查看更多>>摘要：R.F. Boyer recognized the manifestations of a T > T_g transition-relaxation as early as 1963 and named it T_(LL), the liquid-liquid transition. He suggested that it was due to the melting of "local order", a controversial issue conflicting with the dominant theories at the time, led by P. Flory, which asserted a structure-less liquid state for melts. At the same time as this controversy unrolled, de Gennes published his reptation model of polymer physics which, after some modifications and ramifications, quickly became the new paradigm to describe the dynamic properties of polymer flow. The new model of reptation has no theoretical arguments to account for a T > T_g transition occurring in the melt; hence, the current consensus about the existence of T_(LL) is still what it was already in 1979, that it is probably an artifact only existing in the imagination of Boyer. In part I of this paper on the T_(LL) transition we mathematically derive the existence and the characteristics of T_(LL) from a dual-phase description of the free volume using a modification of the Vogel-Fulcher equation (VF), a well-known formulation of the temperature dependence of the viscosity of polymer melts. This new expression of the VF formula, that we call the TVF equation, permits to determine that T_(LL) is in an iso-free volume and iso-enthalpic state when M, the molecular weight, varies. The data analyzed by the TVF equation are the dynamic rheological results for a series of monodispersed, unentangled polystyrene samples taken from the work of Majesté. The new analysis also permits to put in evidence the existence of a new transition, which we call M_(mc), approximately located at M_(mc) ≈ M_c/10, where Mc is the molecular weight for entanglement. A Dual-Phase interpretation of M_(mc) is proposed.
查看更多>>摘要：In Part I of these 2 parts article, we derived mathematically the existence of a unique state for polymeric melts, occurring at a specific temperature above T_g, which we recognized to be the liquid-liquid transition, T_(LL), observed and described by Boyer and others. T_(LL) is the temperature at which the melt is in an iso-free-volume and isoenthalpic state independent of the molecular weight. It is a fundamental property of the material. The purpose of part II is to examine and explain the following: 1) the elusive character of T_(LL) (at the origin of the controversy about the existence of T_(LL) in the past), 2) the increase of free volume at T_(LL), and 3) the endothermal change of heat capacity on heating across T_(LL). Finally, our objective is to provide an explanation of T_(LL) and emphasize its importance as an example of a self-dissipative dynamic process that converts, at T_(LL), into a classical thermally activated process. In this article, the experimental evidence found in the literature for T_(LL) is critically examined to point out the often biased reviews offered by the antagonistic authors of a controversy, here the pros and cons T_(LL). We propose a Dual-Phase origin of the interactions in polymers to explain the weak and elusive manifestations of T_(LL) and show, by DSC, that the T_(LL) manifestations are made much more visible and prominent when the samples' state has been brought out of equilibrium. We analyze, in detail, the thermally activated depolarization of samples which have been submitted to a polarization stage by a voltage field.
查看更多>>摘要：It was shown that methacrylic acid-ethyl acrylate copolymer (P(EAMAA)) emulsion has a good reverse demulsification performance for treatment of water produced in oilfields. Its polymerization mechanism, kinetics and demulsification mechanism are important for its application and scale-up production. Therefore, they were studied in the research described in this paper. It was found that the demulsification mechanism of P(EA-MAA) was related to the ion compositions of the produced water and the conformation change of P(EA-MAA) when it was dissolved in the produced water. The distributions of monomer and surfactant before the polymerization were investigated and we found that there were both homogeneous nucleation and micellar nucleation during the first stage of emulsion polymerization. The relationships among the polymerization rate (Rp), monomer concentration ([M]), initiator concentration ([I]) and surfactant concentration ([S]) were studied. The emulsion copolymerization kinetic equation was Rp∝[M]0.~(64) [I]0.~(68) [S]0.~(41), which is related with the nucleation mechanism of the polymerization mechanism. In addition, the activation energy was 34.50 kJ/mol.
