Fig. 2. Free energy for an RNA virus approaching an air-water interface.

a Approach curve showing the increase in electrostatic free energy ${\mathcal{F}}_{\mathrm{elec}}\left(z_c\right)/k_{B}T$ as a function of distance to the air-water interface. Parameters are as specified in the text. Inset: scaling of the electrostatic free energy increase $\mathrm{\Delta }{\mathcal{F}}_{\mathrm{elec}}={\mathcal{F}}_{\mathrm{elec}}\left(0\right)-{\mathcal{F}}_{\mathrm{elec}}\left({\kappa }_1{z}_c\to -\infty \right)$ in units of k_BT as a function of dimensionless radius of the virion, κ₁R. The line is a fit, and has slope ~1.95, which is close to the predicted value of 2, see Supplementary Note 3. b Plot of the total (electrostatic plus Pickering) free energy change, $\mathrm{\Delta }\mathcal{F}\left({\kappa }_1{z}_c\right)=\mathcal{F}\left({\kappa }_1{z}_c\right)-\mathcal{F}\left({\kappa }_1{z}_c\to -\infty \right)$, as a virion approaches an air-water interface (γ = 70 mN/m). The electrostatic free energy barrier $\mathrm{\Delta }{\mathcal{F}}_{\mathrm{barrier}}$ and the adsorption free energy gain $\mathrm{\Delta }{\mathcal{F}}_{\mathrm{ads}}$ are shown in the plot.