最新刊期
卷 ， 期 3 ， 2014
- 摘要：The relationship between electric field setup and the resultant electrospun nanofiber deposition shape and morphology was studied by using totally four types of electrospinning apparatus including conventional electrospinning setup (the receiver is grounded or connected with negative power),inverse field electrospinning setup,non-contact electrospinning setup,and the 20% PVA(polyvinyl alcohol)solution was electrospun at the same applied voltage,receiving distance,spinning needle diameter,temperature and relative humidity,and the resulting nanofiber deposition shape and morphology were observed via photography.Also in this study,ANSYS finite element software was employed to simulate and analyze the field distribution on the four types of setups,and the influence from ion concentration of spinning solution on the resultant nanofiber morphology on different electrospinning apparatus was interpreted by introducing the electrochemistry theory.The reasons for the differences were analyzed,laying theoretical foundation for the development of new type of electrospinning equipment.关键词：Electrospinning;Ionic concentration;Non-contact electrospinning;Electrochemistry;Electric double layer
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发布时间：2021-03-19 - 摘要：A novel difunctional monomer p-propynyloxyphenyl-2-oxazoline(POPO) was synthesized and characterizaed by 1H-NMR,FTIR,GC-MS and elemental analysis.The curing behavior and thermal performance of POPO were explained by DSC and TGA.Consequently,its melt point is 120 ℃,the initial curing temperature(Ti)is 200 ℃ and the cured POPO shows a good thermal stability:the 5 wt% weight loss temperature is 321 ℃,the residual weight is 28 wt% at 900 ℃.Bisphenol A-benzoxazine(BZ)/POPO resins were prepared via solution blending process,and the curing mechanism and thermal properties of the cured BZ/POPO resins were studied.First,the ring-opening reaction of benzoxazine occurred,then the phenolic hydoroxyl groups generated by the ring-opening reaction of benzoxazine rings reacted with oxazoline rings.While,the polymerization reaction of the alkynyl group of POPO happened throughout the whole reaction process.The results of DSC,TGA and DMA analyses showed that the thermal properties and dynamic mechanical properties of the cured BZ/POPO resins were improved respectively for the cross-linking density of the cured BZ/POPO resins was increased.When the mass fraction of the POPO was 10 wt%,the initial curing temperature(Ti),residual weight and glass transition temperature(Tg) of the cured BZ/POPO resin were 180 ℃,40 wt% and 186 ℃ compared with those of pure bisphenol A-benzoxazine resin (215 ℃,28 wt% and 166 ℃ respectively).POPO is a kind of good modifier for bisphenol A-benzoxazine resin by which the thermal properties and dynamic mechanical properties of the cured BZ resin can be improved to meet the demand of versatile applications.关键词：Oxazoline;Benzoxazine;Curing mechanism;Thermal properties
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发布时间：2021-03-19 - 摘要：The molecular weight (Mw) of the lignin-based superplasticizer GCL1-JB was determined by static light scattering (SLS) and gel permeation chromatography (GPC).Results showed that the Mw value determined by SLS (Mw,SLS) was much larger than that determined by GPC (Mw,GPC) because of the polyelectrolyte effect and aggregation behaviors.To determine the real Mw of GCL1-JB by SLS,NaCl was added into the GCL1-JB solutions to restrain the polyelectrolyte effect,and the GCL1-JB dissolved in NaCl solution was further filtered by micro-filtration membrane with suitable pore size to remove the GCL1-JB aggregates.During DLS measurement of GCL1-JB,there existed two diffusion peaks:a fast mode and a slow mode.The fast mode is related to the GCL1-JB single molecules,and the slow mode is related to the polyelectrolyte effect and the GCL1-JB aggregates.The slow mode was inhibited gradually by adding NaCl followed by filtering,and finally disappeared when NaCl concentration reached 0.1 mol/L.With disappearance of the slow mode,Mw,SLS was determined to be 121300,which was considered to be the real Mw of GCL1-JB single molecules. Mw of GCL1-JB determined by SLS at this stage was still larger than that determined by GPC because of the difference in conformations between GCL1-JB and GPC standards (NaPSS).The conformations of GCL1-JB was more curling than that of NaPSS; therefore,when NaPSS was used as the GPC standard,the Mw,GPC was smaller than the true Mw of the GCL1-JB.This work provides a method to determine the true Mw of GCL1-JB,which is significant for determining the absolute Mw of lignin and its derivatives that having polyelectrolyte effect and aggregation behaviors.关键词：Lignin;Molecular weight;Laser light scattering;Gel permeation chromatography;Polyelectrolyte effect;Aggregation
