Concurrent restructuring and oxidation of the surface of n-hexane plasma polymers during aging in air

Angle-dependent XPS and air/water contact angle (CA) measurements were performed on specimens of n-hexane plasma polymers at various times after fabrication in order to monitor the aging of the surfaces in contact with air. XPS revealed incorporation of oxygen over extended periods of time. The depth distribution of O changed in the course of aging. CAs decreased over the first 3 weeks, then increased again, and finally stabilized at 5 weeks. These results were interpreted in terms of two concurrent processes: spontaneous oxidation (initiated by trapped radicals), which increased the surface polarity, and surface restructuring, which caused the partial removal of polar groups from the interface with air. The former process made a larger contribution to the overall aging of the surfaces but the latter process also contributed measurably. Over the first 3 weeks, oxidation was rapid and surface restructuring was not competitive. Subsequently, the oxygen uptake slowed down markedly, and the outermost surface layers became oxygen depleted relative to the deeper layers, due to partial surface reorientation. The surface topography, assessed by STM, did not change on aging. The aging of n-hexane plasma polymer surfaces thus is due to superimposed effects arising from post-deposition oxidative processes and partial surface reorientation.     

A quantitative model for the surface restructuring of repeatedly plasma treated silicone rubber

Surface restructuring in ambient air of medical grade silicone rubber surfaces modified by repeated RF plasma treatments using various discharge gases including oxygen, argon, carbon dioxide and ammonia, was studied quantitatively. From advancing and receding water contact angle data, the fraction of the surface covered by mobile and immobile polar groups, and a characteristic time constant of the restructuring process were calculated. For argon plasma treated surfaces, the fraction of immobile polar groups increased with repeated plasma treatments, but remained relatively constant for samples repeatedly treated by an ammonia plasma. The use of an oxygen plasma only yielded incorporation of mobile polar groups but not of immobile polar groups. The increase in the restructuring time constants of argon and ammonia plasma treated silicone rubber with the number of plasma treatments suggested enhanced crosslinking of the silicone rubber by these plasmas. In contrast, when an oxygen plasma was repeatedly used, the restructuring time constant decreased suggesting chain cleavage by an oxygen plasma. Tentatively, the carbon dioxide plasma treatment of silicone rubber may initially (up to 3–4 repeated treatments) yield chain cleavage, while the occurrence of crosslinking is indicated after more repetitions.     

Enhancement of OFET performance of semiconducting polymers containing benzodithiophene upon surface treatment with organic silanes

Poly{4,8‐bis(4‐decylphenylethynyl)benzo[1,2‐b:4,5‐b′]dithiophene} ( P1 ) homopolymer and poly{4,8‐bis(4‐decylphenylethynyl)benzo[1,2‐b:4,5‐b′]dithiophene ‐alt‐thiophene} ( P2 ) alternating copolymer have been synthesized by Stille coupling polymerization. The field‐effect mobilities of both polymers were measured on both untreated and silane‐treated OFET devices. Various silanes were selected to allow an incremental increase in the hydrophobicity of the silicon dioxide dielectric. A direct correlation was observed between the hydrophobicity of the silicon dioxide dielectric surface and the enhancement of the field‐effect mobilities. The highest mobilities for both polymers were measured on the OFET devices treated with heptadecafluoro‐1,1,2,2‐tetrahydro‐decyl‐1‐trimethoxysilane (FS) which generated the most hydrophobic surface. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Plasma oxidation of polymers

The rates of plasma oxidation have been measured for homopolymers of several monomers and for copolymers of methyl methacrylate with styrene and vinyl naphthalene. Our results show that relatively small amounts of the aromatic component in the copolymer convey substantially increased resistance to plasma oxidation. Current knowledge of the mechanisms of plasma oxidation is reviewed and new mechanistic explanations are suggested. The implications for improved design of plasma-developable resists systems are considered.A preliminary version of this paper was presented at the Sixth International Symposium on Plasma Chemistry held in Montreal, July, 1983.     

