Role of counter-substrate surface energy in macroscale friction of nanofiber arrays

The effect of counter-substrate surface energy on macroscale friction of nanofiber array is studied. Low-density polyethylene (LDPE) fibrillar array fabricated from silicon nanowire template is tested against glass substrates modified with various self-assembled monolayers, which exhibit a wide range of surface energy. A large drop in friction over a narrow range of surface energy is observed and explained in terms of drastically reduced number of fibers in actual contact, in addition to the reduced surface energy. The relationship between surface energy and fiber engagement is discussed with Johnson-Kendall-Roberts (JKR) and elastic beam models.     

Adhesive effect of low-density polyethylene gels on polyethylene moldings

Adhesive effect of low density polyethylene (LDPE) gels in organic solvents such as decalin, tetralin, ando-dichlorobenzene on high density polyethylene (HDPE) moldings has been investigated by shearing tests, electron microscopy, and DSC measurements. When heated at 110°C for 2 h, all of the gels showed strong adhesive strengths around 30 kg/cm², which is sufficiently strong for practical uses. It has been found that the adhesive strength increases with the heating temperature and that the temperature at which the heated gel begins to exhibit the adhesive effect depends upon solvents and is about 30° lower than that of the HDPE gels.     

Adhesive effect of linear low-density polyethylene gels on polyethylene moldings

Adhesive effect of linear low density polyethylene (LLDPE) gels in organic solvents such as decalin, tetralin, and o-dichlorobenzene on high density polyethylene (HDPE) moldings has been investigated by shearing tests, and DSC measurements. For all of the gels the temperature at which the heated gel starts to exhibit the adhesive effect was about 70 °C, which is similar to the result of LDPE gel. In particular, when heated at 110 °C, LLDPE gel in tetralin showed such a strong bond strength that polyethylene plates of 3 mm in thickness and 20 mm in width gave rise to necking. It was found that LLDPE gel behaved as though it added LDPE gel to HDPE gel namely LDPE-like components in LLDPE resin exerted the adhesive effect at lower heating temperature, HDPE-like components exerted the strong adhesive effect at higher heating temperature.     

Characterization and properties of polyethylene blends II. Linear low-density with conventional low-density polyethylene

Melting and crystallization phenomena in blends of a linear low-density polyethylene (LLDPE) (ethylene butene-1 copolymer) with a conventional low-density (branched) polyethylene (LDPE) are explored with emphasis on composition by differential scanning calorimetry (DSC) and light scattering (LS). Two endotherms are evident in the DSC studies of the blends, which suggests the formation of separate crystals. Light-scattering studies indicate that the blend system is predominantly volume filled by the LLDPE component whereby the LDPE component crystallizes as a secondary process within the domain of the LLDPE spherulites. In contrast to those of the LLDPE/HDPE blends, the mechanical and optical relaxation behavior of the LLDPE/LDPE blends are dominated by the LLDPE component in the vicinities of γ and β regions, whereas the trend reverses at high temperature α regions. This observation is accounted for on the basis of the relative restrictions imposed by the deformation of spherulites (which are primarily made up of the LLDPE component) at different time scales.     

Microscale liquid dynamics and the effect on macroscale propagation in pillar arrays

Liquid dynamics in micropillar arrays have received significant fundamental interest and have offered opportunities for the development of advanced microfluidic, thermal management, and energy-harvesting devices. However, a comprehensive understanding of complex liquid behavior and the effect on macroscopic propagation rates in micropillar arrays is needed. In this work, we investigated the microscopic sweeping behavior of the liquid front along the spreading direction in micropillar arrays where the sweeping distance scales with the one-fifth power of time. We explain the scaling with a simplified model that captures the capillary pressure gradient at the liquid front. Furthermore, we show that such microscopic dynamics is the mechanism that decreases the macroscopic propagation rate. This effect is a result of the reduction in the interfacial energy difference used to generate the capillary pressure, which is explained with an energy-based model and corroborated with experiments. The results indicate the importance of accounting for the microscopic dynamics of the liquid on microstructured surfaces, particularly in sparse geometries.     

Effect of benzil and cobalt stearate on the aging of low-density polyethylene films

We report an investigation of the effect of benzil and cobalt stearate on the degradation behaviour of LDPE films. Thin films (70 μ) containing these additives were prepared by sheeting process. The effect of heating, exposure to UV-B and natural weathering of LDPE films in the presence/absence of additives was investigated. Changes in the tensile properties, carbonyl index and density were used to investigate the degradation behaviour. Attempts have been made to correlate the results as a function of mixed additives. In contrast to the activity of typical triplet activators, benzil was found to be incapable of initiating thermal- or photo-degradation of LDPE films. However, an accelerated rate of oxidation was observed, primarily due to cobalt stearate, in the case of compositions containing a combination of benzil and cobalt stearate. All samples were found to be more susceptible to thermo-oxidation than to UV or natural weathering.     

