Scratch resistant polyimide coatings for aluminosilicate glass surfaces

Several polyimide resins were tested as possible scratch resistant coatings for aluminosilicate glass centrifuge tubes. Tubes with siloxane pretreatments provided the best adhesion between the polyimide and glass surface. Resins synthesized with an alkoxysilane group incorporated into the polyimide chain also showed improved adhesion, but the results were not as significant as when the pretreatment was used. Elastic recovery and effective Young's modulus of the polyimide coatings were calculated from nano-scratching. The results indicate that polyimides with a lower modulus, and higher elastic recovery, protected the glass surface best, exhibiting compression of the coating layer. An example was poly-4-4′-oxydiphenylene pyromellitimide (PMDA-ODA), whereas the coatings with a high effective Young's modulus and low elastic recovery ruptured. An example of a failed coating was poly-4,4′-carbonyldiphenylene 3,3′,4,4′-biphenylenetetracarboximide (BPDA-DABP) which had low amount of elastic recovery, high effective Young's modulus and a large amount of flaking during macroscratch testing.     

A Self-Delamination Method of Measuring the Surface Energy of Adhesion of Coatings

A self-delamination technique is presented to assess the surface energy of adhesion of coatings. By measuring the debond area resulting from a circular hole cut in a film adhered onto a substrate, the surface energy may be determined if the tensile modulus, Poisson's ratio and residual stress level of the film are known. This method is useful for coating thicknesses greater than a critical thickness for self-peeling. Using this technique, the surface energy for a polyimide film (cured up to 220°C) on a glass plate was determined to 3.2 Nm^-1.     

A compression test for adhesion evaluation of diamond coatings

A key requirement of an effective coating is its adequate adhesion to the substrate. Thus, reliable test methods to evaluate coating adhesion and to characterize the deposition parameters affecting it are necessary for the systematic development of such coatings. The conventional technique for measuring diamond coating adhesion, the scratch test, is unreliable because of wear of the stylus and influences of the substrate. Thus, a noncontact technique (compression test) of evaluating the adhesion of diamond coatings on brittle substrates was modelled and developed. This method utilizes the differences in Young's modulus between the coating and the substrate via application of an external load in order to generate interfacial stresses and debond the coating. An innovative three-dimensional numerical model, based on combining the variational and boundary integral approaches, was utilized to link the indirect (i.e. load) to the direct (i.e. debond shear stress or elastic energy of delamination) characteristics of adhesion. Factors affecting the adhesion strength of the diamond coatings are discussed in relation to the process parameters. This test offers an excellent alternative to conventional techniques for measuring the adhesion strength of diamond coatings on brittle substrates.     

Generating and measuring the anisotropic elastic behaviour of Co thin films with oriented surface nano-strings on micro-cantilevers

In this research, the elastic behaviour of two Co thin films simultaneously deposited in an off-normal angle method was studied. Towards this end, two Si micro-cantilevers were simultaneously coated using pulsed laser deposition at an oblique angle, creating a Co nano-string surface morphology with a predetermined orientation. The selected position of each micro-cantilever during the coating process created longitudinal or transverse nano-strings. The anisotropic elastic behaviour of these Co films was determined by measuring the changes that took place in the resonant frequency of each micro-cantilever after this process of creating differently oriented plasma coatings had been completed. This differential procedure allowed us to determine the difference between the Young's modulus of the different films based on the different direction of the nano-strings. This difference was determined to be, at least, the 20% of the Young's modulus of the bulk Co.PACS: 62.25.-g; 81.16.Rf; 68.60.Bs; 81.15.Fg; 68.37.Ef; 85.85.+j.     

