Semicrystalline Polymer Films Research Articles

Effect of SbCl5 Doping on the Electrical and Optical Properties of Polyamide Nylon 6 Films

Polyamide nylon 6 (PA6) films were fabricated using a solution casting method and the films were doped with SbCl5. The electrical conductivity increased with the dopant concentration due to the increase in formation of radical cations through the charge transfer from the isolated double bonds (–C=O–) in the polymer chains. The DC electrical conductivity reached a maximum of 0.01 S/cm for 0.5 ml SbCl5 doped films. Structural and optical characteristics of the pure and doped films were examined using Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR), X-Ray Diffraction (XRD), and Ultraviolet-Visible (UV-Vis) absorption spectra. The doped films exhibited discernible shifts in the optical band gap energy. The direct band gap values of PA6 films were reduced from 4.5 eV to 1.7 eV when doped with 0.5 ml SbCl5. ATR-FTIR spectral studies, and optical studies indicated the formation of charge transfer complexes with the amide group of nylon 6, resulting in the electrical conduction. The XRD studies disclosed the reduction in the crystallinity of the doped films. The thermal stability was studied using differential scanning calorimetry (DSC) and thermogravimetric analysis-derivative thermogravimetric (TGA-DTG) studies. The melting and crystallization temperatures were recorded from the DSC thermograms. The peak melting temperature of PA6 reduced from 217 °C to 186 °C for 0.5 ml SbCl5 doped films. The peak of crystallization observed at 182 °C for pure films was absent, for the doped samples. The peak degradation temperatures for both pure and doped samples were above 400 °C, revealing the thermal stability of both materials. The thermally stable, semi-crystalline and semiconducting polymer films, we suggest, would be suitable for optoelectronic applications.

Three-Dimensional Molecular Orientation Imaging of a Semicrystalline Polymer Film under Shear Deformation

Three-Dimensional Molecular Orientation Imaging of a Semicrystalline Polymer Film under Shear Deformation

Structural and electrical response of poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) copolymer free‐ standing films

AbstractPoly(vinylidene fluoride) (PVDF) based polymers were studied as potential dielectric candidates for polymer film capacitors. The present work focused on the structural and electrical responses of PVDF homopolymer and P(VDF‐CTFE) copolymers (CTFE, chlorotrifluoroethylene). The solvent casting technique was used for the fabrication of free‐standing polymer films. PVDF and P(VDF‐CTFE) copolymer films with different CTFE content were cast under different processing conditions. The structural response of these semicrystalline polymer films showed the existence of crystalline phases and changes in crystallinity depending upon the preparation conditions and CTFE content. The electrical responses of PVDF and P(VDF‐CTFE) copolymers were investigated under the application of low and high electric fields. For the dielectric study, temperature‐dependent dielectric measurements at different frequencies were assessed. Dielectric relaxation in the vicinity of the glass transition temperature was observed along with quantification of activation energies. The effect of CTFE content is also presented. Features such as interface polarization was observed in the high temperature regime. Furthermore, room temperature polarization versus electric field loops of PVDF and P(VDF‐CTFE) copolymers were measured at frequency values of 400 and 10 Hz. All PVDF and P(VDF‐CTFE) copolymers at low frequency showed lossy capacitor behavior which was further investigated by measuring polarization versus electric field loop over a wide range of frequencies, i.e. 0.1–400 Hz. Polarization values of PVDF and P(VDF‐CTFE) copolymer films with different CTFE content were compared on the bases of local dipole moments. © 2022 Society of Industrial Chemistry.

Fabrication and Characterization of Semi-Crystalline and Amorphous Dielectric Polymer Films for Energy Storage

Dielectric polymer films are energy storage materials that are used in pulse power operations, power electronics and sustainable energy applications. This paper reviews energy storage devices with focus on dielectric film capacitors. Two prominent examples of polymer dielectrics Polyetherimide (PEI) and Poly (tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride) (THV) have been discussed. Polyetherimide (PEI) is an amorphous polymer recognized for its high-temperature capability, low dielectric loss and high dielectric strength. THV is a semi-crystalline polymer with high dielectric constant, high-temperature capability and charge-discharge efficiency. The primary focus of this paper is to introduce the reader to the fabrication procedures and characterization techniques used in research labs for processing of dielectric polymers. The fabrication and characterization process of both polymers has been discussed in detail to shed the light on experimental process in this area of research.

