Structure Of Polymer Chains Research Articles

A novel ternary mixed matrix membrane containing glycerol-modified poly(ether-block-amide) (Pebax 1657)/copper nanoparticles for CO2 separation

A novel high-performance mixed matrix membrane (MMM) with a low amount (< 2 wt%) of filler loading was fabricated in which the synthesized copper nanoparticles (Cu) incorporated into a glycerol-modified poly(ether-block-amide) (Pebax 1657, Pe). Glycerol (Gl) as an affordable low molecular weight additive provides a good CO2 affinity. On the other hand, the presence of Cu nanoparticles improves CO2 permeability through a facilitated transport mechanism, with destruction of the well-packed polymer chain structure and breaking the hydrogen-bond between Gl and Pe chains. First, pure Pe membrane was modified by adding different amounts of Gl (0–25 wt%). The optimum membrane (Pe/Gl (15 wt%)) was determined by measuring the CO2/N2 gas permeation properties. It was shown that the selectivity was dramatically increased (~ 172%) from 81.9 (for pure Pe) to 222.7 (for Pe/Gl (15 wt%)), while a fairly significant decrease (over 23%) in CO2 permeability (from 65.71 for pure Pe to 50.42 for Pe/Gl (15 wt%)) was obtained at 25 °C and 10 bar. Second, the synthesized Cu nanoparticles were embedded (0–2 wt%) into the Pe/Gl (15 wt%) matrix to fabricate the Pe/Gl/Cu MMMs. The results revealed that Pe/Gl (15 wt%)/Cu (1.5 wt%) membrane has a higher permeability (63.6 Barrer, 25 °C and 10 bar), and to some extent a lower selectivity (200) in comparison with the Pe/Gl (15 wt%) membrane. However, it presents an approximately similar permeability but a distinct increase (144%) in selectivity compared to the pure Pe. Accordingly, a series of high-performance Pe/Gl/Cu MMMs were fabricated which surpassed the Robeson's upper limit and can be as the promising membranes for CO2 separation.

Atomistic Molecular Dynamic Simulation of Dilute Poly(acrylic acid) Solution: Effects of Simulation Size Sensitivity and Ionic Strength

Physical properties of polyelectrolytes have been shown to be significantly related to their chain conformations. Atomistic simulation has been used as an effective method for studying polymer chain structures, but few simulations have focused on the effects of chain length and tacticity in the presence of monovalent salts. This paper investigated the microscopic conformation behaviors of poly(acrylic acid) (PAA) with different chain sizes, tacticities, and sodium chloride concentrations. The hydrogen behaviors and corresponding radial distribution functions were obtained. The results showed that the increase of salt concentrations led to the collapse of PAA chains, especially for longer chains. It was found that the effects of salt were mainly attributed to the shielding screening effect by sodium ions rather than the hydrogen bonding effect. Two different structures were formed by isotactic PAA and syndiotactic PAA, respectively, which were due to the deprotonation patterns along the PAA chain.

Progress of polymer chain structure regulation of alkaline anion-exchange membranes for fuel cells

