Remedial Measures to Seepage and Instability Aspect of a Dam Near Bombay

The paper describes the distress caused to a minor earth dam constructed at a high elevation in a mountainous area to conserve water. The distress related to instability of the dam and also due to high percolation underneath the dam coupled with formation of piping. The remedial measures taken to rectify instability and reduce percolation are described in this paper

In Situ Swelling Behavior of Chitosan-Polygalacturonic Acid/Hydroxyapatite Nanocomposites in Cell Culture Media

The molecular and mechanical characteristics of in situ degradation behavior of chitosan-polygalacturonic acid/hydroxyapatite (Chi-PgA-HAP) nanocomposite films is investigated using Fourier Transform Infrared spectroscopy (FTIR), Atomic Force Microscopy (AFM), and modulus mapping techniques for up to 48 days of soaking in cell culture media. The surface molecular structure of media-soaked samples changes over the course of 48 days of soaking, as indicated by significant changes in phosphate vibrations (1200–900 cm−1) indicating apatite formation. Chitosan-Polygalacturonic acid polyelectrolyte complexes (PECs) govern structural integrity of Chi-PgA-HAP nanocomposites and FTIR spectra indicate that PECs remain intact until 48 days of soaking. In situ AFM experiments on media-soaked samples indicate that soaking results in a change in topography and swelling proceeds differently at the initial soaking periods of about 8 days than for longer soaking. In situ modulus mapping experiments are done on soaked samples by probing ∼1–3 nm of surface indicating elastic moduli of ∼4 GPa resulting from proteins adsorbed on Chi-PgA-HAP nanocomposites. The elastic modulus decreases by ∼2 GPa over a long exposure to cell culture media (48 days). Thus, as water enters the Chi-PgA-HAP sample, surface molecular interactions in Chi-PgA-HAP structure occur that result in swelling, causing small changes in nanoscale mechanical properties

Mineral and Protein-Bound Water and Latching Action Control Mechanical Behavior at Protein-Mineral Interfaces in Biological Nanocomposites

The nacre structure consists of laminated interlocked mineral platelets separated by nanoscale organic layers. Here, the role of close proximity of mineral to the proteins on mechanical behavior of the protein is investigated through steered molecular dynamics simulations. Our simulations indicate that energy required for unfolding protein in the proximity of mineral aragonite is several times higher than that for isolated protein in the absence of the mineral. Here, we present details of specific mechanisms which result in higher energy for protein unfolding in the proximity of mineral. At the early stage of pulling, peaks in the load-displacement (LD) plot at mineral proximity are quantitatively correlated to the interaction energy between atoms involved in the latching phenomenon of amino acid side chain to aragonite surface. Water plays an important role during mineral and protein interaction and water molecules closer to the mineral surface are highly oriented and remain rigidly attached as the protein strand is pulled. Also, the high magnitude of load for a given displacement originates from attractive interactions between the protein, protein-bound water, and mineral. This study provides an insight into mineral-protein interactions that are predominant in biological nanocomposites and also provides guidelines towards design of biomimetic nanocomposites

The role of fluid polarity in the swelling of sodium-montmorillonite clay: A molecular dynamics and Fourier transform infrared spectroscopy study

Swelling clays are found extensively in various parts of the world, and sodium-montmorillonite (Na-MMT) is the main constituent of an expansive clay mineral. In this work, the swelling behavior of Na-MMT clay with a wide range of organic fluids, high polar through low polar fluids, is studied using a combination of Fourier transform infrared (FTIR) technique and molecular dynamics (MD) simulations. The construction of the representative clay–fluid models is carried out, and the nature of nonbonded interactions between clay and fluids is studied using MD. Our FTIR and MD simulations results suggest the significant nonbonded interactions between Na-MMT clay and polar fluids, such as formamide and water. The nonbonded interactions of Na-MMT with methanol and acetone are significantly less than those in Na-MMT with polar fluids. The interactions of the fluids with various entities of the clay such as SiO, FeOH, MgOH, and AlOH captured via the spectroscopy experiments and modeling provide a finer understanding of the interactions and their contributions to swelling. The MD simulations are able to capture the band shifts observed in the spectra obtained in the spectroscopy experiments. This work also captures the conformations of interlayer sodium ions with formamide, water, methanol, and acetone during swelling. These nonbonded interactions provide insight into the molecular mechanism that the polarity of fluids plays an important role in the initiation of interlayer swelling, alteration in the orientations, and evolution of microstructure of swelling clays at the molecular scale. Keywords: Swelling clays, Montmorillonite, Fourier transform infrared (FTIR) technique, Molecular dynamics (MD), Organic fluids, Polarit

Role of Polymer Interactions with Clays and Modifiers on Nanomechanical Properties and Crystallinity in Polymer Clay Nanocomposites

We present the effect of organic modifier on crystallinity and nanomechanical properties of polymer clay nanocomposites (PCNs) using two different polymers while maintaining the same nanoclay and organic modifier. Experimental results and interaction energy maps of Polybutylene-Terephthalate- (PBT-) PCN system indicate that the underlying mechanisms of change in crystallinity and improvement in mechanical properties as proposed in altered phase theory are valid. Experimental and molecular simulation studies of PBT-PCN and Nylon6-PCN reveal that a higher crystallinity polymer could require significantly higher attractive and repulsive interaction energies between polymer and organic modifiers to change the crystallinity of the polymer in the PCN significantly and thus improve mechanical properties of the PCN