Hatton BD, Wheeldon I, Hancock MJ, Kolle M, Aizenberg J, Ingber DE.
An artificial vasculature for adaptive thermal control of windows. Solar Energy Materials and Solar Cells. 2013;117 :429-436.
Publisher's VersionAbstractWindows 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.
Kolle M, Lethbridge A, Kreysing M, Baumberg JJ, Aizenberg J, Vukusic P.
Bio-Inspired Band-Gap Tunable Elastic Optical Multilayer Fibers. Adv. Mater. 2013;25 (15) :2239-2245.
Full Text Kats MA, Byrnes SJ, Blanchard R, Kolle M, Genevet P, Aizenberg J, Capasso F.
Enhancement of absorption and color contrast in ultra-thin highly absorbing optical coatings. Appl. Phys. Lett. 2013;103 :101104.
Publisher's VersionAbstractRecently a new class of optical interference coatings was introduced which comprises ultra-thin, highly absorbing dielectric layers on metal substrates. We show that these lossy coatings can be augmented by an additional transparent subwavelength layer. We fabricated a sample comprising a gold substrate, an ultra-thin film of germanium with a thickness gradient, and several alumina films. The experimental reflectivity spectra showed that the additional alumina layer increases the color range that can be obtained, in agreement with calculations. More generally, this transparent layer can be used to enhance optical absorption, protect against erosion, or as a transparent electrode for optoelectronic devices.
Kim P, Hu Y, Alvarenga J, Kolle M, Suo Z, Aizenberg J.
Rational Design of Mechano-Responsive Optical Materials by Fine Tuning the Evolution of Strain-Dependent Wrinkling Patterns. Adv. Optical Mater. 2013;1 (5) :381-388.
Publisher's VersionAbstractRational design strategies for mechano‐responsive optical material systems are created by introducing a simple experimental system that can continuously vary the state of bi‐axial stress to induce various wrinkling patterns, including stripes, labyrinths, herringbones, and rarely observed checkerboards, that can dynamically tune the optical properties. In particular, a switching of two orthogonally oriented stripe wrinkle patterns from oxidized polydimethylsiloxane around the critical strain value is reported, as well as the coexistence of these wrinkles forming elusive checkerboard patterns, which are predicted only in previous simulations. These strain‐induced wrinkle patterns give rise to dynamic changes in optical transmittance and diffraction patterns. A theoretical description of the observed pattern formation is presented which accounts for the residual stress in the membrane and allows for the fine‐tuning of the window of switching of the orthogonal wrinkles. Applications of wrinkle‐induced changes in optical properties are demonstrated, including a mechanically responsive instantaneous privacy screen and a transparent sheet that reversibly reveals a message or graphic and dynamically switches the transmittance when stretched and released.