Alkaline anion-exchange membrane fuel cells (AAEMFCs) have attracted worldwide interest due to their advantages including fast oxygen reduction kinetics, high compatibility with non-precious-metal catalyst and low cost. As one of the key components in AAEMFCs, the performance of alkaline anion exchange membranes (AAEMs) directly affects the power output and durability of the fuel cells. During fuel cell operating, AAEMs require high ionic conductivity, excellent dimensional and chemical stability to ensure high efficiency and outstanding durability. However, it is still difficult for any type of the AAEMs to meet all these requirements. This monograph summarizes recent development around the world for AAEMs, especially for the trade-off effect between ionic conductivity and stability of AAEMs as well as the proposed strategies for this issue. The charge carrier in AAEMs is OH-, and it has a lower transporting efficiency owing to its lower mobility, higher dependence on water molecular and the blocking of many hydrophobic domains in AAEMs. The improvement of ion-exchange capacity (IEC) by increasing the grafting degree (GD) of cationic functional groups can, to some extent, solve this issue. however, a high GD always bring the following negative issues: (1) Excessive swelling of AAEMs and significant reducing in the dimensional stability of membranes; (2) the increase of OH- concentration accelerates the kinetics of nucleophilic substitution and Hofmann elimination, leading to the degradation of cationic groups; (3) the enhanced polarization of the cationic groups and the hydrophilicity of the main chain enable the polymer backbone susceptible to nucleophilic attack by OH-, resulting in the degradation of the membrane, and even short-circuit of the fuel cells. In order to solve these issues, various of polymer chain architectures have been designed and regulated. To balance the ionic conductivity and the dimensional stability in AAEMs, double, triple and multi-cations are grafted on one site of polymer backbone to achieve a sufficiently high IEC at relatively low GD. Another realistic strategy is constructing 3D anion channels by the segregated hydrophilic/hydrophobic phase. The alkali stability of the cationic groups is affected by many factors including field effects, steric effects and conformation of substituent groups, and so on. The improvement of chemical stability of AAEMs has been another formidable scientific challenge. Researchers reduce the kinetics of the nucleophilic substitution and elimination reactions, and improve the basic stability of the cationic groups by modulating the structure of substituent groups such as the introduction of electron-donating groups, increased steric hindrance, and adequate hydration of OH-. Among various cationic groups, the piperidinium-based cations show high resistance against both nucleophilic substitution and elimination in alkaline conditions and at elevated temperature. Furthermore, the polymer backbones without ether band and electron-withdrawing groups have been synthesized and exabit highly resistant to alkali hydrolysis. Recently, new strategy for constructing ordered ion channels in AAEMs by novel porous materials such as metal-organic frameworks (MOF), Trogers base, and macrocyclic crown ether compounds, provide for efficient ionic transport. Additionally, highly stable metal complexes have been used as cationic group in AAEMs. These new trends will open up an exciting opportunity to design high-performance AAEMs. The appearance of highly stable AAEMs enables the AAEMFCs to be operated at 80°C, and the cell works stably in a period of study over 100 h. Although this progress is encouraging, there still remains work for improving the cell performance and stability. A 1000 h of stable operation at elevated temperatures will be the next mission for AAEMFCs. In addition, there are some fundamental issues necessary to explore, such as the transport mechanism of OH- in the membrane, the molecular interaction of polyelectrolytes and their self-assembly mechanism in solution and film formation, the mechanism of the influence of morphology on the chemical stability of AAEMs, and the factors affecting the long-term stability of AAEMFCs. These scientific issues will be the focus of future research. The development of AAEMFCs is on its way, and it calls for more efforts in fundamental study, polymer chain architectures and morphology designing, and fuel cell engineering to make it viable.

Controllable synthesis and AIE properties of fluorescent polyesters

For the potential application of functional polyesters in biomedical field, a series of side-chain functional fluorescent polyesters have been designed and prepared through the polymerization of AIE-functionalized carbonate monomer TPETC. The controllable nature of TPETC’s ROP and ROCP using different organocatalysts has been proved. In the dilute solution of these AIE polyesters, the structure of the polymers themselves, concentration of the polymer solution and other external conditions would obviously affect the aggregation of the side groups (TPE derivatives), and thus affecting the AIE phenomenon of the polymers. The structure of polymer chain had certain influences to the distribution and movements of side-groups, and these influences were reflected by the fluorescence intensity here. It is expected that this conclusion would provide a new perspective for the inner characteristics of dilute polymer solutions and broaden the application of AIE macromolecules.

Recent Advances of the Polymer Micro/Nanofiber Fluorescence Waveguide.

