Waseem Sabir Khan

Superhydrophobic electrospun nanofibers

This review describes state-of-the-art scientific and technological developments of electrospun nanofibers and their use in self-cleaning membranes, responsive smart materials, and other related applications. Superhydrophobic self-cleaning, also called the lotus effect, utilizes the right combinations of surface chemistry and topology to form a very high contact angle on a surface and drive water droplets away from it. The high-contact-angle water droplets easily roll off the surface, carrying with them dirt, particles, and other contaminants by way of gravity. A brief introduction to the theory of superhydrophobic self-cleaning and the basic principles of the electrospinning process is presented. Also discussed is electrospinning for the purpose of creating superhydrophobic self-cleaning surfaces under a wide variety of parameters that allow effective control of roughness of the porous structure with hydrophobic entities. The main principle of electrospinning at the nanoscale and existing difficulties in synthesis of one-dimensional materials by electrospinning are also covered thoroughly. The results of different electrospun nanofibers are compared to each other in terms of their superhydrophobic properties and their scientific and technological applications.

Recent progress on conventional and non-conventional electrospinning processes

Electrospinning is a process of producing micro- and nanoscale fibers using electrostatically charged polymeric solutions under various conditions. Most synthetic and naturally occurring polymers can be electrospun using appropriate solvents and/or their blends. Because of the fascinating properties of electrospun fibers, electrospinning has recently attracted enormous attention worldwide. Initially, this method did not receive much industrial attention due to lower production rates, costs, and lack of interest in size, shape, and flexibility of electrospun nanofibers. However, with the advancement of needleless electrospinning, multiple needles in series, near-field electrospinning techniques, and nanotechnology in particular, this is no longer an issue. This paper outlines the recent progress on the production of various sizes and shapes of fibers using conventional and non-conventional electrospinning processes (e.g., rotating drum and disc, translating spinnerets, rotating strings of electrodes in polymeric solutions, and forcespinning) and presents a complete view of electrospun fiber productions techniques and the resultant products’ applications in different fields to date.

Thermal, electrical and surface hydrophobic properties of electrospun polyacrylonitrile nanofibers for structural health monitoring

This paper presents an idea of using carbonized electrospun Polyacrylonitrile (PAN) fibers as a sensor material in a structural health monitoring (SHM) system. The electrospun PAN fibers are lightweight, less costly and do not interfere with the functioning of infrastructure. This study deals with the fabrication of PAN-based nanofibers via electrospinning followed by stabilization and carbonization in order to remove all non-carbonaceous material and ensure pure carbon fibers as the resulting material. Electrochemical impedance spectroscopy was used to determine the ionic conductivity of PAN fibers. The X-ray diffraction study showed that the repeated peaks near 42° on the activated nanofiber film were α and β phases, respectively, with crystalline forms. Contact angle, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) were also employed to examine the surface, thermal and chemical properties of the carbonized electrospun PAN fibers. The test results indicated that the carbonized PAN nanofibers have superior physical properties, which may be useful for structural health monitoring (SHM) applications in different industries.

Electrical and Thermal Characterization of Electrospun PVP Nanocomposite Fibers

Polyvinylpyrrolidone (PVP) solutions incorporated with multiwall carbon nanotubes (MWCNTs) were electrospun at various weight percentages, and then the electrical resistance and some thermal properties of these nanocomposite fibers were determined using a high-accuracy electrical resistance measurement device. During the electrospinning process, system and process parameters, such as concentrations, applied voltage, tip-to-collector distance, and pump speeds, were optimized to receive the consistent nanocomposite fibers. When polymers are used in many industrial applications, they require high electrical and thermal conductivities. Most polymers exhibit low electrical conductivity values; however, in the presence of conductive inclusions, the electrical resistance of the MWCNT fibers was reduced from 50 MΩ to below 5 MΩ, which may be attributed to the higher electrical conductivities of these nanoscale inclusions and fewer voids under the applied loads. This study may open up new possibilities in the field for developing electrically conductive novel nanomaterials and devices for various scientific and technological applications.

Acoustical Properties of Electrospun Fibers for Aircraft Interior Noise Reduction

Electrospun micro and nanofibers produced via electrospinning method were used for the sound absorption purposes. Polymers were initially dissolved in dimethyleformamide (DMF) or ethanol with a ratio of 80:20 and electrospun at 20 kV, 20 cm separation distance and 3 ml/hrs pump speed. The two/microphone transfer function method of the B&K impedance tube was used to determine the acoustical properties of the manufactured nanofibers at various frequencies. The test results showed that the absorption coefficients of nanofibers (~500 nm) drastically increased. The reason behind this phenomenon may be attributed to the higher surface area of nanofibers and their interactions with more sound waves/air molecules. This result may open up new possibilities for the sound absorption problems in many fields, such as aircrafts, other transportation vehicles and infrastructures.

