最新刊期
卷 ， 期 9 ， 2017
- 摘要：A macromolecule consists of many repeating units connected via covalent bonds. Such a chain connectivity results in some unique physical properties and related problems of macromolecules. In this review, we will clarify one intellectual problem that is absent in small molecular systems; namely, small molecules only have soluble and insoluble two states; in 1960's, theorists predicted that even in its soluble state a flexible linear polymer chain can change its conformation from a swollen random coil to a collapsed globule as the solvent quality varies from good to poor. Since the end of 1970's, experimentalists tried hard to confirm such a coil-to-globule transition. However, a stable single-chain collapsed globule had not been experimentally observed up to the middle of 1990's. This unsolved problem has long puzzled many researchers. One theorist even claimed in 1993 that a thermodynamically stable single-chain collapsed globule cannot be observed with our modern instruments and current sample preparation technique. In China, the late Professor Renyuan Qian and some researchers started to study some single-chain problems in the end of 1980's. In 1993, our laboratory used a novel approach to attack such a problem by successfully preparing and using some narrowly distributed high-molar mass linear thermally sensitive water-soluble homopolymers. In 1995, we observed this long-predicted coil-to-globule transition by using laser light scattering. Further, we discovered a novel "molten globule" state during the coil-to-globule transition and revealed that there is no additional knotting and entanglement inside individual single-chain globules. We also studied, for the first time, the opposite globule-to-coil transition and found an unexpected hysteresis in comparison with the coil-to-globule transition, which is related to the formation of additional intrachain hydrogen bonds inside the collapsed globular state. Finally, we investigated the chain folding kinetics by using the infrared pulsed laser-induced temperature jump and unearthed that the coil-to-globule transition has two distinct kinetic stages:the nucleation (formation of small "pearls" made of a limited number of collapsed chain segments along the chain), in dependent of the chain length; and the coarsening (merging of "pearls"). After persisting for nearly twenty years, we have essentially concluded the study of this important intellectual problem in modern polymer physics and revealed some of its related unique physical properties.关键词：Flexible linear polymer chain;Polymer solution;Chain conformation;Thermally sensitive water-soluble polymer;Laser light scattering
- 207
- |
- 58
- |
- 4
发布时间：2021-01-27 - 摘要：Comparing with traditional inorganic semiconductor devices, the organic optoelectronic devices based on organic semiconductors, especially polymer semiconductors, exhibit several distinct advantages, such as low cost, light weight, solution processibility, flexibility and compatibility with roll-to-roll printing etc., and have drawn much attention from both academic and industrial fields. To fulfil solution processed high performance organic optoelectronic devices, one of the major challenges is to avoid interface erosion during solution processing as well as to improve the electron injection/extraction between printable high work function metals and active layers. Water/alcohol soluble conjugated polymers (WSCPs), which are composed of conjugated backbones and highly polar side chains, can be processed from water, alcohol and other polar solvents. The unique solubility of WSCPs provide them with good opportunities to fabricate multilayer organic optoelectronic devices without interface mixing by solution processing, and it is found that WSCPs exhibit promising interface modification capability for high work function metal and/or metal oxide electrodes, which can greatly enhance the performance of organic optoelectronic devices. In this feature article, we gave an overview of our design strategies and achievements on WSCPs, including neutral amine based WSCPs and their quaternized derivatives, WSCPs without mobile counterions, cross-linkable WSCPs, WSCPs towards large area module device, and their applications as interface modification layers in solution processed highly efficient multilayer organic optoelectronic devices. A brief induction and discussion on working mechanisms of WSCPs serving as cathode modification layers in polymer light-emitting diodes (PLEDs) and polymer solar cells (PSCs) were also provided. The excellent cathode modification capability of WSCPs can be ascribed to:(a) WSCPs decrease the work function of cathode to increase the build in potential of devices as well as increase the open voltage (Voc); (b) WSCPs dope contacted PCBM at the interface to increase the conductivity and improve short-circuit current density (Jsc); (c) WSCPs exhibit excellent electron-extraction and hole-blocking properties at the interface and increase the fill factor (FF).关键词：Water/alcohol soluble conjugated polymer;Cathode interlayer;Solution processing;Polymer light-emitting diode;Polymer solar cell
