最新刊期
卷 ， 期 11 ， 2017
- 摘要：As a combination of polymer networks and liquid crystals, cross-linked liquid crystal polymers (CLCPs) exhibit unique properties such as elasticity, anisotropy, self-assembly and molecular cooperation effect. The most important point is that the orientation of liquid crystal (LC) mesogens is strongly coupled with the conformation of polymer backbones, thus change of LC arrangement by stimuli will generate shape change of the whole sample. The macroscopic deformation of CLCPs is reversible because the initial alignment of mesogens is memorized by network. Light is a particularly ideal stimulus since it is a clean energy with wide range of sources and can be precisely and conveniently manipulated in terms of wavelength, intensity and polarization direction. Incorporation of photochromic moieties, such as azobenzene moieties, into CLCPs enables photodeformation of the samples. The reversibletrans-cis isomerization of azobenzenes upon specific light irradiation induces the change of LC order or LC director, and consequently leads to huge deformation of CLCPs. CLCPs containing azobenzene moieties can generate sophisticated movements including contraction/expansion, bending, oscillation and twisting, which directly convert photo energy into mechanical energy. Therefore, the photodeformable CLCPs are fabricated into various soft actuators by rational design, which brings about broad applications in artificial muscles, microrobots, microfluidics and so on. In this review, we mainly describe the development of azobenzene-containing CLCPs, and focus on the influence of molecular structures and alignment on the photodeformation behaviors. Started by introducing the mechanism of photodeformation involving photochemical phase transition and photoinduced reorientation, polyhydrosiloxane and polyacrylate CLCPs were described in details, with emphasis on the processable CLCPs and the novel methods to trigger deformation by visible light and infrared light. The applications of photodeformable CLCPs in the construction of diverse microscopic actuators ane microfluid manipulation are also described. An outlook of existing challenges and opportunities is also given at the end of this review.关键词：Smart material;Liquid crystal polymers;Photodeformable;Azobenzene;Actuators
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发布时间：2021-01-26 - 摘要：Nonfullerene organic solar cell (OPV) is one of the hottest frontiers in chemistry and materials science. China has been leading this hot frontier, and Chinese researchers have made great contribution to this research field. We proposed a novel concept-fused-ring electron acceptor (FREA), established a brand-new, high-performance nonfullerene acceptor system, and invented star molecule ITIC. These FREAs show some advantages:(1) they have high electron mobility similar to those of fullerenes; (2) they exhibit strong and broad absorption, especially in the 700-1000 nm range, and can match with wide-bandgap donor materials to achieve complementary absorption; (3) their energy level can be tuned and thus they match with various high-performance electron donors; (4) their crystallinity and film morphology can be tuned; (5) their synthesis is easy to scale up. Our original and pioneering work has received extensive attention. FREAs are now commercial available. Many well-known research groups across the world have already utilized these FREAs to fabricate high-efficiency OPV. FREA-based OPV now has achieved a power conversation efficiency of 13%-14%, surpassing the fullerene counterpart. Moreover, the FREA-based OPV exhibits better device stability than the fullerene-based counterpart. The emergence of ITIC-like FREAs has overturned predominant position of fullerene acceptor in OPV and is inaugurating the nonfullerene OPV era. In this review, we summarize our progress of FREA design and application in OPV, and give an outlook of the FREAs. We first introduce the background information, concept and working mechanism of OPV; then the advantages and disadvantages of fullerene acceptors are compared with nonfullerene acceptors; and the concept and merits of FREAs are finally discussed. The main text focuses on fused-ring core engineering, electron-withdrawing group engineering and side chain engineering, and we emphasize effects of electron-donating fused-ring cores, electron-withdrawing end groups and side chains on solubility, crystallinity, energy levels, absorption spectra, electron mobilities and photovoltaic properties of FREAs.关键词：Fused-ring electron acceptor;Nonfullerene acceptor;Organic solar cell
