Summarizing the results above, we have demonstrated that ln γ ± can be represented by a multipole expansion of the interaction between the central observation droplet and the surrounding solution (see Equ. 3). Each expansion exponent, λ l , reflects the combination of the thermally averaged interaction between individual multipoles and the effective number of multipoles contributing to the interaction. Along its major axis, the interaction falls of as 1/n 3λ l +1 R . For dipole-dipole interaction (l = 1), the lowest order term in Equ. 3 compares favorably with the simplest form of the Debye-Hückel law (ln γ ± ∝ m 1/2 B ) for dilute solutions where x ∝ m B when choosing λ Dipole = 0.5.