COMPARATIVE STUDY ON EFFECT OF NATURAL AND SYNTHETIC SUPERDISINTEGRANTS IN THE FORMULATION OF RIZATRIPTAN BENZOATE ORAL DISPERSIBLE TABLETS

Objective: In the present study, the effects of a natural superdisintegrant gellan gum, karya synthetic gum superdisintegrants like sodium starch glycolate, crospovidone and combination of natural and synthetic superdisintegrant were compared in the formulations of rizatriptan benzoate oral dispersible tablets. Methods: This oral dispersible tablets were prepared by direct compression method and evaluated for weight variation, hardness, disintegration time, drug content, friability and dissolution. Drug compatibility with excipients was checked by FTIR studies. Stability study of the prepared tablets was done at 40±2°/75%±5% RH for a period of 1 mo. Results: FTIR studies showed that no any chemical interaction between drugs and excipients. The in vitro drug release study revealed that formulation F9 combination of both crospovidone and karya gum was the most successful formulation and disintegrate time within 13 seconds and drug release within 10 min. The drug release from the best formulations followed first-order kinetics, which is concentration-dependent. Short terms stability studies of the tablet for three months showed non-significant drug loss. Conclusion: The formulation containing a combination of natural and synthetic superdisintegrant was found to be the best results. Apart from fulfilling all official and other specifications, the tablets exhibited a higher rate of drug release

Engineering Phonon Polaritons in van der Waals Heterostructures to Enhance In-Plane Optical Anisotropy

Van der Waals heterostructures assembled from layers of 2D materials have attracted considerable interest due to their novel optical and electrical properties. Here we report a scattering-type scanning near field optical microscopy study of hexagonal boron nitride on black phosphorous (h-BN/BP) heterostructures, demonstrating the first direct observation of in-plane anisotropic phonon polariton modes in vdW heterostructures. Strikingly, the measured in-plane optical anisotropy along armchair and zigzag crystal axes exceeds the ratio of refractive indices of BP in the x-y plane. We explain that this enhancement is due to the high confinement of the phonon polaritons in h-BN. We observe a maximum in-plane optical anisotropy of {\alpha}_max=1.25 in the 1405-1440 cm-1 frequency spectrum. These results provide new insights on the behavior of polaritons in vdW heterostructures, and the observed anisotropy enhancement paves the way to novel nanophotonic devices and to a new way to characterize optical anisotropy in thin films

Using the Discrete Dipole Approximation and Holographic Microscopy to Measure Rotational Dynamics of Non-spherical Colloidal Particles

We present a new, high-speed technique to track the three-dimensional translation and rotation of non-spherical colloidal particles. We capture digital holograms of micrometer-scale silica rods and sub-micrometer-scale Janus particles freely diffusing in water, and then fit numerical scattering models based on the discrete dipole approximation to the measured holograms. This inverse-scattering approach allows us to extract the the position and orientation of the particles as a function of time, along with static parameters including the size, shape, and refractive index. The best-fit sizes and refractive indices of both particles agree well with expected values. The technique is able to track the center of mass of the rod to a precision of 35 nm and its orientation to a precision of 1.5$^\circ$, comparable to or better than the precision of other 3D diffusion measurements on non-spherical particles. Furthermore, the measured translational and rotational diffusion coefficients for the silica rods agree with hydrodynamic predictions for a spherocylinder to within 0.3%. We also show that although the Janus particles have only weak optical asymmetry, the technique can track their 2D translation and azimuthal rotation over a depth of field of several micrometers, yielding independent measurements of the effective hydrodynamic radius that agree to within 0.2%. The internal and external consistency of these measurements validate the technique. Because the discrete dipole approximation can model scattering from arbitrarily shaped particles, our technique could be used in a range of applications, including particle tracking, microrheology, and fundamental studies of colloidal self-assembly or microbial motion.Comment: 11 pages, 9 figures, 2 table

Polariton Nanophotonics using Phase Change Materials

Polaritons formed by the coupling of light and material excitations such as plasmons, phonons, or excitons enable light-matter interactions at the nanoscale beyond what is currently possible with conventional optics. Recently, significant interest has been attracted by polaritons in van der Waals materials, which could lead to applications in sensing, integrated photonic circuits and detectors. However, novel techniques are required to control the propagation of polaritons at the nanoscale and to implement the first practical devices. Here we report the experimental realization of polariton refractive and meta-optics in the mid-infrared by exploiting the properties of low-loss phonon polaritons in isotopically pure hexagonal boron nitride (hBN), which allow it to interact with the surrounding dielectric environment comprising the low-loss phase change material, Ge$_3$Sb$_2$Te$_6$ (GST). We demonstrate waveguides which confine polaritons in a 1D geometry, and refractive optical elements such as lenses and prisms for phonon polaritons in hBN, which we characterize using scanning near field optical microscopy. Furthermore, we demonstrate metalenses, which allow for polariton wavefront engineering and sub-wavelength focusing. Our method, due to its sub-diffraction and planar nature, will enable the realization of programmable miniaturized integrated optoelectronic devices, and will lay the foundation for on-demand biosensors.Comment: 15 pages, 4 figures, typos corrected in v

Reconfigurable assemblies of Janus rods in AC electric fields

We investigate the electric field-induced assembly of Janus colloids composed of silica rods patterned with gold patches in both side- and tip-coated motifs. These shape and chemically anisotropic particles assemble into reconfigurable chains, whose structure depends on patch location, AC electric field strength, and frequency