Crystal Structure Of Polymer Research Articles

Tearing properties, crystallization behavior, microstructure, and morphology of LLDPE with different short branched chain distributions

Abstract The length and distribution of comonomers with short-chain branching (SCB) have a significant influence on the crystallization behavior and crystal structure of polymers, as well as the mechanical properties of the material. This study investigates the crystallization behavior and properties of linear low-density polyethylene (LLDPE) samples with similar density, molecular weight, and branching degree but varying SCB distributions. The results show that LLDPE with butene as the comonomer has a stronger ability to suppress crystallization compared to LLDPE with hexene as the comonomer due to its more uniform SCB distribution. Additionally, among LLDPEs with comonomers of octene, hexene, and butene, the LLDPE with the most uniform SCB distribution exhibits the weakest crystallization ability. Small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM) results indicate that LLDPE with more uniform distribution of SCB has smaller long-period and more regular lamellar structure. Therefore, LLDPE with more uniform SCB distribution exhibits weaker inhibition ability towards crystallization, leading to less agglomerated phases and weaker phase separation, resulting in higher tear strength.

Using Bulky Dodecaborane-Based Dopants to Produce Mobile Charge Carriers in Amorphous Semiconducting Polymers.

Conjugated polymers are a versatile class of electronic materials featured in a variety of next-generation electronic devices. The utility of such polymers is contingent in large part on their electrical conductivity, which depends both on the density of charge carriers (polarons) and on the carrier mobility. Carrier mobility, in turn, is largely controlled by the separation between the polarons and dopant counterions, as counterions can produce Coulombic traps. In previous work, we showed that large dopants based on dodecaborane (DDB) clusters were able to reduce Coulombic binding and thus increase carrier mobility in regioregular (RR) poly(3-hexylthiophene-2,5-diyl) (P3HT). Here, we use a DDB-based dopant to study the effects of polaron-counterion separation in chemically doped regiorandom (RRa) P3HT, which is highly amorphous. X-ray scattering shows that the DDB dopants, despite their large size, can partially order the RRa P3HT during doping and produce a doped polymer crystal structure similar to that of DDB-doped RR P3HT; Alternating Field (AC) Hall measurements also confirm a similar hole mobility. We also show that use of the large DDB dopants successfully reduces Coulombic binding of polarons and counterions in amorphous polymer regions, resulting in a 77% doping efficiency in RRa P3HT films. The DDB dopants are able to produce RRa P3HT films with a 4.92 S/cm conductivity, a value that is ∼200× higher than that achieved with 3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), the traditional dopant molecule. These results show that tailoring dopants to produce mobile carriers in both the amorphous and semicrystalline regions of conjugated polymers is an effective strategy for increasing achievable polymer conductivities, particularly in low-cost polymers with random regiochemistry. The results also emphasize the importance of dopant size and shape for producing Coulombically unbound, mobile polarons capable of electrical conduction in less-ordered materials.

Physicochemical Mechanics Approach for Geological Soft Mater (Including Inorganic Polymer and Liquid Crystal Structures) in Analysis of Weathering and Formations of Chemogenic, Mechanogenic and Biogenic Mineral Sediments

Physicochemical Mechanics Approach for Geological Soft Mater (Including Inorganic Polymer and Liquid Crystal Structures) in Analysis of Weathering and Formations of Chemogenic, Mechanogenic and Biogenic Mineral Sediments

The effects of chlorotrifluoroethylene (CTFE) units on the dielectric and energy storage properties of P(VDF‐CTFE)