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发布时间：2021-03-19 - 摘要：An amphiphilic reversible addition-fragmentation chain transfer (RAFT) agent containing alkenyl vinylic bonds was synthesized by the sequential RAFT polymerization of acrylic acid and asymmetric divinyl monomer 4-((but-3-en-1-yloxy)methyl) styrene,where the pendent inert alkene bonds were embedded between hydrophilic and hydrophobic block.Styrene(St) solution polymerization and mini-emulsion polymerization mediated by the amphiphilic RAFT agent were implemented,aiming at investigating the effects of polymerization methods on the reactivity of the pendent alkene groups.During solution polymerization,the alkene groups show extremely low reactivity and remained intact in the studied St conversion range(68.6%).The resulting polymers retained quantitative alkenyl groups and had predictable molecular weights together with narrowed molecular weight distributions.These findings proved the living characters of the solution polymerization.A different case was found for RAFT mini-emulsion polymerization that copolymerization of alkenyl group with St occurred since the early stage of reaction,leading to the coupling between polymer chains or RAFT agents.As a result,experimental molecular weights positively deviated from theoretical values,and polymers had rather high polydispersity index.It was speculated that the reaction of alkenyl groups was enhanced as a result of the adsorption of amphiphilic RAFT agent onto the surface of monomer mini-droplets,since it could cause an increase in either the concentration of propagation radicals or the concentration ratio of alkene group to St in the oil-water interface layer of droplets.关键词：Reversible addition-fragmentation chain transfer;Solution polymerization;Mini-emulsion polymerization;Asymmetric divinyl monomer
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发布时间：2021-03-19 - 摘要：Abstract Two novel poly(arylene ether)s with sulfonic acid groups attached on pendent napthyl rings were prepared from bis(3,5-dimethyl-4-hydroyphenyl)--naphthyl methane via nucleophilic aromatic substitution polycondensation with bis(4-fluorophenyl) ketone and bis(4-fluorophenyl) sulfone,followed by sulfonation with chlorosulfonic acid.The sructrues of polymers were confirmed by 1H-NMR and FTIR.The results showed that the sulfonation position took place only on the pendent naphthalene ring due to the specially designed molecular structure.The sulfonated poly(arylene ether)s can be dissolved in DMAC,DMF,DMSO and other common organic solvents,so they can be cast into smooth and flexible films.The proton conductivity of film 3b can reach 0.042 S/cm at 80 ℃,equal to the conductivity of Nafion 117 in the same condition.In addition,the swelling rate of these polymers is less than 11.5% and the tensile strength is more than 39 MPa.In a word,the films of side-chain-type sulfonated polymers showed high proton conductivity,high mechanical strength,low swelling rate and good oxidation stability,which can meet the requirement of proton exchange membranes.And the two novel poly(arylene ether)s are expected to be used as proton exchange membranes for fuel cells.关键词：-Naphthyl moieties;Sulfonated poly(arylene ether)s;Proton membranes;Oxidation stability
