Lubricant Spin-Off from Magnetic Recording Disks

As the rotation rate of magnetic recording disks increases over the next few years, lubricant spin-off from the disk surface may be significant. Lubricant thickness was measured as a function of spin time at 10000 rpm on typical carbon overcoated magnetic recording disks initially lubricated with 10–135 Å of perfluoropolyether Zdol. The viscosity of the lubricant film increased as the film thickness decreased with spin time. Lubricant spin-off in response to air shear stress on the free surface was approximately described by viscous flow. The rate of lubricant removal by evaporation was compared to the spin-off removal rate in films between 10 and 50 Å thick. Dispersion interaction and chemisorption are expected to retain a molecularly thin film of lubricant on the disk surface.     

The lipids of the alga Spirulina

The blue-green alga, Spirulina maxima, examined in the form of a spray-dried powder, contains 11% of lipid, which has been analysed in detail with a view to establishing both the classes of lipid present and their fatty acid profiles. The dominant lipids are mono-, di- and probably higher galactosyldiglycerides and phosphatidyl glycerol. Unlike other algae, Spirulina synthesises cis-6-cis-9-cis-12 octadecatrienoic acid in contrast to its 9–12–15 isomer.     

Tunable temperature‐ and shear‐responsive hydrogels based on poly(alkyl glycidyl ether)s

We describe the synthesis, characterization and direct‐write 3D printing of triblock copolymer hydrogels that have a tunable response to temperature and shear stress. In aqueous solutions, these polymers utilize the temperature‐dependent self‐association of poly(alkyl glycidyl ether) ‘A’ blocks and a central poly(ethylene oxide) segment to create a physically crosslinked three‐dimensional network. The temperature response of these hydrogels was dependent upon composition, chain length and concentration of the ‘A’ block in the copolymer. Rheological experiments confirmed the existence of sol–gel transitions and the shear‐thinning behavior of the hydrogels. The temperature‐ and shear‐responsive properties enabled direct‐write 3D printing of complex objects with high fidelity. Hydrogel cytocompatibility was also confirmed by incorporating HeLa cells into select hydrogels resulting in high viabilities over 24 h. The tunable temperature response and innate shear‐thinning properties of these hydrogels, coupled with encouraging cell viability results, present an attractive opportunity for additive manufacturing and tissue engineering applications. © 2018 Society of Chemical Industry     

Team Diversity,Learning, and Innovation: A Mediation Model

This study aims to examine the direct and mediating relationships between team diversity, individual and team learning, and individual and team innovation performance. Using a sample of 266 white-collar professionals in Hong Kong, we found that team diversity plays a substantial role in improving both individual and team learning. Individual learning and team learning are independent and positively related to individual and team innovation performance. Individual learning partially mediates the relationship between team diversity and team learning. Individual innovation performance is found to be a partial mediator of team learning and team innovation performance. This study contributes in understanding the unexplored mediating effects of individual learning on team learning, and the individual innovation performance on team innovation performance. Team diversity is found to be the main enabler in the overall model. It is hoped that the research paradigm of this article will generate further development of information systems and technology literature.     

Tribochemistry in contact recording

Even though the flying height is approaching molecular dimensions, it is expected to decrease as the areal recording density is increased. This study employs a new low-velocity test to obtain ultralow flying height with sustained intermittent asperity contacts and random seek accessing in a region near the middle diameter of the disk. Sensitive surface analytical tools are employed to follow tribochemical changes. Profiles are periodically measured across the disk surface using Fourier transform infrared spectroscopy for lubricant thickness and scanning-imaging micro-ellipsometry. Zdol lubricant is removed from the tested region through evaporation of low molecular weight scission fragments. The removal rate increased with increasing chemisorbed fraction and decreasing relative humidity. The increased removal rate is attributed to increases in the Zdol relaxation time. A longer relaxation time allows more time for bond dissociation following asperity contacts. Chemisorption sites in the tested region were occupied by chemisorbed scission fragments with a carboxylic acid end group. Amine and sodium salts of the carboxylic acid were detected on the tested regions of Zdol lubricated, and unlubricated, overcoats. The presence of tribochemically generated carboxylic acid groups on Zdol and overcoat carbon explain the increased water adsorption measured on the tested regions.     

Surface diffusion and flow activation energies of perfluoropolyalkylether

Surface diffusion of perfluoropolyalkylether (PFPE) Fomblin Z15 and Fomblin Zdol (hydroxyl terminated PFPE) on silicon wafers was investigated over the temperature range of 25 to 50°C using scanning microellipsometry. Zdol exhibits a much lower mobility and a distinctly different thickness profile as compared to Z15. The activation energy for surface diffusion of Zdol is higher than that of Z15, reflecting the stronger affinity of its hydroxyl end groups for the substrate. The viscosity flow activation energy E ^* is compared with that of surface diffusion E _d ^* yielding E _d ^* E ^* for Z15, and E _d ^* 1.5E ^* for ZOn leave from Korea Insitute of Science and Technology, PO Box 131, Cheongryang, Seoul, Korea 305-701.     

Evaporation and Flow Properties of Several Hydrocarbon Oils

Two properties that delimit the useful temperature range of synthetic lubricating oils are the vapor pressure and viscosity. This study investigates the ability of fluid theory to model these two properties for diesters with different diacid chain length and alcohol branching, triesters consisting of triglycerides and a trimethylol propane ester, and nonpolar oils including aromatic hydrocarbons, a polyalphaolefin, and two branched alkanes. Within each type of oil there are structural isomers. Isomerism influences the vapor pressure and viscosity, in addition to the well-known dependence on molecular weight. The expressions for the vapor pressure and viscosity are combined using the absolute rate theory of Eyring and equilibrium thermodynamics. A modification of the rate theory allowing for a rotational contribution to the flow-activation entropy was needed to simultaneously fit the vapor pressure and viscosity data between ?20 and 100°C. The flow-activation rotational entropy, calculated from the combined vapor pressure and viscosity data, is a significant contribution to the viscosity. This analysis provides the background for molecular dynamics simulation to assist in designing new low viscosity and vapor pressure synthetic oils.