AbstractPolyvinylidene fluoride‐based ferroelectric polymers are favoured in the field of advanced high‐energy‐storage dielectric capacitors due to their strong spontaneous polarisation and high dielectric constant (εr). It has been confirmed that the ferroelectric behaviour and energy storage performance can be regulated by copolymerising polyvinylidene fluoride with bulky monomers such as chlorotrifluoroethylene, and hexafluoropropylene. Past research based on these copolymers mostly focused on the preparation of composites, yet with limited discussion on the effect of copolymer composition. In this work, a series of P(VDF‐CTFE) films with different chlorotrifluoroethylene contents were fabricated through a solution‐casting method. The introduction of bulky chlorotrifluoroethylene units can tune the polymer crystal structure and crystallinity, alter the state of polymer chains and the response of dipoles to electric fields, and lead to dramatic changes in dielectric properties, breakdown strength (Eb), and energy storage density (Ue). As a result, the copolymer with a chlorotrifluoroethylene content of 15 wt% obtained the best overall performance, and the Ue reached 16.73 J/cm3 at 650 kV/mm. This work provides a basis for the optimisation of the properties of polyvinylidene fluoride‐based ferroelectric polymers and the development of high Ue dielectric.

Fabrication of polymer-based stents: Impact of test specimen manufacturing protocol

Abstract Various manufacturing techniques are available for polymer stent fabrication. Polymer semi-finished products can be prepared using solvent based methods, e.g. dip coating, as well as thermal processes, e.g. extrusion. These different methods may lead to an altered polymer crystal structure, resulting in a different deformation mechanism during mechanical stress. For the material property characterization needed for implant development, the test specimens usually are prepared using laser-cut or die-cut methods. Due to these different preparation protocols, a change in polymer microstructure, causing a material property variation, may also result. For this purpose, comparison of laser-cut versus die-cut of PLLA films has been performed. PLLA films have been prepared by dip-coating and were evaluated with respect to structural, thermal, and mechanical properties. In this study, a combination of uniaxial tensile tests, SEM and DSC studies was used. The results of the mechanical tests showed drastic differences in the elongations at break of die-cut specimens compared to laser-cut ones. The results point out formation of complex crystal structures during the manufacturing process. By the use of SEM imaging and DSC measurements, we were able to attribute these changes to the different plastic deformation mechanisms.

Taming of Organic Pollutants Using Covalent-Organic-Framework-Based Materials: Challenges and Future Prospects

Being available in water and air, organic contaminants have easy access to animal bodies to accumulate in the biological food chain, resisting chemical, biological, and photolytic degradation. Besides, they have the ability to travel great distances to end up being dispersed across a broad area, even in places where they have never been used. Furthermore, they pose a significant risk to both human society and the environment, which forces the international scientific community to plan and act to eradicate organic pollutants from the environment and establish a mechanism to stop their discharge. In this context, covalent organic frameworks (COFs)-based materials are found to be promising to control air and water pollutants because of their unique porous, and polymeric crystal structure. This study highlights the history, design, and applications of COFs for reducing organic pollution, as well as the obstacles and opportunities facing their widespread usage in environmental remediation today.

Photonic Crystal Films Based on Polymer Particles with a Core/Shell Structure Responding to Ethanol.

Responsive photonic crystals assembled from colloidal particles have been increasingly utilized in detection and sensing devices owing to their attractive ability to change color in response to external conditions. Methods of semi-batch emulsifier-free emulsion and seed copolymerization are successfully applied for the synthesis of monodisperse submicron particles with a core/shell structure, a core being formed by polystyrene or poly(styrene-co-methyl methacrylate) and a shell being formed by poly(methyl methacrylate-co-butyl acrylate). The particle shape and diameter are analyzed by the dynamic light scattering method and scanning electron microscopy, and the composition is investigated by ATR-FTIR spectroscopy. As shown by scanning electron microscopy and optical spectroscopy, the thin-film 3D-ordered structures based on poly(styrene-co-methyl methacrylate)@poly(methyl methacrylate-co-butyl acrylate) particles exhibited the properties of photonic crystals with minimum number of defects. For polymeric photonic crystal structures based on core/shell particles, a pronounced solvatochromism with respect to ethanol vapor (less than 10 vol %) is observed. Moreover, the nature of the crosslinking agent has a significant effect on the solvatochromic properties of 3D-ordered films.