查看更多>>摘要：The effect of phenol solubilization on the behavior of (ethylene oxide)78-propylene oxide)_(30)-(propylene oxide)_(78) (EO_(78)-PO_(30)-EO_(78)) triblock copolymer, Pluronic F68 (F68), in aqueous suspensions was investigated by rheology. We have shown that for the ternary F68/ water/phenol mixture, the rheological properties and the conformational changes of F68 depended strongly on the amounts of phenol. The 20% F68 suspensions begin with a Newtonian behavior for small amounts of phenol and lose this behavior to become a non- Newtonian liquid plastic with increasing phenol concentrations (50% phenol); then the suspension became Newtonian again for 75% and 100% phenol. The results are attributed to the addition of phenol resulting in a sphere-to-rod micellar transition.
查看更多>>摘要：Ethylene propylene diene monomer (EPDM) rubber/zinc dimethacrylate (ZDMA)-samarium methacrylate (Sm(MA)_3) rare earth complex as seals were prepared via in-situ formation of Sm(MA)_3 to partially replace the ZDMA. Compared with neat EPDM, incorporation of ZDMA-Sm(MA)3 improved the curing activity of EPDM and a multiple crosslinking network formed with high crosslinking density. Improvement of the interfacial interaction facilitated distribution of the ZDMA-Sm(MA)3 in the matrix and resulted in an increase of the mechanical properties of the composites compared with neat EPDM. In addition, partially replacing the ZDMA with Sm(MA)3 significantly enhanced the durable sealing resilience performance of the composites by improving their free radical scavenging ability and inhibiting the degradation, oxidation and crosslinking reaction of the EPDM during stress-thermal oxidation aging.
查看更多>>摘要：An empirical pressure (P)-volume (V)-temperature (T)-entropy (S) equation of state (P-V-T-S Eos) of polyethylene (PE) has been determined based on the experimental data of P-V-T and isobaric heat capacity at 1 atm for PE. The thermodynamic quantities of P, V, T, and S fall into three ensembles which are an isothermal (T = const), isobaric (P = const), and isochoric (V = const) one and each ensemble has an intrinsic P-V-T-S Eos. Thermodynamic derivatives of (?V/?T)_P and (?S/?T)_P in the isobaric P-V-T-S Eos in the isobaric ensemble, the derivative of (?P/?T)_V and (?S/?T)_V in the isochoric P-V-T-S Eos in the isochoric ensemble and the (?S/?V)_T and (?S/?P)_T in the isothermal P-V-T-S Eos in the isothermal ensemble have been evaluated over the temperature range of 293-343 K and pressure up to ~1.0GPa for PE. The P-V-T-S Eos in this work were checked by the Maxwell's equations, such as (?S/?V)_T = (?P/?T)_(V') and thermodynamic relations expressed by (?C_V/?V)_T = T(?~2P/?T~2)_V and (?C_P/?P)_T = -T(?~2V/?T~2)_P . The thermodynamic significance of the P-V-T-S Eos and the advantage of the P-V-T-S Eos over the P-V-T Eos are discussed.
查看更多>>摘要：Multiwalled carbon nanotube (MWCNT) are widely used as reinforcing fillers for rubber materials due to their excellent mechanical, thermal and electrical properties. However, the MWCNT dispersion in the rubber matrix is normally poor owing to their high aspect ratio and agglomeration characteristics. In this paper we describe our research on natural rubber latex (NRL) composites filled with noncovalent modified multiwalled carbon nanotube (MWCNT), prepared by sodium methylene bis-naphthalene sulfonate (NNO) as an anionic surfactant. The high-performance NRL/NNO/MWCNT composites were prepared by a liquid latex blending method. Transmission electron microscopy (TEM) showed the dispersion of MWCNT modified by NNO in water was significantly improved. The original MWCNT dispersion state in the water was not sufficient, with a range of small to big agglomerates. On the other hand, the entangled bundles of NNO/MWCNT were reduced in size or eliminated. The NNO's interface interaction with the MWCNT was further studied by Raman spectroscopy and thermogravimetric analysis (TGA) which indicated the NNO was capable of modifying the surface of the MWCNT. In addition, the effects of the modified MWCNT on the mechanical and dynamic mechanical properties of rubber composites were also characterized. NNO was absorbed on the surfaces of the MWCNT through noncovalent action, which enabled the MWCNT to more evenly disperse in the rubber matrix, forming a good filler structure in the NRL and improving their composites mechanical properties. We note our approach is an easy and eco-friendly method to enhance the NRL composites.