Subwavelength optical micro/nanofibers have several advantages, such as compact optical wave field and large specific surface area, which make them widely used as basic building blocks in the field of micro-nano optical waveguide and photonic devices. Among them, polymer micro/nanofibers are among the first choices for constructing micro-nano photonic components and miniaturized integrated optical paths, as they have good mechanical properties and tunable photonic properties. At the same time, the structures of polymer chains, aggregated structures, and artificial microstructures all have unique effects on photons. These waveguided micro/nanofibers can be made up of not only luminescent conjugated polymers, but also nonluminous matrix polymers doped with luminescent dyes (organic and inorganic luminescent particles, etc.) due to the outstanding compatibility of polymers. This paper summarizes the recent progress of the light-propagated mechanism, novel design, controllable fabrication, optical modulation, high performance, and wide applications of the polymer micro/nanofiber fluorescence waveguide. The focus is on the methods for simplifying the preparation process and modulating the waveguided photon parameters. In addition, developing new polymer materials for optical transmission and improving transmission efficiency is discussed in detail. It is proposed that the multifunctional heterojunctions based on the arrangement and combination of polymer-waveguided micro/nanofibers would be an important trend toward the construction of more novel and complex photonic devices. It is of great significance to study and optimize the optical waveguide and photonic components of polymer micro/nanofibers for the development of intelligent optical chips and miniaturized integrated optical circuits.

In Situ Real-Time Observation of Polymer Folded-Chain Crystallization by Atomic Force Microscopy at the Molecular Level

The crystallization process of a folded-chain crystal (FCC), the most common crystalline structure of polymer chains, was clearly visualized at the molecular level in situ and in real time for the first time. The sample was an isotactic poly(methyl methacrylate) monolayer deposited on mica in an amorphous state, the crystallization of which occurred under high humidity and was followed by atomic force microscopy. Detailed crystallization behaviors, especially the stepwise growth of the FCC with blocks shorter than the chain, cooperative chain slipping in the FCC, the formation of an anisotropic nucleus and its growth, and the formation of a small nucleus with a short lifetime, were clearly visualized at the molecular level. The stepwise growth of the FCC differed from that expected by the classical Lauritzen–Hoffman theory and was consistent with recent reports that indicated the formation of some ordered state in the amorphous phase. We believe this molecular information will improve our understanding of...

Reverse Mapping Algorithm for Multi-scale Numerical Simulation of Polylactic Acid

An algorithm is proposed to convert the coarse-grained A-graft-B model of polylactic acid into the atomistic representation. In the A-graft-B model the atoms of the backbone are mapped onto A beads, which form the linear backbone of the coarse-grained macromolecule, the methyl groups are mapped onto B side pendants. The algorithm restores atomic positions based on positions of coarse-grained beads with the help of pre-defined chain fragments, called templates. The dimensions of the templates are adjusted by affine transformation to ensure coincidence of the backbone in coarse-grained and atomistic representation. The transition between coarse-grained and atomistic models conserves information about the fine structure of polymer chains. The restored configurations are suitable for further molecular-dynamic simulations. Both atomistic and coarse-grained representations require standard GROMACS software. The algorithm can be used for reverse mapping of other A-graft-B polymer models.

Dynamical structure of entangled polymers simulated under shear flow.

The non-linear response of entangled polymers to shear flow is complicated. Its current understanding is framed mainly as a rheological description in terms of the complex viscosity. However, the full picture requires an assessment of the dynamical structure of individual polymer chains which give rise to the macroscopic observables. Here we shed new light on this problem, using a computer simulation based on a blob model, extended to describe shear flow in polymer melts and semi-dilute solutions. We examine the diffusion and the intermediate scattering spectra during a steady shear flow. The relaxation dynamics are found to speed up along the flow direction, but slow down along the shear gradient direction. The third axis, vorticity, shows a slowdown at the short scale of a tube, but reaches a net speedup at the large scale of the chain radius of gyration.