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发布时间：2021-01-26 - 摘要：As a class of smart materials, shape memory polymers have gained considerable interest in recent years due to their unique shape changing behaviors. Recent advances in shape memory polymer field have led to the emergence of various exciting applications, including deployable biomedical devices and aerospace structures. Beyond the traditional shape memory effect (one way dual-shape memory effect), the recently emerged properties (triple-, multi-and two way shape memory effects) have drastically expanded their potential application. However, these properties focus mainly on the temporary shape manipulation, and the attention on the permanent shapes has been largely ignored. Unlike the classical thermoplastic and thermoset shape memory polymers, the recently emerged shape memory polymers with dynamic covalent bonds in the network have opened up new opportunities in manipulating its permanent shape. Dynamic covalent polymer networks have long been recognized. Early work focused mainly on minimizing stress relaxation in commercial network polymers to improve their mechanical properties. Since 1990's, the attention has been shifted towards purposeful design of dynamic covalent polymer networks with unique adaptive properties, including self-healing and thermoset reprocessing properties. Several new terms (dynamer, CAN, and vitrimer) have been proposed to emphasize the uniqueness of these polymer networks with dynamic covalent bonds. However, these past efforts have been mostly limited to basic research due to the inherently niche chemistry involved. In this article, we briefly overview recent progresses in dynamic covalent polymer networks and shape memory polymers, which sets the stage for further discussion on recently emerged dynamic covalent shape memory polymer networks. On account of the general applicability of the dynamic covalent bonds (e.g. esters and urethanes) involved as well as unique macroscopic properties (solid state plasticity), we propose that dynamic covalent shape memory polymers can form a third class of shape memory polymers, thermadapt shape memory polymers, alongside the widely known thermoplastic and thermoset shape memory polymers.关键词：Dynamic covalent bond;Shape memory polymer;Stress relaxation
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发布时间：2021-01-26 - 摘要：Helical conformation is a representative secondary structure of biomacromolecules such as DNA and proteins in nature, and plays an important role in the metabolism of organisms. Partially inspired by such natural biological helices, considerable studies have been conducted on the design and synthesis of polymers with stable helical conformations in recent decades. The objectives of these researches are not only to mimic the structure and function of biological helices, but also to widen their applications in many fields, as helical polymers can display optical activity based solely on their main-chain helical conformation. In the past decades, various helical polymers, including polythiophene, polypyrrole, polyaniline and polydiacetylene (PDA), have been synthesized through asymmetric polymerization, which can proceed if chiral monomers, dopants or catalysts are involved, or if some external chiral influence is present. One such external influence is circularly polarized light (CPL), which is inherently chiral and has been regarded as one source for the origin of homochirality in nature. Left-and right-handed CPL have been applied in asymmetry photochemical reactions including photosynthetic or photolytic, and modulated the helical structure in supramolecular assemblies of azobenzene-containing compounds and inorganic nanoparticles. In this paper, CPL-triggered enantio-selective synthesis of optically active polymers, including helical polydiacetylene, chiral coordination polymers, chiral linear and hyperbranched polymers, are reviewed for the great efforts done towards the understanding of the mechanism of CPL-triggered enantio-selective polymerization, and the applications of CPL to induce chiral packing structure into azobenzene-containing polymers, polyfluorene and photo-responsive ketone-containing polymers. The enantioselective interaction between CPL and the enantiomers possibly played a key role in above asymmetric photo-polymerization reactions and the helical structural modulation. The unique features, the advantages of CPL-triggered enantio-selective synthesis of chiral polymers as well as modulation of the helical structure, and the involved mechanism are simply revealed. The progress up to now is summarized and a short prospect concerning the development of CPL triggered asymmetry photo-synthesis and structural modulation have been also provided.关键词：Circularly polarized light;Chiral polymer;Asymmetry photo-polymerization;Modulation of helical structure
