The deep building layouts typical in the U.S. have led to a nearly complete reliance on artificial lighting in standard office buildings. The development of daylight control systems that maximize the penetration and optimize the distribution of natural daylight in buildings has the potential for saving a significant portion of the energy consumed by artificial lighting, but existing systems are either static, costly, or obstruct views towards the outside. We report the Dynamic Daylight Control System (DDCS) that in- tegrates a thin cast transparent polydimethylsiloxane (PDMS)-based deformable array of louvers and waveguides within a millimeter-scale fluidic channel system. This system can be dynamically tuned to the different climates and sun positions to control daylight quality and distribution in the interior space. The series of qualitative and quantitative tests confirmed that DDCS exceeds conventional double glazing system in terms of reducing glare near the window and distributing light to the rear of the space. The system can also be converted to a visually transparent or a translucent glazing by filling the channels with an appropriate fluid. DDCS can be integrated or retrofitted to conventional glazing systems and allow for diffusivity and transmittance control.
Reversible Switching of Hydrogel-Actuated Nanostructures into Complex Micropatterns. Science. 2007;315 :487-490..
An aptamer-functionalized chemomechanically modulated biomolecule catch-and-release system. Nat. Chem. 2015;7 (5) :447-454. Full TextAbstract
The efficient extraction of (bio)molecules from fluid mixtures is vital for applications ranging from target characterization in (bio)chemistry to environmental analysis and biomedical diagnostics. Inspired by biological processes that seamlessly synchronize the capture, transport and release of biomolecules, we designed a robust chemomechanical sorting system capable of the concerted catch and release of target biomolecules from a solution mixture. The hybrid system is composed of target-specific, reversible binding sites attached to microscopic fins embedded in a responsive hydrogel that moves the cargo between two chemically distinct environments. To demonstrate the utility of the system, we focus on the effective separation of thrombin by synchronizing the pH-dependent binding strength of a thrombin-specific aptamer with volume changes of the pH-responsive hydrogel in a biphasic microfluidic regime, and show a non-destructive separation that has a quantitative sorting efficiency, as well as the system's stability and amenability to multiple solution recycling.
Adaptive all the way down: Building responsive materials from hierarchies of chemomechanical feedback. Chem. Soc. Rev. 2013;42 (17) :7072-7085. Publisher's VersionAbstract.
A living organism is a bundle of dynamic, integrated adaptive processes: not only does it continuously respond to constant changes in temperature, sunlight, nutrients, and other features of its environment, but it does so by coordinating hierarchies of feedback among cells, tissues, organs, and networks all continuously adapting to each other. At the root of it all is one of the most fundamental adaptive processes: the constant tug of war between chemistry and mechanics that interweaves chemical signals with endless reconfigurations of macromolecules, fibers, meshworks, and membranes. In this tutorial we explore how such chemomechanical feedback – as an inherently dynamic, iterative process connecting size and time scales – can and has been similarly evoked in synthetic materials to produce a fascinating diversity of complex multiscale responsive behaviors. We discuss how chemical kinetics and architecture can be designed to generate stimulus-induced 3D spatiotemporal waves and topographic patterns within a single bulk material, and how feedback between interior dynamics and surface-wide instabilities can further generate higher order buckling and wrinkling patterns. Building on these phenomena, we show how yet higher levels of feedback and spatiotemporal complexity can be programmed into hybrid materials, and how these mechanisms allow hybrid materials to be further integrated into multicompartmental systems capable of hierarchical chemo-mechano-chemical feedback responses. These responses no doubt represent only a small sample of the chemomechanical feedback behaviors waiting to be discovered in synthetic materials, and enable us to envision nearly limitless possibilities for designing multiresponsive, multifunctional, self-adapting materials and systems.
Environmentally responsive active optics based on hydrogel-actuated deformable mirror arrays. Proc. SPIE. 2011;7927 :792705..
Microbristle in gels: Toward all-polymer reconfigurable hybrid surfaces. Soft Matter. 2010;6 :750-755..
An artificial vasculature for adaptive thermal control of windows. Solar Energy Materials and Solar Cells. 2013;117 :429-436. Publisher's VersionAbstract.
Windows are a major source of energy inefficiency in buildings. In addition, heating by thermal radiation reduces the efficiency of photovoltaic panels. To help reduce heating by solar absorption in both of these cases, we developed a thin, transparent, bio-inspired, convective cooling layer for building windows and solar panels that contains microvasculature with millimeter-scale, fluid-filled channels. The thin cooling layer is composed of optically clear silicone rubber with microchannels fabricated using microfluidic engineering principles. Infrared imaging was used to measure cooling rates as a function of flow rate and water temperature. In these experiments, flowing room temperature water at 2 mL/min reduced the average temperature of a model 10×10 cm2 window by approximately 7–9 °C. An analytic steady-state heat transfer model was developed to augment the experiments and make more general estimates as functions of window size, channel geometry, flow rate, and water temperature. Thin cooling layers may be added to one or more panes in multi-pane windows or as thin film non-structural central layers. Lastly, the color, optical transparency and aesthetics of the windows could be modulated by flowing different fluids that differ in their scattering or absorption properties.
Synthetic Homeostatic Materials with Chemo-Mechano-Chemical Self-Regulation. Nature. 2012;487 :214-218..
Bio-inspired Design of Submerged Hydrogel-Actuated Polymer Microstructures Operating in Response to pH. Adv. Mater. 2011;23 (12) :1442–1446..
Dynamic daylight control system implementing thin cast arrays of polydimethylsiloxane-based millimeter-scale transparent louvers. Building and Environment. 2014;82 :87-96. Publisher's VersionAbstract.
Adaptive fluid-infused porous films with tunable transparency and wettability. Nature Materials. 2013;12 :529-534. Full TextAbstract.
Materials that adapt dynamically to environmental changes are currently limited to two-state switching of single properties, and only a small number of strategies that may lead to materials with continuously adjustable characteristics have been reported1-3. Here we introduce adaptive surfaces made of a liquid film supported by a nanoporous elastic substrate. As the substrate deforms, the liquid flows within the pores causing the smooth and defect-free surface to roughen through a continuous range of topographies. We show that a graded mechanical stimulus can be directly translated into finely tuned, dynamic adjustments of optical transparency and wettability. In particular, we demonstrate simultaneous control of the film's transparency and its ability to continuously manipulate various low-surface-tension droplets from free-sliding to pinned. This strategy should make possible the rational design of tunable, multifunctional adaptive materials for a broad range of applications.
Direct Writing and Actuation of Three-Dimensionally Patterned Hydrogel Pads on Micropillar Supports. Angew. Chem. Int. Ed. 2011;123..
Controlled Switching of the Wetting Behavior of Biomimetic Surfaces with Hydrogel-Supported Nanostructures. invited paper, J. Mater. Chem. 2008;18 :3841-3846..
Hydrogel-Actuated Integrated Responsive Systems (HAIRS): Creating Cilia-like "Hairy" Surfaces. In: Cambridge, U.K. RSC ; 2013. pp. 162-185..
Multifunctional Actuation Systems Responding to Chemical Gradients. Soft Matter. 2012;8 (32) :8289-8293..
New nanofabrication strategies: Inspired by biomineralization. MRS Bull. 2010;35 :323-330..