Flow-induced Crystallization Of Polymers Research Articles

Flow-Induced Polymer Crystallization under Pressure and Its Engineering Application in “Structuring” Polymer Processing

Flow-Induced Polymer Crystallization under Pressure and Its Engineering Application in “Structuring” Polymer Processing

A Unified Thermodynamic Model of Flow-induced Crystallization of Polymer

A Unified Thermodynamic Model of Flow-induced Crystallization of Polymer

Measuring Flow-Induced Crystallization Kinetics of Polyethylene after Processing

The flow-induced crystallization of polymers is a ubiquitous aspect of processing where the effect of flow can dramatically alter end-use properties of polymers. Here, we will describe the developm...

Multiscale characterization of semicrystalline polymeric materials by synchrotron radiation X‐ray and neutron scattering

Synchrotron radiation (SR) X-ray and neutron scattering provide excellent probes for the investigation of polymeric material. Based on high brilliant beam with a tunable wavelength of SR, scattering techniques with high time and spatial resolutions have been developed for in situ X-ray study on polymeric materials. With the isotopic sensitivity of neutron, the detailed single chain behavior can be isolated from the polymeric matrix under variant conditions with the help of deuterium labeling and contrast variation/matching. With examples on flow-induced crystallization of polymer and hierarchical structure decomposition of polymer nanocomposite, current review attempts to present the advantages of SR X-ray and neutron scattering in the study of hierarchical and multiscale structural evolutions of polymeric materials. With time resolution up to sub-ms and spatial resolution of 100 nm, SR is expected to promote the understanding of non-equilibrium polymer physics under processing. With the ability to “see” the single chain conformation and turn the contrast of the multicomponent polymeric composites, neutron scattering can benefit the progress of polymer science. Platform based on SR and neutron source provide promising of establishing polymer Materials Genome database, which might strongly benefit industrial processing and accelerate the progress of material innovation.

In Situ Synchrotron Radiation Techniques: Watching Deformation-induced Structural Evolutions of Polymers

Synchrotron radiation (SR) provides highly brilliant light with tunable wavelength from hard X-ray to far infrared, on which scattering, spectroscopy and imaging techniques with high time and spatial resolutions have been developed for in situ study on biological system and materials like polymer. With examples on flow-induced crystallization of polymer, deformation of nanoparticle filler network in rubber composite and necking propagation in tensile stretch, current work attempts to demonstrate the advantages of in situ synchrotron radiation X-ray scattering, X-ray nano-CT and infrared imaging in the study of deformation-induced multi-scale structural evolutions of polymers. With time resolution up to sub-ms, synchrotron radiation is expected to play a great role in understanding non-equilibrium polymer physics under processing and service conditions, while high-throughput characterization platform based on synchrotron radiation opens the possibility to establish polymer Materials Genome database in processing parameter space within reasonable time, which can serve as the roadmap for industrial polymer processing and accelerate material innovation.

Transition from chain- to crystal-network in extension induced crystallization of isotactic polypropylene

With a combination of extensional rheology and in-situ small-angle X-ray scattering measurements, the protocol of two-step extension is proposed to investigate the early stage of flow-induced crystallization (FIC) in supercooled isotactic polypropylene melt at 138 °C. After both step strains, the crystallization half-time presents a nonmonotonic dependence on the interval time between two extensional operations, based on which three different stages of structural evolution are defined. In stage I, both nucleation and chain relaxation occur, which enhances the crystallization rate but reduces the final lamellar crystal orientation. In this stage, each part of the melt is considered to have approximately the same dynamics to respond homogeneously to the second extension and thus the system is still dominated by a chain-network. When entering into stage II, the sparse large-scaled crystal is formed to construct a heterogeneous crystal-network superimposed on the chain-network, which decelerates the second extension induced crystallization by causing stress concentration on the crystal-network at low faction. In stage III, the crystal-network dominates the sample deformation due to the formation of abundant lamellar crystal, which recreates the approximately same dynamics for each part of sample and brings about an enhancement of crystallization rate again. The transition from chain- to crystal-network revealed in this work demonstrates a dynamical coupling of chain relaxation, crystal nucleation, and growth in FIC of polymers.