- 138
- |
- 37
- |
- 5
发布时间：2021-01-27 - 摘要：The crystallite of native cellulose has hydrophilic (110)/(110) facets with abundant hydroxyl groups and hydrophobic (200) facets with C-H bonds. The cellulose chains form crystal via intra-layer hydrogen bonds along (200) plane and van der Waals stacking along (110) and (110) planes. Inspired by these anisotropic interactions, we propose new concepts for manipulating themorphology and properties of nanocellulose. The progress along this line in our group in the last five years is reviewed and the influence of medium polarity on the way of cellulose disintegration is emphasized. Dry (no liquid) milling of cellulose causes its decrystallization, while the presence of a liquid changes the behavior significantly. Addition of nonpolar liquids slows down the decrystallization process, and a new form of cellulose is generated in this process as an intermediate product, namely "cellulose nanosheet", which has a form of flat sheets with basic unit of 2-4 nm thickness, apparently formed by coalescence of elementary fibrils. Addition of polar liquids basically prevents decrystallization, leading to individualization of nanofiber into elementary fibrils or their aggregate bundles. Addition of esterifying agents to cellulose-organic solvent system promotes nanofiber dispersionvia esterification of the surface hydroxyls of cellulose. Here, a characteristic difference is found between polar and nonpolar solvents as reaction medium, suggesting the involvement of specific interaction between solvent molecules and crystallographic planes of the cellulose. One unique discovery is the involvement of pot material in cellulose milling:dry milling of cellulose in PTFE pot was found to result in nano-coating of cellulose particles by PTFE. This phenomenon is interpreted as an instance of friction transfer, which has been observed for PTFE under controlled setups. Its occurrence in ball milling of cellulose may lead to a new class of cellulose-based materials. As a whole, physicochemical modification of crystalline cellulose was found to involve interactions with environments of polar/nonpolar natures. Exploration of this concept may lead to various innovative technologies in cellulose processing.关键词：Medium polarity;Nanocellulos;Hydrophobic nanosheet;Morphology structure
- 70
- |
- 40
- |
- 4
发布时间：2021-01-27 - 摘要：Naturalpolymers such as cellulose, chitin, chitosan and other fungi polysaccharides are derived from renewable resources, which is one kind of main chemical raw materials in the future. The numerous intermolecular and intramolecular hydrogen bonds have made their dissolution difficult in most common solvents. Moreover, their structures are very complex. Clarifying their chain conformation and solution properties is essential in designing their molecular structure, realizing more sophisticated applications. This article introduces the recent results about low temperature dissolution of cellulose, chitin and chitosanin in alkali/urea aqueous solution and their chain conformation and solution properties, as well as solution properties of the active polysaccharides. Cellulose can be dissolved in 7 wt% NaOH-12 wt% urea aqueous solution with precooling (-12℃) within 2 min, whereas chitin can be dissolved in a mixture of NaOH, urea and water atweight ratio of 11:4:85 at -30℃. The weight average molecular weight (Mw), radii of gyration (〈Rg〉z), hydrodynamic radii (〈Rh〉z), the structure-sensitive parameter (ρ) and persistent length (q) values of the natural macromolecules were determined, indicating the worm-like stiff chain conformation of cellulose, chitin and chitosan. Furthermore, TEM, cryo-TEM and AFM images provide direct observation of the extended chain conformation and the visualized nanofibers constructed from the stiff chains in parallel aggregation in the aqueous solution. A water-soluble neutral polysaccharide (AF1) was extracted from A. auricula-judae was and identified as a high branched β-(1→3)-D-glucan. AF1 was proved to exist as stiff chains in water, and as flexible chains in dimethylsulfoxide (DMSO). The high-branched glucan was used to self-assemble into hollow nanofibers with apparent average diameter of 92 nm. Lentinan, a β-(1→3)-D-glucan isolated from Lentinus edodes, exhibited good water solubility, and existed as a triple-helical conformation in the aqueous solution at 25℃. AFM images confirmed that the triple-helical chain conformation of lentinan with highMw formed wormlike patterns in aqueous solution at 25℃. Water-insoluble polysaccharide (TM3a), extracted from sclerotia of Pleurotus tuber-regium, was identified as ahyperbranched β-D-glucan. The degree of branching of TM3a was 65.5%. The dependence of intrinsic viscosity ([η]), radius of gyration (〈S2〉z1/2), and hydradynamic radius (Rh) on the weight-average molecular weight (Mw) was studied, indicating that TM3a existed as a compact chain conformation with a sphere-like structure in LiCl/DMSO solution. Furthermore, TEM image provided direct observation of the sphere-like pattern of the chain conformation.关键词：Natural polysaccharides;Dissolution at low temperature;Solution properties;Chain conformation;Molecular weight
