From Chemical Structure to Macroscopic Properties: Understanding the "Molecular Code" of Silicone Oil Family in One Text
Introduction
Silicone oil is not a single substance, but a collective term for "polydimethylsiloxane" liquids. By changing the length of the main chain Si – O bond, the type of side chain organic group and the end functional group, the same kind of materials can show a variety from low viscosity fluid to high elastic gel. This article uses the perspective of "molecular building blocks" to dissect the chemical code behind the performance of silicone oil.
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Main chain: "inorganic elasticity" of Si-O
The Si-O bond has a length of 1.64 Å and a high bond energy of 452 kJ · mol ⁻¹, combining the temperature resistance of inorganic materials with the flexibility of organic polymers. The longer the main chain, the more entanglement between molecules, and the higher the viscosity index (VI); However, a long main chain will reduce low-temperature fluidity, so the polymerization degree needs to be controlled between 200 and 300 in the -50 ℃ scenario.
Side chains: "functional switches" of methyl, phenyl, and vinyl groups
PDMS is the most versatile, with a surface tension of only 20.4 mN · m ⁻¹;
Introducing 5-10% phenyl can increase the refractive index to 1.46 for LED packaging;
Introducing 0.5-1% ethylene group can achieve crosslinking through Pt catalyzed addition and produce "addition formed silica gel".
Terminal: "Reaction handle" of hydroxyl, alkoxy, and epoxy groups
α. ω - dihydroxysilicone oil (HO-PDMS-OH) is the basis for room temperature sulfurization of RTV-2; If the end is replaced with trimethoxy, a Sol Gel reaction can occur with the glass surface to form a covalently anchored anti fingerprint coating.
Performance Graph: Understanding the "Structure Performance" Mapping with One Graph
The viscosity temperature curve and surface tension side chain polarity coordinate graph are provided in the article to assist R&D personnel in completing preliminary material selection within 5 minutes.
conclusion
The reason why silicone oil is known as "industrial MSG" is that its performance can be precisely designed like a tuning knob. Mastering the three variables of main chain, side chain, and end chain enables one to 'hit where you want' in lubrication, demolding, defoaming, thermal conductivity, personal care, and other scenarios.