Large-area microwave and radiofrequency plasma etching of polymers

We have investigated O₂/CF₄ plasma etching of five commercial polymers: polyimide, polyamide, polyethylene terephthalate, polycarbonate and cured epoxy resin. A new large-area microwave plasma apparatus has been used in this work, but the same apparatus can also be used as a capacitively coupled radiofrequency (13.56 MHz) discharge reactor. The effect of operating parameters such as pressure, etchant gas composition, excitation frequency and sample temperature upon etch kinetics has been examined. We have observed distinct maxima in the etch rate as functions of pressure and CF₄ concentration. Activation, energies evaluated from the Arrhenius plots fall in the range 0.04-0.2 eV, in agreement with data in the literature. Dry etch susceptibility of a given polymer correlates strongly with the degree of unsaturation in the polymer's structure     

Effect of end‐tethered polymers on surface adhesion of glassy polymers

The adhesion between a glassy polymer melt and substrate is studied in the presence of end‐grafted chains chemically attached to the substrate surface. Extensive molecular dynamics simulations have been carried out to study the effect of the areal density ∑ of tethered chains and tensile pull velocity v on the adhesive failure mechanisms. The initial configurations are generated using a double‐bridging algorithm in which new bonds are formed across a pair of monomers equidistant from their respective free ends. This generates new chain configurations that are substantially different than the original two chains such that the systems can be equilibrated in a reasonable amount of cpu time. At the slowest tensile pull velocity studied, a crossover from chain scission to crazing is observed as the coverage increases, while for very large pull velocity, only chain scission is observed. As the coverage increases, the sections of the tethered chains pulled out from the interface form the fibrils of a craze that are strong enough to suppress chain scission, resulting in cohesive rather than adhesive failure. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 199–208, 2004     

Analyzing the surface properties of acrylic-based water-soluble polymers

The surface properties of newly synthesized N-methoxy isopropyl acrylamide, N-methoxy isopropyl methacrylamide, cyclo propyl acrylamide, and cyclo propyl methacrylamide polymers were investigated using inverse gas chromatography. The highest dispersive component of the surface energy value was obtained for cyclo propyl methacrylamide at 30°C. The values obtained for all polymers were decreasing with the increasing temperature. The values obtained for the acidic and the basic parameters revealed strong basic characters for the surface of N-methoxy isopropyl methacrylamide and cyclo propyl methacrylamide polymers and weak basic characters for the surface of N-methoxy isopropyl acrylamide and cyclo propyl acrylamide polymers.     

A multi-technique study of the spontaneous oxidation of N-hexane plasma polymers

Long-term compositional changes were observed when n-hexane plasma polymers were stored in air at ambient temperature. These post-deposition changes were monitored over periods exceeding one year using XPS, grazing angle FTIR, and SEM. A rapid initial increase in the oxygen content was followed by a slower oxygen uptake, which continued for many months. In contrast to the reported autocatalytic acceleration of the oxidation of polyolefins, the rate of oxidation of n-hexane plasma polymers was found to decrease continuously, and it did not proceed to the same extent toward higher oxidation states. The plasma polymer coatings did not show physical manifestations of oxidative degradation such as cracking, reduction in thickness, or loss of physical integrity. Comparison of the XPS and FTIR data suggested that the top few nanometers of the plasma polymer coatings oxidized at a faster rate than the “bulk.” The experimental data were interpreted using a model comprising reactions known from the oxidative degradation of polyolefins: carbon-centered radicals, trapped in the course of the plasma deposition, combine with atmospheric oxygen to form metastable peroxy radicals and hydroperoxides, which decompose to generate a variety of stable product groups such as hydroxyl, carbonyl, and carboxylic groups. There was broad agreement between the XPS data and the time dependence of particular species in model calculations. © 1994 John Wiley & Sons, Inc.     

