Impedance sensor for the early failure diagnosis of organic coatings

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 (θ_10Hz, θ_15kHz), breakpoint frequency (f_b), specific capacitance (C_10Hz, C_15kHz), and impedance modulus (Z_0.1Hz) 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 Z_0.1Hz?<?10⁶ Ω cm², f_b?>?100 Hz, or θ_10Hz?<?20°, the coating may be regarded as completely degraded and fails to protect the metal substrate.     

Novel amphiphilic temperature responsive graft copolymers PCL-<Emphasis Type="Italic">g</Emphasis>-P(MEO<Subscript>2</Subscript>MA-<Emphasis Type="Italic">co</Emphasis>-OEGMA) via a combination of ROP and ATRP: synthesis,characterization, and sol-gel transition

A series of well-defined novel amphiphilic temperature-responsive graft copolymers containing PCL analogues P(αClεCL-co-εCL) as the hydrophobic backbone, and the hydrophilic side-chain PEG analogues P(MEO₂MA-co-OEGMA), designated as P(αClεCL-co-εCL)-g-P(MEO₂MA-co-OEGMA) have been prepared via a combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). The composition and structure of these copolymers were characterized by ¹H NMR and GPC analyses. The self-assembly behaviors of these amphiphilic graft copolymers were investigated by UV transmittance, a fluorescence probe method, dynamic light scattering (DLS) and transmission electron microscopy (TEM) analyses. The results showed that the graft copolymers exhibited the good solubility in water, and was given the low critical temperature (LCST) at 35(±1) °C, which closed to human physiological temperature. The critical micelle concentrations (CMC) of P(αClεCL-co-εCL)-g-P(MEO₂MA-co-OEGMA) in aqueous solution were investigated to be 2.0 × 10^?3, 9.1 × 10^?4 and 1.5 × 10^?3 mg·mL^?1, respectively. The copolymer could self-assemble into sphere-like aggregates in aqueous solution with diverse sizes when changing the environmental temperature. The vial inversion test demonstrated that the graft copolymers could trigger the sol-gel transition which also depended on the temperature.     

A Comprehensive Study on the Synthesis and Micellization of Disymmetric Gemini Imidazolium Surfactants

Two groups of disymmetric Gemini imidazolium surfactants, [C₁₄C₄C _m im]Br₂ (m = 10, 12, 14) and [C _m C₄C _n im]Br₂ (m + n = 24, m = 12, 14, 16, 18) surfactants, were synthesized and their structures were confirmed by ¹H NMR and ESI–MS spectroscopy. Their adsorption at the air/water interface, thermodynamic parameters and aggregation behavior were explored by means of surface tension, electrical conductivity and steady-state fluorescence. A series of surface activity parameters, including cmc, γ _cmc, π _cmc, pC ₂₀, cmc/C ₂₀, Γ _max and A _min, were obtained from surface tension measurements. The results revealed that the overall hydrophobic chain length (N _c) for [C₁₄C₄C _m im]Br₂ and the disymmetry (m/n) for [C _m C₄C _n im]Br₂ had a significant effect on the surface activity. The cmc values decreased with an increase of N _c or m/n. The thermodynamic parameters of micellization (ΔG _m ^θ , ΔH _m ^θ , ΔS _m ^θ ) derived from the electrical conductivity indicated that the micellization process of [C₁₄C₄C _m im]Br₂ and [C _m C₄C _n im]Br₂ was entropy-driven at different temperatures, but the contribution of ΔH _m ^θ to ΔG _m ^θ was enhanced by increasing N _c or m/n. The micropolarity and micellar aggregation number (N _agg) were estimated by steady-state fluorescence measurements. The results showed that the surfactant with higher N _c or m/n can form larger micelles, due to a tighter micellar structure.     

