Nanohybrid Shish-kebab Structure Research Articles

Molecular simulation of crystal nucleation and growth of structurally restricted polymer nanocomposites

This study reveals important features of crystal nucleation and growth in coarse-grained structurally restricted polymer systems (i.e., one end of the chain is grafted on the surface of one-dimensional filler) based on the Monte Carlo simulation on cubic lattice. The structurally restricted polymer system includes two kinds of polymers: terminally grafted and free chains. The existence of more grafted chains increases the crystal nuclei number in the structurally restricted polymer systems, which shortens the nucleation induction time and accelerates crystallization. Intramolecular nucleation occurs when the chain structure is limited. Then, with the increase of restricted chains, the nucleation mechanism changes to intermolecular nucleation. When the interface interaction is introduced into the system, the change of crystallization rate is the result of the competition between conformation entropy and chain mobility. The chain elongation increases with the enhancement of interface interaction, which leads to the increase of the loss of conformational entropy and is conducive to the formation of crystal nucleus. However, the chain mobility slows down with the enhancement of interface interaction, which will hinder the formation of crystal nucleus. By tailoring the interface interaction, the crystal morphologies of polymer nanocomposites can be adjusted to form the unique nanohybrid shish-kebab structures, that is, the filler is used as shish, the crystal regions generated by free chains are attached to the outside of crystal regions generated by restricted chains to form kebabs. Furthermore, the length of grafted chains has different effect on the crystallization depending on the concentration of grafted chains.

Controlled Crystallization of Diblock Copolymers on Carbon materials: Effect of Block Length

The fabrication of sophisticated hybrid mesostructures involving carbon nanomaterials and organic building blocks has attracted great attention due to their tunable properties and potential applications. Herein, we report the precisely controlled structure and morphology of diblock copolymers-carbon materials hybrid mesostructures, in which nano/micron- disc shape and honeycomb structure were fabricated on the surfaces of carbon nanotube (CNT), carbon nanofiber (CNF), and graphite, respectively. Synthesized ethylene/functional cyclic olefin block copolymers (PE-b-HPNBMA) showed a narrow dispersity, allowing the formation of nanohybrid shish-kebab structures (NHSK) with a highly uniform disc-shape crystalline size and period. The tunability of HPNBMA block length and functional substituent enables not only control of the nanocrystal size but also flexible design of the surface chemical structure, which can endow diblock copolymers-carbon materials hybrid mesostructures with specific properties. As proof of the ability, superhydrophobic (contact angle > 150°) NHSK films with tunable adhesion were successfully produced.

Superior mechanical performance of in-situ nanofibrillar HDPE/PTFE composites with highly oriented and compacted nanohybrid shish-kebab structure

Hierarchical structures dominate the mechanical performance of polymer materials. In this work, in-situ nanofibrillar high-density polyethylene/polytetrafluoroethylene (HDPE/PTFE) composites with highly ordered and compacted nanohybrid shish-kebab (NHSK) structure were successfully fabricated using a self-made loop oscillating push-pull molding (LOPPM) equipment. Through the synergistic effect of the oscillatory push-pull shear flow field and PTFE, in-situ nanofibrillar HDPE/PTFE composites with superior strength and toughness were obtained. With the addition of 5 wt% PTFE in HDPE, the tensile strength, Young's modulus and impact strength of in-situ nanofibrillar composites reached 133.4 MPa, 4388.1 MPa and 69.1 kJ/m2, which was about 6.0, 6.0 and 3.1 times higher than that of neat HDPE, respectively. These superior improvements in mechanical performance were attributed to the oriented and compacted NHSK structure. Additionally, two-dimensional small-angle X-ray scattering (2D-SAXS), two-dimensional wide-angle X-ray scattering (2D-WAXS) and differential scanning calorimetry (DSC) results confirmed the synergistic enhancement effect of the flow field and PTFE on the degree of orientation, lamellar thickness, average length of shish and crystallization properties. Overall, it is believed that this proposed strategy can be extended to a wide range for the preparation of polymer materials with superior mechanical properties.

