Full-conjugated rod-rod structures comprising patched-fibrillar, ringed-fibrillar, and double-fibrillar configurations were designed from poly(3-hexylthiophene) (homo-P3HT) and polyaniline (PANI) nanorods in chloroform, p-xylene, and amyl acetate dilute solutions, respectively. Solvent quality, seeding effect, and constituent material were focused while characterizing the developed structures. By exacerbating the processing solvent quality from chloroform to p-xylene, a ringed-fibrillar configuration was detected instead of patched-fibrillar structure. In a poor solvent, double-fibrillar structures were acquired from homo-P3HT chains and PANI nanorods. Towards a poorer solvent, P3HT chains were capable of developing their own crystals by less sensing presence of PANI nanorods as seeds. In another experiment, by copolymerization of both P3HT and PANI with crystallizable PEG blocks, sandwiched rod-rod mixed-brush single crystals were developed. Molecular weight of neither P3HT nor PANI was effective on surface patterning of P3HT/PANI mixed-brushes. Via elevating crystallization temperature, PANI dispersed patterns became more delicate and their width decreased from 80 to 160 nm to 12–30 nm. P3HT backbones were tethered with a extended flat-on orientation onto the PEG substrate at either low or high crystallization temperatures. Beside sandwiched single crystals seeded with homo-PEG tiny crystals, slightly and highly curved half-ring crystals were also developed in the PEG-b-P3HT systems.
Nano-channel single crystals were developed via consecutive growth of various polymer single-crystal channels comprising homo and block copolymers by self-seeding method. Poly(ethylene glycol)-b-polystyrene (PEG-b-PS) and poly(ethylene glycol)-b-poly(methyl methacrylate) (PEG-b-PMMA) block copolymers were synthesized by atom transfer radical polymerization. Self-seeding temperature, concentration, and crystallization time affected the width of the channels. This might provide a new way to investigate directional absorption, diffusion, and immobilization of biomacromolecules on the surface. The crystalline blocks of PEG-b-PS and PEG-b-PMMA diblock copolymers were similar, therefore, the continuity of channel-wire growth was guaranteed. Development of complete square channels next to the channels covered with high molecular weight brushes was infeasible. It was ascribed to a higher hindrance of primarily existing tethered chains on the single-crystal channel. Finally, the consecutive channel-wire single crystals were compared with single-step-grown pyramidal and conic structures. These multilayer crystals grew spirally and formed non-flat channels. The structure and morphology of different crystalline channels were detected by atomic force microscopy (AFM) and small angle X-ray scattering (SAXS). In this work, for the first time, the SAXS data of channel-wire single crystals were reported and they were compared by non-flat channel-like crystals. A profound investigation of PEG-b-PS, PEG-b-PMMA copolymers and PEG homopolymer channel-wire single crystals by SAXS and their comparison with AFM data was a novel work in the field of single-crystal engineering. 相似文献
Poly(ethylene glycol) (PEG), a polymer with excellent biocompatibility, was widely used to form nanoparticles for drug delivery applications. In this paper, based on PEG, a series of pH-sensitive amphiphilic block star polymers of poly(ethylene glycol)-block-poly(ethoxy ethyl glycidyl ether) (PEG-b-PEEGE) with different hydrophobic length were synthesized by living anionic ring-opening polymerization method. The products were characterized using 1H NMR and gel permeation chromatography. These copolymers could self-assemble in aqueous solution to form micellar structure with controlled morphologies. Transmission electron microscopy showed that the nanoparticles are spherical or rodlike with different hydrophilic mass fractions. The pH response of polymeric aggregates from PEG-b-PEEGE was detected by fluorescence probe technique at different pH. A pH-dependent release behavior was observed and pH-responsiveness of PEG-b-PEEGE was affected by the hydrophobic block length. These results demonstrated that star-shaped polymers (PEG-b-PEEGE) are attractive candidates as anticancer drug delivery carriers. 相似文献