Plasma polymerization in the design of new materials: looking through the lens of maleic anhydride plasma polymers

Plasma polymerization is a well-established process for the deposition of thin polymeric films on various types of substrates. The potential of this technique for promoting changes of substrate’s wettability constitutes one of the most basic and often reported applications. However, as novel technological demands emerge, and with it the range of available characterizations, plasma polymers are having their niche of applications and properties expanded. The properties of these materials are commonly tailored through the variation of polymer chemistry, postfunctionalization, or other post-treatment processes. That chemical versatility allows the use of plasma polymers in adhesives, water treatment, biomedicine, and many other fields. The creation of nanostructures via lithography or during the deposition process itself constitutes other dynamic fields for new plasma polymer materials. In the current review, the design of materials through plasma polymerization is addressed with the direction given by our expertise in maleic anhydride plasma polymers (MAPP). A non-exhaustive number of applications of plasma polymers is provided to non-specialists as an overview of the materials coming out from the field of this chemical-vapor deposition process. A complete analysis of the literature on maleic anhydride plasma polymers is also performed.     

An in situ STM study on the long-range surface restructuring of Au(1 1 1) in a non-chloroaluminumated ionic liquid

We report an in situ STM study of a potential-dependent long-range surface restructuring of Au(1 1 1) electrode in neat 1-butyl-3-methylimidazolium tetrafluoroborates (BMIBF₄) ionic liquid. Au(1 1 1) undergoes a significant long-range surface restructuring upon cathodic excursion to −1.0 V vs. Pt quasi-reference. The restructuring involves the formation of tiny pits, which then develops into a stable worm-like network with an average width of the network grids 2 nm. Electrochemical annealing occurs at the cathodic limit with the presence of a reduction product of cation BMI⁺. A smooth surface is recovered with the appearance of the typical (√3 × 22) reconstruction of Au(1 1 1). The surface restructuring is reestablished upon anodic excursion to −1.3 V after the adsorbed reduction product is oxidized. The long-range surface restructuring phenomenon is tentatively explained as a result of partial charge transfer to the weakly adsorbed BMI⁺, which reduces the metal–metal cohesive energy. In addition, the synergetic effect of the counter anion BF₄⁻ may also be involved. The results provide a knowledge of Au(1 1 1) electrode behavior in the neat ionic liquid and are beneficial to understanding in situ STM results involving surface morphological changes in such a media.     

New simple method of measuring the surface glass transition temperature of polymers

A lap‐shear joint mechanical testing method has been probed to measure the surface glass transition temperature (T) of the thick bulk films of high‐molecular‐weight polymers. As T, the temperature transition “occurrence of autoadhesion–nonoccurrence of autoadhesion” has been proposed. The influence of chain flexibility, of molecular architecture, of polymer morphology, and of chain ends concentration on the T has been investigated. The correlation between the reduction in T with respect to the glass transition temperature of the bulk (T) and the intensity of the intermolecular interaction in the polymer bulk in amorphous polymers has been found. The effect of surface roughness on T has been discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2012–2021, 2010     

A novel method to introduce durable hydrophilicity onto hydrophobic polymer surface by plasma treatment

We have examined a novel method to fabricate a durable hydrophilic surface of hydrophobic polymeric materials modified by plasma treatment. The method involves a trapping of maleic anhydride-containing polymer onto poly(ethylene naphthalate) (PEN) by a plasma-induced crosslinking reaction of PEN followed by hydrolysis of maleic anhydride moiety to generate hydrophilic carboxyl groups on the PEN surface. In fact, the PEN film surface thus treated has shown an effective stability of wettability based on the water contact angle measurement.     

Synthesis and applications of polymers containing metallacyclopentadiene moieties in the main chain

Organometallic polymers containing metallacycles in the main chain were prepared by the reactions of diynes with low-valent organometallic complexes such as CpCo(PPh₃)₂, CP₂Ti(CH₂=CHC₂H₅), and (ⁱPrO)₂Ti(CH₂=CHCH₃). Their polymer reactions involving the conversion of the main chain structures gave rise to polymers containing functional groups in their main chain repeating units. Design and synthesis of organometallic polymers that potentially serve as novel functional materials are also described.     

