Morphological study on thermal treatment and degradation behaviors of solution-grown poly(l-lactide) single crystals

Morphological changes of solution-grown crystals (SGCs) of poly(l-lactide) (PLLA) following thermal treatment and enzymatic degradation were investigated using atomic force microscopy in terms of defects in the crystals. PLLA SGCs were grown from a dilute solution of acetonitrile at 5 degrees C. The obtained solution-grown monolamellar crystals have a lozenge-shaped morphology containing unique dimensions, with one side measuring 12mum. To investigate enzymatic degradation behavior, PLLA SGCs were incubated in buffered solution with proteinase-K at 37 degrees C. The initial stage of enzymatic degradation of PLLA SGCs with proteinase-K occurs in loosely folding chains at the surface of the crystal. Thermally treated PLLA SGCs below the melting temperature showed an increase of the lamellar thickness of the SGCs at the treated temperature and partial surface erosion following enzyme exposure. These results indicate that less ordered chains exist throughout the lamellae and their thermal-induced chain extension makes them more susceptible to enzyme attack.     

Bacterially induced degradation of aqueous solutions of poly(l-lysine)-graft-poly(ethylene glycol) and poly(l-lysine)-graft-dextran: consequences for their lubrication properties

Experimental data are presented comparing the degradation in the lubrication behaviour of aqueous solutions of the brush copolymers poly(l -lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) and poly(l -lysine)-graft-dextran (PLL-g-dex) when aged after exposure to bacterial contamination. While PLL-g-PEG solutions appear to be relatively unaffected by bacteria after a storage period of as much as 8 weeks, PLL-g-dex solutions exposed to bacteria during preparation lead to as much as a twofold increase in friction coefficient, when used as a lubricant in tribological tests, over an 8 week period when compared to reference data from freshly prepared and tested samples. Solutions prepared under sterile conditions and aged for up to 8 weeks do not appear to be degraded. Further experiments implementing the anti-bacterial agent sodium azide effectively prevented bacterial colonization and degradation in lubrication behaviour. Copyright © 2009 John Wiley & Sons, Ltd.     

Distinguishing the effects of adhesive wear and thermal degradation on the tribological characteristics of paper-based friction materials under dry environment: A theoretical study

Adhesive wear and thermal degradation are the main aging mechanisms of paper-based friction materials. However, how these aging mechanisms affect the tribological characteristics of such materials is not fully understood. In this paper, the respective influences of the two aging mechanisms on the tribological characteristics of the friction materials are investigated through simulation. It is assumed that adhesive wear pre-dominantly affects the surface topography, while thermal degradation significantly affects the mechanical properties of the friction material. The simulation results show that the static friction coefficient and both normal and tangential contact stiffnesses increase due to adhesive wear, but decrease due to thermal degradation. These trends are qualitatively in agreement with experimental observations reported in the literature and our previous work.     

Basic study on nanofabrication of biodegradable plastics applying biochemical machining

Plastics are regarded as proper materials for microfluidic chips, and, in particular, biodegradable plastics will be more appropriate from the viewpoint of environmental friendliness. In addition, when they are utilized as chip substrate, biochemical machining can be applied. Biochemical machining is a process, which utilizes enzymatic biodegradation. This paper describes studies on application of biochemical machining to nanofabrication of poly(l-lactic acid) (PLLA), which is one of the most widely used biodegradable plastics industrially. The degradation performance of enzyme (proteinase K) was experimentally evaluated to extrapolate a suitable condition for nanofabrication. Additionally, in order to make arbitrary channels with nano-order depth on PLLA, mask fabrication was proposed. It is a fabrication method to control degraded regions and obtain desired shapes with a mask, which has penetrating grooves. Using this method, we achieved fabrication of straight grooves with nano-scale depth. In conclusion, it is clear that biochemical machining can realize an effective process of arbitrarily shaped nanogrooves on PLLA.     

Geometrical effects on spray characteristics of air-pressurized swirl flows

In an effort to obtain the significant features associated with the ALR and length/diameter ratio of the final discharge orifice in swirling flows, experimental observations using a 3-D PDPA system were carried out. Profiles of SMD distributions depending on l _o /d _o , correlation between SMD and turbulence intensities in terms of l _o /d _o and correlations between droplet size and turbulence components were quantitatively analyzed. As discussed in a previous literature, an axisymmetric swirl angle of 30° was selected for this investigation because of its strong turbulence levels in the flow-field and finer droplet disintegrations. Three ALRs of 0.093, 0.106, and 0.122 as well as the length/diameter ratio of 0.15, 0.45, and 0.60 were chosen as parameters. Due to the complex interactions in swirling flows under these variables, this experimental observation will be of fundamental importance to the understanding of geometrical effects on spray trajectory. From the observations, it is indicated that increasing the ALR causes the spray development to be more dependent on number density and volume flux. The results indicated that the SMD decreases discernibly with smaller l _o /d _o , substantiating the fact that turbulence intensities are inversely proportional to the SMD. But, l _o /d _o is quite proportional to the SMD.     

