Improving surface quality of polyethylene terephthalate film for large area flexible electronic applications

Lamination is a method utilized to protect flexible electroluminescence device against environmental hazards, such as dust, moisture, and water vapor. The materials are typically joined together using adhesive or cohesion of the materials during the lamination process. Polyethylene terephthalate (PET) is commonly used as the substrate film where electroluminescence patterns are printed. However, PET film has a relatively low surface energy and high contact angle, which would cause relatively weak laminating strength. This paper discusses the use of atmospheric plasma as a surface treatment method to modify PET and laminating films’ interface to improve bonding and laminating quality. Experimental results revealed that atmospheric plasma process reduced the contact angle of both PET and laminating films. Functional groups favoring hydrophilicity were found on the films’ interface after the atmospheric plasma treatment. These effects consequently increased surface energies of both films and favored bonding between the films. The treated films thus had increased laminating strength by approximately six times without compromising the transparency quality.     

Properties of Aqueous Polyurethane Dispersion Modified by Epoxide Resin and Their Use as Adhesive

The aqueous polyurethane hybrid dispersion modified by the epoxy resin were synthesized using 1,4-butanediol ( BDO ) and dimethylolpropionic(DMPA) as chain extenders. A kind of automobile interior decoration adhesive was made by the modified hybrid dispersions. Effects of the content and the kinds of epoxide resin on the properties of dispersions and dispersion-cast films such as appearance, pot life, viscosity, particle size, molecular mass, hardness, swelling in water, contact angle, strength of stress, elongation at break, and other mechanical properties were studied. At the same time the effect of the E20 content on the peel strength of the adhesive for several automobile interior decoration substrates such as rubber/wood, poly(vinyl chloride)/wood; leather/wood, sponge/wood was investigated. The experimental results show that when the epoxy resin E20 content was 8%, the modified polyurethane hybrid dispersions possess better properties and the adhesive made by the modified dispersions posses better adhesion for automobile interior decoration substrates. The stress-strain curve of the modified aqueous polyurethane hybrid dispersions films shows the modified aqueous cast films possess better rigidity and toughness.     

Influence of substrate morphology on the cohesion and adhesion of thin PECVD oxide films on semi‐crystalline polymers

The influence of the surface morphology of semi‐crystalline poly(ethylene terephthalate) (PET) and polyamide 12 (PA12) films on the adhesion and cohesion of thin oxide coatings is analysed, with attention paid to the role of spherulites and processing additives. The failure mechanisms of the coating are determined by means of fragmentation tests and the results are modelled using a constant interfacial strength approach with a Weibull‐type probability of fracture. Coating failure is shown to be initiated at defect sites such as pinholes and, in the case of PET, the presence of additives in the superficial layers of the polymer leads to a decrease of the crack onset strain by a factor of 20%. Large spherulitic structures found at the surface of PA12 films are shown to lead to preferential delamination at spherulites boundaries. For the two types of semi‐crystalline polymers, the interfacial shear strength is found to be comparable to the bulk shear strength of the polymer. Copyright © 2003 John Wiley & Sons, Ltd.     

PET表面锐钛矿-板钛矿相TiO2薄膜的制备及表征

利用改进的溶胶-凝胶法在经表面改性的PET(聚对苯二甲酸乙二醇酯)表面制备得到TiO2薄膜. 利用X射线衍射(XRD)、原子力显微镜(AFM)、UV-Vis 透光率曲线、接触角测试仪等测试手段对TiO2样品的性能进行表征.结果表明, PET表面过渡层的引入有效地改善了有机基底与无机薄膜之间的界面相容性, 在其表面形成透明、均一、附着力良好且具有光催化活性的TiO2薄膜.通过控制实验过程, 在低温下成功制备了不同锐钛矿/板钛矿比的TiO2薄膜,同时发现适量板钛矿相的存在能有效提高薄膜的光致亲水性.     