Differences in Crystallization Behaviors between Cyclic and Linear Polymer Nanocomposites

Cyclic polymers exhibit fascinating crystallization behaviors owing to the absence of chain ends and more compact conformations. In the current simulation, dynamic Monte Carlo simulations were performed to reveal the underlying mechanism of the effect of chain topology and chain length on crystallization of polymer in solutions containing one-dimensional nanofiller. Simulation results suggested that the filled cyclic polymers exhibit higher melting temperature, higher crystallization temperature, and faster crystallization rate than the analogous linear polymers of identical chain length, especially in the systems with relatively short chains. Based on the Thomson-Gibbs equation, we theoretically analyzed the difference in the melting point between the cyclic and linear polymers under different chain lengths, and derived the dependence of the ratio of the melting point of the linear polymers to that of its cyclic analogs on chain length. In addition, it was also observed that the nanofiller can induce the formation of nanohybrid shish-kebab structure during isothermal crystallization of all systems.

Endothelial Cell Migration on Poly(ε-caprolactone) Nanofibers Coated with a Nanohybrid Shish-Kebab Structure Mimicking Collagen Fibrils.

Regulating cell migration dynamics is of significance in tissue engineering and regenerative medicine. A 3D scaffold was created to provide various topographies based on a poly(ε-caprolactone) (PCL) self-induced nanohybrid shish-kebab structure, which consisted of aligned PCL nanofibers and spaced PCL crystal lamellae grown on the fibers. Electrospinning was applied followed by self-induced crystallization. The results resembled natural collagen fibrils in an extracellular matrix. This variable microstructure enabled control of cell adhesion and migration. The kebab size was controlled by initial PCL concentrations. The geometry of cells seeded on the fibers was less elongated, but the adhesion was more polarized with a higher nuclear shape index and faster migration speed. These results could aid in rapid endothelialization in tissue engineering.

The mobility of PEG chains versus micellar stability towards the formation of PE‐b‐PEG nanohybrid shish‐kebab on carbon nanotubes

A comparative study of the effect of copolymer composition on nanohybrid shish‐kebab (NHSK) architecture on carbon nanotubes (CNTs) is presented. A semi‐crystalline amphiphilic di‐block copolymer, polyethylene‐b‐polyethylene glycol (PE‐b‐PEG) was used in this study. Copolymer composition was varied on the basis of the molecular weight of individual copolymers and the ratio between PE and PEG. NHSK structure was characterized using a combination of scanning and transmission electron microscopy. The mobility of PEG, which is determined by its chain length was found to have a significant impact on the periodic decoration of the copolymer on CNTs. With higher chain length or molecular weight, PEG chains provided better stability to micelles formed by the copolymer. Further, PEG assisted micellar stability to create a foundation for PE chains to interact and orient along the tube axis of CNTs as a function of the copolymer composition. It was found that the stability of NHSK architecture can also be changed over time at the same crystallization temperature. This work offers novel and fundamental insights towards the mobility of PEG in the copolymer and its disk‐shaped crystal's formation and micellar stability during crystallization with CNTs. This study provides a better understanding of a mechanically tunable NHSK where the architecture of copolymer crystals can be modified by adjusting the molecular weight of PEG.

Remarkably Strengthened microinjection molded linear low-density polyethylene (LLDPE) via multi-walled carbon nanotubes derived nanohybrid shish-kebab structure

In this work, linear low-density polyethylene (LLDPE) nanocomposites with different loading levels of multi-walled carbon nanotube (MWCNTs) were prepared by microinjection molding. Interestingly, a similar network structure featured with oriented nanohybrid shish-kebab structure was formed in all the LLDPE/MWCNTs composites. Importantly, the composites with improved strength and modulus in parallel with enhanced toughness were obtained. For example, the tensile strength, modulus and toughness of the composites with 1 wt% MWCNTs were increased by 64.1%, 100% and 134.6%, respectively. This work offers a simple approach to achieve high-performance composites molded by microinjection molding (MIM) together with nanohybrid shish-kebab structure.

The Effect of Grafting Density on the Crystallization Behaviors of Polymer Chains Grafted onto One-Dimensional Nanorod

The crystallization behaviors of five polymer chain systems grafted on a nanorod and the corresponding effect of grafting density were investigated by dynamic Monte Carlo simulations. The segment density near the interfacial regions, the number of crystallites, and the mean square radius of gyration (<Rg2>) increase with increasing grafting density, which are beneficial to the enhancement of crystallizability. Meanwhile, the crystalline morphology is greatly influenced by grafting density and polymer-nanorod interaction. For the grafted system with 52 chains, a nanohybrid shish-kebab (NHSK) structure is formed, when the polymer-nanorod interaction (Eb/Ec) is -0.4. For the system with 128 chains, a NHSK structure is formed, when Eb/Ec is -1.0. For the system with 252 chains, NHSK structure cannot be formed. The findings in this work can supply important theoretical reference for the design, preparation, and application of polymer nanocomposites.