Synthesis of polyimides containing pyridine or triazole moiety to improve their adhesion to sputter-deposited copper

Polyimides containing pyridine as well as triazole were synthesized. The incorporation of pyridine or triazole improves the adhesion between polyimides and sputter-deposited copper. 4,4′-oxydianiline (ODA) was separately mixed with 2,6-diaminopyridine (DAP) and 3,5-diaminol,2,4-triazole (DATA), to form co-diamines. A series of polyimides was obtained in two steps by reacting co-diamines and 3,3′,4,4′-pyromellitic dianhydride (PMDA). The structure of the polyimides was verified by Fourier Transform Infrared spectroscopy (FT-IR) and Nuclear Magnetic Resonance (NMR). Their thermal, mechanical and dielectric properties were investigated. The rigidity of both pyridine and triazole moieties influences the coefficient of thermal expansion, the tensile strength and the elastic modulus of the films. The adhesion strength of the sputter-deposited copper to polyimide films was proportional to the functional group content. At a molar ratio of DAP to ODA of 1 : 6, the 90°-peel strength of copper/polyimide laminates reached a maximum of 990 J/m². At a molar ratio of DATA to ODA of 1 : 6, the 90°-peel strength of copper/polyimide laminates reached a maximum of 696 J/m². The corresponding polyimide films exhibited a good balance in thermal, mechanical and dielectric properties, as did the PMDA-ODA film. The locus of failure (LOF) examination by X-ray photoelectron spectroscopy (XPS) indicated that the LOF of laminates with low to moderate adhesion was mostly at the interface near the polyimide; the LOF of laminates with high adhesion was mostly in the polyimide. The N_1s core level spectra of the delaminated copper surface revealed a peak at 398.4 eV in copper/polyimide with DAP/ODA ratio of 1 : 6 and a peak at 398 eV in copper/polyimide with DATA/ODA ratio of 1 : 6, perhaps due to the formation of N-Cu charge-transfer complex. This complex substantially promoted the adhesion between sputter-deposited copper and polyimides.     

Hertzian-Crack Suppression in Ceramics with Elastic-Modulus-Graded Surfaces

Hertzian (spherical) indentation experiments were carried out in a graded alumina-glass composite whose Young's modulus increased with depth beneath the indented surface. An in situ processing method involving impregnation of a dense, fine-grained alumina by an aluminosilicate glass was employed to fabricate such a composite. With this technique, a monotonic, unidirectional variation in Young's modulus of as much as 50% was introduced over a distance of approximately 2 mm, while keeping the coefficient of thermal expansion and the Poisson ratio for the glass and the alumina nearly the same. The macroscopically graded, elastic composite so produced with nearly full density has essentially no macroscopic, long-range residual stresses following processing. The unidirectional variation in Young's modulus under the indenter is shown to fully suppress the formation of Hertzian cone cracks. Without these elastic-modulus gradients, cone-crack formation was observed in bulk glass and alumina. Finite-element analyses of spherical indentation on elastically graded substrates were also performed to develop a quantitative understanding of the experimental trends. It is reasoned that the present innovations, involving functionally graded surfaces and their in situ processing, provide new possibilities for enhancing certain contact-damage resistance characteristics in various ceramic materials for a broad range of engineering applications. Furthermore, this contact-damage-resistance phenomenon in functionally graded ceramics is elastic in nature, and is, therefore, likely to be immune to mechanical fatigue within the elastic limit.     

Linear and networked blends and copolymers of polyimide

Preparation and characterization of blends and copolymers of a fluorinated polyimide with network constituents is reported. 4,4′‐Hexafluoroisopropylidene diphthalic anhydride and 4,4′‐diaminodiphenyl ether (6FDA–DDE) polyimide were used as the linear hosts and mellitic acid hexamethyl ester ‐ 4,4′‐diaminodiphenyl ether (MAHE–DDE) was employed as the network constituent for the blend and copolymer. Cast films of the polyimides were characterized by FTIR, XPS, DMA, and TGA. The multifunctional nature of MAHE facilitated crosslinking among the constituents. Both blends and copolymers showed significant improvement in the storage modulus and glass transition temperature relative to that observed for the 6FDA homopolymer. The occurrence of a single glass transition temperature for the blends suggests that they were at least partially miscible. Presence of low molecular weight species in the copolyimides, combined with steric hindrance to crosslinking, may have resulted in the existence of an optimum in the amount of the network components for improving the mechanical properties. Inclusion of network components is presented as a facile method for improving the desirable properties of polyimide. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3000–3008, 2006     

