Microlens formation in microgel/gold colloid composite materials via photothermal patterning

We report on the nature of photothermally patterned regions inside self-assembled hydrogel nanoparticle materials containing coassembled colloidal Au. These composite materials are prepared from approximately 226-nm diameter particles composed of the environmentally responsive polymer, poly(N-isopropylacrylamide) (pNIPAm). Upon centrifugation to achieve a proper volume fraction, these close-packed assemblies display a sharp Bragg diffraction peak in the midvisible region of the spectrum and can be reversibly converted into a nondiffracting glassy material as the temperature is raised above the characteristic phase transition temperature of the polymer. The addition of 16-nm colloidal Au prior to centrifugation allows the homogeneous distribution of metal nanoparticles throughout the close-packed material. Localized heating is then possible upon excitation of the Au plasmon absorption with a frequency doubled Nd:YAG laser (lambda = 532 nm). Such localized heating events lead to patterned regions of ordered crystalline phases inside of bulk glassy phases. We illustrate that the nature of the locally patterned area results in the formation of a microlens due to density/refractive index gradient in the patterned crystalline region. The Gaussian power distribution of the incident beam is thought to be a contributing factor in the microlens formation. Microlens formation is shown by observing interference patterns similar to Newton's rings, which change over time as the region is formed. A true hallmark of the lens is also demonstrated by focusing an image through the patterned structure.     

Atomic structure of a (2 x 1) reconstructed NiSi2/Si(001) interface

Nickel disilicide/silicon (001) interfaces were investigated by aberration corrected scanning transmission electron microscopy (STEM). The atomic structure was derived directly from the high spatial resolution high angle annular dark field STEM images without recourse to image simulation. It comprises fivefold coordinated silicon and sevenfold coordinated nickel sites at the interface and shows a 2 x 1 reconstruction. The proposed structure has not been experimentally observed before but has been recently predicted theoretically by others to be energetically favored.     

The total synthesis of tubulysin D

The first total synthesis of tubulysin D is reported. The development and application of new tert-butanesulfinamide methods allowed for rapid syntheses of the tubuvaline and tubuphenylalanine fragments. Most significantly, a route was devised and implemented to introduce and carry forward the highly labile N,O-acetal functionality. Tubulysin D is the most active member of the tubulysin family, and the efficient synthetic route described herein will allow for the rapid syntheses of analogues to probe the biological activity of this important class of natural products.     

Constitutive framework optimized for myocardium and other high-strain, laminar materials with one fiber family

Central to this analysis is the identification of six rotation invariant scalars α_1-6 that succinctly define the strain in materials that have one family of parallel fibers arranged in laminae. These scalars were chosen so as to minimize covariance amongst the response terms in the hyperelastic limit, and they are termed strain attributes because it is necessary to distinguish them from strain invariants. The Cauchy stress t is expressed as the sum of six response terms, almost all of which are mutually orthogonal for finite strain (i.e. 14 of the 15 inner products vanish). For small deformations, the response terms are entirely orthogonal (i.e. all 15 inner products vanish). A response term is the product of a response function with its associated kinematic tensor. Each response function is a scalar partial derivative of the strain energy W with respect to a strain attribute. Applications for this theory presently include myocardium (heart muscle) which is often modeled as having muscle fibers arranged in sheets. Utility for experimental identification of strain energy functions is demonstrated by showing that common tests on incompressible materials can directly determine terms in W. Since the described set of strain attributes reduces the covariance amongst response terms, this approach may enhance the speed and precision of inverse finite element methods.     

Material issues for construction of organic and polymeric driving circuits for display and electronic applications

Organic and polymeric driving circuits may be a possible alternative to realize low cost flexible and large area flat panel displays. Recent efforts have been directed to the discovery of solution processable polymeric semiconductors for the ease of fabrication and low cost. In this paper, we report the investigation of various 3‐substituted regioregular polythiophenes as active semiconductors for field‐effect transistors. The best transistor performance has been found with regioregular poly(3‐heaxylthiophene). The difference in their device performance was correlated to the structure and morphological behavior of these regioregular polythiophenes.     

A novel scandium ortho-methoxynitrosobenzene-dimer complex: mechanistic implications for the nitroso-Diels-Alder reaction

Arylnitroso dienophiles exist in equilibrium with their dimeric counterparts, which in turn form stable bidentate complexes with scandium(III) triflate and react with cyclohexadiene to give the corresponding Diels-Alder adduct at the same rate as the normal thermal process.