One-dimensional nanofiller induced crystallization in random copolymers studied by dynamic Monte Carlo simulations

ABSTRACTUnderstanding crystallization mechanism of random copolymers is beneficial for the design and development of new polymeric materials. We performed dynamic Monte Carlo simulations to investigate the crystallization behaviours of random copolymers in polymer solutions induced by one-dimensional nanofiller. The effects of comonomer content on crystallinity and crystalline morphology were studied in detail. In the copolymers with relatively low comonomer contents, the final absolute crystallinity is independent of comonomer contents, while in the copolymers with relatively high comonomer contents the final absolute crystallinity decreases with increasing comonomer contents. In addition, the one-dimensional nanofiller can induce the formation of nanohybrid shish-kebab structures in the copolymers with low comonomer contents. However, in the copolymer with very high comonomer content, the presence of a large number of comonomers with no ability of parallel arrangements hinders the formation of nanohybrid shish-kebab structures.

Fabrication of Dielectrically Sensitive Carbon Nanotube/Polyethylene Nanohybrid Shish-Kebab Structure for Potential Tissue Engineering Applications

Carbon nanotube (CNT)/polymer nanohybrid shish-kebab (NHSK) structure is a unique approach to functionalize CNTs and mimic the hierarchical architecture of native collagen fibrils in the extracellular matrix (ECM), owing to their favorable geometric similarity. This study thus aimed at combining the unique NHSK architecture of CNTs with their favorable dielectric properties to fabricate a collagen-like, dielectrically sensitive and biocompatible material. The NHSK structure was fabricated with CNTs and polyethylene (PE) by means of a solution crystallization technique. Configuration of PE in terms of molecular weight and structure was found to be one of the important factors that determined the morphology of the NHSK. Moreover, the material was exposed to dielectrophoresis (DEP) to guide the deposition of CNT/PE NHSK into the directional pattern. The PE-decorated CNTs exhibited enhanced dielectrophoretic sensitivity and controllable structural alignment, while the neat CNTs did not. Human osteoblast-like MG-63 cells were cultured on the scaffolds to examine their biocompatibility and results indicated that the nanotopography of the kebab crystals on the CNTs facilitated cell adhesion and proliferation while the DEP-patterned NHSK structure further boosted cell attachment and viability, thus suggesting that the CNT/polymer nanohybrid shish kebab structure has potential applications in tissue engineering.

A Prerequisite of the Poly(ε‐Caprolactone) Self‐Induced Nanohybrid Shish–Kebab Structure Formation: An Ordered Crystal Lamellae Orientation Morphology of Fibers

AbstractThe shish–kebab structure has been extensively applied in many fields; however, the formation mechanism is still an open question. In this study, different electrospun poly(ε‐caprolactone) (PCL) fibers are applied as the shish material in a self‐induced crystallization process, and two different self‐induced crystal structures are obtained. The PCL fibers with an ordered crystalline morphology lead to an induced crystalline structure with the crystal lamellae perpendicular to the fiber axis. However, the PCL fibers with a disordered structure induce a complicated (less ordered) crystalline lamellae morphology. Investigation of the surface crystalline structure reveals that the self‐induced nanohybrid shish–kebab (SINSK) structure follows a lattice matching and epitaxial growth mechanism. The internal crystalline structure of PCL nanofibers plays a dominant role in the formation of the SINSK structure. This study may prove helpful in screening materials for formation of the SINSK structure.

Periodic Functionalization of Graphene‐Layered Alumina Nanofibers with Aromatic Thermosetting Copolyester via Epitaxial Step‐Growth Polymerization

AbstractIn situ epitaxial step‐growth polymerization driven interfacial functionalization of aromatic thermosetting copolyester (ATSP) with multilayered graphene wrapped alumina nanofiber surface is reported. During a thermal condensation polymerization, ATSP dip‐coated fiber strands develop a nanohybrid shish–kebab structure with periodically assembled and off‐surface grown micrometer‐scale lamella ATSP domains. A mechanism combining the Plateau–Rayleigh instability, the Marangoni effect, and the epitaxial growth phenomena is proposed to elucidate controlling parameters in the process. X‐ray diffraction measurements clearly demonstrate the formation of a mesomorphic lamella phase not present within either the neat ATSP or pristine fiber samples. Results of solid‐state nuclear magnetic resonance and thermogravimetric analysis reveal the development of an interfacial coupling between the graphene‐coated ceramic nanofibers and the ATSP matrix.