Enhanced super-hydrophobic and switching behavior of ZnO nanostructured surfaces prepared by simple solution--immersion successive ionic layer adsorption and reaction process

A simple and cost-effective successive ionic layer adsorption and reaction (SILAR) method was adopted to fabricate hydrophobic ZnO nanostructured surfaces on transparent indium-tin oxide (ITO), glass and polyethylene terephthalate (PET) substrates. ZnO films deposited on different substrates show hierarchical structures like spindle, flower and spherical shape with diameters ranging from 30 to 300 nm. The photo-induced switching behaviors of ZnO film surfaces between hydrophobic and hydrophilic states were examined by water contact angle and X-ray photoelectron spectroscopy (XPS) analysis. ZnO nanostructured films had contact angles of ~140° and 160°±2 on glass and PET substrates, respectively, exhibiting hydrophobic behavior without any surface modification or treatment. Upon exposure to ultraviolet (UV) illumination, the films showed hydrophilic behavior (contact angle: 15°±2), which upon low thermal stimuli revert back to its original hydrophobic nature. Such reversible and repeatable switching behaviors were observed upon cyclical exposure to ultraviolet radiation. These biomimetic ZnO surfaces exhibit good anti-reflective properties with lower reflectance of 9% for PET substrates. Thus, the present work is significant in terms of its potential application in switching devices, solar coatings and self-cleaning smart windows.     

Determining the contact angle between liquids and cylindrical surfaces

One of the simplest methods of measuring the quantities for estimating the adhesion properties of materials (i.e., the adhesion work, the surface energy, and the interfacial tension between certain liquids and a surface) requires the determination of the contact angle between the liquid and the surface. In the case of plane surfaces the determination of the drop dimensions makes it possible to calculate the contact angle by the sessile drop method, but in the case of cylindrical surfaces (such as the monofilaments), several methods were developed to improve the accuracy of the contact angle measurements. This paper presents a comprehensive method for precise evaluation of the contact angle between liquid drops and monofilaments by establishing a differential equation describing the drop contour. This equation makes it possible to accurately compute the contact angle using the dimensions of the drop. A comparison of the values of the contact angle calculated by our method and those obtained by other approaches is made. We applied our method in the case of polyamide-6 monofilaments treated using dielectric barrier discharge, knowing their medical applications in surgical sutures.     

Surface characteristics of chitin-based shape memory polyurethane elastomers

Shape memory polyurethanes (SMPUs) were prepared from polycaprolactone diol 4000 (PCL 4000), 1,4-butanediol (BDO), chitin, dimethylol propionic acid (DMPA), triethylamine (TEA) and 4,4′-diphenylmethane diisocyanate (MDI), and the structures of the synthesized materials were verified by infrared spectroscopy. The effects of chitin and DMPA contents in the polyurethane formulation on surface properties were investigated. DMPA provides function of making hydrophilic polyurethanes. The crystalline structure of chitin enhanced the hydrophobicity of the synthesized materials. Contact angle, water absorption, surface free energy, work of water adhesion and swelling behavior of the synthesized polyurethanes were affected by varying the DMPA and chitin contents. The interactions of the PU films with solvents on the surface were clearly related to the contents of DMPA and chitin in the final polyurethane formulation.     

Chemical force spectroscopy in heterogeneous systems: intermolecular interactions involving epoxy polymer,mixed monolayers,and polar solvents

We used chemical force microscopy (CFM) to study adhesive forces between surfaces of epoxy resin and self-assembled monolayers (SAMs) capable of hydrogen bonding to different extents. The influence of the liquid medium in which the experiments were carried out was also examined systematically. The molecular character of the tip, polymer, and liquid all influenced the adhesion. Complementary macroscopic contact angle measurements were used to assist in the quantitative interpretation of the CFM data. A direct correlation between surface free energy and adhesion forces was observed in mixed alcohol-water solvents. An increase in surface energy from 2 to 50 mJ/m(2) resulted in an increase in adhesion from 4-8 nN to 150-300 nN for tips with radii of 50-150 nm. The interfacial surface energy for identical nonpolar surface groups of SAMs was found not to exceed 2 mJ/m(2). An analysis of adhesion data suggests that the solvent was fully excluded from the zone of contact between functional groups on the tip and sample. With a nonpolar SAM, the force of adhesion increased monotonically in mixed solvents of higher water content; whereas, with a polar SAM (one having a hydrogen bonding component), higher water content led to decreased adhesion. The intermolecular force components theory was used for the interpretation of adhesion force measurements in polar solvents. Competition between hydrogen bonding within the solvent and hydrogen bonding of surface groups and the solvent was shown to provide the main contribution to adhesion forces. We demonstrate how the trends in the magnitude of the adhesion forces for chemically heterogeneous systems (solvents and surfaces) measured with CFM can be quantitatively rationalized using the surface tension components approach. For epoxy polymer, inelastic deformations also contributed heavily to measured adhesion forces.     

