Structure of Carbon Materials Explored by Local Transmission Electron Microscopy and Global Powder Diffraction Probes

Transmission electron microscopy and neutron or X-ray diffraction are powerful techniques available today for characterization of the structure of various carbon materials at nano and atomic levels. They provide complementary information but each one has advantages and limitations. Powder X-ray or neutron diffraction measurements provide structural information representative for the whole volume of a material under probe but features of singular nano-objects cannot be identified. Transmission electron microscopy, in turn, is able to probe single nanoscale objects. In this review, it is demonstrated how transmission electron microscopy and powder X-ray and neutron diffraction methods complement each other by providing consistent structural models for different types of carbons such as carbon blacks, glass-like carbons, graphene, nanotubes, nanodiamonds, and nanoonions

Biological impact of nanodiamond particles – label free, high-resolution methods for nanotoxicity assessment

Current methods for the assessment of nanoparticle safety that are based on 2D cell culture models and fluorescence-based assays show limited sensitivity and they lack biomimicry. Consequently, the health risks associated with the use of many nanoparticles have not yet been established. There is a need to develop in vitro models that mimic physiology more accurately and enable high throughput assessment. There is also a need to set up new assays that offer high sensitivity and are label-free. Here we developed ‘mini-liver’ models using scaffold-free bioprinting and used these models together with label-free nanoscale techniques for the assessment of toxicity of nanodiamond produced by laser-assisted technology. Results showed that NDs induced cytotoxicity in a concentration and exposure-time dependent manner. The loss of cell function was confirmed by increased cell stiffness, decreased cell membrane barrier integrity and reduced cells mobility. We further showed that NDs elevated the production of reactive oxygen species and reduced cell viability. Our approach that combined mini-liver models with label-free high-resolution techniques showed improved sensitivity in toxicity assessment. Notably, this approach allowed for label-free semi-high throughput measurements of nanoparticle-cell interactions, thus could be considered as a complementary approach to currently used methods

Nanoscale diamond and carbon materials and architectures for field emission and thermionic energy conversion.

More than 50% of the total energy produced is typically rejected in the form of waste heat from various processes. The grand challenge is that most of this waste heat is released at temperatures much lower than 1000 C, which makes it difficult to recover it using traditional methods which require higher operating temperatures for thermal energy conversion. In addition, these traditional methods involve different intermediate processes and do not offer direct conversion into electricity. In this regard, thermal energy conversion through thermionic emission can offer direct conversion of waste heat into electricity with highest theoretical efficiency. So, waste heat recovery through thermionic emission energy conversion is of great interest and is the motivation for the present work. However the greatest challenge involves the discovery or availability of the material with appropriate work functions and stability criteria. To address the need for developing suitable materials toward thermionic energy conversion, we investigated phosphorus doping in individual diamond nanocrystals, conical carbon nanostructures (CCNTs) and diamond nanocrystals supported on conical carbon nanostructures. Hybrid architectures, diamond nanocrystals supported on high aspect ratio structures will allow the study of true performance of nanocrystals free from grain boundaries and also offer field enhancements. First, the synthesis of CCNTs over large area and flat substrates is investigated. From the experimental results, we successfully synthesized CCNTs on planar graphite and tungsten foil substrates with areas as large as (\u3e0.5 cm2). A detailed underlying nucleation and growth mechanism was also demonstrated supported with regrowth experiments and kinetic growth model. Secondly, selective nucleation of the diamond crystals on the tips or complete coating on CCNTs was demonstrated and a likely mechanism for the nucleation and growth of diamond crystals is also presented. Thirdly, the field and thermionic emission characteristics from the as synthesized CCNTs have shown to exhibit enhanced emission characteristics such as low turn-on voltages, large field enhancement factor and lower work function values owing to their higher aspect ratios and optimum density overcoming field screening effects. Finally, phosphorus doping into these individual diamond crystals and diamond films was performed and thermionic emission characteristics were studied. Work function values as low as 1.8 eV from diamond films and 2.2 eV from diamond crystals was obtained. In summary, the main outcomes of this work include growth of large area CCNTs on flat substrates, discovery of the enhanced field and thermionic emission characteristics of CCNTs, selective nucleation and phosphorus doping of individual diamond nanocrystals on CCNTs free from grain boundaries and work function value as low as 2.2 eV from thermionic emission from these crystals

