We hypothesise that the recent discovery of nanodomains at the air-water interface can be leveraged to nano-functionalize surfaces through casting with incorporated functional species. The interfacial self-assembly of the amphiphilic molecules, 18-methyleicosanoic acid 18-MEA and 4-(tetradecyl)benzene diazonium tetrafluoroborate TDDS, at the air-water interface and cast on silicon wafer has been investigated using Langmuir-Blodgett (LB) techniques and atomic force microscopy. The impact of composition and surface pressure (SP) on the formation of nanodomains and microstructures was examined. TDDS (which can be used to modify the electronic structure of graphene) behaves as a co-surfactant in the 18-MEA film at low concentrations, facilitating the formation of homogeneous nanodomains with functional capacity. At higher TDDS concentrations, there is evidence for phase separation in the domains, and the TDDS furthermore partitions to the aqueous phase at higher pressures. By manipulating the 18-MEA:TDDS ratio and SP, regular nano-patterns can be transitioned into novel 2D structures reminiscent of 3D water-in-oil-in-water (W/O/W) analogues ("cookie systems"), offering a versatile strategy for designing nanoarchitectures with potential applications in graphene patterning.

Organic electrochemical transistors (OECTs) are key bioelectronic devices with applications in neuromorphics, sensing, and flexible electronics. OECTs made using biobased and biodegradable materials are emerging as a sustainable alternative to nondegradable plastic and metal-based electronics. Printing is the key technique used to fabricate these types of devices, enabling fabrication at room temperature and using benign solvents, such as water. However, printing techniques suffer from relatively low resolution (tens to hundreds of micrometers), far below the micrometer resolution achieved via conventional metal deposition and photolithography. Here, we present a high-throughput additive-subtractive microfabrication strategy for carbon-based flexible OECTs using biodegradable materials and room-temperature processing. Additive manufacturing of large features is achieved via extrusion printing of a graphene ink to fabricate electrode contacts on cellulose acetate (CA), which serves both as the substrate and as the insulation layer. Combined with femtosecond (fs) laser ablation, this approach enables micrometer-resolution patterning of freestanding OECTs with channel openings down to 1 μm and sheet resistance below 10 Ω/sq. By tuning laser parameters, we demonstrate both selective and simultaneous ablation strategies, enabling the fabrication of horizontal, vertical, and planar-gated OECTs, as well as complementary NOT gate inverters. Thermal degradation studies in air show that over 80% of the device mass decomposes below 360 °C, providing a low-energy route for device disposal and addressing the environmental impact of electronic waste. This approach offers a lithography-free pathway toward the rapid prototyping of high-resolution, sustainable organic electronics, combining circularity, process simplicity, and architectural versatility for next-generation bioelectronic applications. 

Long, straight chain saturated fatty acids form homogeneous, featureless monolayers on a supramolecular length scale at the water–air interface. In contrast, a naturally occurring saturated branched fatty acid, 18-methyl eicosanoic acid (18-MEA) has been observed to form three-dimensional domains of size 20–80 nm, using a combination of Langmuir trough, Atomic Force Microscopy (AFM) images of the deposited monolayers, and Neutron reflectometry (NR) and X-Ray reflectometry (XRR). It is hypothesized that these domains result from the curvature of the water surface induced by the steric constraints of the methyl branch. Accordingly, in this work, we investigate in situ the structure of such films using Grazing Incidence Small Angle X-ray Scattering and Diffraction (GISAXS and GIXD). The branched fatty acids indeed form curved nanodomains as revealed by their two-dimensional scattering pattern whereas straight chain fatty acids form the expected featureless film, with no GISAXS scattering peaks. Mixed monolayers consisting of 18-MEA and eicosanoic acid (EA) display a phase transition in the structure from hexagonally packed at high 18-MEA ratio to structures with one-dimensional translational ordering (aligned stripes) for 50:50 mol% and lower ratios. Moreover, the GIXD patterns of monolayers containing 18-MEA display a peak with curved distribution of intensity, indicating a continuous distribution of collective molecular orientations, consistent with the local curvature of the water surface. Finally, we report on an unusual double peak phenomenon in the GISAXS data that is interpreted as being due to a hexagonal packing of elliptical domains – i.e. with two characteristic dimensions. Synchrotron X-Ray scattering experiments have thus unambiguously confirmed the self-assembly, out of plane, “cobbling” of the water interface by these branched structures.

Branched fatty acids, such as those found on the surface of hair and wool, have recently been shown to form novel 3D self-assembly curvature structures at the air–water interface—nanocaps. On the hair surface, the branched fatty acid 18-methyleicosanoic acid (18-MEA) is expressed together with shorter, unbranched, straight chain fatty acids to form a protective palisade layer. The biological function of the chain length differences was hitherto unknown. Using a combination of atomic force microscopy and Langmuir isotherms, a safe, versatile route for tuneable nanopatterning of solid surfaces is demonstrated, via fatty acid interfacial nanocap deposition from biomimetic mixtures. Further, it is shown that chain length dependence of the interaction with the branched chain is exquisitely sensitive, leading to profoundly different morphologies in the self-assembly structures. The vastly enhanced properties of the mixed films compared to the individual components alone reveals the biological origin of the hair surface composition.