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发布时间：2021-03-19 - 摘要：The solution behaviors of sulfonated alkali lignin-based polymers (SBAL) at different pH values were investigated by means of dynamic light scattering and transmission electron microscopy (TEM).The results indicated that with the increase of pH,the hydrophilic functional groups of SBAL:sulfonic,carboxyl and phenolic hydroxyl groups were ionized gradually.With the increase of pH,the molecular configuration of SBAL changed from coil chain to extended chain.Moreover,the adsorption characteristics of SBAL on solid/liquid interface at different pH values were determined using a quartz crystal microbalance with dissipation monitoring (QCM-D) and electrostatic layer-by-layer self-assembly,as well as UV-Vis spectroscopy and atomic force microscopy (AFM).The results showed that with the pH increased from 3 to 12,the adsorption amount of SBAL on gold plate and quartz slide decreased at first and then increased,the lowest amount was at pH=9.The adsorption configuration changed from rigid to soft,tight to loose and then tight again.The adsorption conformations of SBAL on gold plate and quartz slide with poly(diallyldimethylammonium chloride) (PDAC) showed mushroom-like structure,pancake-like structure and polymer brushes in the acidic,neutral and alkaline conditions,respectively.Cation- interaction was the main driving force between SBAL and PDAC in the acidic and neutral conditions and the adsorption strength was weak.However,electrostatic interaction played an important role between SBAL and PDAC in the alkaline condition and the adsorption strength was strong.关键词：Sulfonated alkali lignin-based polymer;Adsorption;pH
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发布时间：2021-03-19 - 摘要：A facile method was provided by using biopolymers to mediate and synthesize 3D graphene oxide(GO) based gels.Bovine serum albumin(BSA),chitosan (CS) and deoxyribonucleic acid (DNA) were chosen as bio-polymeric cross-linking agents to approach the gelation,and the gels were freeze-dried to obtain GO/biopolymer gels.The chemical and physical properties of the GO/biopolymer gels were tested by scanning electron microscope (SEM),atomic force microscopy (AFM) and zeta potential measurements.The results indicate that these obtained gels have well-defined and interconnected 3D porous network,which allows the adsorbate molecules to diffuse easily into the absorbent.Fourier transform infrared (FTIR) spectra confirmed that these biopolymers have been immobilized into the GO gels successfully.Then,the hybrid gels were used for the removal of cationic dyes from waste water.Adsorption experiments showed that the GO-biopolymer gels had good adsorption ability for the cationic dyes; meanwhile,the hybrid gels also presented certain amount of adsorption capability for anionic and nonionic toxic molecules.The influence of contacting time,initial concentration and pH value on the adsorption capacities of the prepared GO-biopolymer gels was also studied,and the desorption ratios were also investigated.The GO-biopolymer gels displayed an adsorption capacity as high as 1100 mg/g for MB dye.Furthermore,the adsorption kinetics and adsorption isotherm of MB on the GO-BSA,GO-CS and GO-DNA gels were studied and discussed in detail.As a result,the experimental data of MB adsorption turned out that it fitted well with the pseudo-second-order kinetic model and the Langmuir isotherm,which indicated that the adsorption process was well-regulated monolayer adsorption.Besides,the initial adsorption process was pore diffusion while the later adsorption process was intraparticle diffusion.关键词：Graphene oxide;Biopolymers;Gel;Adsorption;Wastewater treatment
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发布时间：2021-03-19 - 摘要：Based on luminescence quenching of chromophoric probes in oxygen permeable polymer matrix,pressure sensitive paint (PSP) and its devices have been developed as a kind of functional materials in recent years.The pressure sensitivity of PSP not only depends on the probe molecules,but also on the polymer matrix.In this work,tetrakis(pentafluorophenyl)porphyrin platinum (PtTFPP),as a luminescent probe,was composed with polydimethylsiloxane (PDMS),polymethylphenylsiloxane (PMPS),polymethyltrifluoropropylsiloxane (PFS) and trifluorochloroethylene-vinyl acetate copolymer (PFC) respectively,and then their luminescence quenching behaviors were measured at an excitation of =365 nm with various oxygen concentrations from 0% to 100%.The ratio I0/I100 is used as oxygen sensitivity of PSP films,where I0 and I100 represent the fluorescence intensities from films exposed to 100% nitrogen and 100% oxygen,respectively.The I0/I100 values of the PtTFPP-based films are evaluated.It is found that the plots of I0/I versus [O2] with identical Ksv are obtained and a two-site model fits the experiment data very well for the PtTFPP/polymer systems,except PtTFPP/PFC films.The values of I0/I100 and Ksv for such materials increased with increasing the oxygen permeability of the polymer matrix,i.e.PDMS PMPS PFS PFC,which is identical with theoretical reasoning.Therefore it could be concluded that the oxygen quenching for the PSP materials in this work showed a diffusion-controlled mechanism.