Ethylene–co–norbornene copolymerization in the presence of a chain transfer agent

Ethylene (E)-co-norbornene (N) copolymerizations were conducted by using two ansa-metallocenes, isopropyliden(η5-cyclopentadienyl)(η5-indenyl)zirconium dichloride (1) and isopropyliden(η5-3-methylcyclopentadienyl)(η5-fluorenyl)zirconium dichloride (2), activated with dimethylanilinium tetrakis(pentafluorophenyl)borate, in presence of TIBA and variable amounts of Zn(Et)2 as a potential chain transfer agent (CTA). The study evaluated the effect of CTA on microstructure, molecular weight, chain end group and structural, thermal and mechanical properties of poly(E-co-N)s. The analysis of the data revealed that in all copolymerization reactions with metallocenes 1 and 2 in presence of diethyl zinc chain transfer to zinc alkyl occurs along with the typical chain transfers of E-co-N polymerization. The chain transfer to zinc alkyl is more efficient at low N content in copolymers. The two catalysts show different behavior in copolymerization at high N content: molar masses of copolymers produced by 2 are more affected by CTA concentration, that is, the chain shortening with increasing CTA content is greater in copolymers obtained with catalyst 2. The analysis of mechanical properties revealed that CTA affects the polymer chain structure. An increase of CTA caused a change of ductility, rigidity, and mechanical strength; chains produced in presence of Zn(Et)2 are, at least in part, characterized by segments produced as a result of exchange between different metal centers, possibly jointed through ethylene units.

Construction of a Different Polymer Chain Structure to Study π-π Interaction between Polymer and Reduced Graphene Oxide.

In this work, a different polymer chain structure was synthesized to study π-π interactions between polymer and reduced graphene oxide (RGO). Polymers with different chain structures were obtained from free radical copolymerization of styrene with 4-cyanostyrene (containing substituted phenyl rings) and 2-vinylnaphthalene (containing naphthalene rings). In this work, the polystyrene, poly(styrene-co-4-cyanostyrene) and poly(styrene-co-2-vinylnaphthalene) were named as PS, PSCN and PSNP, respectively. RGO was prepared through modified Hummers’ method and further thermal reduction, and nanocomposites were prepared by solution blending. Thus, different π-π interactions were formed between polymers and RGO. Raman and thermal gravimetric analysis (TGA) were used to characterize the interfacial interaction, showing that the trend of the interfacial interaction should be in the order of RGO/PSCN, RGO/PS, and RGO/PSNP. The differential scanning calorimetry (DSC) measurement showed that, compared with polymer matrix, the glass transition temperature (Tg) of RGO/PS, RGO/PSCN and RGO/PSNP nanocomposites with the addition of 4.0 wt% RGO are increased by 14.3 °C, 25.2 °C and 4.4 °C, respectively. Compared with π-π interaction only formed through aromatic rings, substituent groups changed the densities of electron clouds on the phenyl rings. This change resulted in the formation of donor-acceptor interaction and reinforcement of the π-π interaction at the interface, which leads to increased value of Tg. This comparative study can be useful for selecting appropriate interaction groups, as well as suitable monomers, to prepare high performance nanocomposites.

Protonation of polyaniline-coated silica stationary phase affects the retention behavior of neutral hydrophobic solutes in reversed-phase capillary liquid chromatography.

Because of its high conductivity when acid doped, polyaniline is known as a synthetic metal and is used in a wide range of applications, such as supercapacitors, biosensors, electrochromic devices, or solar and fuel cells. Emeraldine is the partly oxidized, stable form of polyaniline, consisting of alternating diaminobenzenoid and iminoquinoid segments. When acidified, the nitrogen atoms of emeraldine become protonated. Due to electrostatic repulsion between positive charges, the polarity and morphology of emeraldine chains presumably change; however, the protonation effects on emeraldine have not yet been clarified. Thus, we investigated these changes by reversed-phase capillary liquid chromatography using a linear solvation energy relationship approach to assess differences in dominant retention interactions under a significantly varied mobile phase pH. We observed that hydrophobicity dominates the intermolecular interactions under both acidic and alkaline eluent conditions, albeit to different extents. Therefore, by tuning the mobile phase pH, we can even modulate the retention of neutral hydrophobic solutes, such as aromatic hydrocarbons, because the pH-dependent charge and structure of polymer chains of the emeraldine-coated silica stationary phase show a mixed-mode separation mechanism.

