Colloidal Microgel Particles: Confinement Of Liquid Crystals And Characterization

Liquid crystals that are confined within curved boundaries are of interest to many scientists due to their important role in optoelectronic technologies. As such, intensive research has been conducted with various types of liquid crystals constrained to droplets or cylindrical environments. Such studies are significant because the curvature of liquid crystals costs elastic energy, and hence, we observe rich physical phenomena such as change in the director field that otherwise would have been hidden. Most of the fundamental studies of liquid crystalline phases of cellulose nanocrystals were conducted in the cells with flat boundaries, limited to certain concentrations. Here, we report cellulose nanocrystals confined to pnipam microspheres using inverse emulsion polymerization technique with microfluidics device. The chiral nematic phase of cellulose nanocrystals are preserved within the polymer matrix, as characterized by optical microscopy. The droplet radius, R of the microgels can be adjusted by changing the volumetric flow rate of oil phase in a microfluidics device. Notably, the fabricated CNCs-PNIPAM microgels are able to exhibit swelling-deswelling behavior upon temperature change with well-organized structure. I will also discuss how one applies a real-space imaging technique, known as Differential Dynamic Microscopy (DDM), to characterize such microgel particles

Control of Anchoring of Nematic Fluids at Polymer Surfaces Created by in Situ Photopolymerization

In situ photopolymerization of alkyl acrylate monomers in the presence of a nematic fluid provides a cellular matrix of liquid crystalline droplets in which the chemical structure of the encapsulating polymer exerts control over the alignment (anchoring) of the liquid crystalline molecules. Control is obtained by variation of the alkyl side chains and through copolymerization of two dissimilar monofunctional acrylates. For example, among a series of poly(methylheptyl acrylate)s, the 1-methylheptyl analogue prefers planar anchoring of a nematic (TL205) over the temperature range studied. However, the polymers of other methylheptyl side chains display a homeotropic-to-planar anchoring thermal transition temperature similar to that of the n-heptyl analogue. Copolymerization of two monofunctional acrylates with opposing tendencies of aligning liquid crystal leads to tunability of anchoring behavior over a wide temperature range. The broad anchoring transitions we observed provide a way of achieving highly tilted anchoring

Microscopic observations and simulations of Bloch walls in nematic thin films

© 2006 American Physical Society. The electronic version of this article is the complete one and can be found online at: http://link.aps.org/doi/10.1103/PhysRevLett.97.157801DOI: 10.1103/PhysRevLett.97.157801We study Bloch wall defects formed by quenching nematic thin films from planar anchoring to homeotropic anchoring through a temperature-driven anchoring transition. The director profiles of the walls are directly visualized using fluorescence confocal polarizing microscopy, and shown to agree well with the simulation based on the Frank elasticity theory. A pure twist wall exists if the ratio of sample thickness to surface extrapolation length p is smaller than or close to 1; while a diffuse Bloch wall is obtained if p is much greater than 1

Clinical profile and predictors of Severe Dengue disease: A study from South India

Background: Dengue is endemic and prevalent in tropical and sub-tropical countries including India and can cause significant mortality and morbidity. There are limited studies available on factors associated with severe dengue from India, to investigate the predictors of severe dengue in south Indian patients. Methods: We recruited 334 patients with dengue admitted in Yashoda Hospital, Hyderabad. Study period was between March 2015 and February 2017. Based on clinical symptoms, we divided patients into severe dengue and non-severe dengue. Univariate and multivariate analysis was performed for prognostic factors of severe dengue. Results: Out of 334 patients, there were 186(55.6%) males with mean age 30.3±14.3 39 years (age range: 10-73 years), severe dengue was seen in 117(35%) and non-severe dengue in 217(65%). Clinical symptoms of diabetes, low platelet count (5days after onset) elevated hematocrit, lymphadenopathy, hepatomegaly, splenomegaly, convulsions and mortality were significantly associated with severe dengue. After multivariate analysis, diabetes (OR: 2.12; 95% CI:1.34-4.65) (<0.0001), elevated hematocrit (OR: 3.14; 95% CI:2.17-6.14) (<0.0001), skin rashes (OR: 1.99; 95% CI: 1.11-3.55) (<0.0001), melena (OR: 2.59; 95% CI:1.40-4.93) (<0.0001), low platelet count (OR: 6.71; 95% CI:4.12-13.6) (<0.0001), lymphadenopathy (OR: 3.12 95% CI: 1.91-7.85) (<0.0001) and delayed admission (OR: 2.40; 95% CI:1.31-3.41) (<0.0001) were significantly associated with severe dengue disease. Conclusions: In our study, it was established that low platelet count, elevated hematocrit, diabetes, skin rash, melena, lymphadenopathy and delayed in admission (>5days) were independently associated with severe dengue

Role of manganese on the structure, crystallization and sintering of non-stoichiometric lithium disilicate glasses

The structural role of Mn was investigated in a relatively simple non-stoichiometric lithium disilicate (Li2Si2O5) based glass composition. Glasses were prepared by partially replacing SiO2 by MnO2 from the base glass belonging to the system Li2O-K2O-Al2O3-SiO2. An overall depolymerization of the glass network was observed according to magic angle spinning nuclear magnetic resonance (MAS-NMR) and Fourier transform infrared (FTIR) spectroscopic studies, suggesting a network modifier role for Mn. However, thermal analysis, phase segregation and nucleation in the glasses suggested that Mn might also act as network former. Moreover, calculated crystal field parameters from UV-Visible spectroscopy, showing high ligand field strength (Do) and Racah inter electronic repulsion (B) indicate the possible existence of Mn as individual molecular entities in the interstitials of the glass network. This paper discusses the implications of this structural role of Mn on the crystallization of bulk glasses and on the sintering behaviour and crystallization of glass powder compacts