Characterization of Nanomaterials for Thermal Management of Electronics

Recently, there has been a growing interest in flexible electronic devices as they are light, highly flexible, robust, and use less expensive substrate materials. Such devices are affected by thermal management issues that can reduce the device’s performance and reliability. Therefore, this work is focused on the study of the thermal properties of nanomaterials and the methods to address such issues. The goal is to enhance the effective thermal conductivity by adding nanomaterials to the polymer matrix or by structural modification of nanomaterials. The thermal conductivity of copper nanowire/polydimethylsiloxane and copper nanowire/polyurethane composites were measured and showed more than threefold enhancement compared to the thermal conductivity values of the neat polymers. Furthermore, identical heat sources were used on the neat polymer as well as the composite samples, and the resulting thermal images were taken, which showed that the resulting hot spot was significantly less severe for the composite sample, demonstrating the potential of copper nanowire/polymer composite as a substrate for flexible electronics with better heat spreading capability. In addition, the thermal properties of cellulose nanocrystals-poly (vinyl alcohol) composite films with different structural configurations of cellulose nanocrystals (such as isotropic and anisotropic configurations) were investigated as an alternative to commonly used petroleum-based materials for potential application in the thermal management of flexible electronic devices. Also, the in-plane thermal conductivity of the anisotropic composite film was as high as ~ 3.45 W m-1 K-1 in the chain direction. Moreover, the composite films showed ~ 4-14 fold higher in-plane thermal conductivity than most polymeric materials used as substrates for flexible electronics. A high degree of cellulose nanocrystal orientation and the inclusion of poly (vinyl alcohol) were the reasons for such improvements. In addition, thermal images showed that the cellulose nanocrystals-poly (vinyl alcohol) composite films had better heat dissipation capability compared to the neat poly (vinyl alcohol) films, indicating its potential application for flexible electronic devices. In another study, thermal properties of nanodiamond films obtained through a solution-based directed covalent assembly were studied as a low-cost and greener alternative to the nanodiamond films grown via chemical vapor deposition method for thermal management of electronics. The results obtained showed cross-plane thermal conductivity as high as 3.50 +/- 0.54 W m-1 K-1 for nanodiamond film of 139.1 +/- 19.5 nm thick. Such a low cross-plane thermal conductivity value can be attributed to higher porosity and poor interface quality compared to that of the nanodiamond films grown via chemical vapor deposition method. Hence, there is still more room for improvement for such nanodiamond films. The above chapters were focused on the study of the thermal properties of various types of nanomaterials for thermal management of electronic devices. In the next chapter, a technique for the fabrication of a device, that is capable of performing characterization nanomaterials was presented. In this work, suspended beam microdevices for electrothermal characterization of nanomaterials were fabricated through a standard photolithography technique that is less time-consuming, less expensive and much simpler than the methods used by other research groups in the past. The agreement of the measured in-plane thermal conductivity of the suspended central silicon nitride bare bridge with the literature validated the microdevice, setup, and the experimental procedure. Furthermore, these microdevices can be used to measure other important thermoelectric properties of nanomaterials such as the Seebeck coefficient, electrical conductivity, and thermoelectric figure of merit

Carbon nano-onions as promising nanomaterial for biomedical and electrochemical applications

Nano-cipolle al carbonio come promettente nanomateriale per applicazioni biomedicali ed elettrochimich

Microwave Impedance Microscopy Of Nanostructured Carbon

Microwave impedance microscopy (MIM) is a scanning probe technique that measures local changes in tip-sample admittance. The imaginary part of the reported change is calibrated with finite element simulations and physical measurements of a standard capacitive sample, and thereafter the output ∆Y is given a reference value in siemens. Simulations also provide a means of extracting sample conductivity and permittivity from admittance, a procedure verified by comparing the estimated permittivity of polytetrafluoroethlyene (PTFE) to the accepted value. Finally, the well-known effective medium approximation of Bruggeman is considered as a means of estimating the volume fractions of the constituents in inhomogeneous two-phase systems. Specifically, we consider the estimation of porosity in nanostructured carbons often used in charge storage devices, such as carbide derived carbon (CDC) and onion-like carbon (OLC)

Diverse Applications of Nanomedicine

The design and use of materials in the nanoscale size range for addressing medical and health-related issues continues to receive increasing interest. Research in nanomedicine spans a multitude of areas, including drug delivery, vaccine development, antibacterial, diagnosis and imaging tools, wearable devices, implants, high-throughput screening platforms, etc. using biological, nonbiological, biomimetic, or hybrid materials. Many of these developments are starting to be translated into viable clinical products. Here, we provide an overview of recent developments in nanomedicine and highlight the current challenges and upcoming opportunities for the field and translation to the clinic. \ua9 2017 American Chemical Society

Nano-refrigerants and nano-lubricants in refrigeration : synthesis, mechanisms, applications, and challenges

Addressing global energy security and environmental concerns, the utilization of nano-refrigerants and nano-lubricants has emerged as an innovative path for enhancing heat transfer. This research focuses on enhancing the thermophysical properties, heat transfer efficiency, and tribological characteristics of nanofluids—nanoparticles dispersed in refrigerants or lubricants. These nanofluids have demonstrated significant potential in applications such as cooling, air conditioning systems, and heat transfer equipment including pumps and pipes. A comprehensive understanding of parameters like thermal conductivity, viscosity, pressure drop, pumping power, and energy performance is delivered, with the aim of enhancing the overall efficiency of refrigeration systems, particularly the coefficient of performance (COP). Additionally, the review covers existing research on flow and pool boiling heat transfer, nano-lubricant tribological enhancement, and nano-refrigerant condensation. The study also addresses the challenges associated with the use of nano-refrigerants and nano-lubricants and offers a prospective outlook for their usage. These novel nanofluids are anticipated to emerge as effective solutions for increasing the COP and reducing energy consumption in the industrial sector, thus extending beyond the scope of previous efforts in this field. This review could serve as a valuable resource for a broad audience interested in this novel approach to energy efficiency

Mechanistic Understanding From Molecular Dynamics Simulation in Pharmaceutical Research 1 : Drug Delivery

In this review, we outline the growing role that molecular dynamics simulation is able to play as a design tool in drug delivery. We cover both the pharmaceutical and computational backgrounds, in a pedagogical fashion, as this review is designed to be equally accessible to pharmaceutical researchers interested in what this new computational tool is capable of and experts in molecular modeling who wish to pursue pharmaceutical applications as a context for their research. The field has become too broad for us to concisely describe all work that has been carried out; many comprehensive reviews on subtopics of this area are cited. We discuss the insight molecular dynamics modeling has provided in dissolution and solubility, however, the majority of the discussion is focused on nanomedicine: the development of nanoscale drug delivery vehicles. Here we focus on three areas where molecular dynamics modeling has had a particularly strong impact: (1) behavior in the bloodstream and protective polymer corona, (2) Drug loading and controlled release, and (3) Nanoparticle interaction with both model and biological membranes. We conclude with some thoughts on the role that molecular dynamics simulation can grow to play in the development of new drug delivery systems.Peer reviewe