关键词：Pressure sensitive paint;Polymer matrix;Chromophoric probe;Luminescence quenching;Oxygen pressure sensitivity
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发布时间：2021-03-19 - 摘要：The hybrid copolymerization of -caprolactone(CL) and N-phenylmaleirnide with 1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)-phosphoranylidenamino]-25,45-catenadi(phosphazene) (t-BuP4) as catalyst was presented.The reaction process and the structure of the polymers have been characterized by nuclear magnetic resonance spectroscopy(NMR),Fourier transform infrared spectroscopy (FTIR),gel permeation chromatography(GPC) and themogravimetric analysis(TGA).The results show that NPMI incorporated into the copolymers via the breakage of vinyl bonds,and t-BuP4 displays high catalytic activity for the hybrid polymerization of CL with NPMI.The resulted polymers were copolymers but not the mixture of CL and NPMI homopolymers.Studying the effect of polymerization conditions including CL to NPMI ratios and temperatures shows that the molar ratio of CL units in the copolymer increased with the increasing of CL monomers,but that was no more than 38.4%.Increasing the reaction temperature from 0 ℃ to 50 ℃,the composition and the molecular weight of the resulted copolymers have a slight change.TGA measurements demonstrate that such a random copolymer exhibits a decomposition temperature between that of either homopolymer.关键词：Hybrid copolymerization;-Caprolactone;N-phenylmaleirnide
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发布时间：2021-03-19 - 摘要：The carboxymethyl chitosan (CMC)/sodium alginate (SA) semi-interpenetrating polymeric network (semi-IPN) hydrogel was prepared by incorporating SA into cross-linked CMC using genipin (GP) as the cross-linker.The semi-IPN formation and cross-linking reaction mechanism of the genipin-cross-linked CMC/SA hydrogel were confirmed by means of the instrinsic viscosity measurement and Fourier transform infrared spectroscopy (FTIR).According to the measurements of mechanical properties,when the weight ratio of CMC and SA was 5:5,the tensile strength of the CMC/SA hydrogel in dry state reached 59 MPa,which was about 47.5% and 63.9% higher than that of pure CMC (40 MPa) and SA (36 MPa).The largest elongation at break of the CMC/SA hydrogel was 13.0% when SA content was 60%.The influences of the pH values and cross-linking agent concentration on the swelling characteristics of the semi-IPN hydrogel were investigated in detail.Experimental results show the swelling ratio of the semi-IPN hydrogel decreases with increasing pH values at pH 3.0,whereas at pH 3.0,the swelling ratio increases with increase of pH values.At pH=3.0,the swelling ratio is the lowest (186%),while at pH=9.0,the swelling ratio is the highest (886%).It exhibits significant pH-sensitivity.In addition,the semi-IPN hydrogel exhibits reversibility and rapid response in swelling to pH changes.This type of semi-IPN hydrogel may be useful for stimuli-responsive drug delivery or as alternative sorbents in the removal or separation of dyes.关键词：Carboxymethyl chitosan;Sodium alginate;Genipin;Semi-IPN;pH-sensitive
