Chemistry of Oil Additives
Here is a comprehensive list (best you'll find outside of the lab) of multifunctional additives and their functions. Notice the same chemicals and compounds perform more than one function.
Multifunctional Additives (in Alphabetical Order) listed as to Functional Agent, additive category, general or specific chemical compound, and how it works, respectively.
Antifoamants or foam inhibitors (Protective Additive): polymers such as silicone polymers and organic copolymers of the silaxane's; creates a lens that reduces the bubble's surface tension.
Antioxidants or oxidation inhibitors (Protective Additive): ZDDP, ZTDC, Moly TDC, Antimony TDC, aromatic amines such as organic tolutriazoles, thiadiazoles, diphenylamines, olefin sulfides, carboxylic acids; decomposes peroxides and terminates free radical reactions. Increases temperature of base oil at which base oil may tend to oxidize. Oxidation of oil promotes polymerization of sludge particles and increases viscosity.
Anti-Wear and Extreme Pressure Additives (Surface Protective Additive):
ZDDP, ZTDC, Moly TDC, Antimony TDC, Organic Sulfur-Phosphorus-Nitrogen compounds, Borates and Borate Esters, Tricresyl Phosphates, amine phostphates, and other phosphate esters, Chlorine compounds, and lead diamylcarbamates, lead and barium naphthenates, sulfurized olefins; protective film interacts at various temperatures and pressures to provide either a plastic interface or to provide a compound which shears at the surface.
Demulsifier (Performance Additive): hydroxyalkyl carboxylic esters, alkenlycarboxylic esters; keeps water separated from lubricant.
Detergents (Surface Protective Additive): metallo-organic compounds of sodium, calcium, magnesium, boron phenolates, phosphates and sulfonates such as alkylbenzene sulfonic acids, alkylphenol sulfides, alkylsalacyclic acids; Lift deposits from surfaces to keep them suspended.
Dispersants (Surface Protective Additive): Alkylsuccinimides, alkylsuccinic esters (alkenyl succinimides); chemical reaction with sludge and varnish precursors to keep them acid neutralized and to keep them soluble. Detergent-dispersants often are the same chemical or come in compounds to accomplish the combined function(s).
Emulsifiers (Protective Additive): Polyisobutylenesuccinimides, alkenylsuccinate ester/salts. polyester amides, alkyl aminoesters; promotes a stable emulsion or mixture of oil and water.
Friction Modifiers or Friction Reducers (Performance Additive): Organic fatty acids and amides, lard oil, high molecular weight organic phosphorus and phosphoric acid esters such as Tricresyl Phosphates, ZDDP, ZTDC, Moly TDC, Antimony TDC, family of diphenylamines and amides, and olefin sulfides. Reduces coefficient of friction formulated lubricant in the boundary lubrication regime. Some VII's also provide friction reduction.
/Deactivator (Protective Additive): ZDDP, ZTDC, Moly TDC, Antimony TDC, family of diphenylamines and amides, and olefin sulfides, heterocyclic sulfur-nitrogen compounds; inhibits corrosive effects of oxygen with metals and decreases metal interaction with oxygen compounds to reduce oxidation of oil.
Oxidation Inhibitors (See Antioxidants).
Rust Inhibitor (Surface Protective Additive): Barium sulfonates, amine phosphates, phosphordithioates, sodium thizoles (for coolants),
Pour Point Depressant (Performance Additive): polymethacrylates (PMA's); reducing wax crystal formation and increases solvency of oil at low temperatures. May be part of VII package.
Seal Swell (Performance Additive): nitriles, specific esters, organic phosphates and aromatic hydrocarbons. Increases volume of elastomeric seals.
Surfactants or Surface Active Agents (Protective Additive): family of diphenylamines and amides; usually part of the antioxidant package. Also provides enhanced friction reduction and allows oils to "climb" or spread on and over surfaces. Decreases but does not destroy surface tension
Soot Control or Soot Inhibitor (Protective Additive for diesels): Organic Barium compounds; keeps soot in suspension. Usually part of the dispersant package in diesel formulations.
Tackifiers (Performance Enhancement): copolymers of ethylene and propylene; helps oil cling to surfaces. Very useful in geared machines such as transmissions, differentials, and chains.
Viscosity Index Improver or Viscosity Modifier (Performance Additive): Olefin copolymers (OCP's), hydrogentated styrene-diene copolymers, styrene esters, polymetharylates (PMA's), mixed alkyl methacrylate-vinyl-pyrrolidines, aminated ethylene propylene, mixed alkylmethacrylate ethylene/propylenes; reduces viscosity change with temperature. Increases viscosity of base oil as temperature rises when base oil tends to thin. Some VII's may also act as dispersants by incorporating dispersant compounds. https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/530321/Additives_XII-Multifunctional_