Multi‐Level Information Encryption/Decryption of Fluorescent Hydrogels Based on Spatially Programmed Crystal Phases

The growing urgence of information protection promotes continuously the development of information-encryption technique. To date, hydrogels have become an emerging candidate for advanced information-encryption materials, because of their unique stimulus responsiveness. However, current methods to design multi-level information-encrypted hydrogels usually need sophisticated chemistry or experimental setup. Herein, a novel strategy is reported to fabricate hydrogels with multi-level information encryption/decryption functions through spatially programming the polymorphic crystal phases. As homocrystalline and stereocomplex crystal phases in fluorescent hydrogels have different solvent stabilities, the transparency and fluorescence of the hydrogels can be regulated, thereby enabling the multi-level encryption/decryption processes. Moreover, the structural origins behind these processes are discussed. It is believe that this work will inspire future research on developing advanced information-encryption materials upon programming the polymer crystal structure.

Copper Ion Imprinted Hydrogel Photonic Crystal Sensor Film

An ion-imprinted photonic crystal (IIPC) sensor for visual detection of copper ions was prepared by the combination of ion-imprinting polymer and colloidal photonic crystal (CPC) structure. Monodisperse polystyrene (PS) colloidal nanospheres synthesized by the boiling soap-free emulsion polymerization method were used to prepare the CPC template by the solvent evaporation method. An ion-imprinted polymer based on poly(vinyl alcohol) and chitosan (PVA/CS) is infiltrated therein. The IIPC sensor film was then prepared by solvent-assisted freeze–thaw method while the CPC template was strengthened as the air pores of the template were replaced by PVA/CS hydrogel. The shift of the diffraction wavelength can be directly observed by the naked eye through the color change of the IIPCS according to the concentration change of copper ion. Such sensor film showed good selectivity and sensitivity with a lower detection limit of 10–4 M.

Poly(l-lactide)s with tetraphenylethylene: role of polymer chain packing in aggregation-induced emission behavior of tetraphenylethylene

The AIE behavior of tetraphenylethylene in biocompatible poly(l-lactide)s is found to be sensitive to the polymer chain packing, polymer crystal structure, solvent, and temperature.

Solution-processable and functionalizable ultra-high molecular weight polymers via topochemical synthesis

Topochemical polymerization reactions hold the promise of producing ultra-high molecular weight crystalline polymers. However, the totality of topochemical polymerization reactions has failed to produce ultra-high molecular weight polymers that are both soluble and display variable functionality, which are restrained by the crystal-packing and reactivity requirements on their respective monomers in the solid state. Herein, we demonstrate the topochemical polymerization reaction of a family of para-azaquinodimethane compounds that undergo facile visible light and thermally initiated polymerization in the solid state, allowing for the first determination of a topochemical polymer crystal structure resolved via the cryoelectron microscopy technique of microcrystal electron diffraction. The topochemical polymerization reaction also displays excellent functional group tolerance, accommodating both solubilizing side chains and reactive groups that allow for post-polymerization functionalization. The thus-produced soluble ultra-high molecular weight polymers display superior capacitive energy storage properties. This study overcomes several synthetic and characterization challenges amongst topochemical polymerization reactions, representing a critical step toward their broader application.

In situ x-ray diffraction of high density polyethylene during dynamic drive: Polymer chain compression and decomposition

Polymers are widely implemented materials often used for safety and security in our daily lives. However, we do not have a thorough understanding of the phase transformations of these materials when exposed to extreme condition, high strain rate events. To study polymers in these severe environments, we performed plate impact experiments that impart a one-dimensional shockwave, at high pressures and temperatures, to observe the materials response. Generally, velocimetry is the experimental diagnostic used to capture the movement of high velocity interfaces to then calculate the mechanical variables associated with shock compression. However, when a material undergoes a phase transition, such as between two crystalline phases or melting to decomposition during shock compression, velocimetry does not explicitly indicate what structural change occurred. At the Dynamic Compression Sector at the Advanced Photon Source, gas gun driven compression has been paired with x-ray diffraction, providing the ability to study both the shock parameters and structural changes concurrently. We explored high density polyethylene (HDPE) both on its reactants Hugoniot (<10.12 GPa) and within its transition region (24.3 GPa) where HDPE is hypothesized to decompose from reactants to products. With x-ray diffraction, we observed both polymer chain compression and crystal structure reorientation from orthorhombic to monoclinic above 6 GPa as well as either a possible phase change or chemical decomposition at 24.3 GPa. With these experiments, we were able to determine the crystalline and amorphous Hugoniot loci at pressures below the polymer transition region.

