Biomimetic Meta‐Structured Electro‐Microfluidics

Flexible membranes (i.e., paper, cloth, and polydimethylsiloxane (PDMS)) have received extensive attention. The rapid development of flexible microfluidics and electronics and their integration calls for complex substrate structures to allow for multiple functions. Inspired by nature, meta‐structured membranes (MSMs) as substrates for fabricating integrated microfluidics and electronics are presented. These flexible and freestanding MSMs are generated by the self‐assembly of elastic plastic copolymer nanoparticle photonic crystals on micropatterned PDMS templates. The final MSMs constitute with integrated ordered micro‐ and nanostructures and exhibit spontaneous liquid transfer, fluorescence enhancement, and intimate skin contact. MSMs with designed patterns can be fabricated by assembling polymer nanoparticles on patterned molds; complicated and highly integrated electro‐microfluidics are generated on one slice of MSMs by utilizing these patterns as microfluidic channels and electrocircuits. They can be used as chip‐on‐skin sensors for biochemical–physiological hybrid monitoring sensing of the human body and as organ chips for cell culture and metabolite analysis under drug treatment. Their excellent properties show their potential value in cross‐scale sensing and have broad potential applications.     

Electro‐optical Materials: Switching of Electrically Responsive,Light‐Sensitive Colloidal Suspensions of Anisotropic Pigment Particles (Adv. Funct. Mater. 3/2011)

An unusual electro‐optical behavior of colloidal suspensions of dichroic, elongated (rod‐shaped) pigment particles is reported. These suspensions exhibit nematic liquid crystal order at low volume fraction of the suspended particles (<15 wt%) and show a strong electric and optical response to an external electric field. Additionally, the characteristics of the optical response can be reversibly manipulated by illuminating the sample with light in its absorption band. The suspensions show a number of interesting phenomena like homeotropic‐planar orientational transitions and light‐induced pattern formation.     

Microactuators: Control of the Properties of Micrometer Sized Actuators from Liquid Crystalline Elastomers Prepared in a Microfluidic Setup (Adv. Funct. Mater. 24/2010)

In this article new results on the preparation of monodisperse particles from a liquid crystalline elastomer in a microfluidic setup are presnted. For this, droplets from a liquid crystalline monomer are prepared in a microfluidic device and polymerized while they are flowing inside a microtube. The parti­cles obtained by this method possess an internal orientation, which gives them actuating properties. When they are heated into the isotropic phase of the liquid crystalline material they show a reversible change in shape whereby they change their length in one direction by almost 100%. It is shown how the variation of experimental parameters during their synthesis impacts the properties of these micro‐actuators. Influence over their primal shape, the strength of their shape changing properties, their size, and their mechanical properties is demontrated. From the systematic variation of experimental parameters a deep understanding of the complex processes taking place in a flowing droplet of a liquid crystalline material is obtainted. Additionally NMR analysis and swelling experiments on these actuating materials are provided.     

Cover Picture: Enhanced Electro‐Optic Behavior for Shaped Polymer Cholesteric Liquid‐Crystal Flakes Made Using Soft Lithography (Adv. Funct. Mater. 2/2005)

The cover shows a variety of shaped flakes fabricated from polymer cholesteric liquid‐crystal material using soft lithography. In work reported by Jacobs and co‐workers on p. 217, the micrometer‐sized flakes exhibit brilliant circularly polarized selective reflection colors without polarizers or color filters when placed in a fluid‐filled electro‐optic cell. With the application of a low‐magnitude alternating current field, the flakes reorient in hundreds of milliseconds and the colors disappear. Polymer cholesteric liquid‐crystal (PCLC) flakes were investigated for their electro‐optical behavior under an applied alternating‐current field. Shaped flakes, fabricated using soft lithography and suspended in dielectric‐fluid‐filled cells, reoriented more uniformly than randomly shaped flakes made by fracturing of PCLC films. Extensive characterization found shaped flakes to be smooth and uniform in size, shape, and thickness. Reorientation in applied fields as low as tens of mV_rms μm^–1 was fastest for flakes with lateral aspect ratios greater than 1:1, confirming theoretical predictions based on Maxwell–Wagner polarization. Brilliant reflective colors and inherent polarization make shaped PCLC flakes of interest for particle displays.