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LUBRICATION FUNDAMENTALS Dr. Robert M. Gresham / Contributing Editor Editor’s Note: This article is reprinted from the March 2008 issue of TLT.

When oil and do mix

Thanks to the fascinating world of surface chemistry, you might have more options than you think when it comes to combining fl uids.

Key concePTs According to conventional wisdom, oil and • There are several materials that derive some or water don’t mix. While most oils and have some very minute in each other (on a macro scale, for exam- all of their properties from the use of . ple), you really can’t mix the two to get a true . • The physical and chemical behavior of I remember the old DuPont adage: “Better living through chemistry.” Both Mother Nature and Mankind have shown ad- cannot be understood without taking surface mirable skills in this regard. What I’m referring to, of course, tension into account. is the wonderful and fascinating world of surface chemistry. As tribologists we are concerned very much with certain • The difference between suspensions, dispersions aspects of surface chemistry such as wear processes, tribo- and is their inherent stability or chemical reactions, friction, etc.—the whole nanoworld where tendency not to separate or settle. certain atoms or molecules on surfaces come in contact with other chemicals to produce interesting results. In the case

22 • AUGUST 2011 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG Surface-active agents allow us to mix incompatible materials in a generally synergistic manner for some purpose.

innovation starts with ™ of oil and water, I’m referring to the 3. colloid. A solid, or gas- SpectraSyn Elite chemistry of surfactants or surface-ac- eous substance made up of mPAO tive agents. Surface-active agents allow very small, insoluble particles SpectraSyn Elite™ metallocene us to mix incompatible materials in a (as single large molecules or polyalphaolefi n (mPAO) base stock generally synergistic manner for some masses of smaller molecules) uses a proprietary catalyst process purpose. that remain in in that results in a PAO with improved There are all kinds of materials a surrounding solid, liquid or properties, which enables the fl exibility around us that derive some or all of gaseous medium of different to develop fi nished that address formulators’ challenges, their properties from the use of sur- matter. Colloids usually are particularly in industrial applications. factants, including engine oils, met- pretty stable; thus a stable col- Benefi ts include: alworking fluids, certain lubricants, loidal suspension such as milk higher VI for low and high face creams, lotions, conditioners and consists of an immiscible liquid temperature performance cosmetics, shaving cream, water-based ( ) dispersed and held improved shear stability and coatings and products in another liquid by substances for durability conjured by man. called emulsifiers. lower pour point for increased We all know chemical companies fl ow in cold environments can do some pretty amazing things, 4. Dispersion. A colloidal system but what about Mother Nature? One with its dispersed particles and example that we encounter virtually at the medium in which these are index (vi)

210 Conventional 100 cSt PAO birth is obviously the most common suspended. These are materi- T SpectraSyn Elite™ 150 cSt :10” and best formulated: mammalian milk. als that sort of fit in the mid- 200 190

To understand all of this, we first dle. Most dispersions need or 180 204 need to review the following defini- should be shaken or stirred be- 170 160 170 test method: tions and, yes, I know there is a bit to fore use. Some salad dressings iscosity Index (VI) V 150 ASTM D 2270 digest here. immediately come to mind. SpectraSyn Elite™ 150 cSt has a PRoPeRTies oF higher VI than conventional 5. surface Tension. The effect with- 100 cSt PAO. suRFace chemisTRy in the surface layer of a liquid 1. Wetting. The spreading and pen- that causes the layer to behave etrating properties of a liquid as an elastic sheet. Surface ten- low temperature performance

caused by lowering its surface sion allows insects to walk on -28 Conventional 100 cSt PAO -29 tension—that is, the tendency water. It also allows small met- -30 SpectraSyn Elite™ 150 cSt of its molecules to adhere to al objects such as needles, razor -30 C

o -33 each other. blades or foil fragments to float -31 -32 test method: on water, causing capillary ac- ASTM D 97 /

