Scratch resistance of automobile clearcoats: Chemistry and characterization on the micro-and nanoscale

The scratch resistance of polymeric clearcoats intended for automobile exterior surfaces was tested with scanning 3D nanoindentation and laboratory car wash simulation (AMTEC). It could be shown by using “real world” samples with comparable scratch resistance that the applied methods were suitable for discriminating even small differences in scratch resistance with high accuracy. In the area of physical characterization of scratch resistance, the results of this investigation demonstrate the ability of microscopic, single-contact testing methods to reproduce the macroscopically experienced results. By using a combination of different scratch methods, insight into the fundamentals, e.g., chemistry, that are responsible for good or bad scratch resistance, is achieved. One key for this goal is the imaging and analytical evaluation of the damage pattern after the indent, which leads to additional results and models presented in this article. It was found that an essential key to obtaining scratch resistant surfaces is a strengthening of rubber-like elasticity as well as minimizing interactions between individual polymeric chains.     

Highly moisture-proof polysilsesquioxane coating prepared via facile sol-gel process

A highly moisture-proof polysilsesquioxane coating was obtained from a new bis-silylated precursor, which was synthesized from 3-aminopropyltriethoxysilane (APTES) and m-xylylene diisocyanate (m-XDI) in tetrahydrofuran (THF) and verified by ¹H MAS NMR. For direct comparison purposes, an SiO₂ coating was also prepared by the Stöber method using tetraethoxysilane (TEOS) as the reactant. Interestingly, the coating obtained from the polysilsesquioxane sol exhibited a much higher moisture resistance capability than its counterpart, which was attributed to its more compact feature between nanoparticles as characterized by N₂ absorption experiment and transmission electron microscopy (TEM). Furthermore, its high transparency of about 92% showed potential for application in the protection of optical crystals.     

Relationship between chemical degradation and thickness loss of an amine-cured epoxy coating exposed to different UV environments

The relationship between chemical degradation and thickness loss of an unpigmented, non UV-stabilized, crosslinked amine-cured epoxy coating exposed to three UV conditions was investigated. Spin-coated samples having a thickness of approximately 7 μm on an Si substrate were prepared from a stochiometric mixture of a bisphenol A epoxy resin and a tetra-functional amine curing agent. Samples were exposed outdoors and to two accelerated laboratory UV environments. Chemical degradation and thickness loss were measured by transmission Fourier transform infrared spectroscopy (FTIRS) and laser scanning confocal microscopy (LSCM), respectively. In addition, surface roughness and morphological changes were measured by atomic forcemicrosocopy (AFM) and LSCM. Substantial chemical degradation, thickness loss, and morpholocal changes occurred in the exposed films, and the rate of chemical degradation was greater than that due to the thickness loss. This additional chemical loss was attributed to an inhomogeneous degradation process in which nanoscale localized depressions initiate at certain sites on the surface, which then enlarge and deepen with exposure time. The results of this study provide a better understanding of the degradation mechanism and should lead to the development of scientific-based models for predicting the service life of crosslinked amine-cured epoxy coatings. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004, in Chicago, IL     

Microstructure and morphology of amine-cured epoxy coatings before and after outdoor exposures—An AFM study

Atomic force microscopy (AFM) has been used to study the morphology and microstructure of an amine-cured epoxy before and after outdoor exposure. Measurements were made from samples prepared in an essentially CO₂-free, H₂O-free glove box and from samples prepared in ambient conditions. For those prepared in a CO₂-free glove box, AFM imaging was conducted on (1) an unexposed air/coating surface, (2) an unexposed coating bulk, (3) an unexposed coating/substrate interface, and (4) a field exposed air/coating surface. For samples prepared in ambient conditions, only the unexposed air/coating surface was investigated. The same regions of the exposed samples were scanned periodically by the AFM to monitor changes in the surface morphology of the coating as UV exposure progressed. Small angle neutron scattering and Fourier transform infrared spectroscopy (FTIR) studies were performed to verify the microstructure and to follow chemical changes during outdoor exposure, respectively. The results have shown that amine blushing, which occurs only under ambient conditions, had a significant effect on the surface morphology and microstructure of the epoxy. The surface morphology of the samples prepared under CO₂-free, dry conditions was generally smooth and homogeneous. However, the interface and the bulk samples clearly revealed a two-phase structure consisting of bright nodular domains and dark interstitial regions, indicating an inhomogeneous microstructure. Such heterogeneous structure of the bulk was in good agreement with results obtained by small angle neutron scattering of unexposed samples and by AFM phase imaging of the degraded sample surface. The relationship between submicrometer physical changes and molecular chemical degradation is discussed. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004, in Chicago, IL.     

