Photonic crystal devices

We developed photochemically controlled photonic crystals which may be useful in novel recordable and erasable memories and/or display devices. These materials can operate in the UV, visible or near IR spectral regions. Information is recorded and erased by exciting the photonic crystal with ∼ 360 nm UV light or ∼ 480 nm visible light. The recorded information is read out by measuring the photonic crystal diffraction wavelength. The active element of the device is an azobenzene functionalized hydrogel which contains an embedded crystalline colloidal array. UV excitation forms cis-azobenzene while visible excitation forms trans-azobenzene. Larger dipole moment of the cis-form results in decrease of the free energy of mixing which causes the hydrogel to swell and to red-shift the photonic crystal diffraction with a 36 s time constant. We also observed fast ms and sub-ms transient dynamics associated with convection due to heating of the medium by UV excitation. Convective motion of the medium stretches the PCCA for about 6 μs within which the convection decays and the elastic restoring force of the PCCA brings back the stretched PCCA to its equilibrium state with 33 μs time constant. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Nanogel nanosecond photonic crystal optical switching

We developed a robust nanosecond photonic crystal switching material by using poly(N-isopropylacrylamide) (PNIPAM) nanogel colloidal particles that self-assemble into crystalline colloidal arrays (CCAs). The CCA was polymerized into a loose-knit hydrogel which permits the individual embedded nanogel PNIPAM particles to coherently and synchronously undergo their thermally induced volume phase transitions. A laser T-jump from 30 to 35 degrees C actuates the nanogel particle shrinkage; the resulting increased diffraction decreases light transmission within 900 ns. Additional transmission decreases occur with characteristic times of 19 and 130 ns. Individual NIPAM sphere volume switching occurs in the approximately 100 ns time regime. These nanogel nanosecond phenomena may be useful in the design of fast photonic crystal switches and optical limiting materials. Smaller nanogels will show even faster volume phase transitions.     

Stereospecific elimination of acetic acid in 3- and 4-arylcyclohexyl acetates under electron impact

The elimination of CH₃COOH from the molecular ions of trans-3- and 4-arylcyclohexyl acetates takes place to a greater extent than in the cis isomers. Deuterium labelling shows that the elimination involves mainly the benzylic hydrogen in the trans-acetates, but not in the cis isomers. This behaviour is similar qualitatively to that of the corresponding alcohols and methyl ethers, but entirely different from that of t-butylcyclohexyl acetates, which do not exhibit any stereospecificity. Substituent effects on the elimination for both cis and trans isomers are discussed.     

Stereoselective H2O eliminations in 3- and 4-arcylcyclohexanols under electron impact

The elimination of H20 from the molecular ions of trans-4- and trans-3-arylcyclohexanois takes place to a greater extent than in the corresponding cis isomers. The remarkable differences in abundance taken together with substituent effects and the results of deuterium labelling, show that configuration is retained in the molecular ions which undergo the elimination, and that this process is a cis-1,4 and cis-1,3 elimination in the trans-4- and trans-3- arylcyclohexanois, respectively. Possible mechanisms for the elimination in the cis isomers are discussed.     

Synthesis and utilization of monodisperse hollow polymeric particles in photonic crystals

We developed a process to fabricate 150-700 nm monodisperse polymer particles with 100-500 nm hollow cores. These hollow particles were fabricated via dispersion polymerization to synthesize a polymer shell around monodisperse SiO(2) particles. The SiO(2) cores were then removed by HF etching to produce monodisperse hollow polymeric particle shells. The hollow core size and the polymer shell thickness, can be easily varied over significant size ranges. These hollow polymeric particles are sufficiently monodisperse that upon centrifugation from ethanol they form well-ordered close-packed colloidal crystals that diffract light. After the surfaces are functionalized with sulfonates, these particles self-assemble into crystalline colloidal arrays in deionized water. This synthetic method can also be used to create monodisperse particles with complex and unusual morphologies. For example, we synthesized hollow particles containing two concentric-independent, spherical polymer shells, and hollow silica particles which contain a central spherical silica core. In addition, these hollow spheres can be used as template microreactors. For example, we were able to fabricate monodisperse polymer spheres containing high concentrations of magnetic nanospheres formed by direct precipitation within the hollow cores.     

Artificial red cells with crosslinked hemoglobin membranes

Artificial cells containing concentrated hemoglobin (Hb) solution were prepared by interfacial polymerization of Hb with glutaraldehyde (GA) in liquid membrane capsules (LMC). A solution containing 30% of Hb was emulsified in mineral oil as red cell-size microdroplets, and this emulsion was dispersed in an aqueous phase containing glutaraldehyde to form LMC. The LMC were semipermeable templates that held the microdroplets of Hb in suspension while GA diffused through the oil to the microdroplet surfaces. The GA crosslinked Hb at the surface of each microdroplet to form an artificial red-cell membrane encapsulating Hb solution. A water-soluble surfactant was used to eject the cells from the LMC and suspend them in saline. Several surfactants were evaluated. Cell size was controlled by agitation speed during preparation of the original emulsion. Cells of 2.52 = ±1.69 μm were prepared. The encapsulated Hb retained capacity to bind and release O₂. The cells had aP ₅₀ of 8.9 torr (1200 Pa) and a capacity of 0.55 cc O₂/g of total Hb, indicating that the crosslinked portion of the Hb did not contribute to O₂ transport.     

Studies in mass spectrometry—XV: Retro-diels-alder fragmentation and double hydrogen migration in some polycyclic diketones

In contrast to adducts I of bi-1-cycloalken-1-yls and p-benzoquinone, their reduction products II do not exhibit a double hydrogen migration from δ positions accompanying a ‘retro-Diels-Alder’ type fragmentation. An ordinary retro-Diels-Alder fragmentation was found to take place, with charge retention in the diene portion of the molecule. A double hydrogen migration has been detected in II leading to m/e 112 ion c₂, which differed, however, from that in I in charge retention and in the origin of the migrating hydrogen atoms. Adducts III of di-1-cycloalken-1-yls and naphthoquinone behave similarly to II. They exhibit relatively low abundance ions a, however, due to a double hydrogen migration from δ positions, similarly to I. The origin of the migrating hydrogen atoms have been determined by deuterium labelling. Mechanistic suggestions are presented to explain the observed facts.     

Recursive definition for elements of reality

Elements of reality are defined as in the work of Einstein, Podolsky, and Rosen. It is further assumed that the sum or product of twocommuting elements of reality also is an element of reality. An algebra contradiction ensues.Dedicated to Sir Karl Popper, on the occasion of his 90th birthday.