Overview of the Method
Immersion thermo-optic phase spectroscopy (I-TOPS) measures the thermal conductivity of small fluid volumes. The technique employs an optical mirage configuration to probe the refractive index gradient established near a heated transducer.
A thin metal transducer deposited on a fused quartz substrate and immersed in the liquid is heated by a modulated laser pump beam, generating a periodic temperature oscillation in the adjacent fluid. Because the refractive index of the liquid depends on temperature (dn/dT), the resulting thermal gradient produces an optical phase deflection. Modulating the heating source at frequencies above the convective threshold suppresses buoyancy-driven convection, isolating purely conductive transport in volumes as small as 100 µL.
Technical Specifications
Sample Fluid Types
Organic solvents, ionic liquids, nanofluids, dielectric fluids, electrolytes, and polymer solutions.
Required Sample Volume
Small fluid volumes (~100 µL to 1 mL), enabling characterization of novel formulations.
Metrology Configuration
Immersion photothermal phase deflection (mirage technique) with lock-in detection.
Convective Suppression
High-frequency temperature modulation isolates conduction from convection.
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