The n-type vertically aligned metal doped ZnO nanorods (NRs) and p-type proton acid doped polyaniline (PANI) inorganic/organic heterojunction diodes have been fabricated. Aluminium (Al) and iron (Fe) doped ZnO NRs were grown on seed ZnO layer on fluorine doped tin oxide coated glass substrates by high temperature chemical bath deposition method. The elemental analysis using EDAX confirm doping of Al and Fe in ZnO. The morphology of doped ZnO nanorods and ZnO/PANI heterojunction exhibit well defined uniform nanorod arrays and interface between nanorods and polyaniline matrix respectively. The dark current–voltage curves confirmed the rectifying diode like behaviors of the heterojunctions, whereas under illumination, the junction revealed good sensitivity to UV and visible range with increased current densities. The highest ideality factor and lowest barrier height was found for FeZnO/PANI heterojunction under dark and under light compared to that of ZnO/PANI, AlZnO/PANI. This research is innovative with respect to low cost synthesis of efficient and sensitive hybrid p–n junction diodes and possibly serves as the building blocks for future optoelectronic applications. 相似文献
Compatibilizer plays very important roles in preparing high performance polymer composites, not only for the ternary immiscible polymer blends, but also for the recycled and reused of waste plastics mixture. Generally, the compatibilizers can be used as the toughening agent in blending polymer materials. In the present work, the poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) or maleic anhydride-grafted poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS-g-MA) acts as the compatibilizer and toughening agent for the preparation of R-PET/LDPE/SEBS (70/20/10) ternary blends. It must be pointed that the ternary blends are costlessly and conveniently prepared from the recycled poly(ethylene terephthalate) (R-PET) and linear low density polyethylene (LLDPE) through a melt blending in a co-rotating twin-screw extruder and injection moulded. The morphologies of the ternary blends are characterized by scanning electron microscopy (SEM). It was found that the blends contains reactive or non-reactive compatibilizer, the morphology originates from the LLDPE particles encapsulated by both SEBS and SEBS-g-MA. So, it results to the reduced interfacial tension between of the R-PET and SEBS-g-MA, in which the grafted chains of PET-g-SEBS-g-MA formed through in situ reaction between R-PET and SEBS-g-MA phases. Therefore, core–shell particles with smaller diameter disperse uniformly in the blends. Moreover, the good compatibilization and corresponding morphologies induce in balanced mechanical and thermal properties. DSC analysis show the dispersed phase particles could act as nucleating agent in the R-PET matrix, which results the improvement of the crystallization temperature. And it was also observed the decreased nucleation activity in graft copolymers in the R-PET/LLDPE/SEBS-g-MA blends. Notched Charpy impact strength and elongation at break are improved by the addition of compatibilizer. 相似文献
In the present study, we have discussed the bulk ring opening polymerization (ROP) of rac-lactide (rac-LA) and ε-caprolactone (ε-CL) using Cd(OAc)2. Cd(OAc)2 appeared to be a good catalyst for the polymerization of rac-LA and ε-CL yielding high molecular weight (Mn) polymers with narrow molecular weight distributions (MWDs). The catalytic activity of the system can be increased markedly upon using catalytic amount of BnOH as external alcoholic initiator. There is a first order dependence of the rate constant with respect to monomer concentrations as understood from the kinetic studies. The rate was found to be faster in the presence of BnOH. The polymerization process was controlled. The polymerization proceeded via the coordination-insertion mechanism without BnOH as well as activated monomer mechanism in the presence of BnOH. In the absence of BnOH, the acetyl group initiated the polymerization as understood from the 1H NMR and MALDI-TOF analysis. The benzyloxy group initiated the polymerization in the presence of BnOH. Moderate activity towards the polymerization of ethylene was observed using MAO as alkyl aluminum activator. The polymerization parameters towards the polymerization of ethylene were widely investigated.
Graphical abstract The catalytic activity of Cd(OAc)2 towards the ROP of rac-LA and ε-CL and precatalyst for the polymerization of ethylene were investigated.
