Surface chemistry and optical property of TiO2 thin films treated by low-pressure plasma

The low temperature RF plasma treatment was used to control the surface chemistry and optical property of TiO₂ thin films deposited by RF magnetron sputtering with a very good uniformity at 300 °C substrate heating temperature. The XRD pattern indicates the crystalline structure of the film could be associated to amorphous structure of TiO₂ in thin film. The plasma treatment of TiO₂ film can increase the proportion of Ti³⁺ in Ti2p and decrease in carbon atoms as alcohol/ether group in C1s at the surface. The optical transmittance of the film was enhanced by 50% after the plasma treatment. The surface structure and morphology remain the same for untreated and low-pressure plasma-treated films. Therefore, increase in the optical transmission could be due to change in surface chemistry and surface cleaning by plasma treatment.     

Synthesis and properties of polyimide/silver nanocomposite containing dibenzalacetone moiety in the main chain

A new thermally stable polyimide–silver nanocomposite containing dibenzalacetone moiety in the main chain was synthesized by a convenient ultraviolet irradiation technique. A precursor such as AgNO₃ was used as the source of the silver nanoparticles. Polyimide 6 as a source of polymer was prepared by polycondensation reaction of 2,5-bis(4-aminobenzylidene) cyclopentanone 4 with pyromellitic anhydride 5 in m-cresol solution and in the presence of iso-quinoline as a base. The resulting nanocomposite film was characterized by FTIR spectroscopy, X-ray diffraction (XRD), Scanning electron microscopy (SEM), Thermal gravimetric analyses (TGA), differential gravimetric analyses (DTG) and differential scanning calorimetry (DSC). Scanning electron microscopy (SEM) confirmed the formation and dispersion of silver nanoparticles in polymer matrix having average size of ～20 nm. Incorporation of inorganic metal silver nanoparticles has improved the thermal behavior of the nanocomposite film as compared to pure polyimide film. Also 2,5-bis(4-aminobenzylidene) cyclopentanone 4 was synthesized by using a two-step reaction.     

Preparation and Characterization of Chitosan-Coated DBD Plasma-Treated Natural Rubber Latex Medical Surgical Gloves with Antibacterial Activities

The natural rubber latex (NRL) film taken from medical surgical gloves was surface-modified with a dielectric barrier discharge (DBD) plasma treatment under an air environment. The results showed that surface hydrophilicity of the NRL film increased after the plasma treatment due to the presence of oxygen-containing polar groups on the plasma-treated surface. An increase in plasma treatment time increased the surface roughness of the NRL film, and eventually decreased the mechanical properties. From the obtained results, the optimum plasma treatment time of 20?s was chosen. After immersion in a chitosan solution, the amount of chitosan deposited on the plasma-treated NRL film increased with increasing chitosan concentrations. The chitosan coating smoothed the surface of the plasma-treated NRL film and also improved the mechanical properties. The highest antibacterial activities of the chitosan-coated DBD plasma-treated NRL film against both Staphylococcus aureus and Escherichia coli were achieved when a 2?%(w/v) chitosan solution was used for the coating.     

Surface sol–gel synthesis of silica films on polyimide substrate

Silica films were grown on polyimide substrate using surface sol–gel reaction, and the film growth process was characterized by ellipsometry, atomic force microscopy, and X-ray photoelectron spectroscopy. On the activated polyimide surface, silica film was grown by sequential immersion in SiCl₄ solution and H₂O. The thickness of silica films is linear with the depositing cycle, about 5.0 nm per cycle. The silica films present an island-like growth type and are not a strict equilibrium SiO₂ structure. Moreover, the result of the tensile test suggests that the silica films have a good adhesion to the polyimide substrate.     

Preparation and properties of a high temperature, flexible and colorless ITO coated polyimide substrate

A new high temperature, flexible and colorless indium-tin-oxide (ITO) coated plastic substrate has been prepared from a thermally stable, high glass transition temperature (T_g) and colorless polyimide film. The polyimide was synthesized from 3,3′-diaminodiphenylsulfone (3,3′-DDS) and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) monomers. Its heat distortion temperature was 278 °C. The ITO was deposited on the polyimide film using the magnetron-sputtering process. After annealing at 250 °C under nitrogen for 1 h, the resistivity of the ITO film was 4.0 × 10⁻⁴ Ω cm, and its transmittance was 83.5%. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were used to observe the surface and morphology of the ITO film. UV-visible spectroscopy and the four-probe method were used to study their optical and electrical properties. The high performance ITO-plastic substrate can be used in the next generation flat panel displays.     

