Enhancement of wettability in low density polyethylene films using low pressure glow discharge N2 plasma

Low pressure glow discharge nitrogen plasma has been used to improve wettability in a low density polyethylene (LDPE) film for technical applications. The plasma treatment was carried out at a power of 300 W for different exposure times in the 1–20 min range. Wettability changes were analyzed using contact angle measurements. In addition to this, plasma‐treated samples were subjected to an aging process to determine the durability of the plasma treatment. X‐ray photoelectron spectroscopy, atomic force microscopy, and scanning electron microscopy were used for surface characterization. The nitrogen plasma treatment considerably reduced contact angle values thus indicating an increase in surface wettability. The spectroscopic study showed presence of oxygen‐based species on the plasma‐treated samples, which are mainly generated after the plasma treatment as a consequence of air exposure. These polar species contribute to improve surface functionalization, but this is almost lost during aging due to the hydrophobic recovery process. Microscopic studies revealed that also small changes in surface roughness occurred during the plasma treatment but these are very low compared to surface activation. The results confirmed that low pressure nitrogen can be considered as an environmentally efficient process to improve wettability in low density polyethylene films. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2390–2399, 2007     

Ultraviolet grafting of methacrylic acid and acrylic acid on high‐density polyethylene in different solvents and the wettability of grafted high‐density polyethylene. I. Grafting

Methacrylic acid (MAA) and acrylic acid (AA) were grafted onto high‐density polyethylene (PE) with UV initiation and a range of solvents. With acetone as the solvent, MAA was more easily grafted onto PE when the photoinitiator benzophenone was precoated on PE than when it was dissolved in the monomer solution. The grafting was faster in aliphatic solvents than in polar solvents or a UV‐adsorbing aromatic solvent (toluene). Acetone itself could initiate the photografting of both MAA and AA onto PE when it was mixed with water. The extent of grafting of MAA onto PE showed a maximum when there was about 40% acetone in the mixture. For AA, when the acetone/water concentration was 10%, the extent of grafting increased rapidly with the irradiation time. At higher acetone concentrations, the extent of grafting was low. Atomic force microscopy images showed that the surface topography of PE grafted with MAA in acetone/water was quite different from that obtained when the grafting was performed in other organic solvents. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 253–262, 2004     

Atomic force microscopy of extended-chain crystals of polyethylene

Extended-chain crystals of polyethylene grown at elevated pressure and temperature were analyzed for the first time by atomic force microscopy. It was possible to compare the typical fracture surface striation features with those obtained earlier by electron microscopy. High resolution atomic force microscopy on flat surfaces enabled the recording of an atomic scale regularity that could not be fully indentified. © 1993 John Wiley & Sons, Inc.     

Atomic force microscopy observations of the structural development during the uniaxial stretching of crosslinked low-density polyethylene in partial and fully molten states

The effect of uniaxial deformation in partially and fully molten states on the morphology of crosslinked low-density polyethylene has been investigated. At low temperatures, the morphology is predominantly fibrillar, with little kebabs appearing on the fibril surfaces. As the deformation temperature is increased into the melting range, the shish density decreases, and overgrowths of kebabs on the fibrils concurrently increase in length. This gives rise to added twisting of the kebabs reflected in the orientation factor analysis. This shish/twisted lamellar kebab texture is observed only in a partially molten state. Studies in a substantially molten state indicate the absence of shish, althugh short lamellae are observed that are oriented in the transverse direction. This morphology indicates a high chain orientation factor as a result of short lamellae that exhibit small twisting similar to Matsumura's rod model. The absence of shishes in the final films stretched isothermally in a substantially molten stage agrees with Schultz's model, in which imperfectly formed shishes dissolve if they are not stabilized by rapid cooling, as is the case in these studies. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2228–2237, 2004     

Stretched polymer surfaces: Atomic force microscopy measurement of the surface deformation and surface elastic properties of stretched polyethylene

The surface structure and surface mechanical properties of low‐ and high‐density polyethylene were characterized by atomic force microscopy (AFM) as the polymers were stretched. The surfaces of both materials roughened as they were stretched. The roughening effect is attributed to deformation of nodular structures, related to bulk spherulites, at the surface. The surface‐roughening effect is completely reversible at tensile strains in the elastic regime and partially reversible at tensile strains in the plastic regime until the polymers are irreversibly drawn into fibers. AFM force versus distance interaction curves, used to measure changes in the stiffness of the surface and the surface elastic modulus as a function of elongation, show that the surfaces become softer as the polymers are drawn into fibers at high strains. At low elastic strains, however, the surface elastic modulus of HDPE increases—attributed to elastic energy stored by the amorphous regions. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2263–2274, 2001     

The AFM observation of linear chain and crystalline conformations of ultrahigh molecular weight polyethylene molecules on mica and graphite