The application potential of nanocellulose has been previously hindered by the costly and slow drying methods that this material requires, including freeze/supercritical drying process. The main issue for nanocellulose commercialization is how effectively and rapidly its high water contents (90–99%) can be removed, all of which raise its transportation and processing costs. Oven-drying is the fastest, most economical, and most scalable method for dehydrating nanocellulose, but causes strong interfibrillar aggregation and leads to poor aqueous re-dispersion. Here, we report that the problems of nanocellulose oven-drying are comprehensively overcome by adding tert-butanol (t-BuOH) to the nanocellulose solution at >90%. In a lab-scale comparison, the t-BuOH-mediated oven-drying of aqueous nanocellulose showed lower drying times by a factor of 2–12 compared to water only oven-drying and freeze drying of the same material. The dispersibility of this dried nanocellulose is as high as the never-dried material in terms of particle size, light transmittance, and sedimentation. t-BuOH reduces interfibrillar shrinkage due to the lower surface tension of t-BuOH compared to water, and a remaining t-BuOH/water mixture decreases interfibrillar adhesion and contact.
Graphical abstract This paper suggests a strategy to improve the aqueous re-dispersibility of oven-dried nanocellulose, and to accelerate oven-drying rate.
A well-defined thermo- and pH-responsive ABC-type triblock copolymer monomethoxy poly(ethylene glycol)-b-poly(2-(2-methoxyethoxy) ethyl methacrylate-co-N-hydroxymethyl acrylamide)-b-poly(2-(diethylamino) ethyl methacrylate), mPEG-b-P(MEO2MA-co-HMAM)-b-PDEAEMA, was synthesized by reversible addition-fragmentation chain transfer polymerization (RAFT). The ABC-type triblock copolymer was endowed thermo- and pH-responsive, corresponding to the thermosensitive properties of P(MEO2MA-co-HMAM) and pH-responsive properties PDEAEMA segments, respectively. The thermo- and pH-responsive properties of copolymer aqueous solutions were studied by UV transmittance measurements, dynamic light scattering (DLS), transmission electron microscopy (TEM). The results showed that the N-hydroxymethyl acrylamide (HMAM) content in triblock copolymer affected the lower critical solution temperature (LCST) of the triblock copolymer aqueous solution. The copolymer self-assembled into core-shell micelles, with the thermoresponsive P(MEO2MA-co-HMAM) block and the hydrophilic PEG block as the shell, the hydrophobic PDEAEMA block as the core, in alkaline solution at room temperature. While in acidic media, when the temperature above the lower critical solution temperature (LCST) of the triblock copolymer aqueous solution, the copolymer self-assembled into P(MEO2MA-co-HMAM)-core micelles with mixed hydrophilic PEG and pH-responsive PDEAEMA coronas. Sol-gel transition temperature (Tsol-gel) for the triblock copolymer determined by vial inversion test further indicated that it is dependent on the concentration of the triblock copolymers and solution pH. Copolymer hydrogel loaded with bovine serum albumin (BSA) were used for the sustained release study. The results indicated that the hydrogel was a promising candidate for controlling protein drug delivery. 相似文献
Here, we report the successful synthesis of series of stimuli responsive amphiphilic diblock copolymers (SRABCs) poly(N-isopropylacrylamide-b-N-vinylcarbazole) [poly(NIPAAm-b-NVK)] through reversible addition fragmentation chain transfer (RAFT) polymerization. Copolymers with fixed hydrophilic [poly(NIPAAm)] block length and variable (with three different) hydrophobic [poly(NVK)] block lengths were synthesized and the block length ratio was confirmed from their molecular weight data. The self-assembly nature of synthesized block copolymers was confirmed by determining critical micelle concentration (CMC). Self-assembled block copolymers showed rice-grain like morphology for copolymers having equivalent hydrophobic/hydrophilic chain length but in case of block copolymers having smaller and bigger hydrophobic chain length with respect to hydrophilic chain length displayed vesicular morphology. The thermo and pH responsiveness of the block copolymers was found to be influenced by variation in length and chemical composition of the blocks. Due to their thermo and pH responsiveness resulted self-assembled structures underwent morphology transitions from vesicular and rice grain like to micellar structure in aqueous medium. The probable applications of the studied stimuli responsive amphiphilic diblock copolymers can be found in the nanotechnology and biotechnology are indicated.