Photopatterning Crystal Orientation in Shape-Morphing Polymers.

Shape-morphing polymers have gained particular attention due to their unique capability of shape transformation under numerous external stimuli such as light, pH, and temperature. Their shape-morphing properties can be used in various applications such as robotics, artificial muscles, and biomedical devices. To take advantage of the stimuli-responsive properties of the smart polymers in such applications, programming shape change precisely through a facile synthetic procedure is essential. Programmable shape-morphing is readily obtained in hydrogels and liquid crystal polymer networks, but shape programming of semicrystalline polymers usually relies on low-resolution mechanical deformation. In this paper, a semicrystalline shape-morphing polymer with a controlled shape programmability was developed via photopatterning crystal orientation using a spatially controlled photopolymerization technique. The semicrystalline polymer network forms aligned crystallites at the boundaries between dark and bright regions during photopolymerization using a projector, which introduces an anisotropic stimulus response in the films. The semicrystalline polymer films with photoaligned crystallites expand 9-15% in the direction perpendicular to the patterned lines when heated above the melting temperature. Furthermore, spatially patterning the crystal orientation enables the formation of various complex 3D structures including a helical coil, a coil with a handedness inversion, a cone, a saddle, and a twisting flower. Finally, the magnitude of the shape transformation was controlled by varying the polymerization temperatures, and the actuation temperature was tuned by changing the amount of crystallinity in the polymer films. The simplicity and ease of control of our approach to program complex 3D structures from 2D semicrystalline polymer films make it a promising system for the aforementioned applications.

Charge transport and thermoelectric conversion in solution-processed semicrystalline polymer films under electrochemical doping

Charge transport and thermoelectric conversion mechanisms in doped semicrystalline polymer films are key issues in the field of wearable electronics, whereas the complex film structure consisting of crystalline domains and non-crystalline boundaries prevents sufficient understanding of them. In this study, we fully clarify the roles of the domains and the boundaries in a typical semicrystalline polymer on macroscopic charge transport under continuous electrochemical doping. In the crystalline domains, a multi-step transformation of the transport properties from effectively metallic behavior to weak localization (WL) to variable-range hopping (VRH) is found with decreasing temperature and doping level. On the other hand, at the domain boundaries, the effectively metallic conduction changes directly to VRH. Based on these results, the extremely complicated phase diagram, including the coexistence of the WL and VRH processes, is well explained. The proposed transport mechanism further explains the thermoelectric properties of the film.

Superior Energy Dissipation by Ultrathin Semicrystalline Polymer Films Under Supersonic Microprojectile Impacts.

Distinct deformation mechanisms that emerge in nanoscale enable the nanostructured materials to exhibit outstanding specific mechanical properties. Here, we present superior microstructure- and strain-rate-dependent specific penetration energy (up to ∼3.8 MJ kg-1) in semicrystalline poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) thin films subjected to high-velocity (100 m s-1 to 1 km s-1) microprojectile (diameter: 9.2 μm) impacts. The geometric-confinement-induced nanostructural evolutions enable the sub-100 nm thick P(VDF-TrFE) films to achieve high specific penetration energy with high strain delocalization across the broad impact velocity range, superior to both bulk protective materials and previously reported nanomaterials. This high specific penetration energy arises from the substantial stretching of the two-dimensionally oriented highly mobile polymer chains that engage abundant viscoelastic and viscoplastic deformation mechanisms that are further enhanced by the intermolecular dipole-dipole interactions. These key findings provide insights for using nanostructured semicrystalline polymers in the development of lightweight, high-performance soft armors for extreme engineering applications.

Real-time observation of structural change in semi-crystalline polymer films through mid-IR transmission spectroscopy: determination of instantaneous film temperature during recrystallization.

We report the real-time observation of entire structural change in dye-doped semi-crystalline polymer (polyethylene) films through mid-IR transmission spectroscopy. The laser-heated dye molecules heat the polymer film through thermal diffusion, and accordingly the polymer film undergoes the structural change from the crystalline to amorphous structures, which is followed by the reverse structural change, namely recrystallization, during the natural cooling. By tuning the mid-IR probe pulse to one of the few structure-sensitive vibrational modes and varying the time delay between the pump and probe pulses we can monitor the structural change of the polymer film and time-varying film temperature during recrystallization through the transmission change of the resonant mid-IR probe pulse with the time-resolution of sub-μs.

