What forces are expected when a polymer swells by a solvent.

Can't give you any precise data, but you could try to look at those "smart" polymers, which are candidates for artificial muscles. Their bending is mainly due to osmotically controlled swelling, IIRC.

Oliver

Your problem is harnessing the force generated. The polymer will generally expand into the water, giving no NET increase in volume.

For big forces look to inorganics. I believe gypsum/cement brews have been formulated which will crack rock if cured in drillings in the rock. Of course if you need reversability theyre no good!

alan

Of course you need a somewhat crosslinked polymer. Otherwise the polymer will completely dissolve in the solvent.

For that you do not need cement. Frozen water will do.

Oliver

Crosslinked polymer in a pipe will not swell the pipe, it just expands along the length, absorbing as it goes. One would need to play with granular polymers trapped in a tough mesh.

alan

On swelling the crosslinked polymer (=gel) will exert a force on the pipe-walls. If you a have a rod-shaped gel the absolute length difference will be different parallel and perpendicular to the main axis. Same is probably true for the forces.

Oliver

Quite so. The radial forces will be minimal unless you have some semipermeable screen blocking lengthways movement. Also since the water can only enter from the lengthways direction, that will be the preferred direction of movement. I envisage an experiment of diaper-grade sodium poly acrylate granules in a teabag, immersed in water with a weight on top.

alan

Or dry wood, first iserted into a drilling, and then slowly soaked with water... I guess you could call that swelling of polymers. ;) This method was used even relatively recently, to crack rocks where dynamite cannot be used.

J. Macan

From the Dowex Ion Exchange Resins technical information:

"Also, in some applications resins may swell significantly and care must be taken to avoid column breakage. (NOTE: Resin expansion requires that column configuration be such that the volume change can occur vertically. Tall, narrow columns might restrain this expansion and cause strong lateral pressures to develop in the column, resulting in resin being crushed, or in a column being ruptured."

Regards, Oliver

I think we are basically in agreement. A tall narrow column would have the longtitudinal expansion constrained by friction, and I imagine an ion exchange column has something (tough mesh??) to prevent the resin being washed away.

alan