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发布时间：2021-01-26
Feature Articles
- 摘要：Monodisperse hard colloid particles, such as SiO2, PS and PMMA colloids, can self-assemble into highly ordered colloidal crystals, and have important applications in a wide range of fields, including photonic crystals, surface patterning, chemical and biosensing, etc. Monodisperse PNIPAM microgel, a soft colloid, can also self-assemble into highly ordered colloidal crystals. Monodisperse PNIPAM microgel particles with size varying from tens of nanometers to several microns can be facilely synthesized by free-radical precipitation polymerization. Thanks to its soft nature and ability to respond to external stimuli, PNIPAM microgels exhibit self-assembly behavior different from that of hard colloids. The volume fraction, which is a key parameter for the crystallization of a colloidal dispersion, can be facilely tuned by temperature. In addition, because of the soft nature of the microgel spheres, microgel colloidal crystals are intrinsically defect-tolerant. Therefore large arrays of colloidal crystals with highly ordered structure can be facilely fabricated from these spheres. The highly ordered structure and the unique responsiveness to external stimili also make the microgel colloidal crystals highly promising for applications in various fields. Here we review the progress in the fabrication of both 3D and 2D microgel colloidal crystals. The general features of microgel colloidal crystals, such as crystallization and melting kinetics, and packing structures, were summarized. Emphasis was put on the recent efforts, e.g., the assembly of binary microgel colloidal crystals, the stabilization of the highly ordered structure of microgel colloidal crystals, the introduction of artificial defects into microgel colloidal crystals, and the assembly of large area, highly ordered 2D microgel colloidal crystals. The applications of microgel colloidal crystals already emerged were also reviewed, including their applications as colloidal atoms to study the process of crystallization and melting of the real crystals, as template to synthesize new materials with ordered structure and microgel clusters with ordered crystalline structure, and optical switcher and sensors.关键词：Microgels;Colloidal crystals;Stimuli-responsivity;Self-assembly
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发布时间：2021-01-26
Reviews
- 摘要：Poly(vinyl acetate)-g-polytetrahydrofuran graft copolymer with silver (Ag) nanoparticles, PVAc-g-PTHF/Ag, could be in situ prepared via combination of living cationic opening polymerization of tetrahydrofuran (THF) with allylBr/AgClO4 initiating system at 0 ℃ with "grafting onto" synthetic approach. Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (1H-NMR) and multi-angle laser light scattering-gel permeation chromatography (MALLS-GPC) were used to characterize the chemical structure, absolute weight-average molecular weight (Mw), molecular weight distribution (Mw/Mn) and branching degree (g') of the resulting PVAc-g-PTHF graft copolymers. The micromorphology and crystallization behavior of the branched PTHF segments were investigated by atomic force microscope (AFM), differential scanning calorimetry (DSC) and polarization microscopy (POM). The effect of the number of PTHF branches (Nb, PTHF) and number-average molecular weight (Mn, PTHF) of the PTHF branches on the micromorphology and crystallization rate of the resulting PVAc-g-PTHF graft copolymers was also investigated. The PVAc-g-PTHF graft copolymer with very high Mw of 4.52×105, relatively narrow molecular weight distribution (Mw/Mn~1.8) and high branching degree of 0.19 was achieved. The Mw of the PVAc-g-PTHF graft copolymers increased remarkably with increases in both Nb, PTHF and Mn, PTHF of the PTHF branches. The glass transition temperature of PVAc backbone (Tg, PVAc) in the PVAc-g-PTHF graft copolymers increased with increasing Mn, PTHF of the PTHF branches by keeping the grafting density constant. The obvious phase separation was formed from the PVAc-g-PTHF graft copolymers and the micromorphology was dependent on the copolymer composition and Nb, PTHF of the PTHF branches