Microscopic Model of Osmosis

Hi all. BIPH study is now underway...
I was re-reading the section in Nelson about osmotic pressure as the rectification of Bronwian motion (remember all of us walked away from that chapter feeling a little nonplussed?) and decided that I'd like to understand what on earth he was going on about.

My biggest issue was the way that osmotic flow was ascribed to entrainment of fluid allowing solvent to be 'sucked' across the membrane: surely the situation is symmetrical, because the particles also entrain fluid as they head toward the membrane (therefore they presumably pull fluid toward the membrane just as fast as they suck it away).

I found a very nice, readable and detailed paper which goes through the same sort of reasoning as Nelson, but I think a bit more maths helps to understand it a lot better (this is also a good reference for basic low-Re fluid mechanics).

The basic ideas are all the same as Nelson, but there was one line that really grabbed me;
"... the membrane acts on the fluid using the particles as its agent[s]."
The argument goes like so: the fluid is responsible for excitation of Brownian motion (creation of fluctuations) and the dissipation of energy, so every force which acts on the particle also induces fluid motion. At the membrane there is (on average) only a net force on the fluid when the particles bounce off the membrane, so they really do 'suck' solute through the membrane by rectifying the Brownian motion of the fluid using the particles as agents!