Functional polymer brushes of poly(acrylonitrile-g-N,N?-dimethylaminoethyl methacrylate) were efficiently synthesized by a novel approach of combining Cu(0)-mediated controlled/“living” radical polymerization and nitrile click chemistry. The poly(acrylonitrile-g-N,N?-dimethylaminoethyl methacrylate) as a promising material exhibited excellent hydrophile–lipohile balance in the process of self-assembly and could autonomously develop the orderly structure micelle in N,N?-dimethylformamide/water mixture solvent for the potential application of a new drug delivery carrier. In the process of self-assembly, polyacrylonitrile acted as a backbone of the functional polymer brushes due to its hydrophobic feature and poly(N,N?-dimethylaminoethyl methacrylate) as the branch of functional polymer brushes due to its hydrophilic characteristic, which both were prepared by Cu(0)-mediated controlled/“living” radical polymerization with ethyl-bromoisobutyrate as initiator. Poly(N,N?-dimethylaminoethyl methacrylate) containing azide end group was synthesized by substitution reaction of poly(N,N?-dimethylaminoethyl methacrylate) containing bromine end groups with sodium azide in N,N?-dimethylformamide. The click reaction between the nitrile of polyacrylonitrile and the azide group of poly(N,N?-dimethylaminoethyl methacrylate) was carried out under ammonium chloride as catalyst in N,N?-dimethylformamide. The polymer was further confirmed by GPC, FTIR, 1H NMR and TGA. Meanwhile, the micelles with different morphologies were observed by TEM, and the particle diameter distribution of self-assembled micelle from the PAN-g-PDMAEMA brushes was determined by DLS. 相似文献
The polyurethane pressure sensitive adhesive (PUPSA) films have been prepared on polypropylene sheets with coating bars. The topographical information of the dried films is investigated using phase images by using Atomic Force Microscope (AFM) in tapping mode. The film develops a segmental architecture by using different compositions. Various samples of PUPSA comprising of polypropylene glycol PPG (Mn?=?425, 1000, 2000 and 2700 g-mol?1) and hydroxyl terminated polybutadiene HTPB (Mn?=?1984 and 2912 g-mol?1) along with three different isocyanates: 1,6 hexane diisocyanate (HDI), isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (H12MDI) have been used for capturing the images through AFM. The samples contained 40 wt.% of solid content containing different nature of macrodiols and diisocyanate. Due to varying composition, dispersion in domain area along with different contour and dimension has been observed in the images. Apparently, there seems no correlation of spherulites and lamellae in different domains. However, the properties imparted by high molecular weight HTPB resulted in non-adhesive stiff material.
A new approach to the preparation of hydrophobic porous polymers has been proposed. Three series of porous polymers which pores equally well-absorbed as water and organic liquids (benzene and iso-octane) were synthesized by visible light polymerization from compositions based on three different dimethacrylic esters with n-butanol. Three block copolymers based on N-vinylpyrrolidone and 2,2,3,3-tetrafluoropropyl methacrylate, differing in the length of the poly-(2,2,3,3-tetrafluoropropyl methacrylate) block, were synthesized for the purpose of hydrophobization of such porous polymers. A distinctive feature of synthesized block copolymers is that they are soluble only in methanol. It has been found that the treatment of porous polymers only with 2 wt.% of block copolymer methanol solution leads to a decrease water uptake by an order of magnitude, and the absorption of organic liquids does not change. In the course of the study it was possible to obtain a hydrophobic porous polymer sample that has water contact angle θ?=?121° and a low value of the polar component of the surface Gibbs energy (\( {\gamma}_s^p=0.2 \) mJ·m?2). The fundamental possibility of using such material for purification of organic liquids from water is shown.
