Chee Huei Lee

Rheological Properties and Chemical Bonding of Asphalt Modified with Nanosilica

AbstractThe objective of this study is to evaluate the rheological properties and chemical bonding of nano-modified asphalt binders blended with nanosilica. In this study, the nanosilica was added to the control asphalt at contents of 4% and 6% based on the weight of asphalt binders. Superpave binder and mixture tests were utilized in this study to estimate the characteristics of the nano-modifed asphalt binder and mixture. The rotational viscosity (RV), dynamic shear rheometer (DSR), bending beam rhometer (BBR), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), asphalt pavement analyzer (APA), dynamic modulus (DM) and flow number (FN) tests were used to analyze rheological properties and chemical bonding changes of the nano-modified asphalt binder and the performance of the nano-modified asphalt mixture. In addition, the performance of nano-modified asphalt after rolling thin-film oven (RTFO) short-term and pressure-aging vessel (PAV) long-term aging was assessed as well...

Origins of Thermodynamically Stable Superhydrophobicity of Boron Nitride Nanotubes Coatings

Superhydrophobic surfaces are attractive as self-cleaning protective coatings in harsh environments with extreme temperatures and pH levels. Hexagonal phase boron nitride (h-BN) films are promising protective coatings due to their extraordinary chemical and thermal stability. However, their high surface energy makes them hydrophilic and thus not applicable as water repelling coatings. Our recent discovery on the superhydrophobicity of boron nitride nanotubes (BNNTs) is thus contradicting with the fact that BN materials would not be hydrophobic. To resolve this contradiction, we have investigated BNNT coatings by time-dependent contact angle measurement, thermogravimetry, IR spectroscopy, and electron microscopy. We found that the wettability of BNNTs is determined by the packing density, orientation, length of nanotubes, and the environmental condition. The origins of superhydrophobicity of these BNNT coatings are identified as (1) surface morphology and (2) hydrocarbon adsorbates on BNNTs. Hydrocarbon molecules adsorb spontaneously on the curved surfaces of nanotubes more intensively than on flat surfaces of BN films. This means the surface energy of BNNTs was enhanced by their large curvatures and thus increased the affinity of BNNTs to adsorb airborne molecules, which in turn would reduce the surface energy of BNNTs and make them hydrophobic. Our study revealed that both high-temperature and UV-ozone treatments can remove these adsorbates and lead to restitution of hydrophilic BN surface. However, nanotubes have a unique capability in building a hydrophobic layer of adsorbates after a few hours of exposure to ambient air.

Superhydrophobicity of Boron Nitride Nanotubes Grown on Silicon Substrates

Partially vertical aligned boron nitride nanotubes (BNNTs) on Si substrates are found to be superhydrophobic in contrast to boron nitride (BN) thin films. While the hexagonal-phase BN films are partially wetted by water with advancing contact angle of about 50 degrees , partially vertically aligned BNNTs can achieve superhydrophobic state with advancing water contact angle exceeding 150 degrees . Our results show that the pH value of water does not affect the wetting characteristics of BNNTs. Since BN is chemically inert, resistive to oxidation up to 900 degrees C, and transparent to visible-UV light, BNNTs could potentially be useful as self-cleaning, transparent, insulating, anticorrosive coatings under rigorous chemical and thermal conditions.

A simplified in vivo approach for evaluating the bioabsorbable behavior of candidate stent materials

Metal stents are commonly used to revascularize occluded arteries. A bioabsorbable metal stent that harmlessly erodes away over time may minimize the normal chronic risks associated with permanent implants. However, there is no simple, low-cost method of introducing candidate materials into the arterial environment. Here, we developed a novel experimental model where a biomaterial wire is implanted into a rat artery lumen (simulating bioabsorbable stent blood contact) or artery wall (simulating bioabsorbable stent matrix contact). We use this model to clarify the corrosion mechanism of iron (≥99.5 wt %), which is a candidate bioabsorbable stent material due to its biocompatibility and mechanical strength. We found that iron wire encapsulation within the arterial wall extracellular matrix resulted in substantial biocorrosion by 22 days, with a voluminous corrosion product retained within the vessel wall at 9 months. In contrast, the blood-contacting luminal implant experienced minimal biocorrosion at 9 months. The importance of arterial blood versus arterial wall contact for regulating biocorrosion was confirmed with magnesium wires. We found that magnesium was highly corroded when placed in the arterial wall but was not corroded when exposed to blood in the arterial lumen for 3 weeks. The results demonstrate the capability of the vascular implantation model to conduct rapid in vivo assessments of vascular biomaterial corrosion behavior and to predict long-term biocorrosion behavior from material analyses. The results also highlight the critical role of the arterial environment (blood vs. matrix contact) in directing the corrosion behavior of biodegradable metals.

