Molecular characteristics and surface layer structure of poly(siloxane imides)

The effects of spontaneous ordering of molecular chains of poly(siloxane imide) block copolymers in the surface layers of thin films on glass and gold supports have been studied by the oblique polarized beam and photoelasticity methods. The effective thermodynamic rigidity of molecular chains of the block copolymers (the statistical segment length) has been found to be A = 10.4 × 10^?7 cm. The orientational ordering of molecular chains in poly(siloxane imide) surface layers is characterized by small values of the orientational order parameter (S ₀ ～ 0.007). This finding is explained by the microphase separation of the block copolymers. The evaporated gold layer contributes to the effect of surface birefringence owing to formation of the ordered system composed of islets—clusters of gold atoms.     

Simulation of melting in crystalline polyethylene

We carry out a molecular dynamics simulation of the first stages of constrained melting in crystalline polyethylene (PE). When heated, the crystal undergoes two structural phase transitions: from the orthorhombic (O) phase to the monoclinic (M) phase, and then to the columnar (C), quasi-hexagonal, phase. The M phase represents the tendency to the parallel packing of planes of PE zigzags, and the C phase proves to be some kind of oriented melt. We follow both the transitions O→M and M→C in real time and establish that, at their beginning, the crystal tries (and fails) to pass into the partially ordered phases similar to the RI and RII phases of linear alkanes, correspondingly. We discuss the molecular mechanisms and driving forces of the observed transitions, as well as the reasons why the M and C phases in PE crystals substitute for the rotator phases in linear alkanes.     

Simulation of the surface structure of butylmethylimidazolium ionic liquids

Molecular dynamics simulations of the liquid/vacuum surfaces of the room temperature ionic liquids [bmim][PF(6)], [bmim][BF(4)] and [bmim][Cl] have been carried out at various temperatures. The surfaces are structured with a top monolayer containing oriented cations and anions. The butyl side chains tend to face the vacuum and the methyl side chains the liquid. However, as the butyl chains are not densely packed, both anions and rings are visible from the vacuum phase. The effects of temperature and the anion on the degree of cation orientation is small, but the potential drop from the vacuum to the interior of the liquid is greater for liquids with smaller anions. We compare the simulation results with a range of experimental observations and suggest that neutron reflection from samples with protiated butyl groups would be a sensitive probe of the structure.     

Flame surface modification of polyethylene sheets

High density polyethylene sheets 2 mm thick were flame treated to modify the surface properties. Sheets treated using a flame with air to gas (methane) ratio ∼ 10:1 at different distances between the inner cone tip of the flame and the polymer surface were investigated. Grafting of selected monomers as maleic anhydride, acrylamide and glycidyl methacrylate was attempted by flame treatment of sheets covered with a monomer layer. Good grafting results were obtained with acrylamide and maleic anhydride. The surface temperature-time dependence during the flame treatment was measured with a high resolution thermocouple. Scanning Electron Microscopy (SEM) allowed evidencing a modified thickness of about 120 μ. The chemical surface modification was studied by X ray Photoelectron Spectroscopy (XPS) and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT). The hydroxyl, carbonyl and carboxyl content was measured after derivatization with reagents containing an elemental tag to facilitate XPS analysis of surface functional groups. In comparison to the untreated polyethylene, wetting tension and contact angle of the flamed materials showed a strong variation. This variation was almost independent of the distance between the flame and the polymer surface. Adhesion between treated polyethylene and a polyurethane adhesive was determined using T-peel test measurements. High adhesion levels were found with flame treated polyethylene at 5 mm distance. XPS results indicate that when adhesion is high, the hydroxyl is in excess compared to the other measured functions, i.e. carbonyl and carboxyl species.     

Deformation and structure of doubly oriented polyethylene

Doubly oriented low-density polyethylene with parallel lamellae was compressed along the initial draw direction (i.e., at right angles to the lamellar surfaces) at 20°C. Wide- and low-angle x-ray diffraction were used to determine the changes in the molecular orientation and in the texture. During the compression, specimens previously annealed at or near 102°C were found to undergo changes in length, in long spacing, and in molecular orientation which were consistent with an (001) chain slip mechanism. In specimens annealed at higher temperatures x-ray diffraction indicated that during compression some series component of the long spacing was compressed by a much smaller amount than the remainder of the long spacing, which deformed by chain slip; in these cases it was found that the macroscopic strain along the compression axis (ε_y) was greater than the strain in the long spacing along that axis (ε_d). It is suggested that the missing strain which makes ε_y greater than ε_d is due to partial melting and the consequent development of amorphous regions between the stacks of lamellae.     

