SciCombinator

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Concept: Lubricant

188

Because lubricants may decrease trauma during coitus, it is hypothesized that they could aid in the prevention of HIV acquisition. Therefore, safety and anti-HIV-1 activity of over-the-counter (OTC) aqueous- (n = 10), lipid- (n = 2), and silicone-based (n = 2) products were tested. The rheological properties of the lipid-based lubricants precluded testing with the exception of explant safety testing. Six aqueous-based gels were hyperosmolar, two were nearly iso-osmolar, and two were hypo-osmolar. Evaluation of the panel of products showed Gynol II (a spermicidal gel containing 2% nonoxynol-9), KY Jelly, and Replens were toxic to Lactobacillus. Two nearly iso-osmolar aqueous- and both silicone-based gels were not toxic toward epithelial cell lines or ectocervical or colorectal explant tissues. Hyperosmolar lubricants demonstrated reduction of tissue viability and epithelial fracture/sloughing while the nearly iso-osmolar and silicon-based lubricants showed no significant changes in tissue viability or epithelial modifications. While most of the lubricants had no measurable anti-HIV-1 activity, three lubricants which retained cell viability did demonstrate modest anti-HIV-1 activity in vitro. To determine if this would result in protection of mucosal tissue or conversely determine if the epithelial damage associated with the hyperosmolar lubricants increased HIV-1 infection ex vivo, ectocervical tissue was exposed to selected lubricants and then challenged with HIV-1. None of the lubricants that had a moderate to high therapeutic index protected the mucosal tissue. These results show hyperosmolar lubricant gels were associated with cellular toxicity and epithelial damage while showing no anti-viral activity. The two iso-osmolar lubricants, Good Clean Love and PRÉ, and both silicone-based lubricants, Female Condom 2 lubricant and Wet Platinum, were the safest in our testing algorithm.

Concepts: HIV, In vivo, Tissues, In vitro, Condom, Lubricant, Personal lubricant, Spermicide

47

The widespread prevalence of commercial products made from microgels illustrates the immense practical value of harnessing the jamming transition; there are countless ways to use soft, solid materials that fluidize and become solid again with small variations in applied stress. The traditional routes of microgel synthesis produce materials that predominantly swell in aqueous solvents or, less often, in aggressive organic solvents, constraining ways that these exceptionally useful materials can be used. For example, aqueous microgels have been used as the foundation of three-dimensional (3D) bioprinting applications, yet the incompatibility of available microgels with nonpolar liquids, such as oils, limits their use in 3D printing with oil-based materials, such as silicone. We present a method to make micro-organogels swollen in mineral oil, using block copolymer self-assembly. The rheological properties of this micro-organogel material can be tuned, leveraging the jamming transition to facilitate its use in 3D printing of silicone structures. We find that the minimum printed feature size can be controlled by the yield stress of the micro-organogel medium, enabling the fabrication of numerous complex silicone structures, including branched perfusable networks and functional fluid pumps.

Concepts: Polymer, Polymer chemistry, Liquid, Glass transition, Elasticity, Linear elasticity, Oil, Lubricant

44

Decarbonizing the transportation sector is critical to achieving global climate change mitigation. Although biofuels will play an important role in conventional gasoline and diesel applications, bioderived solutions are particularly important in jet fuels and lubricants, for which no other viable renewable alternatives exist. Producing compounds for jet fuel and lubricant base oil applications often requires upgrading fermentation products, such as alcohols and ketones, to reach the appropriate molecular-weight range. Ketones possess both electrophilic and nucleophilic functionality, which allows them to be used as building blocks similar to alkenes and aromatics in a petroleum refining complex. Here, we develop a method for selectively upgrading biomass-derived alkyl methyl ketones with >95% yields into trimer condensates, which can then be hydrodeoxygenated in near-quantitative yields to give a new class of cycloalkane compounds. The basic chemistry developed here can be tailored for aviation fuels as well as lubricants by changing the production strategy. We also demonstrate that a sugarcane biorefinery could use natural synergies between various routes to produce a mixture of lubricant base oils and jet fuels that achieve net life-cycle greenhouse gas savings of up to 80%.

