Novel in situ carbon nanofiber/polydimethylsiloxane nanocomposites: Synthesis,morphology, and physico‐mechanical properties

A series of carbon nanofiber (CNF)/polydimethylsiloxane (PDMS)‐based nanocomposites was prepared by anionic ring opening polymerization of octamethylcyclotetrasiloxane (D₄) in presence of pristine CNF and amine‐modified CNF. A detailed study of morphology–property relationship of the nanocomposites was carried out in order to understand the effect of chemical modification and loading of filler on property enhancement of the nanocomposites. An elaborate comparison of structure and properties was carried out for the nanocomposites prepared by in situ and conventional ex situ methods. Pronounced improvement in degree of dispersion of the fillers in the matrix on amine modification of CNFs was reflected in mechanical properties of the modified nanocomposites. Maximum upliftment in mechanical properties was observed for in situ prepared amine modified CNF/hydroxyl PDMS nanocomposites. For 8 phr filler loading, tensile strength increased by 370%, while tensile modulus showed an increase of 515% compared with the virgin elastomer. Furthermore, in situ prepared unmodified CNF/hydroxyl PDMS nanocomposites showed an increase of 141°C in temperature of maximum degradation (T_max) for 8 phr CNF loading. These results were correlated with the morphological analysis through transmission electron microscopic studies. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis,characterization and properties of a castor oil modified biodegradable poly(ester amide) resin

A biodegradable poly(ester amide) resin was synthesized from N,N-bis(2-hydroxy ethyl) fatty amide of castor oil with maleic anhydride, phthalic anhydride and isophthalic acid (100:30:35:35 mole ratio) by the polycondensation process. The fatty amide of the oil was obtained for the first time with 95% yield. The chemical structure of the synthesized resin was characterized by spectroscopic techniques like FTIR, ¹H NMR and ¹³C NMR. Various physical properties such as acid value, saponification value, iodine value, specific gravity and viscosity of the resin were also determined. Further the rheological behavior, studied in the steady shear mode showed shear thinning behavior of the resin. The epoxy cured poly(ester amide) thermoset using poly(amido amine) hardener exhibited better properties than with the cycloaliphatic amine hardener cured system. TGA studies also revealed higher thermal stability of the former system than the latter. In vitro-biodegradation study of the poly(ester amide) thermoset using Pseudomonas aeruginosa and Bacillus subtilus bacteria revealed superior biodegradability of the thermoset using the former bacterial strain. Excellent chemical resistance against various chemical media including alkali was observed for epoxy-poly(amido amine) cured poly(ester amide) resin over epoxy-cycloaliphatic amine one. The epoxy-poly(amido amine) cured poly(ester amide) thermoset thus has the potential to be used as surface coating material.     

An experimental study on cracking evolution in concrete and cement mortar by the b-value analysis of acoustic emission technique

Notched three point bend (TPB) specimens made with plain concrete and cement mortar were tested under crack mouth opening displacement (CMOD) control at a rate of 0.0004 mm/s and simultaneously acoustic emissions (AE) released were recorded during the experiments. Amplitude distribution analysis of AE released during concrete was carried out to study the development of fracture process in concrete and mortar specimens. The slope of the log-linear frequency–amplitude distribution of AE is known as the AE based b-value. The AE based b-value was computed in terms of physical process of time varying applied load using cumulative frequency distribution (Gutenberg–Richter relationship) and discrete frequency distribution (Aki's method) of AE released during concrete fracture. AE characteristics of plain concrete and cement mortar were studied and discussed and it was observed that the AE based b-value analysis serves as a tool to identify the damage in concrete structural members.     

High-temperature degradation of butadiene-based model elastomers by reactive molecular dynamics simulation

Thermal degradation of butadiene-based model elastomers was analyzed via a novel reactive molecular dynamics simulation (ReaxFF) method. The molecular simulation was carried out on 40 monomer units connected together. Degradation pathways of both homopolymer and copolymer of butadiene-based model elastomers such as polybutadiene (BR) and poly (styrene-co-butadiene) (SBR) were studied. The evolution of different fragmented products was examined as a function of time and heating rate. The formation mechanisms of different degraded fragments were visualized via the simulation method. The major decomposition products obtained from these model compounds were the monomers and comonomers. Pyrolysis gas chromatography–mass spectrometry (py-GC–MS) analysis was performed on the commercial samples of BR and SBR to verify the simulation results. The results obtained from the reactive simulation were very consistent with the experimental results. The activation energy required for the thermal decomposition of butadiene-based model elastomers were calculated both from the ReaxFF simulation and thermogravimetric analysis (TGA). The results were also in good agreement. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48592.     