- 124
- |
- 61
- |
- 0
发布时间：2021-01-27
Feature Articles
- 摘要：Nonfullerene polymer solar cells (PSCs) based onp-type conjugated polymer as donor and n-type organic semiconductor (n-OS) as acceptor have attracted great attention in recent years, due to the advantages of the n-OS acceptors, such as strong and broad absorption in visible-NIR region, easy tuning of absorption and electronic energy levels, and good morphology stability in comparison with the traditional fullerene derivative acceptors. This article reviews the recent research progress of the n-OS acceptors (including n-type conjugated polymers and n-OS solution-processable organic small molecules) and the conjugated polymer donor photovoltaic materials for the application in nonfullerene PSCs. The n-type conjugated polymer acceptor materials include the perylene diimide (PDI)-and naphthalene diimide (NDI)-based D-A copolymers, as well as the D-A copolymers based on the new B←N bonded acceptor unit. The highest power conversion efficiency (PCE) reached 8.24% for the all polymer PSCs with a medium bandgap p-type conjugated polymer J51 as donor and a narrow bandgap n-type NDI-based D-A copolymer N2200 as acceptor. The n-OS small molecules acceptors include the PDI-or NDI-based molecules, the narrow bandgap A-D-A structured small molecules with a fused ring central donor unit and two electron-withdrawing end groups (such as ITIC), and other n-OS small molecules. The p-type conjugated polymer donor materials, matching with the nonfullerene acceptors, include the narrow bandgap oligothiophene-or banzodithiophene (BDT)-based copolymers, and the medium bandgap two-dimension-conjugated D-A copolymers based on BDT with thiophene conjugated side chains. The best nonfellerene PSCs, with a medium bandgap polymer as donor and a narrow bandgap A-D-A structured n-OS as acceptor, have been recently demonstrated to have high PCE of over 12%. The complementary absorption in the visible-NIR region, matching electronic energy levels of the donor and acceptor materials, is very important for the high performance nonfullerene PSCs. In the end of the article, we give some comments and point out the key issues for the next-step studies and future development of the nonfullerene PSCs.关键词：Polymer solar cells;n-type organic semiconductors;Nonfullerene acceptors;Conjugated polymers donor materials;Power conversion efficiency
- 181
- |
- 55
- |
- 7
发布时间：2021-01-27
Reviews
- 摘要：Influence of shear homogeneity on rheology and flow-induced crystallization (FIC) behavior of polymer is investigated by contrasting the sudden startup shear with the slow shear rate ramp-up procedure. The shear experiments are performed via changing only the rate ramp-up time at a fixed shear rate of 17.7 s-1 and a constant strain of 20. And the corresponding motor acceleration time is set to 0, 0.5, 1.0 and 1.5 s, respectively. Combining wide angle X-ray scattering and polarized microscopy characterization, this set of experiments is designed to study the rate ramp-up time dependence of the rheological properties and FIC at the same shear rate and strain. When the rate ramp-up time is 0.5 s, it is found that a slow acceleration cannot completely eliminate the flow inhomogeneity. The stress overshoot still occurs in the stress-strain curve and the sample orientation is only slightly improved. As the rate ramp-up time is further increased to 1.0 s, the stress overshoot disappears, indicating that the inhomogeneity induced by destruction of melt structures vanishes. In this case, the degree of sample orientation is further improved, and the amount of oriented crystals is increased. However, when the rate ramp-up time is 1.5 s, the effect of flow induced crystallization is weakened, which is indicated by a decrease in orientation degree and the amount of oriented structures. Results obtained sufficiently illustrate that the FIC is dependent on the rate ramp-up time. However, a slower rate ramp-up procedure is not always associated with a better the flow-induced crystallization. Actually, there exists an optimal rate ramp-up time for a fixed shear rate. In addition, the optimal rate ramp-up time is not the same for different shear rates. These results suggest that rate ramp-up time should be considered as a critical parameter for FIC. And the underling mechanism still needs further investigation.关键词：Shear homogeneity;Rate ramp-up time;Rheology;Crystallization