Kinetics and Morphology of Flow Induced Polymer Crystallization in 3D Shear Flow Investigated by Monte Carlo Simulation

To explore the kinetics and morphology of flow induced crystallization of polymers, a nucleation-growth evolution model for spherulites and shish-kebabs is built based on Schneider rate model and Eder model. The model considers that the spherulites are thermally induced, growing like spheres, while the shish-kebabs are flow induced, growing like cylinders, with the first normal stress difference of crystallizing system being the driving force for the nucleation of shish-kebabs. A two-phase suspension model is introduced to describe the crystallizing system, which Finitely Extensible Non-linear Elastic-Peterlin (FENE-P) model and rigid dumbbell model are used to describe amorphous phase and semi-crystalline phase, respectively. Morphological Monte Carlo method is presented to simulate the polymer crystallization in 3D simple shear flow. Roles of shear rate, shear time and shear strain on the crystallization kinetics, morphology, and rheology are analyzed. Numerical results show that crystallization kinetics, morphology and rheology in shear flow are qualitatively in agreement with the theoretical, experimental and other numerical works which verifies the validity and effectiveness of our model and algorithm. To our knowledge, this is the first time that a model and an algorithm revealing the details of crystal morphology have been applied to the flow induced crystallization of polymers.

Flow-Induced Crystallization of Polymers: Molecular and Thermodynamic Considerations

Flow-induced crystallization (FIC) of polymers is a long-standing, industrial relevant, nonequilibrium thermodynamic challenge. Thanks to the development of in situ time and spatial resolved techniques like rheology and synchrotron radiation X-ray scattering, substantial progress on the understanding of FIC has been achieved in past 20 years. In this Perspective, we first discuss some recent modifications and improvements on early coarse-grained approaches like the coil–stretch transition model for shish formation and the entropic reduction model for the enhancement of nucleation rate. Then breaking out the two-phase model of classical nucleation theory, flow-induced coil–helix transition, density fluctuation or phase separation, and isotropic–nematic transition are considered as intermediate orders in FIC. Establishing flow morphology and phase diagrams is essential for revealing the nonequilibrium nature of FIC, which will serve as structural roadmap for the processing of high performance polymer products.

Flow-enhanced solution printing of all-polymer solar cells.

Morphology control of solution coated solar cell materials presents a key challenge limiting their device performance and commercial viability. Here we present a new concept for controlling phase separation during solution printing using an all-polymer bulk heterojunction solar cell as a model system. The key aspect of our method lies in the design of fluid flow using a microstructured printing blade, on the basis of the hypothesis of flow-induced polymer crystallization. Our flow design resulted in a ∼90% increase in the donor thin film crystallinity and reduced microphase separated donor and acceptor domain sizes. The improved morphology enhanced all metrics of solar cell device performance across various printing conditions, specifically leading to higher short-circuit current, fill factor, open circuit voltage and significantly reduced device-to-device variation. We expect our design concept to have broad applications beyond all-polymer solar cells because of its simplicity and versatility.

繊維工業と結晶学

Our modern confortable lifestyles are supported by advanced fibers and the application fields of the fibers have spread into not only clothing textiles but also industrial uses. The industry of the high strength fibers, which is a typical example of the advanced fiber, has concurrently been grown with the progress of the fiber science including crystallography of polymer crystals. The history of the high strength fibers shedding light on the technologies of molecular manipulation giving rise to the high strength fibers and the related crystallography are summarized in this article. Moreover, a new mechanism of the formation of the flow-induced super structure, “shish-kebab”, with regard to the key-structure of the high strength fibers is shown as a recent topic of flow-induced polymer crystallization.

