Polyethylene multiwalled carbon nanotube composites

Polyethylene (PE) multiwalled carbon nanotubes (MWCNTs) with weight fractions ranging from 0.1 to 10 wt% were prepared by melt blending using a mini-twin screw extruder. The morphology and degree of dispersion of the MWCNTs in the PE matrix at different length scales was investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and wide-angle X-ray diffraction (WAXD). Both individual and agglomerations of MWCNTs were evident. An up-shift of 17 cm(-1) for the G band and the evolution of a shoulder to this peak were obtained in the Raman spectra of the nanocomposites, probably due to compressive forces exerted on the MWCNTs by PE chains and indicating intercalation of PE into the MWCNT bundles. The electrical conductivity and linear viscoelastic behaviour of these nanocomposites were investigated. A percolation threshold of about 7.5 wt% was obtained and the electrical conductivity of PE was increased significantly, by 16 orders of magnitude, from 10(-20) to 10(-4) S/cm. The storage modulus (G') versus frequency curves approached a plateau above the percolation threshold with the formation of an interconnected nanotube structure, indicative of 'pseudo-solid-like' behaviour. The ultimate tensile strength and elongation at break of the nanocomposites decreased with addition of MWCNTs. The diminution of mechanical proper-ties of the nanocomposites, though concomitant with a significant increase in electrical conductivity, implies the mechanism for mechanical reinforcement for PE/MWCNT composites is filler-matrix interfacial interactions and not filler percolation. The temperature of crystallisation (T.) and fraction of PE that was crystalline (F-c) were modified by incorporating MWCNTs. The thermal decomposition temperature of PE was enhanced by 20 K on addition of 10 wt% MWCNT. (c) 2005 Elsevier Ltd. All rights reserved.

Highly-ordered hybrid organic-inorganic isoporous membranes from polymer modified nanoparticles

atomic force microscopy (AFM); atom transfer radical polymerization (ATRP); block copolymers; self-assembly; silica nanoparticles.

Structure and thermal stability of Langmuir-Blodgett films of barium arachidate

The structures of multilayer Langmuir-Blodgett films of barium arachidate before and after heat treatment have been investigated using both atomic force microscopy (AFM) and grazing incidence synchrotron X-ray diffraction (GIXD). AFM gave information on surface morphology at molecular resolution while GIXD provided quantitative details of the lattice structures of the films with their crystal symmetries and lattice constants. As-prepared films contained three coexisting structures: two triclinic structures with the molecularchains tilted by about 20degrees from the film normal and with 3 x 1 or 2 x 2 super-lattice features arising from height modulation of the molecules in the films; a rectangular structure with molecules perpendicular to the film surface. Of these, the 3 x 1 structure is dominant with a loose correlation between the bilayers. In the film plane both superstructures are commensurate with the local structures, having different oblique symmetries. The lattice constants for the 3 x 1 structure are a(s) = 3a = 13.86 Angstrom, b(s) = b = 4.31 Angstrom and gamma(s) = gamma = 82.7degrees; for the 2 x 2 structure a(s) = 2a = 16.54 Angstrom, b(s) = 2b = 9.67 Angstrom, gamma(s) = gamma = 88degrees. For the rectangular structure the lattice constants are a = 7.39 Angstrom, b = 4.96 Angstrom and gamma = 90degrees. After annealing, the 2 x 2 and rectangular structures were not observed, while the 3 x 1 structure had developed over the entire film. For the annealed films the correlation length in the film plane is about twice that in the unheated films, and in the out-of-plane direction covers two bilayers. The above lattice parameters, determined by GIXD, differed significantly from the values obtained by AFM, due possibly to distortion of the films by the scanning action of the AFM tip. (C) 2004 Published by Elsevier B.V.

London-van der Waals adhesiveness of rough particles

Van der Waals forces often dominate interactions and adhesion between fine particles and, in turn, decisively influence the bulk behaviour of powders. However, so far there is no effective means to characterize the adhesive behaviour of such particles. A complication is that most powder particles have rough surfaces, and it is the asperities on the surfaces that touch, confounding the actual surface that is in contact. Conventional approaches using surface energy provide limited information regarding adhesion, and pull-off forces measured through atomic force microscope (AFM) are highly variable and difficult to interpret. In this paper we develop a model which combines the Rumpf-Rabinovich and the JKR-DMT theories to account simultaneously for the effects of surface roughness and deformation on adhesion. This is applied to a 'characteristic asperity' which may be easily obtained from AFM measurements. The concept of adhesiveness, a material property reflecting the influences of elastic deformability, surface roughness, and interfacial surface energy, is introduced as an efficient and quantitative measure of the adhering tendency of a powder. Furthermore, a novel concept of specific adhesiveness is proposed as a convenient tool for characterizing and benchmarking solid materials. This paper provides an example to illustrate the use of the proposed theories. (c) 2005 Elsevier B.V. All rights reserved.