Effect of cobalt carboxylates on the photo-oxidative degradation of low-density polyethylene. Part-I

The effect of three cobalt carboxylates of increasing chain length, namely cobalt laurate, cobalt palmitate and cobalt stearate on the photo-oxidative degradation of low-density polyethylene (LDPE) films has been investigated. LDPE films containing cobalt carboxylates were irradiated with UV-B light at 30 °C for extended time periods. FTIR spectroscopy, mechanical testing, morphological studies, molecular weight, density and MFI measurements were performed to monitor the degradation behaviour. The results of these studies were analysed to explain the structural and chemical modifications taking place in the polyethylene matrix due to UV-B exposure. FTIR studies indicate that the degradation is dominated by formation of carbonyl and vinyl species. The studies on mechanical properties reveal that samples containing cobalt carboxylates, become mechanically fragile after UV exposure for 400 h, while neat LDPE exhibits insignificant changes during this period. The degradation was found to increase proportionally with increasing chain length and follows the order CoSt₃ > CoPal₃ > CoLau₃. Migration studies were performed on food simulant systems to investigate the applicability of these films for food packaging.     

Characterizing blends of linear low-density and low-density polyethylene by DSC

Summary A two-step isothermal annealing (TSIA) procedure is described that enables the endothermic peaks of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE) and their blends, to be satisfactorily resolved during analysis by differential scanning calorimetry. A modified form of multistep isothermal annealing, the TSIA procedure produces a highly characteristic profile of the blend components by facilitating the segregation of the phases based on branch density. It is proposed that the TSIA procedure may have significant merit in the identification and quantification of the components in an unknown blend as well as increasing the sensitivity in analytical procedures aimed at blend component quantification.     

The colloid-structure of semicrystalline low-density polyethylene

The length-distribution of stereoregular sequences in low-density polyethylene (LDPE) is determined by a computer-aided analysis of cp-melting curves within the framework of thermodynamics of eutectoid copolymers. Small-angle x-ray scattering patterns are then described by using the structure data derived. One of the results is that fluctuations of the mean electron-density are increasingly reduced with an increasing degree of crystallinity.Dedicated to Prof. Dr. W. Pechhold on the occasion of his 60th birthday     

Synthesis of ordered Al nanowire arrays

Ordered Al nanowire arrays with the same nanowire density but the diameters decrease radially embedded in one piece of anodic alumina membranes were successfully fabricated by two-step synthesis: electrodeposition of Zn and replacement in AlCl₃ solution. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected-area electron diffraction techniques were used to characterize the Al nanowires obtained. SEM and TEM images taken from the different areas of Al nanowire arrays show that we can control the growth of aligned Al nanowires with different diameters in a single process at the same time. The investigation results not only have potential applications in photoelectric devices but also open up a new method for fabricating nano-scale materials.     

Self-assembled two-dimensional ordered arrays of tripod-type molecules on graphite

Tripod-type molecules with long alkyl chains, 1,1,1-tris(4-alkoxyphenyl)ethanes with octadecyloxy or docosyloxy chains, self-assemble into two-dimensional crystallites on drop-casting onto the surface of highly oriented pyrolytic graphite. In the two-dimensional crystalline domain, the molecules are organized in a mortise-and-tenon motif, as revealed by scanning tunneling microscopy. The time evolution of the crystallite formation has been followed by the dynamic force mode atomic force microscopy. The tripods may be used as a basis for the extension of a two-dimensional order into three-dimensional molecular architectures.     

Adhesion of linear low-density polyethylene and oligomers

A pressure vessel design is put forward taking the form of a two-layer bottle, the inner sealing layer of which is made of linear low density polyethylene by rotational molding and the external power layer of which is made by winding an oligomer impregnated roving or moldable filament on the inner layer. It is shown that, to achieve the highest adhesion strength, it is necessary to preliminarily prepare the surface of the polyethylene sample by obtaining a particular microstructure and to use epoxy or polyester oligomers with a viscosity low enough to provide complete filling of the polyethylene sample surface texture.     

Electrochemical synthesis of ordered alumina nanowire arrays

Ordered Al₂O₃ nanowire arrays embedded in the nanochannels of anodic alumina membranes (AAMs) were synthesized by electrodepostion at room temperature. Our synthetic route yielded large quantities of Al₂O₃ nanowires of uniform size and shape that are ~40 μm long with diameters of 70 nm. The Al₂O₃ nanowire structures were characterized by scanning and transmission electron microscopies, high-resolution transmission electron microscopy, energy dispersive spectroscopy and X-ray photoelectron spectroscopy. Electronic Publication     

Characterization and properties of polyethylene blends I. Linear low-density polyethylene with high-density polyethylene