Development of natural and synthetic polymer-based semi-interpenetrating polymer network for controlled drug delivery: optimization and in vitro evaluation studies

This research paper describes the development, optimization and in vitro characterization of chemically cross-linked pectin–polyvinyl alcohol-co-poly(2-Acrylamido-2-methylpropane sulfonic acid) semi-interpenetrating polymer network hydrogel [pectin–PVA-co-poly(AMPS) semi-IPN hydrogel] for controlled delivery of model drug tramadol HCl. Response surface methodology based on 3² factorial design was used for optimization and investigating the effect of independent factors: polymer-blend ratio (pectin:PVA = X ₁) and monomer (AMPS = X ₂) concentration on the dependent variables, swelling ratio (q _18th), percent drug release (R _18th, %), time required for 80 % drug release (t _{80 %}, h), drug encapsulation efficiency (DEE, %) and drug loaded contents (DLC, mg/g) in pectin-PVA-co-poly(AMPS) gels prepared by free radical polymerization. The optimized semi-IPN gel (FPP-10) showed controlled in vitro drug release (R _18th) of 56.34 % in 18 h, t _{80 %} of 30 h, and DEE of 23.40 %. These semi-IPN hydrogels were also characterized through SEM, FTIR, sol–gel analysis, swelling studies and drug release characteristics. Therefore, this newly synthesized polymeric network could be a potential polymeric system for controlled drug delivery of tramadol HCl for prolonged drug release.     

Seasonal N<Subscript>2</Subscript>O emissions respond differently to environmental and microbial factors after fertilization in wheat–maize agroecosystem

Biogeochemical processes regulating cropland soil nitrous oxide (N₂O) emissions are complex, and the controlling factors need to be better understood, especially for seasonal variation after fertilization. Seasonal patterns of N₂O emissions and abundances of archaeal ammonia monooxygenase (amoA), bacterial amoA, nitrate reductase (narG), nitrite reductase (nirS/nirK), and nitrous oxide reductase (nosZ) genes in long-term fertilized wheat–maize soils have been studied to understand the roles of microbes in N₂O emissions. The results showed that fertilization greatly stimulated N₂O emission with higher values in pig manure-treated soil (OM, 2.88 kg N ha^?1 year^?1) than in straw-returned (CRNPK, 0.79 kg N ha^?1 year^?1) and mineral fertilizer-treated (NPK, 0.90 kg N ha^?1 year^?1) soils. Most (52.2–88.9%) cumulative N₂O emissions occurred within 3 weeks after fertilization. Meanwhile, N₂O emissions within 3 weeks after fertilization showed a positive correlation with narG gene copy number and a negative correlation with soil NO₃^? contents. The abundances of narG and nosZ genes had larger direct effects (1.06) than ammonium oxidizers (0.42) on N₂O emissions according to partial least squares path modeling. Stepwise multiple regression also showed that log narG was a predictor variable for N₂O emissions. This study suggested that denitrification was the major process responsible for N₂O emissions within 3 weeks after fertilization. During the remaining period of crop growth, insufficient N substrate and low temperature became the primary limiting factors for N₂O emission according to the results of the regression models.     

Enhanced Thermoelectric Performance of <Emphasis Type="Italic">c</Emphasis>-Axis-Oriented Epitaxial Ba-Doped BiCuSeO Thin Films

We reported the epitaxial growth of c-axis-oriented Bi_1?xBa_xCuSeO (0?≤ x ≤?10%) thin films and investigated the effect of Ba doping on the structure, valence state of elements, and thermoelectric properties of the films. X-ray photoelectron spectroscopy analysis reveal that Bi³⁺ is partially reduced to the lower valence state after Ba doping, while Cu and Se ions still exist as +?1 and ??2 valence state, respectively. As the Ba doping content increases, both resistivity and Seebeck coefficient decrease because of the increased hole carrier concentration. A large power factor, as high as 1.24 mWm^?1 K^?2 at 673 K, has been achieved in the 7.5% Ba-doped BiCuSeO thin film, which is 1.5 times higher than those reported for the corresponding bulk samples. Considering that the nanoscale-thick Ba-doped films should have a very low thermal conductivity, high ZT can be expected in the films.     