Mechanical properties of BPDA-ODA polyimide fibers

An aromatic polyimide was synthesized via a one-step polycondensation reaction between biphenyltetracarboxylic dianhydride (BPDA) and 4,4′-oxydianiline (ODA) in p-chlorophenol. The polyimide (BPDA-ODA) solution dopes were spun into fibers by means of dry-jet wet spinning. The as-spun fibers were drawn and treated in heating tubes for improving the mechanical properties. The thermal treatment on the fibers resulted in a relatively high tensile strength and modulus. Thermal mechanical analysis (TMA) was employed to study the linear coefficient of thermal expansion (CTE). Thermal gravimetry analysis (TGA) spectra showed that the BPDA-ODA fibers possessed an excellent property of thermo-oxidative degradation resistance. The sonic modulus E_s of the polyimide fibers was measured.     

Effect of atmospheric-pressure plasma on adhesion characteristics of polyimide film

In this work, the effect of atmospheric-pressure plasma treatments on surface properties of polyimide film are investigated in terms of X-ray photoelectron spectroscopy (XPS), contact angles, and atomic force microscopy (AFM). The adhesion characteristics of the film are also studied in the peel strengths of polyimide/copper film. As experimental results, the polyimide surfaces treated by plasma lead to an increase of oxygen-containing functional groups or the polar component of the surface free energy, resulting in improving the adhesion characteristics of the polyimide/copper foil. Also, the roughness of the film surfaces, confirmed by AFM observation, is largely increased. These results can be explained by the fact that the atmospheric-pressure plasma treatment of polyimide surface yields several oxygen complexes in hydrophobic surfaces, which can play an important role in increasing the surface polarity, wettability, and the adhesion characteristics of the polyimide/copper system.     

Thermal degradation kinetics of polyimide containing 2,6-benzobisoxazole units

A novel polyimide (PI) based on 2,6-bis(p-aminophenyl)-benzo[1,2-d;5,4-d′]bisoxazole has been synthesized via a conventional two-stage procedure with bis(ether anhydrides) (HQDPA). The intermediate poly(amic acid) had inherent viscosities of 1.70 dl/g and could be thermally converted into light yellow polyimide film. The resulted polyimide showed excellent thermal stability, and the glass transition temperatures (T_g) were above 283 °C, the 5% weight loss temperature of the polymer was at 572 °C in N₂. The thermal degradation of the polyimide was studied by thermogravimetric analysis (TGA) in order to determine the actual reaction mechanisms of the decomposition process. The activation energy of the solid-state process was determined using Flynn-Wall-Ozawa method, which does not require knowledge of the reaction mechanism, which resulted to be 361.36 kJ/mol. The activation energy of different mechanism models and pre-exponential factor (A) were determined by Coats-Redfern method. Compared with the value obtained from the Ozawa method, the actual reaction mechanism obeyed nucleation and growth model, Avrami-Erofeev function (A₃) with integral form g(X) = [−ln(1−X)]³.     

Preparation, morphology and properties of nano-sized Al2O3/polyimide hybrid films

Nano-sized Al₂O₃/polyimide (PI) hybrid films based on 4,4′-oxydianiline (ODA) and pyromellitic dianhydride (PMDA) were prepared by incorporation with different content of nano-sized Al₂O₃ via in situ polymerization. The TEM and SEM micrographs indicated that the Al₂O₃ particles were homogenously dispersed in the polyimide matrix by means of the ultrasonic treatment and the addition of coupling agent. The mechanical properties and thermal stability of the pure PI film can be improved by adequate addition of Al₂O₃. The PI hybrid film was strengthened and toughened simultaneously by the introduction of the well-dispersed Al₂O₃ particles. The PI hybrid films showed improved electrical aging performance as compared with pure PI film. Especially, the PI hybrid films with 10 wt.% of Al₂O₃ content exhibited obviously enhanced electrical aging performance with the time to failure of 3.4 times longer than that of pure PI film. The improved electrical aging performance of the hybrid film was attributed to the nano-sized Al₂O₃ particles highly dispersed in the hybrid film, which confirmed by the investigation of the morphology and the surface composition of PI hybrid film before and after electrical aging.     

