Shape memory functions and motility of amphiphilic polymer gels

Amphiphilic polymer gels which can swell in both organic fluid and water ha ve been widely investigated. We have discovered that this class of gels sho ws two special characteristics, i.e. the shape memory function and the spon taneous motion. The principle of the shape memory is based on a reversible order-disorder transition associated with interactions between the alkyl si de chains of the stearyl acrylate units. This effect is completely differen t from the one of shape memory alloys. When the swollen gel is heated, its Young's modulus decreases by about three orders of magnitude, from 10(7) dy n/cm(2) at 25 degreesC to 10(4) dyn/cm(2) at 50 degreesC. These drastic cha nges in the mechanical properties enable the gel to show the shape memory f unction. Another feature of these gels is the spontaneous motion. The mecha nism of the motion originates from the difference of surface tension betwee n water and organic solvent that is pumped out by osmotic and hydrostatic p ressures from the gel. Recently, we have succeeded to change the random mot ion to a translational one with a velocity of 77 mm/sec or rotational one w ith a maximum speed of 400 rpm. Motivated by this, electric power generator called "solvent-driven chemical motor" has been constructed. The generator produced an electric power with a maximum electromotive force of 15 mV and electric power of 0.2 muW. Copyright (C) 2001 John Wiley & Sons, Ltd.