Synthesis and Characterization of pH-Responsive Organic–Inorganic Hybrid Material with Excellent Catalytic Activity

Poly(N-isopropylmethacrylamide-co-methacrylic acid) [p(NipAam-Mac)] microgels were synthesized and used as microreactors to fabricate silver nanoparticles. Pure and hybrid microgels were characterized using Ultraviolet–Visible (UV/Vis) spectroscopy, Fourier transform infra-red (FTIR) spectroscopy and transmission electron microscopy (TEM). Catalytic activity of hybrid microgels and mechanism of catalysis by this system was explored using different reaction conditions. At the same temperature, apparent rate constant (k_app) was found to be varied from 0.0414 to 0.7852 min^?1 by increasing the concentration of NaBH₄ from 2.49 to 22.41 mM at constant concentration of substrate and catalyst. However upon extra increase in concentration of NaBH₄ from 22.41 to 37.35 mM reduced the value of k_app to 0.2178 min^?1. Likewise, the value of k_app was found to be increased from 0.1242 to 0.5495 min^?1 with increasing the concentration of 4-nitrophenol [Para-nitrophenol (p-Np)] from 0.063 to 0.079 mM keeping other parameters constant. Further increase in concentration of p-Np caused decline in the value of k_app. Kinetic data reveals that catalytic reduction of p-Np obeys Langmuir–Hinshelwood mechanism and p-Np is converted to p-Ap on the surface of the silver nanoparticles passing through various reaction intermediates.     

Synthesis and characterization of polyimides from 4,4′-(3-(<Emphasis Type="Italic">tert</Emphasis>-butyl)-4-aminophenoxy)diphenyl ether

A novel diamine 4,4′-(3-(tert-butyl)-4-aminophenoxy)diphenyl ether (4) was synthesized from 2-tert-butylaniline and 4,4′-oxydiphenol through iodination, acetyl protection, coupling reaction and deacetylation protection. Then some polyimides (PIs) were obtained by one-pot polycondensation of diamne 4 with several commercial aromatic dianhydrides respectively. They all exhibit enhanced solubility in organic solvents (such as NMP, DMF, THF and CHCl₃ etc.) at room temperature. Their number-average molecular weights are in the range of (2.1–3.7)?×?10⁴ g/mol with PDI from 2.25 to 2.74 by GPC. They can form transparent, tough and flexible films by solution-casting. The light transparency of them is higher than 90% in the visible light range from 400 nm to 760 nm and the cut-off wavelengths of UV–vis absorption are below 370 nm. They also display the outstanding thermal stability with the 5% weight loss temperature from 525 °C to 529 °C in nitrogen atmosphere. The glass transition temperatures (T _g s) are higher than 264 °C by DSC. XRD results demonstrate that these PIs are amorphous polymers with the lower water absorption (<0.66%). In summary, the incorporation of tert-butyl groups and multiple phenoxy units into the rigid PI backbones can endow them excellent solubility and transparency with relatively high T _g s.     

Synthesis and Characterization of Novel Aryl Alkyl Sulfonates Based on Nonylphenol

A series of nonylphenol-substituted alkyl sulfonates (C _x NPAS, x = 8, 10, 12, 14, 16) with two hydrocarbon chains and two different hydrophilic groups has been synthesized from α-olefins and nonylphenol. The respective products have a “pseudo-gemini” surfactant structure. The structures of the C _x NPAS have been characterized by IR, UV, ¹H nuclear magnetic resonance, electrospray ionization mass spectrometry, and elemental analysis. The effects of carbon chain length of the obtained surfactants on properties such as the critical micelle concentrations (CMC) in aqueous solutions, surface tension at the CMC (γ _CMC), and efficiency of adsorption at the water/air interface (pC ₂₀) have been determined. The γ _CMC of the surfactants first decreased and then increased with increasing length of the carbon chain x, and reached a minimum of 29.25 mN/m at x = 10, which is much lower than that of α-olefin sulfonate (AOS) (33.52 mN/m). The CMC decreased and pC ₂₀ increased with increasing x. The introduction of the hydroxyl group is responsible for multiple molecular conformations at the water/air interface and leads to a greater molecular area A _min and smaller Γ_max than those of AOS.     