Multi-step surface functionalization of polyimide based evanescent wave photonic biosensors and application for DNA hybridization by Mach-Zehnder interferometer

The process of surface functionalization involving silanization, biotinylation and streptavidin bonding as platform for biospecific ligand immobilization was optimized for thin film polyimide spin-coated silicon wafers, of which the polyimide film serves as a wave guiding layer in evanescent wave photonic biosensors. This type of optical sensors make great demands on the materials involved as well as on the layer properties, such as the optical quality, the layer thickness and the surface roughness. In this work we realized the binding of a 3-mercaptopropyl trimethoxysilane on an oxygen plasma activated polyimide surface followed by subsequent derivatization of the reactive thiol groups with maleimide-PEG₂-biotin and immobilization of streptavidin. The progress of the functionalization was monitored by using different fluorescence labels for optimization of the chemical derivatization steps. Further, X-ray photoelectron spectroscopy and atomic force microscopy were utilized for the characterization of the modified surface. These established analytical methods allowed to derive information like chemical composition of the surface, surface coverage with immobilized streptavidin, as well as parameters of the surface roughness. The proposed functionalization protocol furnished a surface density of 144 fmol mm⁻² streptavidin with good reproducibility (13.9% RSD, n = 10) and without inflicted damage to the surface. This surface modification was applied to polyimide based Mach-Zehnder interferometer sensors to realize a real-time measurement of streptavidin binding validating the functionality of the MZI biosensor. Subsequently, this streptavidin surface was employed to immobilize biotinylated single-stranded DNA and utilized for monitoring of selective DNA hybridization. These proved the usability of polyimide based evanescent photonic devices for biosensing application.     

PREPARATION OF POLYIMIDE-BaTiO3 HYBRID FILMS BY A DISPERSION PROCESS AND THEIR MICROSTRUCTURE*

 Barium titanate (BaTiO₃) powders with particle sizes of 30～50 nm were prepared from barium stearate, titanium alkoxides and stearic acid by stearic acid-gel method. Dispersing the agglomerate of BaTiO₃ nanoparticles into poly(amic acid) solution followed by curing led to the formation of polyimide hybrid films. The hybrid films were transparent and well distributed with BaTiO3 nanoparticles when the BaTiO₃ content was less than 1 wt%. Highly loaded hybrid film containing 30 wt % BaTiO₃ was tough, had a smooth surface and possessed much higher dielectric and piezoelectric constants than the parent polyimide.     

High performance polymer films 4. Mechanical behavior

Tensile properties of the polyimide and copolyimide films based on two dianhydrides, pyromellitic dianhydride (PMDA) and 3,3^′,4,4^′-benzophenonetetracarboxylic dianhydride (BTDA) and two diamines, 4,4^′-oxydianiline (ODA), and a proprietary aromatic diamine (PD) have been described. The tensile strength of the films containing higher proportions of BTDA or PMDA and PD is much higher (except the fully rigid film based on PMDA-PD which is brittle in nature) than the films containing higher proportion of ODA moiety. The films containing PD as the diamine moiety exhibit high initial moduli than the films containing exclusively or mainly ODA as the diamine moiety. The films having higher concentration of the -O- linkage originated from diamine ODA are found to exhibit higher elongation values. There is found to be no direct correlation between η_inh of the precursor casting solutions and mechanical properties of structurally different polyimide/copolyimide films. For a particular polyimide or copolyimide film, the tensile strength value is found to be less sensitive than the elongation to the variation of η_inh value of the precursor poly(amic acid) or copoly(amic acid). Tensile strength and elongation of the film, basically rigid in nature, may be improved by post-curing at 360°C/370°C. While Kapton H film retains 78% and 63.5% of its tensile strength and % elongation at break (% E_b) respectively after hot-wet mechanical test, the film based on BTDA 80, PMDA 20 and PD shows an increase of about 27% and 22% in its tensile strength and % E_b respectively.     

