Introduction of Rare-Earth Oxide Nanoparticles in CNT-Based Nanocomposites for Improved Detection of Underlying CNT Network

17 USC 105 interim-entered record; under review.The article of record as published may be found at https://doi.org/10.3390/nano11092168Epoxy resins for adhesive and structural applications are widely employed by various industries. The introduction of high aspect ratio nanometric conductive fillers, i.e., carbon nanotubes, are well studied and are known to improve the electrical properties of the bulk material by orders of magnitude. This improved electrical conductivity has made carbon nanotube-based nanocomposites an attractive material for applications where their weight savings are at a premium. However, the analytical methods for validating carbon nanotube (CNT) nanofiller dispersion and for assuring that the properties they induce extend to the entire volume are destructive and inhibited by poor resolution between matrix and tube bundles. Herein, rare-earth oxide nanoparticles are synthesized on CNT walls for the purpose of increasing the contrast between their network and the surrounding matrix when studied by imaging techniques, alleviating these issues. The adherence of the synthesized nanoparticles to the CNT walls is documented via transmission electron microscopy. The crystalline phases generated during the various fabrication steps are determined using X-ray diffraction. Deep ultraviolet-induced fluorescence of the Eu:Y2 O3 -CNT nanostructures is verified. The impacts to nanocomposite electrical properties resulting from dopant introduction are characterized. The scanning electron microscopy imaging of CNT pulp and nanocomposites fabricated from untreated CNTs and Eu:Y2O3-CNTs are compared, resulting in improved contrast and detection of CNT bundles. The micro-CT scans of composites with similar results are presented for discussion.U.S. Government affiliation is unstated in article text

IN-SITU IMAGING OF LASER-MATTER INTERACTIONS AND HEAT TRANSFER AT THE NANOSCALE

   The investigation of laser-matter interactions has gained interest over the years due to the importance of these interactions in materials synthesis, diagnostics, electronics, and photonics. In-situ transmission electron microscopy (TEM) techniques are invaluable for real-time monitoring of dynamic processes in these systems at the nanoscale. In this work, the effect of pulsed laser heating on the reactions of energetic materials, plasmonic structures, and multilayer thin films has been studied by utilizing ultrafast transmission electron microscopy (UTEM) techniques. Heat transfer and electric field calculations have been carried out to compare and support the experimental findings.  The photothermal reaction of an aluminum-fluoropolymer composite is studied to show the effect of pulsed laser heating on reactions of reactive materials. An aluminum nanoparticle - THV (terpolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride) sample is subjected to rapid heating and cooling cycles by employing the integrated laser system of an UTEM. TEM images and real-time movies (30 frame/s) are acquired to reveal the changes during the reaction. Heat transfer simulations proved that the temperature of the sample was high enough to trigger the decomposition of THV and start its reaction with Al nanoparticles. Electron diffraction patterns revealed that the reaction product was the rare and metastable η-phase aluminum fluoride (AlF3). The experimental and theoretical results showed that rapid pulsed laser heating and subsequent cooling of a nanoscale sample influences the phases that can form and be utilized to investigate other systems. Pulsed laser-assisted merging and alloying of noble metals are also studied to explore the fabrication of beaded gold-silver nanowires with a variety of morphology and composition. In-situ laser heating of plasmonic silver nanowire (Ag NW) - gold nanoparticle (Au NP) couples are performed inside an UTEM, and direct visualization of the evolution process gives insights into the formation mechanism. Experimental results show that silver melts at the surface to bridge the nanometer-sized gap between the NP and the NW, forming a cup-like morphology underneath the Au NP via capillary action. Progressive laser irradiation leads to wetting of the Au NP and the formation of a valley in the Ag NW around the NP, which flattens gradually by partial embedding of the NP. Inter-diffusion of Au into Ag and vice versa sets in at this stage, leading to depletion of Au from the Au-rich NP region. Prolonged irradiation and heating lead to gradual inter-mixing of Au-Ag, forming a beaded Au-doped Ag nanowire with homogeneous composition. Such a step-by-step understanding of the merging and alloying process has implications in nanowelding, which holds a future in designing efficient, transparent conductors and printed electronics. Numerical simulations are performed to calculate the electromagnetic enhancement at the interface of adjacent NPs and NWs and provide information on heat generation rates in NP-NW couples at the early stages of the nanowelding process.  In the third chapter, laser-induced irreversible dynamics in electron beam sensitive organic energetic crystals and ultrathin multilayer films are studied by single-shot UTEM imaging. After various sample preparation methods are developed and compared for the well-controlled synthesis of nanoscale ammonium perchlorate samples on TEM grids, decomposition dynamics of ammonium perchlorate crystals are captured via single-shot imaging. The experimental data showed that the sublimation and decomposition are visible ~30 ns after the sample excitation laser in crystals smaller than 5 µm. Dependency of decomposition to crystal porosity and thickness is also observed with crack formation in some cases. In the following section, pulsed-laser irradiation is utilized to realize deformation in thin multilayer films under high temperatures, and triggered dynamic processes are investigated through single-shot imaging. Laser-assisted periodic wrinkle formation is demonstrated on SiN membranes coated with Ti/Ni bilayers. The resulting structures showed periodic wrinkling of the SiN membrane and corrugated surface formation on both sides of the film. Overall, the dissertation highlights the potential of ultrafast transmission electron microscopy in discovering fundamental processes related to, but not limited to, reactive materials, plasmonic nanomaterials, and ultrathin multilayer films. </p

Musculoskeletal system disorders among surgical nurses related to the health industry in northwestern Turkey: a cross-sectional study

Objectives. Nurses may encounter musculoskeletal disorders (MSDs) and pain episodes stemming from regular exposure to health industry risk factors. This study aimed to determine the prevalence of MSDs and associated factors among Turkish surgical nurses. Methods. A cross-sectional design using self-administered questionnaire surveys was employed with 169 surgical nurses. The survey included an individual data questionnaire and the Nordic musculoskeletal questionnaire - extended (NMQ-E). Results. In total, 88.8% of the surgical nurses had musculoskeletal system disorders, and most experienced these problems related to the health industry. The interventions causing physical strain in the participants were identified as constant standing up, patient care, carrying heavy loads, sudden movements, patient transfer and pulling-pushing practices. The nurses used coping methods including walking, exercising, receiving physiotherapist support, pilates and yoga. The most frequently encountered problems were in the back region. A significant relationship was found between musculoskeletal system problems and the clinic of work, years of work, age and gender (p < 0.05). Conclusions. Nurses experience musculoskeletal problems related to the health industry. It is crucial to determine the real causes of musculoskeletal problems and take appropriate preventive measures to improve workplace ergonomics

Anisotropic phase-separated morphology of polymer blends directed by electrically pre-oriented clay platelets

We describe a general pathway to prepare an anisotropic phase-separated blend morphology by using electrically pre-orientated clay platelets.</p