Relaxation processes and structure of ultradrawn polyethylene

Solid-state extruded polyethylene fibers have been prepared, with a wide range of draw ratios and constant processing temperature. The draw ratios vary from 4 up to 30, and the processing temperature was always 398 K. The extruded material behaves anisotropically, owing to the high degree of chain orientation in the drawing direction. The modulus and linear expansion coefficients in the fiber axis direction have been measured, over a wide temperature range, from 140 K up to 320 K. These two properties are closely related to the degree of structural continuity of the fibers. A fibrous structure model is proposed to explain the temperature effects and the values obtained for the modulus and expansion coefficients, in terms of crystallinity and volumetric fraction of extended-chains structure. At least three relaxation processes can be identified which cause the structural continuity of the fibers to change with temperature.     

Piled-lamellae structure in polyethylene film and its deformation

The fine structure of polyethylene film has been investigated by using a high-resolution scanning electron microscope equipped with a field emission source. The original film surface of a-axis-oriented blown polyethylene film and the surface of a necked region formed by drawing the film in the machine direction were observed. High magnification electron micrographs indicate that the basic unit of internal texture of this film consists of piled-lamellae units, each pile containing three to ten lamellar crystal sheets. The piled-lamellae unit acts as one body and does not separate into single lamellae during deformation. Many tie fibrils are formed between adjacent piled-lamellae units, when the film is drawn in the machine direction. Although little attention has been given to this mechanism, it is important in deformation. This fact seems to be reflected in different shapes of the stress-strain curves of films drawn the machine direction and perpendicular to it.     

Hyperelastic characterization of the interlamellar domain and interphase layer in semicrystalline polyethylene

The interphase layer in semicrystalline polyethylene (PE) serves as the transition between the crystalline lamellae and the amorphous domains and is recognized as the third constituent of PE. When PE undergoes large deformations, this interphase layer together with the amorphous phase behaves hyperelastically. Because of the metastable nature and nanometric size of the interphase and its intimate mechanical coupling to the neighboring crystal and amorphous domains, detailed characterization of its hyperelastic properties have eluded detailed experimental evaluation. To extract these properties, a combined algorithm is proposed based on applying the constitutive relations of an isotropic, compressible, hyperelastic continuum to the molecular dynamics simulation results of a PE stack from Lee and Rutledge (Macromolecules 2011, 3096–3108). The simulation element is incrementally deformed to a large strain, during which the stress–strain information is recorded. Assuming a neo‐Hookean model, the tensorial constitutive equation is derived. The hyperelastic parameters for the central amorphous phase, the interphase layer, and the interlamellar domain are identified with the help of the optimization notion and a set of nonnegative objective functions. The identified hyperelastic parameters for the interlamellar domain are in good agreement with the ones estimated experimentally and frequently used in the literature for the noncrystalline phase. The specifically developed sensitivity analysis indicates that the shear modulus is identified with a higher degree of certainty, in contrast to the bulk modulus. It is also revealed that the presented continuum mechanics analysis is able to capture the melting/recrystallization and rotation of crystalline chains that take place during the deformation. The evolutions of the boundaries of the hyperelastic elements are also identified concurrently with the hyperelastic parameters as the by‐product of the presented methodology. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1692–1704     

The morphology of the spherulitic surface in polyethylene

Studies of lamellar shapes and profiles in linear polyethylene have often been implemented by microscopic examination of appropriately etched random slices through spherulitic specimens. However, since a spherulite crystallized from a bulk specimen is a three-dimensional assembly of radially oriented lamellae with a twisting orientation (except for very high T_cs), it may be difficult to draw appropriate conclusions from a random slice. A technique has been developed that allows one to prepare spherulitic surfaces such that their distance relative to the geometric center can be well characterized. A computer-based graphical representation is also presented which suggests that the projection of lamellae on such surfaces is adequately represented by a radially oriented assembly of helicoidally twisted lamellae. Based on the agreement between the experimental results and the computer model, it is suggested that the C and S shapes previously observed by other researchers are not necessarily intrinsic to the lamellar profile but may arise due to geometrical effects as the lameliae project onto a surface at various angles. From these results it is also evident that in ringed spherulites lamellae undergo continuous twisting rather than successive misalignment of essentially untwisted segments.     

