Ga-Young Gu

Surface control and cryogenic durability of transparent CNT coatings on dip-coated glass substrates

Transparent carbon nanotube (CNT) coatings were deposited on boro-silicate glass substrates by dip-coating. Ultraviolet-visible (UV) spectra, surface resistance measurement, and the wettability tests were used to investigate the optical transmittance and electrical properties of these CNT coatings. The changes in electrical and optical properties of these coatings were observed to be functions of the number of dip-coating cycles. The surface resistance of the CNT coated substrates decreased dramatically as the number of dip-coatings was increased, whereas the increases in the CNT layer thickness beyond that for the first dipping cycle had little effect on the transparent-properties. Static contact angle measurements proved to be an effective means for evaluating the surface morphology of CNT coatings. The interfacial durability of the CNT coatings on a glass substrate was much better than that of ITO coatings over the temperature range from -150°C to +150°C.

Dispersion and Related Properties of Acid-Treated Carbon Nanotube/Epoxy Composites using Electro-Micromechanical, Surface Wetting and Single Carbon Fiber Sensor Tests

Studies of dispersion and related properties, in carbon nanotube/epoxy composites, were conducted using electro-micromechanical and wettability tests. Specimens were prepared from neat epoxy as well as composites with untreated and acid-treated carbon nanotube (CNT). The degree of dispersion and its standard deviation were evaluated by turbidity of the dispersing solution, as well as by volumetric electrical resistivity. Acetone was a better dispersing solvent than purified water and various acid treatments of the CNT also enhanced dispersion. Contact resistivity responded differently with dispersion degree. The apparent Youngs modulus was higher for composites with acid treated CNT. The interfacial shear strength between a single carbon fiber and CNT/epoxy was lower than that between a single carbon fiber and neat epoxy. This difference is attributed to increased viscosity and decreased bonding availability in the matrix due to the added CNT. The optimum CNT treatment, for maximizing interfacial adhesion while maintaining good electrical conductivity was the sulfuric acid treatment. The CNT composites can also sense micro-damage in terms of the stepwise increments of electrical resistivity combined with acoustic emission.

Mechanical and electrical properties of electrospun CNT/PVDF nanofiber for micro-actuator applications

Electrospun polyvinylidene fluoride (PVDF)-containing carbon nanotubes (CNT) were prepared for use in fabricating actuator materials. Actuating displacement was measured in an electrochemical environment. The electrospun nanofibers were arranged using a drum-type collector, and morphology was investigated using a field emission-scanning electron microscope. The uniformity of dispersion of CNT in the PVDF nanofibers was monitored by electron probe X-ray micro-analysis. Tensile strength and electrical resistivity results were used as an indication of the state of alignment. The electrospun CNT/PVDF nanofiber sheets exhibited better mechanical and electrical properties in the arranged direction. The efficiency and electrical capacities of electrospun CNT/PVDF nanofiber sheet were compared with those of cast PVDF sheets for use in actuator applications in electrochemical environments. The electrospun CNT/PVDF nanofiber sheets exhibited much better actuator performance than PVDF sheets, which are attributed to their superior electrical properties. Highlights (1) The interfacial durability of CNT/PVDF nanofibers was enhanced to increase contact area by reinforcing CNT. (2) The efficiency of CNT/PVDF actuators was improved due to interfacial properties. (3) Thin thickness drum-type collector was made to enhance nanofiber alignment. (4) The arranged CNT/PVDF nanofibers exhibited better mechanical and actuating displacements.

A new strategy of carbon fiber reinforced plastic drilling evaluation using thermal measurement

Carbon fiber reinforced plastic composites are being increasingly used for more applications. The evaluation of hole-drilling in these composites remains a difficult and unsolved problem. The drilling process for multi-material composites is quite different than those for their more conventional metal counterparts. In the research reported here, the drilling ability and durability of drills used for drilling carbon fiber reinforced plastic composites, made with a diamond layer was deposited by chemical vapor deposition are evaluated with different r/min. Spindle speed was fixed reasoning based in abundant previous works. A thermal camera and related techniques were used to evaluate chip removal, temperature measurement inside the hole, associated thermal damage during the drilling operation, in an effort to ascertain optimal drilling conditions. Currently, chemical vapor deposition diamond drills appear to produce better holes at lower r/min.

Stress and Cure Sensing of Single-Shape Memory Alloy (SMA) Fiber/Epoxy Composites using Electro-micromechanical Technique

SMA (shape memory alloy) is well known to change the microstructure from martensite to austenite with either temperature or stress. Stress and temperature response were investigated for SMA fiber/epoxy composites using an electro-micromechanical technique during curing. SMA fiber can be used in practical applications, including stress or cure-monitoring sensors, due to its inherent shape recovery properties, i.e., it exhibits a shape memory effect (SME) when subjected to applied stress or temperature. Superelasticity was observed for SMA fiber/epoxy composites under cyclic stress–strain curve. Under a certain stress, the original modulus was reduced steeply but then recovered under further stress. A sudden transitional change in electrical resistance was also observed around 87°C with an increase of temperature. Under cyclic loading the stress was suddenly leveled-off with a certain stress, which resulted in a different stress hysteresis repeatedly with two differing matrices and surface treatment. In SMA fiber/epoxy composites, residual stress of single-SMA fiber with and without embedding epoxy matrix exhibited the incomplete and complete recovery, respectively, during the curing process. Interfacial effect between SMA fiber and matrix can be important factor for practical applications including feasible sensing and actuator.