The tribology of laminated magnetic recording heads

This thesis investigates the mechanisms that lead to pole tip recession (PTR) in laminated magnetic recording heads (also known as "sandwich heads"). These heads provide a platform for the utilisation of advanced soft magnetic thin films in practical recording heads suitable for high frequency helical scan tape recording systems. PTR results from a differential wear of the magnetic pole piece from the tape-bearing surface of the head. It results in a spacing loss of the playback or read signal of 54.6dB per recording wavelength separation of the poles from the tape. PTR depends on the material combination used in the head, on the tape type and the climate - temperature and relative humidity (r.h.). Five head materials were studied: two non-magnetic substrate materials- sintered multi granular CaTi03 and composite CaTi03/ZrTi04/Ti02 and three soft magnetic materials- amorphous CoNbZr, and nanocrystalline FeNbSiN and FeTaN. Single material dummy heads were constructed and their wear rates measured when cycling them in a Hi-8 camcorder against commercially available metal particulate (MP) and metal evaporated (ME) tapes in three different climates: 25°C/20%r.h., 25°C/80%r.h. and 40°C/80%r.h. X-ray photoelectron spectroscopy (XPS) was used to examine changes the head surface chemistry. Atomic force microscopy (AFM) was used to examine changes in head and tape surface topography. PTR versus cycling time of laminated heads of CaTi03/ZrTiO4/Ti02 and FeTaN construction was measured using AFM. The principal wear mechanism observed for all head materials was microabrasion caused by the mating body - the tape surface. The variation in wear rate with climate and tape type was due to a variation in severity in this mechanism, except for tape cycling at 40°C in which gross damage was observed to be occurring to the head surface. Two subsidiary wear mechanisms were found: third body scratching (all materials) and grain pullout (both ceramics and FeNbSiN). No chemical wear was observed, though tribochemical reactions were observed on the metal head surfaces. PTR was found to be caused by two mechanisms - the first differential microabrasion of the metal and substrate materials and which was characterised by a low (~10nm) equilibrium value. The second was by deep ploughing by third body debris particles, thought mainly to be grain pullout particles. This level of PTR caused by this mechanism was often more severe, and of a non-equilibrium nature. It was observed more for ME tape, especially at 40°C/80%r.h. and 25°c/20%r.h. Two other phenomena on the laminated head pole piece were observed and commented upon: staining and ripple texturing.

Interactions at the head-tape interface of a linear tape system

Many of the recent improvements in the capacity of data cartridge systems have been achieved through the use of narrower tracks, higher linear densities and continuous servo tracking with multi-channel heads. These changes have produced new tribological problems at the head/tape interface. It is crucial that the tribology of such systems is understood and this will continue since increasing storage capacities and faster transfer rates are constantly being sought. Chemical changes in the surface of single and dual layer MP tape have been correlated to signal performance. An accelerated tape tester, consisting of a custom made cycler ("loop tester"), was used to ascertain if results could be produced that were representative of a real tape drive system. A second set of experiments used a modified tape drive (Georgens cycler), which allowed the effects of the tape transport system on the tape surface to be studied. To isolate any effects on the tape surface due to the head/tape interface, read/write heads were not fitted to the cycler. Two further sets of experiments were conducted which included a head in the tape path. This allowed the effects of the head/tape interface on the physical and chemical properties of the head and tape surfaces to be investigated. It was during the final set of experiments that the effect on the head/tape interface, of an energised MR element, was investigated. The effect of operating each cycler at extreme relative humidity and temperature was investigated through the use of an environmental chamber. Extensive use was made of surface specific analytical techniques such as XPS, AFM, AES, and SEM to study the physical and chemical changes that occur at the head/tape interface. Results showed that cycling improved the signal performance of all the tapes tested. The data cartridge drive belt had an effect on the chemical properties of the tape surface on which it was in contact. Also binder degradation occurred for each tape and appeared to be greater at higher humidity. Lubricant was generally seen to migrate to the tape surface with cycling. Any surface changes likely to affect signal output occurred at the head surface rather than the tape.

