Improving viscosity-temperature performance (as a viscosity index improver)
Molecular structure characteristics basis
Poly methyl methacrylate has a unique molecular structure, with its main chain being relatively flexible, and the lengths, structures, and quantities of the side chains can be designed and regulated. For example, side chains of different carbon chain lengths will give it different performance characteristics. Long side chains can prevent the close aggregation of molecules at low temperatures, allowing the lubricating oil to maintain good fluidity at low temperatures; while at high temperatures, the main chain can maintain a certain intermolecular force through appropriate stretching and winding, ensuring the strength of the oil film and preventing the lubricating oil from becoming too thin and losing its lubricating effect due to temperature increase.
Temperature response mechanism
At low temperatures, the poly methyl methacrylate molecules present a relatively relaxed and dispersed state, and the interactions between them are weak, which will not cause the viscosity of the lubricating oil to increase excessively, allowing the lubricating oil to flow smoothly and reach the surface of the components requiring lubrication quickly. As the temperature rises, the molecular thermal motion intensifies, and the poly methyl methacrylate molecules begin to form a relatively stable network structure through interactions such as chain segment interlocking, such as winding and cross-linking, to resist the sharp decrease in lubricating oil viscosity at high temperatures, allowing the lubricating oil to maintain a relatively stable viscosity over a wide temperature range and play a role in improving the viscosity index.
Reducing pour point (as a pour point depressant)
Crystallization interference effect
Base oil has a tendency to crystallize and grow at low temperatures, which will cause the fluidity of the oil to deteriorate and eventually solidify. The poly methyl methacrylate additive can adsorb on the surface of the tiny crystallization nuclei that just form in the base oil, preventing these crystallization nuclei from further growing and aggregating to form large crystalline particles, so that the base oil will only crystallize at a lower temperature. For example, the long-chain poly methyl methacrylate molecules can interact with the hydrocarbon molecules in the base oil through their non-polar parts, while the polar groups preferentially adsorb on the crystallization nuclei, disrupting the orderly growth process of the crystals and achieving the effect of inhibiting crystallization.
Altering wax crystal morphology
When the wax in the base oil begins to crystallize, the poly methyl methacrylate can change the growth morphology of the wax crystals, transforming them from large and regular sheet-like, needle-like, etc., forms that are prone to causing the oil to solidify into dispersed, fine particles, thus avoiding the formation of continuous, obstructive crystalline networks that prevent the oil from flowing, and reducing the pour point of the lubricating oil and improving the low-temperature fluidity.
Anti-wear effect
Forming a protective film
Poly methyl methacrylate can undergo a series of reactions such as adsorption and decomposition on the friction surface, forming a layer with a certain strength of protective film. This layer can separate the two moving metal surfaces, avoiding direct contact and wear between metals. During friction, the polar groups in the molecules will preferentially adsorb on the metal surface, and as the friction continues, the molecular chain segments will continuously spread and accumulate on the surface, eventually forming a continuous, and having certain load-bearing capacity, protective film, reducing metal wear and scratching during the friction process.
Improving the lubrication state of the friction interface
It can regulate the lubrication state of the friction interface, reducing the friction coefficient. By optimizing the adsorption performance and rheological properties of the lubricating oil on the friction surface, the lubrication between the friction pair changes from boundary lubrication to mixed lubrication or even fluid dynamic lubrication, reducing energy loss and component wear during the friction process, and improving the operating efficiency and service life of the equipment.
Antioxidant effect
Free radical capture
Some specific structures and functional groups in the poly methyl methacrylate molecules can capture the free radicals produced by the oxidation reaction of the lubricating oil during use, preventing the chain-like oxidation reactions initiated by the free radicals. For instance, the reactive sites such as the unsaturated bonds in molecules can first react with free radicals, converting the free radicals into relatively stable substances, thereby delaying the oxidation process of the lubricating oil and maintaining the stability of its performance, and extending its service life.
Inhibiting the oxidation reaction
This additive can, through its synergistic effect with other additives such as antioxidants in the lubricating oil, interfere with the progress of the oxidation reaction. It can alter the reaction pathway of the oxidation reaction or reduce the rate constant of the oxidation reaction, making the hydrocarbons and other components in the lubricating oil less prone to oxidation, reducing the generation of oxidation products (such as acids, aldehydes, ketones, etc.), and avoiding these oxidation products from causing corrosion to equipment components and adversely affecting the performance of the lubricating oil itself.