Preparation of PDMS/EEC/SiO2 composite super-hydrophobic coatings with excellent anti-guano adhesion performance

A low-cost and no-toxicity approach was presented to fabricate super-hydrophobic coatings via depositing hydroxy-terminated poly-dimethylsioxane and 3,4-epoxycyclohexylmethyl-3′, 4′-epoxycyclohexane carboxylate grafted nano-silica particles on substrates. The surface morphology, wettability, and anti-guano adhesion performance of as-prepared coatings were investigated. Results show the micro-nano hierarchical structures were formed on the surface of as-prepared coatings. The coatings exhibit super-hydrophobicity with a water static contact angle of 156° and sliding angle of 3°. Excellent anti-guano adhesion performances are also exhibited by the coatings, and the residue amount of guano captured by the coating only accounts for 0.3% of that captured by glass surface, making the as-prepared coating a promising candidate as an anti-guano strategy for both industry and everyday life (e.g. insulators for overhead power lines, buildings, statues and cars).     

Determination of Young's Modulus in Chemically Vapor-Deposited SiC Coatings

Young's modulus of CVD and SiC coatings was measured in situ (on the substrate) using strain gage/flexure and dynamic resonance techniques. The average Young's moduli of CVD SiC from these techniques were 446 and 415 Gpa, respectively, and were considered to be in good agreement. The determination of a representative coating thickness and cross section is critical in order to accurately estimate Young's modulus of coatings.     

Antireflective coatings using organically modified silica and polyimide via solution casting method

Antireflective (AR) coatings were prepared using a polyimide and two types of organically modified silica colloids via a solution casting method. The optically transparent polyimide was prepared from 2,2′‐Bis[4‐(3,4‐dicarboxyphenoxy)phenyl]propane dianhydride (BPADA) and 4,4′‐oxydianiline (ODA). The silica colloids were driven to the coating‐air interface by either the fluorinated alkyl group or PDMS (Polydimethylsiloxane) segment tethered onto the silica colloids. The amount of fluorinated alkyl groups and the molecular weight of the siloxane grafted on the silica colloid were varied. The PDMS‐silica and fluorosilica colloids were characterized by TEM (Transmission Electron Microscopy), DLS (Dynamic Light Scattering), FTIR (Fourier Transform Infrared Spectroscopy), solid‐state ¹³C NMR (Nuclear Magnetic Resonance) and solid‐state ²⁹Si NMR. The AR coatings were characterized by UV–vis (Ultraviolet–Visible Spectroscopy) transmittance spectra, AFM (Atomic Force Microscope), and SEM (Scanning Electron Microscope). The effects of modified silica loading and type of solvent on AR properties were studied. An enhancement in AR activity was observed for 1 wt% PDMS‐modified (low molecular weight) silica coatings and 3 wt.% fluorosilica‐10 in dimethylacetamide (DMAc). In comparison with cyclopentanone (CPT), DMAc favors migration of silica particles toward coating‐air interface giving higher transmittance. The migration of particles to the surface and consequently increased surface roughness was observed by SEM. POLYM. ENG. SCI., 53:2228–2241, 2013. © 2013 Society of Plastics Engineers     

Reactive diluents and properties of ultraviolet-cured polycarbonate urethane acrylates

Polymer films obtained from photocurable formulations were investigated by tensile methods and dynamic mechanical analysis. The polymer formulations contained photoinitiator, urethane diacrylate oligomer, and acrylic reactive diluent. It was found that diluent concentration may strongly affect the glass transition temperature and elastic modulus of the cured coating. When the diluent homopolymer glass transition temperature is larger than that of oligomer homopolymer, the glass transition temperature and elastic modulus of the coating film increase with the increase of the diluent concentration. When the diluent homopolymer has lower glass transition temperature than the homopolymer of the oligomer, the increase in diluent concentration leads to a decrease in glass transition temperature and elastic modulus of the UV-cured coating film. The effect of the testing temperature on tensile storage modulus of the films containing different concentrations of reactive diluents was studied as well. The data indicated that a variety of coatings with wide ranging but predictable properties can be formulated from previously examined starting materials but used at different concentrations. © 1995 John Wiley & Sons, Inc.     

