Crystal Polymer Research Articles

Correction to “Nanodiffraction Imaging of Polymer Crystals”

Correction to “Nanodiffraction Imaging of Polymer Crystals”

Micromechanical modeling of the effects of crystal content on the visco-hyperelastic-viscoplastic behavior and fracture of semi-crystalline polymers

In this work, we present a novel physically based visco-hyperelastic-viscoplastic micromechanical constitutive model, which establishes a link between the evolution of the macromolecular network properties to the mechanical and fracture behavior of variable-crystallinity semi-crystalline polymers. Unlike previous micromechanical constitutive models that were only time independent, we propose a time-dependent scheme. It employs the computational effective eight-chain model for micro-macro transition while assuming a composite structure for the polymer. Thus, an innovative approach that couples the deformation and damage of individual polymer chains is developed. The proposed constitutive framework assumes that the stress developed through the deformation of semi-crystalline polymers is the sum of a macromolecular network and an intermolecular part. The macromolecular part accounts for the conformational change associated with Kuhn segments reorientation and the bond potential associated with the deformation of the bonds between Kuhn segments. Meanwhile, the intermolecular part accounts for the deformation of the crystalline and the amorphous phases. The constitutive equations are integrated using a mixed explicit/implicit integration algorithm. To validate and calibrate our model, we utilize uniaxial tensile experimental data obtained from three different polyethylene materials with varying crystallinity levels and different strain rates. We propose a robust calibration procedure, ensuring the identification of a single set of parameters that remain independent of crystal content and strain rate. Finally, we assess the model's predictive capabilities in predicting the mechanical behavior and fracture at different strain rates for variable-crystallinity polyethylene is evaluated. This comprehensive approach enhances our understanding and predictive capacity in modeling the intricate mechanical response up to fracture of semi-crystalline polymers under diverse conditions.

H‐Bonded Amorphous Polymer Glass Nanofibers with Simultaneously Large Enhancement in Strength, Toughness, Ductility, and Thermal Stability

AbstractUnderstanding the direct effects of hydrogen bonding (H‐bonding) on the mechanical response of glassy state polymers remains a challenge, largely owing to the use of semicrystalline polymers in such studies, wherein, separating the contributions due to the changes in degree of crystallinity and direct H‐bonding effects on the observed mechanical properties is extremely difficult. This limitation is overcome by studying the mechanical behavior of amorphous, glassy polyvinylpyrrolidone (PVP), H‐bonded with tannic acid (TA). Uniaxial tension experiments on individual submicron scale PVP fibers (0.6–1.0 µm diameters) with different TA concentrations are conducted to capture their elasto‐plastic deformation characteristics. Amorphous PVP‐TA complexes exhibited some distinctive trends in elasto‐plastic properties with increasing H‐bond density, which are not observed earlier. These distinctive trends are discussed in terms of the competing effects of H‐bond driven crosslinking and TA‐induced reduction in entanglement density, and their differing roles during elastic and plastic deformation. The improvements in elasto‐plastic properties (particularly ductility and toughness) are simultaneously accompanied by uniquely significant thermal stability (i.e., glass transition temperature, Tg) improvements, that can help improve the practical applicability, operational life, and performance of these materials.

Defect-Induced Secondary Crystals Drive Two-Dimensional to Three-Dimensional Morphological Evolution in the Co-Self-Assembly of Polyferrocenylsilane Block Copolymer and Homopolymer.