Unraveling the Main Chain and Side Chain Effects on Thin Film Morphology and Charge Transport in Quinoidal Conjugated Polymers

AbstractThree series of low‐bandgap polymers based on a novel quinoidal para‐azaquinodimethane (p‐AQM) unit are devised and synthesized, enabling an in‐depth study of the impact of structural factors such as polymer main chain, branching point of the side chain, and the length of the branch chains on the thin film morphologies and charge transport properties. Morphological studies reveal that the polymers composed of larger repeating units exhibit a stronger tendency to form edge‐on lamella. On the other hand, altering the side chain structures of polymers with the same main chain configuration indicates that the branching point position has a more deterministic impact than the branch chain length on the interchain interactions and the crystallite orientation. These results demonstrate a compound odd‐even effect of the branching point on the chain packing and morphology, which correlates well with the corresponding field effect transistor performances. The polymer with the branching point at the fourth carbon displays the highest charge carrier mobility over 1.0 cm2 V−1 s−1, concurrent with a bimodal texture. This study provides a comprehensive description of the correlations between polymer structures, thin film morphology, and device performances, providing a clear path to desirable bimodal thin film texture for charge transport.

(Invited) Flexible and Self-Healing Aqueous Supercapacitors By Polyampholyte Gel Electrolytes with Biochar Electrodes and Their Unique Low Temperature Properties

Quenched polyampholytes provide a novel class of tough hydrogel that has self-healing ability, strong adhesion, and mechanical flexibility. Understanding the structure of polymer chains in the hydrogel and the phase behavior of water therein has broad impact on various applications, such as lubrication, adhesion, and electrical conductivity, as well as the hydrogel’s low temperature properties. In this paper, the structure of polymer chains of hydrogels made of a model charge-balanced polyampholyte, a random copolymer of poly(4-vinylbenzenesulfonate-co-[3-(methacryloylamino) propyl] trimethylammonium chloride), was investigated by small- and wide-angle x-ray scattering (SAXS and WAXS). The SAXS results suggested a networked globule structure in the charge-balanced polyampholyte hydrogels prevented freezing of water in the hydrogel, while the evidence of non-frozen water at low temperatures, such as –45 °C was monitored by solid-state 2H NMR. Correspondingly, we observed high ionic conductivity at low temperatures using electrochemical impedance spectroscopy (EIS). Interestingly, multiple freezing-thawing cycles did not impact the phase behavior of water in the hydrogel. We also found evidence that the crosslinked network structure of the polyampholyte chains disrupts the crystalline growth of ice, resulting in ‘slush-like’ ice formation. Utilizing the scientific investigations, a flexible and self-healing supercapacitor with high energy density in low temperature operation was fabricated using a polyampholyte hydrogel electrolyte. The electrode material was a biochar (produced from the low-temperature pyrolysis of biological wastes) bound by self-assembled reduced graphene oxide. Our novel sample preparation technique to enable the self-reinforcing wrapping of reduced graphene oxide sheets is turned out to have universal efficacy. The procedures of this technique will be introduced in the presentation. At the room temperature, the fabricated supercapacitor showed high energy density of 30 Wh/kg with 90% capacitance retention after 5000 charge-discharge cycles at room temperature at a power density of 50 W/kg. At –30 °C, the supercapacitor exhibited an energy density of 10.5 Wh/kg at a power density of 500 W/kg, which is threefold increase compared to control sample that do not incorporate polyampholyte hydrogel electrolyte. We also harnessed the tunable optical property of the polyampholyte hydrogel to fabricate a smart window. Specifically, we modulated the overall hydrophilicity/phobicity of polyampholyte chains when synthesizing the random copolymer and adjusted the upper critical solution temperature (UCST) at high precision, thus achieved a fine-tuning of UCST between 15 and 65 °C. Finally, we developed a stretchable, high-contrast, optically tunable stretchable window which consists of the PA hydrogel and a printed stretchable electric heater by our own ink recipe. In summary, we performed fundamental studies on the phase behavior of polymer chains and water molecules in quenched polyampholyte hydrogels by using synchrotron SAXS/WAXS, solid-state NMR, EIS, and DSC. We utilized the understanding in energy storage and smart window applications, both of which are unconventional for the application of tough hydrogels. In addition, we utilized renewable resource of biochar to fabricate low-cost, high-performance electrode material.

