The interfacial tension analysis between mineral oil and water involves intermolecular forces, measurement methods, and influencing factors. Below are the key findings from comprehensive research:
1. Nature and Numerical Range of Interfacial Tension
The interfacial tension between mineral oil (non-polar hydrocarbons) and water is primarily determined by differences in intermolecular forces:
· Water molecules: Highly polar, with hydrogen bonds and orientation forces, exhibiting a surface tension of ~72 mN/m (20°C).
· Mineral oil molecules: Non-polar, relying only on van der Waals forces (dispersion forces), typically showing surface tension below 50 mN/m.
· Oil-water interfacial tension: Typically ranges from 35 to 50 mN/m (e.g., 35.66 mN/m measured in a lubricant-water system).
2. Measurement Methods
Common standard methods include:
· Platinum ring method (du Nouy ring method): Based on GB/T 6541-1986, calculates interfacial tension by measuring the force required to detach a ring from the liquid surface.
· Injection method: Suitable for oils less dense than water (e.g., mineral oils), records interfacial tension changes using a tensiometer.
3. Influencing Factors
| Factor |
Mechanism |
Example Data |
| Temperature |
↑Temperature → Volatilization of light oil components → Reduced intermolecular force difference → ↓Interfacial tension |
~1–2 mN/m decrease per 10°C rise |
| Dissolved gas |
↑Dissolved gas → Oil phase expansion → Increased intermolecular force difference → ↑Interfacial tension |
Peaks at gas saturation levels |
| Polar substances |
Polar additives (e.g., oxygenates) in oil → Reduced oil-water intermolecular force difference → ↓Interfacial tension |
10–15% reduction with 5% additive |
4. Practical Applications
· Oil-water separation: High interfacial tension (>30 mN/m) facilitates phase separation, while low tension requires demulsifiers.
· Cosmetic formulations: Water-in-oil emulsions need surfactants (e.g., HLB 3–6) to reduce interfacial tension to 10–20 mN/m for stable dispersion.
5. Instruments and Standards
· Interfacial tensiometers: e.g., KF100C type, measuring range 2–200 mN/m with reproducibility error <0.3%.
· Standard references: GB/T 6541-1986 (ring method) and GB/T 7702.4-2013 (platinum plate method).
SH107 automatic interfacial tensiometer is designed and manufactured by GB/T6514. It measures the surface tension of various liquids (liquid-gas interface) and the interfacial tension of mineral oil and water (liquid-liquid interface) under non-equilibrium conditions by the annular method.
The instrument adopts microprocessor technology, high degree of automation, simple operation, reliable work, after the sample is injected into the sample cup, as long as press the start button, the instrument can automatically complete the measurement of the sample, and can automatically calculate the tension value of the test sample according to the specific parameters of the input.
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