Bottom-up fabrication protocols for uniform 3D hierarchical structures in solution are rare. We report two different approaches to fabricate uniform 3D spherulites and their precursors using mixtures of poly(ferrocenyldimethylsilane) (PFS) block copolymer (BCP) and PFS homopolymer (HP). Both protocols are designed to promote defects in 2D assemblies that serve as intermediate structures. In a multistep seeded growth protocol, we add the BCP/HP mixture to (1D) rod-like PFS micelles in a selective solvent as first-generation seeds. This leads to 2D platelet structures. If this step is conducted at a high supersaturation, secondary crystals form on the basal surface of these platelets. Co-crystallization and rapid crystallization of BCP/HP promote the formation of defects that act as nucleation sites for secondary crystals, resulting in multilayer platelets. This is the key step. The multilayer platelets serve as second-generation seeds upon subsequent addition of BCP/HP blends and, with increasing supersaturation, lead to the sequential formation of uniform (3D) hedrites, sheaves, and spherulites. Similar structures can also be obtained by a simple one-pot direct self-assembly (heating-cooling-aging) protocol of PFS BCP/HP blends. In this case, for a carefully chosen but narrow temperature range, PFS HPs nucleate formation of uniform structures, and the annealing temperature regulates the supersaturation level. In both protocols, the competitive crystallization kinetics of HP/BCP affects the morphology. Both protocols exhibit broad generality. We believe the morphological transformation from 2D to 3D structures, regulated by defect formation, co-crystallization, and supersaturation levels, could apply to various semicrystalline polymers. Moreover, the 3D structures are sufficiently robust to serve as recoverable carriers for nanoparticle catalysts, exhibiting valuable catalytic activity and opening new possibilities for applications requiring exquisite 3D structures.

The Impact of Carbon Nanotube on the Thermal Properties of Polypropylene

This research paper investigates the effect of the addition of carbon nanotubes (0.5 and 1.0% by weight) on crystallisation procedure in isotactic polypropylene. The study found that the crystallisation temperature increased with increasing nanotube content, while the crystallisation of polymers did not substantially change. The critical cooling speed, at which PP does not crystalize, increases with the increase in carbon nanotube content. Using the critical cooling speed and nanotube content, a nucleation effectiveness parameter was developed, that is not dependent on the crystallisation temperature or the CNT load. The study also found that carbon nanotubes only speed up the development of α-phase in isothermal crystallisation experiments. The control fibers had a shrinkage of 27% to 160°C, while the shrinkage of the composite fibers was less than 5%. The melting temperature of PP and its nanocomposites was approximately 150 to 152°C. However, the values for the degree of crystallinity of the nanocomposites rose along with the CNT content.

Derived Coarse-Grained Potentials for Semicrystalline Polymers with a Blended Multistate Iterative Boltzmann Inversion Method.

In this article, we employ the multistate iterative Boltzmann inversion (MS-IBI) method to develop coarse-grained potentials capable of representing molecular structure in both the amorphous and crystalline phases of semicrystalline polymers with improved accuracy while allowing for tunable control over the dynamics governing the α-relaxation process. A unique feature of this method is that the potentials are blended using the product of the target structural distributions, for example, the radial density function, for each phase and a weighting factor. To demonstrate this approach, a family of potentials for polyethylene is developed where the weighting factor of the crystalline phase ranges is varied from zero, incorporating information only from the amorphous phase, to unity, where the model is trained from only the crystalline phase. The most accurate representation of structural distributions was obtained when the crystalline phases is weighted at 50%. However, we show that when the crystalline phase is weighted at 90%, the model more accurately represents dynamics of the α-relaxation process, with realistic predicted values of activation energy and diffusion rates, with relatively minor impact on accuracy in structure.

Unlocking superior properties in polypropylene/polyethylene terephthalate (PP/PET) blends using an ethylene-butylene-acrylate terpolymer reactive compatibilizer

The increasing global plastic production has created an urgent demand for energy-efficient processes to transform mixed plastic waste into value-added products via upcycling. Compatibilization of polypropylene (PP) and poly(ethylene terephthalate) (PET), two used semi-crystalline polymers in industry, is investigated in this study. We evaluate the effectiveness of an ethylene-butylene-acrylate terpolymer (PTW) at different contents in a 70/30 PP/PET blend, examining the resulting physico-chemical characteristics. Adding PTW as compatibilizer significantly reduces the droplet size in the PP/PET blend, improving rheological and mechanical properties. Remarkably, the blend containing 1.5 % PTW exhibits maximum enhancement in mechanical properties. To understand deeply the chemical compatibilization mechanism, Fourier transform infrared spectroscopy (FTIR-ATR), Atomic Force Microscopy combined with infrared spectroscopy (AFM-IR), and Proton Nuclear Magnetic Resonance Spectroscopy (1H NMR) techniques were employed. The compatibilizer was located at the interphase, and the chemical reaction using AFM-IR and 1H NMR was tracked. These advanced techniques prove the chemical compatibilization mechanism in PP/PET blends with PTW. These findings contribute to understanding the compatibilization processes, offering valuable guidance for developing efficient upcycling processes for mixed plastic waste.