CNT-Based Inherent Sensing and Interfacial Properties of Glass Fiber-Reinforced Polymer Composites

Carbon nanotubes (CNTs) are ideal candidates for reinforcement in composite materials due to their nanoscale structure, outstanding mechanical, thermal and electrical properties. Consideration has been given to introducing CNTs into conventional fiber reinforced composites, forming a hierarchical structure, where nanoscale reinforcement is made to work alongside more traditional microscale architecture. CNTs grafting onto fiber surface have been used to create electrically conductive interphases for introducing sensing capabilities in bulk nanocomposites. The intrinsic mechanical properties of CNTs have resulted in considerable interest in their use as reinforcement for composites. Nanocomposites filled with CNT have high stiffness, strength and good electrical conductivity at relatively low concentrations of these reinforcing materials. Gradient specimen which contains electrical contacts with gradually-increasing spacing is an effective test to observe the contact resistance at interface of CNT-polymer nanocomposites. Due to the presence of hydrophobic domains on the heterogeneous surface, CNT-polymer nanocomposites exhibit a hydrophobic property. Strong and durable interfacial adhesion is expected to transfer the stress efficiently from the matrix to the fiber, which may result in greatly improved mechanical properties in composites. Inherent sensing and interfacial properties of fiber reinforced CNT-polymer nanocomposites could be evaluated by electro-micromechanical and wettability measurements.

Optoelectronic and acoustic properties and their interfacial durability of GnP/PVDF/GnP composite actuators with nano-structural control

Nano- and hetero-structures of carbon nanotube (CNT), indium tin oxide (ITO), and Graphene nano Platelet (GnP) can control significantly piezoelectric and optoelectronic properties in Microelectromechanical Systems (MEMS) as acoustic actuators. Interfacial durability and electrical properties of CNT, ITO or GnP coated poly(vinylidene fluoride) (PVDF) nanocomposites were investigated for use in acoustic actuator applications. The GnP coated PVDF nanocomposite exhibited better electrical conductivity than either CNT or ITO, due to the unique electrical properties of GnP. GnP nanocomposite coatings also exhibited good acoustical properties. Contact angle, surface energy, work of adhesion, and spreading coefficient measurements were used to explore the interfacial adhesion durability between neat CNT (or plasma treated CNT) and plasma treated PVDF. The acoustic actuation performance of GnP coated PVDF nanocomposites were investigated for different radii of curvature and different coating conditions, using a sound level meter. GnP is considered to be a more appropriate acoustic actuator than either CNT or ITO because of its characteristic electrical properties. A radius of curvature of about 15 degrees was established as being most appropriate. Sound characteristics differed with varying coating thicknesses. The results of this study suggest that it should be possible to manufacture transparent actuators with good sound quality.

Evaluation of surface control and durability CNT and ITO coated PET transparent electrode under different dry conditions

Transparent electrodes using carbon nanotube (CNT) have recently been studied as potential replacements for convention ITO. In this work, CNT or ITO coated polyethylene terephthalate (PET) samples were prepared and studied. The degree of cohesion is dependent on the drying conditions. To explore effects of changing surface conditions, three drying temperatures, 20 °C, 80 °C, and 120 °C, were used. Electrical resistance measures were used to evaluate the interfacial durability and electrical properties of prepared transparent electrodes. FE-SEM was used to investigate surface changes and UV-spectroscopy was used to evaluate transparency as functions of the different drying temperatures. The electronic properties for these nanoparticle coated surfaces were evaluated using a cyclic voltametry method. Interfacial durability was evaluated by static contact angle measurement changes with elapsed time. The pH values of the coatings were measured in a water solution. The durability of the CNT coated surfaces was found to be better than that of the ITO coated surfaces. The higher drying temperatures were found to produce better surfaces because of improved cohesion between the nanoparticles which resulted in improved electrical properties and improved durability of the coated surfaces.

Evaluation of surface control and durability of carbon nanotube and indium tin oxide coated polyethylene terephthalate transparent electrodes under different drying conditions

Transparent electrodes using carbon nanotube (CNT) have recently been studied as potential replacements for conventional indium tin oxide (ITO). In this work, CNT and ITO coated polyethylene terephthalate samples were prepared and studied. The degree of cohesion is dependent on the drying conditions. To explore affects of changing surface conditions, three drying temperatures, 20, 80, and 120°C, were used. Electrical resistance measurements were used to evaluate the interfacial durability and electrical properties of prepared transparent electrodes. A field emission scanning electron microscope was used to investigate surface changes and UV-spectroscopy was used to evaluate transparency as functions of the different drying temperatures. The electronic properties for these nanoparticle coated surfaces were evaluated using a cyclic voltametry method. Interfacial durability was evaluated by static contact angle measurement versus elapsed time. The pH values of the coatings were measured in a water solution. The durability of the CNT coated surfaces was found to be better than that of the ITO coated surfaces. The higher drying temperatures were found to produce better coated surfaces because of improved cohesion between the nanoparticles which resulted in improved electrical properties and improved durability.