A three-terminal magnetic thermal transistor.

Three-terminal thermal analogies to electrical transistors have been proposed for use in thermal amplification, thermal switching, or thermal logic, but have not yet been demonstrated experimentally. Here, we design and fabricate a three-terminal magnetic thermal transistor in which the gate temperature controls the source-drain heat flow by toggling the source-drain thermal conductance from ON to OFF. The centimeter-scale thermal transistor uses gate-temperature dependent magnetic forces to actuate motion of a thermally conducting shuttle, providing thermal contact between source and drain in the ON state while breaking contact in the OFF state. We measure source-drain thermal switch ratios of 109 ± 44 in high vacuum with gate switching temperatures near 25 °C. Thermal measurements show that small heat flows into the gate can be used to drive larger heat flows from source to drain, and that the switching is reversible over >150 cycles. Proof-of-concept thermal circuit demonstrations show that magnetic thermal transistors can enable passive or active heat flow routing or can be combined to create Boolean thermal logic gates. This work will allow thermal researchers to explore the behavior of nonlinear thermal circuits using three-terminal transistors and will motivate further research developing thermal transistors for advanced thermal control.

Necrobotics: Biotic Materials as Ready-to-Use Actuators.

Designs perfected through evolution have informed bioinspired animal-like robots that mimic the locomotion of cheetahs and the compliance of jellyfish; biohybrid robots go a step further by incorporating living materials directly into engineered systems. Bioinspiration and biohybridization have led to new, exciting research, but humans have relied on biotic materials-non-living materials derived from living organisms-since their early ancestors wore animal hides as clothing and used bones for tools. In this work, an inanimate spider is repurposed as a ready-to-use actuator requiring only a single facile fabrication step, initiating the area of "necrobotics" in which biotic materials are used as robotic components. The unique walking mechanism of spiders-relying on hydraulic pressure rather than antagonistic muscle pairs to extend their legs-results in a necrobotic gripper that naturally resides in its closed state and can be opened by applying pressure. The necrobotic gripper is capable of grasping objects with irregular geometries and up to 130% of its own mass. Furthermore, the gripper can serve as a handheld device and innately camouflages in outdoor environments. Necrobotics can be further extended to incorporate biotic materials derived from other creatures with similar hydraulic mechanisms for locomotion and articulation.

Colloid Separation by CO2-Induced Diffusiophoresis.

We present a microfluidic crossflow separation of colloids enabled by the dissolution of CO2 gas in aqueous suspensions. The dissolved CO2 dissociates into H+ and HCO3- ions, which are efficient candidates for electrolytic diffusiophoresis, because of the fast diffusion of protons. By exposing CO2 gas to one side of a microfluidic flow channel, a crossflow gradient can be created, enabling the crossflow diffusiophoresis of suspended particles. We develop a simple two-dimensional model to describe the coupled transport dynamics that is due to the competition of advection and diffusiophoresis. Furthermore, we show that oil nanoemulsions can be effectively separated by utilizing highly charged particles as a carrier vehicle, which is otherwise difficult to achieve. These results demonstrate a portable, versatile method for separating particles in broad applications including oil extraction, drug delivery, and bioseparation.