Additive Manufacturing of Poly(phenylene Sulfide) Aerogels via Simultaneous Material Extrusion and Thermally Induced Phase Separation.

Additive manufacturing (AM) of aerogels increases the achievable geometric complexity, and affords fabrication of hierarchically porous structures. In this work, a custom heated material extrusion (MEX) device prints aerogels of poly(phenylene sulfide) (PPS), an engineering thermoplastic, via in situ thermally induced phase separation (TIPS). First, pre-prepared solid gel inks are dissolved at high temperatures in the heated extruder barrel to form a homogeneous polymer solution. Solutions are then extruded onto a room-temperature substrate, where printed roads maintain their bead shape and rapidly solidify via TIPS, thus enabling layer-wise MEX AM. Printed gels are converted to aerogels via postprocessing solvent exchange and freeze-drying. This work explores the effect of ink composition on printed aerogel morphology and thermomechanical properties. Scanning electron microscopy micrographs reveal complex hierarchical microstructures that are compositionally dependent. Printed aerogels demonstrate tailorable porosities (50.0-74.8%) and densities (0.345-0.684g cm-3), which align well with cast aerogel analogs. Differential scanning calorimetry thermograms indicate printed aerogels are highly crystalline (≈43%), suggesting that printing does not inhibit the solidification process occurring during TIPS (polymer crystallization). Uniaxial compression testing reveals that compositionally dependent microstructure governs aerogel mechanical behavior, with compressive moduli ranging from 33.0 to 106.5MPa.

Dual Ratiometric Fluorescence Monitoring of Mechanical Polymer Chain Stretching and Subsequent Strain-Induced Crystallization.

Tracking the behavior of mechanochromic molecules provides valuable insights into force transmission and associated microstructural changes in soft materials under load. Herein, we report a dual ratiometric fluorescence (FL) analysis for monitoring both mechanical polymer chain stretching and strain-induced crystallization (SIC) of polymers. SIC has recently attracted renewed attention as an effective mechanism for improving the mechanical properties of polymers. A polyurethane (PU) film incorporating a trace of a dual-emissive flapping force probe (N-FLAP, 0.008 wt %) exhibited a blue-to-green FL spectral change in a low-stress region (<20 MPa), resulting from conformational planarization of the probe in mechanically stretched polymer chains. More importantly, at higher probe concentrations (∼0.65 wt %), the PU film showed a second spectral change from green to yellow during the SIC growth (20-65 MPa) due to self-absorption of scattered FL in a short wavelength region. The reversibility of these spectral changes was demonstrated by load-unload cycles. With these results in hand, the degrees of the polymer chain stretching and the SIC were quantitatively mapped and monitored by dual ratiometric imaging based on different FL ratios (I525/I470 and I525/I600). Simultaneous analysis of these two mappings revealed a spatiotemporal gap in the distribution of the polymer chain stretching and the SIC. The combinational use of the dual-emissive force probe and the ratiometric FL imaging is a universal approach for the development of soft matter physics.

Modeling Sorption of Hydrocarbons in Polyethylene with the SAFT-γ Mie Approach Combined with a Statistical-Mechanical Model to Describe Semicrystalline Polymers.

