Fabrication and characterization of inverse opals with tunable stopbands

Inverse opals, a major type of self-assembled structures, provide good examples of photonic crystals that result from the periodic arrangement of voids. The periodic arrays of voids interfere with the light passing through them and prevent the propagation of certain wavelengths (stopband). The ability to tune the stopband of an inverse opal is important in applications such as photonics and sensing. Inverse opal films can be fabricated by filling the interstitial sites of self-assembled colloids with a precursor solution and then removing the template (assembly of colloids) by means of heat or chemical dissolution. However, the fabrication of inverse opals with long range ordering of voids by using traditional methods is challenging due to the introduction of defects. Co-assembly is an evolving technique that is used to generate inverse opals with minimal defects but the use of experimental conditions to control the defects has not been widely explored. In this study, silica-based inverse opals were fabricated by using co-assembly technique and the quality of the resultant films was evaluated with respect to the colloidal concentration and sol-gel precursor concentration. To tune the stopband, the size of voids was altered by varying the size of colloids. Also, another type of inverse opals was produced from a cross-linked polymer based on 2-hydroxyethyl methacrylate which can result tunable stopbands in response to the external stimuli. The mechanical and dimensional stability of the polymer inverse opals were improved using a poly(dimethylsiloxane) mold. Overall, defect-free inverse opal photonic crystals with tunable stopbands in the visible region of the electromagnetic spectrum have been produced using inexpensive and simple techniques

Radiation spectra of laser-driven quantum relativistic electrons

A procedure to calculate the radiation spectrum emitted by an arbitrarily prepared Dirac wave packet is developed. It is based on the Dirac charge current and classical electrodynamic theory. Apart from giving absolute intensity values, it is exact in terms of relativistic retardation effects and angular dependence. We employ a laser driven free electron to demonstrate the advantages of our method as compared to traditional ones that merely rely on the Fourier transform of the dipole operator's expectation value. Classical reference calculations confirm the results obtained for the low-frequency part of the spectrum, especially in terms of the observed red-shifts, which clearly deviate from non-relativistic calculations. In the high-frequency part of the spectrum, we note appreciable deviations to the purely classical calculations which may be linked to quantum averaging effects.Comment: 30 pages, 7 figure

Analog Modeling of Worm-Like Chain Molecules Using Macroscopic Beads-on-a-String

This paper describes an empirical model of polymer dynamics, based on the agitation of millimeter-sized polymeric beads. Although the interactions between the particles in the macroscopic model, and those between the monomers of molecular-scale polymers, are fundamentally different, both systems follow the Worm-Like Chain theory.Chemistry and Chemical BiologyPhysic

2-[2-(2,6-Dichloro­anilino)phen­yl]-N-[(2S)-2-methyl-3-oxo-8-phenyl-1-thia-4-aza­spiro­[4.5]dec-4-yl]acetamide

In the title compound, C29H29Cl2N3O2S, the phenyl ring is disordered over two orientations with occupancies of 0.55 (3) and 0.45 (3). The mol­ecular packing in the crystal is stabilized by inter­molecular N—H⋯O inter­actions, linking the mol­ecules into infinite chains along the c axis. In addition, there are weak C—H⋯S and C—H⋯π inter­actions

Fabrication of Low-Cost Paper-Based Microfluidic Devices by Embossing or Cut-and-Stack Methods

This communication describes the use of embossing, and “cut-and-stack” methods of assembly, to generate microfluidic devices from omniphobic paper, and demonstrates that fluid flowing through these devices behaves similarly to fluid in an open-channel microfluidic device. The porosity of the paper to gasses allows processes not possible in devices made using PDMS or other non-porous materials. Droplet generators and phase separators, for example, could be made by embossing “T”-shaped channels on paper. Vertical stacking of embossed or cut layers of omniphobic paper generated three-dimensional systems of microchannels. The gas permeability of the paper allowed fluid in the microchannel to contact and exchange with environmental or directed gases. An aqueous stream of water containing a pH-indicator, as one demonstration, changed color upon exposure to air containing HCl or NH3 gases.Chemistry and Chemical Biolog

From Mexico to Beijing: "Women in Development" Twenty Five Years On

During the past twenty five years the Women in Development (WID)approach has become an increasingly important issue in the literature on Third World development. WID issues and related activities have now been incorporated into the aid practice of most development agencies. This paper critically analyses the diverse and conflicting ideologies that have emerged in the WID literature since the early seventies

The Schwinger Variational Method

Variational methods have proven invaluable in theoretical physics and chemistry, both for bound state problems and for the study of collision phenomena. For collisional problems they can be grouped into two types: those based on the Schroedinger equation and those based on the Lippmann-Schwinger equation. The application of the Schwinger variational (SV) method to e-molecule collisions and photoionization has been reviewed previously. The present chapter discusses the implementation of the SV method as applied to e-molecule collisions