Biochar composition-dependent impacts on soil nutrient release, carbon mineralization, and potential environmental risk: A review

Biochar application has multiple benefits for soil fertility improvement and climate change mitigation. Biochar can act as a source of nutrients and sequester carbon (C) in the soil. The nutrient release capacity of biochar once applied to the soil varies with the composition of the biochar, which is a function of the feedstock type and pyrolysis condition used for biochar production. Biochar has a crucial influence on soil C mineralization, including its positive or negative priming of microorganisms involved in soil C cycling. However, in various cases, biochar application to the soil may cause negative effects in the soil and the wider environment. For instance, biochar may suppress soil nutrient availability and crop productivity due to the reduction in plant nutrient uptake or reduction in soil C mineralization. Biochar application may also negatively affect environmental quality and human health because of harmful compounds such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzodioxins, and dibenzofurans (PCDD/DF). In this review, we discuss the linkage between biochar composition and function, evaluate the role biochar plays in soil fertility improvement and C sequestration, and discuss regulations and concerns regarding biochar's negative environmental impact. We also summarize advancements in biochar production technologies and discuss future challenges and priorities in biochar research

Drying colloidal systems: laboratory models for a wide range of applications

The drying of complex fluids provides a powerful insight into phenomena that take place on time and length scales not normally accessible. An important feature of complex fluids, colloidal dispersions and polymer solutions is their high sensitivity to weak external actions. Thus, the drying of complex fluids involves a large number of physical and chemical processes. The scope of this review is the capacity to tune such systems to reproduce and explore specific properties in a physics laboratory. A wide variety of systems are presented, ranging from functional coatings, food science, cosmetology, medical diagnostics and forensics to geophysics and art

Optics in the Natural World: Iridescent Colors of Butterflies and the Twisted Beetle!

Mohan Srinivasarao presented a lecture at the Nano@Tech Meeting on January 8, 2013 at 12 noon in room 1116 of the Marcus Nanotechnology Building.Dr. Mohan Srinivasarao is a Professor with the School of Polymer, Textile & Fiber Engineering. Dr. Srinivasarao received his Ph.D. in Chemistry in 1990 from Carnegie Mellon University, a M.Sc in Applied Chemistry in 1981 from PSG College of Technology (University of Madras, India), and a B.Sc in Applied Science in 1979 from Madurai University, India. Dr. Srinivasarao specializes in physical chemistry of polymers, physics of nematic liquid crystals, optics of liquid crystals, rheology/rheo-optics of polymeric fluids and liquid crystals, polymer/liquid crystal dispersions, various forms of light microscopy including confocal microscopy and photon tunneling microscopy, color science, and nano-optics in the biological world (color of butterfly wings, beetles, moths, and bird feathers). Dr. Srinivasarao is a member os several professional organizations including the American Chemical Society, Materials Research Society, Optical Society of America, Society of Rheology, American Physical Society, and the American Association for the Advancement of Science. He has published several articles and papers in a variety of journals.Runtime: 57:55 minutesThe study of photonics in nature contains beautiful and diverse examples of sub-wavelength structural features that create observed colors through thin layered or multilayered interference, diffraction, zero order diffraction and light scattering. In this talk I will discuss two such examples: Butterflies and Beetles, both of which attracted the attention of great scientists including Newton, Rayleigh, Michelson and Raman, among others. Structural coloration based on diffraction, multilayer reflection, cholesteric analogues or photonic crystal-like structures is pervasive especially in the world of insects. The color of Papilio palinurus results from microbowl lined with a multilayer of air and chitin. The green color is the result of color mixing of the yellow light reflecting from the bottom of the bowl and the blue light reflecting from the sides of the bowl. We have used breath-figure templated assembly as the starting point to mimic the structure of Papilio palinurus. We were able to produce microbowls which were then coated with a multilayer of alternating titanium oxide and aluminum oxide. The resulting structure exhibits the same color mixing as the original butterfly structure does. In the second part of the talk, we take a closer look at the colors produced by iridescent, metallic green beetle, Chrysina Gloriosa that selectively reflects left circularly polarized light when illuminated with unpolarized light which is observed to possess a nearly hexagonal cellular pattern on its exoskeleton. Using crystallographic concepts and Voronoi analysis of the structure present on the exoskeleton, we determine that these cells (~10 microns each) are organized with pentagons and heptagons, interdispersed typically as clusters, between hexagons. In an optical microscope, each cell appears to contain a bright yellow core, placed in greenish cell that has yellowish borders. Using confocal microscope and the auto-fluorescence of the exoskeleton matrix, we visualize that these cells consist of nearly concentric, nested arcs that lie on surface of a shallow cone. The observed textures are reminiscent of the texture of a cholesteric liquid crystalline phase with a free surface, and present an interesting analogy that provides the basis for structure and color present on beetles

Analysis of the fluorescence intensity profile in contact lenses using laser scanning confocal microscope

Issued as final reportVistakon Corporatio