Defence Bioengineering and Electromedical Laboratory

ABSTRACT Nanofiber interleaving in composites has found a niche in many applications wherein improving their mechanical properties without significant weight increase is of primary concern. In this study, electrospun nanofibers of Polyamide‐6 (PA6), polyvinylidene fluoride (PVDF), and acrylonitrile‐butadiene‐styrene (ABS) were interleaved in aramid‐epoxy novolac composite laminates. An attempt is made to use the lauric acid (LA) surfactant‐modified matrix to reduce its brittleness. The obtained composites by nanofiber interleaving and matrix modification were evaluated for their stiffness and damping ability using the dynamic mechanical thermal analyzer (DMTA), interlaminar shear strength (ILSS), tensile strength by universal testing machine (UTM), and impact strength with the help of a drop weight impact tester. The damping properties of these composites improved by ca. 59%, while the ILSS enhanced ca. 54%. The improvement in the overall mechanical properties of the composites has been suggested to be due to the synergistic effect of nanofiber interleaving and matrix modification.

This paper presents the design of an ultra-low power Series Resonant Converter-based auxiliary power supply for a sensing application with high isolation requirements. A split planar high-frequency transformer design is utilized to achieve a high isolation voltage of $25 \mathrm{kV}_{\text {pk }}$. High isolation requirements are met by physically isolating the primary and secondary PCB-based coils and using a resin to encapsulate the entire transformer. The converter is switched at 400 kHz. The design considerations for the converter and that for the split planar transformer are presented. Finite element electrostatic and magnetostatic simulations have been performed to validate the analytical models. A hardware prototype is developed, and hardware-based experimental results are provided to validate the converter operation. High potential $\left(25 \mathrm{kV}_{\mathrm{pk}}\right)$ tests have been performed on the prototype for 60 s, and the high isolation capability of the designed split planar transformer has been verified.

Abstract A well, with very low bottomhole pressure, required frequent workover operations due to pump failures from sand production. A gravel pack was designed to minimize the production sand issues. However, to sustain low pore pressure (less than 0.1 psi/ft) without affecting well productivity, lower drawdown was needed during an acceptable sand control completion. This presented a challenge due to massive completion brine losses and increased risk of formation damage. These challenges could create impairment in well productivity. Usually, a rig utilizing coiled tubing is used to handle the flowback and unload the well. To increase the amounts of flowback fluid, and minimize formation damage, the completion of this well used a neutral wet proppant. The proppant, which had surfaces that are neither oil nor water wet, was used in this gravel pack to improve the flowback fluids recovery. The expected benefits of this proppant were to (1) eliminate capillary pressure within the proppant pack and (2) alter the interaction between aqueous/organic (hydrocarbons) and the proppant surfaces. This would be accomplished by decreasing the intra-molecular interactions between the fluids and the proppant surfaces thus resulting in improved flow compared to native surfaces. Lightweight ceramic (LWC), neutral-wettability proppant was used to improve clean-up and enhance fluid flowback recovery. Extensive laboratory testing on the proppant was performed ahead of the job, including properties and compatibility with stimulation fluid. This proppant had both hydro- and oleophobic properties. The hydrophobic properties improve the flow of the aqueous fluids, while the oleophobic properties improve the flow of the hydrocarbon phase. The proppant was pumped similarly to any other conventional proppant and no changes in the procedures were needed. After completion of the job, the well was shut-in and the flowback un-loading was performed a week later. This completion relied on using ESP to perform the cleanup and producing the well concurrently to reduce the operation time and cost spent during well unloading. After completion, 100% of all pumped brine was recovered leading to an enhanced production rate with no impairment or coiled tubing lifting post treatment required. The cleanup was carried out after one week from the treatment date. The well cleanup, in comparison with wells that used conventional proppant, was much faster and saved $50,000. The calculated productivity index is 3.2 compared with 2.8 bpd/psi before the treatment representing 15 % gain. No sand production was observed during production performance nor seen in the wellbore during pump replacement after two years of continuous production period. The average run life prior to this treatment was 3 months, thus impacting not only the well productivity but also the run well life.

Chitosan and chitosan/hexamethylenetetramine (HMT) macrospheres were prepared respectively by dropping the solution of chitosan and chitosan/HMT (in wt/wt ratios of 1:1 and 1:3) in aq. NaOH solution. Here, HMT served as an additional nitrogen precursor for in situ N-doping with chitosan derived activated carbon (AC). The as-formed macrospheres were impregnated using ZnCl2, freeze-dried and carbonized at 500 °C under inert atmosphere to yield ACs of size ranging from 2.5 to 2.8 mm. All the samples were characterized using SEM, EDS, CHNS Analyzer, TGA, FT-IR, Raman, XRD and BET surface area analyzer. All the samples showed mesoporous characteristics. The surface area of the AC without HMT, with 1:1 HMT and 1:3 HMT were 391.502, 259.017 and 111.717 m2/g respectively. Similarly, the pore volumes of AC without HMT, with 1:1 HMT and 1:3 HMT were 0.138, 0.095 and 0.075 cc/g respectively. The chitosan/HMT derived AC possessed higher N-content and better thermal stability, however exhibited lower surface properties with increasing HMT content. The CO2 adsorption capacity of chitosan derived AC was 97.98 mg/g while that of AC with 1:1 HMT and 1:3 HMT were 72.95 mg/g, 55.11 mg/g respectively at 25 °C and 1 bar. Deterioration in adsorption capacity of chitosan/HMT derived AC may be attributed to the physical cross-linking of chitosan polymer chains induced by increase in pH with addition of HMT and also the intermolecular H-bonding interaction between HMT and chitosan, which in turn reduces the surface area of as-formed N-doped ACs progressively.

A series of modified epoxy novolac resins (ENRs) were prepared by incorporating dodecyl chain surfactants with polar groups such as amine, carboxylic acid, phenol, resorcinol and benzene sulfonic acid. Except for the case of benzene sulfonic acid, no macrophase separation is seen in any of the modified ENRs. The addition of these dodecyl surfactants to ENR hinders the cross-linking reaction as revealed from their dynamic and isothermal DSC curing measurements and reduced glass transition temperatures (Tg). The cross-link density evaluated from the storage modulus (E') in the rubbery region using DMTA measurements is found to be low with the addition of surfactants in agreement with their plasticization behavior. The stiffness of the materials obtained at low temperatures showed a moderate increase for ENRs with carboxylic acid and phenol surfactants. Upon heating, their storage modulus drops at low temperatures compared to ENR supporting the mechanism of plasticization in them. This high value of E' for the plasticized material in the glassy phase is different from the generally known behavior. Such unusually high storage modulus together with increased 'd' spacing from the XRD results seems to indicate 'partial segmental confinement' of epoxy chains. It is believed that high damping obtained in these two materials is due to 'partial segmental confinement' of epoxy chains because of interaction with lauric acid and phenolic surfactants and the associated internal and interfacial friction in them. Dielectric relaxation measurements support the plasticization process based on the high dielectric loss and ionic conductivity in the surfactant modified ENR, as compared to the pristine ones.