Crystallization Behavior Of Polymers Research Articles

Enabling Polymer Single Crystals to Be High-Performance Dielectric.

Semicrystalline polymer dielectrics (SPDs) are highly sought-after state-of-the-art dielectric materials. As the disorder in SPDs degrades their electrical properties, homogeneously ordered SPDs are desired. However, complex crystallization behaviors of polymers make such homogeneity elusive. Polymer lamellar single crystals (PLSCs), the most regularly-ordered form of SPDs possible under mild crystallizing conditions, are ideal platforms for understanding and developing high-performance dielectric materials. Here, a typical and widely used SPD, polyethylene (PE) is selected as the model material. We successfully obtained, large, uniform, and high-quality PE PLSCs and devised a non-destructive strategy to construct PE PLSC-based vertical capacitors. These nanometer-thick capacitors exhibit exceptional dielectric properties, with a high breakdown strength of 6.95 MV/cm and a low dielectric constant of 2.14±0.07, that outperform the properties of any existing neat PE. This work provides novel insights into exploring the performance possibility of ordered SPDs and reveals the PLSCs as potential high-performance dielectric materials.

Enabling Polymer Single Crystals to Be High‐Performance Dielectric

AbstractSemicrystalline polymer dielectrics (SPDs) are highly sought‐after state‐of‐the‐art dielectric materials. As the disorder in SPDs degrades their electrical properties, homogeneously ordered SPDs are desired. However, complex crystallization behaviors of polymers make such homogeneity elusive. Polymer lamellar single crystals (PLSCs), the most regularly‐ordered form of SPDs possible under mild crystallizing conditions, are ideal platforms for understanding and developing high‐performance dielectric materials. Here, a typical and widely used SPD, polyethylene (PE) is selected as the model material. We successfully obtained, large, uniform, and high‐quality PE PLSCs and devised a non‐destructive strategy to construct PE PLSC‐based vertical capacitors. These nanometer‐thick capacitors exhibit exceptional dielectric properties, with a high breakdown strength of 6.95 MV/cm and a low dielectric constant of 2.14±0.07, that outperform the properties of any existing neat PE. This work provides novel insights into exploring the performance possibility of ordered SPDs and reveals the PLSCs as potential high‐performance dielectric materials.

Effects of molecular weight on stereocomplex and crystallization of PLLA/PDLA blends

The chain dynamics affects the chain motions and the crystallization behaviors of polymers, and the crystallization ability of poly(lactic acid) (PLA) homopolymers can be substantially enhanced by incorporating stereocomplex-PLA (s-PLA). The effects of s-PLA molecular weight on the enhanced crystallization of the homopolymer were characterized and analyzed in this study. The crystallization behaviors, morphologies and structures of the homopolymer in PLA/s-PLA blends were investigated using DSC, POM, WAXD and FTIR during or after isothermal and non-isothermal crystallization. The blends compose homopolymer and the same content of the s-PLAs with three different molecular weights. The DSC results showed that the homopolymer in the blends containing the higher molecular weight of the s-PLA crystallizes at higher crystallization temperature than that containing the lower molecular weight of the s-PLA during the non-isothermal crystallization. The crystallization half-time of the homopolymer blending with the higher molecular weight s-PLA is shorter than that blending with the lower molecular weight of the s-PLA during the isothermal crystallization. POM images showed that the spherulite density of the homopolymer blending with the higher molecular weight of the s-PLA is significantly higher than that with the lower molecular weight of the s-PLA. The Mpemba effect was first experimentally observed in the melting crystallization of polymer blends containing PDLA and s-PLA. A possible explanation is proposed and discussed to elucidate the impact of s-PLA molecular weight on the crystallization behaviors of PLA homopolymer in the blends.