Thermal transitions in semi-crystalline polymer thin films studied via spectral reflectance

Herein we report the finding that spectral reflectance (SR) can be used to identify thermal transitions in semi-crystalline polymer thin films. By studying film thickness as a function of temperature, we found that semi-crystalline polymers exhibit characteristic expansion and contraction profiles during the melting (Tm) and crystallization (Tc) transitions, respectively. Prior to this discovery, studies on the crystalline Tm in thin films have involved more expensive and complex techniques such as atomic force microscopy (AFM), ellipsometry, and grazing-incidence wide-angle X-ray scattering (GIWAXS). We correlate Tm and Tc as measured by SR with differential scanning calorimetry (DSC) in the bulk and temperature-controlled GIWAXS or AFM in thin films. We show that SR is accurate for measuring changes in films with thicknesses of 500 nm down to 21 nm and for detecting melting point depression due to thin film confinement. Thus, we demonstrate that SR is a powerful tool for measuring thermal transitions in semi-crystalline polymer films with single-degree resolution.

Tuning Morphology and Melting Temperature in Polyethylene Films by MAPLE

The control of structure and thermal stability in semicrystalline polymer films remains an important challenge in applications ranging from solar energy devices to packaging films. Here, we demonstrate the ability to dramatically alter the morphology and melting temperature (Tm) of low-molecular-weight linear polyethylene (PE) by employing an innovative vapor-assisted deposition process termed matrix assisted pulsed laser evaporation (MAPLE). We report the ability to tune Tm of PE films by 20 °C by simply adjusting the deposition temperature during MAPLE processing. This unique capability stems from the ability of MAPLE to exploit confined crystallization during thin film growth. In addition, we demonstrate the ability to exploit MAPLE to design PE films that exhibit the same Tm as their melt-crystallized analogues but have an ∼25% higher degree of crystallinity. Our investigation offers new insights into how confinement effects in polymer crystallization can be utilized in the emerging field of polymer f...

Thermal transport in semicrystalline polyethylene by molecular dynamics simulation

Recent research has highlighted the potential to achieve high-thermal-conductivity polymers by aligning their molecular chains. Combined with other merits, such as low-cost, corrosion resistance, and light weight, such polymers are attractive for heat transfer applications. Due to their quasi-one-dimensional structural nature, the understanding on the thermal transport in those ultra-drawn semicrystalline polymer fibers or films is still lacking. In this paper, we built the ideal repeating units of semicrystalline polyethylene and studied their dependence of thermal conductivity on different crystallinity and interlamellar topology using the molecular dynamics simulations. We found that the conventional models, such as the Choy-Young's model, the series model, and Takayanagi's model, cannot accurately predict the thermal conductivity of the quasi-one-dimensional semicrystalline polyethylene. A modified Takayanagi's model was proposed to explain the dependence of thermal conductivity on the bridge number at intermediate and high crystallinity. We also analyzed the heat transfer pathways and demonstrated the substantial role of interlamellar bridges in the thermal transport in the semicrystalline polyethylene. Our work could contribute to the understanding of the structure–property relationship in semicrystalline polymers and shed some light on the development of plastic heat sinks and thermal management in flexible electronics.

Polypropylene copolymer films: Heat sealing and oligomer/additive migration

Ease of heat sealing and oligomer/additive migration are two important and often interrelated phenomena that affect the engineering performance of high clarity polypropylene random copolymer (RCP) films. From a fundamental standpoint, this work investigates the non‐standard microstructural aspects that play a critical role in the heat sealing process of semicrystalline polymer films. Two different propylene–ethylene copolymers having widely different seal initiation temperatures (SITs) but similar melting points were chosen for this study. The contribution of both the amorphous phase and the crystalline phase to heat sealing was investigated utilizing dynamic mechanical analysis and thermal fractionation differential scanning calorimetry, respectively. Results indicate that the melting distribution of the thermally fractionated material plays a critical role in determining SIT while the effect of the mobility of the amorphous phase was found to be insignificant. In order to deeply understand the molecular origin of this difference in melting distribution or lamellar thickness distribution, the composition distribution of the co‐monomer was measured using Gel Permeation Chromatography‐Infra‐Red (GPC‐IR) and found to be fundamentally different. In addition, this work systematically studies the effect of oligomer/additive migration on optics, co‐efficient of friction (CoF), and most importantly heat sealing behavior. Migration is found to dramatically increase the SIT and haze while decrease the CoF of PP RCP films. POLYM. ENG. SCI., 58:1479–1484, 2018. © 2017 Society of Plastics Engineers