Pour Point, ASTM D 5950 2. suspension. The condition of a tion. Whenever a rain drop falls -33 substance whose particles are or a is mixed SpectraSyn Elite™ 150 cSt has a dispersed through a fluid but with water or an alcoholic bev- lower pour point than conventional not dissolved in it; the condi- erage is stirred in a glass, the ef- 100 cSt PAO. tion of one having relatively fects of surface tension are read- large particles that will separate ily visible. Everyone is familiar exxonmobilsynthetics.com on standing. These are materi- with water droplets forming als that always say, “shake well large beads (because of water’s before using” on labels. In na- high surface tension ~72) on a ADVANCED Innovative SYNTHETIC lubricants ture, a muddy river might be an waxed surface (low surface ten- BASE STOCKS start here example—once it stops flowing, sion ~<22), like a clean, freshly the mud settles and the water is waxed automobile hood. The clear again. physical and chemical behavior

WWW.STLE.ORG TRIBOLOGY & LUBRICATION TECHNOLOGY AUGUST 2011 • 23 ME MagNwp Slug Name: or shaking (mixing with a fair amount of energy). In addition, we can make an emul- sion with a different (a better one for our particular system—an emulsifier), of liquids cannot be understood mixed with energy, resulting in a stable withoutHydrocarbon taking surfaceTail tension Polar Head . So with a little magic, we have into account. It governs the Polar and functional groups on molecules generally Figureshape 1. that small masses of liq- have some kind of ionic character. Now let’s strip away the alchemist’s uid can assume and the degree of contact a liquid can make with robes, cowl, incantations and crow feathers another substance. and look at what’s going on. First, the sur- For example, imagine with a . The engine dirt tends to be factant is a molecule that typically has a 6. Surfactant. A substance such addition, we can make a dispersion pasta on the end of it. long chain tail with some kind of polar, soas thean emulsifier,polar heads detergent of the ordispersant by adding a surfactant and stirring or The polar head generally likes po- polar head attached, as shown in Figure 1. attach towetting the polaragent partsthat lowers of the the dirt toshaking keep (mixing with a fair amount of lar solvents such as water, while the You can think of it as kind of like a piece of it in suspensionsurface tension in the of oil the until its timeenergy). for a In addition, we can make an tail generally likes non- in which it is dissolved or the emulsion with a different surfactant (a polar solvents such as oil or other spaghetti with something very different oil change or the particles agglomerate to a large enoughtension sizeat the to interface catch in between the oil filterbetter (see one for our particular system— similarly long, straight-chain non- two immiscible liquids. Add just an emulsifier), mixed with energy, re- polar chemicals. Polar solvents and Figure 2). The polar head generally likes polar sol- a little soap to the water in the sulting in a stableThe emulsion. physical andSo with functional groups on molecules gener- vents such as water, while the hydrocarbon As shownexample in Figureabove, and3 (see the page water 26 ), imaginea little magic, we have mixed oil and ally have some kind of ionic character: tail generally likes nonpolar solvents such very polarno longer calcium beads carbonate on the car hood (CaCO 3water.with chemical behavior of plus or minus charges, partial plus or as oil or other similarly long, straight-chain positivebut charges forms a onsmooth calcium) sheet. dispersed inNow a let’s strip away the alchemist’s minus charges or just atoms with a lot robes, cowl, incantationsliquids cannot and becrow of loosely held electrons. nonpolar chemicals. Polar solvents and nonpolar solvent like oil, , etc., and OPTIONS feathers and lookunderstood at what’s going without on. The polar heads of the surfactant functional groups on molecules generally containing a dispersant that has a polar sul- Okay, let’s try to cut- to the chase. If we First, the surfactant is a molecule that like water; they align themselves like a have some kind of ionic character: plus or fonatewant tohead mix oil(SO and3 water,with wea canminus do charge).typically has a takinglong carbon surface chain ten- tail ball in the water with the polar heads minus charges, partial plus or minus Thus,a poor the job nonpolar by making tails a suspension, are to the outsidewith some kind sionof polar into head account. attached, on the outside (because they like wa- charges or just atoms with a lot of loosely of whichthe micelle, depends onmaking the nature the of calcium the oil carbon-as shown in Figure 1. You can think of ter) and the long nonpolar tails to the ateor compatiblemaybe by just with shaking the it nonpolar up a lot solvent.it as kind of like a piece of spaghetti inside (because they don’t like water). so it will be stable for a little while. In with something very different from These structures are called micelles. In The polar heads of the surfactant like Hopefully, you’ll see a pattern begins to emerge. nonpolar solvents, they do just the re- water; they align themselves like a ball in verse; that is, the polar heads align to the water with the polar heads on the out- One of the key things that characterize the interior of the ball and the nonpo- littleside while.