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发布时间：2021-03-19 - 摘要：The sericite mica was first treated by heating and acid dipping followed by LiNO3 treatment.The organophilic clay was subsequently achieved by inorganic-organic ion exchange in the hydrothermal reaction of LiNO3-treated sericite mica with intercalating agent-hexadecyltrimethylammonium bromide solution.Finally, a series of polyimide (PI)/sericite mica composites were prepared via in situ polymerization reaction.The effects of the reaction temperature and the amount of intercalating agent added on the modification of sericite mica were investigated.The structures of modified and original sericite mica were systemically characterized with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), showing the best intercalating effect was observed when the reaction temperature was 180 ℃ and the amount of intercalating agent added was fifteenfold the cation exchange capacity (CEC).Under the above reaction conditions, the d002 basal spacing of the sericite mica was increased from 0.99 nm to 2.77 nm.The structure of the composites was investigated by XRD and high resolution transmission electron microscopy (HRTEM), and the thermal stability and the mechanical properties were studied by means of thermogravimetric analysis (TGA) and mechanical property measurements, indicating that the PI/original sericite mica composite was a simple physical blend of PI and pure sericite mica, while the PI/organic sericite mica nanocomposites was an exfoliated structure with 5 wt% loading, and the nanocomposites with the content of 1 wt%~7 wt% organophilic sericite mica exhibited no observable peaks in the range of 0.5~10 (2), which revealed that majority of the d002-spacing of organophilic sericite mica had been intercalated to a distance of more than 4.42 nm (21).When the mass ratio of sericite mica and PI was 5:100, the tensile strength, Young's modulus and elongation at break of the PI/organic sericite mica nanocomposites are 1.79, 1.40 and 1.83 times those of the PI/original sericite mica counterpart, respectively.The thermogravimetric analysis showed that the thermal stability was tremendously enhanced with the increasing organophilic sericite mica content and the nanocomposites with 7 wt% loading revealed a 36 K increment in T5 (the temperature at 5 wt% weight loss) compared with pristine PI.关键词：Sericite mica;Modification;Hexadecyltrimethylammonium bromide;Polyimide;Composites
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发布时间：2021-03-19 - 摘要：A series of long glass fiber reinforced polystyrene composites with different contents of compatibilizer were prepared by using a self-designed impregnation device. The matrix resin is polystyrene, the compatibilizer is polystyrene grafted maleic anhydride, and the toughening agent is a thermoplastic polyurethane elastomer. Effects of compatibilizer content on performance of long glass fiber reinforced polystyrene composites were studied. The results demonstrates that the storage modulus of long glass fiber reinforced polystyrene composites first increases and then decreases with increasing compatibilizer content, which predicts that the mechanical properties of long glass fiber reinforced polystyrene composites first increase and then decrease with increasing compatibilizer content; the tan values of long glass fiber reinforced polystyrene composites first decrease and then increase with increasing compatibilizer content, which demonstrates that the compatibility of the composites first increases and then decreases with increasing compatibilizer content; SEM results demonstrated that glass fibers were coated by the matrix resins, when the compatibilizer was added into the composites, and the compatibility mechanism was analyzed.关键词：Compatibilizer;Polystyrene;Long glass fibers;Toughening agent;Composites
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发布时间：2021-03-19 - 摘要：A molecularly imprinted polymer (MIP) with specific molecule identification properties for L-carnitine was synthesized on the surface of modified silica, using L-carnitine as template molecule, ethyleneglycol dimethacrylant (EGDMA) as the cross-linker, methacrylic acid (MAA) as functional monomer and 2,2'-azobisisobutyronitrile (AIBN) as the initiator respectively. The binding effect of the complex formed between the template and the functional monomer were obtained by UV spectrophotometry. The MIP was characterized by IR spectroscopy and SEM, and the results demonstrated the formation of a grafted polymer layer on the modified silica gel surface.The absorption kinetics experiments indicated that compared with non-imprinted polymer, MIP showed better recognition ability and absorptivity. Moreover, the polymer was investigated in static adsorption equilibrium experiments and the Scatchard analysis to evaluate the adsorption characteristics. The results showed that the homogeneous binding sites were formed in the MIP, and the dissociation constants (Kd) and the apparent maximum number (Qmax) of binding sites were estimated to be 2.7610-4 mol/L and 71.00 mol/g, respectively.The selective binding experiment for substrates shows that the affinity and selectivity of the MIP for L-carnitine are higher than those for D-carnitine and two other different substrates. MIP also showed good selectivity for L-carnitine through the resolution experiments.