Reevaluation of the Crystallization Kinetics of Precisely Synthesized, Discrete Oligo(γ-butyrolactone)s

The crystallization behavior of polymers has always been an important part of polymer physics. The data from a previous paper, “Crystallization Kinetics of Precisely Synthesized Discrete Oligo(γ-butyrolactone)s” published in Acta Polymerica Sinica (2022), are further discussed here in order to clarify some issues which could easily be confused. We show here that the crystallization process was affected not only by the molecular weight, but also by the end group. In the case of oligo(γ-butyrolactone)s, the crystallization rate was restrained by the end group, t-butyl diphenyl silicon, within the oligomer chain due to its different structure from the repeat unit and its steric effect. As the content of the end groups was relatively high for the lower molecular weight, the crystallization was inhibited. With the increasing molecular weight, the influence of the end groups decreased. Since the content of the end group t-butyl diphenyl silicon was below 10 wt%, the crystallization rate with higher molecular weight was slower than that with lower molecular weight, similar to the general rule. In the case of polydisperse oligomers with relatively high molecular weight, the components with not too low molecular weight which crystallization would not be affected by the terminal groups, such as the components with 32 structural units, would make a greater contribution to the crystallization process resulting in faster crystallization rate, rather than those with higher molecular weight than the average molecular weight.

The influence of Scutellaria baicalensis extract obtained from traditional Chinese herbal medicine on the thermo‐oxidative degradation and stabilization of plasticized polylactic acid

AbstractDespite the advantage of biodegradability, polylactic acid (PLA) has some processing and application drawbacks, such as poor thermal oxygen stability. Herein, the modified PLA samples were prepared by mixing PLA granules, acetyl tributyl citrate (ATBC), and Scutellaria baicalensis extract (SBE) obtained from traditional Chinese herbal medicine. Results revealed that the introduction of SBE improves the thermal oxidation stability of PLA‐ATBC matrix. When the content of SBE was 2.0 wt%, the oxidation onset temperature value of the modified sample is increased by 68°C versus PLA‐ATBC. The excellent antioxidant performance is attributed to the outstanding free radical quenching capacity of SBE. The introduction of SBE slightly decreased the degradation rate of PLA‐ATBC in an enzyme degradation process, which may be due to the SBE reducing the enzyme activity. Moreover, the addition of small amounts of SBE into the PLA‐ATBC matrix has little influence on polymer crystallization behavior, just decreased by ca. 8.6% (PLA‐ATBC‐SBE2.0 sample). SBE has no obvious effect on the water vapor permeability and surface wettability of PLA‐ATBC membranes. All results reveal that the SBE could play a role in the thermal oxygen stability of PLA‐ATBC without much change in its other performances.

Effect of gamma-irradiation on hydrolysis of commercial poly(L-lactide) at elevated temperature

The present study aimed to examine the effect of gamma-irradiation on subsequent hydrolytic degradation of poly(L-lactide) (PLLA) and polymer crystallization behavior during this process. Absorbed doses were 29 and 75 kGy, unirradiated sample was also studied. Hydrolysis was performed at 60 °C for up to 50 days. Radiation treatment of PLLA accelerates hydrolysis process. It affects polymer mass loss, molecular weight distribution, change of hydrolysis media pH, and values of the hydrolytic degradation rate constant. Preliminary irradiation makes it possible to eliminate the induction period of PLLA mass loss during hydrolysis. However, a decrease of polymer molecular weight during irradiation leads to an increase of PLLA crystallization rate upon hydrolysis. It was found that α crystals can be formed during hydrolytic degradation. Parameters of PLLA unit cell were calculated. When polymer degree of crystallinity becomes high enough its hydrolytic degradation slows down. Thus, faster crystallization of irradiated PLLA reduces the acceleration effect of radiation treatment on polymer hydrolysis.

Self-nucleation and heterogeneous nucleation in ethylene/1-octene random copolymer and its linear polyethylene blends

Self-nucleation normally denotes an increase in the crystallization temperature during cooling down from certain preheated (seeding) temperature due to the existence of unmolten crystalline nuclei or some heterogenous structures which can induce melt memory effect. It is one of the crucial parts in the study of polymer crystallization behavior which provides a meaningful guidance in both academia and industry to accelerate crystallization of polymers. In this work, self-nucleation effects of a commercial ethylene/1-octene random copolymer with 12 mol% 1-octene content and its blends with small amount of linear polyethylene (LPE) were investigated. The ethylene/1-octene random copolymer possesses strong self-nucleation effect whereas in the blends the crystallization temperature increases with the seeding temperature and eventually stabilized at certain constant temperature when the seeding temperature is high enough. This result is clearly due to the heterogenous nuclei generated by the crystallization of LPE during cooling. The strength of the heterogenous nucleation effect i.e. the crystallization temperature is positively related to the degree of dispersion of LPE in the mixture.