Toward Achieving Highly Ordered Fluorinated Surfaces of Spin-Coated Polymer Thin Films by Optimizing the Air/Liquid Interfacial Structure of the Casting Solutions.

Thin polymer films with well-assembled fluorinated groups on their surfaces are not easily achieved via spin-coating film-fabrication methods because the solution solidifies very rapidly during spin-coating, which hinders the fluorinated moieties from segregating and organizing on the film surface. In this contribution, we have proposed a comprehensive strategy toward achieving well-ordered fluorinated thin films surfaces by optimizing the molecular organization at air/liquid interface of the film-formation solutions. To validate such a route, poly(methyl methacrylate) (PMMA) end-capped with several 2-perfluorooctylethyl methacrylate (FMA) units was employed as the model polymer for investigations. The air/solution interfacial structures were optimized by systematically changing the polymer chain structures and properties of the casting solvents. It was found that the polymers that form loosely associated aggregates (e.g., FMA1- ec-PMMA65- ec-FMA1) and a solvent with better solubility to FMA while having not too low surface tension (i.e., toluene) can combine to produce solutions with well-assembled FMA at the interfaces. By spin-coating the solutions with well-organized interfaces, an ultrathin film with perfluorinated groups that were highly oriented toward the film surface was readily achieved, exhibiting surface energies as low as 7.2 mJ/m2, which is among the lowest reported so far for the spin-coated thin films, and a very high F/C ratio (i.e., 0.98).

Betulin-Constituted Multiblock Amphiphiles for Broad-Spectrum Protein Resistance.

Multiblock-like amphiphilic polyurethanes constituted by poly(ethylene oxide) and biosourced betulin are designed for antifouling and synthesized by a convenient organocatalytic route comprising tandem chain-growth and step-growth polymerizations. The doping density of betulin (DB) in the polymer chain structure is readily varied by a mixed-initiator strategy. The spin-coated polymer films exhibit unique nanophase separation and protein resistance behaviors. Higher DB leads to enhanced surface hydrophobicity and, unexpectedly, improved protein resistance. It is found that the surface holds molecular-level heterogeneity when DB is substantially high due to restricted phase separation; therefore, broad-spectrum protein resistance is achieved despite considerable surface hydrophobicity. As DB decreases, the distance between adjacent betulin units increases so that hydrophobic nanodomains are formed, which provide enough landing areas for relatively small-sized proteins to adsorb on the surface.

Structural and physicochemical characterization of thermoplastic corn starch films containing microalgae

This work provides an in-depth analysis on how the addition of different microalgae species (Nannochloropsis, Spirulina and Scenedesmus) affected the structural and physicochemical properties of thermoplastic corn starch biocomposites. Structural characterization was conducted by combined SAXS/WAXS experiments and it was correlated with mechanical and barrier properties of the biocomposites. A water vapour permeability drop of ca. 54% was observed upon addition of the different microalgae species. The oxygen permeability and the mechanical properties of biocomposites containing Spirulina or Scenedesmus were not improved since the presence of microalgae hindered the re-arrangement and packing of the lamellar structure of starch polymeric chains, according to the SAXS results. Nannochloropsis caused a great reduction of the matrix rigidity and, the oxygen permeability was also improved.Therefore, all of these features make the Nannochloropsis biocomposites an alternative to generate biodegradable food packaging materials with the additional advantage that they can be easily scaled-up.

