Analysis of the GISAXS data: The GISAXS pattern was further analyzed with the aim to estimate the thickness of the regions composing the lamellar structure. We recall that the SAXS intensity can be well described by the general equation: 𝐼(𝑞)=Δρ2𝑃(𝑞)𝑆(𝑞) (S1) where Δρ2 is the contrast term defined by the electron density difference within the system, 𝑃(𝑞) is the so-called form factor, describing the scattered intensity from the objects of a certain shape and size, and 𝑆(𝑞) is the structure factor, describing the spatial correlation between adjacent scattering objects. The many reflections observed in the GISAXS pattern (Figure 4c) are due to the presence of a multilayer structure, generated by the alternating repetition of the peptide and alkyl layers assembled in a stacked fashion (Figure 4d). The absence of the 5th diffraction reflection is directly related to the thickness of the layers. Since the system is molecularly well-defined, destructive interference between the minimum of the lamellar form factor and the 5th reflection maxima occurs. To confirm this, in Figure S6 we present the simulated intensity for the form factor (𝑃(𝑞)) of a layer with thickness h = 0.83 nm and the structure factor (𝑆(𝑞)) for a multilayered structure with periodicity d = 4.19 nm. For completeness, the simulated background and the total fitted curve are also included in the figure. In these simulations, the scattering from a homogeneous layer with thickness, h, and a lateral size larger than 1000 nm was used, while the structure factor using paracrystalline disorder was used.1 The simulations and fitting were performed using MATLAB. It can be clearly seen that the minimum of the form factor cancels the maximum of the structure factor. Assuming that the system is two phase, the thickness of the second phase must be 4.19 nm - 0.83 nm = 3.36 nm. We note that the mismatch in the relative peak height is most probably due to the texture of the sample, as the fitted data have been extracted from the vertical cut along the qz direction of the GISAXS patterns. Pendant Drop Interfacial Tensiometry: A drop shape analyser (Krüss, FTA DSA1000B) was used for pendant drop tensiometry to measure the interfacial tension at the interface between the oil and different aqueous solutions. In these experiments, the aqueous phase was either DI-water, pH 7.0 buffer, 0.5 mg/mL 2T solutions in DI-water, or 0.5 mg/mL 2T in pH 7.0 buffer solution. A drop of the aqueous phase with a volume of approximately 7 μL was injected and hung from a 0.5 mm diameter needle in the less dense oil phase. Images of the drop shape were recorded using the video camera system on the apparatus and analyzed (using FTA32 software) to obtain the interfacial tension value over time. The experiments were conducted in a temperature-controlled room with a temperature of 22 +/-1 °C. The forces that determine the shape of the pendant drop are mainly the balance of surface tension, buoyancy force and gravitation. The surface tension seeks to minimize the surface area and make the drop take a spherical shape. The difference of gravitation and buoyancy force, on the other hand, stretches the drop from this spherical shape and a typical pear-like shape results. The interfacial tension for a drop with a diameter of 𝐷𝑒𝑞 at its equator was calculated as: 𝛾=𝛥𝜌·𝑔𝐷𝑒𝑞2𝐻 (S2) where 𝛥𝜌 is the density difference between water and oil, 𝑔 is the acceleration due to gravity (taken as 9.8 m/s2), and 𝐻 is a shape factor that is decided by the shape of the drop. Here, the water density was taken to be ρw = 0.998 g/cm3 (obtained from the FTA32 software), and the density of sunflower oil3 was taken as ρo = 0.918 g/cm3. Six replicate measurements were performed on the sunflower oil/DI water interface. The standard deviation was 0.4 mN/m. In pH 7.0 buffer solutions, there is a self-assembly of 2T platelets. The platelets are large enough to be subject to gravitational effects, which made the interfacial tension measurements unreliable.-- Licensed under CC-BY 4.0.

Size, SAXS, and microscope images of 2T in pH 7.0 buffer, water, and pH 4.0 buffer; description of coarse-grained simulations; molecular model; photograph of the 2T films from the oil/water interface; Raman spectrum of pure sunflower oil; interfacial tension measurements; aging of the emulsion; destabilization of a β-carotene emulsion; SEM image of the spin-coated emulsion; and EDS measurements of the elements in a dried 2T-stabilized oil drop (PDF) Coarse-grained simulation of the peptide in water, demonstrating the formation process of the 2D peptide assembly (MP4) All-atom simulation of 2T attaching to the oil/water interface (MP4)

Z.H. acknowledges the Chinese Scholarship Council (CSC 201906950049) and the Vice-Chancellor’s Scholarship Fund for providing a PhD studentship. E.C. acknowledges the Faculty of Science and Engineering at the University of Groningen for PhD funding. [...] This research was supported by the Aragón Regional Government (project E25_20R) [...].

Peer reviewed