Coherently moving flocks of birds, beasts, or bacteria are examples of living matter with spontaneous orientational order. How do these systems differ from thermal equilibrium systems with such liquid crystalline order? Working with a fluidized monolayer of macroscopic rods in the nematic liquid crystalline phase, we find giant number fluctuations consistent with a standard deviation growing linearly with the mean, in contrast to any situation where the central limit theorem applies. These fluctuations are long-lived, decaying only as a logarithmic function of time. This shows that flocking, coherent motion, and large-scale inhomogeneity can appear in a system in which particles do not communicate except by contact.

different core block chemistry. The key point for choosing the different chemistries of the two hydrophobic blocks is that the two blocks experience a high degree of mutual immiscibility. In the current experiment, polystyrene (PS) and poly(2,3,4,5,6-pentafluorostyrene) (PPFS) were employed as the different, third hydrophobic blocks in the two triblock copolymers (PAA 94 -b-PMA 103 -b-PS 117 and PAA 93 -b-PMA 99 -b-PPFS 100 ) (29). Equal molar amounts of the two triblock copolymers with different respective third blocks were dissolved in pure THF. EDDA was then added to reach a final 1:1 molar ratio of amine groups to acid groups. The diamines underwent complexation with the PAA blocks, thereby forming aggregates with PAA-diamine cores. Notably, these aggregates contained each of the triblock copolymers with both PS and PPFS hydrophobic blocks because of the simple trapping of unlike hydrophobic blocks in the same aggregate by PAA-diamine complexation. Next, introduction of water into the THF solution to a final ratio of THF:water = 1:2 provided for the formation of cylindrical micelles. However, the existence of the original mixed triblock copolymer aggregates, as a result of PAA and diamine complexation, forced the local co-assembly of unlike third hydrophobic blocks into the same micelle core. In addition, the lack of chain exchange in solution that disallows global chain migration and maintains nonequilibrated micelle structures, combined with the fact that the PAA chains in the corona of the newly formed micelles were still complexed with diamines and were not freely mobile within the micelle, guarantee the stability of the mixed-core micelle. The immiscibility of the two different hydrophobic blocks, PS and PPFS, eventually resulted in internal phase separation on the nanoscale, producing multicompartment micelles. The images shown in Fig. 4, A to D were taken after 4 days of aging a solution of mixed hydrophobic core cylinders. Internal phase separation is clearly indicated by the strong undulations along the cylinder surfaces and the TEM contrast variation along the cylinders. The larger, darker, and more spherical regions within the cylinders are hypothesized to be regions that are concentrated in PAA 94 -b-PMA 103 -b-PPFS 100 triblock copolymer. First, there is a higher interfacial energy between PPFS and PMA, relative to PS and PMA, causing more chain stretching within PPFS-rich core domains so as to limit PPFS interactions with surrounding PMA blocks. Second, the greater electron density of the PPFS block provides a greater ability to scatter electrons and produce darker images in the TEM. The thinner region of the undulating cylinder would then be occupied primarily by PAA 93 -b-PMA 99 -b-PS 117 (Fig. 4G). This internal cylinder phase separation only occurred at relatively higher amounts of water in the mixed solvent solutions. Cryo-TEM showed uniform cylinders without undulation on the surface at only 40% water/THF solution after 4 days (Fig. 4E). However, multicompartment cylinders could be obser...