by keeping Mn, PTHF of the PTHF branches or branching chain length unchanged. Compared to the unconfined free PTHF macromolecules, the crystallization rate of PTHF branches in the PVAc-g-PTHF graft copolymer was sharply decreased by setting the molecular weights of PTHF segments at the same. The crystallization rate of PTHF segments was increased by increasing the molecular weights of PTHF segments. However, the molecular weight of PTHF presented less effect on its crystallization rate of PTHF branches in PVAc-g-PTHF graft copolymers than that in the unconfined free PTHF homopolymers. Both the melting point of crystalline from PTHF segments and the melting enthalpy of PTHF crystalline increased slightly with increasing Mn, PTHF of the PTHF branches. Moreover, All the resulting PVAc-g-PTHF graft copolymer with different numbers of PTHF branches and different branching lengths or molecular weights of PTHF branches with silver (Ag) nanoparticles show good antibacterial property, suggesting their potential applications in biological and medical fields.关键词：Cationic polymerization;Poly (vinyl acetate);Polytetrahydrofuran;Graft copolymer;Nanocomposite
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发布时间：2021-01-26 - 摘要：A series of well-defined isotactic polypropylene ionomers containing up to 6.47 mol% of-NR3+X- ionic groups were synthesized using dimethyl (pyridylamino) hafnium catalyst, and proved to possess high molecular weight, narrow molecular weight distribution and high isotacticity. The propylene/11-iodo-1-undecene copolymers were taken as intermediates and the iodine groups underwent nucleophilic substitution reaction with triethylamine or N-methylimidazole to give isotactic polypropylene ionomers. N-methylimidazole polypropylene ionomers with different counter ions were prepared by ion exchange reaction, including bis (trifluoromenthylsulfonyl) imide ion (Tf2N-), tetrafluoroborate ion (BF4-) and hexafluorophosphate ion (PF6-). For the synthesized ionomers, their thermal stability, hydrophilic and mechanical properties were studied in depth. First of all, the thermogravimetric analysis results showed that the thermal stability of the N-methylimidazole polypropylene ionomer was significantly higher than that of the triethylamine polypropylene ionomer. It was demonstrated that the N-methylimidazole polypropylene ionomers without β-H could improve the thermal stability of the copolymer. With increasing ion content, the average length of the polypropylene segments decreases, leading to the decreases of crystallization temperature and melting point for the polypropylene ionomers. Secondly, the surface hydrophilicity of the polypropylene ionomers was improved compared with PP. The critical ion contents for behaving as hydrophilic material (with water contact angle < 90°) are 5.42 mol% and 2.97 mol% for triethylamine polypropylene ionomer and N-methylimidazole polypropylene ionomer, respectively. Thirdly, compared with polypropylene, the strain at break of polypropylene ionomers is remarkably increased, which even reaches 900%. For N-methylimidazole polypropylene ionomers, an ion content as low as 0.91 mol% can effectively improve the break strain to 815%. Among these various ionomers, the triethylamine polypropylene ionomers with 2.02 mol% and 2.97 mol% incorporation have good yield stress and break strain simultaneously. Furthermore, the type of the counter ion also has an impact on the yield strength and fracture strength of polypropylene ionomers, of which for the 6.47 mol% ion content, theN-methylimidazole polypropylene ionomer possessing Ⅰ-anions has the highest yield and fracture strength among those with other counter ions (Tf2N-, BF4- and PF6-).关键词：Polypropylene ionomer;Reaction intermediate;Counter ion;Thermal stability;Hydrophilic property;Mechanical property
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发布时间：2021-01-26 - 摘要：We report here a facile and controllable synthesis of bimodal poly(ethylene glycol) (PEG) brushes grafted on silica nanoparticles (NPs) through mixture of good and poor solvents. Methoxypolyethylene glycol (MPEG) (Mw=750 and 4000) was modified in a control manner to prepare epoxide terminated PEG (MPEG-EO). The silica, with well-defined siloxane structure and modified by amino groups, was prepared through silanization coupling reaction with, N-(2-aminoethy)-3-aminopropylmethyldimethoxysilane (AMDS). A two step method was used to get the bimodal polymer brushes grafted onto the nanoparticles (NPs). MPEG-EO with low molecular weights (Mw=750) was first