A blend system of linear low-density polyethylene (LLDPE) (ethylene butene-1 copolymer) with high-density (linear) polyethylene (HDPE) is investigated by differential scanning calorimetry (DSC), wide-angle x-ray diffraction (WAXD), small-angle x-ray scattering (SAXS), Raman longitudinal-acoustic-mode spectroscopy (LAM), and light scattering (LS). For slowly cooled or quenched samples, one single endotherm is evident in the DSC curve which depends on the composition. No separate peaks are observed in the WAXD, SAXS, Raman-LAM, and LS studies on the LLDPE/HDPE blends. This observation along with the fact that no peak broadening is observed suggests that these peaks are associated with the presence of a single component. In no case did we see double peaks or a broadened peak that might be associated with two closely spaced unresolved peaks. This suggests that segregation has not taken place at the structural levels of crystalline, lamellar, and spherulitic textures. A single-step drop in the scattered intensity (I_Hv) as a function of temperature is seen in the LS studies. It is therefore concluded that cocrystallization between the LLDPE and HDPE components occurs. The mechanical and optical α, β, and γ relaxations of these blends are explored by dynamic birefringence. The 50/50 blend displays the intermediate relaxation behavior between those of the components in all α, β, and γ regions. This observation is reminiscent of the characteristic of the typical miscible blends.     

Multi-component analysis of low-density polyethylene oxidative degradation

The oxidative degradation of polyethylene in various conditions has been studied. In order to gain insight into the oxidation process, a method for the curve-fitting analysis of the IR carbonyl band between 1800 cm⁻¹ and 1600 cm⁻¹ in oxidized low-density polyethylene (LDPE) has been developed. Up to 10 components were needed to fit the band envelope, whose assignments and peak positions were based on the literature and on the synthesis of an appropriate model compound. The determination of the other band parameters, such as peak width and peak shape, necessary for reliable best fitting of the absorbance envelopes, was obtained by overall fitting optimization process. By using the available extinction coefficients, the quantitative determinations of the main oxidized species, i.e. ketones, carboxylic acids, esters, γ-lactones and ketoacids, were obtained with a reasonable confidence by rigorous parameter setting. The method was applied to the IR analysis of LDPE samples oxidized in different conditions (under thermal and irradiation stimulation), either as beads or films, as a function of time. Total hydroperoxide concentrations were also quantitatively estimated by a modified iodometric titration procedure. A good linear correlation between concentrations estimated by chemical titration and by intensity analysis of the free hydroperoxide IR band was observed.     

Simulation of an amorphous polyethylene nanofiber on a high coordination lattice

Monte Carlo simulations of polyethylene (PE) melts and thin films have previously been performed on the second nearest neighbor diamond (2nnd) lattice by including short and long range interactions. A fiber can be obtained from equilibrated thin film snapshots by increasing another (normal to thin film plane) periodic side to infinity. There is only one effective periodic boundary condition in the simulation. The presence of attractive long range interactions gives cohesion to the fiber. PE fibers, which contain up to 72 chains of C₉₉ and have the radius ≈ 5.0 nm, have been produced and equilibrated on the 2nnd lattice. In these fibers, the density profiles are hyperbolic, with end beads being more abundant than the middle beads at the surface. There are orientational preferences at the surface on the scale of individual bonds and whole chains. Comparison of fibers with different thickness, which contain different number of chains, does not indicate any significant differences in local and global equilibrium properties – for thickness in the range 5.6 to 7.6 nm. Surface energies are calculated directly from the on‐lattice energetics and presented as a function of the fiber radius     

ESR study on radical conversions in irradiated low-density polyethylene

ESR studies were carried out on radical conversions by thermal and photochemical mechanisms in low-density polyethylene irradiated mainly with electron beams at ?196°C both in vacuum and in the presence of CO. According to the spectral change, the following radical conversions were elucidated for the samples irradiated in vacuo [eqs. (1) and (1′)] and in the presence of CO [eqs. (2) and (2′)]. From the resemblance of the ESR spectrum observed after direct photolysis of polyethylene to that observed after photo-induced radical conversions of the allylic radicals, it is concluded that an eight-line ESR spectrum observed immediately after photolysis of polyethylene at ?196°C could be attributed more reasonably to the alkyl radicals ? CH₂CHCH₃ than to ? CH₂CH₂ and ? CH₂CHCH₂? .     

Effect of sterilization on non-woven polyethylene terephthalate fiber structures for vascular grafts

Non-woven polyethylene terephthalate (PET) fibers produced via melt blowing and compounded into a 6 mm diameter 3D tubular scaffold were developed with artery matching mechanical properties. This work compares the effects of ethylene oxide (EtO) and low temperature plasma (LTP) sterilization on PET surface chemistry and biocompatibility. As seen through X-ray photoelectron spectroscopy (XPS) analysis, LTP sterilization led to an increase in overall oxygen content and the creation of new hydroxyl groups. EtO sterilization induced alkylation of the PET polymer. The in vitro cytotoxicity showed similar fibroblastic viability on LTP- and EtO-treated PET fibers. However, TNF-α release levels, indicative of macrophage activation, were significantly higher when macrophages were incubated on EtO-treated PET fibers. Subcutaneous mice implantation revealed an inflammatory response with foreign body reaction to PET grafts independent of the sterilization procedure.