On the Effect of Particle Size, Shape, Concentration, and Aggregation on the Flow-Induced Crystallization of Polymers

In this work, the combined effect of particles and flow on the crystallization of polymers has been investigated, using a rheo-optical approach. The effect of particle size, concentration, shape, and aggregation on the kinetics of flow-induced crystallization is investigated. It is shown that at high enough flow rates, flow will dominate the nucleation process, independent of the presence of particles, whatever their size, shape and concentration. Moreover, a framework will be presented to explain the additive effect of the presence of particles and flow on polymer crystallization. Finally, possible deviations from this additive rule (“synergetic effects”) will be discussed.

Multi-scale molding and numerical simulation of the flow-induced crystallization of polymer

A numerical simulation for the isothermal flow-induced crystallization (FIC) of polymer melt in a simple shear flow is presented. The model is based on a two-phase suspension model established for crystallization and has the advantage of taking into account the polymer melt rheological behavior through the first normal stress difference calculation. A FENE dumbbell model and a rigid dumbbell model are used to describe the amorphous phase and the semi-crystalline phase, respectively. Crystallization is described as a spherulitical nucleation and growth process. The results show that the short-term shear has a large effect on the crystallization dynamics of polymer.

Extensional rheometer for in situ x-ray scattering study on flow-induced crystallization of polymer

We designed and constructed an extensional rheometer for in situ small and wide angle x-ray study on flow-induced crystallization of polymer. Two rotating drums with an axis distance of 20 mm are employed to impose extensional deformation on the samples. With a constant angular velocity, the two drums generate a constant Henkcy strain rate as sample length for testing keeps constant during deformation. An ionic liquid is used as heating medium to prevent polymer melt from bending downward due to gravity, which is excellent in terms of high thermal stability, low viscosity, and relative low adsorption on x-ray. Flow-induced crystallization experiments are conducted with this apparatus on x-ray scattering station in Shanghai Synchrotron Radiation Facility (SSRF), which allows us to collect rheological and structural data simultaneously and may lead to a better understanding on flow-induced crystallization of polymer.

On the Onset of Oriented Structures in Flow-Induced Crystallization of Polymers: A Comparison of Experimental Techniques

On the Onset of Oriented Structures in Flow-Induced Crystallization of Polymers: A Comparison of Experimental Techniques

Some fundamental aspects of the kinetics of flow-induced crystallization of polymers

Some indispensable fundamental aspects of the kinetics of polymer crystallization are summed up. Those aspects are of particular interest in the development of crystalline structures during polymer processing. In this connection also a monograph (Janeschitz-Kriegl 2009) must be mentioned, which has been written last year by the first author of this article. The present paper contains a selection of particularly interesting subjects. It turns out that many of these subjects have eluded a mathematical treatment. The pertinent list is given in the introduction. And those people, who feel pressed to produce computer programs, are exhorted to mind the content of the present article and also of the mentioned monograph in avoiding arbitrary assumptions.

Hierarchical Orientational Relaxation Inducing Shish-Kebab Formations in Polymer Melt Crystallization

We studied athermal relaxation of bulk extended chains by means of dynamic Monte Carlo simulations, and we got intermediately relaxed melts with a memory of chain orientations but no more crystalline order. The orientational memory in the melts dominated the crystal orientation and nucleation types. The difference in crystallization behaviors induced by orientational relaxation suggested the mechanism of hierarchical crystallization. Thus, we studied the isothermal crystallization of a binary blend of different relaxed chains. We observed the prior crystallization of less relaxed chains could act as a shish to induce epitaxial crystallization of more relaxed chains to form kebabs. This mechanism had demonstrated the structure of precursors and gave insight into the formation of shish-kebab crystals in polymer melts. The results suggested that in flow-induced polymer crystallization the hierarchical orientational relaxation of chains decided the formation of shish-kebabs.

