智能软材料水凝胶概要1.pptVIP

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Soft Active Materials Zhigang Suo Harvard University III. Polyelectrolytes * Polyelectrolyte: polymer with electrolyte group In a solvent, the electrolyte dissociates. solvent fixed charge counterion co-ion counterion covalent bond ionic bond polymer chain * Polyelectrolyte gel Fixed charges Counterions Co-ions - + - A network of polymers Solvent (e.g., water) Crosslinks * Many tissues are polyelectrolyte gels Structure and function: Cartilage is polyelectrolyte. Does this fact have anything to do with low friction of a joint? * Plant cell walls are polyelectrolytes Pectin * Gels regulate flow in plants Zwieniecki, Melcher, Holbrook, Hydrogel control of xylem hydraulic resistance in plants Science 291, 1095 (2001) Missy Holbrook * Osmosis in a polyelectrolyte gel membrane solution solvent Osmosis balanced by gravity Network tatters fixed charges. To maintain electroneutrality, fixed charges are balanced by counterions. Counterions cause osmosis crosslink - - - - - - - - - - + + + + + + + + + fixed charge counterion water network Osmosis balanced by elasticity * Super absorbent diaper Sodium polyacrylate: polyelectrolyte Masuda, Trends in the development of superabsorbent polymers for diapers, pp. 88-89, Superabsorbent polymers: science and technology (1994). * Ion exchanger * pH-sensitive gel fixed mobile * pH-sensitive hydrogel * pH-sensitive valves in microfluidics Beebe, Moore, Bauer, Yu, Liu, Devadoss, Jo, Nature 404, 588 (2000) Deformation and force regulated by physiological variables (pH, salt, temperature…) Mechanics and chemistry David Beebe * Adaptive optics with soft materials Dong, Agarwal, Beebe, Jiang, Nature 442, 551 (2006) * Electric potential Electrochemical potential Gibbs (1878) electrode battery, F pump, m electrons, dq Ions, dM electroneutrality equilibrium Material A Material B electrode Battery does work on electrons, Fdq Pump does work on ions, mdM Helmholtz fre