The solubility of dimethyl silicone oil (polydimethylsiloxane, PDMS) follows the principle of like dissolves like. Due to its highly non-polar molecular structure (the main chain is a silicon-oxygen bond and the side groups are two methyl groups), it is insoluble in water, strong polar solvents and most alcohols, but is easily soluble in non-polar or weakly polar organic solvents. The following are its main soluble solvent categories and specific examples:
Common good solvents (completely miscible or highly compatible)
- Hydrocarbon solvents:
Aliphatic hydrocarbons: n-hexane, n-heptane, cyclohexane, petroleum ether (light gasoline).
Aromatic hydrocarbons: toluene, xylene, benzene (rarely used due to high toxicity).
Application: The preferred economic solvent for industrial cleaning and dilution of silicone oil.
- Chlorinated hydrocarbons:
Dichloromethane, chloroform (trichloromethane), carbon tetrachloride, 1,1,1-trichloroethane.
Features: Strong solubility, but some are toxic or environmentally restricted (such as carbon tetrachloride).
- Ethers:
Ethyl ether, tetrahydrofuran (THF), dioxane.
Note: Ethyl ether is flammable, and THF is soluble in some silicones.
- Esters (partial):
Ethyl acetate, butyl acetate (medium solubility, viscosity effect needs to be verified).
- Special silicone solvents:
Cyclic siloxanes: octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5).
Linear siloxanes: hexamethyldisiloxane (MM), low-viscosity dimethyl silicone oil.
Advantages: Excellent compatibility with silicone oil, no residual risk, widely used in cosmetics and medicine.
Solvents with limited solubility or compatibility under specific conditions
- Ketones:
Acetone, methyl ethyl ketone (MEK) - low-viscosity silicone oil can be partially dissolved, and high-viscosity is easy to separate.
- Long-chain alcohols:
n-octanol, n-decanol - weakly polar long-chain alcohols have certain compatibility, but are not completely miscible.
- Fluorinated solvents:
Perfluorohexane, HFE (hydrofluoroether) - experimental verification is required, some fluorinated solvents can disperse silicone oil.
Key insoluble solvents (important distinction)
Polar solvents: water, methanol, ethanol, isopropanol, ethylene glycol.
Strong polar solvents: DMF (dimethylformamide), DMSO (dimethyl sulfoxide), acetonitrile.
Glycerol, liquid paraffin: incompatible, will stratify.
Precautions for use
- Viscosity effect:
High viscosity silicone oil (such as above 10,000 cSt) dissolves slowly and requires stirring or heating.
Low viscosity silicone oil (such as 50-100 cSt) is easily soluble in most non-polar solvents.
- Solubility limit:
Even good solvents have a concentration limit, and excessive silicone oil will precipitate (form gel or stratify).
- Application scenario orientation:
Industrial cleaning: hydrocarbons (such as n-hexane) or chlorinated hydrocarbons (such as dichloromethane) are preferred.
Cosmetics/pharmaceuticals: Choose cyclic siloxane (D5) or linear siloxane (MM).
Electronics: High-purity solvents (such as chlorofluorocarbon substitutes) are required to avoid ion residues.
Exceptions to modified silicone oils
Water-soluble silicone oils (such as polyether-modified silicone oils): Soluble in water and alcohols, but not standard dimethyl silicone oils.
Summary:
The core solvents of dimethyl silicone oils are non-polar hydrocarbons (n-hexane, toluene), chlorinated hydrocarbons (dichloromethane), ethers (ethyl ether) and siloxane solvents (D4/D5). When choosing, you need to balance dissolution efficiency, safety and application scenarios. If you need to further optimize the formula or solve specific dissolution problems, you can provide specific applications (such as cleaning, coatings, cosmetics), and SANFAN will give targeted suggestions.