Heated Atomic Force Microscope Cantilevers For Polymer Based Additive Nanomanufacturing

This dissertation demonstrates the design, simulation, fabrication and characterization processes of a novel heated atomic force microscope cantilever for polymer based additive nanomanufacturing. Fabrication and integration of heterogeneous nanostructures is an essential task for manufacturing next generation organic electronic devices. Current state-of-the-art in heated tip additive manufacturing has a limited write time and cannot accurately control polymer deposition rate. The new design presented here includes two embedded joule heaters connected by a microchannel, where thermocapillary forces induced by the temperature gradient between heaters can deliver about 40 ng of polymer to the tip. The heated tip design presented here was informed by multiphysics finite element analysis to optimize the thermo-mechanical and thermo-fluidic performance of the device. Computational fluid dynamics simulations of molten polymer flowing in the microchannel shows the velocity of the leading edge depends significantly on the imposed temperature gradient. Thus, the cantilever tip can be inked, cleaned, and re-inked by controlling the temperature of the integrated heaters. Following design optimization, this work details the step-by-step microfabrication processes for manufacturing the heated cantilevers. Electrical and thermal characterizations are performed to evaluate the temperature response and electrical resistance of the fabricated cantilevers, and is compared to the developed models. Preliminary results show a maximum temperature of 500 °C before thermal runaway occurs in the fabricated cantilevers, with temperature gradients as large as 2.0E6 C/m. Investigation of solid-liquid interactions at the nanoscale is crucially important to understand the mechanism of polymer spreading along the cantilever microchannel and tip. A new AFM-based measurement technique for dynamic measurement of polymer nanodroplet spreading at elevated temperatures is developed. The experimental setup is used to measure the spreading dynamics of polystyrene droplets with 2 µm diameters at 115-175 °C on flat surfaces. Custom image processing algorithms determine the droplet height, radius, volume, and contact angle of each AFM image over time to calculate the droplet spreading dynamics. The new cantilever design and the AFM-based spreading measurement technique presented here, provide a framework to make better tools for wafer scale heterogeneous polymer nanostructure fabrication with high throughput, multiple feature registration, and high spatial resolution

Promoting Role of MXene Nanosheets in Biomedical Sciences : Therapeutic and Biosensing Innovations

MXene nanosheets have emerged as biocompatible transition metal structures, which illustrate desirable performance for various applications due to their unique structural, physicochemical, and compositional features. MXenes are currently expanding their usage territory from mechanical, optical, chemical, and electronic fields toward biomedical areas. This is mainly originated from their large surface area and strong absorbance in near-infrared region, which in combination with their facile surface functionalization with various polymers or nanoparticles, make them promising nanoplatforms for drug delivery, cancer therapy, precise biosensing and bioimaging. The facile surface modification of the MXenes can mediate the better in vivo performance of them through reduced toxicity, enhanced colloidal stability, and extended circulation within the body. Herein, the synthesis and state-of-the-art progresses of MXene nanosheets designed for biomedical applications, including structural- and dose-dependent antimicrobial activity, photothermal therapy, drug delivery, and implants are emphasized. Furthermore, biosensing applications are highlighted and a comprehensive discussion on photoacoustic imaging, magnetic resonance imaging, computed tomography imaging, and optical imaging of MXenes is presented. The challenges and future opportunities of applying MXene nanomaterials in the area of biomedicine are also discussed.Peer reviewe

Water-based graphene quantum dots dispersion as a high-performance long-term stable nanofluid for two-phased closed thermosyphons

Water-based graphene quantum dots (GQD) suspension has great potential for different heat transfer applications as a novel coolant due to their unique colloidal stability, high thermal conductivity and low penalty for rheological properties once loading GQD. To this end, graphene quantum dots were firstly prepared through a new and cost-effective exfoliation procedure. Based on the morphological characterization, the average thickness and diameter of the synthesized amine treated-GQD (AGQD) were determined as mostly less than 1 nm and in the range of 5–20 nm, respectively. Case studies show that water-based AGQD nanofluid at very low weight fractions shows a considerably higher thermal conductivity than that of base fluid. In a detailed rheological investigation of the water-based AGQD nanofluid, no noteworthy increase was observed in comparison with the base fluid, which is considered as a major benefit for this novel generation of coolants. The water-based AGQD nanofluids were also found to be especially more effective in the thermosyphon in terms of overall thermal properties such as net heat transfer, and thermal efficiency, and rheological property such as effective viscosity, as well as, total pressure drop in comparison to the distilled water. Since the water-based AGQD nanofluids show no sedimentation, high thermal conductivity and fairly no effect on rheological properties, it would provide an economical approach for enhancing the performance of industrial heat pipes and thermosyphons

Investigation of the thermophysical properties and stability performance of non-covalently functionalized graphene nanoplatelets with Pluronic P-123 in different solvents

The employment of nanofluids involving the dispersion of nanomaterials in the base fluid has become a major interest of the researchers due to great potential in enhancing the thermophysical properties and heat transfer coefficients. The stability of nanoparticles in base fluids is a major concern with heat transfer applications. The main purpose of this research was to study the stability of graphene nanoplatelets (GNPs) in the presence of Pluronic P-123 surfactant (P-123) in aqueous media and to compare with other common surfactants such as sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB) and Triton X-100 (TX). Each of the surfactants was mixed with GNPs at different ratios of 1:1, 1:2, 1:3 and 1:4. Then, the best ratio with the most stable sample was selected and compared with other samples. The stability of samples was evaluated by using UV-vis spectrometry, zeta potential and particle size distribution. The viscosity and thermal conductivity of the best sample were also measured at different temperatures. High resolution-transmission Electron Microscopy (HR-TEM) was used to characterize the morphology of GNPs. Interestingly, P-123 as a new surfactant showed the best colloidal stability between our samples. Furthermore, the presence of SDS, CTAB and TX surfactants in the nanofluids caused the formation of excessive foam, while P123-GNPs showed no foam-formation after shaking within the given time. It is worthy to highlight that the rises in thermal conductivity and stability in the presence of P-123 were higher than those of other surfactants. Also, the addition of rheological property (viscosity) was found to be insignificant once loading P-123