Oxidation and sulfonation of cellulosics

Bleached hardwood (HW) kraft pulp and derived nanocellulosic structures were modified by a periodate oxidation followed by treatment with sodium bisulfite to yield the corresponding C2/3 sulfonates. The impact of this oxidative–reductive protocol on the chemical and physical properties of cellulose was evaluated by determining physical dimensions, functional groups, and their water absorbency properties. It was found that the water absorbency of cellulosic material can be enhanced by 8.0–199.0% with this oxidation/sulfonation protocol. Distinct differences were observed between sulfonated pulp fibers and nanocellulosic structures, with the latter exhibiting relatively higher water retention values (WRV).     

Remarkable influence of surface composition and structure of oxidized iron layer on orange I decomposition mechanisms

Although the decomposition of water pollutants in the presence of metallic iron is known, the reaction pathways and mechanisms of the decomposition of azo-dyes have been meagerly investigated. The interface phenomena taking place during orange I decomposition have been investigated with the use of infrared external reflection spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. The studies presented in this paper establish that there are close relationships between the composition and structure of the iron surface oxidized layers and the kinetics and reaction pathway of orange decomposition. The influence of the molecular structure of azo-dye on the produced intermediates was also studied. There are remarkable differences in orange I decomposition between pH 3 and pH 5 at 30 degrees C. Decomposition at pH 3 is very fast with pseudo-first-order kinetics, whereas at pH 5 the reaction is slower with pseudo-zero-order kinetics. At pH 3, only one amine, namely 1-amino-4-naphthol, was identified as an intermediate that undergoes future decomposition. Sulfanilic acid, the second harmful reduction product, was not found in our studies. At pH 3, the iron surface is covered only by a very thin layer of polymeric Fe(OH)(2) mixed with FeO that ensures orange reduction by a combination of an electron transfer reaction and a catalytic hydrogenation reaction. At pH 5, the iron surface is covered up to a few micrometers thick, with a very spongy and porous layer of lepidocrocite enriched in Fe(2+) ions, which slows the electron transfer process. The fastest decomposition reaction was found at a potential near -300 mV (standard hydrogen electrode). An addition of Fe(2+) ions to solution, iron preoxidation in water, or an increase of temperature all result in an increasing decomposition rate. There is no single surface product that would inhibit the decomposition of orange. This information is crucial to perform efficient, clean and low cost waste water treatment. The findings presented here make the treatment of wastewater in the presence of metallic iron a very promising solution.     

Elastic moduli and structure of low density polyethylene

Summary Low density polyethylene film is drawn at room temperature four times the original length and subjected to thermal annealing at 60, 80, and 100 °C keeping the film length constant. Long spacing measured by SAXS increased with increasing temperature of annealing; the increase of the long spacing is presumed to be due to the decrease of the number of micelles through relaxation during the annealing. Simultaneous measurement of the changes of the long spacing and the film length by stretching is carried out and stress-extension curves are obtained. The values of the initial moduli of the long spacingE ₁ and the film lengthY are very near to each other. Elastic modulus of the crystal latticeE _c is known to be 235 GN/m² and that of the amorphous regionE _a is found to be 0.15 GN/m². When higher stress is applied than in the case of the initial modulus, the percentage of extension of film is much greater than that of the long spacing. The discrepancy is explained by the increase of the number of micelles through stress crystallization.Dedicated to Professor Dr. K. Ueberreiter on the occasion of his 70th birthday.     

Properties and structure of compositions of polyethylene and san-copolymer

Some strength-deformation and rheological properties of compositions of PE and SAN-copolymer obtained by three methods were studied. Light-microscopy analyses were made. It was established that the structural characteristics and the properties of the mixtures depend on the method of production rather than on composition.