Kunpeng Cui

Flow-induced crystallization (FIC) is a typical nonequilibrium phase transition and a core industry subject for the largest group of commercially useful polymeric materials: semicrystalline polymers. A fundamental understanding of FIC can benefit the research of nonequilibrium ordering in matter systems and help to tailor the ultimate properties of polymeric materials. Concerning the crystallization process, flow can accelerate the kinetics by orders of magnitude and induce the formation of orie

Understanding the energy dissipation mechanism during deformation is essential for the design and application of tough soft materials. We show that, in a class of tough and self-healing polyampholyte hydrogels, a bicontinuous network structure, consisting of a hard network and a soft network, is formed, independently of the chemical details of the hydrogels. Multiscale internal rupture processes, in which the double-network effect plays an important role, are found to be responsible for the larg

Significance Life provides the best demonstration of complex and adaptive nonequilibrium system, which executes biological functions through nonequilibrium structure transformation. Creating lifelike materials to achieve part of or full biological functions is a grand challenge. Traditional memories from hard and dry materials are static, with no ability of forgetting; here we propose to use soft and wet hydrogels to achieve dynamic memories with spontaneous but learning-strength-dependent forge

Polyampholyte hydrogels (PA gels) are drawing great attention for their excellent mechanical properties including self-healing, high toughness, and fatigue resistance. These mechanical performances are found to be attributed to the hierarchical structure of the PA gels, consisting of reversible ionic bonds at the 1 nm scale, permanent polymer network at the 10 nm scale, and bicontinuous phase network at the 100 nm scale. In this work, we systematically studied the phase network formation of thes

Extension flow induced crystallization of isotatic polypropylene (iPP) has been studied with a combination of extension rheological and in situ small-angle X-ray scattering (SAXS) measurements at 140 °C. Rheological data of step extension on iPP melt are divided into before and beyond fracture strain zones in strain–strain rate space, where intermediate strains between them lead to fracture of samples. Coincidently, weak and strong accelerations of nucleation are observed in the before and beyon

Based on classical nucleation theory, the current entropic reduction model (ERM) of flow-induced crystallization (FIC) treats external work as perturbation on the framework of equilibrium thermodynamics, which, however, obscures the nonequilibrium nature of FIC. In this work, in situ investigation on FIC under strong flow by combining a unique homemade extensional rheometer and ultrafast X-ray scattering reveals a constant critical strain or time for nucleation in isotactic polypropylene melt in

On the basis of the duality of the shish-kebab superstructure, coil–stretch transition (CST) is well recognized as the molecular mechanism for shish-kebab formation in polymer melts, which, however, is challenged by recent results in flow-induced crystallization (FIC). In this work, we perform a real time investigation on FIC of polyethylene bimodal blends by combing a unique homemade extensional rheometer and synchrotron radiation small-angle X-ray scattering. The results show that the critical

Recent studies reported a multiscale structure in tough and self-healing hydrogels containing physical associations. For example, a type of tough and self-healing hydrogel from charge-balanced polyampholytes (PA) has a mesoscale bicontinuous double network structure with structural length around 400 nm. This mesoscale network structure plays an essential role in the multistep rupture process, which leads to the high toughness of PA hydrogels. In this work, by using an osmotic stress method, we s

Recently, we have developed a series of charge balanced polyampholyte (PA) physical hydrogels by random copolymerization in water, which show extraordinarily high toughness, self-healing ability and viscoelasticity. The excellent performance of PA hydrogels is ascribed to dynamic ionic bond formation through inter- and intra-chain interactions. The randomness results in ionic bonds of wide strength distribution, the strong bonds, which serve as permanent crosslinking, imparting the elasticity, w

The tough and self-healing hydrogels composed of polyampholytes (PA gels) are drawing great attention due to their multiscale structures and the resultant multiple mechanical properties. This work studies the stress relaxation behavior of PA gels and reveals the underlying multiscale structure evolutions by combining birefringence and small-angle X-ray scattering measurements. The PA gels show a fast and strong stress relaxation that obeys the stress-optical rule, which could be associated with

The role of long chains in extension flow-induced crystallization was studied with a combination of extension rheological and in situ small-angle X-ray scattering (SAXS) measurements at 52 °C. To elucidate the effects of long chains, bidisperse blends of poly(ethylene oxide) (PEO) with the long-chain concentration above the overlap concentration were prepared, constructing long-chain entanglement network in short-chain matrix. Rheological data of step extension on PEO melt are divided into two r

Tough soft materials usually show strain softening and inelastic deformation. Here, we study the molecular mechanism of abnormally large nonsoftening, quasi-linear but inelastic deformation in tough hydrogels made of hyperconnective physical network and linear polymers as molecular glues to the network. The interplay of hyperconnectivity of network and effective load transfer by molecular glues prevents stress concentration, which is revealed by an affine deformation of the network to the bulk d

Abstract During industrial processing, such as film blowing and injection molding, semicrystalline polymers have to be subjected to external flow. Flow changes the nucleation rate, crystal morphology and polymorphism of polymers. As flow can be tunable, polymeric products with different macroscopic performance and versatile applications can be obtained. Understanding polymer crystallization with the presence of flow, or namely flow‐induced crystallization (FIC), is crucial to optimize polymer pr

Understanding the physical principle that governs the stimuli-induced swelling and shrinking kinetics of hydrogels is indispensable for their applications. Here, we show that the shrinking and swelling kinetics of self-healing hydrogels could be intrinsically asymmetric. The structure frustration, formed by the large difference in the heat and solvent diffusions, remarkably slows down the shrinking kinetics. The plateau modulus of viscoelastic gels is found to be a key parameter governing the fo

Understanding the deformation mechanism of amorphous polymeric materials is indispensable for their applications but is quite challenging. Here, with amorphous plasticized poly(vinyl butyral) (PVB) as a model system, we studied its structural change in situ during uniaxial deformation with ultrasmall-angle X-ray scattering (USAXS). We observed a stretch-induced phase separation behavior characterized by a butterfly scattering pattern in plasticized PVB for the first time. This phase separation,