Micro-surface texturing design is becoming an important part of surface engineering since engineering practices and analyses have indicated that surface textures may significantly affect the tribological performance of contact interfaces. Advances in the manufacturing technologies of surface finishing and micro-machining, such as laser surface texturing, photolithography, and etching, LIGA process, have made it possible to fabricate different fine structures on various engineering surfaces. Though the influence of micro-surface texturing on hydrodynamic lubrication has been widely investigated over the last decade, such an influence may be complicated and difficult to characterize with only a few statistic surface parameters. Thus, very little attention has been paid to the effects of different textural shapes and orientations on hydrodynamic lubrication, which is the main topic of this article. A theoretical model based on a single dimple was established to investigate the geometric shape and orientation effects on the hydrodynamic pressure generated between conformal contacting surfaces. Using the Successive Over Relaxation method, the average hydrodynamic pressure generated by the texture pattern with the dimples in shapes of circle, ellipse, and triangle at different orientations to the direction of sliding are obtained. The results indicate that geometric shape and orientation have obvious influences on load-carrying capacity of contacting surfaces. With the same dimple area, area ratio and dimple depth given in this research, ellipse dimples perpendicular to the sliding direction showed the best load-carrying capacity. This result agrees with previous experimental results very well.

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A three-stage linear gradient strategy using reverse-phase high-performance liquid chromatography (HPLC) was optimized for rapid, high-quality, and simultaneous purification of the lipopeptide isoforms of iturin, fengycin, and surfactin, which may differ in composition by only a single amino acid and/or the fatty acid residue. Matrix-assisted laser desorption ionization time-of-flight tandem mass spectrometry (MALDI-TOF-MS/MS) was applied to detect the lipopeptides harvested from each reversed-phase HPLC peak. Amino acid analysis based on phenyl isothiocyanate derivatization was further used for confirmation of the amino acid species and molar ratio in a certain HPLC fraction. By this MALDI-TOF-MS/MS coupled with amino acid analysis, it was revealed that iturin at m/z 1,043 consists of a circular Asn-Tyr-Asn-Gln-Pro-Asn-Ser peptide and C14 β-OH fatty acid. Surfactin homologs from Bacillus subtilis THY-7 at m/z 1,030, 1,044, 1,058, and 1,072 possess a circular Glu-Leu-Leu-Val-Asp-Leu-Leu peptide and the β-OH fatty acid with a different length (C13-C16). Fengycin species at m/z 1,463 and 1,477 are homologs possessing the circular peptide Glu-Orn-Tyr-Thr-Glu-Ala-Pro-Gln-Tyr-Ile linked to a C16 or C17 γ-OH fatty acid, whereas fengycin at m/z 1,505 contains a Glu-Orn-Tyr-Thr-Glu-Val-Pro-Gln-Tyr-Ile sequence with a Val instead of Ala at position 6. The method developed in this work provided an efficient approach for characterization of diverse lipopeptide isoforms from the iturin, fengycin, and surfactin families.

Iron nanoparticles are highly desirable for their potential applications in magnetic and catalytic industry. However, their shape-controlled fabrication is still an important challenge. Here we successfully synthesized icosahedral face-centered cubic (fcc) Fe nanoparticles with size of 5-13 nm by a specifically designed thermodynamic governed synthetic route, which is facile but highly efficient and reproducible. With the aberration-corrected transmission electron microscopy (TEM), the unique icosahedral structure's pseudo-2-fold, 3-fold, and pseudo-5-fold axes were directly observed for the first time and verified by computer simulation, which reveals that nanoparticles' orientations have a large impact on HRTEM images at ultrahigh resolution. It is expected that as-synthesized Fe nanoparticles with sharp corners and edges would be beneficial for tailoring chemical and physical properties at the nanoscale.

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In this study, the effect of different dimple shapes on the tribological performance of surface texture has been investigated. First, a numerical model was developed to study the effect of dimple shapes on hydrodynamic pressure generation. The selected dimple shapes include circle, square, and ellipse, and the flow direction of lubricant is perpendicular to the major axis of elliptical dimples or the sides of square dimples. The results showed that the dimple shape can be optimized for greater hydrodynamic pressure generation. Then, the reciprocating sliding tests were carried out under oil lubrication and face-contact conditions. Tests were conducted for rotational speeds in the range 50-500 r/min and test loads of 200 and 400 N. Surface texture patterns with different dimple shapes were used, the dimple shapes and orientations were the same as those used in the numerical model, and the dimple depth and dimple area ratio were varied under fixed dimple area conditions. The test results indicated that a better friction reduction effect compared with untextured specimens can be obtained by selecting a suitable dimple area ratio and dimple depth for each dimple shape. Comparing the friction reduction effect, the elliptical dimples showed the best performance, the square dimples showed the second best results, and the circular dimples performed worst. However, as the test load increased, the friction reduction effect of all dimple shapes decreased; moreover, the differences between the shapes became smaller.

The appealing and enigmatic properties of biological surfaces inspire people that a smooth surface is not always the best. Currently, the patterns of microdimples have attracted more attentions since such closed texture cells are supposed to generate hydrodynamic pressure easily. The advanced manufacturing techniques provide precision and freedom for the fabrication of microdimples, which enables the optimisation of dimple geometry and distribution to obtain better tribological performances. Over the past decade, experiments were carried out to investigate the effects of microdimples on various materials under different operating conditions. Analytical models were established to evaluate the hydrodynamic effect of the dimple patterns. The results suggest that the design of dimple pattern following hydrodynamic principle would obtain good tribological performance under high‐speed low‐load conditions; however, for the case of low‐speed high‐load conditions, shallow and small dimples would have more obvious friction reduction effect than those designed based on hydrodynamic pressure generation. Copyright © 2011 John Wiley & Sons, Ltd.