The need for materials with improved functionality has led to the development of metamaterials, or artificially engineered materials possessing properties determined by their structure instead of composition. The building blocks of metamaterials are traditionally organized in fixed structure within a lattice pattern.
In a recent study, scientists have revealed an intelligent programmable liquid which possesses a unique structure that enables alteration of its properties according to programming.
Programmable Fluids From Tiny Rubber Spheres
At Harvard University, a team of experts conducted a study where they used a simple hydraulic gripper with no control systems and no sensors. They only needed silicon oil and plenty of tiny rubber balls to develop a metafluid with a programmable response to pressure. The details of their study are discussed in the paper "Shell buckling for programmable fluids."
Led by Adel Djellouli, the team created a sphere which measured 10 millimeters wide with 2-millimeter-thick rubber walls surrounding a pocket of air. The sphere was placed in a container with 300 milliliters of water. When the researchers increased the pressure in the container, the sphere began to buckle. Meanwhile, the pressure remained steady even though the volume of the fluid continued to drop. According to the scientists, the liquid containing the sphere did not behave like water anymore, but instead had a pronounced plateau in its pressure/volume curve.
Next, the research team started to explore various sizes and numbers of the spheres in the medium. The pressure at which the spheres activate are tuned by changing their radius and thickness of walls. Making the spheres thicker means more energy and thus, higher activation pressure.
Other parameters can be altered to program desired properties in the metafluid. These include the structure of the spheres and volume fraction. They can be tuned by using various mixtures of spheres with different properties.
Very tight variation in size and thickness of the spheres would result in a very flat plateau of pressure upon activation. On the other hand, a wider distribution would result in a smoother transition from all unbuckled to buckled.
Self-Controlled Robots
Creating a robot that can pick up delicate objects requires lots of control algorithms. These sets of rules process inputs from advanced vision systems or sensors that imitate the human sense of touch. The other approach is in the realm of soft robotics which involves a robot with limited strength and durability.
By tuning the pressure/volume curve, Djellouli's team was able to create a smart hydraulic gripper which functions without requiring sensors or control systems. The gripper was designed to grab and hold an egg, a water bottle, and a blueberry without crushing them. Its basic design involves one static finger and a second one which opens and closes the grip based on the movement of a hydraulic piston.
Even more profound discovery was made when the spheres were miniaturized. Doing so enabled the researchers to tune the rheology of the fluid. They also noticed that a fluid with compressed spheres can flow faster than the one with non-activated spheres. This happened even when driven by the same pressure difference between the outlet and the input.
RELATED ARTICLE : Electrochemistry Reconfigures Morphing Metamaterials
Check out more news and information on Metamaterials in Science Times.