Facile fabrication of superhydrophobic polyimide/polytetrafluoroethylene composite coatings with high water adhesion

A facile casting method was used to fabricate superhydrophobic polyimide/polytetrafluoroethylene composite coatings with high water adhesion. The water contact angles of the composite coatings were larger than 150 °, expressing superhydrophobic property. But water droplets pinned tightly on the composite coating, even if it was upside down. The X‐ray photoelectron spectrum analysis indicated that polyimide and polytetrafluoroethylene coexisted in the resulting coating. The observation with scanning electron microscopy showed that the composite coating formed lotus‐like structure with many spherical polyimide papillae randomly bonding on the surface. But the tops of the polyimide papillae were not covered by lance‐shaped Teflon fibres, forming an inhomogenous and discontinuous surface structure. This special surface chemical distribution and lotus‐like structure combined to contribute to the high adhesive superhydrophobicity. This simple method may greatly extend the application range of high adhesive superhydrophobic surfaces in microcontrollable and microfluidic application. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42810.     

TEM,XPS and thermo-mechanical properties of novel sustainable hybrid coatings

This work contributes to the development of a new generation of protective coatings composed of organic–inorganic materials. A silica based hybrid film was used in this work as high performance materials. The silica sol–gel film reveals enhanced thermo-mechanical properties in comparison with the pure polymer film. Herein, we demonstrate the possibility of employing cheap SiO₂ as prospective nano-fillers for hybrid coatings with active thermo-mechanical properties. Organic–inorganic hybrid coatings based on polyimide and silica were synthesized through a simple physical mixing technique. 3,3′,4,4′-Biphenyltetracarboxylic dianhydride (BPDA), benzene-1,3-diamine (BDA), 3,3′-oxydianiline (ODA) and SiO₂, were used as precursors for the hybrid coatings. These hybrid coatings were deposited via spin coating onto a galvanized iron, aluminum and copper in order to study the adhesive strength. The effects induced by the silica content on the mechanical properties of the coated samples were investigated. The mechanical properties of hybrid composite were found to be enhanced compared to polyimide coating. The main objective was to observe potential improvements in the mechanical and thermal properties of PI–silica hybrid films. Morphology, and structural changes in the composite films were studied as well as adhesion and impact strength and these characteristics were compared with those of unreinforced polyimide films.     

Structural-mechanical and biomedical surface properties of elastic polyurethane after PECVD of Ar/C2H2

Plasma treatment of polymers has many perspective applications in biomedical area. Carbon or carbon-like coatings of elastic polymers are of interest. However, deformation of the polymeric substrates easily damages the modified surface. Such flaws cancel all the benefits of the treatment and should be avoided. In this paper, a surface of elastic polyurethane (PU) (elastic modulus is 25 MPa) is treated by plasma-enhanced chemical vapor deposition (PECVD) of acetylene/argon. As a result, inhomogeneous carbon-containing nanolayers are formed: discontinuous and solid coatings with heterogeneous stiffness and thickness (from 2 to 11 nm). Structural peculiarities and relatively low elastic modulus (several GPa) of the coatings prevent their fracture under uniaxial deformation of at least up to 50% (however, the thickest coating is covering by a mesh of local nanocracks). The coatings have improved biomedical properties: better albumin adsorption and resistance to bacteria of Escherichia coli.     

Carbon nanotube reinforced hydroxyapatite composite coatings produced through laser surface alloying

Carbon nanotube (CNT) reinforced hydroxyapatite composite coatings have been successfully fabricated by laser surface alloying. The phase compositions and the microstructure of the composite coatings were studied using X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). TEM observation showed that a large amount of CNTs can be found with their original tubular morphology in the composite coatings, even though some CNTs react with titanium element in the substrate during laser irradiation. Additionally, measurement on the elastic modulus, hardness of the composite coatings by nanoindentation tests indicated that the mechanical properties are affected by the amount of CNTs in the starting precursor materials. Therefore, CNT reinforced hydroxyapatite composite coating is a promising coating material for high-load-bearing metal implants.     