Inhomogeneous Morphologies of Ultrathin Semicrystalline PolymerFilms Induced by Polymer Nanolayers Irreversibly Adsorbed on Solids

Inhomogeneous Morphologies of Ultrathin Semicrystalline PolymerFilms Induced by Polymer Nanolayers Irreversibly Adsorbed on Solids

Rapid assessment of crystal orientation in semi-crystalline polymer films using rotational zone annealing and impact of orientation on mechanical properties.

Crystal orientation in semi-crystalline polymers tends to enhance their performance, such as increased yield strength and modulus, along the orientation direction. Zone annealing (ZA) orients the crystal lamellae through a sharp temperature gradient that effectively directs the crystal growth, but the sweep rate (VZA) of this gradient significantly impacts the extent of crystal orientation. Here, we demonstrate rotational zone annealing (RZA) as an efficient method to elucidate the influence of VZA on the crystal morphology of thin films in a single experiment using isotactic poly(1-butene), PB-1, as a model semi-crystalline polymer. These RZA results are confirmed using standard, serial linear ZA to tune the structure from an almost unidirectional oriented morphology to weakly oriented spherulites. The overall crystallinity is only modestly changed in comparison to isothermal crystallization (maximum of 55% from ZA vs. 48% for isothermal crystallization). However, the average grain size increases and the spherulites become anisotropic from ZA. Due to these structural changes, the Young's modulus of the oriented films, both parallel and perpendicular to the spherulite orientation direction, is significantly increased by ZA. The modulus does become anisotropic after ZA due to the directionality in the crystal structure, with more than a threefold increase in the modulus parallel to the orientation direction for the highest oriented film in comparison to the modulus from isothermal crystallization. RZA enables rapid identification of conditions to maximize orientation of crystals in thin polymer films, which could find utility in determining conditions to improve crystallinity and performance in organic electronics.

A 3-phase model for the numerical analysis of semi-crystalline polymer films in finite elastoplastic strains

In this paper, the mechanical behavior of semi-crystalline polymer films in finite elastoplastic strains is investigated. A 3-phase constitutive model has been specially developed in a previous paper and validated for various materials in both uniaxial and biaxial uniform hot drawing. In the present study, the numerical implementation of this 3-phase model in a finite element software is outlined in the perspective of using this model in more general non-uniform cases of complex geometries and/or loadings. In the present case, only polyethylene films at room temperature are considered. First, uniaxial tensile experimental tests are performed so as to calibrate the model parameters. Then, for validation purposes, two series of experimental tests are conducted on tensile specimens with central holes and double edge notched tensile (DENT) specimens. During these tests, digital image correlation is used to analyze the strain (or displacement) field history during loading. Finally, numerical computations are performed with the help of the finite element software including the 3-phase model previously implemented (cohesive elements are also needed for the simulation of the crack propagation in DENT specimens). In both cases, the comparison between the experimental and numerical force–displacement curves, together with the comparisons between the experimental and numerical strain fields at different times, give very satisfactory results.

Controlled Crystallization of Conjugated Polymer Films from Solution and Solvent Vapor for Polymer Electronics

Over the years, solution‐processable conjugated oligomers and polymers have proven to be very promising for application in organic electronic devices. In addition to tuning the chemical structure of the materials, the role of morphology has been identified as a key parameter in determining device performance. Conjugated polymers are typically semicrystalline in nature consisting of both crystalline and amorphous domains giving rise to a wealth of superstructures. In comparison to classical non‐conjugated semicrystalline polymers, they bear the additional advantage of absorbing light. This makes UV‐vis absorption spectroscopy an excellent tool to monitor polymer aggregation and crystallization in‐situ both in solution and in films. With this feature article we point out the delicate interplay between solution processing and the obtained morphology in polythiophenes and low bandgap copolymers. Subtle changes in the preparation protocol lead to significant changes in textures and also give rise to polymorphism. Solvent vapor annealing and solution crystallization are highlighted as tools to control the nucleation and growth processes in semicrystalline polymer films. Structure‐function relationships between morphological, optical and electronic properties are demonstrated.

