Does dimethyl silicone oil have fluorescence reaction? What substances can trigger fluorescence reaction?
1. Does pure dimethyl silicone oil have fluorescence?
High-purity dimethyl silicone oil (PDMS) has no obvious fluorescence reaction and barely glows under 365nm ultraviolet light.
Its molecular structure consists of Si–O main chains and methyl side groups, with no conjugated double bonds or aromatic rings, and it does not contain typical fluorescent groups.
In accordance with pharmacopoeia specifications, medical-grade dimethyl silicone oil stipulates that the fluorescence intensity of mineral oil impurities shall not exceed that of the reference standard, which confirms that pure dimethyl silicone oil is non-fluorescent.
Fluorescence occurrence is mainly caused by impurities, modified components or degradation products:
- Residual mineral oil / white oil (the most common cause): contains polycyclic aromatic hydrocarbons such as naphthalene, anthracene and phenanthrene, emitting blue or white fluorescence under 365nm UV light.
- Incompletely hydrolyzed silane monomers and oligomers: contain Si–OH, Si–H or short-chain conjugated structures, producing weak fluorescence.
- Additives and foreign impurities: residual antioxidants, catalyst residues (platinum, tin compounds), fumed silica contaminants and other trace impurities.
- Aging and degradation products: structural defects formed under high temperature or ultraviolet exposure will induce weak fluorescence.
2. What are fluorescent substances?
Fluorescent substances refer to matters that can emit visible light under ultraviolet irradiation (usually 365nm). Their core structural feature is fluorophores with conjugated π-bond systems and rigid planar structures.
Common natural intrinsic fluorescent substances
- Aromatic compounds: naphthalene, anthracene, phenanthrene, pyrene and other aromatic hydrocarbons.
- Natural substances with conjugated double bonds: vitamin B2, tocopherol, plant grease and natural alkaloids.
- Biomacromolecules: tryptophan and tyrosine in proteins, purine and pyrimidine bases in nucleic acids.
Synthetic fluorescent substances
- Fluorescein series, rhodamine series, coumarin compounds, triphenylmethane dyes and stilbene derivative optical brighteners, which are widely used in daily chemicals, papermaking and coating industries.
Main fluorescent substances in silicone oil system
- Polycyclic aromatic hydrocarbons (PAHs) brought by mineral oil impurities are the leading cause of fluorescence in silicone oil.
- Short-chain siloxane oligomers and trace heavy metal complex compounds will also generate faint fluorescence.
3. Quick Judgment Standard
- Pure dimethyl silicone oil: no or extremely weak fluorescence under 365nm UV lamp.
- Blue or white fluorescence: excessive mineral oil and polycyclic aromatic hydrocarbon impurities.
- Yellow-green or orange-red fluorescence: artificially added fluorescent agents or excessive aromatic impurities.
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