Disordered hyperuniform structures are an exotic state of matter having vanishing long-wavelength density fluctuations similar to perfect crystals but without long-range order. Although its importance in materials science has been brought to the fore in past decades, the rational design of experimentally realizable disordered strongly hyperuniform microstructures remains challenging. Here we find a new type of nonequilibrium fluid with strong hyperuniformity in two-dimensional systems of chiral active particles, where particles perform independent circular motions of the radius R with the same handedness. This new hyperuniform fluid features a special length scale, i.e., the diameter of the circular trajectory of particles, below which large density fluctuations are observed. By developing a dynamic mean-field theory, we show that the large local density fluctuations can be explained as a motility-induced microphase separation, while the Fickian diffusion at large length scales and local center-of-mass-conserved noises are responsible for the global hyperuniformity.

Significance: Recently, an exotic hyperuniform fluid state was found in a number of nonequilibrium systems, which shows the promise for fabrication of novel lifelike functional materials capable of self-healing and self-adapting. However, the general mechanism of fluidic hyperuniformity (HU) and its fundamental difference from equilibrium fluids remain unclear, which hinders the rational design of nonequilibrium hyperuniform fluids. In this work, we propose a nonequilibrium hard-sphere model of hyperuniform fluids and formulate a full hydrodynamic description based on the generalized Navier–Stokes equations. Our theory reveals the mechanism of fluidic HU in a simple and intuitive way, which is confirmed by simulating a realistic active spinner system.

Designing protocols to dynamically direct the self-assembly of colloidal particles has become an important direction in soft matter physics because of promising applications in the fabrication of dynamic responsive functional materials.

Thermodynamic behavior of polymer chains out of equilibrium is a fundamental problem in both polymer physics and biological physics. By using molecular dynamics simulation, we discover a nonequilibrium mechanism that controls the conformation and dynamics of polar active polymer; i.e., head activity commands the overall chain activity, resulting in a re-entrant swelling of active chains and a nonmonotonic variation of the Flory exponent $\nu$. These intriguing phenomena are the result of two competing nonequilibrium effects arising from the head-controlled railway motion of the chain, i.e., dynamic chain rigidity and the curling of chain conformation characterized by the negative bond vector correlation. Moreover, we identify several generic dynamic features of polar active polymers, i.e., linear decay of the end-to-end vector correlation function, polymer-size-dependent crossover from ballistic to diffusive dynamics, and diffusion coefficients sensitive to head activity. A simple dynamics theory is proposed to faithfully explain these interesting dynamic phenomena. These sensitive structural and dynamical responses of active polymer to its head activity provide us a practical way to control active agents with applications in biomedical engineering.

Recently developed linker-mediated vitrimers based on metathesis of dioxaborolanes with various commercially available polymers have shown both good processability and outstanding performance, such as mechanical, thermal, and chemical resistance, suggesting new ways of processing cross-linked polymers in industry, of which the design principle remains unknown [M. Röttger et al., Science 356, 62–65 (2017)]. Here we formulate a theoretical framework to elucidate the phase behavior of the linker-mediated vitrimers, in which entropy plays a governing role. We find that, with increasing the linker concentration, vitrimers undergo a reentrant gel–sol transition, which explains a recent experiment [S. Wu, H. Yang, S. Huang, Q. Chen, Macromolecules 53, 1180–1190 (2020)]. More intriguingly, at the low temperature limit, the linker concentration still determines the cross-linking degree of the vitrimers, which originates from the competition between the conformational entropy of polymers and the translational entropy of linkers. Our theoretical predictions agree quantitatively with computer simulations, and offer guidelines in understanding and controlling the properties of this newly developed vitrimer system. Significance The recently developed linker-mediated vitrimers based on metathesis reactions offer new possibilities of processing cross-linked polymers with high mechanical performance in industry, while the design principle remains unknown. Here we propose a theoretical framework for describing the system of linker-mediated vitrimers, in which entropy is found to play a dictating role. Our mean field theory agrees quantitatively with computer simulations, and provides guidelines for the rational design of the linker-mediated vitrimers with desired properties.