A direct correlation of x-ray diffraction orientation distributions to the in-plane stiffness of semi-crystalline organic semiconducting films

Large charge mobilities of semi-crystalline organic semiconducting films could be obtained by mechanically aligning the material phases of the film with the loading axis. A key element is to utilize the inherent stiffness of the material for optimal or desired alignment. However, experimentally determining the moduli of semi-crystalline organic thin films for different loading directions is difficult, if not impossible, due to film thickness and material anisotropy. In this paper, we address these challenges by presenting an approach based on combining a composite mechanics stiffness orientation formulation with a Gaussian statistical distribution to directly estimate the in-plane stiffness (transverse isotropy) of aligned semi-crystalline polymer films based on crystalline orientation distributions obtained by X-ray diffraction experimentally at different applied strains. Our predicted results indicate that the in-plane stiffness of an annealing film was initially isotropic, and then it evolved to transverse isotropy with increasing mechanical strains. This study underscores the significance of accounting for the crystalline orientation distributions of the film to obtain an accurate understanding and prediction of the elastic anisotropy of semi-crystalline polymer films.

Harnessing ALD to directly map the morphology of organic photovoltaic bulk heterojunctions

The selective diffusion of small molecules into the amorphous domains of semi-crystalline polymer films is used here to probe the complex morphology of all-organic photovoltaic films. In this case, the ALD precursors of ZnO diffuse into poly(3-hexylthiophene-2,5-diyl):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) BHJs and spatially map the distribution of P3HT amorphous and crystalline domain, and probe the distribution and miscibility of PCBM and P3HT.

Effect of degree of crystallinity on charge transport in ferroelectric semicrystalline polymer film

This paper describes 3D particle-in-cell (PIC) simulation of charge injection and transport through ferroelectric semicrystalline polymer (e.g. PVDF) film comprised of nanocrystallites in an amorphous matrix with varying degrees of crystallinity. The classical electrical double layer (EDL) model for a monopolar core is extended (eEDL) to represent the nanocrystallite by replacing it with a dipolar core. Charge injection at the electrodes assumes metal-polymer Schottky emission at low to moderate fields and Fowler-Nordheim tunneling at high fields. Injected particles propagate via field-dependent Poole-Frenkel mobility. In the eEDL model, the initial attachment of charge particles forms the bound Stern-Helmholtz layer leading to Maxwell-Wagner-Sillars polarization. Subsequent waves of charge particles are repelled by the attached charge resulting in the diffuse Gouy- Chapman transport layer. The simulation algorithm uses a boundary integral equation method (BIEM) for solution of the Poisson equation coupled with a second-order predictorcorrector scheme for robust time integration of the equations of motion. The stability criterion of the explicit algorithm conforms to the Courant-Friedrichs-Levy (CFL) limit assuring robust and rapid convergence. The model is capable of simulating a wide dynamic range spanning leakage current to pre-breakdown levels. Simulation results for semicrystalline film with varying degrees of crystallinity indicate that charge transport behavior depends on nanoparticle polarization with anti-parallel orientation showing the highest conduction and therefore lowest level of charge trapping in the interaction zone. Charge attachment to nanocrystallites increase with vol% loading or degree of crystallinity, and saturates at 40 vol% for the set of simulation parameters. The eEDL model predicts the intuitive meandering pathways of charge particle trajectories, which get progressively more inclined from normal incidence with increasing vol% loading.

Reversible thermosensitive biodegradable polymeric actuators based on confined crystallization.

We discovered a new and unexpected effect of reversible actuation of ultrathin semicrystalline polymer films. The principle was demonstrated on the example of thin polycaprolactone-gelatin bilayer films. These films are unfolded at room temperature, fold at temperature above polycaprolactone melting point, and unfold again at room temperature. The actuation is based on reversible switching of the structure of the hydrophobic polymer (polycaprolactone) upon melting and crystallization. We hypothesize that the origin of this unexpected behavior is the orientation of polycaprolactone chains parallel to the surface of the film, which is retained even after melting and crystallization of the polymer or the "crystallization memory effect". In this way, the crystallization generates a directed force, which causes bending of the film. We used this effect for the design of new generation of fully biodegradable thermoresponsive polymeric actuators, which are highly desirable for bionano-technological applications such as reversible encapsulation of cells and design of swimmers.