coupled to modified silica in toluene at 110 ℃, the obtained sample was again reacted with MPEG-EO with high molecular weight (Mw=4000) in a mixed solvent of n-decane/toluene. Based on the thermogravimetric (TGA) results, more poor solvent (n-decane) in the solvent mixture resulted in a higher grafting density for MPEG-EO. The grafting density could be controlled easily by changing the composition of the mixed solvent, which was different from the traditional ways to control the grafting density through changing temperature, time and concentration of the coupling agent. The grafting density was found to be about 0.85 and 0.4 chains/nm2 for MPEG-EO with molecular weight of 750 and 4000, respectively. These values are extremely high compared to those previously reported. This high grafting density is explained by the decreased chain dimension of PEG in the presence of poor solvent, which lowers the excluded volume interaction and subsequent inter-chain repulsion, allowing a better packing at the silica surface, and the energy barrier of the surface coupling chemistry is effectively overcomed. This technique, efficiently controllable and facile, provides theoretical guidance for the development of silica NPs and may promote tethering polymer to silica NPs based on the connection between the chain dimension and the grafting density.关键词：Stöber silica particles;Poly (ethylene glycol);Mixed solvent;Bimodal brush
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发布时间：2021-01-26 - 摘要：The anionic molecular brush conjugated polyelectrolyte PFPANa with a lot of grafted side chains was used in this work. Considering the special molecule structure and advanced photophysical properties of molecular brush conjugated polymer PFPANa, the single-step modification of the targeted functional molecules peptides including Arg-Gly-Asp in part of side chains of polymer PFPANa through covalent linkage was completed and the targeted brush copolymer PFPARGD was prepared. Then the anti-cancer drug DOX was electrostatically combined to polymer PFPARGD as a result of the abundant negative charged carboxyl groups in the remained side chains, and the final combined system for targeted imaging and drug delivery based molecular brush conjugated polymer was prepared. The UV-Vis absorption spectra and the zeta potentials of the polymer before and after modified were measured and the results proved the successfully covalent bonding of cyclic peptides c(RGDyK) to the grafted side chains of PFPANa. The experimental results of the fluorescence quenching assay by the positively charged anti-cancer drug DOX showed that the drug delivery system could still loading about 13.3 wt% DOX even after modification. The cell culture experimentsin vitro and the MTT assay in NIH-3T3 cells showed no significant toxicity of the modified polymer PFPARGD. For targeted imaging, the modified polymer PFPARGD was added in both cancer cell and normal cell culture experiments and the laser scanning confocal microscopy images showed that the introduction of targeting ligand c(RGDyK) to the polymer helped to achieve selective recognition of the tumor cells and targeted imaging. The results of flow cytometry showed that the drug delivery system significantly promoted cellular uptake of drug and also showed a good effect of anti-tumor cell growth. This work would provide a new simple strategy for the brush copolymers application in biological drug delivery and molecular imaging of multi-functional system in the future.关键词：Arg-Gly-Asp;Brush-like conjugated polymers;Cellular imaging;Drug delivery
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发布时间：2021-01-26 - 摘要：Peptide (Gly-Pro-Leu-Gly-Ile-Ala-Gly-Gln), which can be specifically degraded by matrix metalloproteinases 2 (MMP-2), was conjugated into polylactic acid (PLA), constructing therefore a new type of MMP-responsive drug delivery system (DDS). Microparticles with core-shell structure were fabricated using coaxial electrospray. PEG was used as the shell and PLA-b-peptide-b-PLA as the core material. The water-soluble PEG shell was quickly removed from aqueous environment and the size of the microspheres was reduced from micron to nanometer scale. Eventually, MMP-2 responsive nanoparticles with a diameter of about 100 nm were obtained through coaxial electrospray-template removal method. MMP-2 response of the nanoparticles was investigated by the change of particle size and morphology with DLS and TEM. After coculturing with MMP-2 protease, the spherical skeleton of the nanoparticles was partly