- 32
- |
- 22
- |
- 1
发布时间：2021-01-27 - 摘要：An isolated single polymer suspending in the dilute solution exhibits a collapse transition when switched from good solvent to poor solvent. The transition passes through a thermally reversible intermediate molten globule state holding a characteristic core-shell structure with a concentrated core and a dilute shell, which appears more obvious for shorter chains. Therefore, the collapse transitions of short-chain polymers appear more gradual than those of long-chain polymers. This intermediate molten globule state is interesting because it allows a better understanding of the protein folding and its bio-functions as well as of polymer interface properties. We performed dynamic Monte Carlo simulations to compare the intermediate molten globule state of a single ring polymer to that of a single linear polymer. Their molten globule structures appeared very similar. This observation thus ruled out the specific effect of chain ends, and allowed us to focus on the surface effect of the globules in the intermediate states, which was also obvious for the limited chain length. We observed that, right below the theta point as the critical demixing point for solution of the polymer with infinite chain lengths, the intermediate molten globule states showed two energy states of monomers separately in the core and in the shell, appearing as a coexistence of two concentrations separately deviating from the criticalθ point. We, therefore, considered the molten globule state as a result of pre-dissolution, similar to the pre-melting phenomenon of single-chain single crystals around their equilibrium melting points. The surface dissolution model was then applied to describe the characteristic core-shell structures near the critical point during collapse transition of single-chain polymers. According to the surface dissolution model, near the critical theta point, the globule-solvent interface energy of the collapsed globules became high, which was then optimized by forming a thin layer of coexisting dilute phase, i.e. replaced by the globule-coil plus coil-solvent interface energy. The situation is something similar to the complete wetting of the vapour on a solid substrate, except that the partial surface dissolution achieves a minimum free energy with an equilibrium thickness of the surface layer. In fact, on the phase diagram, right below the theta point, any concentration deviation from the theta state will enter the metastable region for first-order phase transition. The equilibrium layer thickness defines the soluble length of chain segments on the surface. For a real single-chain polymer, however, the extent of surface dissolution may not be able to reach the equilibrium end, because the topological constraint inside the globule, for example, a knotting, will not allow the equilibrium lengths of chain segments to release at the globule surface. This kind of pre-dissolution behaviours could be unique for polymers at interfaces near the critical point. Since shorter chains make smaller globules, their surface dissolution phenomena become more obvious and their collapse transitions appear more gradual. Owing to the surface dissolution near the critical point for phase separation, the distribution of monomer energy states becomes discontinuous along the direction normal to interface. This behaviour reveals a discrepancy at the molecular level if compared to the traditional theoretical treatment of a continuous concentration gradient along this normal direction for the critical interfaces. Thus, the pre-dissolution model may provide a profound approach to better understand the microscopic nature of polymers at the near-critical fluid-fluid interfaces.关键词：Collapse transition;Computer simulation;Critical phenomenon
- 62
- |
- 23
- |
- 7
