Effect of manufacturing method and aging environment on painted automotive carbon fibre composite surfaces

In this paper, the effect of various aging environments on the painted surface finish of unidirectional carbon fibre composite laminates, manufactured by autoclave and a novel out-of-autoclave technique was investigated. Laminates were exposed to water immersion, 95 % relative humidity and cyclic environments for 552 h and the surface finish was evaluated using visual and wave-scan distinctness of image (DOI) techniques. It was found that the laminate surface finish was dependent on the amount of moisture in the aging test. Minor surface waviness occurred on the laminates exposed to the cyclic test, whereas, surface waviness, print through and DOI values were all significantly higher as the laminates absorbed larger quantities of moisture from the hygrothermal and hydrothermal tests. The water immersion test, which was the most detrimental to the surface finish of the painted laminates, produced dense blistering on the autoclave manufactured laminate surface whereas the out-of-autoclave laminate surface produced only a few. It was found that the out-of-autoclave laminate had high substrate surface roughness which resulted in improved paint adhesion and, therefore, prevented the formation of surface blistering with aging. © 2012 Springer Science+Business Media Dordrecht.

Hygrothermal effects on painted carbon fibre composite surfaces

In this article, the effect of hygrothermal aging on the painted surface finish of unidirectional and fabric carbon fibre composite laminates, with and without surfacing film was investigated. The results highlighted the importance of ensuring that the composite surface directly beneath the paint layer is made from a uniform material with a consistent thickness in order to minimise surface defects from occurring during aging. The surfacing film was found to minimise the print through development on the painted unidirectional and twill composite surfaces. However, the surfacing film layer was found to intermingle with the carbon fibre plies during cure, which resulted in an uneven film thickness that caused increased levels of orange peel. The twill laminate painted surface produced high levels of print through and surface waviness that was caused by the large resin rich regions located within the tow intersections at the surface which enlarged due to thermal expansion and swelling of the matrix with hygrothermal aging. It was also noted that the small resin rich regions between the individual carbon fibres on the unidirectional composite surface were sufficiently large to print through the painted surface.

Azide photochemistry for facile modification of graphitic surfaces : preparation of DNA-coated carbon nanotubes for biosensing

A facile, two-step method for chemically attaching single-stranded DNA to graphitic surfaces, represented here by carbon nanotubes, is reported. In the first step, an azide-containing compound, N-5-azido-nitrobenzoyloxy succinimide (ANB-NOS), is used to form photo-adducts on the graphitic surfaces in a solid-state photochemical reaction, resulting in active ester groups being oriented for the subsequent reactions. In the second step, pre-synthesized DNA strands bearing a terminal amine group are coupled in an aqueous solution with the active esters on the photo-adducts. The versatility of the method is demonstrated by attaching pre-synthesized DNA to surfaces of carbon nanotubes in two platforms—as vertically-aligned multi-walled carbon nanotubes on a solid support and as tangled single-walled carbon nanotubes in mats. The reaction products at various stages were characterized by x-ray photoelectron spectroscopy. Two different assays were used to check that the DNA strands attached to the carbon nanotubes were able to bind their partner strands with complementary base sequences. The first assay, using partner DNA strands tethered to gold nanoparticles, enabled the sites of DNA attachment to the carbon nanotubes to be identified in TEM images. The second assay, using radioactively labelled partner DNA strands, quantified the density of functional DNA strands attached to the carbon nanotubes. The diversity of potential applications for these DNA-modified carbon-nanotube platforms is exemplified here by the successful use of a DNA-modified single-walled carbon-nanotube mat as an electrode for the specific detection of metal ions.

Transmission electron microscopy investigation of substitution reactions from carbon nanotube template to silicon carbide nanowires

Substitution reactions between multiwalled carbon nanotubes and silicon monoxide vapour have been investigated using transmission electron microscopy. Different reactions occurred inside the multiwalled nanotubes and on the nanotube external surfaces, resulting in the formation of silicon carbide nanowires with a core–shell structure. The substitution reaction process and end products are strongly affected by nanotube structures and a ball milling treatment of the starting materials.

Measurement of the mass transfer coefficient at workpiece surfaces in heat treatment furnaces

The mass (e.g. carbon) transfer coefficient at a workpiece surface is an important kinetic factor to control the heat treatment process of the workpiece and to evaluate heat treatment equipment. The coefficient can be calculated from the carbon concentration at the surface of a sample carburized in a carburizing furnace for a given time. Two common measurement methods which use a thin plate and employ a component as samples respectively are evaluated and compared for sensitivity and uncertainty. The comparison shows that the use of a component produces higher measurement precision and also has the advantage in measuring the carbon transfer coefficients at different treated positions. This method is then extended and discussed methodologically. Also two equations are proposed to calculate the carbon transfer coefficient and its uncertainty, respectively. This method is also applied to measure the carbon transfer coefficient in a fluidized bed heat treatment furnace.

Particle trapping using dielectrophoretically patterned carbon nanotubes

This study presents the dielectrophoretic (DEP) assembly of multi-walled carbon nanotubes (MWCNTs) between curved microelectrodes for the purpose of trapping polystyrene microparticles within a microfluidic system. Under normal conditions, polystyrene particles exhibit negative DEP behaviour and are repelled from microelectrodes. Interestingly, the addition of MWCNTs to the system alters this situation in two ways: first, they coat the surface of particles and change their dielectric properties to exhibit positive DEP behaviour; second, the assembled MWCNTs are highly conductive and after the deposition serve as extensions to the microelectrodes. They establish an array of nanoelectrodes that initiates from the edge of microelectrodes and grow along the electric field lines. These nanoelectrodes can effectively trap the MWCNT-coated particles, since they cover a large portion of the microchannel bottom surface and also create a much stronger electric field than the primary microelectrodes as confirmed by our numerical simulations. We will show that the presence of MWCNT significantly changes performance of the system, which is investigated by trapping sample polystyrene particles with plain, COOH and goat anti-mouse IgG surfaces.