Study of Hydrophilic Electrospun Nanofiber Membranes for Filtration of Micro and Nanosize Suspended Particles

Polymeric nanofiber membranes of polyvinyl chloride (PVC) blended with polyvinylpyrrolidone (PVP) were fabricated using an electrospinning process at different conditions and used for the filtration of three different liquid suspensions to determine the efficiency of the filter membranes. The three liquid suspensions included lake water, abrasive particles from a water jet cutter, and suspended magnetite nanoparticles. The major goal of this research work was to create highly hydrophilic nanofiber membranes and utilize them to filter the suspended liquids at an optimal level of purification (i.e., drinkable level). In order to overcome the fouling/biofouling/blocking problems of the membrane, a coagulation process, which enhances the membrane’s efficiency for removing colloidal particles, was used as a pre-treatment process. Two chemical agents, Tanfloc (organic) and Alum (inorganic), were chosen for the flocculation/coagulation process. The removal efficiency of the suspended particles in the liquids was measured in terms of turbidity, pH, and total dissolved solids (TDS). It was observed that the coagulation/filtration experiments were more efficient at removing turbidity, compared to the direct filtration process performed without any coagulation and filter media.

Synthesizing Magnetic Nanocomposite Fibers for Undergraduate Nanotechnology Laboratory

Flexible magnetic nanocomposite fibers were produced by an electrospinning method using a polymeric solution containing poly(acrylonitrile) and magnetite nanoparticles. The educational objective of this study was to demonstrate nanomanufacturing to undergraduate students in the College of Engineering at Wichita State University (WSU). Magnetic nanoparticles (∼10 nm) were prepared using a chemical co-precipitation of ferric and ferrous chloride salts in the presence of an ammonium hydroxide solution. The effect of magnetic particle concentrations (e.g., 0%, 1%, 5%, 10%, 20%, and 30%) on nanocomposite fibers, distribution, and morphology were studied using scanning electron microscopy (SEM). This experimental study indicated that the average diameter of the magnetic nanocomposite fibers ranged from 400 nm to 1.0 μm. The magnetic responses were found to increase linearly with increasing percent loading of the magnetic nanoparticles.

Acoustical Properties of Electrospun Nanofibers for Aircraft Interior Noise Reduction

Electrospun micro and nanofibers produced via electrospinning method were used for the sound absorption purposes. Polymers were initially dissolved in dimethyleformamide (DMF) or ethanol with a ratio of 80:20 and electrospun at 20 kV, 20 cm separation distance and 3 ml/hrs pump speed. The two-microphone transfer function method of the B&K impedance tube was used to determine the acoustical properties of the manufactured nanofibers at various frequencies. The test results showed that the absorption coefficients of nanofibers (∼500 nm) drastically increased. The reason behind this phenomenon may be attributed to the higher surface area of nanofibers and their interactions with more sound waves/air molecules. This result may open up new possibilities for the sound absorption problems in many fields, such as aircrafts, other transportation vehicles and infrastructures.© 2009 ASME

Chapter 1 – Nanotechnology emerging trends, markets, and concerns

Nanotechnology is the fastest-growing technology in the world, and it is also called the Industrial Revolution of the twenty-first century. Many research, development, and manufacturing methods have been used globally to develop better and safer nanomaterials for various applications. Nanotechnology teaches us the critical properties of day-to-day materials and structures. The invention of the scanning tunneling microscope (STM), carbon nanotubes (CNTs), and fullerenes (or buckyballs) laid a path toward nanotechnology because atomic- and molecular-level studies could be performed using the STM and nanomaterials. Today this technology is employed in various fields such as engineering, technology, applied sciences, biomedical, pharmaceuticals, food and agriculture, and construction industries. The number of technical articles and patents related to nanotechnology and nanoproducts has been continuously increasing for nearly two decades. Within 10 or 15 years, it is expected that the industrial production of nanotechnology will be worth over

Electrical Properties of Nanocomposite Fibers Under Various Loads and Temperatures

1 trillion. Thus, this technology will drastically change science, education, manufacturing, and the lifestyles of people around the world.