Atomic force microscopy (AFM) has been applied to visualize expanded linear chain and compact crystalline conformations of ultrahigh molecular weight polyethylene (PE) molecules deposited on mica and graphite from diluted solutions at elevated temperatures. Isolated PE chains are visualized on mica with the apparent negative AFM height and the contour length much shorter than the molecular length. The chain conformations have both the kinked random‐coil sites and the sites of the unexpectedly large two‐dimensional expansion. The crystalline conformations on mica are small single‐molecule rod‐like nanocrystallites and the isolated block‐type “edge‐on” nanolamellae comprising several PE molecules. Noticeable fluctuations of the fold length in the range of approximately 10–20 nm around the averaged value of about 15 nm are observed for nanocrystallites and on tips of some nanolamellae. The explanation of the experimentally observed features of chain surface conformations on mica is proposed. It implies the immobilization of PE molecules in the nm‐thickness salt layer formed on mica surface at ambient conditions after PE deposition and the presence along the chain of multiple expanded chain folds. Only isolated lamellae and lamellar domains of a monolayer height are observed on graphite samples. The substrate/polymer epitaxial incommensurability important for the observation of the PE linear chain surface conformations is discussed from the comparison of the results obtained for mica and graphite, the coil‐to‐crystal intramolecular transformation is assumed to be inhibited on mica surface. The slow disintegration of the original gel structure of PE stock‐solution used for the high‐temperature depositions was found to result in the characteristic large‐scale morphological heterogeneity of the samples. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 766–777, 2010     

End‐grafting copolymers of styrene and 4‐vinylpyridine on an interacting solid surface

Copolymers of styrene and 4‐vinylpyridine with a styrene fraction f varying from 1 to 0 were grafted onto a silicon substrate in the melt. The grafting reaction and the stability of the grafted chains were investigated by Fourier transform infrared and X‐ray photoelectron spectroscopy. The thickness and surface morphology of the grafted copolymer layers were characterized with ellipsometry and atomic force microscopy (AFM). The copolymer chains were successfully grafted to the surface of the silicon substrate by a reaction between the hydroxyl groups of the nitroxide moiety at the end of the copolymers and the silanol groups on the surface of the silicon wafer. A measurement of the thickness of the grafted copolymer layers showed that the ratio of grafted‐layer thickness to the unperturbed chain radius of gyration decreased with the increasing fraction of 4‐vinylpyridine in the copolymer; this indicated that the grafted layer was strongly attracted to the substrate. In addition, an accelerated grafting process was observed at grafting times ranging from 48 to 72 h for pure poly(4‐vinylpyridine) and copolymers with f values of 0.3 and 0.5. AFM observation revealed that the grafted layers densely and homogeneously covered the silicon substrate. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1332‐1343, 2005     

UV grafting of methacrylic acid and acrylic acid on high‐density polyethylene in different solvents and the wettability of grafted high‐density polyethylene. II. Wettability

The wettability of high‐density polyethylene grafted with methacrylic acid is strongly influenced by the nature of the grafting solvent. Here, the wettability is expressed by the water contact angle and absorbency. The initial (10‐s) contact angle of polyethylene (PE) grafted in acetone/water solution decreased rapidly with the extent of grafting at low grafting levels and then remained independent of the grafting level at about 50°. When a water droplet was left on the surface for a longer time, its contact angle decreased to a very low value in the period of about 10 min. For the PE samples grafted in dichloromethane, petroleum ether, cyclohexane, and chloroform, there was only a small decrease (10°) in the contact angle of water from that observed on pure PE, even when the extent of grafting was very large. The PE films grafted in these organic solvents also took a much longer time than PE films grafted in acetone/ water solution to obtain equilibrium water absorbency. The water absorbency of PE films grafted in 30% acetone/water solution was about twice that of PE films grafted in the other solvents at the same extent of grafting. These results suggested that for the solvents other than acetone/water, the grafted layer is partially buried below the surface of PE. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 263–270, 2004     

Compatibilizing effect of isocyanate functional group on polyethylene terephthalate/low density polyethylene blends

To evaluate the compatibilizing effects of isocyanate (NCO) functional group on the polyethylene terephthalate/low density polyethylene (PET/LDPE) blends, LDPE grafted with 2-hydroxyethyl methacrylate-isophorone diisocyanate (LDPE-g-HI) was prepared and blended with PET. The chemical reaction occurred during the melt blending in the PET/LDPE-g-HI blends was confirmed by the result of IR spectra. In the light of the blend morphology, the dispersions of the PET/LDPE-g-HI blends were very fine over the PET/LDPE blends. DSC thermograms indicated that PET microdispersions produced by the slow cooling of the PET/LDPE-g-HI blends were largely amorphous, with low crystallinity, due to the chemical bonding. The tensile strengths of the PET/LDPE-g-HI blends were higher than those of the PET/LDPE blends having a poor adhesion. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 447–453, 1998     

