Unique wrinkling behavior of stiff thin films on shape memory polymers

Shape memory polymers (SMPs) can remember two or more distinct shapes, and therefore can have many applications. We here presents combined experimental and theoretical studies on the wrinkling of stiff thin films on SMPs. Experimental results show well-defined, wavy profiles of the thin films. Time and temperature dependent wrinkle formation and evolution were observed. It was shown that both wrinkling wavelength and amplitude increase with SMP relaxation. This is different from earlier observations of thin film wrinkling on soft substrates, which show decreasing wavelength and increasing amplitude when compression increases. Finite element simulations accounting for the thermomechanical behavior of SMPs were used to study wrinkling of thin films on SMPs, which show good agreement with experiments. This study can have important implications in surface engineering, stretchable electronics, and advanced manufacturing

Electronic eyes enabled by stretchable electronics: mechanics, materials, and optics

Stretchable electronics combines the electronic performance of conventional wafer-based semiconductor devices and mechanical properties of a rubber band, and thus can have very broad applications that are impossible for hard, planar integrated circuits that exist today. Examples range from surgical and diagnostic implements that integrate with the human body to provide advanced therapeutic capabilities, to structural health monitors and inspection systems for civil engineering. In this discussion, I will discuss our development of electronic eye-ball cameras enabled by stretchable electronics and mechanics. Electronic eye-ball cameras have high performance photodetectors distributed on curvilinear surfaces and offer advantages over comparable systems that use conventional, flat detector arrays. Our recently developed artificial compound eye with designs inspired by arthropod eyes will also be introduced. This artificial compound eye can achieve wide-angle field of view, low aberrations, high acuity to motion and an infinite depth of field, which were not possible through conventional technology. Mechanics, materials, and optics of these systems will be discussed

Iridacycles for hydrogenation and dehydrogenation reactions

Iridacycles are a group of cyclometalated metal complexes, which have recently been shown to be versatile catalysts for a range of reactions.</p

Metal oxide semiconductor nanomembrane-based soft unnoticeable multifunctional electronics for wearable human-machine interfaces

Wearable human-machine interfaces (HMIs) are an important class of devices that enable human and machine interaction and teaming. Recent advances in electronics, materials, and mechanical designs have offered avenues toward wearable HMI devices. However, existing wearable HMI devices are uncomfortable to use and restrict the human body&apos;s motion, show slow response times, or are challenging to realize with multiple functions. Here, we report sol-gel-on-polymer-processed indium zinc oxide semiconductor nanomembrane-based ultrathin stretchable electronics with advantages of multifunctionality, simple manufacturing, imperceptible wearing, and robust interfacing. Multifunctional wearable HMI devices range from resistive random-access memory for data storage to field-effect transistors for interfacing and switching circuits, to various sensors for health and body motion sensing, and to microheaters for temperature delivery. The HMI devices can be not only seamlessly worn by humans but also implemented as prosthetic skin for robotics, which offer intelligent feedback, resulting in a closed-loop HMI system

Transition-Metal-Free Hydrogen Autotransfer: Diastereoselective N-Alkylation of Amines with Racemic Alcohols.

A practical method for the synthesis of α-chiral amines by alkylation of amines with alcohols in the absence of any transition-metal catalysts has been developed. Under the co-catalysis of a ketone and NaOH, racemic secondary alcohols reacted with Ellman's chiral tert-butanesulfinamide by a hydrogen autotransfer process to afford chiral amines with high diastereoselectivities (up to >99:1). Broad substrate scope and up to a 10 gram scale production of chiral amines were demonstrated. The method was applied to the synthesis of chiral deuterium-labelled amines with high deuterium incorporation and optical purity, including examples of chiral deuterated drugs. The configuration of amine products is found to be determined solely by the configuration of the chiral tert-butanesulfinamide regardless of that of alcohols, and this is corroborated by DFT calculations. Further mechanistic studies showed that the reaction is initiated by the ketone catalyst and involves a transition state similar to that proposed for the Meerwein-Ponndorf-Verley (MPV) reduction, and importantly, it is the interaction of the sodium cation of the base with both the nitrogen and oxygen atoms of the sulfinamide moiety that makes feasible, and determines the diastereoselectivity of, the reaction