The effect of nano-TiO2 and SiO2 on bonding strength and structural properties of poly (vinyl acetate) composites

Polyvinyl acetate (PVAc) is a thermoplastic polymer widely used in the furniture industry. It has many advantages such as easy processing, cheap, biodegradable; but, resistance to water and hot medium is not enough to the application area. In this study, the effect of nano-TiO₂ and nano-SiO₂ on bonding performance and structural properties of PVAc were investigated. Bonding strength with block shear test and structural properties with thermogravimetric analysis-TGA, X-ray diffraction-XRD, and transmission electron microscopy-TEM of PVAc were determined. The obtained results showed that bonding strength with cooperating both TiO₂ and SiO₂ for 1% and 2% were improved. XRD and TEM results proved to be the homogenously interactions for 1% and 2% between nano fillers and matrix. TGA results showed that thermal stability of PVAc blends was largely improved.     

Effect of nanoparticles on the tribological behaviour of short carbon fibre reinforced poly(etherimide) composites

The tribological behaviour of nano-TiO₂ particle filled polyetherimide (PEI) composites, reinforced additionally with short carbon fibre (SCF) and lubricated internally with graphite flakes, was investigated. The wear tests were conducted on a pin-on-disc apparatus, using composite pins against polished steel counterparts under dry sliding conditions, different contact pressures and various sliding velocities. It was found that the conventional fillers, i.e. SCF and graphite flakes, could remarkably improve both the wear resistance and the load-carrying capacity. With the addition of nano-TiO₂, the frictional coefficient and the contact temperature of the composite were further reduced, especially under high pv (the product of the normal pressure, p, and the sliding velocity, v) conditions. Based on microscopic observations of worn surfaces and transfer films on the counterparts, possible wear mechanisms were discussed.     

The Influence of Anchoring-Group Structure on the Lubricating Properties of Brush-Forming Graft Copolymers in an Aqueous Medium

We have compared the lubricating properties of two different PEG-grafted, polycationic, brush-forming copolymers to gain a deeper understanding of the role of the polyionic backbone in the lubricating behavior of such materials, when used as additives in aqueous lubricant systems. Previously, poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) has been shown to adsorb onto oxide surfaces from aqueous solution and substantially lower frictional forces. Poly(allylamine)-graft-poly(ethylene glycol) (PAAm-g-PEG), which also has a polycationic backbone, has been synthesized in several different architectures, and its performance investigated via adsorption tests, rolling- and sliding-contact tribometry, and the surface forces apparatus. These tests show a clear reduction of friction forces with PAAm-g-PEG compared to water alone. However, when compared with PLL-g-PEG, while PAAm-g-PEG copolymers did not adsorb to the same extent or exhibit as high a lubricity in sliding geometry, they showed a similar lubricating effect under rolling conditions. The difference in the chemical structure of the backbones, especially the flexibility of the anchoring groups, appears to significantly influence both the extent and kinetics of polymer adsorption, which in turn influences lubrication behavior.

End-grafted Sugar Chains as Aqueous Lubricant Additives: Synthesis and Macrotribological Tests of Poly(<Emphasis Type="SmallCaps">l</Emphasis>-lysine)-<Emphasis Type="Italic">graft</Emphasis>-Dextran (PLL-<Emphasis Type="Italic">g</Emphasis>-dex) Copolymers

Comb-like graft copolymers with carbohydrate side chains have been developed as aqueous lubricant additives for oxide-based tribosystems, in an attempt to mimic biological lubrication systems, whose surfaces are known to be covered with sugar-rich layers. As adopted in the previous studies of the graft copolymer poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG), which showed both excellent lubricating and antifouling properties, a similar approach was chosen to graft dextran chains onto the same backbone, thus generating PLL-g-dex. PLL-g-dex copolymers readily adsorb from aqueous solution onto negatively charged oxide surfaces. Tribological characterization at the macroscopic scale, either under pure sliding conditions or a mixed sliding/rolling contact regime, shows that PLL-g-dex is very effective for the lubrication of oxide-based tribosystems. The relative lubricating capabilities of PLL-g-dex copolymers compared with PLL-g-PEG copolymers were observed to be highly dependent on the molecular structure of the copolymers (in particular, side-chain density along the backbone) and the measurement conditions (in particular, time between tribocontacts); the PLL-g-dex copolymers with a low degree of grafted side chains (≤20% grafting of available protonated primary amine groups along the backbone) showed better lubricating performance than their PLL-g-PEG counterparts at high tribocontact frequency (≥ca. 0.32 Hz).     

