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Controlling the self-assembly of supramolecular structures is vital for living cells, and a central challenge for engineering at the nano- and microscales. Nevertheless, even particles without optimized shapes can robustly form well-defined morphologies. This is the case in numerous medical conditions where normally soluble proteins aggregate into fibres. Beyond the diversity of molecular mechanisms involved, we propose that fibres generically arise from the aggregation of irregular particles with short-range interactions. Using a minimal model of ill-fitting, sticky particles, we demonstrate robust fibre formation for a variety of particle shapes and aggregation conditions. Geometrical frustration plays a crucial role in this process, and accounts for the range of parameters in which fibres form as well as for their metastable character.

A central challenge in nano- and mesoscale materials research is facile formation of specific structures for catalysis, sensing, and photonics. Self-assembled equilibrium structures, such as three-dimensional crystals or ordered monolayers, form as a result of the interactions of the constituents. Other structures can be achieved by imposing forces (fields) and/or boundary conditions, which Whitesides termed “self-organization”. Here, we demonstrate contact line pinning on locally curved surfaces (i.e., a self-assembled monolayer of SiO2colloidal particles) as a boundary condition to create extended arrays of uniform rings of Au nanoparticles (NPs) on the SiO2colloids. The mechanism differs from the well-known “coffee-ring” effect; here the functionalized NPs deposit at the contact line and are not driven by evaporative transport. Thus, NP ring formation depends on the hydrophobicity and wetting of the SiO2colloids by the chloroform solution, ligands on the NPs, and temperature. The NP rings exhibit size scaling behavior, maintaining a constant ratio of NP ring-to-colloid diameter (from 300 nm to 2 μm). The resultant high-quality NP ring structures are expected to have interesting photonic properties.

We have studied anion exchange membrane/polycationic systems with different percentages of fluoride and chloride as counterions by molecular dynamics simulations. We also experimentally measured the self-diffusion constant of fluoride in a diblock copolymer that has the same hydrophilic block and found satisfactory agreement with simulations within a factor of 2. At 300 K, our simulations showed that the self-diffusion constant of fluoride increases by about 70% when fluoride content decreases from 100% to 40% (and 60% Cl), and it increases by about 140% when fluoride content decreases from 100% to 10%. Increasing % Cl also slightly decreases the attraction between fluoride and the cations. We hypothesize that the root cause of the enhancement in fluoride mobility is due to the larger size of the chloride ion, which more readily loses its water solvation shells because of a lower charge/radius squared (surface electric field). This in turn frees up more water for ion transport. We believe this effect is likely more general than just the fluoride/chloride case reported here.

There is increasing interest in the alkaline exchange membrane (AEM) fuel cells as this device, if realized, could allow the use of inexpensive metal catalysts and the oxidation of a variety of convenient liquid fuels. While there have been some dramatic early achievements, there is still a need for a fundamental study of anion transport, cation stability and the formation of robust thin films in this area. We have undertaken a comprehensive study of AEMs where theory is linked to well-defined model systems, both in solution and in the solid state, which are characterized using very careful environmental control such that the models can be validated and used predictively. We are also fabricating a number of random copolymer AEMs that can be produced readily in large quantities, allowing us to understand film formation coupled with transport and stability. Those based on perfluorinated backbones invite interesting comparisons with the analogous proton exchange membranes.

A Correction to this paper has been published: https://doi.org/10.1038/s41586-021-03444-z.

Extensive transport and modeling studies have been performed on a series of polymers based on the benzyltrimethylamonium cations. We have created a realistic reactive model of solvated hydroxide that has interesting properties in the polymer matrix. In ordered di-block polymers we have strong theoretical evidence for a heterogeneous distribution of water across the channel. Fluoride is used as a non-reactive surrogate for hydroxide to increase the computational efficiency of transport calculations that can be performed. In addition to these studies we are discovering new base stable processable robust polymer backbones and cations. These bulky cations seem to dramatically affect the transport properties of the anions showing a VTF rather than an Arrhenius behavior with temperature.

Extensive transport and modeling studies have been performed on a series of polymers based on vinylbenzyltrimethylamonium cations. Flouride is used as a non-reactive surrogate for hydroxide to increase the computational efficiency of transport calculations that can be performed. Interesting effects of water and residual chloride in the film have been explained. In ordered di-block polymers we have strong theoretical evidence for narrow water domains that facilitate rapid transport of anions. With this model we will be able to predict diblock polymer structures that require less water for efficient anion transport. In addition to these studies we are discovering new base stable polymer backbones and cations. A large part of this effort is dedicated to discovering new methods for the production of robust thin anion exchange membranes.

There is increasing interest in the alkaline exchange membrane (AEM) fuel cells as this device, if realized, could allow the use of inexpensive metal catalysts and the oxidation of a variety of convenient liquid fuels. While there have been some dramatic early achievements, there is still a need for a fundamental study of anion transport, cation stability and the formation of robust thin films in this area. We have undertaken a comprehensive study of anion transport and AEMs where theory is linked to well-defined model systems, both in solution and in the solid state, which are characterized using very careful environmental control such that the models can be validated and used predictively. We are also fabricating a number of structured copolymer AEMs that can be produced readily in large quantities, allowing us to understand film formation coupled with transport and stability.

There is increasing interest in the alkaline exchange membrane (AEM) fuel cells as this device, if realized, could allow the use of inexpensive metal catalysts and the oxidation of a variety of convenient liquid fuels. While there have been some dramatic early achievements, there is still a need for a fundamental study of anion transport, cation stability and the formation of robust thin films in this area. We have undertaken a comprehensive study of AEMs where theory is linked to well-defined model systems, both in solution and in the solid state, which are characterized using very careful environmental control such that the models can be validated and used predictively. We are also fabricating a number of random copolymer AEMs that can be produced readily in large quantities, allowing us to understand film formation coupled with transport and stability. Those based on perfluorinated backbones invite interesting comparisons with the analogous proton exchange membranes.