Modelling tribology of slider and disk in a computer hard drive system

Issues of wear and tribology are increasingly important in computer hard drives as slider flying heights are becoming lower and disk protective coatings thinner to minimise spacing loss and allow higher areal density. Friction, stiction and wear between the slider and disk in a hard drive were studied using Accelerated Friction Test (AFT) apparatus. Contact Start Stop (CSS) and constant speed drag tests were performed using commercial rigid disks and two different air bearing slider types. Friction and stiction were captured during testing by a set of strain gauges. System parameters were varied to investigate their effect on tribology at the head/disk interface. Chosen parameters were disk spinning velocity, slider fly height, temperature, humidity and intercycle pause. The effect of different disk texturing methods was also studied. Models were proposed to explain the influence of these parameters on tribology. Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) were used to study head and disk topography at various test stages and to provide physical parameters to verify the models. X-ray Photoelectron Spectroscopy (XPS) was employed to identify surface composition and determine if any chemical changes had occurred as a result of testing. The parameters most likely to influence the interface were identified for both CSS and drag testing. Neural Network modelling was used to substantiate results. Topographical AFM scans of disk and slider were exported numerically to file and explored extensively. Techniques were developed which improved line and area analysis. A method for detecting surface contacts was also deduced, results supported and explained observed AFT behaviour. Finally surfaces were computer generated to simulate real disk scans, this allowed contact analysis of many types of surface to be performed. Conclusions were drawn about what disk characteristics most affected contacts and hence friction, stiction and wear.

Surface:plasma interactions in GaAs subjected to capacitively coupled RF plasmas

Surface compositional changes in GaAs due to RF plasmas of different gases have been investigated by XPS and etch rates were measured using AFM. Angular Resolved XPS (ARXPS) was also employed for depth analysis of the composition of the surface layers. An important role in this study was determination of oxide thickness using XPS data. The study of surface - plasma interaction was undertaken by correlating results of surface analysis with plasma diagnosis. Different experiments were designed to accurately measure the BEs associated with the Ga 3d, Ga 2P3/2 and LMM peaks using XPS analysis and propose identification in terms of the oxides of GaAs. Along with GaAs wafers, some reference compounds such as metallic Ga and Ga2O3 powder were used. A separate study aiming the identification of the GaAs surface oxides formed on the GaAs surface during and after plasma processing was undertaken. Surface compositional changes after plasma treatment, prior to surface analysis are considered, with particular reference to the oxides formed in the air on the activated surface. Samples exposed to ambient air for different periods of time and also to pure oxygen were analysed. Models of surface processes were proposed for explanation of the stoichiometry changes observed with the inert and reactive plasmas used. In order to help with the understanding of the mechanisms responsible for surface effects during plasma treatment, computer simulation using SRIM code was also undertaken. Based on simulation and experimental results, models of surface phenomena are proposed. Discussion of the experimental and simulated results is made in accordance with current theories and published results of different authors. The experimental errors introduced by impurities and also by data acquisition and processing are also evaluated.

Pole tip recession in linear tape systems

The tribology of linear tape storage system including Linear Tape Open (LTO) and Travan5 was investigated by combining X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES), Optical Microscopy and Atomic Force Microscopy (AFM) technologies. The purpose of this study was to understand the tribology mechanism of linear tape systems then projected recording densities may be achieved in future systems. Water vapour pressure or Normalized Water Content (NWC) rather than the Relative Humidity (RH) values (as are used almost universally in this field) determined the extent of PTR and stain (if produced) in linear heads. Approximately linear dependencies were found for saturated PTR increasing with normalized water content increasing over the range studied using the same tape. Fe Stain (if produced) preferentially formed on the head surfaces at the lower water contents. The stain formation mechanism had been identified. Adhesive bond formation is a chemical process that is governed by temperature. Thus the higher the contact pressure, the higher the contact temperature in the interface of head and tape, was produced higher the probability of adhesive bond formation and the greater the amount of transferred material (stain). Water molecules at the interface saturate the surface bonds and makes adhesive junctions less likely. Tape polymeric binder formulation also has a significant role in stain formation, with the latest generation binders producing less transfer of material. This is almost certainly due to higher cohesive bonds within the body of the magnetic layer. TiC in the two-phase ceramic tape-bearing surface (AlTiC) was found to oxidise to form TiO2.The oxidation rate of TiC increased with water content increasing. The oxide was less dense than the underlying carbide; hence the interface between TiO2 oxide and TiC was stressed. Removals of the oxide phase results in the formation of three-body abrasive particles that were swept across the tape head, and gave rise to three-body abrasive wear, particularly in the pole regions. Hence, PTR and subsequent which signal loss and error growth. The lower contact pressure of the LTO system comparing with the Travan5 system ensures that fewer and smaller three-body abrasive particles were swept across the poles and insulator regions. Hence, lower contact pressure, as well as reducing stain in the same time significantly reduces PTR in the LTO system.