The effect of vacancies on the annular dark field image contrast of grain boundaries: a SrTiO(3) case study

The analysis of grain boundary structure in high resolution electron microscopy is often hindered by contrast variation within the grain boundary region which is not explained by simple models of the grain boundary structure. Recent work suggests that structural disorder along the beam direction and the presence of vacancies contribute significantly to this effect. One might expect a significant reduction in contrast in a Z-contrast image of a grain boundary would imply that vacancies present must result from the absence of heavier elements. Using a [001](210) Σ5 grain boundary in SrTiO₃ as a test case and first principles structure relaxation to calculate stable defect structures, we show that the reduction in the intensity from fully occupied Sr columns due to the structural distortion resulting from a nearby O vacancy can be as great as that due to introducing a Sr vacancy in the column itself. The effect on energy dispersive X-ray spectroscopy signals is also considered, but found to be smaller than that on Z-contrast images.     

Preparation of silane modified SiO2 abrasive particles and their Chemical Mechanical Polishing (CMP) performances

Surface modified SiO₂ particles in an aqueous environment with γ-aminopropyl triethoxysilane (APTS)/methyl trimethoxysilane (MTMOS) are introduced as abrasive in the slurry. The modified silica particles are characterized by Particle Size/Zeta Potential Analysis, Fourier Transform Infrared Spectroscopy (FTIR), Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). In addition, the enhancement of polishing rate owning to the modified silicon particles in silicon wafer Chemical Mechanical Polishing (CMP) is observed.     

Effect of heat treatment on the sliding wear behaviour of aluminium alloy (Al–Zn–Mg) hard particle composite

Effect of heat treatment on the sliding wear behaviour of aluminium alloy hard particle composite was studied under varying applied load and sliding speed, giving emphasis on the parameters such as wear rate, temperature rise, coefficient of friction and seizure pressure. Hardness is improved due to heat treatment irrespective of the material. Maximum hardness is noted when the materials are aged for 6 h. These facts have been discussed on the basis of nature of worn surface produced after wear. In the present investigation, aging time has been varied from 4 to 10 h at a regular increment of 2 h.     

The effects of particle size and volume fraction of Al2O3 on electronic thermal conductivity of α-Al2O3 particulate reinforced aluminum composites (Al/Al2O3MMC)

The effects of particle size and volume fraction of Al₂O₃ on the thermal conductivity properties of α-Al₂O₃ particulate reinforced aluminum composites (Al/Al₂O₃MMC) are investigated herein. It is found that the thermal conductivity of composites is higher with an Al₂O₃ particle size of 15 μm than with a particle size of 30 μm. The increase in the thermal conductivity could be due to the greater stability of thermal conductive paths with smaller Al₂O₃ particles.     

基于HPLC-ESI-MS~n的杂多酸化学转化原人参三醇型皂苷Re,20(S)-Rf研究

采用高效液相色谱-电喷雾-多级串联质谱技术(HPLC-ESI-MSn)定性分析Keggin型杂多酸(12-磷钨酸)化学转化原人参三醇型皂苷Re和20(S)-Rf的产物结构。在负离子模式下,结合化合物的保留时间、碎片离子的质荷比、中性丢失以及人参皂苷同分异构体的极性差异,分析鉴定了Re的8种主要转化产物为20(S)-Rf2、20(R)-Rf2、20(S)-Rg2、20(R)-Rg2、25-OH-Rg6、25-OH-Rg4、Rg6和Rg4;20(S)-Rf的7种主要转化产物为20(R)-Rf、20(S)-Rf3、20(R)-Rf3、25-OH-Rg8、25-OH-Rg9、Rg8和Rg9。并通过化学转化方法获得了苷元结构3β,12β,25-三羟基-达玛烷-20(21/22)-烯(3β,12β,25-trihydroxy-dammar-20(22)-ene)。12-磷钨酸显示出良好的Re和20(S)-Rf转化率,在90min和4h内的转化率接近100%。该方法可以快速有效地鉴定人参皂苷结构并区分其同分异构体,能够为杂多酸等固体酸催化剂应用于皂苷类中药有效成分的化学转化研究奠定基础。