The effect of glow discharge sputtering on the analysis of metal oxide films

The potential of radiofrequency glow discharge optical emission spectrometry (rf-GD-OES) for the quantification and the solid-state speciation of metal oxide films has been investigated in this work. Two types of oxide coatings, an iron oxide film deposited on silicon and a chromate conversion coating (CCC), were studied at 700 Pa of pressure and 30 W of forward power. The metal to oxygen ratios in the quantitative depth profiles (Fe/O and Cr/O, respectively) were used to evaluate the oxidation states of iron and chromium in the oxide films, demonstrating the capability of GD-OES technique for depth-resolved solid-state speciation. Furthermore, the effect of glow discharge sputtering on the samples surface in terms of modifications in the surface morphology and species transformations, were investigated by using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The iron and chromium oxidation states were carefully studied by XPS at the original samples surface and at the bottom of GD craters, and a systematic reduction of metal elements was observed after rf-GD-OES analysis. In the case of thin oxide films, preferential sputtering can be considered as a critical factor since oxygen atoms can be preferentially sputtered, leaving a metal-enriched surface and, therefore, promoting the reduction of metal elements. In the present study preferential sputtering was found to be sample dependent, changing the proportion of the metal reduction in the oxide film with its composition. Additionally, alternative sputter-depth-profiling techniques such as secondary ion mass spectrometry (SIMS), femtosecond laser ablation (fs-LA), and XPS ion gun were used for the analysis of the CCC in order to evaluate the reduction of Cr⁶⁺ to Cr³⁺ depending on the sputtering mechanism.     

Pre-irradiation grafting of span 60-IAH onto polyethylene to improve dripping properties of water on polyethylene films

A reactive type dripping anti-condensation agent, Span 60-IAH, was grafted onto linear low density polyethylene (LLDPE) by β-ray pre-irradiation and reactive extrusion. Effects of total dose, monomer concentration and extrusion temperature and rate on the degree of grafting were studied in detail. It was shown that the optimum conditions for grafting were the extrusion temperature of 130–220°C, screw run speed of 90 rpm and total β-ray dose of 12.5 kGy. The structure of the LLDPE-g-(Span 60-IAH) (LS) was characterized by Fourier-transform infrared spectroscopy (FT-IR). The tensile properties and light transmission properties of extruded films were determined. The thermal behavior of the LS was investigated by using differential scanning calorimetry (DSC). Compared with pure LLDPE, the crystallization temperature (T_c) of LS increased about 3°C. Accelerated dripping properties of film samples were investigated. The dripping duration of the LS film and a commercial anti-fog dripping film at 60°C were 45 days and 17 days, respectively, indicating a significant improvement.     

Substituent effects of methoxy,methyl, and vinyl groups on glow discharge polymerization

Glow discharge polymerizations in systems of trimethoxymethylsilane, trimethoxyvinylsilane, tetramethylsilane, and trimethylvinylsilane were compared by elemental analysis, infrared (IR) spectroscopy, and ESCA to reveal effects of methoxyl, methyl, and vinyl substituents. The substituent effects appeared in the chemical composition of the polymers formed especially at low W/FM values. Methoxy groups depressed the C/Si and H/Si ratios of the polymers rather than the methyl groups, whereas vinyl groups increased the C/Si and H/Si ratios. On IR spectra the polymers formed from silanes that contained methoxy groups showed fewer absorptions due to Si? H groups and strong absorptions due to Si? OH groups. The polymers from those that contained no methoxy groups showed absorptions of Si? H groups and no absorptions of Si? OH groups. These differences in the environment of Si atoms of polymeric chains also appeared in the Si_2p core level spectra, thus indicating the different fragmentation patterns of the starting materials in glow discharge.     

Effect of the substituents on radical copolymerization of dialkyl fumarates with some vinyl monomers

Radical copolymerization of dialkyl fumarates (DRF) with various vinyl monomers was carried out in benzene at 60°C. The monomer reactivity ratios, r₁ and r₂, were determined from the comonomer-copolymer composition curves. The relative reactivity of DRFs with various ester substituents toward a polystyryl radical was revealed to depend on both steric and polar effects of the ester groups. It has also been clarified that α-substituents of the polymer radical have a significant role in addition of DRF, from the comparison of the monomer reactivity ratios determined in copolymerizations with monosubstituted and 1,1-disubstituted ethylenes. The absolute cross-propagation rate constants were also evaluated and discussed. © 1992 John Wiley & Sons, Inc.     