关键词：Surface-molecular imprinting;L-carnitine;Methacrylic acid;Chiral recognition;Specific adsorption
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发布时间：2021-03-19 - 摘要：An amiphiphilic phosphorylcholine based copolymer (PMC) bearing hydrophilic phosphorylcholine (PC) and hydrophobic cholesteryl (Chol) side groups was designed and prepared by free radical polymerization. It was used to modify the hydrophilic feature of the surface of microporous polypropylene hollow fiber (PPHF) membrane using another phosphorylcholine based copolymer PML (containing n-dodecyl hydrophobic side groups) as control.1H-NMR and DSC were used to determine the chemical structure of the obtained phosphorylcholine based copolymer. The surface chemical composition was measured by X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance infrared spectroscopy (ATR-IR). The hydrophilicity of the modified membranes and reorganization behavior of surface functional groups were characterized by static and dynamic contact angle, respectively. The results showed that the ratio of the monomer units in the amphiphilic random copolymers were similar to the ratios in feed. The melting temperature of PMC (190.5 ℃) was much higher than that of PML (90.3 ℃). Compared with the virgin PPHF membrane surface, the static water contact angle of PMC-PPHF was greatly decreased from 117 to 44. Moreover, when PMC-PPHF was heated at 100 ℃ for 2 h and placed in air at room temperature for 8 months, respectively, the water contact angle and the relative amount of P element almost did not change, which indicated the improved surface stability in comparison with PML-PPHF.关键词：Phosphorylcholine;Hydrophilic modification;Surface stability;Reorganization of surface functional groups
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发布时间：2021-03-19 - 摘要：-Methacryloxypropyltrimethoxysilane (MPS) was grafted onto the surface of attapulgite rod to obtain the modified particles AT-MPS. Subsequently, the graft polymerization of methyl methacrylate on the surface of attapulgite was realized by using reversible addition-fragmentation chain transfer (RAFT) radical polymerization method, using cyanopropyl dithiobenzoat (CPDB) as the RAFT chain agent and azodiisobutyronitrile (AIBN) as the initiator, and the grafted particles AT-g-PMMA with a grafting degree of 16.33% were prepared. The modified particles were characterised by FTIR and TGA respectively. The polymerization kinetics and grafting degree of graft polymerization with different amounts of initiator (azodiisobutyronitrile, AIBN) and CPDB were discussed in detail. Experimental results showed that MPS was grafted onto the surface of attapulgite rod crystals, and PMMA was grafted via RAFT polymerization successfully. A longer graft polymerization time and a higher grafting degree were obtained in the presence of RAFT chain transfer agent. Polymerization deviated from linear kinetics behavior due to the premature termination of graft polymerization caused by accelerated bimolecular termination reaction as the AIBN amount increased. The controllability was improved when CPDB was excessive, but polymerization rate and ultimate conversion were decreased obviously. The relatively suitable polymerization conditions are: [MMA]/[CPDB]/[AIBN]=400/1/0.5 and polymerization temperature=70 ℃. Under these conditions, polymerization was living and controllable, and PDI of PMMA in solution was 1.2~1.3. The grafting degree of PMMA decreased with the excessive AIBN or CPDB.关键词：Attapulgite;Methyl methacrylate;RAFT polymerization;Kinetics;Grafting degree
