<p>To clarify the influence of molecular structure on interfacial behaviors of extended surfactants, interfacial rheological properties of three extended surfactants with different ionic heads (C₈P₁₀E₅C and C₈P₁₀E₅S) and different hydrophobic tails (C₈P₁₀E₅C and phP₁₀E₅C) were investigated by the droplet analysis method. The effects of adsorption time, interfacial pressure, oscillating frequency, and concentration on the dilational modulus and phase angle of C₈P₁₀E₅C, C₈P₁₀E₅S, and phP₁₀E₅C were determined. Results indicate that interfacial films of these three extended surfactants exhibit predominantly elastic behavior. The modulus and phase angle of C₈P₁₀E₅C and C₈P₁₀E₅S with different ionic heads exhibit little variation at variable experimental conditions, indicating that different ionic heads have a negligible effect on interfacial film properties. At low interfacial pressures, the adsorption layer is in a local thermodynamic quasi-equilibrium state with negligible intrinsic relaxation processes. At high interfacial pressures, the diffusion exchange process may play a more important role in the interfacial film of C₈P₁₀E₅C. Compared to C₈P₁₀E₅C, phP₁₀E₅C with a different hydrophobic group maintains a higher dilational modulus over a wider concentration range due to its rigid phenyl groups. Compared to ionic heads, hydrophobic tails exert a more pronounced influence on the interfacial rheological behavior of extended surfactants. These findings are expected to contribute to the rational design of extended surfactants with a short hydrophobic group.</p>