Concepts: Petroleum, Climate change, Hydrocarbon, Alkane, Coal, Lubricant, Internal combustion engine, Fuel

30

Arthritis is a leading cause of disability, and when nonoperative methods have failed, a prosthetic implant is a cost-effective and clinically successful treatment. Metal-on-metal replacements are an attractive implant technology, a lower-wear alternative to metal-on-polyethylene devices. Relatively little is known about how sliding occurs in these implants, except that proteins play a critical role and that there is a tribological layer on the metal surface. We report evidence for graphitic material in the tribological layer in metal-on-metal hip replacements retrieved from patients. As graphite is a solid lubricant, its presence helps to explain why these components exhibit low wear and suggests methods of improving their performance; simultaneously, this raises the issue of the physiological effects of graphitic wear debris.

Concepts: Critical thinking, Avicenna, Hip replacement, Graphite, Friction, Tribology, Lubricant, Molybdenum disulfide

29

Nano-objects have been investigated for drug delivery, oil detection, contaminant removal, and tribology applications. In some applications, they are subjected to friction and deformation during contact with each other and their surfaces on which they slide. Experimental studies directly comparing local and global deformation are lacking. This research performs nanoindentation (local deformation) and compression tests (global deformation) with a nanoindenter (sharp tip and flat punch, respectively) on molybdenum disulfide (MoS2) multi-walled nanotubes (MWNTs), ~500 nm in diameter. Hardness of the MoS2 nanotube was similar to bulk and does not follow the “smaller is stronger” phenomenon as previously reported for other nano-objects. Tungsten disulfide (WS2) MWNTs, ~300 nm in diameter and carbon nanohorns (CNHs) 80-100 nm in diameter were of interest and also selected for compression studies. These studies aid in understanding the mechanisms involved during global deformation when nano-objects are introduced to reduce friction and wear. For compression, highest loads were required for WS2 nanotubes, then MoS2 nanotubes and CNHs to achieve the same displacement. This was due to the greater number of defects with the MoS2 nanotubes and the flexibility of the CNHs. Repeat compression tests of nano-objects were performed showing a hardening effect for all three nano-objects.

Concepts: Molybdenum, Graphite, Materials science, Sulfide, Friction, Tribology, Tungsten, Lubricant

29

Friction, wear and the associated energy dissipation are major challenges in all systems containing moving parts. Examples range from nanoelectromechanical systems over hip prosthesis to off-shore wind turbines. Bionic approaches have proven to be very successful in many engineering problems, while investigating the potential of a bio-inspired approach in creating morphological surface textures is a relatively new field of research. Here, we developed laser-created textures inspired by the scales found on the skin of snakes and certain lizards. We show that this bio-inspired surface morphology reduced dry sliding friction forces by more than 40%. In lubricated contacts the same morphology increased friction by a factor of three. Two different kinds of morphologies, one with completely overlapping scales and one with the scales arranged in individual rows, were chosen. In lubricated as well as unlubricated contacts, the surface texture with the scales in rows showed lower friction forces than the completely overlapping ones. We anticipate that these results could have significant impact in all dry sliding contacts, ranging from nanoelectromechanical and micro-positioning systems up to large-scale tribological contacts which cannot be lubricated, e.g. because they are employed in a vacuum environment.

Concepts: Mass, Force, Classical mechanics, Friction, Tribology, Texture, Normal force, Lubricant

28

The use of ethylcellulose (EC) polymers as a means to structure edible oils for fat replacement is beginning to show great promise and the use of these ‘oleogels’ has recently been shown to be feasible in food products. These gels are very versatile, as the mechanical properties can be tailored by altering either the fatty acid profile of the oil component, or the viscosity or concentration of the polymer component. Here we report the observation that certain formulation of EC oleogels tend to separate into two distinct phases; a soft interior core surrounded by a firm exterior sheath. It was found that the extent of this effect depends on EC viscosity, and can also be induced through the addition of certain surfactants, such as sorbitan monostearate and sorbitan monooleate, though not by glycerol monooleate. Although the two visually distinct regions were shown to be chemically indistinct, the cooling rate during gel setting was found to play a large role; rapid setting of the gels reduces the fractionation effect, while slow cooling produced a completely homogeneous structure. In addition, by reheating only the soft region of the gel, a firm and soft fractionated gel could again be produced. Finally, it was observed that oleogels prepared with castor oil or mineral oil have the ability to remove or induce the gel separation, respectively. Taken together, these results indicate chemical interactions may incite the separation into two distinct phases, but the process also seems to be driven by the cooling conditions during gel setting. These findings lend insight into the EC-oleogel gelation process and should provide a stepping stone for future research into the manufacturing of these products.