A recently developed statistical-mechanical model is applied systematically to estimate the fraction of tie-molecules (polymer chains linking different crystals directly or via entanglements) in semicrystalline polyethylene (PE) samples. The amorphous domains of the polymer are divided into constrained interlamellar domains and "free" outer-lamellar domains. A set of model parameters is assigned to each sample by correlating previous experimental measurements and minimizing the difference between the predicted solubility of pure hydrocarbons in the sample and the experimental values. We show that the sorption isotherms of multiple pure fluids in each sample can be described by a single parameter set, proving that the polymer-solute interactions (described accurately by the SAFT-γ Mie EoS) are decoupled from the sample-specific properties of the polymer. We find that ∼30% of the crystalline stems in the lamellae of PE are connected to tie-molecules, within the bounds suggested by previous theoretical and computational work. The transferability of the sample-specific parameters is assessed by predicting cosolubility effects and solubility at different temperatures, leading to good agreement with experimental data.

Evolution of the Deformation‐ and Flow‐Induced Crystallization and Characterization of the Microstructure of a Single Spherulite, Lamella, and Chain of Isotactic Polypropylene

AbstractIsotactic polypropylene (iPP) is a frequently used polymer in industrial processing and scientific research, used as a model material. This review highlights some current and forefront issues in polymer science and engineering. This review alludes to classical deformation schemes to interpret the complicated deformation in isotactic polypropylene as a semicrystalline polymer. Also, due to the complex hierarchical structures of crystallized polymers, the progress on the multiscale and multistage microstructural evolution covering each deformation stage from the initiation of plasticity until failure is mainly concerned, particularly in terms of crystalline morphology changes. Specifically, the characterization of the microstructure evolution of a single spherulite, lamella, and chain of isotactic polypropylene will be emphasized and mentioned. Here, the authors are most interested in the results obtained from stretching (strain‐induced) orientation and crystallization studies accompanied by the in situ scattering and spectroscopy techniques offering a detection window from nano to micrometer scale, which should be able to reflect the microstructural changes at different length scales of interest. During polymer processing, the melts are frequently subjected to shear or/and elongation flow fields, producing flow‐induced molecular chain orientation in the melt. The oriented molecular chains crystallize differently than those encountered under quiescent conditions. Thus, orientation‐induced crystallization has long been an object of intense interest. A vast body of research is reported about the effects of preorientation on the crystallization of various polymers. Among them, iPP is most frequently studied since its diversified structure and morphology are very sensitive to changes in processing conditions and molecular parameters.

The evidences for the existence of evanescent wave-induced scattering in the transmission SAXS of high-density polyethylene

In an earlier study of ours (Li et al., IUCrJ,2019 6, 968–983), we conjectured that small-angle X-ray scattering (SAXS) in semicrystalline polymers might be from evanescence wave-induced scattering (Ievi) rather than claimed by classical scattering theory, the incident X-ray-induced scattering (Iin). In this study, we systematically compared Ievi and Iin under the influence of various factors, i.e., linear crystallinity, the number of lamellar crystals (N), the characteristic penetration depth of evanescent wave (dp*) and long period distribution, identifying the method to distinguish SAXS in semicrystalline polymers is from Iin or Ievi. Applying this method to SAXS of a high-density polyethylene (HDPE) sample, it was found that even excluding the influence of instrumental broadening and lamellar thickness/long period dispersity, the SAXS peak in HDPE is still greater than theoretically maximum peak width induced by Iin, indicating the SAXS in HDPE is not induced by incident X-ray directly. Excluding the interference of long period dispersity, it was found that dp* was around 5.9 nm, clearly demonstrating the existence of evanescent wave. Besides, results indicated that the lateral size determined with new theory is accurate, which in turn demonstrated that our assumption that Ievi is from a lamellar stack parallel to incident X-ray is reasonable. Taking all evidences together, it can be concluded safely that SAXS in HDPE is induced by evanescent wave.

Spherulites of supramolecular polymers formed from undercooled melts, and their adhesive properties

Abstract The solid-state properties of crystalline supramolecular polymers have generally remained unexplored. Herein, we investigated the isothermal crystallization of a supramolecular polymer and showed that, depending on the temperature, it formed distinct structures at a higher hierarchical level. Interestingly, the resulting crystalline forms showed distinct adhesive properties and mechanical-failure modes (adhesive or cohesive).