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发布时间：2021-03-19 - 摘要：Well-defined tadpole-shaped hybrid copolymers including POSS-poly(trifluoroethyl acrylate) (POSS-PTFEMA), POSS-poly(trifluoroethyl acrylate-b-methyl methacrylate) (POSS-PTFEMA-PMMA) and POSS-poly(methyl methacrylate-b-trifluoroethyl acrylate) (POSS-PTFEMA-PMMA) were used as precursors for the formation of well-ordered honeycomb porous films via breath figure method, and the film morphologies were characterized by scanning electron microscope (SEM). The effects for porous formation including molecular architectures, solvents utilized, solution concentrations and substrates selection were investigated, and the hydrophobic and oleophobic properties along with thermal resistance were also analyzed simultaneously. It was found that all of the three hybrid copolymers were good candidates for honeycomb films and could form highly ordered porous structures under solution concentrations ranging from 5 mg/mL to 30 mg/mL, and the pore sizes increased with the solution concentrations. The regularity of pore structures would also increase with the inducing of TFEMA groups. Compared with dichloromethane, toluene and tetrahydrofuran, chloroform was proven to be the robust solvent to form the well-ordered porous film owing its suitable volatility as well as the solubility for the hybrid copolymer. With the substrate changed from the glass slide to silicon wafer, the average pore sizes decreased, accompanying a reduction of regularity. The obtained films were proven to have well heat-resistance, hydrophobicity and oleophobicity, with contact angles for water in the range of 98~116 and 43~66 for dihexyl.关键词：Breath figure method;Honeycomb porous film;Tadpole-shaped hybrid polymer;POSS;Trifluoroethyl acrylate
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发布时间：2021-03-19 -
Studies on Lamellar Thickening of A Four-arm Poly(ethylene oxide) Using Small-angle X-Ray Scattering
摘要：Studies on the lamellar thickening of a 4-arm poly(ethylene oxide) with Mn=5000 for each arm are reported. The samples were prepared by quenching from 70 ℃ to 10 ℃. Small-angle X-ray scattering (SAXS) was used to track the variation of lamellar structure during heating process. Then the SAXS data were further analyzed using one-dimensional correlation function. The following parameters, such as long period, linear crystallinity, crystalline layer thickness and amorphous layer thickness, were determined. Their changes with increasing temperature suggest three temperature regions. Region Ⅰ is in 26~45 ℃. There are three broad scattering peaks with low scattering intensity. They correspond to lamellae with different thicknesses. The crystalline layer thickness of the dominated lamella is about 9.3 nm. Importantly, the parameters mentioned above remain unchanged in Region Ⅰ. Region Ⅱ within 45~52 ℃ is a transition one. The main peak of the SAXS curves turns into two. The long period, linear crystallinity, crystalline layer thickness and amorphous layer thickness began to increase. Region Ⅲ (52~60 ℃) is a thickening region within which the crystalline layer thickness clearly increased with increasing temperature. At 60 ℃ its value is 15.8 nm. These observed results found in the three regions were further explained based on the role of metastable states of polymer lamellae. Within region Ⅰ macromolecules were in a frozen state, thus it was impossible to detect any change related to the lamellar structure. Within region Ⅱ, the temperature is higher enough to let some thin crystalline layers melt and then the melted macromolecules would recrystallize around the thicker ones. In region Ⅲ the continuous melting-recrystallization process proceeds until the melting point of the sample. The observed melting-recrystallization process reflects the metastability of polymer lamellae: Thinner lamellae are in a metastable state with a lower stability, thus will melt to recrystallize to form thicker lamellae with a higher stability. Acctually, the continuous melting-recrystallization process is a typical Ostwald ripening of polymer lamellae.关键词：Poly(ethylene oxide);Small-angle X-ray scattering;Lamellar thickening;Metlting-recrystallization;Ostwald ripening- 14
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发布时间：2021-03-19
Research Article
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