Coking coal of the same rank from different countries and fields may be distinguished in terms of use value by rating on the basis of seven technological and petrographic characteristics that determine the coke yield and properties: the ash content Ad; the total sulfur content Std; the yield of volatiles Vdaf; the plastic-layer thickness y; the vitrinite reflection coefficient Ro; the content of vitrinite-group macerals Vt; and the basicity index Bb. A range of values and a rating (on a scale from 1 to 10) are established for each of these parameters. Each rating corresponds to a particular score (from 0.1 to 1.0). Ranges of Ad, Std, Vt, and Bb are established for the whole metamorphic series, while ranges of Vdaf, y, and Ro are established for individual ranks and groups of ranks. Altogether, 105 coking coals from Ukraine, Russia, the United States, Australia, and Canada that are used at Ukrainian coke plants are investigated. The range of rating scores and their mean values are determined for individual coal ranks and groups. As an example, three bituminous coals from Ukraine, the United States, and Australia are compared by the proposed method. This method permits objective assessment of the technological value of coal within a single rank and the selection of the best purchase option. 相似文献
A method for the synthesis of particle brushes by grafting polylactic acid onto TiO2 nanoparticle is reported. The efficiency of grafting was enhanced by combining azeotropic separation of water with polycondensation in a single pot. PLA/TiO2 brushes synthesized with different ratio of lactic acid and TiO2 were characterized by various techniques such as FT-IR, XRD, TEM, XPS, 1H and 13C NMR. TEM analysis indicates that the sizes of TiO2 nanoparticles are between 2 and 8 nm. DLS was used to determine overall size of particle brush and average size varied between 59.68–65.83 nm. Zeta potential measurement indicated high stability of water dispersed particles brushes with measured values of ?30.1 to ?37.1 mV for brushes prepared with PLA/TiO2 ratio of 50:1 and 20:1 respectively. The DSC and TGA analysis showed that PLA/TiO2 nanocomposites have good thermal stability.
Three amidosulfobetaine surfactants were synthesized namely: 3-(N-pentadecanamidopropyl-N,N-dimethyl ammonium) propanesulfonate (2a); 3-(N-heptadecanamidopropyl-N,N-dimethyl ammonium) propanesulfonate (2b), and 3-(N-nonadecanamidopropyl-N,N-dimethyl ammonium) propanesulfonate (2c). These surfactants were prepared by direct amidation of commercially available fatty acids with 3-(dimethylamino)-1-propylamine and subsequent reaction with 1,3-propanesultone to obtain quaternary ammonium salts. The synthesized surfactants were characterized by IR, NMR and mass spectrometry. Thermogravimetric analysis (TGA) results showed that the synthesized surfactants have excellent thermal stability with no major thermal degradation below 300 °C. The critical micelle concentration (CMC) values of the surfactants 2a and 2b were found to be 2.2 × 10?4 and 1.04 × 10?4 mol/L, and the corresponding surface tension (γCMC) values were 33.14 and 34.89 mN m?1, respectively. The surfactants exhibit excellent surface properties, which are comparable with conventional surfactants. The intrinsic viscosity of surfactant (2b) was studied at various temperatures and concentrations of multi-component brine solution. The plot of natural logarithm of relative viscosity versus surfactant concentration obtained from Higiro et al. model best fit the surfactant behavior. Due to good salt resistance, excellent surface properties and thermal stability, the synthesized surfactant has potential to be used in various oil field applications such as enhanced oil recovery, fracturing, acid diversion, and well stimulation. 相似文献
A miniature impedance sensor used for field diagnosis of the early failure of coatings has been developed based on microelectronics and electrochemical impedance spectroscopy (EIS). The aging process of polyurethane-based coatings in salt spray test chamber was studied using the impedance sensor. Several critical indexes related to EIS such as phase angle (θ10Hz, θ15kHz), breakpoint frequency (fb), specific capacitance (C10Hz, C15kHz), and impedance modulus (Z0.1Hz) were proposed to evaluate the severity of coating degradation. The results indicated that the impedance sensor could accurately monitor the degradation process of coatings, and once Z0.1Hz?<?106 Ω cm2, fb?>?100 Hz, or θ10Hz?<?20°, the coating may be regarded as completely degraded and fails to protect the metal substrate. 相似文献