degraded. Meanwhile, part of the degraded particles got aggregated. This is because MMP-2 protease specifically cleave the peptide, resulting in the partly disassembly of the nanoparticles and random reassembling of PLA. Doxorubicin (DOX) was used as a model chemotherapeutic drug and loaded in the core of the nanoparticles. The drug loading content and entrapment efficiency of DOX were 0.326% and 75.3%, respectively. Thein vitro release profile of DOX from the electrosprayed particles was studied. It was found that the encapsulated DOX was released from the nanoparticles, and the release was controlled by the stimulus of overexpressed MMP-2 protease, and the process lasted more than 20 days. The results show that coaxial electrospray-template removal method did not affect the matrix metalloproteinases response of the peptide, and thus the nanoparticles prepared have good MMP-2 responsiveness. Meanwhile, the size of the particles can be modulated by the coaxial electrospray-template removal method, and the nano-sized particles can be simply and effectively achieved. The study suggests that the coaxial electrospray-template removal method is a promising route to the preparation of stimuli-responsive drug delivery system.关键词：Electrospray;Matrix metalloproteinases (MMPs);Core-shell structure;Antitumor
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发布时间：2021-01-26 - 摘要：A novel functionalized α-zirconium phosphate (F-ZrP) was synthesized by phosphazene derivative via in situ intercalation, modified by dicyandiamide (DICY), and then combined with hexachlorocyclotriphosphazene (HCCP) through nucleophilic substitution and further reacted with excessive DICY. Flame retardant silicone rubber composites (FRSR) were prepared via incorporation of F-ZrP and ammonium polyphosphate (APP) with silicone rubber by mechanical blending. The structure of F-ZrP and its morphology in silicone rubber were tested by X-ray diffraction (XRD), transmission electronic microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR) and scanning electronic microscopy (SEM). The results show that the interlayer spacing of F-ZrP was larger compared with that of α-ZrP and phosphazene derivative efficiently combined with α-ZrP. F-ZrP existed with a structure of the intercalated components in FRSR. The effect of F-ZrP on the thermal stability and flame retardancy of FRSR in combination with APP was studied by TGA, vertical burning test (UL-94), limiting oxygen index (LOI) and Cone calorimeter test. TGA results illustrated that an optimal F-ZrP content could improve the thermal stability and char residue. The addition of F-ZrP to FRSR increased the LOI value and enhanced the UL-94 rating. When the total content of the flame retardants was 20 phr and the mass ratio of F-ZrP to APP was 1:19, LOI value of FRSR was increased from 30.0 to 31.4, UL-94 rating was enhanced to V-0, and the peak heat release rate was 265.3 kW/m2. The morphology and structure of the char residue were characterized by SEM. The results suggested that the combination of F-ZrP and APP could make the char residue more stable, compact, and continuous, delaying therefore the volatilization of the decomposition product and inhibiting underlying FRSR from contacting heat and oxygen. These results indicated that there was a synergistic flame retardancy effect in gas phase and condensed phase between F-ZrP and APP for FRSR. Moreover, the mechanical properties could be reinforced with an appropriate content of F-ZrP.关键词：Flame retardant silicone rubber;Zirconium phosphate;Flame retardancy;Mechanical properties;In situ intercalative
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发布时间：2021-01-26 - 摘要：Polyphenylene sulfide (PPS) filter was firstly treated by lauryl sodium sulfate (SDS) to activate the surface of PPS. Because of the electrostatic interaction between SO4- and H+, the potassium permanganate (KMnO4) can transform into nano flower of manganese dioxide by redox reaction on the surface of PPS. The as-prepared functional composites were denoted as nf-MnO2/PPS. The preparation conditions were optimized as follows:mass ratio of KMnO4 to PPS was 0.5 and reaction time 5.5 h. The best preparation condition was obtained through studying the relationship between the mass ratio of KMnO4/PPS, reaction time and the performance of the composites. Field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and SCR activity test were used to investigate the structure, properties and the performance of the composites. FESEM displayed that flake-like MnO2 catalyst was uniformly distributed