Controllability of Polymer Crystal Orientation Using Heterogeneous Nucleation of Deformed Polymer Loops Grafted on Two-Dimensional Nanofiller.

Nowadays, it is a research hotspot to realize the controllability of polymer crystal structure in polymer nanocomposites. However, polymer crystals induced by two-dimensional filler always exhibit random orientation, which somewhat limit the improvement of physical properties of polymer materials. In the current paper, dynamic Monte Carlo simulations were performed to explore the methods preparing crystals with uniform orientation. Heterogeneous nucleation of deformed polymer loops grafted on two-dimensional filler can induce the appearance of a special nanohybrid shish-kebab (NHSK) structure, in which the two-dimensional filler acts as "shish" and induces the formation of crystals with uniform orientation. The grafted deformed chains are first heterogeneously nucleated on filler surface, and then free chains participate in crystallization, resulting in the formation of the NHSK structure. The NHSK structure can only be formed in the systems with high interfacial interactions at high temperatures or moderate interfacial interactions at moderate temperatures or low interfacial interactions at low temperatures. The method proposed here can be used to achieve the controllability of polymer crystal orientation in experiments.

Nanohybrid shish-kebab supramolecular structure of single-walled carbon nanotubes/N,N′-dioctyl perylene tetracarboxylic diimide

In the present work, carbon nanotubes (CNTs)-induced solution crystallization of N, N′-dioctyl perylene tetracarboxylic diimide (PTCDI-C8) in o-dichlorobenzene was studied. It is found that the nanohybrid shish-kebab (NHSK) supramolecular structure, wherein the single-walled carbon nanotubes (SWCNTs) serve as the shish and PTCDI-C8 crystals are the kebabs, with regular arrangement of the kebabs can be formed. UV–vis, photoluminescence spectroscopy and XPS studies reveal that there exist strong π-π interaction between PTCDI-C8 and SWCNTs, and some PTCDI-C8 molecules are already adsorbed on SWCNTs surface prior to crystallization. This is the first example of NHSK structure formed by CNTs and organic small molecules. Nevertheless, multi-walled carbon nanotubes (MWCNTs) cannot induce PTCDI-C8 to form NHSK structure under the same conditions. This indicates that geometric confinement may be the predominant factor affecting the orientation of the pre-adsorbed PTCDI-C8 molecules and epitaxial growth of the crystals.

The formation of a nanohybrid shish-kebab (NHSK) structure in melt-processed composites of poly(ethylene terephthalate) (PET) and multi-walled carbon nanotubes (MWCNTs)

The combination of synchrotron Small- and Wide-Angle X-ray scattering (SAXS/WAXS), and thermal analysis was used to follow the evolution of crystalline morphology and crystallization kinetics in a series of melt-processed composites of poly(ethylene terephthalate) (PET) and multiwall carbon nanotubes (MWCNT). The as-extruded PET-MWCNT composites underwent both hot and cold isothermal crystallizations where a final oriented nanohybrid shish-kebab (NHSK) crystalline structure was observed. An oriented NHSK structure was seen to persist even after melting and recrystallization of the composites. From the scattering data, we propose a model whereby the oriented MWCNTs act as heterogeneous nucleation surfaces (shish) and the polymer chains wrap around them and the crystallites (kebabs) grow epitaxially outwards during crystallization. However, depending on crystallization temperature, unoriented crystallites also grow in the polymer matrix, resulting in a combination of a NHSK and lamellar morphology. In contrast, the neat PET homopolymer showed the sporadic nucleation of a classic unoriented lamellar structure under the same isothermal crystallization conditions. These results provide a valuable insight into the distinctive modification of the crystalline morphology of melt-processed polymer-MWCNT composites prior to any secondary processing, having a significant impact on the use of MWCNTs as fillers in the processing and modification of the physical and mechanical properties of engineering polymers.

Relaxation and Crystallization of Oriented Polymer Melts with Anisotropic Filler Networks.