(because In addition,they like wewater) can andmake the a longdis- the difference between suspensions, disper- lar tail to the outside. persionnonpolar by tailsadding to thea surfactant inside (because and stirring they sions and emulsions is their inherent stabil- OK, so what does this have to do ordon’t shaking like water). (mixing These with structures a fair amount are called of ity or tendency not to separate or settle. with mixing oil and water? Well, in a polar solvent the oil would be hap- energy). In addition, we can make an emul- Aside from the relative goodness of the sur- micelles. In nonpolar solvents, they do just piest in the center of the micelle be- factant, the most important part is the par- sionthe reverse;with a different that is, surfactantthe polar heads (a better align one to cause the long straight carbon chains forthe our interior particular of the ballsystem—an and the nonpolaremulsifier), tail ticle size (whether gases, solids or liquids) are like the oil molecules. Conversely, mixed with energy, resulting in a stable of the materialHydrocarbon being Tail dispersed. They settle Polar Head if we had only a little water in our oil, emulsion.OK, so Sowhat with does a littlethis havemagic, to we do havewith the micelle would reverse and the wa- ter would move to the interior of the mixing oil and water? Well, in a polar sol- Figure 1 CONTINUED ON PAGE 26 Figure 1. micelle. When this happens to the mi- ventNow the oillet’s would strip be away happiest the inalchemist’s the center celle in a chemical system, we call it robes,of the cowl,micelle incantations because the and long crow straight feathers car- an inversion. While these descriptions andbon look chains at what’sare like going the oil on. molecules. First, the Con-sur- For example, imagine motor oil with a are a little simplistic, a polar material factantversely, is if awe molecule had only that a little typically water hasin our a dispersant. The engine dirt tends to be is made more or less compatible with longoil, thecarbon micelle chain would tail reverse with some and the kind water of polar, so the polar heads of the dispersant a nonpolar material. The following are some visual examples that might make polarwould head move attached, to the interioras shown of inthe Figure micelle. 1. attach to the polar parts of the dirt to keep it in suspension in the oil until its time for a this easier to understand. YouWhen can this think happens of it as kindto theof likemicelle a piece in ofa For example, imagine motor oil spaghettichemical systemwith something we call itvery an inversion.different oil change or the particles agglomerate to a with a dispersant. The engine dirt While these descriptions are a little simplis- large enough size to catch in the oil filter (see tends to be polar, so the polar heads of tic, a polar material is made more or less Figure 2). the dispersant attach to the polar parts The polar head generally likes polar sol- The physical and ventscompatible such as with water, a nonpolar while the material. hydrocarbon Below As shown in Figure 3 (see page 26), imagine of the dirt to keep it in suspension in Figure 2 the oil until its time for an oil change are some visual examples that might make veryFigure polar 2. calcium carbonate (CaCO3 with chemical behavior of tail generally likes nonpolar solvents such or the particles agglomerate to a large as oil or other similarly long, straight-chain positive charges on calcium) dispersed in a liquids cannot be nonpolar chemicals. Polar solvents and nonpolar solvent like oil, hexane, etc., and STLE University’s all-new online offerings include certificate courses,understood short courses, without Webinars and podcasts. Details at www.stle.org. 25 functional groups on molecules generally containing a dispersant that has a polar sul- TRIBOLOGY- & LUBRICATION TECHNOLOGY MARCH 2008 25 have some kind of ionic character: plus or fonate head (SO3 with a minus charge). taking surface ten- To make an emulsion, sometimes you must have vigorous mixing or even milling or grinding to get enough surfactant on the surface to do the job.