Concepts: Nutrition, Fatty acid, Fat, Colloid, Gel, Palm oil, Lubricant, Aerogel

27

Hybrid nano-materials offer potential scope for an increasing number of novel applications when engineered to deliver usefully functional properties. Recent advancement in the design of new material products that result from interactions among different compositions at the nano and micro scale has led to innovative ways to fabricate and process hybrids with altered structural physicochemical properties. An example is the development of novel ‘lubricants’ that make use of ionic liquids (ILs) and their ability to induce exploitable molecular assemblies at the IL-graphene interface. In the present study, we report the potential of graphene-ionic liquid hybrid nanomaterials for engineering applications with a focus on ‘lubricant’ properties to reduce frictional forces to enhance tribological performance. The present contribution outlines the wear and tribological properties (friction and lubrication) of a highly viscous ionic liquid [BMIM][I] IL and its comparison with its nanohybrid material counterpart. Detailed structural-microstructural investigations of the nano-hybrid materials were performed using X-ray diffraction and microscopic techniques employing scanning electron (SEM) and transmission electron (TEM) microscopies. A comparative study of the morphology of friction track and wear behaviour was observed by SEM. These characteristic properties within and outside the friction track were further correlated with physical and chemical interactions obtained by contact angle measurements and Raman spectroscopy.

Concepts: Spectroscopy, X-ray, Liquid, Materials science, Ionic liquid, Friction, Tribology, Lubricant

27

Blends of entirely bio-sourced polymers, namely polylactide (PLA) and starch, have been melt-compounded by lab-scale co-extruder with castor oil (CO) as a plasticizer. The enrichment of castor oil on starch had great effect on the properties of the blends. If the castor oil was mainly dispersed in PLA matrix, the properties of the blends were poor, but when the hexamethylenediisocyanate (HDI) was grafted on starch granules the ready reactions between the hydroxyl on CO and the isocyante on the HDI-grafted starch (HGSTs) brought CO molecules enriched on starch particles. DSC analysis shows that the CO layer on starch has a positive effect on the crystallization of PLA in the ternary blend. The accumulation of CO on starch greatly improves the toughness and impact strength of PLA/starch blends. The grafting content of HDI on the starch granules primarily determined the compatibility and properties of the resulted blends.

Concepts: Grafting, Wax, Differential scanning calorimetry, Plant reproduction, Castor oil, Lubricant, Plant propagation

20

The use of lubricants (solid or liquid) is a well-known and suitable approach to reduce friction and wear of moving machine components. Another possibility to influence the tribological behaviour is the formation of well-defined surface topographies such as dimples, bumps or lattice-like pattern geometries by laser surface texturing. However, both methods are limited in their effect: surface textures may be gradually destroyed by plastic deformation and lubricants may be removed from the contact area, therefore no longer properly protecting the contacting surfaces. The present study focuses on the combination of both methods as an integral solution, overcoming individual limitations of each method. Multiwall carbon nanotubes (MWCNT), a known solid lubricant, are deposited onto laser surface textured samples by electrophoretic deposition. The frictional behaviour is recorded by a tribometer and resulting wear tracks are analysed by scanning electron microscopy and Raman spectroscopy in order to reveal the acting tribological mechanisms. The combined approach shows an extended, minimum fivefold longevity of the lubrication and a significantly reduced degradation of the laser textures. Raman spectroscopy proves decelerated MWCNT degradation and oxide formation in the contact. Finally, a lubricant entrapping model based on surface texturing is proposed and demonstrated.

Concepts: Liquid, Raman spectroscopy, Graphite, Scanning electron microscope, Friction, Tribology, Texture, Lubricant