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1. Liquid Crystal Elastomer with Integrated Soft Thermoelectrics for Shape Memory Actuation and Energy Harvesting

   https://doi.org/10.1002/adma.202200857  

   Zadan, Mason; Patel, Dinesh_K; Sabelhaus, Andrew_P; Liao, Jiahe; Wertz, Anthony; Yao, Lining; Majidi, Carmel (May 2022, Advanced Materials)

   Abstract Liquid crystal elastomers (LCEs) have attracted tremendous interest as actuators for soft robotics due to their mechanical and shape memory properties. However, LCE actuators typically respond to thermal stimulation through active Joule heating and passive cooling, which make them difficult to control. In this work, LCEs are combined with soft, stretchable thermoelectrics to create transducers capable of electrically controlled actuation, active cooling, and thermal‐to‐electrical energy conversion. The thermoelectric layers are composed of semiconductors embedded within a 3D printed elastomer matrix and wired together with eutectic gallium–indium (EGaIn) liquid metal interconnects. This layer is covered on both sides with LCE, which alternately heats and cools to achieve cyclical bending actuation in response to voltage‐controlled Peltier activation. Moreover, the thermoelectric layer can harvest energy from thermal gradients between the two LCE layers through the Seebeck effect, allowing for regenerative energy harvesting. As demonstrations, first, closed‐loop control of the transducer is performed to rapidly track a changing actuator position. Second, a soft robotic walker that is capable of walking toward a heat source and harvesting energy is introduced. Lastly, phototropic‐inspired autonomous deflection of the limbs toward a heat source is shown, demonstrating an additional method to increase energy recuperation efficiency for soft systems. 

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2. Fundamentals of soft thermofluidic system design

   https://doi.org/10.1039/D0SM00504E  

   Kotagama, Praveen; Manning, Kenneth C.; Rykaczewski, Konrad (July 2020, Soft Matter)

   The soft composition of many natural thermofluidic systems allows them to effectively move heat and control its transfer rate by dynamically changing shape ( e.g. dilation or constriction of capillaries near our skin). So far, making analogous deformable “soft thermofluidic systems” has been limited by the low thermal conductivity of materials with suitable mechanical properties. By remaining soft and stretchable despite the addition of filler, elastomer composites with thermal conductivity enhanced by liquid-metal micro-droplets provide an ideal material for this application. In this work, we use these materials to develop an elementary thermofluidic system consisting of a soft, heat generating pipe that is internally cooled with flow of water and explore its thermal behavior as it undergoes large shape change. The transient device shape change invalidates many conventional assumptions employed in thermal design making analysis of this devices’ operation a non-trivial undertaking. To this end, using time scale analysis we demonstrate when the conventional assumptions break down and highlight conditions under which the quasi-static assumption is applicable. In this gradual shape modulation regime the actuated devices’ thermal behavior at a given stretch approaches that of a static device with equivalent geometry. We validate this time scale analysis by experimentally characterizing thermo-fluidic behavior of our soft system as it undergoes axial periodic extension–retraction at varying frequencies during operation. By doing so we explore multiple shape modulation regimes and provide a theoretical foundation to be used in the design of soft thermofluidic systems undergoing transient deformation. 

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3. A computationally efficient approach for immersion cooling of a Li-Ion battery cell

   https://doi.org/10.1016/j.icheatmasstransfer.2025.108856  

   Tripathi, Piyush Mani; Marconnet, Amy (May 2025, International Communications in Heat and Mass Transfer)

   Immersion-cooled battery thermal management systems (BTMSs) are generally designed and analyzed using numerical simulations. These models must couple the electrochemical and thermal–fluid physics for accurate results. However, such a numerical approach is computationally expensive and may not be feasible, particularly for large systems. Here, we develop a computationally efficient approach to study immersion cooling-based BTMSs with the coupled physics. After validating the simplified immersion-cooled battery model for fixed convection coefficient, we then define two simplified immersion cooling models: one using existing heat transfer correlations and the other employing customized correlations trained from fully-coupled numerical models. The trained models are highly accurate (error <3%). Moreover, they are very flexible as they can be formulated to study different combinations of mass flow rates, fluids, and discharge rates using a single heat transfer correlation. Additionally, the trained models are data-frugal, requiring only data from two mass flow rates (for a given fluid and discharge rate) to predict the response for other mass flow rates. The significant reduction in computation cost [from hours or days for the fully-coupled numerical models to seconds for proposed models] makes the proposed approach more suitable for rapid analysis, optimization, and real-time implementation of the immersion-cooled BTMSs. 