Development and evaluation of terminally epoxidized triglycerides for coatings applications

Epoxidized 10-undecenoic acid triglyceride, an experimental seed oil derivative that has a terminal epoxy group on each of the three acyl glyceride segments, has been found to have good reactivity with amine curatives and allows room temperature cures to be obtained. Coatings based on epoxidized 10-undercenoic acid triglyceride have also shown excellent UV stability. As an example, coatings samples placed in a QUVA chamber exhibit no loss in gloss after 3000 hr of a cycled exposure to high intensity UV lamps and moisture at temperatures of 50–60°C. In comparison, coatings based on standard liquid epoxy resins (LERs) and commercially available hydrogenated LERs lose gloss due to chalking/decomposition within 200–800 hr. Presented at the 81 st Annual Meeting of the Federation of Societies for Coatings Technology, November 12–14, 2003, in Philadelphia, PA.     

Quantification of contact oviposition stimulants for black swallowtail butterfly,Papilio polyxenes,on the leaf surfaces of wild carrot,Daucus carota

Ovipositing black swallowtail butterflies,Papilio polyxenes, make their final host-selection decisions on the basis of compounds present on the leaf surface. Little information is available, however, on the chemistry of leaf surfaces. The purpose of this study was to develop a technique to extract and quantify the concentrations of compounds from the leaf surfaces ofDaucus carota, one of the main host species forP. polyxenes, with particular reference to compounds already identified as contact oviposition stimulants, namelytrans-chlorogenic acid (CA) and luteolin-7-O-(6-O-malonyl)--d-glucopyranoside (L7MG), as well as its degradation product luteolin-7-glucoside (L7G). Plant surfaces were extracted by dipping leaves sequentially in pairs of solvents: (1) CHCl₃-MeOH, (2) near-boiling H₂O, (3) CHCl₃-near-boiling H₂O, and (4) CH₂Cl₂-CH₂Cl₂. The resulting extracts were fractionated and analyzed using high-performance liquid chromatography. The leaf-surface concentrations of each compound were calculated using regressions relating leaf surface area to leaf weight that were obtained from measurements of field-collected carrot plants. All four methods removed the three compounds from carrot leaf surfaces, but the solvent systems differed in effectiveness. The chloroform-near-boiling water solvent system performed better than the other solvent combinations, but not significantly so. This system also extracted the highest number of polar, UV-absorbing compounds. Methylene chloride was significantly less efficient than the other methods. An additional test confirmed that the chloroform-near-boiling water method removed compounds from the surface alone and probably not from the apoplast or symplast. Surface concentrations of CA (up to 600 ng/cm² leaf surface) were substantially greater than those of the two flavonoid compounds. No clear seasonal trend in concentrations was evident from the limited number of sampling dates.     

A flow cell for transient voltammetry and in situ grazing incidence X-ray diffraction characterization of electrocrystallized cadmium(II) tetracyanoquinodimethane

An easy to fabricate and versatile cell that can be used with a variety of electrochemical techniques, also meeting the stringent requirement for undertaking cyclic voltammetry under transient conditions in in situ electrocrystallization studies and total external reflection X-ray analysis, has been developed. Application is demonstrated through an in situ synchrotron radiation-grazing incidence X-ray diffraction (SR-GIXRD) characterization of electrocrystallized cadmium (II)-tetracyanoquinodimethane material, Cd(TCNQ)₂, from acetonitrile (0.1 mol dm⁻³ [NBu₄][PF₆]). Importantly, this versatile cell design makes SR-GIXRD suitable for almost any combination of total external reflection X-ray analysis (e.g., GIXRF and GIXRD) and electrochemical perturbation, also allowing its application in acidic, basic, aqueous, non-aqueous, low and high flow pressure conditions. Nevertheless, the cell design separates the functions of transient voltammetry and SR-GIXRD measurements, viz., voltammetry is performed at high flow rates with a substantially distended window to minimize the IR (Ohmic) drop of the electrolyte, while SR-GIXRD is undertaken using stop-flow conditions with a very thin layer of electrolyte to minimize X-ray absorption and scattering by the solution.     

A Novel Bioassay for Yponomeuta cagnagellus Oviposition in Response to Extracts of Host and Nonhost Plant Surface Compounds

Yponomeuta cagnagellus is a phytophagous moth species specialized on Euonymus europaeus. Host discrimination by the adult female is an important aspect of host specialization and is based mainly on the distinctive secondary chemistry of host and nonhosts. This paper describes a bioassay that was developed to study the effect of isolated plant surface compounds on Yponomeuta oviposition. Adult moths recognize their hosts through chemical stimuli on the leaf or twig surface. Relatively apolar compounds extracted from the host twig surface by washing in dichlormethane do not stimulate oviposition. More polar, methanol-soluble compounds do, and this stimulation is dose dependent. Moths are able to recognize hosts solely by their surface compounds: females show a strong preference for artificial twigs treated with methanolic extracts of their hosts compared to those treated with methanolic extracts of nonhosts Crataegus monogyna and Prunus spinosa (both of which are hosts for closely related Y. padellus). Shape and surface characteristics of the oviposition substrate also influence oviposition. The substrate needs to resemble the basic form of a twig (i.e., cylindrical), and females prefer a coarse surface with irregularities over a smooth one.