Synthesis and characterization of polyimide–silica nanocomposites using novel fluorine‐modified silica nanoparticles

Polyimide–silica nanocomposites were synthesized with 4,4′‐oxydianiline, 4,4′‐(4,4′‐isopropylidenediphenoxy)bis(phthalic anhydride), and fluorine‐modified silica nanoparticles. Fluorinated precursors such as 4″,4?‐(hexafluoroisopropylidene)bis(4‐phenoxyaniline) (6FBPA) and 4,4′‐(hexafluoroisopropylindene)diphenol (BISAF) were employed to modify the surface of the silica nanoparticles. The microstructures and thermal, mechanical, and dielectric properties of the polyimide–silica nanocomposites were investigated. An improvement in the thermal stability and storage modulus of the polyimide nanocomposites due to the addition of the modified silica nanoparticles was observed. The microstructures of the polyimide–silica nanocomposites containing 6FBPA‐modified silica exhibited more uniformity than those of the nanocomposites containing BISAF‐modified silica. The dielectric constants of the polyimide were considerably reduced by the incorporation of pristine silica or 6FBPA‐modified silica but not BISAF‐modified silica. The addition of a modifier with higher fluorine contents did not ensure a lower dielectric constant. The uniformity of the silica distribution, manipulated by the reactivity of the modifier, played an important role in the reduction of the dielectric constant. Using 6FBPA‐modified silica nanoparticles demonstrated an effective way of synthesizing low‐dielectric‐constant polyimide–silica nanocomposites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 882–890, 2007     

Synthesis and properties of poly(imide siloxane) block copolymers with different block lengths

Several poly(imide siloxane) block copolymers with the same bis(γ‐aminopropyl)polydimethylsiloxane (APPS) content were prepared. The polyimide hard block was composed of 4,4′‐oxydianiline and 3,3′,4,4′‐diphenylthioether dianhydride (TDPA), and the polysiloxane soft block was composed of APPS and TDPA. The length of polysiloxane soft block increased simultaneously with increasing the length of polyimide hard block. For better understanding the structure–property relations, the corresponding randomly segmented poly(imide siloxane) copolymer was also prepared. These copolymers were characterized by FT‐IR, ¹H‐NMR, dynamic mechanical thermal analysis, thermogravimetric analysis, polarized optical microscope, rheology and tensile test. Two glass transition temperatures (T_g) were found in the randomly segmented copolymer, while three T_gs were found in the block copolymers. In addition, the T_gs, storage modulus, tensile modulus, solubility, elastic recovery, surface morphology and complex viscosity of the copolymers varied regularly with increasing the lengths of both blocks. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

搪瓷浴缸专用涂料的研制

阐述搪瓷浴缸专用涂料的研制过程及在浴缸上的应用情况 ,讨论了附着力促进剂对该涂料和釉面密着性的影响及消光剂对涂料光泽的影响。     

室温固化硅酸盐耐高温防腐蚀涂料

制备了一种室温固化的硅酸盐耐磨防腐涂料,该涂料具有优异的耐磨防腐蚀性能,能广泛应用于金属、陶瓷、塑料、玻璃等材料表面,并且具有良好的附着力和匹配性,该涂料固化后还具有低的介电常数。     

Contact-induced Damage in Ceramic Coatings on Compliant Substrates: Fracture Mechanics and Design

Simple explicit relations are presented for the onset of competing fracture modes in ceramic coatings on compliant substrates from Hertzian-like contacts. Special attention is given to a deleterious mode of radial cracking that initiates at the lower coating surface beneath the contact, in addition to traditional cone cracking and quasiplasticity in the near-contact area. The critical load relations are expressed in terms of well-documented material parameters (elastic modulus, toughness, hardness, and strength) and geometrical parameters (coating thickness and sphere radius). Data from selected glass, Al₂O₃ and ZrO₂ coating materials on polycarbonate substrates are used to demonstrate the validity of the relations. The formulation provides a basis for designing ceramic coatings with optimum damage resistance.