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4. Transient topology optimization for efficient design of actively cooled microvascular materials

   https://doi.org/10.1007/s00158-024-03774-2  

   Gorman, Jonathan; Pejman, Reza; Kumar, Sandeep R.; Patrick, Jason F.; Najafi, Ahmad R. (March 2024, Structural and Multidisciplinary Optimization)

   Abstract Microvascular materials containing internal microchannels are able to achieve multi-functionality by flowing different fluids through vasculature. Active cooling is one application to protect structural components and devices from thermal overload, which is critical to modern technology including electric vehicle battery packaging and solar panels on space probes. Creating thermally efficient vascular network designs requires state-of-the-art computational tools. Prior optimization schemes have only considered steady-state cooling, rendering a knowledge gap for time-varying heat transfer behavior. In this study, a transient topology optimization framework is presented to maximize the active-cooling performance and mitigate computational cost. Here, we optimize the channel layout so that coolant flowing within the vascular network can remove heat quickly and also provide a lower steady-state temperature. An objective function for this new transient formulation is proposed that minimizes the area beneath the average temperature versus time curve to simultaneously reduce the temperature and cooling time. The thermal response of the system is obtained through a transient Geometric Reduced Order Finite Element Model (GRO-FEM). The model is verified via a conjugate heat transfer simulation in commercial software and validated by an active-cooling experiment conducted on a 3D-printed microvascular metal. A transient sensitivity analysis is derived to provide the optimizer with analytical gradients of the objective function for further computational efficiency. Example problems are solved demonstrating the method’s ability to enhance cooling performance along with a comparison of transient versus steady-state optimization results. In this comparison, both the steady-state and transient frameworks delivered different designs with similar performance characteristics for the problems considered in this study. This latest computational framework provides a new thermal regulation toolbox for microvascular material designers. 

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5. Active Membranes on Rigidity Tunable Foundations for Programmable, Rapidly Switchable Adhesion

   https://doi.org/10.1002/admt.202000676  

   Swift, Matthew_D; Haverkamp, Cole_B; Stabile, Christopher_J; Hwang, Dohgyu; Plaut, Raymond_H; Turner, Kevin_T; Dillard, David_A; Bartlett, Michael_D (September 2020, Advanced Materials Technologies)

   Abstract Rapidly controlling and switching adhesion is necessary for applications in robotic gripping and locomotion, pick and place operations, and transfer printing. However, switchable adhesives often display a binary response (on or off) with a narrow adhesion range, lack post‐fabrication adhesion tunability, or switch slowly due to diffusion‐controlled processes. Here, pneumatically controlled shape and rigidity tuning is coupled to rapidly switch adhesion (≈0.1 s) across a wide range of programmable adhesion forces with measured switching ratios as high as 1300x. The switchable adhesion system introduces an active polydimethylsiloxane membrane supported on a compliant, foam foundation with pressure‐tunable rigidity where positive and negative pneumatic pressure synergistically control contact stiffness and geometry to activate and release adhesion. Energy‐based modeling and finite element computation demonstrate that high adhesion is achieved through a pressure‐dependent, nonlinear stiffness of the foundation, while an inflated shape at positive pressures enables easy release. This approach enables adhesion‐based gripping and material assembly, which is utilized to pick‐and‐release common objects, rough and porous materials, and arrays of elements with a greater than 14 000xrange in mass. The robust assembly of diverse components (rigid, soft, flexible) is then demonstrated to create a soft and stretchable electronic device. 

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