One low density polyethylene (LDPE) resin with high-speed extrusion coating property is fractionated through solvent gradient fractionation (SGF) technique using 1,2,4-trimethylbenzene (TMB) and ethyl cellosolve (ECS) as good/poor solvent pair at 115 °C. The pristine sample and its fractions are characterized by high-temperature gel permeation chromatography (HT-GPC) coupled with triple detectors (refractive index RI, light scattering LS, viscometer VIS), 13C–nuclear magnetic resonance spectroscopy (13C–NMR), differential scanning calorimetry (DSC) and successive self-nucleation/annealing (SSA) thermal fractionation. By adjusting the ratio of good/poor solvent, the obtained fractions show their molecular weight from 1.58?×?103 g/mol to 4.76?×?105 g/mol. It is found that the fractions with high molecular weight (fractions 10–13) occupy about 55.85% in resin. Particularly, the molecular weight distribution (MWD) of most fractions is in the range of 1.1–1.2. Each fraction contains more short chain branch (SCB) and less long chain branch (LCB) simultaneously. With increasing the molecular weight, the branching content shows no regular change. The lowest SCB and total branch content regions correspond to molecular weight 1.97?×?104 to 4.10?×?104 g/mol. The melting and crystallization temperatures of fractions firstly increase and then decrease with the molecular weight. The crystallinity decreases gradually from 51.7% to 31.1%. In the SSA thermal fractionation, each fraction shows a broad range of endotherm with multiple melting peaks in DSC curve corresponding to the different methylene sequence length (MSL) (Ln and Lw). The longest Ln (Lw) region occurs in the molecular weight of 8.95?×?103 to 3.14?×?104 g/mol. The relationship between chain microstructure and properties is also discussed.
Graphical Abstract One coating LDPE resin is effectively fractionated by solvent gradient fractionation using TMB/ECS as good/poor solvent pair according to molecular weight. The component with high molecular weight is more than that with low molecular weight. Higher molecular weight and LCB improve the melt strength synergetically, and suitable component with low molecular weight provides better flowability.
Poly(aniline-co-(m-aminobenzoic acid)) was synthesized electrochemically at graphite electrode under galvanostatic conditions. Aqueous electrolyte for synthesis was consisted of HCl and different amount of aniline and m-aminobenzoic acid. The presence of the meta positioned carboxylic group in m-aminobenzoic acid influenced higher co-polymerization potential, different morphology and electrochemical behavior of copolymers compared to polyaniline. Electrochemical activity is achieved by proton exchange in neutral environment that can result in a faster charge/discharge process, which is in the case of PANI limited by slow anion exchange, making this material promising for consideration in super-capacitors and in biological system. 相似文献
In this study, the effect of crosslinking conditions was investigated to obtain insoluble poly(ethylene oxide) (PEO) nanofiber mats having an ultraviolet (UV) initiating and crosslinking agent, pentaerythritol triacrylate (PETA), with various ratios in the presence or absence of UV irradiation at 366 nm. At first, PEO nanofibers were electrospun from 400,000 and 600,000 g/mole molecular weights of PEO and they were compared in terms of diameter and fiber morphology. Whereas applied voltage in the range of 10–25 kV had no significant effect on the fiber morphology, fiber diameters varied by voltage. An increase in the flow rate from 0.25 to 1.00 mL h?1 had an effect in favor of fabricating thicker fibers. The effect of distance to collector on the diameter and morphology was not distinctive. Fibers having irregular morphology and beads appeared with increasing the polymer concentration from 4 to 8 % w/v. Prior crosslinking, electrospinning process at selected conditions was applied to the PEO (600,000) including PETA and PEO-PETA nanofibers were obtained. Besides PETA concentration and UV application, drying conditions before UV irradiation were also found effective to obtain stable fibers in aqueous media. PEO nanofibers electrospun in the presence of 10 % PETA (w/w), dried for 8 days at 37 °C in an air atmosphere and then, irradiated with UV for 50 min were found most stable in aqueous media. However, crosslinking was also achieved in the absence of UV.
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