Statistical mechanical theory of equilibrium structure and miscibility of polymer nanocomposites: effects of polymer chemical heterogeneity and architecture, and nanoparticle surface corrugation and softness

Motivated by the persistent interest in different nanoparticles added to various polymer matrices, the Polymer Reference Interaction Site Model (PRISM) theory is extended and applied to study the thermodynamics, statistical structure, and miscibility of diverse polymer nanocomposites (PNCs). Under chemistry-matched conditions and in the absence of interfacial attractions between a spherically smooth nanoparticle and the matrix fluid, the polymer-induced depletion attraction is dominant and induces entropic phase separation. The depletion attraction can be potentially reduced by modifying the nanoparticle surface topography as recently observed in experiments. Two types of surface-modified nanoparticles have been considered in this thesis – (1) spheres with ordered roughness on the surface and (2) soft polymeric nanoparticles with surface fluctuations and fuzziness. Monte Carlo integration and other computational techniques have been developed to compute the effective interactions between such particles. The morphologically diverse particles introduce additional length scales, making the physics non-monotonic, subtle, and rich. The common advantage with using either of the particles is reduced contact aggregation and enhanced miscibility. Optimal surface corrugation and/or particle softness allow monomer penetration resulting in favourable (entropic) mixing. However, high enough degree of corrugation/softness can also result in destabilization by excluding the polymer from its interior. Another route of developing new nanocomposites is by tuning the polymer-particle interfacial chemistry. Prior work has established three states of spatial organization, namely depletion, steric stabilization and bridging, depending upon the effective interfacial attraction strengths. Introducing polymer chemical heterogeneity via the use of AB copolymers offers additional control over the equilibrium structure. Specifically, two types of copolymers are considered – (1) random copolymers (RCP) of disordered sequence and (2) ordered, alternating multiblock copolymers (MBCP). Quantum chemical calculations are combined with the polymer liquid state theory to predict structure and miscibility. The chain connectivity, monomer sequence, copolymer composition and differential wettability results in unique frustration in the system leading to novel states of organization of the polymer around the nanoparticles. In the context of strongly attractive nanoscopic fullerenes, this results in improved miscibility relative to the corresponding homopolymers. For some of the systems studied, maximum dispersion is predicted at an intermediate copolymer composition due to packing correlations and differential wetting effects with favourable comparison to experiments

Assembly of particle strings via isotropic potentials

Assembly of spherical colloidal particles into extended structures, including linear strings, in the absence of directional interparticle bonding interactions or external perturbation could facilitate the design of new functional materials. Here, we use methods of inverse design to discover isotropic pair potentials that promote the formation of single-stranded, polydisperse strings of colloids "colloidomers" as well as size-specific, compact colloidal clusters. Based on the designed potentials, a simple model pair interaction with a short-range attraction and a longer-range repulsion is proposed which stabilizes a variety of different particle morphologies including (i) dispersed fluid of monomers, (ii) ergodic short particle chains as well as porous networks of percolated strings, (iii) compact clusters, and (iv) thick cylindrical structures including trihelical Bernal spirals

Physicochemical and Biological Properties of Land and Water Bodies Surrounding Major Dumpsites in Kolkata

In this paper we have investigated the data acquired from the analysis of the soil and water samples from and around the dump sites in Kolkata and North 24 Paragana district of West Bengal where the population density is extremely high. The treatment of disposal of municipal solid wastes and waste water has been inadequate to negligible in these areas and as a result the quality of soil and water bodies is subject to deterioration. We have made use of GPS enabled Satellite acquired images and its associated softwares to identify and demarcate the areas that come under the direct impact of the dumping sites, and which ultimately are the areas prone to diseases and degradation in the coming years. The pH, salinity, Total Dissolved Solvents and oxidation reduction potential has been investigated for the basic characterization of the samples. An estimate of heavy metals has also been made. Estimation of salts and oxides from the various sediments and soil samples were acquired. Identification of bacteria, under the purview of biological studies and the dependence of their growth on physiochemical parameters of the surrounding has portrayed an alarming result.  Adjacent to these areas there are agricultural fields where leached water from the dumping site directly drain into and cause biomagnifications. Contamination of the ground water is also sizable. This research will help to control pollution and biological outbreaks as well as suggest areas where immediate care should be taken to set up environmental restoration. The findings of the paper will further enlighten the planning and designing of waste disposal in urban areas and assist in its policy making in urban areas and thereby improve the quality of life of the scavengers who are left to equate their survival with the garbage mounds