Carbon fiber–polyetheretherketone-reinforced PVA composites for bone graft applications

Poly(vinyl alcohol) (PVA) is a synthetic, bioinert, semicrystalline, biodegradable, non-toxic and thermoplastic polymer extensively used in the field of biomedical engineering. The weak mechanical properties of PVA, such as low strength and Young’s modulus, limit its application as a bone implant. However, PVA can be reinforced with a suitable material to improve its mechanical properties. Carbon fiber (CF)–polyetheretherketone (PEEK) is a superior thermoplastic synthetic biomaterial with good tensile strength, stiffness, wear properties and X-ray translucence. In this study, CF–PEEK-reinforced PVA composites were prepared by varying the CF–PEEK concentration (0, 0.25, 0.50, 0.75, 1.00, 2.00 and 3.00% w/v) in the PVA matrix (10% w/v) using the solvent-casting method. The physical, chemical, biological and mechanical properties of the prepared PVA–CF–PEEK composites were studied. The environmental scanning electron microscopy micrographs showed agglomeration of CF–PEEK at higher concentrations – that is, 1, 2 and 3% w/v. With the inclusion of CF–PEEK in PVA, the contact angle of the composites was found to increase. The increased hydrophobicity of the samples resulted in reduced swelling and degradation rate. In the hemolysis study, the percentage hemolysis values were found to be &lt;5%, revealing the hemocompatible nature of the developed composites. An increase in in vitro protein adsorption was observed, and cell viability studies showcased the biocompatible nature of the prepared composite samples. Thus, the developed CF–PEEK–PVA polymer composites present great potential for bone graft applications.

Identification of novel organic polar materials: A machine learning study with importance sampling

Recent advances in the synthesis of polar molecular materials have produced practical alternatives to ferroelectric ceramics, opening up exciting new avenues for their incorporation into modern electronic devices. However, in order to realize the full potential of polar polymer and molecular crystals for modern technological applications, it is paramount to assemble and evaluate all the available data for such compounds, identifying descriptors that could be associated with an emergence of ferroelectricity. In this paper, we utilized data-driven approaches to judiciously shortlist candidate materials from a wide chemical space that could possess ferroelectric functionalities. A machine learning study with importance sampling was employed to address the challenge of having a limited amount of available data on already-known organic ferroelectrics. Sets of molecular- and crystal-level descriptors were combined with a Random Forest Regression algorithm in order to predict the spontaneous polarization of the shortlisted compounds. First-principles simulations were performed to further validate the predictions obtained from the machine learning model.

Polymer Composites With High Thermal Conductivity for HVDC Cable Insulation: A Review

With the development of high voltage direct current (HVDC) transmission technology, the voltage level and transmission capacity of power cable need to be further improved. Joule heat originating from the current in the cable conductor brings a great challenge to extruded cable insulation because of the low thermal conductivity of polymer insulation materials. This paper reviews the harms caused by heat accumulation in cable insulation and methods for improving the thermal conductivity of polymer materials. First, the effects of heat on cable insulation are summarized. Second, the mechanism, influencing factors, and structure design of filler-based polymer composites with high thermal conductivity are introduced. Subsequently, investigations on cable insulation materials with enhanced thermal conductivity are reviewed. At last, some problems with the design of thermal conductive networks in semi-crystalline polymer materials are discussed, and our suggestions for future work are proposed.

A comparative analysis of flexible pvdf based smart films for advanced electromagnetic shielding applications using a machine learning approach