Gold particles containing plasma-polymerized styrene as an X-ray absorber

Gold particles containing plasma-polymerized styrene film were formed simultaneously by plasma polymerization and evaporation using an inductively coupled argon gas flow type reactor. Gold was used as the evaporated metal and styrene as the monomer. The plasma etching characteristics of the film were evaluated by O₂ and CO₂ plasmas using a reactor with parallel-plate electrodes. A structure of lines and spaces of 4m width was successfully fabricated in the film on Si wafer by CO₂ plasma etching through a mask pattern of plasma-polymerized resist. A self-developed pattern was obtained through the X-ray mask with polyimide substrate by synchrotron radiation. The molecular structure and atomic composition of the film were investigated by ESCA and TEM.     

Photoreactive fluorinated polyimide protected by a tetrahydropyranyl group (THP) based on photo-induced acidolysis

A polyimide (6F-THP) with a tetrahydropyranyl group (THP) in its side chain has been synthesized. The THP group exhibits a high acidolysis rate in this polymer's film. This rate was faster than that of a tertbutoxycarbonyl group (t-BOC), which has been previously reported [1]. Furthermore, the deprotected fluorinated polyimide (6FDA-AHHFP) became soluble in an aqueous base due to the presence of a hydroxyl group attached to the phenyl group of the diamine segment. The polyimide thus provides high performance as a photopolymer when used in conjunction with a photoacid generator after the post-exposure baking process (PEB). The photoacid generators used in this study were p-nitrobenzyl-9,10-dimethoxyanthoracene-2-sulfonate (NBAS) and diphenyliodonium-9,10-dimethoxyanthoracene-2-sulfonate (DIAS). The quantum yields of photodissociation and photoacid generation were also measured. The photoacid-generating quantum yields closely corresponded to the photosensitivities of the photoreactive polyimide system. It was confirmed that the THP group was easily deprotected even in the 6F-THP film with p-toluenesulfonic acid as a model acid catalyst. The activation energy of the THP deprotection reaction was determined to be 12.8 kcal/mol (19.5 kcal/mol in the case of t-BOC). The relationships between the THP deprotecting rate constant (k_d) and acid molecular size and between k_d and polyimide structure were further investigated.     

Preparation and adhesion of ultrathin polyimide films on polycrystalline silver

4.4-oxydianiline (ODA) and 1,2,3,5-benzenetetracarboxylic anhydride (PMDA) were deposited from the vapor phase onto a polycrystalline silver substrate and polymerization of the two components to form ultrathin polyimide films (d≈ 11 Å) was followed by X-ray photoelectron spectroscopy. Both PMDA and ODA chemisorb on the clean surface under partial fragmentation. Co-deposition of ODA and PMDA followed by heating of the substrate led to formation of thermally stable (T<450°C) polyimide films. Our data indicate that adhesion of the polyimide film to the surface involves chemical bonding to fragmented PMDA and/or ODA chemisorbed on the substrate. Our experiments show that polyimide films can be prepared sufficiently thin to allow the application of surface sensitive techniques to probe the substrate-polymer interface and to study the basic physics and chemistry of adhesion.     

Design and synthesis of novel perfluoroalkyl-containing zinc pyrithione biocide

Novel perfluoroalkyl-containing zinc pyrithione biocide 2 was designed and synthesized in six steps. Reaction of 4-methyl-pyridine with C₈F₁₇(CH₂)₃I in the presence of LDA followed by further oxidization of the resultant pyridine derivative 6 gave the pyridine N-oxide 9. Treatment of 9 with phosphorous oxychloride afforded the desirable chloride 12. Oxidization of compound 12 with H₂O₂ gave N-oxide 14, which was treated with NaSH to give the sulfide 3. Finally, treatment of compound 3 with NaOH/ZnSO₄ smoothly delivered perfluoroalkyl-containing zinc pyrithione biocide 2 in good yield.     