Noncovalent Functionalization of Boron Nitride Nanotubes with Poly(p-phenylene-ethynylene)s and Polythiophene

Boron nitride nanotubes (BNNTs) are functionalized and solubilized in organic solvents such as chloroform, methylene chloride, and tetrahydrofuran by using conjugated poly(p-phenylene ethynylene)s (PPEs) (polymers A and B) and polythiophene (polymer C) via a noncovalent functionalization approach through strong pi-pi stacking interactions between the conjugated polymers and BNNTs. The functionalization of BNNTs with PPEs enhanced planarization of PPEs with red shifts in both absorbance and emission of the composite materials with reference to free PPEs, whereas the functionalization of BNNTs with polythiophene disrupts the pi-conjugation, resulting in blue shifts in both the absorption and emission of the composite material.

Strain-induced formation of carbon and boron clusters in boron carbide during dynamic indentation

The authors found that the level of amorphization or structural disorder in boron carbide is higher when induced by dynamic indentation compared to static indentation. Visible and uv Raman spectroscopies indicate that sp2-bonded aromatic carbon clusters were formed, consistent with the detected photoluminescence spectra. Infrared absorption shows that amorphous boron clusters were created by dynamic indentation which has strain rates ∼108 order higher than that introduced by static indentation. The decreased intensity of infrared stretching mode of carbon-boron-carbon (CBC) chains also suggests that amorphization is due to the collapse of B11C(CBC) unit cells, which reorganize into the energetically favorite carbon and boron clusters.

Room‐Temperature Tunneling Behavior of Boron Nitride Nanotubes Functionalized with Gold Quantum Dots

One-dimensional arrays of gold quantum dots (QDs) on insulating boron nitride nanotubes (BNNTs) can form conduction channels of tunneling field-effect transistors. We demonstrate that tunneling currents can be modulated at room temperature by tuning the lengths of QD-BNNTs and the gate potentials. Our discovery will inspire the creative use of nanostructured metals and insulators for future electronic devices.

Multiwalled Boron Nitride Nanotubes: Growth, Properties, and Applications

This chapter provides a comprehensive review on the current research status of boron nitride nanotubes (BNNTs), especially the multiwalled nanostructures. Experimental and theoretical aspects of the properties, synthesis, and characterization of BNNTs, as well as their potential mechanical, electronic, chemical, and biological applications are compiled here.

Water purification: oil–water separation by nanotechnology and environmental concerns

Organic pollutants from volatile organic compounds (VOCs), synthetic organic compounds (SOCs), oil spills, and waste disposal have significantly contaminated water and our food chain. The science and engineering of water purification, in particular oil–water separation, has attracted increasing attention in the past five years. As reviewed in this article, both organic chemistry and nanotechnology have been employed for oil–water separation. This can be achieved using materials with specific wettability. Three general approaches have been reported: 1) the filtration technique using specific wettability that only allows oil or water to penetrate, 2) the absorption method using porous sponges, fibers and aerogels that can selectively absorb oil or water, and 3) filtration or absorption technology that is switchable and controllable in functionality. On the other hand, the increased use of nanomaterials in water purification, sports equipment, and industrial and household products has raised concern about water contamination by nanoparticles. This concern will be discussed at the end of the review. The goals of this article are 1) to provide a comprehensive review about oil–water separation by nanotechnology and organic chemistry and 2) to increase the awareness of environmental concerns about using nanotechnology for water purification.

Introduction to B–C–N Materials

B–C–N is an emerging material system consisting of novel nanostructures of boron (B), carbon (C), boron nitride (BN), carbon nitride (CN x ), boron-carbon nitride (B x C y N z ), and boron carbide (B x C y ). These B–C–N materials are sometimes called as frontier carbon materials, because of their flexibility in forming materials of various types of hybridizations similar to those in the pure carbon system. This chapter provides a concise introduction on all these materials. Readers are referred to various references and other chapters compiled in this book for further reading.