We find that the effects of a localized perturbation in a chaotic classical many-body system-the classical Heisenberg chain at infinite temperature-spread ballistically with a finite speed even when the local spin dynamics is diffusive. We study two complementary aspects of this butterfly effect: the rapid growth of the perturbation, and its simultaneous ballistic (light-cone) spread, as characterized by the Lyapunov exponents and the butterfly speed, respectively. We connect this to recent studies of the out-of-time-ordered commutators (OTOC), which have been proposed as an indicator of chaos in a quantum system. We provide a straightforward identification of the OTOC with a natural correlator in our system and demonstrate that many of its interesting qualitative features are present in the classical system. Finally, by analyzing the scaling forms, we relate the growth, spread, and propagation of the perturbation with the growth of one-dimensional interfaces described by the Kardar-Parisi-Zhang equation.

No abstract

Using the framework of nonlinear fluctuating hydrodynamics (NFH), we examine equilibrium spatio-temporal correlations in classical ferromagnetic spin chains with nearest neighbor interactions. In particular, we consider the classical XXZ-Heisenberg spin chain (also known as Lattice Landau Lifshitz or LLL model) evolving deterministically and chaotically via Hamiltonian dynamics, for which energy and z-magnetization are the only locally conserved fields. For the easy-plane case, this system has a low-temperature regime in which the difference between neighboring spin's angular orientations in the XY plane is an almost conserved field. According to the predictions of NFH, the dynamic correlations in this regime exhibit a heat peak and propagating sound peaks, all with anomalous broadening. We present a detailed molecular dynamics test of these predictions and find a reasonably accurate verification. We find that, in a suitable intermediate temperature regime, the system shows two sound peaks with Kardar-Parisi-Zhang (KPZ) scaling and a heat peak where the expected anomalous broadening is less clear. In high temperature regimes of both easy plane and easy axis case of LLL, our numerics show clear diffusive spin and energy peaks and absence of any sound modes, as one would expect. We also simulate an integrable version of the XXZ-model, for which the ballistic component instead moves with a broad range of speeds rather than being concentrated in narrower peaks around the sound speed. arXiv:1901.00024v1 [cond-mat.stat-mech]

Recovery of the compromised antifouling property because of perturbation in the essential chemistry on top of the hierarchical topography of a superhydrophobic coating is commonly achieved through some stimuli (temperature, humidity, pH, etc.)-driven reassociation of the low surface energy molecules. However, self-healing of superhydrophobicity in physically damaged materials having inappropriate topography is difficult to achieveand extremely important for the practical utility of this bioinspired property. Recently, very few materials have been introducedthat are capable of recovering the hierarchical featuresbut only after the application of appropriate external stimuli. Further, the optimization of appropriate stimuli is likely to be a challenging problem in practical scenarios. Here, we have strategically exploited a simple and robust 1,4-conjugate addition reaction between aliphatic primary amine and aliphatic acrylate groups for appropriate and covalent integration of a modified-graphene oxide nanosheetwhich is well recognized for its exceptional mechanical properties. The synthesized material exhibited a remarkable ability to protect the antifouling property from various harsh physical insults, including physical erosion of the top surface of the polymeric coating and various physical manipulations etc. However, after application of pressure on the same polymeric coating, the bioinspired, nonadhesive (contact angle hysteresis <5°) superhydrophobicity was compromised, and the physically damaged polymeric coating became highly adhesive (contact angle hysteresis ∼50°) and superhydrophobic. But, after releasing the pressure, the native nonadhesive (contact angle hysteresis <5°) extreme wettability was self-restored in the polymeric coating through recovery of the essential hierarchical topographywithout requiring any external stimulus. This unique material, having impeccable durability and absolute self-healing capability, was further explored in (i) developing rewritable aqueous patterns on the extremely water-repellent surface and (ii) selective impregnation of water-soluble agents on the surface of polymeric coatingwithout any permanent change in the extreme water repellency property. The unique self-healing process eventually provided a superhydrophobic printthat was made out of hydrophilic small molecules. This printing was performed directly from an aqueous medium, which is extremely hard to achieve using the conventional superhydrophobic materials. Such multifunctional interfaces could be an important avenue for various smart applications, including delivery of hydrophilic small molecules, catalysis, self-assembly of colloids, reusable chemical sensing, etc.

Stretchable and nature inspired multilayers are developed through covalent and layer-by-layer integration of functional nanomaterials. These nanomaterials are amino graphene oxide and a chemically reactive polymeric nanocomplex, and the synthesized material is capable of sustaining various forms of severe physical damage and large tensile deformations simultaneously.

Different bio-inspired liquid wettability are derived through modulation of chemistry and topography—but the chemical modulation process emerged as a superior approach for embedding desired wettability and other relevant physical properties.

No abstract

Covalent organic frameworks (COFs) having high specific surface area, tunable pore size and high crystallinity are mostly post modified following fluorinebased and complex synthetic approaches to achieve a bio-inspired liquid wettability, i.e. superhydrophobicity. Herein, a facile, non-fluorinated and robust chemical approach is introduced for tailoring the water wettability of a new COF-which was prepared through Schiff-base condensation reaction. A silane precursor was readily reacted with selected alkyl acrylates through 1,4-conjugate addition reaction, prior to grafting on the prepared C4-COF for tailoring different water wettability-including robust superhydrophobicity. The superhydrophobic C4-COF (SH-C4-COF) that displayed significantly enhanced (> 5 times; from 220 wt. % to 1156 wt. %) oil-absorption capacity, was extended to address the relevant challenges of "oil-in-water" emulsion separation, rapidly (< 1 minute) and repetitively (50 times) at diverse and harsh conditions.