Tailoring the surface chemistry of carbon fiber and E-glass composites for improved adhesion

The main challenges in the manufacture of composite materials are low surface energy and the presence of silicon-containing contaminants, both of which greatly reduce surface adhesive strength. In this study, carbon fiber (CF) and E-glass epoxy resin composites were surface treated with the Accelerated Thermo-molecular adhesion Process (ATmaP). ATmaP is a multiaction surface treatment process where tailored nitrogen and oxygen functionalities are generated on the surface of the sample through the vaporization and atomization of n-methylpyrrolidone solution, injected via specially designed flame-treatment equipment. The treated surfaces of the polymer composites were analyzed using XPS, time of flight secondary ion mass spectrometry (ToF-SIMS), contact angle (CA) analysis and direct adhesion measurements. ATmaP treatment increased the surface concentration of polar functional groups while reducing surface contamination, resulting in increased adhesion strength. XPS and ToF-SIMS showed a significant decrease in silicon-containing species on the surface after ATmaP treatment. E-glass composite showed higher adhesion strength than CF composite, correlating with higher surface energy, higher concentrations of nitrogen and CO functional groups (from XPS) and higher concentrations of oxygen and nitrogen-containing functional groups (particularly C₂H₃O⁺ and C₂H₅NO⁺ molecular ions, from ToF-SIMS).

Modeling and comparative analysis of carbon nanotube and boron nitride nanotube cantilever biosensors

This paper investigates the bending deformation of a cantilever biosensor based on a single-walled carbon nanotube (CNT) and single-walled boron nitride nanotube (BNNT) due to bioparticle detection. Through 3-D modeling and simulations, the performance of the CNT and BNNT cantilever biosensors is analyzed. It is found that the BNNT cantilever has better response and sensitivity compared to the CNT counterpart. Additionally, an algorithm for an electrostatic-mechanical coupled system is developed. The cantilever (both BNNT and CNT) is modelled by accounting that a conductive polymer is deposited onto the nanotube surfaces. Two main approaches are considered for the mechanical deformation of the nanotube beam. The first one is differential surface stress produced by the binding of biomolecules onto the surface. The second one is the charge released from the biomolecular interaction. Also, different ambient conditions are considered in the study of sensitivity. Sodium Dodisyl Sulphate (SDS) provides better bending deformation than the air medium. Other parameters including length of beam, variation of beam's location, and chiralities are considered in the design. The results are in excellent agreement with the electrostatic equations that govern the deformation of cantilever.

Substrate-induced coagulation (SIC) of nano-disperse carbon black in non-aqueous media : a method of manufacturing highly conductive cathode materials for Li-ion batteries by self-assembly

Substrate-induced coagulation (SIC) is a coating process based on self-assembly for coating different surfaces with fine particulate materials. The particles are dispersed in a suitable solvent and the stability of the dispersion is adjusted by additives. When a surface, pre-treated with a flocculant e.g. a polyelectrolyte, is dipped into the dispersion, it induces coagulation resulting in the deposition of the particles on the surface. A non-aqueous SIC process for carbon coating is presented, which can be performed in polar, aprotic solvents such as N-Methyl-2- pyrrolidinone (NMP). Polyvinylalcohol (PVA) is used to condition the surface of substrates such as mica, copperfoil, silicon-wafers and lithiumcobalt oxide powder, a cathode material used for Li-ion batteries. The subsequent SIC carbon coating produces uniform layers on the substrates and causes the conductivity of lithiumcobalt oxide to increase drastically, while retaining a high percentage of active battery material.

Structuring in liquid alkanes between solid surfaces : force measurements and mean-field theory

Measurements have been made of the solvation forces between mica surfaces in the even-numbered n-alkanes from hexane to hexadecane. In all cases the force law is qualitatively very similar, characterized by a decaying oscillatory function of distance, as occurs for simple isotropic liquids. The spacing between successive minima in the force does not increase with carbon number, and is comparable to the width of a linear alkane molecule rather than its length or any average diameter. This suggests that the alkanes have some tendency towards a parallel orientation near the mica surfaces. The measurements give no indication of any strong repulsive component expected from mean-field theories of higher alkanes or polymers. The results of one such theory are presented, and the reasons for its failure to match the experimental data are discussed.

Practical amine functionalization of multi-walled carbon nanotubes for effective interfacial bonding

 Improved methods of functionalizing the surfaces of multi-walled carbon nanotubes (MWCNTs) have been investigated. It is shown that a level of primary amines of 2.3%, higher than previously reported for any nitrogen-containing gas plasma treatment, can be achieved using a mixture of N2 and H2, which is preferable to using NH3. Even higher levels (3.5%) of primary amines can be achieved by coating the MWCNTs with a thin layer of plasma polymerized heptylamine. In both cases, the highest levels were achieved using a combined continuous plus pulsed plasma mode which was superior to either continuous wave or pulsed wave alone. The integrity of the MWCNT structure is maintained by the plasma treatments, and the functionalized surface improves the dispersion of the MWCNTs and their interfacial bonding with epoxy, giving superior nanoindentation performance of the composites.