发布时间：2021-01-27 - 摘要：The distribution of counterions around the charged chain of polyelectrolyte is the key aspect of its physical and chemical properties. In the current study, the spatial profile of counterion concentration along the radial direction of the molecular chain of sodium polystyrene sulfonate (NaPSS) is investigated by single molecule fluorescence technique, fluorescence correlation spectroscopy (FCS) and photon counting histogram (PCH) technique. FCS measures the diffusion coefficient (therefore the hydrodynamic radius) of a single PSS- chain while PCH measures the molecular brightness of a single fluorophore attached to the chain end. By chemical reactions, a pH responsive fluorophore (Oregon Green 488, OG488) is precisely positioned at different distances to the end of PSS- chain, using hydrophilic polypeptide chains of different length as spacers. The concentration distribution of hydronium ions at the vicinity of the PSS- chain is measured by examining the molecular brightness of OG488, by numerical fitting the PCH data using super-Poisson distribution function. The results demonstrate that the concentration of hydronium in the vicinity of the PSS- chain is 2-3 orders of magnitude higher than that in the bulk solution (at the infinite distance to the chain), evidencing the existence of counterion cloud around the charged chain. By varying the position of the probe with the adjustment of chain length of polypeptide, the local pH value at different distances to the PSS- chain end is measured and therefore the spatial profile of counterion concentration around the direction towards away from the chain is probed. The results show that the counterion concentration decreases very sharply with the increase of the distance (within 2.0 nm) to the PSS- chain. It is further discovered that the concentration gradient decreases with the increase of the bulk pH, demonstrating the expansion of the counterion cloud as the result of the entropy effect by dilution of hydronium ions. The results clearly prove that the counterions distribution around a charged macromolecule is the result of balance of electrostatic attraction and the process of entropy maximization, i.e. the process of counterion adsorption, instead of the conventional counterion condensation.关键词：Polyelectrolyte;Counterions;Single molecule fluorescence
- 52
- |
- 14
- |
- 2
发布时间：2021-01-27 - 摘要：Vitrification and gelation are two main paths for matters to transform from liquid to solid in nature. During these transition processes, the dynamics of the systems becomes slower, and there appears a relatively fast and slow dynamics, which finally results in the heterogeneous distribution of dynamics in the space and time. This dynamic heterogeneity in the space and time has been reported to diverge following the power law when approaching to the glass transition. However, it is still unclear for the dynamic heterogeneity evolution when approaching to the gelation. In this work, the dynamic heterogeneity in a gelatin solution during isothermal gelation at 22℃ was monitored by the probe particle tracking microrheology. The gel point was determined as the waiting timetw=8 min through the ensemble averaged dynamic modulus, which was obtained from the mean square displacement of the particles using the generalized Stokes-Einstein relation (GSER). The spatial distribution of the loss angle tanδ was established from the particle trajectories to represent heterogeneous viscoelasticity in the gelatin during the gelation. Then, the dynamic heterogeneity change during the gelation was quantitatively evaluated by the van Hove function and the non-Gaussian parameter α2. The dynamics was found to be heterogeneous after gelation in both respects of space and time, and the fast dynamics contributed more after gelation when compared with that before gelation. To further investigate the spatial and time correlation for this dynamic heterogeneity, the 4-point correlation function and 4-point susceptibility were measured on the base of particle tracking statistics. The results indicated that, before gelation of the gelatin solution, the fast relaxation proceeded independently, while the slow relaxation occurred with a large spatial correlation containing more surrounding units. On the other hand, after gelation both the fast and slow relaxations processed correlatively and cooperatively with more surrounding units. This was consistent with the result from molecular dynamics simulation for the chemically crosslinked polymer gels.关键词：Gelation;Dynamic heterogeneity;van Hove function;4-Point susceptibility
- 60
- |
- 26
- |
- 2
发布时间：2021-01-27 - 摘要：As a precursor of polyimide, poly(amic acid) (PAA) has significant influence on the properties of the final materials. The stability of PAA solution under different conditions is also important to control the properties of PI. In this work, soluble 6FDA-TFDB PAA was synthesized and its solution was obtained. Using FTIR, 1H-NMR and GPC techniques, the molecular information of PAA was obtained. The degradation behavior was investigated by rheometer under different conditions (temperature, heating rate, water content, etc.). It was found that the degradation rate in a high temperature region was much faster than that in a low temperature region, and a critical temperature was found to exist between these two temperature regions. Influence of added water amount in PAA solution on degradation behavior was also considered. In order to analyze precisely the influence of water amount on PAA