enough size to catch in the oil filter their inherent stability or tendency particle size small enough (because (see Figure 2). not to separate or settle. Aside from small particles have more surface area As shown in Figure 3, imagine very the relative goodness of the surfactant, relative to their mass than larger par-

polar calcium carbonate (CaCO3 with the most important part is the particle ticles) to get enough surfactant on the positive charges on calcium) dispersed size (whether gases, solids or liquids) surface to do the job. in a nonpolar solvent like oil, hexane, of the material being dispersed. They As a further example, back in those etc., and containing a dispersant that settle because the particle size is too thrilling days of yesteryear when I was

has a polar sulfonate head (SO3- with large and/or not enough surfactant is a young chemist, I developed a pro- a minus charge). Thus, the nonpolar on the surface to keep them from set- cess for a particular chemical. The fi- tails are to the outside of the micelle, tling. nal step in the process resulted in the making the calcium carbonate com- In emulsions, the particle sizes chemical precipitating (coming out of patible with the nonpolar solvent. tend to be quite small, usually well less solution) into a nice crystalline slurry Hopefully, you’ll see a pattern begins that you can see with dispersions be- form that could be filtered like beach to emerge. ing larger and suspensions very large, sand from the reaction mass, dried and One of the key things that charac- indeed. To make an emulsion, some- sold as a final product. When I scaled terize the difference between suspen- times you must have vigorous mixing it up in the plant to 5,000 gallons, low sions, dispersions and emulsions is or even milling or grinding to get the and behold, instead of a slurry I got something that looked more like a gi- Figure 3. ant beer head containing my product. Alas, I couldn’t pump it to the filter, as the kettle drain was on the bottom and the beer head would hang up in the kettle and plug the drain. “It didn’t happen like that in the lab!” Ever hear that one before? I was lower than a snake’s belly in a wagon rut. Oh, woe, what to do? Enter the MPS (Magic Pinch of Stuff), in this case a product called Trition100X. I don’t know if it is still on the market, but it either is or was an excellent surfactant. Any- way, I added an ounce to the kettle and Shazam! I got my slurry of beach sand and off to the filter we went. What happened? The solids en- trained small air bubbles from the more vigorous mixing in the bigger kettle and the differences in surface tension between my product and the reaction mass. The solids did not wet out but, rather, had tiny air bubbles coating each crystal, causing them to float. The addition of the surfactant caused the surface tension to change at the surface of the solids, the foam broke immediately, the slurry returned and my job was secured until the next Figure 3 crisis. because the particle size is too large and/or behold, instead of a slurry I got something 26 • AUGUST 2011 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG not enough surfactant is on the surface to that looked more like a giant beer head con- keep them from settling. taining my product. In one of our case histories in might go through the waste treatment STLE’s Metalworking Fluid Manage- plant (depending on its design) and ment Certificate education course, we The better the emulsion, out into the waste stream. Not good! have a similar example where metal the longer the fluid lasts in So the waste treatment manager treats fines are floating in a metalworking the emulsion with acid, the emulsion central system with the lack of wetting the system and the happier breaks and then the waste system can being the problem. To carry the previ- the customer. capture and concentrate the waste, ous story a little further, Triton 100X leaving the waste stream to the envi- (I have to use the trade name because ronment clean. I have forgotten the chemistry) could So if you want to mix oil and wa- be used in higher concentrations as a termilk and can’t get to the store, she ter—no problem. And if you don’t dispersant or emulsifier or, in much takes regular whole milk, adds a little want to mix oil and water—no prob- higher concentrations, as I understand vinegar, stirs it up and presto—she has lem. Like DuPont says, “Better living it, to make a stable foam for shaving buttermilk! What she did was break through chemistry!” cream. A great MPS! Mother Nature’s emulsion by adding So now you know how to mix oil acid, which ties up the polar heads of and water! That was the prime pur- Mother Nature’s surfactant, and the pose of this article, and if this infor- butter drops out in globs. mation is all you are interested in you Many MWFs are emulsions. The can stop reading here. But if you want better the emulsion, the longer the flu- extra credit, read on. id lasts in the system and the happier What do you do if you don’t want the customer. But eventually it is time to mix oil and water—that is, you to finally send the fluid to the waste Bob Gresham is STLE’s director of don’t want a stable emulsion? Ask treatment system. What happens? professional development. You can reach your Mom. When she runs out of but- Well, a really good emulsion just him at [email protected].

WWW.STLE.ORG TRIBOLOGY & LUBRICATION TECHNOLOGY AUGUST 2011 • 27