Interfacial tension and wetting behavior of air/oil/ionic liquid systems

We measured the interfacial tension and the density of air/n-hexane, n-decane, 1-perfluorohexane/1-hexyl-3-methyl-imidazolium hexafluorophosphate systems as a function of temperature. From the air/ionic liquid surface tension values, it was suggested that Coulombic interaction between imidazolium cations and counter anions are not so much different between the surface and bulk. The density values indicated that the decrease of surface tension by saturating organics was closely correlated to the mutual solubility between ionic liquid and organics. Interfacial tension at the oil/ionic liquid interfaces suggested that ionic liquid molecules were more ordered at the oil/ionic liquid interfaces compared to the air/ionic liquid interfaces, but the decrease of the entropy due to the interfacial orientation of ionic liquid was compensated by the increase of the entropy due to the contact of different chemical species. The initial spreading coefficients and the Hamaker constants indicated that all the oil phases spread at the air/ionic liquid interfaces spontaneously, and form the complete wetting films.     

Improvement of surface wettability and interfacial adhesion ability of poly(p-phenylene benzobisoxazole) (PBO) fiber by incorporation of 2,5-dihydroxyterephthalic acid (DHTA)

By introducing 2,5-dihydroxyterephthalic acid (DHTA) into poly(p-phenylene benzoxazole) (PBO) macromolecular chains, dihydroxy poly(p-phenylene benzobisoxazole) (DHPBO) was synthesized and then DHPBO fibers were prepared by dry-jet wet-spinning method. Effects of hydroxyl polar groups on surface wettability and interfacial adhesion ability of PBO fiber were investigated. With the incorporation of double hydroxyl polar groups, contact angle on PBO fiber for water can decrease from 71.4° to 50.70°, and contact angle for ethanol can decrease from 37.2° to 27.40°. The wetting time on DHPBO fibers for water can be as short as 650 ms, which is half of that of PBO fibers. The interfacial shearing strength (IFSS) between DHPBO (10% mol content DHTA) fibers and epoxy resin is 18.87 MPa, 92.55% higher than that of PBO fibers. SEM images indicate that the PBO/epoxy composite failure mode may change from fiber/matrix adhesive failure to partially cohesive failure.     

Surface modification and adhesion characteristics of polycarbonate films after graft copolymerization

The surfaces of ozone-pretreated polycarbonate films were subjected to further modification by thermally induced graft copolymerization with acrylic acid (AAc), sodium salt of styrene sulfonic acid (NaSS), N,N-dimethylacrylamide (DMAA), N,N-(dimethylamino)ethyl methacrylate (DMAEMA) and 3-dimethyl(methacryloyl ethyl)-ammonium propanesulfonate (DMAPS) monomers. The structure and composition at the copolymer interface were studied by angle-resolved X-ray photoelectron spectroscopy (XPS). For polycarbonate films with a substantial amount of grafted polymer, the hydrophilic graft penetrates or becomes partially submerged beneath a thin surface layer of dense substrate chains. This microstructure was further supported by the water contact angle measurements. Adhesive-free adhesion studies revealed that the AAc, DMAA or DMAPS graft copolymerized polycarbonate film surface adhered strongly to another similarly modified surface (homo-interface) when brought into direct contact in the presence of water and subsequently dried. The development of the lap shear strength is dependent on the concentration of the surface graft, the microstructure of the grafted surface, the adhesion (drying) time, and the nature of the interfacial interaction. The simultaneous presence of chain entanglement and electrostatic interaction readily results in substantially enhanced adhesion strengths between two DMAPS graft copolymerized surfaces or between an AAc and a DMAA graft copolymerized surface (hetero-interface). XPS analyses of the delaminated surfaces suggest that failure occurred cohesively below the graft-substrate interface. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 357–366, 1998     

PU/PSt型复合乳液粒子热力学平衡形态预测

以水性聚氨酯分散液为种子采用无皂乳液聚合新技术合成出了具有核壳结构的聚氨酯 聚苯乙烯(PU PSt)型复合聚合物乳液 .采用界面张力简化计算方法 ,通过界面自由能变化最小的热力学判据对合成的复合乳液粒子的热力学平衡形态进行了预测 .并利用透射电子显微镜和接触角法测定的膜的表面极性对其进行了证实 .结果表明 ,界面自由能变化的最小判据可以推广到PU PSt体系 ,文中给出的界面张力的简化计算方法是可行的 .     