Utilization of a montmorillonite-Ca-modified carbon paste electrode for the stripping voltammetric determination of diflunisal in its pharmaceutical formulations and human blood

A highly sensitive square-wave adsorptive anodic stripping voltammetric method was described for the determination of diflunisal in its formulations and human blood, utilizing a developed montmorillonite-Ca-modified carbon paste electrode (CPE). The peak current was significantly enhanced due to the strong adsorptive properties of montmorillonite-Ca clay. The optimal procedural parameters were frequency f = 80 Hz, scan increment ΔE _a = 10 mV, pulse-amplitude ΔE _i = 25 mV, and an accumulation potential E _acc of 0.0 V versus Ag/AgCl/3M KCl in acetate buffer of pH 5.0 using 10% (w/w) MMT-Ca-modified CPE. The described method was successfully applied for assay of diflunisal in different pharmaceutical formulations (Doloban^®, Dolozal^®, and Maxipan^® tablets) with mean percentage recoveries of 98.72 ± 0.35, 99.24 ± 0.89, and 98.20 ± 1.38, respectively. Furthermore, the method was successfully applied for assay of diflunisal in spiked human serum without the necessity of sample pretreatment or time-consuming extraction prior to the analysis. Mean percentage recovery of diflunisal in human serum was 99.16 ± 1.03 with a limit of detection of 3.0 × 10^?9 M (0.75 ng mL^?1). Due to this extremely low limit of detection, the proposed method was used to follow up the concentration of drug in blood samples of two male volunteers after oral administration of a single dose of Dolozal^®, 500 mg tablet.     

Effect of Sodium Carbonate on the Cloud Point in Alkyl Ether/Brine Systems: Apparent Relation with Dynamic Interfacial Tension Minimum

The effect of Na₂CO₃ on the cloud point in Na₂CO₃/surfactant/brine was investigated using two series of nonionic surfactants, C₁₃EO _x and C₁₇EO _x . The cloud point, T _cp, was found to decrease linearly with increasing Na₂CO₃ concentration. This was attributed to Na⁺ and particularly to CO₃ ^2?salting-out effect. The slope a = dTcp/d[Na₂CO₃] became more and more negative as the degree of ethoxylation is increased, suggesting that the higher the number of ethylene oxide (EO) groups the stronger is the cloud point depression for a given increment in Na⁺and CO₃ ^2?ions in solution. This was also illustrated by the linear variation of ΔT _cp = T _cp,0 ? T _cp,[Na2CO3] with the surfactant degree of ethoxylation.     

Synthesis,Characterization and Surface Properties of Amidosulfobetaine Surfactants Bearing Odd-Number Hydrophobic Tail

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 (γ_CMC) 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.     

Crystal structure and thermal expansion of ammonium pentaborate NH<Subscript>4</Subscript>B<Subscript>5</Subscript>O<Subscript>8</Subscript>

Anhydrous ammonium pentaborate NH₄B₅O₈ has been synthesized by thermal dehydration of larderellite NH₄[B₅O₇(OH)₂] · H₂O at a temperature of 290°C for 7 h. The crystal structure has been determined from the X-ray powder diffraction data: a = 7.58667(5) Å, b = 12.00354(8) Å, c = 14.71199(8) Å, R _p = 6.23, R _wp = 7.98, R _B = 12.7, R _F = 8.95, and β-KB₅O₈ structure type. The double interpenetrating framework is formed by pentaborate groups, each consisting of a boron-oxygen tetrahedron and four triangles, in which all oxygen atoms are bridging. The thermal behavior of the NH₄B₅O₈ compound has been investigated using thermal X-ray diffraction. As for other pentaborates of this type, the thermal expansion of the NH₄B₅O₈ compound is anisotropic and reaches a maximum along the a axis. The thermal expansion coefficients are as follows: α _a = 39 × 10^?6, α _b = 6 × 10^?6, α _c = 20 × 10^?6, and α _V = 65 × 10^?6 °C^?1.     

