where r is surface concentration, Cb is bulk concentration. and D is he diffusion coefficient of the particle. Eq. 1 assumes that Cb is unchanging and that there is no back diffusion from the in terface (22). We can estimate rmax (for 100% surface coverage) to be 1.57 mg m from transmission electron microscopy (TEM) images of the BIA 2D lattice (vide infra: Fig- 3A), while D was measured to be 9 87 x 10- cmsi for monomeric BA using dynamic light scattering (SI Appendix. Fig. S5). In cases where the error of the Laplace fit increased before a decrease in IFT was observed, then the onset time of any increase in the error of the Laplace fit was used (SI Appendix, Fig. S6) Fig. 1 shows a plot of regime I time against BA concentration for WT-RIA as well as the "ideal" regime I times calculated from Eq. 1 (Fig. 1, dashed line). The results clearly demonstrate that WT-BA slower to decrease the interfacial tension of a is droplet (or increase the error of Laplace fit) in air than would be expected for a system that did not exhibit an adsorption bamer or back diffusion. If, however, we introduce a mutation into the cap region that replaces Leucine at position 77 with Lysine (177K), the mutant showed no adsorption barrier, reducing the interfacial tension of the droplet within the maximum calculated time for particles of equivalent size (Fig. 1). Under diffusion- limiting conditions (Eq. 1) BslA at a concentration of 0.03 mg mL' should take 22 s to reach a surface concentration of 1.57 mg m As the IFT will begin to decrease at a surface coverage below 100%, BSA should require less than 22 s to reduce the IFT of a droplet. At 0.03 mg mL' regime I time he for WT-Bs!A was 97 t 18 s, compared with 12 t 4 s for BslA L77K, confirming that BAL77K adsorption is purely diffusion limited. whereas WT-BSA faces an additional barrier to ad- sorption. This finding is consistent with the hypothesis that the WT protein undergoes a conformational change before adsorp- tion. This energy barrier is not high, as dimensional anaiysis tion. his energy barrier is not high, as dimensional analysis suggests that it is in the order of -10 kBT (SI Appendir. Fig. S. consistent with a limited structural rearrangement. We infer thet introducing the positively charged lysine disrupts the conforma- tion in aqueous solution so that not all of the hydrophobic groups pack optimally, and their partial exposure facilitates the in teraction with the interface, abolishing the barrier to adsorption.