Three-dimensional laser scanning confocal microscopy has revealed that filamentous actin, when complexed with the cross-linking protein $\alpha$-actinin, will spontaneously assemble on a micron scale into a structure comprised of a relatively rigid, frequently branching, 3D network of bundles with characteristic mesh size of the order of the persistence length of F-actin. In contrast, additional nanoscale ordering is observed, as synchrotron x-ray diffraction has revealed a disordered, distorted square lattice of actin fibers within the individual bundles.

The structures of the liquid crystalline chiral subphases exhibited by several materials containing either a selenium or sulphur atom have been investigated using a resonant x-ray scattering technique. This technique provides a unique structural probe for the ferroelectric, ferrielectric, antiferroelectric, and Sm$C_{\alpha }^{*}$ phases. An analysis of the scattering features allows the structural models of the different subphases to be distinguished, in addition to providing a measurement of the helical pitch. This paper reports resonant scattering features in the antiferroelectric hexatic phase, the three- and four-layer intermediate phases, the antiferroelectric and ferroelectric phases and the Sm$C_{\alpha }^{*}$ phase. The helicoidal pitch has been measured from the scattering peaks in the four-layer intermediate phase as well as in the antiferroelectric and ferroelectric phases. In the Sm$C_{\alpha }^{*}$ phase, an investigation into the helical structure has revealed a pitch ranging from 5 to 54 layers in different materials. Further, a strong resonant scattering signal has been observed in mixtures of a selenium containing material with as much as 90% nonresonant material.

The isotropic to nematic liquid crystal (LC) phase transition is used to create organized assemblies of CdSe/ZnS core/shell quantum dots (QDs). Under controlled conditions, well dispersed QDs are expelled from the ordered domains of nematic LC into the remaining isotropic domains. The final LC phase produces three dimensional QD assemblies that are situated at the defect points in the LC volume. Through the luminescence of the QDs we are able to track the movement of the nanoparticles as the phase is formed as well as spectrally probe the resulting QD assemblies. Forster resonance energy transfer (FRET) measurements, combined with small angle X-ray scattering (SAXS) data reveal that the QD assemblies have a consistent inter-particle spacing of approximately 7.6 nm. Additionally, the location of the assemblies is shown to be controllable by utilizing beads as defect nucleation points.

Significance: Methods to manipulate and control the dynamics of spontaneously flowing active materials are vital if these fluids are to lead to technological applications. We report the development of an easy-to-implement technique to achieve tunable, local control over active nematic films, the preeminent example of active fluids. We establish that micropatterns, fully submersed below active films, have a pronounced impact on dynamics. To showcase the adaptability of our technique, we present four proof-of-concept microstructures: trenches, undulated sinusoids, stairways, and pillars. Each illustrates a particular strength of our approach, including enacting abrupt virtual boundaries to trap topological defects, separating distinct flow states at constant levels of biochemical fuel, gently guiding self-propelled defects, and modifying local active nematic composition.