Influence of isotactic polypropylene grafted with styryl-group on the polymer crystallization behavior

4-Furfuryloxymethylstyrene (Sf) grafted isotactic polypropylene (iPP-g-Sf) was prepared by melt grafting reaction. The crystallization temperature of iPP after grafting increased to ∼130 °C. The isothermal and non-isothermal crystallization kinetics of iPP-g-Sf containing up to 1.50 mol% grafted Sf groups were compared with that of virgin iPP, and the isothermal and non-isothermal crystallization kinetics parameters of the polymers, including the fold surface free energy σe, the chain folding work q, and the crystallization activation energy ΔE, were calculated by Lauritzen-Hoffman theory and Kissinger method respectively. The results showed that iPP-g-Sf exhibited a unique self-nucleation phenomenon, which accelerating the crystallization rate of iPP and produced tiny crystal morphology than that for iPP. The introduction of only 0.23–1.50 mol% grafted Sf groups reduced the σe of the crystals by 44–57%. This might provide guidance for the design of polymer crystallization rate by controlling the molecular structures.

Backbone flexibility on conjugated polymer's crystallization behavior and thin film mechanical stability

AbstractExtensive efforts have been made to develop flexible electronics with conjugated polymers that are intrinsically stretchable and soft. We recently systematically investigated the influence of conjugation break spacers (CBS) on the thermomechanical properties of a series n‐type naphthalene diimide‐based conjugated polymer and found that CBS can significantly reduce chain rigidity, melting point, as well as glass transition temperature. In the current work, we further examined the influence of CBS on the crystallization behaviors of PNDI‐C3 to C6, including isothermal crystallization kinetics, crystal polymorphism and subsequently time‐dependent modulus, in a holistic approach using differential scanning calorimetry, X‐ray scattering, polarized optical microscopy, atomic force microscopy, and pseudo‐free‐standing tensile test. Results demonstrate that increasing the length of CBS increases the crystallization half‐time by 1 order of magnitude from PNDI‐C3 to PNDI‐C6 from approximately 103 to 104 s. The crystallization rate shows a bimodal dependence on the temperature due to the presence of different polymorphs. In addition, crystallization significantly affects the mechanical response, a stiffening in the modulus of nearly three times is observed for PNDI‐C5 when annealed at room temperature for 12 h. Crystallization kinetic is also influenced by molecular weight (MW). Higher MW PNDI‐C3 crystallizes slower. In addition, an odd–even effect was observed below 50°C, odd‐number PNDI‐Cxs (C3 and C5) crystallize slower than the adjacent even‐numbered PNDI‐Cxs (C4 and C6). Our work provides an insight to design flexible electronics by systematically tuning the mechanical properties through control of polymer crystallization by tuning backbone rigidity.

Synergistic effects of chain dynamics and enantiomeric interaction on the crystallization in PDLA/PLLA mixtures

Intra- and inter-molecular interactions play an important role in polymer chain dynamics. Polymer crystallization behavior and crystalline structure are affected by the chain dynamics. The enantiomer containing PLLA and PDLA is considered as an important nucleation for PLA crystallization since it was found. The mixtures containing PDLA and stereocomplex (SC) crystal were prepared via different solvents or without any solvent. The effect of the stereocomplex promoted homopolymer crystallization and the non-isothermal crystallization behaviors of the prepared mixtures were characterized by DSC. The DSC results showed that the crystallization temperature of the homopolymer in the PDLA/SC mixtures increases with the stereocomplex contents as cooling from 200 °C at 10 °C/min. The increased crystallization temperature reduces with decreasing of cooling rate, and the increasing is even negligible when the cooling rate is 1 °C/min or lower. The promoted crystallization behavior could be influenced by melting temperature and melting time. FTIR results indicated the CH3⋯O interactions between the enantiomers of polylactide is related to the solvents with different solubility parameters for sample preparations. The stereocomplex effect on the PDLA crystallization in the mixtures was discussed based on the molecular interactions between enantiomers and chain dynamics in presence of obstacles.

