Asymmetric liquid-core cylindrical lens used to measure liquid diffusion coefficient.

We design and fabricate an asymmetric liquid-core cylindrical lens (ALCL), which is used to measure the binary liquid diffusion coefficient (D). Acting as both diffusion cell and key imaging element, ALCL is of the function to measure the refractive index (RI) of liquid filled in its core in the way of spatial resolution. Comparing the ALCL with a symmetric liquid-core cylindrical lens (SLCL), the spherical aberration is reduced from about 300 μm (SLCL) to less than 5 μm (ALCL) when the RI of filled liquid is near 1.333, while the measurement accuracy of the RI of the ALCL is superior to 0.0002, which is much better than that of the SLCL. Equipped with the ALCL, the D value of triethylene glycol diffusing in water is measured at 25°C. The result is D=0.7515×10⁻⁵ cm²/s, a value very close to the literature value. The rational design of ALCL gives the optical method for measuring the D value good measurement precision and direct observation of the diffusive process as well as a simple experimental instrument.