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Nirmalya Bachhar

Bio: Nirmalya Bachhar is an academic researcher from National Chemical Laboratory. The author has contributed to research in topics: Materials science & Fused filament fabrication. The author has an hindex of 6, co-authored 10 publications receiving 77 citations. Previous affiliations of Nirmalya Bachhar include Indian Institute of Technology Bombay & Indian Institute of Technology, Jodhpur.

Papers
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Journal ArticleDOI
TL;DR: In this paper, a simple geometric model that accounts for the distributions of the NP core size and the number of grafted chains on each NP was proposed to quantitatively model the aggregate shape distribution.
Abstract: It is now well-accepted that hydrophilic nanoparticles (NPs) lightly grafted with polymer chains self-assemble into a variety of superstructures when placed in a hydrophobic homopolymer matrix or in a small molecule solvent. Currently, it is thought that a given NP sample should only assemble into one kind of superstructure depending on the relative balance between favorable NP core–core attractions and steric repulsion between grafted polymer chains. Surprisingly, we find that each sample shows the simultaneous formation of a variety of NP-assemblies, e.g., well-dispersed particles, strings, and aggregates. We show through the generalization of a simple geometric model that accounting for the distributions of the NP core size and the number of grafted chains on each NP (which is especially important at low coverages) allows us to quantitatively model the aggregate shape distribution. We conclude that, in contrast to molecular surfactants with well-defined chemistries, the self-assembly of these NP analog...

33 citations

Journal ArticleDOI
02 Oct 2019
TL;DR: Fused filament fabrication (FFF) three-dimensional (3D) printing of semicrystalline polymers such as high-density polyethylene (HDPE) is challenging because crystallization-induced shrinkage of the...
Abstract: Fused filament fabrication (FFF) three-dimensional (3D) printing of semicrystalline polymers such as high-density polyethylene (HDPE) is challenging because crystallization-induced shrinkage of the...

24 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of the brim size on the warpage of the printed object was investigated, as well as infilling during 3D printing of isotactic polypropylene.
Abstract: Fused filament fabrication (FFF) is an extrusion-based 3D printing technique for thermoplastic polymers. In this technique, molten polymer is extruded through a print nozzle and is laid down layer by layer to build up the printed object. Currently, FFF is used primarily to print amorphous or low-crystallinity polymers, such as acrylonitrile butadiene styrene copolymer (ABS) or polylactic acid (PLA). Printing of semicrystalline polymers, such as polyethylene or polypropylene remains particularly challenging. During FFF of semicrystalline polymers, large thermomechanical stresses are generated when the polymer solidifies on cooling. These stresses result in warpage of the printed part. Here, we analyse the factors that influence stresses generated during FFF 3D printing of a commercial semicrystalline polymer, isotactic polypropylene. We investigate the effect of height of the printed object on part warpage, as well the effect of infilling during printing. We demonstrate that the stresses generated during FFF can be substantially decreased by incorporation of a ‘brim’, viz. a thin layer at the base of the printed object, and by adhering the brim to the print substrate using common polyvinyl acetate-based glue. We systematically investigate the effect of the brim size on the warpage of the printed object. We support our experimental findings with finite element method (FEM) simulations that explain the mechanism of stress buildup during printing. The trend in stresses calculated in the FEM simulations parallel the warpage measured in the experiments. Thus, this work represents an important methodological advance towards warpage-free FFF printing of semicrystalline polymers.

22 citations

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TL;DR: In this paper, DNA encapsulation in silica containing magnetic cores (iron oxide) of two different shapes (spheres and cubes) has been reported for hydrological monitoring.
Abstract: To monitor and manage hydrological systems such as brooks, streams, rivers, the use of tracers is a well-established process. Limited number of potential tracers such as salts, isotopes and dyes, make study of hydrological processes a challenge. Traditional tracers find limited use due to lack of multiplexed, multipoint tracing and background noise, among others. In this regard, DNA based tracers possess remarkable advantages including, environmentally friendly, stability, and high sensitivity in addition to showing great potential in the synthesis of ideally unlimited number of unique tracers capable of multipoint tracing. To prevent unintentional losses in the environment during application and easy recovery for analysis, we hereby report DNA encapsulation in silica containing magnetic cores (iron oxide) of two different shapes—spheres and cubes. The iron oxide nanoparticles having size range 10–20 nm, have been synthesized using co-precipitation of iron salts or thermal decomposition of iron oleate precursor in the presence of oleic acid or sodium oleate. Physico-chemical properties such as size, zeta potential, magnetism etc. of the iron oxide nanoparticles have been optimized using different ligands for effective binding of dsDNA, followed by silanization. We report for the first time the effect of surface coating on the magnetic properties of the iron oxide nanoparticles at each stage of functionalization, culminating in silica shells. Efficiency of encapsulation of three different dsDNA molecules has been studied using quantitative polymerase chain reaction (qPCR). Our results show that our DNA based magnetic tracers are excellent candidates for hydrological monitoring with easy recoverability and high signal amplification.

