Synthetic active systems capable of autonomous motion or driving fluid flow are of great current interest owing to their potential applications in nanomachinery, cargo capture and delivery, reversible assemblies, and chemical/biochemical sensing. Designing self-powered micro/nanomotors and understanding their propulsion mechanisms and ensemble behavior are now areas of great interest in low-Reynolds-number mechanics. In this article, we classify prototypes of existing small-scale motors on the basis of the materials used in synthesis and fabrication, with the aim of understanding the importance of material selection in designing functional motors for futuristic applications.

We have developed a highly efficient, bubble-free autonomous nanomotor based on a nanobattery. Bimetallic silver-platinum nanorods are powered by self-electrophoresis and show speeds much higher than those of other electrophoretic motors at similar fuel concentrations. The fuel (I2) can be regenerated by exposure to ambient light, leading to renewed motion of the motor. This versatile system can also be made into a micropump that transports fluid and particles.

Self-propelled, active colloidal systems are of great current interest from both fundamental as well as practical standpoints, with potential applications in nanomachinery, nanoscale assembly, robotics, fluidics, and chemical/biochemical sensing. This perspective focuses on chemicallypowered catalytic nano and micromotors. We review the major advances to date in motor design, propulsion mechanisms and directional control, and inter-motor communication leading to collective behavior. We conclude by discussing the next steps in going forward: the fundamental questions that remain to be addressed and new design principles required for useful applications.

Polymers that are capable of depolymerizing completely from head-to-tail upon cleavage of an end-cap from the terminus of the polymer have emerged recently as a new strategy for creating stimuli-responsive solid-state materials with amplified responses. In theory, solid-state materials made from these polymers will respond most efficiently to a stimulus in solution when the polymer end-caps are displayed into solution at the solid−liquid interface, rather than being buried in the solidstate material. This article defines two strategies for increasing the likelihood that end-caps are displayed at this interface. A microscale-pump made from films of depolymerizable poly(phthalaldehyde) serves as a test system for evaluating the location of end-caps in the films. By measuring the flow rate initiated by depolymerization of the polymers within the films, we determined that both the polymer length and hydrophilicity of the end-caps affect the density of end-caps at the solid−liquid interface.

a b s t r a c tThis paper describes a template-assisted synthesis of silver halide nanowires by anodization of silver nanowires in hydrohalic acid solution within an alumina template. The length of the silver halide nanowires was controlled by the charge passed during the anodization process. The silver halide nanowires were characterized using SEM and EDS to determine structural differences, electron beam sensitivity, Ag:X ratios, and other. The template-assisted synthesis is superior to traditional solution-based methods due to the uniformity and controlled shape of the silver halide nanowire product.