Preparation of a superhydrophobic rough surface

The relationship between the contact angles, surface tension, and surface roughness is reviewed. Numerical formulas related to the superhydrophobic rough surfaces of polymers are predicted with two approaches, the Wenzel and Cassie–Baxter models. With these models as a guide, an artificial superhydrophobic surface is created. Rough nylon surfaces mimicking the lotus leaf are created by the coating of a polyester surface with nylon‐6,6 short fibers via the flocking process. Poly(acrylic acid) chains aregrafted onto nylon‐6,6 surfaces, and this is followed by the grafting of 1H,1H‐perfluorooctylamine onto the poly(acrylic acid) chains. Water contact angles as high as 178° are achieved. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 253–261, 2007.     

Analytical solutions to mathematical models of the surface and bulk erosion of solid polymers

The process by which polymeric materials hydrolyze and disappear into their environments is often called erosion. Two types of erosion have been defined according to how the hydrolysis takes place. If hydrolysis occurs throughout the entire specimen at the same time, it is called bulk erosion. If the hydrolysis is mainly confined to a region near the surface of the specimen and the surface continuously degrades by moving inward, it is termed surface erosion. In this article, a kinetic relationship for bulk erosion is developed. This relationship provides a method for estimating the hydrolysis kinetic constants for bulk‐eroding polymers. This same relationship is also applicable to surface erosion at a microscopic level. Through its combination with a diffusion–reaction equation and the provision of moving boundary conditions, an analytical solution to the steady‐state surface‐erosion problem is obtained. The erosion rate, erosion front width, and induction time can all be expressed as simple functions of the rate of polymer bond hydrolysis, water diffusivity, and solubility, plus other parameters that can be experimentally determined. The erosion front width is the product of the induction time and the erosion rate. The ratio of the erosion front width to the polymer specimen thickness is a parameter that determines whether the specimen undergoes surface or bulk erosion. Theoretical results are compared with experimental observations from the literature, and agreement is found. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 383–397, 2005     

Condensation polymers containing silicon and germanium in the main chain

Poly(carbonates), poly(thiocarbonates) and poly(esteres) containing silicon and/or germanium in the main chain were obtained under phase transfer conditions. Polymers were synthesized in a biphasic system NaOH/CH₂Cl₂ at 20°C using several phase transfer catalysts, and characterized by IR and ¹H and ¹³C NMR. The results were evaluated by the yields and the inherent viscosity values. The process was effective observing an increase of both parameters in comparison with the essays without catalyst. The increases depended of the nature of the polymer and the catalyst. In poly(ester) synthesis there was an increase of these parameters when the NaOH concentration was increased due to a salting out effect of the diphenolate from the aqueous phase to the organic one. Also poly(amides) containing silicon or germanium were synthesized by solution polymerization.     

多层碳纳米球的研究

用弧光放电法制备了碳的巴基葱.用原子力显微镜（AFM）、扫描隧道显微镜（STM）和透射电镜（TEM）研究了在高定向石墨(HOPG)和金(Au)基底上的巴基葱的行为和电学特性.扫描隧道谱表明,巴基葱的电学特性具有与单壁碳纳米管相似的非线性特性.较小尺寸的巴基葱呈半导体特性,尺寸增大倾向金属线性.AFM/STM图像显示,在HOPG和Au基底上的巴基葱能够聚集成二聚体.利用较小尺寸巴基葱的电学非线性特性,有希望构造纳米电子学的单电子器件.     

Synthesis and optoelectronic properties of novel benzodifuran semiconducting polymers

Two new semiconducting polymers poly{4,8‐bis(4‐decylphenylethynyl)benzo[1,2‐b:4,5‐b′]difuran} ( P1 ) and poly {4,8‐bis(4‐decylphenylethynyl)benzo[1,2‐b:4,5‐b′]difuran‐alt‐4,8‐bis(4‐decylphenylethynyl)benzo[1,2‐b:4,5‐b′]dithiophene} ( P2 ) have been synthesized. These polymers were tested in bulk heterojunction solar cells yielding power conversion efficiencies of 1.19% for P1 and 0.79% for P2 . The surface morphology of the solar cell devices indicated that both the polymers display a granular morphology with smoother films displaying higher power conversion efficiencies. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012