on the surface of PPS filter material, the as-prepared nf-MnO2 catalyst was coated on PPS material by a redox method, and the results showed that all the composite filter materials presented excellent SCR activity, and the conversion of NO could reach 100% at 180 ℃. In addition, the above-mentioned composite filter material, denoted as nf-MnO2/PPy@PPS, was then covered by a layer of polypyrrole (PPy) compositesvia the interfacial polymerization technique. The structure properties and performance of nf-MnO2/PPy@PPS were also studied using. FESEM, TEM, XPS, FTIR and SCR activity test. Finally, as shown by SCR activity test, the nf-MnO2/PPS, fabricated under the optimized conditions, led to the conversion of NO to 36%-100% in the temperature range of 80-180 ℃. The nf-MnO2/PPy@PPS demonstrated higher mechanical strength of combination and catalytic stability, with slightly decreased conversion of NO.关键词：Polyphenylene sulphide;Polypyrrole;In situ polymerization;Strength of combination;Catalytic stability
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发布时间：2021-01-26 - 摘要：The expression obtained by Nakamura et al. on the radius of gyration of regular comb-shaped copolymers, where both the backbone and the side chains are described by the wormlike chain (WLC) model, was reformulated. It was demonstrated that in certain limiting cases their result conforms to classical expressions of the radius of gyration for a linear WLC (the Benoit-Doty equation), a symmetric star-shaped polymer with WLC arms (the Mansfield-Stockmayer equation), and the branching parameters for symmetric star and regular comb-shaped, derived by Zimm & Stockmayer and Berry & Orofino, respectively, under the assumption of ideal Gaussian chain statistics. Depending on the synthesis method and monomer reactivity, comb-shaped copolymers often possess a non-even distribution of side chains along the polymer backbone. To understand the effects of side-chain distribution on the radius of gyration of comb-shaped copolymers, the method by Nakamura et al. was extended to the case where the side chains were not regularly distributed, but followed a gradient-type distribution, modelled using geometric progressions. On the application side, the afore-derived WLC theory was applied to comb-shaped copolymers made of a negatively charged poly(methacrylate acid) (PMAA) backbone, partially grafted with poly(ethylene glycol) (PEG) side chains, referred to as polycarboxylate-based superplasticizers, or MPEG-type PCEs, in cement and concrete research. Particular focus was placed on rational choices of model parameters, which is an essential step in applying theory to practice. Based on data in the literature and model fitting, methods and recommended parameter values were developed for converting experimental characteristics of MPEG-type PCEs to their corresponding WLC model parameters. Furthermore, effects of backbone stiffness, side-chain distribution, side-chain persistence length, and grafting density on the unperturbed radius of gyration were explored in detail in the relevant range of parameter values of MPEG-type PCEs. The present work may shed light on how to arrive at a compromise between a mathematically tractable theory and its application to complicated industrial polymeric products. Although the present model is still rather idealized in the sense that it does not take into account of detailed monomer-monomer, monomer-solvent interactions such as the often discussed excluded volume and electrostatic interactions, it can serve as an important reference for assessing the contributions of those complicated interactions in further studies.关键词：Comb-shaped copolymer;Wormlike chain;Radius of gyration;Persistence length;Polycarboxylate-type superplasticizers
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发布时间：2021-01-26 - 摘要：Suspensions were prepared by mixing hydrophilic fumed silica (FS) with low-molecular polyethylene glycol (PEG, weight-averaged molecular weight 400). By differential scanning calorimeter and broadband dielectric spectrometer, influences of FS volume fraction (φ) on α-relaxation and crystallization behaviors of bulk PEG phase were investigated. Furthermore, influences of φ on the linear and nonlinear rheology behaviors of the suspensions were also investigated using stress-controlled rheometer. For the bulk PEG phase, α-relaxation is retarded and glass transition temperature (Tg) is increased due to the addition of FS. On the other hand, FS significantly retard the diffusion of global PEG molecules, which leads to a