Electrostatic self-assembly of ordered perylene-diimide/polyelectrolyte nanofibers in fluidic devices: from nematic domains to macroscopic alignment

Sequential deposition of nanofibrous composites of charged perylene diimide (PDI) dyes and oppositely charged polyelectrolyte (PE) is demonstrated within fluidic devices. The PDIs employed include an amphiphilic, singly charged PDI (C(7)OPDI(+)) and a doubly charged species (TAPDI(2+)). Anionic poly(acrylate) (PA(-), 5100 and 250K MW) is used as the PE. As previously demonstrated [Weitzel, C. R.; Everett, T. A.; Higgins, D. A. Langmuir, 2009, 25, 1188], dip-coated PDI/PE composites form nanofibrous films that exhibit flow-induced alignment due to gravitational draining of the dipping solution. In this study, the potential for producing patterned, flow-aligned PDI/PE composites by deposition using pressure-driven flow within fluidic channels is explored. The influence of flow profile, PE molecular weight (MW) and PDI structure on deposition efficiency, macroscopic and microscopic morphology, and the potential for nanofiber alignment are also investigated. Optical absorbance microscopy and tapping mode AFM data demonstrate that C(7)OPDI(+)/PA(-) deposition is controlled by PDI aggregation, while TAPDI(2+)/PA(-) composites are more dependent upon PE MW. Optical dichroism images show that C(7)OPDI(+)/PA(-) composites form serpentine, partially aligned nanofibers under all conditions explored, while TAPDI(2+)/PA(-) films incorporate more tightly packed nanofibers that form randomly oriented nematic-like domains when high MW PA(-) is employed. In-plane organization in C(7)OPDI(+)/PA(-) films is concluded to result from flow-induced alignment of solution-formed C(7)OPDI(+) aggregates, while the unaligned domains found in TAPDI(2+)/PA(-) films are concluded to form on the substrate surface by the complexation of small TAPDI(2+) aggregates or monomers with PE.

Functional properties of metallomesogens modulated by molecular and supramolecular exotic arrangements

New concepts for the synthesis of metallomesogens have been recently developed in order to use the metal centre as a scaffold for grafting different functionalities and inducing non-conventional shapes and properties in the resulting complexes. Our strategy was based on the synthesis of mesogenic coordination complexes whose molecular architectures are controlled by the modulation of different and tunable molecular motifs: the nature of the metal ion and the surrounding ligands as central unit, the number of flexible chains at the periphery, and the nature of counter-ions in ionic complexes. The appropriate choice of molecular construction motifs allows control at global architectures and induces pre-selected properties from the level of single molecule to supramolecular network, confirming that metal coordination provides a helpful tool for obtaining multifunctional soft materials.

Discotic nematic liquid crystals: science and technology

The nematic phase of discotic liquid crystals, although rarely observed, has made very significant progress over the past three decades since their discovery. It has made its way from a mere scientific curiosity to application in commodities. The negative birefringence films formed by polymerized nematic discotic liquid crystals have been commercialized as compensation films to enlarge the viewing angle and enhance the contrast ratio of commonly used twisted nematic liquid-crystal displays. High strength and high performance carbon fibers for industrial applications have been obtained from the carbonaceous mesophase and a liquid-crystal display device with wide and symmetrical viewing angle has been demonstrated by using discotic nematic liquid crystals. Discotic films with patterned colours have been obtained from cholesteric lyo-mesophases of discotic liquid crystals. Various molecular architectures have been designed and synthesized to exhibit the discotic nematic phase over a wide range of temperature. This critical review focuses on the synthesis and physical properties of these fascinating materials. It deals with the structure of various nematic phases, different discotic cores exhibiting the nematic phase, novel designing and transition temperature engineering principles, alignment and physical properties, and finally the application of discotic nematic LCs as the active switching component and as optical compensation films for widening the viewing angle and contrast ratio of liquid-crystal display devices (98 references).

Controllable side-by-side and end-to-end assembly of Au nanorods by lyotropic chromonic materials

We present a simple and universal technique for assembling gold nanorods (NRs) using self-assembled stacks of lyotropic chromonic materials, without covalent bonding between NRs and the linking agent. The anisotropic electrostatic interaction between the chromonic stacks and NRs allows one to achieve either side-by-side or end-to-end assembly, depending on the surface charge of NRs. The assembled superstructures are stable within an extended temperature range; the degree of NR aggregation can be controlled by a number of factors influencing the self-assembly of chromonic materials, such as the concentration and pH of the solution.