The coexistence of nanofillers and shear flow can influence crystallization of polymer melts. However, the microscopic mechanism of the effect is not completely revealed yet. Thus, dynamic Monte Carlo simulations were used to study the effect of the filler networks formed by one-dimensional nanofillers on relaxation and crystallization of oriented polymer melts. The filler networks restrict the relaxation of oriented polymers and impose confinement effect on the chains inside the filler networks, resulting in higher orientation and lower conformational entropy of the inside chains compared to those of the outside chains. Thus, the confined inside chains have stronger crystallizability. During crystallization, the confined chains are nucleated on the filler surface and then form nanohybrid shish-kebab structures. Furthermore, the effect of fillers and chain orientation closely depends on some factors, such as polymer-filler interaction, filler content, and filler spacing. Our simulation results are consistent with some experimental findings. Thus, these results can provide new insights into the mechanism of crystallization of filled polymers and also guide researchers to develop new polymer nanocomposites with high performance.

Fabrication of biocompatible nanohybrid shish-kebab-structured carbon nanotubes with a mussel-inspired layer

The first report investigating the biocompatibility of the (polydopamine coated) carbon nanotubes/polymer nanohybrid shish-kebab structure for tissue engineering.

Nucleation details of nanohybrid shish-kebabs in polymer solutions studied by molecular simulations

Understanding of crystal nucleation mechanism of nanohybrid shish-kebab (NHSK) structures will guide researchers to design new polymer materials with high performance. We performed dynamic Monte Carlo simulations to reveal the nucleation details of the NHSK structures in polymer solutions at molecular scale. The formation of the NHSK structures was induced by nanofillers with small lateral size under attractive polymer-filler interactions. The synergic effect of the filler geometry and the polymer-filler interaction induced the anisotropic absorption of chain segments onto the filler surface. Namely, the nanofiller absorbed the segments, which simultaneously oriented along the long axis of the nanofiller, resulting in the formation of a polymer coating with some local oriented segments on the filler surface. Those local oriented segments participated in the subsequent heterogeneous nucleation, and eventually developed into kebabs with uniform orientation.

Numerical analysis of the elastic–plastic properties of the composites incorporating nanohybrid shish-kebab structures

The nanohybrid shish-kebab (NHSK) structure, in which randomly dispersed and wavy carbon nanotubes (CNTs) serve as shish and crystal lamellas periodically decorated onto the CNTs serve as kebabs, has attracted extensive attentions due to its more excellent enhancement in comparison with pristine CNT for polymer matrix composites. In this paper, a new method, based on a modified random sequential adsorption (RSA) algorithm, is proposed to construct the 3D finite element model of the NHSK reinforced composites. The Young’s modulus calculated by this model agrees with the experimental result. Moreover, we present a comparison between the pristine CNT reinforced composite and the NHSK reinforced composite in terms of elastic–plastic behavior. Different load transfer mechanisms are analyzed for the two kinds of composites. Furthermore, we explore the effects of the crystal kebab’s material property, diameter and the periodicity of the kebabs on the elastic–plastic properties of the composite. The results show that the effective mechanical properties of the composites have a large improvement with the existence of crystal kebabs in comparison to the pristine CNT reinforced composite, which indicates that the NHSK structure can improve the load transfer efficiency between the CNT and the matrix and act as another enhanced phase in the composite. The proposed model can be used for the virtual design and optimization of CNT/semicrystalline polymer composites since it has proven capable of assessing the effects of different material and geometrical parameters on the elastic–plastic properties of the composites.

A comparative study of the load transfer mechanisms of the carbon nanotube reinforced polymer composites with interfacial crystallization

With the help of shear-lag theory, load transfer analysis is performed on the carbon nanotube reinforced polymer composites with interfacial crystallization of different morphologies, including transcrystallinity layer (TCL) and nanohybrid shish-kebab (NHSK) structures. By comparison, we find that the TCL structures can ease the burden of the CNT while the NHSK structures can lead to a fluctuating distribution of the axial stress in the CNT. Both structures can improve the effective elastic modulus of the composites, though the effect of the TCL structures is more pronounced. Besides, the enhancement of the load transfer efficiency of the composites is also observed, the study of the interfacial stress on different kinds of interfaces shows that the reinforcing effect of the TCL structures is sensitive to both the CNT/crystalline polymer interface and crystalline polymer/amorphous polymer interface, while the major decisive factor for the NHSK structures is confined to be the CNT/crystalline polymer interface because of the interlocking effect. Based on these features, some suggestions are given for tailoring the high-performance carbon nanotube reinforced polymer composites.