The Effect of Orientation Relaxation on Polymer Melt Crystallization Studied by Monte Carlo Simulations

We use dynamic Monte Carlo simulations to study the athermal relaxation of bulk extended chains and the isothermal crystallization in intermediately relaxed melts. It is found that the memory of chain orientations in the melt can significantly enhance the crystallization rates. The crystal orientation and lamellar thickness essentially depend on the orientational relaxation. Moreover, there is a transition of the nucleation mechanism during the isothermal crystallization from the intermediately relaxed melts. These results explain the mechanism of the self-nucleation by orientation and suggest that in flow-induced polymer crystallization, the orientational relaxation of chains decides the crystal orientation.

Flow-induced crystallization of polymer: theory and experiments

In this work we analyze the crystallization kinetics under steady shear flow conditions of different samples obtained by blending two isotactic poly(1-butene)s with different average molecular weights. It is observed that the addition of a small amount of high MW-polymer (<10 wt%) to a low MWsample does not produce any appreciable effect upon the crystallization kinetics under both quiescent and shear flow conditions. This behavior can be attributed to constraint release of high MW chains due to the relaxation of the shorter chains and can be described by the double reptation theory, which coupled with classical nucleation models allows for good quantitative predictions of the experimental results by using the relaxation times of the two blend components as the only fitting parameters.

Simultaneous birefringence, small- and wide-angle X-ray scattering to detect precursors and characterize morphology development during flow-induced crystallization of polymers

An experimental configuration that combines the powerful capabilities of a short-term shearing apparatus with simultaneous optical and X-ray scattering techniques is demonstrated, connecting the earliest events that occur during shear-induced crystallization of a polymer melt with the subsequent kinetics and morphology development. Oriented precursors are at the heart of the great effects that flow can produce on polymer crystallization (strongly enhanced kinetics and formation of highly oriented crystallites), and their creation is highly dependent on material properties and the level of stress applied. The sensitivity of rheo-optics enables the detection of these dilute shear-induced precursors as they form during flow, before X-ray techniques are able to reveal them. Then, as crystallization occurs from these precursors, X-ray scattering allows detailed quantification of the characteristics and kinetics of growth of the crystallites nucleated by the flow-induced precursors. This simultaneous combination of techniques allows unambiguous correlation between the early events that occur during shear and the evolution of crystallization after flow has stopped, eliminating uncertainties that result from the extreme sensitivity of flow-induced crystallization to small changes in the imposed stress and the material. Experimental data on a bimodal blend of isotactic polypropylenes are presented.

Molecular Aspects of Flow-Induced Crystallization of Polymers

Like teeth, bone and sea shells, semicrystalline polymers combine strength with toughness by forming a nano-scale composite with platelet-like crystals stacked with noncrystalline material between them. The morphology and orientation distribution of the nanostructure dictate the material properties. Dynamics of polymer in the melt play an important role in controlling the morphology, especially under the influence of flow. Using bimodal isotactic polypropylenes to reveal the effects of small concentrations of very long chains, in collaboration with Mitsubishi Chemical, we show that long have a profound effect when they are so long that they can undergo chain stretching, particularly when the long chain concentration is at or above their overlap concentration. When subjected to identical stress at identical subcooling, the blends containing long undergo dramatically faster crystallization with very strong orientation. The “long chains enhance formation of highly oriented crystallization precursors (“shish) on which oriented lamellae (“kebabs) subsequently grow. In collaboration with Sumitomo Chemical and The University of Tokyo, we test the hypothesis that the kebabs are actually composed of long using isotopic labelling of selected fractions and small angle neutron scattering (SANS). The results show that long in the shish are at the same concentration as they are everywhere else: there is no neutron scattering contrast when the long are the deuterium labelled ones! The long are essential for the formation of shish and they play their role by “recruiting adjacent into formation of the shish. Placing molecular defects on the longest inhibits their ability to serve this role, providing a molecular tool to independently control the melt elasticity (by choice of the length and concentration of the long chains) and the flow-induced crystallization behavior (by selecting the comonomer content, for example, of the long chains).