Surface-initiated growth of copper using isonicotinic acid-functionalized aluminum oxide surfaces

Isonicotinate self-assembled monolayers (SAM) were prepared on alumina surfaces (A) using isonicotinic acid (iNA). These functionalized layers (iNA-A) were used for the seeded growth of copper films (Cu-iNA-A) by hydrazine hydrate-initiated electroless deposition. The films were characterized by scanning electron microscopy (SEM), electron-dispersive X-ray spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and advancing contact angle measurements. The films are Cu⁰ but with surface oxidation, and show a faceted morphology, which is more textured (R _q = 460 ± 90 nm) compared to the SAM (R _q = 2.8 ± 0.5 nm). In contrast, growth of copper films by SnCl₂/PdCl₂ catalyzed electroless deposition, using formaldehyde (CH₂O) as the reducing agent, shows a nodular morphology on top of a relatively smooth surface. No copper films are observed in the absence of the isonicotinate SAM. The binding of Cu²⁺ to the iNA is proposed to facilitate reduction to Cu⁰ and create the seed for subsequent growth. The films show good adhesion to the functionalized surface.     

Partition of <Emphasis Type="Italic">n</Emphasis>-Butanol Among Phases and Solubilization Ability of Winsor type III Microemulsions

The partition of n-butanol in Winsor type III (W-III) microemulsions was investigated in this work. Three kinds of anionic surfactants (sodium dodecyl sulfate (SDS), sodium dodecyl sulfonate (DSS), and sodium dodecyl benzene sulfonate (SDBS)) and two kinds of anionic/cationic surfactant mixtures (SDS/octadecyl trimethyl ammonium chloride (OTAC) mixtures and DSS/OTAC mixtures) were studied. Internal standard gas chromatography was employed in n-butanol content analysis. The results showed that no water exists in the excess oil (EO) phase and no oil exists in the excess water (EW) phase. For the W-III microemulsions obtained by salinity scanning, relatively constant n-butanol content in the EO (11–12 v%) and EW (1–4 v%) was found under different salinities. Accurate measurement of n-butanol content in each phase is important for those systems having low solubilization ability. For the W-III microemulsions prepared using SDS/OTAC surfactant mixture, the percentage of n-butanol distributed into the interfacial layer decreased while the fraction of n-butanol in the interfacial layer first increased sharply and then tended to be stable with the addition of n-butanol. For the different optimum W-III microemulsion systems tested, most of the surfactant-to-alcohol molar ratio data are near 1:3, but obvious deviation could be observed for some data. On the basis of the accurate measurement of n-butanol content in the EO and EW phases, the standard free energy, ΔG _o→in ^* (T = 298.15 K) of n-butanol transferring from the EO phase to the interfacial region was calculated. The results show negative ΔG _o→in ^* values. For microemulsions with the same components, n-butanol content is an important factor influencing the ΔG _o→in ^* value, and a high absolute value of ΔG _o→in ^* leads to high solubilization ability.     

Solid-state polyetherimide (PEI) nanofoams: the influence of the compatibility of nucleation agent on the cellular morphology

The introduction of polyhedral oligomeric silsesquioxane (POSS) particles which act as heterogeneous nucleation agent was applied to improve the cellular morphology of nanocellular polyetherimide (PEI) foams. The loading of POSS particles increases the solubility and diffusivity characteristics of gases in nanocomposite sheets by changing the distribution of the free volume and enlarging the unoccupied volume in polymer matrix. When the range of content of POSS particles is 0.2?~?1.0 wt. %, the range of the calculated surface tension of PEI/scCO₂ (γ _mix ) and radius of the critical nucleus (r*) are 30.98?~?28.14 mN/m, and 6.88?~?6.25 nm, respectively. However, the small aggregated POSS particles are favour of heterogeneous nucleation bacause the actual diameter of the aggregated POSS particles is approximate to twice r*, so the addtion of 0.5 wt. % POSS to PEI matrix presents excellent heterogeneous nucleation performance for foaming. The average cell size of 0.5 wt. % POSS/PEI nanofoams compared with neat PEI decreases from 108 to 66 nm and the cell density increses from 5.96?×?10¹⁴ to 3.34?×?10¹⁵ cells/cm³.     