Hydrophobic Properties of Thin Films of Comb-Shaped Perfluorohexylethyl Methacrylate-Polydimethylsiloxane Copolymers Deposited from Supercritical Carbon Dioxide Solutions

Comb-shaped copolymers of perfluorohexylethyl methacrylate and methacryloxypropyl-terminated polydimethylsiloxane are synthesized by radical polymerization in supercritical carbon dioxide, solubility of the copolymers in supercritical carbon dioxide is studied, and hydrophobic properties of thin films obtained via precipitation of the copolymers from trifluorotrichloroethane and supercritical carbon dioxide solutions on substrates are examined. On the basis of water and dimethyl sulfoxide contact angle measurements, the specific free surface energy of the formed films is calculated. It is shown that the thin films of the copolymers have a lower surface energy and are characterized by a smaller water contact angle hysteresis than the films based on homopolymer poly(perfluorohexylethyl methacrylate). A comparative testing of coatings based on the homopolymer and copolymer deposited from solutions in supercritical carbon dioxide on the surface of nylon fabrics is performed. It is found that copolymer-coated fabrics have on average higher water contact angles.     

Synthesis of a novel polyester-ether copolymer and its derivatives as antistatic additives for thermoplastic films

Development of antistatic thermoplastic elastomer composites is gaining much interest in scientific and industrial aspects. In this contribution, a novel type of polyester-block-ether copolymer (PEBE), PEBE with ionic liquid (PEBE-IL) and quaternized PEBE (PEBE-Q) were synthesized, characterized and compounded with a commercial bottle grade polyester (PET) resin. It was found that the surface resistivity of the PET composite films was around 10⁹–10¹⁰ Ω/sq. The addition of the PEBE copolymers as an antistatic agent into PET matrix resulted in almost 10⁶ times enhancement in surface resistivity compared to neat PET film. Among the PET films with an antistatic agent, it was emphasized that PEBE-IL and ionic liquid doping to PET matrix led to a relatively lower crystallization degree, surface resistivity, contact angle and breaking force with a translucent appearance compared to neat PET film. Furthermore, it was illustrated that antistatic PET films with fine-tune physical, mechanical and morphological properties can be achieved by choosing appropriate antistatic agent type and amount.     

SHAPE MEMORY EFFECT OF PU IONOMERS WITH IONIC GROUPS ON HARD-SEGMENTS

SMPU （shape memory polyurethane） non-ionomers and ionomers, synthesized with poly（c-caprolactone） （PCL）, 4, 4＇-diphenylmethane diisocyanate （MDI）, 1,4-butanediol （BDO）, dimethylolpropionic acid （DMPA） were measured with cyclic tensile test and strain recovery test. The relations between the structure and shape memory effect of these two series were studied with respect to the ionic group content and the effect of neutralization. The resulting data indicate that, with the introduction of asymmetrical extender, the stress at 100% elongation is decreased for PU non-ionomer and ionomer series, especially lowered sharply for non-ionomer series; the fixation ratio of ionomer series is not affected obviously by the ionic group content; the total recovery ratio of ionomer series is decreased greatly. After sufficient relaxation time for samples stretched beforehand, the switching temperature is raised slightly, whereas the recovery ratio measured with strain recovery test method is lowered with increased DMPA content. The characterization with FT-IR, DSC, DMA elucidated that, the ordered hard domain of the two series is disrupted with the introduction of DMPA which causes more hard segments to dissolve in soft phase; ionic groups on hard segment enhance the cohesion between hard segments especially at high ionic group content and significantly facilitate the phase separation compared with the corresponding non-ionomer at moderate ionic group content.     

Wetting of TiC by Al-Cu alloys and interfacial characterization

The wetting behavior and the interfacial reactions that occurred between molten Al-Cu alloys (1, 4, 8, 20, 33, and 100 wt% Cu) and solid TiC substrates were studied by the sessile drop technique in the temperature range of 800-1130 degrees C. The effect of wetting behavior on the interfacial reaction layer was studied. All the Al-Cu alloys react with TiC at the interface forming an extensive reaction layer. The interface thickness varied with the samples, and depends on the temperature, chemical composition of the alloy and the time of the test. Wetting increases with increasing concentration of copper in the Al-Cu alloy at 800 and 900 degrees C. In contrast, at higher temperature such as 1000 degrees C wetting decreases with increasing copper content. The spreading kinetics and the work of adhesion were evaluated. The high values of activation energies indicated that spreading is not a simple viscosity controlled phenomenon but is a chemical reaction process. The spreading of the aluminum drop is observed to occur according to the formation of Al4C3, CuAl2O4, CuAl2, TiCux mainly, leading to a decreases in the contact angle. As the contact angle decreases the work of adhesion increases with increasing temperature. Al-Cu/TiC assemblies showed cohesive fracture corresponding to a strong interface. However, using pure Cu the adhesion work is poor, and the percentage of cohesion work is also too low (27-34%).     