A Comparative Study of Visco-Elastic Properties of non-Polar and Polar Polymer Dielectrics

The samples of the polymers PVA, PEG, PVDF and PVDF/NiO composites were prepared by solution casting technique. Investigations showed that PVDF (polar dielectric) shows comparatively better visco-elastic properties as compared to the non-polar polymer dielectrics (PVA & PEG) due to the existence of permanent dipole moment of PVDF polymer chain structure and it’s higher crystalline (50%-60%) nature. The mechanical stability of PVDF/NiO composites was investigated to find their suitability as high K materials for the dielectric applications. The visco-elastic properties, the mechanical stability, the nonlinear elastic behavior of the PVDF/NiO composite samples were explained. All the polymers and the composites of PVDF/NiO show the non-newtonian like fluid behavior. The effect of NiO in these composite was investigated and has been found that the mechanical properties are either remaining constant or enhanced on addition of NiO filler into the matrix, which are of supportive evidence for PVDF/NiO composites as suitable materials for flexible dielectric and energy storage applications.

Optical properties of phenylene–thiophene-based polyazomethine thin films

Thin films of new aromatic polyazomethines, containing thiophene rings in their polymer chain structures, were obtained by the chemical vapor deposition method, via a polycondensation process from thiophene-2,5-dicarbaldehyde and one of four different aromatic diamines, as initial monomers. Spectroscopic ellipsometry, attenuated total reflectance mode of Fourier transform infrared spectroscopy, atomic force microscopy, and wide-angle X-ray diffraction techniques have been used to characterize these films. However, the optical transmission and reflectivity measurements, within the wide spectral UV-Vis-NIR range (0.5–6.2 eV), were the basic method of presented investigations. On the basis of optical measurements, the absorption coefficient spectra of these thin films were obtained and the absorption edge parameters, that is, the energy gap ( EG) and Urbach energy ( EU), were calculated in a way typical for amorphous semiconductors. These parameters allowed one to evaluate the length of conjugation and the extension of localized, defect states inside the energy gap, respectively, and to discuss the electronic transitions, being dependent on the chemical structure and conformation of polymer chains. Optical properties of these new phenylene–thiophene-based polyazomethine films were compared with their entirely phenylene counterparts. In general, the energy gaps of investigated films were clearly smaller (about 0.2 eV) than those of their phenylene counterparts, confirming that the presence of thiophene rings in polyazomethine structures improves conjugation.

Enhanced antifungal activities of four Zn(II) complexes based on uniconazole

Four Zn(II) complexes, [ZnL2(SO4)]n (1), [ZnL4(H2O)2]•2(NO3)•4EtOH (2), [ZnL2Cl2]•L (3), and [ZnL2Br2]•L (4) (L = uniconazole), were synthesized using a hydrothermal method and characterized by elemental analysis, FT‐IR spectroscopy, and single‐crystal XRD. Complex 1 formed a one‐dimensional polymer chain. However, complexes 2‐4 were obtained as zero‐dimensional mononuclear coordination compounds. The antifungal activities of these complexes were then evaluated against four selected fungi using the mycelial growth rate method. The resulting data indicate that all complexes show better antifungal activities than their ligands and mixtures. In addition, the interactions between the metal salts of complexes 1‐4 and uniconazole seem to be synergistic. Furthermore, the polymer chain structure of complex 1 significantly enhanced the bioactivity, especially against Botryosphaeria ribis (I). Density functional theory (DFT) calculations were carried out to help explain the enhanced bioactivity after the formation of Zn(II) complexes. The resulting data show that the HOMO–LUMO energy gaps of complexes 1‐4 (0.0578, 0.0946, 0.1053, and 0.1245 eV) are smaller than that of the free ligand (0.1247 eV) and correlate with the antifungal activity of the zinc complexes.

Theoretical Interpretation of Conformation Variations of Polydimethylsiloxane Induced by Nanoparticles

There has been controversy as to whether the addition of nanoparticles to a polymer melt causes perturbed chain structure of polymers. In this work, the chain conformations of polydimethylsiloxane (PDMS) with addition of polyhedral oligomeric silsesquioxane (POSS) nanoparticles have been studied using a classical density functional approach. Under the strong interactions of POSS-PDMS, the radius of gyration of PDMS in the nanocomposites can either increase or decline depending on particle loading. After adding nanoparticles with larger size or weaker interactions, both the increasing and the declining amplitudes can be largely suppressed. The results provide a deep understanding of chain conformation in polymer nanocomposites.