Research progress of single molecule force spectroscopy technology based on atomic force microscopy in polymer materials: Structure, design strategy and probe modification

AbstractWith the rapid development of polymer materials, the simultaneous acquisition of micro‐nano structure and mesoscopic mechanical properties from the material surface with the transverse resolution of nanoscale has become a hot spot in the research of polymer materials. Atomic force microscopy‐based high‐resolution imaging and single‐molecule force spectroscopy techniques have been widely used in various related fields. This review introduces the basic design and working principles of atomic force microscopy as well as single‐molecule force microscopy and their applications in the characterization of polymer surface morphologies, polymer film phase separation, polymer crystallization behavior, polymer chain stretching, protein folding/unfolding, G quadruplex intermolecular and intramolecular interactions, living cell surface proteins, and sugars. The research status of AFM probe modification strategies such as nanomaterial processing, single molecule manipulation and biomolecule etching is reviewed, finally, the limitations and improvement potential of single molecule force spectroscopy based on atomic force microscopy (AFM‐ SMFS) are summarized and discussed, and the new research practice in the field of polymer materials is prospected.

The effect of grafting density on the crystallization behavior of one‐dimensional confined polymers

AbstractGrafting density and confinement scale of the nano‐area are significant elements affecting the crystallization behavior of polymers. In this work, the crystallization processes of confined and unconfined polymer systems with different grafting density were systematically studied by MC simulation. The results show that when the grafting density of confined systems is low, the crystallization rate is faster and the final crystallinity is higher. However, the crystallization ability is reduced for higher grafting density. We found that for this confined system, the segmental density of interfacial region is larger, and the movement of chain segment is lower. Due to the higher grafting density, the crowding effect of polymer chains is strong, which leads to the intermolecular nucleation. The critical nucleation free energy barrier is higher. Moreover, only homogeneous nucleation occurs in confined polymer systems. With the increasing grafting density, the crystals change from lying on the substrate surface to being perpendicular to the substrate surface in unconfined polymer systems. The crystals are mainly lying on the substrate surface in confined polymer systems. These simulation results are helpful to understand the microscopic mechanism of crystallization behaviors of polymer nanocomposites and provide a theoretical basis for the design of nanocomposites with excellent physical properties.

Molecular simulation of crystallization of polymers confined in cylindrical nanodomain

The crystallization behavior of polymers confined in nanocylinders has been investigated by dynamic Monte Carlo simulation. For confined polymer systems with different molecular weights, the evolution of crystallinity with Monte Carlo time shows first-order kinetics, which means that homogeneous nucleation controls the whole crystallization process. At this time, the nucleation mechanism changes from intermolecular nucleation to intramolecular nucleation with the increase of molecular weights. For confined polymer systems with different interface interactions, the nucleation mode changes from homogeneous nucleation to heterogeneous nucleation when the interface interaction changes from 0 to −1.5. For confined polymer systems with different lateral sizes, the nucleation mode changes from homogeneous nucleation to heterogeneous nucleation with the decrease of lateral sizes. During crystallization, crystal orientation and morphology are also closely related to molecular weights, interface interactions and lateral sizes. These simulation results may provide theoretical guidance for the design and preparation of high-performance confined polymer materials.

Calorimetric analysis of the crystallization of PBT considering the dynamic cooling condition of real processing

The crystallization behavior of polymers is usually investigated by the Differential Scanning Calorimetry (DSC) under isothermal or non-isothermal conditions, the latter one at constant cooling rates. The results of such experiments are used to calculate the crystallization during the dynamic cooling of processing, for instance with the Nakamura crystallization model. In contrast, in this article the crystallization of Polybutylene Terephthalate (PBT) was measured directly calorimetrically at dynamic cooling. For this purpose, the Fast Scanning Calorimetry (FSC) was used in particular, which can perform fast changes in scan rates. With this new approach, for example, the crystallinity can be determined across the part thickness, without calculating it with a crystallization model. At the same time, the subsequent melting behavior of structures formed during dynamic cooling was investigated. Thus a better interpretation of the first heating run of processed samples is possible.

Correlation between molecular weight and confined crystallization behavior of polymers grafted onto a zero-dimensional filler

In this work, polymer chains of different molecular weights are grafted onto a zero-dimensional filler.

Effect of Alkyl Chain Length in POSS Nanocage on Non-Isothermal Crystallization Behavior of PCL/Amino-POSS Nanocomposites.