Diarrhoeal health risks attributable to water-borne-pathogens in arsenic-mitigated drinking water in West Bengal are largely independent of the microbiological quality of the supplied water

Abstract: There is a growing discussion about the possibility of arsenic mitigation measures in Bengal and similar areas leading to undesirable substitution of water-borne-pathogen attributable risks pathogens for risks attributable to arsenic, in part because of uncertainties in relative pathogen concentrations in supplied and end-use water. We try to resolve this discussion, by assessing the relative contributions of water supply and end-user practices to water-borne-pathogen-attributable risks for arsenic mitigation options in a groundwater arsenic impacted area of West Bengal. Paired supplied arsenic-mitigated water and end-use drinking water samples from 102 households were collected and analyzed for arsenic and thermally tolerant coliforms [TTC], used as a proxy for microbiological water quality, We then estimated the DALYs related to key sequelae, diarrheal diseases and cancers, arising from water-borne pathogens and arsenic respectively. We found [TTC] in end-use drinking water to depend only weakly on [TTC] in source-water. End-user practices far outweighed the microbiological quality of supplied water in determining diarrheal disease burden. [TTC] in source water was calculated to contribute <1% of total diarrheal disease burden. No substantial demonstrable pathogen-for-arsenic risk substitution attributable to specific arsenic mitigation of supplied waters was observed, illustrating the benefits of arsenic mitigation measures in the area studied

Arsenic in Peruvian rice cultivated in the major rice growing region of Tumbes river basin

Arsenic (As) exposure from surface and groundwater in Peru is being recognised as a 16 potential threat but there are limited studies on As in the food-chain and none on As in 17 Peruvian rice. In this study, we have determined the As content in rice cultivated in the 18 Tumbes river basin located in the northern province of Peru, an area known for extensive rice 19 cultivation. We collected rice and soil samples from agricultural fields, soil was collected 20 using grid sampling technique while rice was collected from the heaps of harvested crop 21 placed across the fields. The average total As concentration in rice was 167.94 ± 71 μg kg-1 22 (n=29; range 68.39-345.31 μg kg-1). While the rice As levels were not highly elevated, the As 23 content of few samples (n=7) greater than 200 μg kg-1 could contribute negatively to human health upon chronic exposure. Average concentration of As in soil was 8.63 ± 7.8 mg kg-1 25 (n=30) and soil to grain transfer factor was 0.025 ± 0.018 for 12 matched samples. Compared 26 to our previous pilot study in 2006 (samples collected from the same agricultural fields but 27 not from exact locations) there was a 41% decrease in As soil concentration in this study. 28 Rice samples collected in 2006 (n=5) had a mean concentration of 420 ± 109 μg kg-1. Our 29 data provides a baseline of rice grain As concentrations in Peruvian province of Tumbes and 30 warrants further studies on factors affecting uptake of As by the rice varieties cultivated in 31 Peru and any potential human health risks

Protein Folding Activity of the Ribosome (PFAR) : A Target for Antiprion Compounds

Prion diseases are fatal neurodegenerative diseases affecting mammals. Prions are misfolded amyloid aggregates of the prion protein (PrP), which form when the alpha helical, soluble form of PrP converts to an aggregation-prone, beta sheet form. Thus, prions originate as protein folding problems. The discovery of yeast prion(s) and the development of a red-/white-colony based assay facilitated safe and high-throughput screening of antiprion compounds. With this assay three antiprion compounds; 6-aminophenanthridine (6AP), guanabenz acetate (GA), and imiquimod (IQ) have been identified. Biochemical and genetic studies reveal that these compounds target ribosomal RNA (rRNA) and inhibit specifically the protein folding activity of the ribosome (PFAR). The domain V of the 23S/25S/28S rRNA of the large ribosomal subunit constitutes the active site for PFAR. 6AP and GA inhibit PFAR by competition with the protein substrates for the common binding sites on the domain V rRNA. PFAR inhibition by these antiprion compounds opens up new possibilities for understanding prion formation, propagation and the role of the ribosome therein. In this review, we summarize and analyze the correlation between PFAR and prion processes using the antiprion compounds as tools