12 citations

Journal ArticleDOI
TL;DR: In polymer-grafted nanoparticles (PGN), covalent tethering of apolar polymer chains to a polar inorganic nanoparticle core induces the formation of self-assembled aggregates.
Abstract: In polymer-grafted nanoparticles (PGN), covalent tethering of apolar polymer chains to a polar inorganic nanoparticle core induces the formation of self-assembled aggregates. Since the nature of th...

10 citations


Cited by
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TL;DR: Recent advances in the polymer-guided self-assembly of inorganic nanoparticles in both bulk thin films and solution are summarized, with an emphasis on the role of polymers in the assembly process and functions of resulting nanostructures.
Abstract: The self-assembly of inorganic nanoparticles is of great importance in realizing their enormous potentials for broad applications due to the advanced collective properties of nanoparticle ensembles. Various molecular ligands (e.g., small molecules, DNAs, proteins, and polymers) have been used to assist the organization of inorganic nanoparticles into functional structures at different hierarchical levels. Among others, polymers are particularly attractive for use in nanoparticle assembly, because of the complex architectures and rich functionalities of assembled structures enabled by polymers. Polymer-guided assembly of nanoparticles has emerged as a powerful route to fabricate functional materials with desired mechanical, optical, electronic or magnetic properties for a broad range of applications such as sensing, nanomedicine, catalysis, energy storage/conversion, data storage, electronics and photonics. In this review article, we summarize recent advances in the polymer-guided self-assembly of inorganic nanoparticles in both bulk thin films and solution, with an emphasis on the role of polymers in the assembly process and functions of resulting nanostructures. Precise control over the location/arrangement, interparticle interaction, and packing of inorganic nanoparticles at various scales are highlighted.

173 citations

Journal ArticleDOI
TL;DR: In this article, the synthesis of polymer materials for radiation protection, with focus on the role of the nanofillers, is discussed and the effectiveness of polymeric materials for the absorption of fast neutrons.
Abstract: The rising use of radioactive elements is increasing radioactive pollution and calling for advanced materials to protect individuals. For instance, polymers are promising due to their mechanical, electrical, thermal, and multifunctional properties. Moreover, composites made of polymers and high atomic number fillers should allow to obtain material with low-weight, good flexibility, and good processability. Here we review the synthesis of polymer materials for radiation protection, with focus on the role of the nanofillers. We discuss the effectivness of polymeric materials for the absorption of fast neutrons. We also present the recycling of polymers into composites.

141 citations

Journal ArticleDOI
TL;DR: Particle brush materials have attracted interest as model systems to understand the effect of surface modification on the structure and interactions in polymer modified colloidal systems as discussed by the authors, which play a role across fields as diverse as functional coatings, cosmetics, foods or pharmaceuticals.

112 citations

Journal ArticleDOI
TL;DR: This Review follows the structure of the chains as grafting density increases, and how this structure slows relaxation of polymer chains and affects macroscopic material properties.
Abstract: Grafting polymers to nanoparticle surfaces influences properties from the conformation of the polymer chains to the dispersion and assembly of nanoparticles within a polymeric material. Recently, a small body of work has begun to address the question of how grafting polymers to a nanoparticle surface impacts chain dynamics, and the resulting physical properties of a material. This Review discusses recent work that characterizes the structure and dynamics of polymers that are grafted to nanoparticles and opportunities for future research. Starting from the case of a single polymer chain attached to a nanoparticle core, this Review follows the structure of the chains as grafting density increases, and how this structure slows relaxation of polymer chains and affects macroscopic material properties.

80 citations

Journal ArticleDOI
TL;DR: A broad overview of FFF processing of semicrystalline polymers can be found in this paper, where the impact of processing conditions and feedstock modifications, such as the incorporation of fillers or the formation of blends, on crystallinity as well as the microstructure of printed parts, the impact on the micro-structure on the mechanical performance, and general part quality.

56 citations