degradation behavior, the amount of water in DMAc was analyzed by Karl Fischer method and demonstrated that it was too small to influence the relevant results. It was found that water accelerated the degradation rate of PAA solution in the low temperature region, but was irrelevant in the high temperature region. Based on Andrade equation, the viscous-flow activation energy was obtained and compared to evaluate the degradation rate of PAA in solution under different conditions, through a semi-quantitative way. Different results were found at low/high storage temperatures:at low storage temperature the viscosity of PAA solution was kept constant at first, then increased to a maximum and finally decreased; at high storage temperature it decreased gradually to a low value and remained constant. Based on degradation mechanism of PAA chains, the degradation behavior under different conditions was explained. This work provides a guide to tune the solution properties of PAA, and also to control the properties of polyimide materials.关键词：Poly (amic acid);Degradation behavior;Rheometer;Viscosity;Viscous-flow activation energy
- 33
- |
- 17
- |
- 0
发布时间：2021-01-27 - 摘要：An unusual phase behavior, showing the disordered phase at low temperatures and the ordered phase at high temperatures, which is known as the "isotropic phase reentry", has been observed in mesogen-jacketed liquid crystalline polymers and other side-chain jacketed polymers, for example, in some poly(di(alkyl) vinylterephthalates) (PDAVTs). In general, such a phase behavior is considered entropy dominant. However, the mechanism underneath is not fully addressed yet. Here, we study in detail the feature of phase transition of the PDAVT samples with the alkyl group of butyl, hexyl and octyl (denoted as P4, P6 and P8, respectively) by differential scanning calorimetry (DSC), X-ray diffraction (XRD), rheology, and solid-state NMR. Undetectable in DSC experiment, the columnar liquid crystalline (Col) phase formation is demonstrated by XRD upon heating the PDAVT samples from isotropic state. It is also evidenced by rheology measurement, showing that, after glass transition, the samples have their shear storage modulus increased by two orders of magnitude at high temperature. Upon cooling, P4 retains its Col phase probably due to the molecular motion frozen by glass transition, while P6 and P8, which have quite low glass transition temperature (Tg), can fully return to the isotropic state, exhibiting the typical behavior of "isotropic phase reentry". It is found that the Col phase formation is nucleation-limited, with the feature of one-dimensional growth. At higher temperature, the nucleation barrier is drastically reduced, resulting in a much faster growth rate of Col phase. Sufficient development of the Col phase at the temperature above Tg makes the samples solid-like. Solid-sate NMR experiment reveals that increasing the temperature activates the alkyl tail motion first, which in fact triggers the Col phase formation. Effects of shearing and stretching on the Col phase formation are further examined. It is found that the external fields applied cannot induce the isotropic-to-Col transition of PDAVT when the temperature is close to the transition temperature, although the PDAVT chains can be oriented to some extent. On the basis of the experimental data obtained using these techniques, we conclude that the maximization of side-chain entropy is the driving force for the isotropic-to-Col phase transition. Namely, only at sufficiently high temperature can the strong side-chain motion enhance the "side-chain jacketing" effect, making the chains more rod-like which will pack parallelly to form the Col phase.关键词：Jacketing effect;Columnar liquid crystalline phase;Isotropic phase reentry;Entropy driven ordering
- 61
- |
- 16
- |
- 3
发布时间：2021-01-27 - 摘要：Conductive polyaniline is an important material to improve the capacity and cycle stability of Lithium-sulfur battery, but lithium-sulfur cathode with conductive polyaniline still faces poor capacity retention and cycle stability at temperature below 0℃ due to slow equilibration of sulfur or polysulfides. A novel concept using redox mediator to accelerate electrochemical reaction at low temperature was proposed. By adding a redox mediator with its redox potential below S and between Li and S, the electrochemical reaction is accelerated and the low temperature performance of Li-S battery is therefore improved. More specifically, when pyrene is used as the redox mediar (RM), it can be oxidized to RM+ at the cathode surface by sulfur or polysulfides, then RM+ attains electron from cell system regenerating RM. The mediator acts as an electron transfer agent permitting efficient reduction of sulfur or polysulfides. Pyrene is identified from cyclic voltammogram (CV) test