Oxidation of polyethylene surface by glow discharge and subsequent graft copolymerization of acrylic acid

Plasma-induced graft copolymerization of acrylic acid, which was incorporated into PE films, was investigated here. The influence of plasma conditions such as plasma treatment gases, power, pressure, time, monomer concentration, and graft copolymerization time on polymerization yield was determined. The samples were characterized by ESCA, IR, and water contact angle. A respective chemical shift of the C1s signal of Ar or O₂ plasmatreated and untreated PE films was revealed by ESCA, in which the presence of the grafted PAAc was also verified. An increase in polymerization yield with plasma treatment duration and power was found. That the grafted copolymerization was limited to a very thin surface region was revealed by optical microscopy on the cross section of the grafted film. © 1993 John Wiley & Sons, Inc.     

Observation of adhesive force and energy of adsorbents on rubber substrates by atomic force microscopy

We observed the surface morphology and adhesive interaction of adsorbents on rubber substrates by atomic force microscopy (AFM). The detachment of adsorbents from rubber substrates is an important issue for various machines like home appliances and laundry machine. Since a clean surface of the functioning parts is required, a frequent cleaning process must be developed. In particular, dust and lint have a tendency to bind to the rubber surface of a laundry machine. Several practical methods have been attempted to remove these particles from the surface. Pure water, detergent, sodium hypochlorite (65 °C), and cold water (18 °C) are treated onto artificial dust and lint mixtures on rubber with water fluid by rapid rpm. The dust‐and‐lint adsorbents are investigated by AFM after the treatment, and topographic images and force–distance (F–D) curves were generated for the samples. The roughness, measured as the root mean square, is a key factor to judge the cleaning quality. From the F–D curves, we are able to obtain adhesive energy in addition to adhesive force which will yield qualitative measures of the interactions between the remaining adsorbents and the rubber surface. Considering the values that were measured, hot water with water fluid by rapid rpm offers the best performance when cleaning the surface. The chemical like sodium hypochlorite is good for thinning the materials, but it solidifies them, which is eventually detrimental to proper functioning. Copyright © 2014 John Wiley & Sons, Ltd.     

Sugar end-capped polyethylene: Ceric ammonium nitrate initiated oxidation and melt phase grafting of glucose onto polyethylene and its microbial degradation

Low density polyethylene (LDPE) was modified to introduce biodegradability by grafting highly hydrophilic monomers (which can act as nutrients for microorganisms) such as glucose by a novel melt phase reaction using Brabender plasti-corder in the presence of ceric ammonium nitrate (CAN) to obtain 4-O-hydroxymethyl d-arabinose (sugar) end-capped LDPE (Su-g-LDPE) at a maximum grafting of 16%. The grafted polymers were characterized by FTIR, thermal analysis, WAXD and mechanical property measurements. The biodegradability of Su-g-LDPE was carried out by soil-burial test and by optical density measurements in presence of an aerobic bacterium Pseudomonas sp. The degraded polymer shows changes in weight, crystallinity and inherent viscosity. Optical density of the medium registered an increase with degradation. FTIR spectra of the degraded samples showed 70% decrease in the ketone carbonyl index (ν₁₇₁₉/ν₁₄₆₅) of Su-g-LDPE indicating microbial degradation of LDPE matrix, which was further confirmed by SEM micrographs. The present data support a microbial oxidation process involving β-oxidation whereby the carbonyl is further oxidized to carboxylic acid and affects cleavage of the LDPE chain at the ends.     

Argon glow discharge plasma‐reduced palladium nanoparticles supported on activated carbon for Suzuki and Heck coupling reactions

Palladium nanoparticles supported on activated carbon were prepared by argon glow discharge plasma reduction (Pd/C‐P) without any chemical reducing agents and protective agents. The as‐prepared Pd/C‐P catalyst was characterized using nitrogen adsorption–desorption, X‐ray diffraction and transmission electron microscopy analyses. The results showed that the palladium nanoparticles reduced by plasma are well dispersed with a smaller particle size than commercial Pd/C. Pd/C‐P exhibited a high catalytic activity in Suzuki and Heck coupling reactions. Moreover, there was no obvious loss of catalytic activity even after eight repeated cycles, showing good reactivity and recyclability.     

Atomic force microscopy and transmission electron microscopy of cellulose from Micrasterias denticulata; evidence for a chiral helical microfibril twist

Atomic force microscopy (AFM), tapping mode atomic force microscopy (TM-AFM) and transmission electron microscopy (TEM) have been used to image the cell wall, ultrathin sections of whole cells and cellulose microfibrils prepared from the green alga Micrasterias denticulata. Measurements of the microfibril dimensions are in agreement with earlier observations carried out by electron microscopy. Images at the molecular level of the surface of the microfibrils were obtained with AFM and show regular periodicities along the microfibril axis that correspond to the fibre and glucose repeat distances of cellulose. Twisted regions visible at intervals along the microfibrils dried down onto substrates were noted to be right-handed in over 100 observations by TEM, AFM and TM-AFM. This revised version was published online in August 2006 with corrections to the Cover Date.