High resolution quantitative piezoresponse force microscopy of BiFeO3 nanofibers with dramatically enhanced sensitivity

Piezoresponse force microscopy (PFM) has emerged as the tool of choice for characterizing piezoelectricity and ferroelectricity of low-dimensional nanostructures, yet quantitative analysis of such low-dimensional ferroelectrics is extremely challenging. In this communication, we report a dual frequency resonance tracking technique to probe nanocrystalline BiFeO(3) nanofibers with substantially enhanced piezoresponse sensitivity, while simultaneously determining its piezoelectric coefficient quantitatively and correlating quality factor mappings with dissipative domain switching processes. This technique can be applied to probe the piezoelectricity and ferroelectricity of a wide range of low-dimensional nanostructures or materials with extremely small piezoelectric effects.     

Evaluation of standard and real fire exposures on thermal response of rail car floor assembly

This work developed a computational methodology to evaluate and compare standard fire exposures such as those outlined in ASTM E119 with real fire exposures and determine the difference in the temperature rise of a rail car floor assembly. The real fire exposures simulated in this work were identified in a review of incidents and consisted of a constantly-fed diesel fuel spill, a localized trash fire, and a gasoline spill simulated from a collision of the railcar with an automobile. These realistic fire exposures were applied to a variety of exemplar rail cars representative of single-level and bi-level passenger cars. These floor assembly models exposed to realistic fires were simulated in Fire Dynamics Simulator (FDS). The thermal exposure at the underside of railcar provided by FDS was coupled with a thermal model in ABAQUS, which provided the evolution of temperature in different components of the floor assembly. The standard scenarios were simulated for 2 hours instead of the typical 30 minutes to identify the appropriate exposure duration in ASTM E119, which can better represent a real fire scenario. The average and maximum temperatures predicted at the unexposed surface for both scenarios were compared with the threshold values given in NFPA 130.     

An optimization study for preventing silica gelation and improving filtration effectiveness during pH reduction of high concentration silica solutions

The steam generation processes at the steam-assisted gravity drainage facilities result in huge quantities of wastewater streams, which are characterized by high pH and high silica levels. These concentrated streams need to be neutralized before their disposal via down-hole injection. The neutralization of these high-pH brines results in the formation of a gel-like substance, which makes it difficult to filter the amorphous silica gel. The wastewater used in this study was synthetically prepared using sodium metasilicate to mimic high-concentration silica solutions. Our experiments did not show any advantage of a two-step pH-neutralization process over the single-step process for suppressing silica gelation. A systematic experimental campaign was undertaken to investigate the effects of SiO₂ concentration, NaCl:SiO₂ ratio, and pH on the residual silica concentration, percent silica removal, filtration rate, and filtration effectiveness. For NaCl:SiO₂ ratios higher than 4.5, silica precipitation during pH reduction did not lead to the formation of gel or sol. The response surface methodology (RSM), based on the Doehlert design of experiments, was implemented to optimize the responses and provide high efficacy with fewer experiments. The results from the analysis of variance (ANOVA) analyses of the experimental data were used to evaluate the significance of each term in the quadratic model. 3D response surfaces and 2D contour plots were generated for determining the optimal ranges of independent factors for achieving the maximum silica removal, the highest filtration rate, the best filtration effectiveness, and the minimum residual silica concentration. An optimum operating region was established from the RSM analysis and overlay plot.     

Optimization of fused filament fabrication process parameters for mechanical responses of weather-resistant polymer (acrylonitrile styrene acrylate)

Additively manufactured polymeric products for automotive, aerospace, and biomedical applications are usually intended for service in an outdoor environment with high mechanical loading conditions. The strength and sustainability of the products can be significantly degraded due to the outdoor environmental conditions such as UV light, moisture, heat, and so forth. In this research work, a novel weather-resistant polymer (WRP) material, that is, acrylonitrile styrene acrylate (ASA), has been studied. Furthermore, this work aims to study the effect of process parameters and enhance the strength of WRP (ASA) specimens using the FFF process. The optimized process parameters, that is, build orientation (BO), extrusion temperature (ET), layer thickness (LT), and printing speed (PS), were identified based on the tensile and flexural strength using the Taguchi technique and statistical analysis. The best tensile and flexural strengths for the specimen were achieved at both orientations (XYZ and ZXY) TS: 255°C ET, 0.14 mm LT, 50 mm/s PS; and FS: 245°C ET, 0.28 mm LT, 50 mm/s PS, respectively. Regression model was developed to investigate the correlation between the process parameters with tensile and flexural strength. A validation test confirmed the findings, and the error between the actual and predicted values is less than ±10%.     

Simulation Based Investigation of Triple Heterojunction TFET (THJ-TFET) for Low Power Applications

Silicon - We designed a new model tunnel field-effect transistor (TFET) based on Triple Heterojunction Tunnel Field Effect Transistor (THJ-TFET) is investigated and designed in this paper. This...