as electrochemical active substance around the high-plateau in discharge process, which meets the requirement of redox mediator in Li-S battery at low temperature. When pyrene was dissolved in electrolyte, it may act as an effective electron transfer agent to increSase the electron transfer rate, permitting efficient reduction of sulfur to polysulfides Li2SX (4 ≤ X ≤ 8), thereby accelerating the equilibration process, and finally enhanced the low temperature performance of Li-S battery. To analyze the influence of pyrene on the composition of reduction products of sulfur, ex situ X-ray photoelectron spectroscopy (XPS) is used to test the cathode material after discharging to 2.2 V at the 10th cycle. XPS experiments confirm that the addition of pyrene may accelerate the polysulfides equilibration rate and prolong the first plateau. When ultrathin sulfur-wrapped PANI nanocomposite (S-PANI) is used as cathode material, taking the capacity of 25℃ as reference, the addition of 0.1 mol/L pyrene into electrolyte could raise the 50th capacity retention rate from 68.9% to 84.6% at 0℃, i.e. by 22.8%. This capacity retention rate is increased by 25.2% from 56.0% to 70.1% at -15℃.关键词：Polyaniline;Pyrene;Lithium-sulfur battery;Low temperature performance;Redox mediator
- 85
- |
- 31
- |
- 1
发布时间：2021-01-27 - 摘要：Highly oriented polyethylene (PE) ultrathin films were prepared by a melt-draw process. The obtained PE ultrathin films of ca. 50 nm in thickness consist of parallel oriented edge-on lamellae. The electron diffraction experiment indicates that the prepared PE thin films exhibit high degree of fiber orientation with crystallographic c-axis aligned along the drawing direction, while the a-and b-axes rotate randomly about the c-axis. These oriented PE thin films were used to initiate crystallization of poly(L-lactic acid)/poly(ε-caprolactone) (PLLA/PCL) blends to check the mutual influence of PLLA and PCL on the related epitaxial crystallization. To this end, double-layered samples of PE and PLLA/PCL blends were prepared by spin-coating a 0.5 wt% PLLA/PCL solution in choloform on the highly oriented PE thin films. The PLLA/PCL blend ratios are 100/0, 95/5, 90/10, 80/20, 50/50, 40/60, 30/70, 20/80, 10/90 and 0/100. After evaporation of the solvent choloform, the samples were heat-treated at 120℃ for 8 h first to ensure the cold-crystallization of PLLA, and then at 40℃ for isothermal crystallization of PCL. It was confirmed that pure PLLA cold-crystallized on oriented PE substrate epitaxially with its molecular chains arranged mainly in the direction perpendicular to the PE molecular chains. On the other hand, the epitaxial crystallization of PCL on the PE substrate led to the formation of highly oriented PCL lamellar structure with moelcular chains aligned along the PE chains. For the blends, when the PCL content was 5 wt%, the epitaxial crystallization of PLLA on PE was not affected at all. A 10 wt% PCL resulted in a more pronounced perpendicular chain alignment of PLLA and PE. When PCL content reached 20 wt%, both perpendicular chain orientation of PLLA-PE and parallel chain orientation of PCL-PE were observed, indicating the cooccurrence of both epitaxial crystallization. For the blends with more than 40 wt% PCL, the epitaxial crystallization of PLLA on PE substrate was inhibited but the existence of PLLA did not influence the epitaxial crystallization of PCL. Epitaxially grown parallel aligned PCL edge-on lamellae were always observed regardles of PLLA content. However, the PLLA/PCL blends at ratio of 50/50 and 30/70 displayed evident phase seperation. In the PCL-rich domains, PCL still crystallized epitaxially on the PE substrate and formed parallel aligned lamellar structure with molecular chains oriented in the same direction as PE substrate. In contrast, the PLLA-rich regions were structureless. The phase seperation was not obvious in the blends with PLLA of less than 20 wt%. This indicates that a small amount of PLLA can be dispersed into amorphous PCL region between parallel aligned epitaxially grown PCL lamellae.关键词：Poly (L-lactic acid);Poly (ε-caprolactone);Polyethylene;Epitaxial crystallization;Orientation
- 39
- |
- 17
- |
- 0
