Common dimethyl silicone oil emulsion cannot truly cure, but it can dry to form a film. There is an essential difference between the two: drying only involves the evaporation of water to form a physical film, while curing refers to the formation of an irreversible three-dimensional network structure through chemical reactions.
1. Intrinsic Properties of Common Dimethyl Silicone Oil Emulsion
Common dimethyl silicone oil emulsion consists of the following components:
- Main component: Linear dimethyl silicone oil (polydimethylsiloxane, PDMS)
- Auxiliary components: Emulsifiers (such as nonionic surfactants) and water
- Structural feature: Silicone oil is dispersed in water as tiny droplets to form a stable emulsion
Key issue: Common dimethyl silicone oil molecules lack sufficient reactive functional groups (such as hydroxyl groups, vinyl groups, etc.) on their chains. This prevents them from forming a cured structure through self-crosslinking.
2. Essential Difference Between "Drying" and "Curing"
| Characteristic | Drying (common dimethyl silicone oil emulsion) | Curing (special-formula silicone oil) |
|---|---|---|
| Mechanism | Water evaporation, with silicone oil droplets aggregating to form a physical film | Chemical reaction (crosslinking) to form a three-dimensional network structure |
| Reversibility | Re-dissolvable in organic solvents | Irreversible; will not soften or flow even when heated |
| Film performance | Low strength, easy to wipe off, solvent-intolerant | High strength, elastic, solvent-resistant |
| Typical time | 2 hours at room temperature; about 30 minutes at 50-60℃ | Several hours to several days, depending on the formula |
| Intrinsic change | Physical state change (liquid → solid) | Chemical structure change (linear → network) |
Note: The film formed by the drying of common dimethyl silicone oil emulsion is essentially still flowable silicone oil, with only a change in form. It will flow again when exposed to high temperatures or solvents.
3. Practical Performance of Common Dimethyl Silicone Oil Emulsion
The "curing" phenomenon of common dimethyl silicone oil emulsion in applications is actually a film-forming process through drying:
- As a release agent: Forms a lubricating film on the mold surface to facilitate product demolding — this is drying, not curing.
- Automotive dashboard polishing: The description of "curing" actually refers to "natural drying at room temperature for 2 hours, or accelerated drying in an oven at 50-60℃ (30 minutes)", forming a physical protective film rather than a cured product.
- Personal care products: Forms a smooth film on the skin or hair to provide a silky feel — this is also film formation through drying, not curing.
4. Necessary Conditions for True Curing
To achieve true curing (formation of an irreversible three-dimensional network) of dimethyl silicone oil emulsion, the following conditions must be met:
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Add a curing system:
- Crosslinker (such as hydrosilicone oil, silane coupling agent)
- Catalyst (such as organotin, organotitanium compounds)
- May require: Photoinitiator (for UV curing)
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Provide external conditions:
- Heat curing: 80-120℃, holding time for 30-60 minutes
- UV curing: Ultraviolet irradiation (wavelength 365-405nm), irradiation time 5-30 seconds
- Moisture curing at room temperature: Room temperature (20-30℃), ambient humidity 40%-70%, curing time 24-48 hours
5. Summary and Application Insights
Common dimethyl silicone oil emulsion can only dry to form a film, not truly cure — this is an intrinsic property determined by its molecular structure. If curing performance is required, it is necessary to select special-formula curable silicone oil emulsion (such as hydroxyl silicone oil emulsion) or add a complete curing system to the common emulsion.
Application suggestions:
- If only temporary protection or lubrication is needed, the film formation of common emulsion through drying is sufficient.
- If a durable, solvent-resistant coating is required, specialized curable silicone rubber or a formula with added curing agents must be used.
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