In order to estimate the diffusivity in the short time limit, we use the time 𝑡 0 that is elapsed before the first sign of organic liquid is detected in UV. Taking 𝜑 ≈ 1 at 𝑡 = 𝑡 0 , diffusivity can be estimated from equation (2) using 𝑥 2 = 𝜋𝐷𝑡 0 . These diffusivities are normalized by dividing their values with the respective Stokes-Einstein diffusivities: 𝐷 𝑒 = 𝑘 𝐵 𝑇/(6𝜋𝜂𝑟) , where 𝑘 𝐵 is the Boltzmann constant, 𝑇 is the temperature, 𝜂 is the viscosity of the aqueous phase. r is the average radius of the droplet, which was estimated using CHDF (capillary hydrodynamic flow chromatography; Figure , Supplementary Materials). Since the fluctuation of concentration below the interface encodes the magnitude of the diffusivity of the emulsion droplets, we found it convenient to show the wide range of the value of 𝐷/𝐷 𝑒 , by plotting it against mean square value of fluctuation 𝜎 𝐴 2 of UV absorbance (which is a measure of 𝜎 𝐶 2 ) as obtained from Figure . and (Supplementary Materials).