Adhesion plaque formation dynamics between polymer vesicles in the limit of highly concentrated binding sites

This work examines the process of adhesion plaque formation between pairs of copolymer vesicles presenting dense surface concentrations of avidin (NeutrAvidin) and biotin. Micropipet aspiration maintains constant membrane tension, as the low-tension vesicle membrane spreads over a second, more tensed vesicle. Spreading rates near 1 microm/s but as high as 7 microm/s (the adhesion plaque diameter) and contact angle growth rates of 2-14 deg/s are observed. The ultimate contact angles, in the range of 120-140 degrees, are independent of membrane tension and also exceed those previously reported. Adhesion plaque formation occurs in three phases: an initial step in which contact is established, typically lasting from a few seconds to a minute, an abrupt jump into contact in which both vesicles undergo substantial deformation, and a slower continued growth of the contact angle and area. Vesicle pairs are irreversibly bound at the plaque such that attempts to peel them apart cause membrane rupture at critical tensions as high as 4 mN/m, setting a lower bound on the interfacial strength. When the quantity tau(1 - cos theta) (with tau the membrane tension and theta the contact angle) is plotted as a function of time during plaque formation for different values of tau, the curves fail to collapse, indicating the chemical driving force for adhesion greatly exceeds the mechanical resisting tension.     

Surface modification and adhesion improvement of polyester films

Facile surface modification of polyester films was performed via chemical solutions treatment. Surface hydrolysis was carried out by means of sodium hydroxide solutions, leading to the formation of carboxylate groups. Three commercial polyester films of 100 μm in thickness were used in this work: AryLite?, Mylar?, and Teonex?, hydrolysis time being the main modification parameter. FTIR-ATR analysis, topography and contact angle (CA) measurements, surface free energy (SFE) and T-Peel adhesion tests were carried out to characterize the modified films. A quantitative estimate of the carboxylates surface coverage as a function of treatment time was obtained through a supramolecular approach, i.e. the ionic self-assembly of a tetracationic porphyrin chromophore onto the film surface. The surface free energy and critical surface tension of the hydrolyzed polyesters was evaluated by means of Zisman, Saito, Berthelot and Owens-Wendt methods. It was shown that NaOH solution treatment increases roughness, polarity and surface free energy of polymers. As a result, T-Peel strengths for modified Mylar? and Teonex? films were respectively 2.2 and 1.8 times higher than that for the unmodified films, whereas AryLite? adhesion test failed.     

Electroless deposition of nickel on fluoropolymers modified by surface graft copolymerization

Surface modification of Ar plasma-pretreated poly(tetrafluoroethylene) (PTFE) and poly(vinylidene fluoride) (PVDF) films via UV-induced graft copolymerization with 4-vinylpyridine (4VP), 2-vinylpyridine (2VP) or 1-vinylimidazole (VIDz) was carried out. Electroless deposition of nickel could be carried out on these graft-modified fluoropolymer surfaces after PdCl₂ activation. The surface compositions of the graft-modified films were studied by X-ray photoelectron spectroscopy. The adhesion strength between the surface graft-copolymerized fluoropolymer film and the electrolessly deposited nickel was affected by the type of monomers used for graft copolymerization and the graft concentration. The optimum T-peel adhesion strengths of the electrolessly deposited Ni on the 4VP graft-copolymerized PTFE and PVDF surfaces were about 7 and 13 N/cm, respectively. The metal/fluoropolymer assemblies delaminated by cohesive failure inside the fluoropolymer substrates. The enhanced adhesion between the electrolessly deposited Ni and the surface-modified fluoropolymers is attributable to the interfacial charge transfer interactions between the grafted polymer chains and the deposited metals (Pd and Ni), the spatial distribution of the graft chains into the metal matrix and the covalent tethering of the graft chains on the fluoropolymer surface.