Osmotic Propulsion: The Osmotic Motor

California Institute Of Technology, Pasadena CA

Investigators

Abstract

CBET-0754967 Brady Intellectual Merit: The design of nanoengines that can convert stored chemical energy into motion is a key transformative challenge of nanotechnology, especially for nano-engines that can operate autonomously. Recent experiments have demonstrated that it is possible to power the motion of nanoscale and microscale objects by using surface catalytic reactions so-called catalytic nanomotors. The precise mechanism responsible for this motion is not known, although a number of ideas have been put forth. This project involves a very simple mechanism is proposed: osmotic propulsion. A surface chemical reaction creates local concentration gradients of the reactive and product species which generate a net osmotic force on the motor. The motor is able to harness the ever present random thermal motion via a chemical reaction to achieve directed autonomous motion. This research demonstrates that such an 'osmotic' motor is possible and addresses such questions as: How fast can the motor move? How large of a force can it generate? How much 'cargo' can it carry? How much fluid can it pump? How can its motion be controlled and directed? What chemistry can be used? What is the efficiency of such an osmotic motor? Broader Impact: Osmotic propulsion provides a very simple and general means to convert chemical energy into mechanical motion and work. Exploiting the random thermal motion in colloidal systems via osmotic propulsion can revolutionize the design and operation of microfluidic and nanodevices, with applications in directed self-assembly of materials, thermal management of micro- and nanoprocessors, and the design and operation of chemical and biological sensors. This research will provide explicit prescriptions for the construction and operation of colloidal particles that can be used as osmotic motors. This fundamental and transformative study must be undertaken if we wish to enable many of the nano-scale technologies envisioned for the future: tiny medical 'nanobots' that can access human illness inside the body, at the cellular level, and repair it. Or devices that can sense their way through micro channels in 'lab on a chip' devices, stirring or separating nano-liters of chemicals. Or even a nano-motor that senses intrusion of a specific molecule, swims toward it, and closes a channel in the process triggering an alarm switch for biological contaminants. Any of these types of devices is possible provided the physics of motion at that scale is correctly understood and utilized. And finally, studies of autonomous motors may help to understand more generally chemomechanical transduction as occurs in biological systems, and also create novel artificial motors that mimic living organisms and which can be harnessed to perform useful tasks.