019). Interestingly these phenomena have gained renewed interest over the last two decades, in particular thanks to the development of microfluidic technologies which allow for an exquisite control of the physical conditions of the experiments, electric fields or concentration gradients.…”

“…However, in contrast to electrophoresis, diffusiophoresis has been much less investigated since the pioneering work of Anderson and Prieve. Its amazing consequences in a broad variety of fields have only started to emerge, see Marbach & Bocquet (2019)…”

Improved osmotic energy conversion in heterogeneous membrane boosted by three-dimensional hydrogel interface

“…he ionic gradient between fresh water and sea water has been identified as a promising source of renewable energy, also known as blue and osmotic energy, or salinity gradient energy in engineering community 1,2 . In the past decades, membrane-based reverse electrodialysis has been developed as a main technology to capture this worldwide energy [3][4][5][6][7] .…”

Fluid pumping and active flexoelectricity can promote lumen nucleation in cell assemblies

“…(15) contains a contribution that stems directly from active cell pumping, but also an additional one which can be understood as an electroosmotic contribution to the active pumping. Electroosmotic flows are generated when an electric field is applied to a fluid close to a charged surface [35] and recent studies suggest that these electroosmotic flows could be for instance dominant in the corneal fluid transport [11,36]. In our analysis, an inward effective pumping ensures lumen nucleation if the spheroid is large enough.…”