Diamond lattices formed by atomic or colloidal elements exhibit remarkable functional properties. However, building such structures via self-assembly has proven to be challenging due to the low packing fraction, sensitivity to bond orientation, and local heterogeneity. We report a strategy for creating a diamond superlattice of nano-objects via self-assembly, and demonstrate its experimental realization by assembling two variant diamond lattices, one with and one without atomic analogs. Our approach relies on the association between anisotropic particles with well-defined tetravalent binding topology and isotropic particles. The constrained packing of triangular binding footprints of truncated tetrahedra on a sphere defines a unique three-dimensional lattice. Hence, the diamond self-assembly problem is solved via its mapping onto two-dimensional triangular packing on the surface of isotropic spherical particles.

The change in shape inducible in some photo-reversible molecules using light can effect powerful changes to a variety of properties of a host material. The most ubiquitous natural molecule for reversible shape change is the rhodopsin-retinal protein system that enables vision, and this is perhaps the quintessential reversible photo-switch. Perhaps the best artificial mimic of this strong photo-switching effect however, for reversibility, speed, and simplicity of incorporation, is azobenzene. This review focuses on the study and application of reversible changes in shape that can be achieved with various systems incorporating azobenzene. This photo-mechanical effect can be defined as the reversible change in shape inducible in some molecules by the adsorption of light, which results in a significant macroscopic mechanical deformation of the host material. Thus, it does not include simple thermal expansion effects, nor does it include reversible but nonmechanical photo-switching or photo-chemistry, nor any of the wide range of optical and electrooptical switching effects for which good reviews exist elsewhere.

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Nanoparticles coated with DNA molecules can be programmed to self-assemble into three-dimensional superlattices. Such superlattices can be made from nanoparticles with different functionalities and could potentially exploit the synergetic properties of the nanoscale components. However, the approach has so far been used primarily with single-component systems. Here, we report a general strategy for the creation of heterogeneous nanoparticle superlattices using DNA and carboxylic-based conjugation. We show that nanoparticles with all major types of functionality--plasmonic (gold), magnetic (Fe2O3), catalytic (palladium) and luminescent (CdSe/Te@ZnS and CdSe@ZnS)--can be incorporated into binary systems in a rational manner. We also examine the effect of nanoparticle characteristics (including size, shape, number of DNA per particle and DNA flexibility) on the phase behaviour of the heterosystems, and demonstrate that the assembled materials can have novel optical and field-responsive properties.

Fuel cells based on polymer electrolyte membranes (PEM) show promise as a means of energy conversion for a wide range of applications both in the transportation sector and for stationary power production due to their high charge density and low operating temperatures. While the structure and transport of bulk PEMs for fuel cell applications have been studied extensively, much less is known about these materials at interfaces and under confinement, conditions that are highly relevant in the membrane electrode assembly of a working PEM fuel cell. Using X-ray reflectivity, neutron reflectivity, grazing-incidence small-angle X-ray scattering, quartz crystal microbalance, and polarization-modulation infrared reflection–absorption spectroscopy, we have studied the structure, swelling, water solubility, and water transport kinetics as a function of relative humidity for confined polyelectrolyte films thinner than 222 nm. While the humidity-dependent equilibrium swelling ratio, volumetric water fraction, and effective diffusivity are relatively constant for films thicker than ca. 60 nm, we observe measurable suppressions of these properties in films less than ca. 60 nm. These effects occur at length scales that are relevant to transport (ion and water) in the polyelectrolyte binders found in the catalyst layer of the membrane–electrode assembly (MEA) of a functional fuel cell. The thin film methodology and findings presented here provide a platform to quantify and validate models of interfacial impedance used within the fuel cell community and have the potential to lead to improvements in MEA materials, design, and optimization.

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Controlling the interparticle spacing in quantum dot (QD) thin films is the most readily accessible way to control transport rates between neighboring QDs and a critical component of device optimization. Here, we use X-ray scattering measurements to accurately measure the interparticle spacing in films of highly monodisperse lead sulfide (PbS) QDs that have undergone a variety of device-relevant ligand exchanges. We tabulate these values for use in simulations and data analysis. We find that monothiol and dithiol ligand species typically result in interparticle spacing values that are equal to the length of a single monothiol or dithiol ligand. Additionally, we find that spin-coating a thick film of QDs followed by a long-duration ligand exchange results in a more complete ligand exchange than spin-coating many thin layers with short-duration ligand exchanges in between. The former method also preserves a remarkable degree of the long-range ordering that was present in the film prior to ligand exchange. These results shed light on ways to produce highly-ordered QD solids with compact and functional ligands, which could lead to enhanced interdot coupling and transport phenomena.

For the promise of self-assembly to be realized, processing techniques must be developed that simultaneously enable control of the nanoscale morphology, rapid assembly, and, ideally, the ability to pattern the nanostructure. Here, we demonstrate how photothermal gradients can be used to control the ordering of block copolymer thin films. Highly localized laser heating leads to intense thermal gradients, which induce a thermophoretic force on morphological defects. This increases the ordering kinetics by at least 3 orders of magnitude compared to conventional oven annealing. By simultaneously exploiting the thermal gradients to induce shear fields, we demonstrate uniaxial alignment of a block copolymer film in less than a second. Finally, we provide examples of how control of the incident light field can be used to generate prescribed configurations of block copolymer nanoscale patterns.