发布时间：2021-01-27 - 摘要：A series of amphiphilic polymer brushes with a high grafting density as a new polymeric surfactant are developed. A great deal of research on amphiphilic block polymers has been reported to apply as the surfactants, but the research on polymer brush is still scarce. Nevertheless, amphiphilic polymer brushes would be good surfactants due to their rich surface properties and various morphologies. Therefor, a series of polymer brushes with mixed hydrophilic and hydrophobic side chains were designed and synthesized via a grafting-onto approach. Firstly, a polymeric backbone of poly(glycidyl methacrylate) (PGMA) with pendent azide groups was prepared by reversible addition-fragmentation chain transfer (RAFT) mediated radical polymerization followed by post-modification. Two PGMA polymers with degrees of polymerization (DP) of 100 and 390 were obtained by tuning the ratio of the monomer to initiate. Then, an alkynyl-terminated polystyrene (PS, DP=44) as a hydrophobic side chain was preparedvia RAFT polymerization using an alkynyl-containing chain transfer agent, and an alkynyl-terminated poly(ethylene oxide) (PEO, DP=113) as a hydrophilic side chain was obtained by a nucleophilic substitution reaction of PEO with propargyl bromide. Finally, the two types of side chains were simultaneously coupled onto the PGMA backbone by a copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction, to yield the PGMA-g-(PS44r-PEO113) polymer brush. The results from size exclusion chromatography (SEC) indicated that the grafting ratios of both PS44 and PEO113 were above 90%, with a molar feeding ratio of azide to alkynyl group at 1:1 at 50℃ in dimethyl formamide. A series of polymer brushes with different compositions were obtained by tuning the DP of the backbone and the feeding ratio of the two side chains. All samples have narrow molecular weight distributions (Mw/Mn < 1.20). The emulsifying ability of these amphiphilic polymer brushes in a toluene/water system was characterized. To stabilize toluene/water emulsion, the required amount of PGMA 100-g-(PS44r-PEO113) decreased with an increase in the content of PS44 side chain. A stable emulsion can be formed using PGMA100-g-[(PS44)70r-(PEO113)30] at a concentration of as low as 0.002 wt% versus the weight of toluene. In addition, the polymer brush with a long backbone of PGMA390 was not beneficial to emulsion stability. In comparison with the other polymer brushes, the polymer brush with a short backbone of PGMA100 and a molar ratio of the side chains PS44:PEO113 of 70:30 was found to exhibit the most efficient emulsifying ability.关键词：Polymer brush;Grafting-onto;Click chemistry;Emulsifying function
- 35
- |
- 17
- |
- 0
发布时间：2021-01-27 - 摘要：Mesomorphic propylene/ethylene copolymer (PPR) was obtained by quenching quiescent melt. Its microstructural evolution during continuous heating process was studied by in situ Fourier transform infrared spectroscopy (FTIR), in situ wide/small angle X-ray diffraction (WAXD/SAXS), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). No structural change was detected by WAXD in temperature range of 30-50℃, while IR results showed the molecular segments experienced conformational changes in this temperature range. Considering the presence of large amount of rigid amorphous fraction (RAF) in the mesomorphic sample, the IR results, in combination with DMA and DSC results of annealed mesomorphic samples, implied that this conformational changes may originate from the helical sequences destruction of partial segments in RAF. The helical conformation regularity bands showed different variation trends during heating. The relative intensity of the conformation bands associated with the long helical sequences (n > 13, the number of monomers in helices) showed no evident change in the temperature range of 30-50℃, while the relative intensity of the conformation bands assigned to the helical sequences with medium length ( n ≤ 13) gradually decrease in this temperature range. Therefore, the presence of the helical sequences with n ≤ 13 was deduced in RAF. Variation of fractions of mesophase, α crystal and amorphous phase during the continuous heating process was evaluated by in situ WAXD. The long periods of the sample at different temperatures during heating were derived from SAXS result. The results of IR and XRD indicated that, during the continuous heating process, the tranformation of mesomorphic PPR mainly experienced four stages:helical conformation destruction of partial segments in RAF, transformation of mesophase to α crystal, perfection of imperfect α crystal and melting of α crystal. IR results of isothermal crystallization process showed the transformation from mesophase to α crystal was a nucleation-growth process via heterogeneous nucleation. The activation energy of meso-α transformation in isothermal crystallization process was determined to be ΔE=67.94 kJ/mol.关键词：Polypropylene random copolymer;Mesophase;Infrared spectroscopy
- 37
- |
- 14
- |
- 0
发布时间：2021-01-27
Research Article
- Postal code：100190
- Tel：010-62588927 Email：gfzxb@iccas.ac.cn
- Technical support is provided by Beijing Founder electronics co., LTD 京ICP备05002797号-8
京公网安备11010802024621 - It is recommended to read the content of this site in Chrome&IE9+. Please switch to extreme mode in browser 360.
- Cookies We use cookies to help provide and enhance our service and tailor content. By continuing, you agree to the use of cookies.
0