Incorporation of N-heterocyclic cations into proteins with a highly directed chemical modification

N-Heterocyclic cations are incorporated into proteins using 5-(2-bromoethyl)phenanthridinium bromide, which selectively reacts with either cysteine or lysine residues, resulting in ethylphenanthridinium (Phen) or highly stable cyclised dihydro-imidazo-phenanthridinium (DIP) adducts respectively; these modifications have been found to manipulate the observed structure of lysozyme and bovine serum albumin by AFM.

Influence of impact angles on penetration rates of CRAs exposed to a high velocity multiphase flow

A combined flow loop - jet impingement pilot plant has been used to determine mass loss rates in a mixed gas - saltwater - sand multiphase flow at impact velocities up to 70 m/s. Artificial brine with a salt content of 27 g/1 was used as liquid phase. Sand content, with grain size below 150 µ, was 2.7 g/l brine. CO at a pressure of 15 bar was used as gas phase. The impact angle between jet stream (nozzle) and sample surface was varied between 30 and 90°. Rectangular stainless steel disc samples with a size of 20 × 15 × 5 mm were used. They were mechanically ground and polished prior to testing. Damaged surfaces of specimens exposed to the high velocity multiphase flow were investigated by stereo microscopy, scanning electron microscopy (SEM) and an optical device for 3D surface measurements. Furthermore, samples were investigated by applying atomic force microscopy (AFM), magnetic force microscopy (MFM) and nanoindentation. Influence of impact velocity and impact angle on penetration rates (mass loss rates) of two CRAs (UNS S30400 and N08028) are presented. Moreover effects of chemical composition and mechanical properties are critically discussed. © 2008 by NACE International.

Les motivations pour le magasinage:démêler les impacts des motivations individuelles et des motivations liées au contexte

La définition des motivations du consommateur est souvent ambigüe. Elles sont parfois considérées comme des caractéristiques permanentes de l’individu influençant son comportement général (traits motivationnels) et elles sont parfois définies comme des variables contextuelles expliquant pourquoi un individu agit d’une certaine façon dans un contexte donné (états motivationnels). Notre objectif est de clarifier ces deux concepts et d’étudier leur impact respectif sur le comportement du consommateur. En appliquant notre étude aux motivations pour le shopping, nous démontrons l’existence d’une forte interaction entre ces deux types de motivations.

Déterminer les réponses publicitaires des marques par médias

Les responsables marketing doivent allouer leurs dépenses publicitaires entre les différents médias afin de maximiser l’efficacité de la publicité. La plupart des modèles existant ne prennent pas en compte les caractéristiques des marques dans la prévision de l’efficacité de cette allocation sur les ventes. Pourtant, de nombreuses recherches montrent que l’élasticité publicitaire peut être différente selon des variables propres aux marques comme leur position sur le marché où la phase de leur cycle de vie. Cette recherche propose l’élaboration d’un modèle capable de mesurer l’influence de ces caractéristiques sur l’efficacité de leurs dépenses publicitaires sur les différents médias utilisés.

Solid bridge formation between spray-dried sodium carbonate particles

Moisture migration caking of pharmaceutical excipients in the absence of load is a significant quality and stability issue. This study uses Atomic Force Microscopy (AFM) to examine a solid bridge formed between two 20µm spray-dried sodium carbonate particles. The bridge is grown by repeatedly exposing the system to 70% RH and 30% RH cycles at 25?C. A comparison is made with the idealised bridge model developed by Tanaka (1978) which was previously verified using crystalline systems. The resulting system was found to be more complex and grew in two stages. The first stage consisted of linear growth to 5 cycles, followed by a more gradual expansion and the appearance of crystalline structures.