The study of the non-isothermal crystallization behavior of polymers is of great importance due to the effect of degree of crystallinity and crystallization process on the polymer properties. The effect of aminopropylisobutyl polyhedral oligomeric silsesquioxane (APIBPOSS) and aminopropylisooctyl polyhedral oligomeric silsesquioxane (APIOPOSS) on poly(ε-caprolactone) (PCL) crystallization is studied by differential scanning calorimetry (DSC) under non-isothermal conditions and polarized optical microscopy (POM). The crystallization kinetics is analyzed using the Avrami and Mo models, and effective activation energies are evaluated by the Friedman isoconversional method. The results show that the compatibility between polyhedral oligomeric silsesquioxanes (POSS) and PCL and POSS loading affect the crystallization process. A higher crystallization temperature, a narrower size distribution of crystallite, and a faster crystallization rate are obtained in the presence of all the studied contents of APIBPOSS and at lower contents of APIOPOSS. At APIOPOSS contents higher than 2 wt %, the crystallization temperature is lowered, the size distribution of crystallite is broadened, and the crystallization process is retarded. The presence of POSS leads to an increase in the number of nucleation sites, and a reduction in the size of the crystallite and the overall degree of crystallinity, as a result of the confinement of PCL chains caused by POSS nanoparticles.

Segmental Dynamics Govern the Cold Crystallization of Poly(lactic acid) in Nanoporous Alumina

How segmental mobility influences the crystallization behavior of polymers in confined spaces is still not fully understood. In the present work, a systematic study of the segmental dynamics was ca...

The effect of molecular weight of polymers grafted in two-dimensional filler on crystallization behaviors studied by dynamic Monte Carlo simulations

The crystallization behaviors of polymers can be changed by grafting them onto the surface of fillers. In this work, the effect of molecular weight of polymers grafted in two-dimensional filler on the isothermal crystallization behaviors was studied by the dynamic Monte Carlo simulation. The result shows that the grafted polymer system can shorten the nucleation induction period compared with ungrafted polymer systems, but its ultimate crystallinity is reduced. With increasing molecular weight, the nucleation induction period becomes shorter and the final crystallinity becomes higher. The polymer system with low molecular weight shows the intermolecular nucleation, while it exhibits the intramolecular nucleation for the one with high molecular weight. In addition, at lower molecular weights, the crystalline bonds tend to perpendicular to the filler. As the molecular weight increases, the crystalline bonds progressively inclined to deviate from the Z direction and return to the direction parallel to the Z axis ultimately. These simulation results can illustrate the micro-mechanism of the effect of molecular weight on crystallization behaviors of polymer composites from a microscopic perspective, which can provide important theoretical basis for improving the properties of polymer composites.

Crystallization behavior of polymer derived silicon carbide sintered through microwave heating technique

A self-crosslinkable liquid highly branched polycarbosilane (LHBPCS) with 5.07% vinyl group and a C/Si ratio of 1.33 was used as the precursor to prepare SiC ceramic material. Microwave heating technique and conventional heating method were applied for the heating treatment process. It was found that, compared with conventional heating method, microwave heating technique could enhance the crystallinity of SiC ceramic material with small grain size at much lower curing temperature and within shorter time. In addition, the SiO2 additive could lead to less α-SiC and excess carbon, but worsen the crystallinity of β-SiC in the final samples.

Effects of Covalent Functionalization of MWCNTs on the Thermal Properties and Non-Isothermal Crystallization Behaviors of PPS Composites.

In this study, a PPS/MWCNTs composite was prepared with poly(phenylene sulfide) (PPS), as well as pristine and covalent functionalized multi-walled carbon nanotubes (MWCNTs) via melt-blending techniques. Moreover, the dispersion of the MWCNTs on the PPS matrix was improved by covalent functionalization as can be seen from a Field-Emission Scanning Electron Microscope (FE-SEM) images. The thermal properties of the PPS/MWCNTs composites were characterized using a thermal conductivity analyzer, and a differential scanning calorimeter (DSC). To analyze the crystallization behavior of polymers under conditions similar with those in industry, the non-isothermal crystallization behaviors of the PPS/MWCNTs composites were confirmed using various kinetic equations, such as the modified Avrami equation and Avrami-Ozawa combined equation. The crystallization rate of PPS/1 wt % pristine MWCNTs composite (PPSP1) was faster because of the intrinsic nucleation effect of the MWCNTs. However, the crystallization rates of the composites containing covalently-functionalized MWCNTs were slower than PPSP1 because of the destruction of the MWCNTs graphitic structure via covalent functionalization. Furthermore, the activation energies calculated by Kissinger’s method were consistently decreased by covalent functionalization.