Dielectric properties of silver-doped nanoporous silicate glasses in the temperature range between –50 and +250°C

The results of measuring dielectric parameters of nanoporous silicate glasses with a nanopore size of 3.5 and 25.7 nm, either doped with silver or not, in the temperature range between–50 and +250°C and the frequency range of 0.1–10⁶ Hz are reported. It is demonstrated that when silver nanoparticles are formed in glass pores, some silver remains in the form of subnanosized molecular clusters Ag _n and molecular complexes Ag _n –(OH) _m . The key dielectric properties of the relaxation centers are determined for different temperature ranges.     

Reinforcement of electroactive characteristics in polyvinylidene fluoride electrospun nanofibers by intercalation of multi-walled carbon nanotubes

This research work reports on development and characterization of multi-walled carbon nanotube (MWCNT)-doped polyvinylidene difluoride (PVDF) nanofibers by the electrospinning method. PVDF is an extensively studied polymer both theoretically and experimentally due to its appealing ferroelectric, piezoelectric, and pyroelectric properties which strongly favors its promising applications in the development of micro/nanostructure devices. The foremost reason for its ferroelectric and piezoelectric behaviors has been attributed to its crystalline structure, specifically the presence of β-phase; however, the existence of the small percentage of β-phase in pristine PVDF limits its applications. To enhance the electroactive features in the PVDF, MWCNTs have been doped in it to prepare electrospun nanofibers, as electrospinning is a single-step approach. These nonwoven nanofibers were prepared at a DC voltage of 20 kV which were subsequently calcined at 100 °C for 12 h. The estimation of crystal structure and phase identification in these nanofibers have been determined by attenuated FT-IR and XRD, while the morphology, microstructure, mean diameter, and length have been examined by FE-SEM. The observed electrical conductivity, capacitance, permittivity (ε), conductivity (δ), and impedance (Z) in these samples have been tailored by doping a range of MWCNT contents and optimizing the experimental conditions.     

Microstructure characterization of one high-speed extrusion coating polyethylene resin fractionated by solvent gradient fractionation

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) (L _n and L _w ). The longest L _n (L _w ) 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.

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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.

     

The cyclization index and toughness of gel spun polyacrylonitrile (PAN) proportionality with its heat of stabilization

The spun tapes of synthesized PAN, its copolymer with 1 wt% itaconic acid, and doped version with 1 wt% sodium dodecyl sulfate (SDS) all showed stripy, even, and compact cross-sections as the hallmark of gel forming products. PAN doping with SDS and acrylonitrile copolymerization with itaconic acid reduced its dimethylformamide (DMF) solution structural viscosity index (Δη) by 50% and 30%, respectively, at 675 s^??1. In addition, the modification of synthesized PAN through doping and acrylonitrile copolymerization with itaconic acid led to severe and mild gelation temperature decrease, respectively. The stabilization peak of the synthesized PAN tape was enhanced as much as 25 °C by 900% hot drawing, decreased by about 10 °C through copolymerization, while experienced small temperature changes through doping. The second derivative of Fourier transform infrared and Gaussian fitting was used to analyze the tapes cyclization due to stabilization treatment through introducing I_sd index. 10 min I_sd index was raised as much as 430% and 800% in comparison with the synthesized PAN through its doping or acrylonitrile copolymerization with itaconic acid, respectively. Further 180 min of I_sd index, however, showed the same proportional increase as toughness of the drawn tapes versus their heat of stabilization through their physical and chemical modifications.