great increase in viscosity of the suspensions along with significant reductions in crystallization and fusion enthalpy of the bulk PEG phase. The suspensions demonstrate different rheology and crystallization behaviors with varyingφ. The low-filled suspensions exhibit an apparent sol-like rheological response, in which FS plays a nucleating role to promote PEG crystallization. However, the high-filled suspensions apparently behave like gels, in which FS restrains the chain diffusion and crystallization. The role of FS changes in the vicinity of φ=0.16, where the system undergoes an apparent sol-to-gel transition. In the close vicinity of this transition, the nonlinear dynamic rheology shows the most obvious strain hardening, while the linear dynamic rheology demonstrates the most significant frequency-dependence. Due to the extremely complicated nonlinear rheological response of the suspensions, it is hard to observe the pure hydrodynamics region experimentally, and in the frequency range achieved, complex viscosity (η*) as a function of φ at given frequencies does not fit classical hydrodynamics equations that do not consider the effect of nanoparticles on the polymer chains diffusion. To account for the effect of nanoparticles on the diffusion of PEG chains, data of liner dynamic rheology of the suspensions are shifted horizontally and vertically to create master curves with pure PEG as the reference. The creation of master curves reveals that FS greatly retards the diffusion of global PEG chains in the constrained bulk phase, which plays a major role in the reinforcement and dissipation of the suspensions. In addition to the dynamically retarded bulk PEG chains, both the inter-particle friction in the low-filled sols and the in-cage rattling motion of nanoparticles in the high-filled gels additionally contribute to the dissipation behavior of the suspensions, resulting in the complicated dynamic rheological behavior.关键词：Fumed silica;Polyethylene glycol;Interfacial layer;Shear thickening;Molecular relaxation
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发布时间：2021-01-26 - 摘要：Solvent evaporation has proven to be a remarkably successful tool for directing the self-assembled nanostructures of block copolymers, yet the mechanisms of how its control parameters affect the nanostructure and its principles governing the structural formation remain poorly understood. In this paper, the simulated annealing and Monte Carlo method are used to study the self-assembly of cylinder-forming diblock copolymer films confined between two flat walls and under solvent evaporation on a simple cubic lattice model. Specific attention is paid to the orientation control of cylinders in the films. For films confined between two identical homogeneous flat walls, the effects of surface preference, solvent selectivity and swelling ratio on the cylinder orientation are investigated. The surface preference window for the formation of perpendicular cylinders is wider with a solvent of stronger affinity for the majority block, especially when the swelling ratio is higher. Whereas a neutral solvent leads to the formation of perforated lamellae, making the surface preference window for the formation of perpendicular cylinders narrower. For films under solvent evaporation, the effects of surface preference and film thickness on the resulting morphology of films are also studied. The maximum surface preference that leads to the formation of perpendicular cylinders varies with film thickness cyclically. The surface preference window for the formation of perpendicular cylinders after solvent evaporation is wider than that after thermal annealing, indicating that perpendicular orientation is promoted by the solvent evaporation. To unravel the mechanism of perpendicular cylinders forming, film morphology at different stages during solvent evaporation is plotted and compared to those of the films swollen to the corresponding thicknesses. It is noted that cylinder orientation after solvent evaporation is the same as that in a swollen film with a swelling ratio at which the spheres in the film begin to merge into cylinders. The surface preference window for the formation of perpendicular cylinders in this swollen case is determined by the commensurability between the film thickness and the bulk period.关键词：Diblock copolymer films;One-dimensional confinement;Solvent evaporation;Cylinder orientation
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发布时间：2021-01-26
Research Article
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