查看更多>>摘要：Characterizing the relationships between the water repellency and moisture permeability (breathability) of hydrophilic polyurethane and its supramolecular structure, including the phase inversion temperature in the soft phase, is unavoidable when developing intelligent, breathable textile products. In this study, a two-step technique was employed to prepare hydrophilic nonionic polyurethanes (PU) with various polyether (PE) soft segments. The hard segments of the samples were composed of 4,40-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BDO), while the soft segments consisted of polyethylene glycol 1000 (PEG), polytetramethylene glycol 1000 (PTMG), or their mixture. The relationships between the chemical and physical structure and the breathability were studied. The results showed that the samples with better separated structure between the soft and hard domains had a special microstructure of partial compatibility and simultaneously partial separation between the polyether soft and hard domains. In addition, the distribution of the mixed polyethers in the soft domains was homogeneous. The microphase structure, especially the hydrophilic ether bond content, exhibited a specific corresponding relevancy to the water resistance, moisture permeability and hydrophilicity of the PU membrane. The moisture permeability and water resistance were also directly related to their film-forming properties. Enhanced microphase separation intensified the positive effects of ether bonds on the moisture permeability, while worsened microphase separation weakened their negative influence on the water resistance/hydrophobicity.
查看更多>>摘要：Nanosized semiconducting cadmium selenide particles were successfully distributed within the polymer matrix of polyvinyl alcohol (PVA) utilizing the method of heat induced chemical synthesis. The structural characterization of the prepared nanocomposite was conducted using X-ray diffraction for the phase analysis of the nanocrystallites, Transmission electron microscopy (TEM) was used for size and shape determination of the nanoparticles and Fourier transform infrared (FTIR) spectroscopy for identification of the various chemical functional groups possessed by the PVA/CdSe nanocomposites. Various properties of hybrid nanocomposites have been widely scrutinized by researchers during the past few decades because of their unique properties and versatility. The present study involved the behavioral analysis of various optical properties, such as optical absorbance (A), transmittance (T), optical band gap (E_g), refractive index (n), extinction coefficient (k), real and imaginary dielectric constants (ε1 and ε2) and optical conductivity (r_(opt)), of nanocomposite thin films produced by solution casting at temperatures ranging from 303 K to 343 K. The present study also deals with the evaluation of various ultrasonic acoustical properties, like adiabatic compressibility (β_(ad)), acoustic impedance (Z), intermolecular free length (L_f), relaxation time (s) and attenuation coefficient, α, as a function of the square of the frequency (f~1), i.e., (α/f~1), to permit detailed understanding of behavioral changes in particle-fluid interactions with variation in the solution temperature of the nanocomposite.
查看更多>>摘要：Hot-press compression molding was used to resinify a renewable source-derived linear 1,4-linked β-D-glucan copolymer, i.e., konjac glucomannan (KGM), via the generation of reactive aldehyde groups that tend to crosslink with hydroxyl groups of the glucans. The optimal molding temperature was found to be around 170℃, with keeping the pressure at 20MPa for 3.5 min and controlling the water content of the starting KGM powder to be around 22%. The molded KGM resin sheets were found to be crystallized in the annealed KGM polymorph form. Dynamic mechanical analysis revealed that the softening initiation temperature of the KGM resin was ca. 100℃ due to an onset of an increase in the loss modulus, E''. The representative KGM resin sheets obtained under the optimal molding conditions were transparent, colored brown, and exhibited a tensile strength of 20.8 ± 4.5MPa, Young's modulus of 2.2 ± 0.3 GPa and elongation at break of 1.1 ± 0.2%.
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