Arens Lukas, Weißenfeld Felix, Klein Christopher O, Schlag Karin, Wilhelm Manfred
Institute for Technical Chemistry and Polymer Chemistry (ITCP) Karlsruhe Institute of Technology (KIT) 76131 Karlsruhe Germany.
Adv Sci (Weinh). 2017 May 30;4(9):1700112. doi: 10.1002/advs.201700112. eCollection 2017 Sep.
Poly(acrylic acid)-based hydrogels can swell up to 100-1000 times their own weight in desalinated water due to osmotic forces. As the swelling is about a factor of 2-12 lower in seawater-like saline solutions (4.3 wt% NaCl) than in deionized water, cyclic swelling, and shrinking can potentially be used to move a piston in an osmotic motor. Consequently, chemical energy is translated into mechanical energy. This conversion is driven by differences in chemical potential and by changes in entropy. This is special, as most thermodynamic engines rely instead on the conversion of heat into mechanical energy. To optimize the efficiency of this process, the degree of neutralization, the degree of crosslinking, and the particle size of the hydrogels are varied. Additionally, different osmotic engine prototypes are constructed. The maximum mean power of 0.23 W kg dry hydrogel is found by using an external load of 6 kPa, a polymer with 1.7 mol% crosslinking, a degree of neutralization of 10 mol%, and a particle size of 370-670 µm. As this is achieved only in the first round of optimization, higher values of the maximum power average over one cycle seem realistic.
基于聚丙烯酸的水凝胶由于渗透力，在淡化水中能膨胀至自身重量的100到1000倍。由于在类似海水的盐溶液（4.3 wt% NaCl）中的膨胀比在去离子水中低约2到12倍，循环膨胀和收缩有可能用于驱动渗透马达中的活塞。因此，化学能被转化为机械能。这种转化由化学势的差异和熵的变化驱动。这很特别，因为大多数热力发动机依靠的是将热能转化为机械能。为了优化这个过程的效率，改变了水凝胶的中和度、交联度和粒径。此外，还构建了不同的渗透发动机原型。通过使用6 kPa的外部负载、交联度为1.7 mol%的聚合物、中和度为10 mol%以及粒径为370 - 670 µm，发现干水凝胶的最大平均功率为0.23 W/kg。由于这只是在第一轮优化中实现的，在一个循环中最大功率的更高值似乎是现实的。