Degradation of Laser Sintered polyamide 12 parts due to accelerated exposure to ultraviolet radiation

Laser Sintering is an additive manufacturing technology capable of producing robust, geometrically complex polymer parts, with polyamide 12, also known as nylon-12, the most common and well understood feedstock powder. While Laser Sintering has drawn increased interest from industry for producing end-use components directly, little information is currently available regarding the effects of in-service conditions on mechanical performance. When considering applications where parts spend significant periods of time outdoors, such as the automotive sector, the effect of exposure to natural UV light is an obvious concern. To assess their suitability for long-term outdoor applications, Laser-sintered polyamide 12 parts were subjected to up to 2 months of constant UVB radiation. UV exposure was found to cause significant yellowing of the parts, evidenced by their reflectance of blue light decreasing continually as exposure time was increased beyond 24 h. Results from UV/visible spectroscopy demonstrated an increase in UV absorbance with exposure time, attributed to increasing carbonyl concentration. Similarly, X-ray photo-electron spectroscopy showed increases in surface oxygen concentration proportional to UV exposure, with changes to the O 1s and C 1s environments after 2 months of exposure consistent with the generation of new carboxylic acid groups. Photo-degradation led to substantial decreases in both Ultimate Tensile Strength and Elongation at Break, with the deterioration first becoming appreciable between one and two weeks of exposure. Mono-energetic Positron Spectroscopy, a non-destructive surface analysis technique, demonstrated a correlation between these mechanical properties and free volume at the parts’ surfaces. Decreases in free volume were concluded to be due to changes in the nature of the polymer crystal structure and an increase in overall crystallinity at the part surfaces after UV exposure, identified using DSC. Overall, it was concluded that UV exposure causes significant deterioration of Laser-sintered polyamide 12 parts and this should be mitigated against prior to use in long-term outdoor applications.

Building crystal structures of conjugated polymers through X‐ray diffraction and molecular modeling

AbstractCrystal structure of conjugated molecules and polymers is fundamentally critical to understand their multilevel microstructures, carrier transport, and diverse functions. However, to determine the crystal structure of conjugated polymers is a significant challenge, mainly due to the poor crystallinity, weak diffraction, and instability under high‐energy radiation. Here, we build the possible crystal structures of eight typical conjugated polymers, covering several widely used molecular segments in organic optoelectronics. We model the packing structures of these seed polymers based on synchrotron X‐ray diffractions and molecular simulations. These crystal structures provide a new platform to predict the packing structures of more related polymer systems, extending the molecular scope. Based on this polymer crystal structure database, the multiscale microstructures and charge transport properties of conjugated polymers can be predicted before experiments. This study sets up a polymer crystal structure database to eliminate the current trial‐and‐error approaches and accelerating the design of high‐performance conjugated polymers.

The Power of Fiber Twist.