Due to emerging technology, the usage of electronic gadgets has paved a route for the arousal of Electromagnetic Interference (EMI) pollution. Electromagnetic pollution is considered a global threat that can harm all biological systems and technological equipment. To overcome this issue, a suitable shielding material has to be implemented to attenuate the incoming electromagnetic waves. On the other hand, compared to traditional materials, recently, polymers have grabbed excellent responses in various fields of material science and modern chemistry. Specifically, functional polymers are increasing their scope in industry and academia due to their unique features, such as magnetic, catalysis, optical and piezoelectric properties. In this regard, Polyvinylidene Fluoride (PVDF), a well-known semicrystalline polymer from the family of Fluoropolymers, has achieved remarkable in various applications of sensors, actuators, biomedical scaffolds and energy harvesting devices. PVDF has also contributed excellent outcomes as a shielding material as they are transparent to light and flexible. Hence, this research work attempts to fabricate PVDF thin films with various weight percentages of nanofillers such as Zinc oxide (ZnO), Zirconium oxide (ZrO2), and Titanium dioxide (TiO2). Further, all the samples were tested for electromagnetic shielding effectiveness (SE). Further, these experimental results were compared with statistical and computational approaches such as the Gradient Descent Algorithm (GDA) and Response Surface Methodology (RSM). Based on the experimental results, it was observed that the PVDF nanofilm fabricated with 0.3 wt% of ZrO2, 0.5 wt% of TiO2and 0.3 wt% of ZnO nanofillers had achieved a maximum EMI SE of 11.4 dB at X-band frequency of 8–12 GHz.

Preparation and Characterization of ZrO2 -PVA Doped TiO2 Nanocomposite in Solar Cell Application

The objective of the project is to presents the research results of PVA-Zr-Ti nanocomposite synthesis. Polymer nanotechnology is a growing technology which is really useful in solar cells. Solar cells which are made from using nanocomposite were environmentally friendly and uses natural methods to prepare nanocomposites. Among the all zirconium and titanium nanoparticles draws more attention due to their significant bio compatible, electrical, mechanical and optical properties. Polyvinyl alcohol is a semicrystalline and water-soluble polymer with a non-toxic nature, biocompatible and has better chemical resistance. The PVA-Zr-Ti nanocomposite prepared using solution casting method. Which is an effective and rapid method to prepare nanocomposite. The prepared sample characterized by FTIR, XRD and EDX. The FTIR analysis displays the functional groups of nanoparticles and the structural properties were given by XRD.To determine the types of the elements, present in the compounds, the EDX analysis of all the samples was carried out.

An ultrasmall organic synapse for neuromorphic computing

High‐performance organic neuromorphic devices with miniaturized device size and computing capability are essential elements for developing brain‐inspired humanoid intelligence technique. However, due to the structural inhomogeneity of most organic materials, downscaling of such devices to nanoscale and their high‐density integration into compact matrices with reliable device performance remain challenging at the moment. Herein, based on the design of a semicrystalline polymer PBFCL10 with ordered structure to regulate dense and uniform formation of conductive nanofilaments, we realize an organic synapse with the smallest device dimension of 50 nm and highest integration size of 1 Kb reported thus far. The as‐fabricated PBFCL10 synapses can switch between 32 conductance states linearly with a high cycle‐to‐cycle uniformity of 98.89% and device‐to‐device uniformity of 99.71%, which are the best results of organic devices. A mixed-signal neuromorphic hardware system based on the organic neuromatrix and FPGA controller is implemented to execute spiking‐plasticity‐related algorithm for decision-making tasks.

Controlled and Regioselective Ring-Opening Polymerization for Poly(disulfide)s by Anion-Binding Catalysis.

Poly(disulfide)s are an emerging class of sulfur-containing polymers with applications in medicine, energy, and functional materials. However, the constituent dynamic covalent S-S bond is highly reactive in the presence of the sulfide (RS-) anion, imposing a persistent challenge to control the polymerization. Here, we report an anion-binding approach to arrest the high reactivity of the RS- chain end to control the synthesis of linear poly(disulfide)s, realizing a rapid, living ring-opening polymerization of 1,2-dithiolanes with narrow dispersity and high regioselectivity (Mw/Mn ∼ 1.1, Ps ∼ 0.85). Mechanistic studies support the formation of a thiourea-base-sulfide ternary complex as the catalytically active species during the chain propagation. Theoretical analyses reveal a synergistic catalytic model where the catalyst preorganizes the protonated base and anionic chain end to establish spatial confinement over the bound monomer, effecting the observed regioselectivity. The catalytic system is amenable to monomers with various functional groups, and semicrystalline polymers are also obtained from lipoic acid derivatives by enhancing the regioselectivity.