Silver nanoparticles dispersed in electrospun polyacrylonitrile nanofibers via chemical reduction

Silver (Ag) nanoparticles were prepared in PAN nanofibrous film by a sol–gel derived electrospinning and subsequent chemical reduction for 30 min in hydrazine hydroxide (N₂H₅OH) aqueous solution. Antimicrobial properties of the AgNO₃/PAN precursor solution against gram positive Staphylococcus aureus ATCC 6538 and gram negative Escherichia coli ATCC 25922 were investigated. The formation of clear zone suggested that the PAN solution containing Ag⁺ ions were effective on the inhibition of bacterial growth. The Ag/PAN nanocomposite film, characterized by XRD, TEM and UV absorption spectrophotometer, revealed that highly crystallized cubic Ag particles with diameters of less than 5.8 nm were dispersed homogeneously in PAN nanofibers.     

The effect of the change in the microscopic structures of the iron on corrosion resistance and passivated properties

The passive film of iron showed n‐type semiconductor characteristic in borate buffer solution, and its donor concentration increased slightly after tensile strain in the present study. However, comparing with solution‐annealed sample, the anodic passive film formed on tensile‐strained one was highly protective. The more dislocations on tensile‐strained sample promoted the diffusion of iron and oxygen vacancy. Moreover, more donor density (mainly oxygen vacancies) promoted the diffusion of oxygen. They all facilitated tensile‐strained sample to form Fe₂O₃ and thicker passive film on the surface. More Fe₂O₃ and thicker passive film on the surface of tensile‐strained iron could improve corrosion resistance. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and characterization of novel hyperbranched poly(imide silsesquioxane) membranes

A new family of hyperbranched polymers with chemical bonds between the hyperbranched polyimide and polysilsesquioxane network was synthesized by the reaction of an amine‐terminated aromatic hyperbranched polyimide with 3‐glycidoxypropyl trimethoxysilane, followed by hydrolysis and polycondensation in the presence of an acid catalyst. The hyperbranched poly(imide silsesquioxane) membranes were fabricated by the casting the aforementioned polymer solution onto a NaCl optical flat, which was followed by heating at 80 °C for 24 h. The membranes were characterized by Fourier transform infrared, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy, N₂ adsorption and desorption, and CO₂ adsorption and desorption. The presence of covalent bonds between the hyperbranched polyimide and polysilsesquioxane segments had a significant effect on the properties of the membranes. N₂ adsorption–desorption isotherms for these membranes showed surface areas of 6–16 m²/g, whereas CO₂ adsorption–desorption isotherms showed much higher surface areas in the range of 106–127 m²/g. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3736–3743, 2003     

Effect of Low Temperature Air Plasma Treatment on Wetting and Flow Properties of Kaolinite Powders

It was found in this study that the air plasma treatment of particular kaolinite has led to the change of its wettability, which was reflected in the decreased values of water contact angles of wetting from 88.7° for virgin kaolinite to 86.3° for 30?min air plasma treated one. Plasma treated samples show higher average surface energies in the wide range of coverage regimes in comparison to the virgin samples as determined by inverse gas chromatography. Results of these measurements confirmed our assumption, that air plasma treatment activates surface energy of the crystal planes of the kaolinite as reflected in the broadened dispersive surface energy distribution after 10?min treatment time. However with prolonged 30?min treatment time the dispersive surface energy distribution profile was decreased. We assume, that the latter decrease reflects the distorsion of the crystal lattice of the kaolinite as confirmed by FTIR analysis as reflected in changes of Si?CO?CSi and Al₂O?CH characteristic absorption bands. Calculated dispersive surface free energy for 24?% surface coverage was increased from original 35?mJ/m² to 40.3 and 40.8?mJ/m² for 10 and 30?min treatment times. There were determined yield locus and flow function dependencies at different stress levels for virgin and different time plasma treated samples (flow index??ff _c , effective angle of internal friction???? _e , unconfined yield strength???? _c ). It was found that by plasma treatment the character of the flow was shifting from region of very cohesive (ff _c ?=?2.39) to the cohesive (ff _c ?=?3.19). For untreated samples effective angle of internal friction was decreased with increasing applied consolidation stress, while for plasma treated kaolinite it was increased.