Nature's evolution over billions of years has led to the development of different kinds of twisted structures in a variety of biological species. Twisted fibers from nanoscale- to micrometer-scale diameter have been prepared by mimicking natural twisted structures. Mechanically inserting twist in a yarn is an efficient and important method, which generates internal stress, changes the macromolecular orientation, and increases compactness. Recently, twist insertion has been found to produce interesting fiber properties, including chemical, mechanical, electrical, and thermal properties. This Account summarizes recent progress in how twist insertion affects the chemical and physical properties of fibers and describes their applications in artificial spider silk, artificial muscles, refrigeration, and electricity generation.Twist and associated chirality widely arise in nature from molecules to nano- and microscale materials to macroscopic objects such as DNA, RNA, peptides, and chromosomes. Such twisted architectures play an important role in improving the mechanical properties and enabling biological functions. Inspired by the beauty and interesting properties of twisted structures, a wide range of artificial chiral materials with twisted or coiled structures have been prepared, from organic and inorganic nanorods, nanotubes, and nanobelts to macroscopic architectures and buildings.An efficient way to prepare twisted materials is by inserting twist in fibers or yarns, which is an ancient technique used to make yarns or ropes (Wang, R., et al. Science 2019, 366, 216-221. Mu, J., et al. Science 2019, 365, 150-155). During the twisting process, torque is generated in fibers or yarns, the structure of the polymer chains becomes helically oriented, and the fibers in a yarn become more compact. Therefore, the twisting of fibers and yarns can produce novel chemical, mechanical, electrical, and thermal properties (Dou, Y., et al. Nat. Commun. 2019, 10, 1-10. Kim, S. H., et al. Science 2017, 357, 773-778). This Account focuses on the novel properties generated by twist insertion. The mechanical stress and strain can be optimized in a yarn by twist insertion, and different types of fibers exhibit rather different mechanisms.In the first section, we will focus on recent progress in improving the mechanical properties of twisted fibers, including carbon nanotube yarns, single-filament fibers, and hydrogel fibers. Torque was generated by twist insertion in a fiber or a yarn, and the balance of internal torsional stress can be changed by causing a change in yarn volume. This will result in twist release and torsional and tensile actuations of the yarn, which will be described in the second section. Twisting a yarn generally makes it more compact, which will result in a mechanically induced change in capacitance, supercapacitance, and other useful electrochemical properties when a conducting yarn is in an electrolyte. Such processes were used to develop novel devices for twist-based electricity generation, called twistrons, which will be discussed in the third section. Twist insertion or release also changes the polymer chain orientation or crystal structure, resulting in changes in entropy. This is called the twistocaloric effect, which was used to develop a new cooling method, and will be discussed in the last section.

QUANTUM CHEMICAL STUDY OF THE STABILITY OF COPPER-PALLADIUM COMPLEXES IN THE GAS PHASE

Heterometallic coordination compounds based on copper(II) and palladium(II) β-diketonates $$\text{ }\!\![\!\!\text{ Cu}{{\text{L}}_{\text{2}}}\cdot \,\text{Pd}{{\text{L}}_{\text{2}}}]$$ (L = 2-methoxy-2,6,6-trimethylheptane-3,5-dionato) and $$\text{ }\!\![\!\!\text{ Cu}{{(\text{hfa})}_{\text{2}}}\,\cdot \text{Pd}{{\text{L'}}_{\text{2}}}]$$ (hfa = hexafluoroacetylacetonate, L′ = 1,1,1-trifluoro-5-methoxy-5-methylhexane-2,4-dionato) with a polymeric chain-like crystal structure can be used to prepare Cu–Pd films by MOCVD. It was previously suggested that the Pd:Cu ratio in the films is related to the stability of binuclear complexes $$\text{Cu}{{\text{L}}_{\text{2}}}\cdot \,\text{Pd}{{\text{L}}_{\text{2}}}$$ and $$\text{Cu}{{(\text{hfa})}_{\text{2}}}\,\cdot \,\text{Pd}{{\text{L'}}_{\text{2}}}$$ (the forms these compound adopt in the gas phase). In the present work, the most probable structure of such binuclear complexes at 0 K is determined, their stability is studied, and interatomic interactions are analyzed by density functional theory calculations. The monometallic fragments of the complexes are connected by a network of weak non-covalent interactions, the Cu⋯O contact being the strongest one. When modeling such systems, empirical corrections are shown to be essential for the account of dispersion interactions.

Polymer Structure Prediction from First Principles.

Developing a large database of polymers structures and properties, for which suitable polymer structural models are a prerequisite, is critical for polymer informatics. We present a simple strategy, referred to as polymer structure predictor (PSP), for predicting the crystal structural models of linear polymers, given their chain-level atomic connectivity information. The PSP, which was designed specifically for polymers, relies on properly defining and sampling the configuration space. Using this approach, we have successfully recovered eight known crystal structures of six common linear polymers, including polyethylene, polyvinylidene fluoride, poly(vinyl chloride), poly(p-phenylene sulfide), polyacrylonitrile, and poly-2,5-benzoxazole, while discovering some new stable structures of three of them, i.e., polyvinylidene fluoride, polyacrylonitrile, and poly(p-phenylene sulfide). The PSP is very simple, highly scalable, suitable for automatic workflows, and comparable to the best major structure prediction method in terms of efficiency in polymer crystal structure prediction. Although challenges in comprehensively accounting for possible chain-level conformations remain, the PSP will be very useful in efficiently generating polymer data and strengthening the emerging polymer informatics ecosystems.

