Surface Tension lubricating oils

Figure 5. Relationship between the efficiency of lubrication and the surface tension of oils for steel/POM microbearings.

Foam Inhibitors. Methyl sihcone polymers of 300-1000 mm /s(= cSt)) at 40°C are effective additives at only 3—150 ppm for defoaming oils in internal combustion engines, turbines, gears, and aircraft appHcations. Without these additives, severe churning and mixing of oil with air may sometimes cause foam to overflow from the lubrication system or interfere with normal oil circulation. Because sihcone oil is not completely soluble in oil, it forms a dispersion of minute droplets of low surface tension that aid in breaking foam bubbles. 

The molecular dipstick microscope is related to the AFM. It measures lubricant film thickness. The probe is lowered into the oil film on a surface (like the automobile engine crankcase dipstick). The tip is attracted to the surface by the surface tension of the film but repelled by van der Waal s forces from the hard substrate. By noting the height of the probe from the two surfaces as it makes contact, the film thickness can be measured with a precision of about 0.5 nm. 

This product is designed to break water-in-oil emulsions, especially for fuel oils, lubricating oils, or waste oils. This emulsion breaker lowers the surface tension of the oil and, because it is immiscible in water, it is not lost when the water is decanted from the oil. 

Industrially, silicone surfactants are used in a variety of processes including foam, textile, concrete and thermoplastic production, and applications include use as foam stabilisers, defoamers, emulsifiers, dispersants, wetters, adhesives, lubricants and release agents [1]. The ability of silicone surfactants to also function in organic media creates a unique niche for their use, such as in polyurethane foam manufacture and as additives to paints and oil-based formulations, whilst the ability to lower surface tension in aqueous solutions provides useful superwetting properties. The low biological risk associated with these compounds has also led to their use in cosmetics and personal care products [2]. 

Because of their chemical inertness, low surface tension and antisurfactant activity polyorganosiloxane (silicone) oils have found varied applications in medicine. These have included use as an artificial lubricant for arthritic joints191, as a means of soft tissue augmentation, and as an additive in creams and oils for burn treatment. Di-methylpolysiloxane fluids have been injected as replacement for aqueous and vitreous humour in eyes. Reactive organosilicon compounds comprise a new class of potential prophylactic and therapeutic agents192. Protection against atherosclerosis... 

A variation in the time of flow when the walls of the tube are covered with an immiscible liquid, such as oleic acid, is really due to changes of surface tension, which are iniportant with some types of viscometer. It is possible, however, that some slip may occur with some lubricating oils, due to the regular reflexion of large molecules from the walls, as contrasted with the diffuse scattering of smaller molecules by irregularities of molecular dimensions in the walls. ... 

Another type of foam has been observed when a multicomponent liquid has a composition close to a separation into two liquid phases. Surface tension drops to a very low value, allowing easy formation of bubbles. An example is found in solvent recovery from lubricating-oil extraction processes. This type of foam has been referred to as Ross foam,f ° named after an investigator of these foams. 

Surface creep must be very low, both to restrict loss of lubricant from bearings, etc. and to avoid contamination of other components. Creep is a surface tension effect where oil surface tensions are typically in the range 18-30 mN/m. To mitigate surface creep, thermal gradients should be avoided or minimised and the surface finish of components should be optimised. Capillary creep occurs if Ra> 0.1 mm, thermal creep occurs if Ra < 0.6 mm. 

Very similar findings resulted in a contact angle study of a per-fluormated lubricating oil on paraffin wax. The surface tension, y, was 20.2 dynes per cm., but the contact angles on two wax surfaces gave y values of 13.5 dynes per cm. (see Figure 4). 

In the lubrication of ball bearings, oil is transported by surface creep from the grease supply to the raceway this creep is favored by the molecular heterogeneity of ordinary petroleum oils, whose more volatile components have lower surface tensions than the total oil mixture. If one imdertakes to lubricate with a radiation-resistant alkyl aromatic oil, however, the situation may be reversed, and the deliberate inclusion of a minor amount of an oil of lower surface tension is indicated. The recession phenomena reported for silicone liquids on a 400° surface remind us that at the high temperatures and temperature gradients existing in some military equipment oil films maybe expected... 

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