Rheologically controlled design of nature-inspired superhydrophobic and self-cleaning membranes for clean water production

Conventional fabrication technologies of superhydrophobic and self-cleaning membranes for wastewater treatment often involve complex surface modifications, and massive usage of nanomaterials or organic solvents. In this work, we developed a pure rheological spray-assisted nonsolvent induced phase separation (SANIPS) approach to fabricate self-cleaning polyvinylidene fluoride (PVDF) membranes with high porosity and hierarchical micro/nanostructures. The resultant membranes exhibit water contact angles and sliding angles in the range of 151.9–156.2° and 9.6–22.6°, respectively. We found that the spraying step caused local distortion of the membrane surface and induced a two-stage phase inversion, leading to the formation of multilevel polymeric crystal structures. Moreover, the morphological structures and other membrane properties (e.g., mechanical strength and liquid entry pressure) could be tuned by applying spraying materials with different physicochemical properties. The superior anti-wetting and self-cleaning properties of the resultant membranes have been demonstrated by treating hypersaline wastewater, comprising 10% sodium chloride and 2000 p.p.m. Rose Bengal dye via direct contact membrane distillation (DCMD) tests. The SANIPS membrane showed a remarkably stable vapor flux of 36.0 kg m−2 h at a feed temperature of 60 °C, and a salt rejection over 99.9% throughout the long-term test of 100 h. We envision this facile and green fabrication method will pave the way for large-scale production of superhydrophobic and self-cleaning membranes for diverse water treatment processes.

Effect of Plasma Modification of Surface and Sterilization on Optical Characteristics of Polyethylene Terephthalate Track Membranes

Effect of plasma modification of surface and sterilization processes on optical characteristics of a polyethylene terephthalate (PET) track membrane (TM) is studied. The TMs are fabricated with the aid of irradiation of PET using 40Ar+8 ion beam and etching in a 1.5-M solution of NaOH. The TMs are modified using low temperature plasma and sterilized with the aid of autoclave treatment and gamma irradiation. The PET TMs exhibit low transmittance and refractivity due to formation of structural inhomogeneities and polymer crystal structure. The effect of plasma and sterilization leads to a decrease in the TM transmittance owing to an increase in the degree of crystallinity and formation of membrane artifacts.

New tri- and di-alkylstannyl 2-(1H-indol-3-yl)ethanoates: synthesis, characterization and biological screenings

A series of triorganotin(IV) compounds {Me3SnL (1), Bu3SnL (2), Ph3SnL (3)} and di-organotin(IV) complexes {Me2SnL2 (4), Bu2SnL2 (5) and Ph2SnL2 (6)}, where Me = methyl, Bu = butyl, Ph = phenyl and L = 2-(1H-indole-3-yl)acetate) have been synthesized and characterized by FT-IR and multinuclear NMR (1H-, 13C- and 119Sn-NMR) spectroscopy. Tri- and diorganotin(IV) derivatives exhibited five- and six-coordinate geometries, respectively, in solid state as evident from the Δν value. Five-coordinate trigonal bipyramidal and six-coordinate octahedral geometry was assigned to 1 and 4 in solution state based on NMR data as evident from 2J(119Sn,1H) and 1J(119Sn-13C) coupling constant values, which was further attested by 119Sn NMR. Single crystal XRD analysis on 1 revealed that it exhibited polymeric crystal structure with distorted trigonal bipyramidal geometry around the tin center with two unequal Sn–O bonds. The screening of the synthesized compounds for cytotoxicity showed good activity in comparison to cis-platin. They have also displayed moderate to good antimicrobial activities.