Phase separation and rheological behavior in thermoplastic modified epoxy systems

The relationship between rheological behavior and phase separation in polyesterimide modified epoxy systems was studied by rheometry, time-resolved light scattering (TRLS), and Differential Scanning Calorimetry (DSC). The rheological behaviors of blends during phase separation showed an exponential grow of complex viscosity, while the phase separation was inhibited by the vitrification of the polyesterimide-rich matrix phase rather than gelation of dispersed epoxy-rich particles. The characteristic relaxation time obtained by the simulation of complex viscosity could be described well by the Williams–Landel–Ferry equation, which corresponded well with the light scattering results. Therefore, this work would further provide the experimental proofs that the exponential relaxation behavior of complex viscosity could be attributed to the viscoelastic flow of epoxy-rich escaping from polyesterimide-rich matrix during phase separation.     

Polymerization-induced viscoelastic phase separation in polyethersulfone-modified epoxy systems

The polymerization-induced phase-separation process of polyethersulfone (PES)-modified epoxy systems was monitored in situ continuously on a single sample throughout the entire curing process by using optical microscopes, time-resolved light scattering (TRLS), scanning electronic microscopes (SEM), and a rheometry instrument. At specific PES content a viscoelastic transformation process of phase inversion morphology to bicontinuous was found with an optical microscope. The rheological behavior during phase separation corresponds well with the morphology development. Light-scattering results monitoring the phase-separation process of systems with final phase inversion morphology show a typical exponential decay procedure of scattering vector qm. The characteristic relaxation time of phase separation can be described well by the WLF equation.     

Curing reaction characteristics and phase behaviors of biphenol type epoxy resins with phenol novolac resins

Diglycidyl ether of 4,4′-dihydroxybiphenol (BPDGE) is a liquid crystalline epoxy. The biphenyl epoxy (diglycidyl ether of 3,3′,5,5′-tetramethyl-4,4′-biphenyl, TMBPDGE) has found great applications in plastic encapsulated semiconductor packaging. Phenol novolac (PN) was used as curing agent. The reaction kinetics of BPDGE/PN and TMBPDGE/PN systems in the presence of triphenylphosphine (TPP) were characterized by an isoconversional method under dynamic conditions using differential scanning calorimetry (DSC) measurements. The results showed that the curing of epoxy resins involves different reaction stages and the values of activation energy are dependent on the degree of conversion. The effects of curing temperature on their phase structure have been investigated with polarized optical microscopy and Wide-angle X-ray diffraction. With proper curing process, BPDGE showed a nematic phase when cured with PN.     

Reaction-induced phase separation in polyethersulfone-modified epoxy-amine systems studied by temperature modulated differential scanning calorimetry

In epoxy-amine systems with a thermoplastic additive, the initially homogeneous reaction mixture can change into a multi-phase morphology as a result of the increase in molecular weight or network formation of the curing matrix. Temperature modulated DSC (TMDSC) allows the real-time monitoring of this reaction-induced phase separation. A linear polymerizing epoxy-amine (DGEBA–aniline) and a network-forming epoxy-amine (DGEBA–methylene dianiline), both with an amorphous engineering thermoplastic additive (polyethersulfone, PES), are used to illustrate the effects of phase separation on the signals of the TMDSC experiment. The non-reversing heat flow gives information about the reaction kinetics. The heat capacity signal also contains information about the reaction mechanism in combination with effects induced by the changing morphology and rheology such as phase separation and vitrification. In quasi-isothermal (partial cure) TMDSC experiments, the compositional changes resulting from the proceeding phase separation are shown by distinct stepwise heat capacity decreases. The heat flow phase signal is a sensitive indication of relaxation phenomena accompanying the effects of phase separation and vitrification. Non-isothermal (post-cure) TMDSC experiments provide additional real-time information on further reaction and phase separation, and on the effect of temperature on phase separation, giving support to an LCST phase diagram. They also allow measurement of the thermal properties of the in situ formed multi-phase materials.     

流变和光学法研究PAN/DMSO/H_2O体系的凝胶化和相分离行为

碳纤维是非常重要的增强材料,在军工以及高档民用产品中用途广泛。因为聚丙烯腈原丝的结构会"遗传"到最终的碳纤维结构中,因此原丝结构对碳纤维的性能影响很大。原丝的结构是纺丝液在凝固浴中的相分离和凝胶化两个过程决定的,因此研究这两个过程的规律并进一步控制它们的进程,达到调控原丝结构的目的是非常重要的。本文介绍了本课题组利用流变学及光学的方法研究PAN/DMSO/H2O体系凝胶化及相分离行为的最新研究成果,主要探索了PAN/DMSO/H2O浓溶液中凝胶化行为,发现了二次自相似结构的形成并对其机理进行了分析,并对PAN/DMSO/H2O亚浓溶液中凝胶化与相分离的耦合过程进行了研究,分析了最终凝胶的结构特性及Winter-Chambon模型在此过程中的适用性。最后,对PAN/DMSO/H2O体系凝胶化及相分离行为的下一步研究进行了展望。     

Reaction-induced phase separation in rubber-modified epoxy resin

The phase separation mechanism,and structure development during curing of epoxy with a novel liquid rubber-ZR were investigated by time-resolved light scattering,optical microscope and differential scanning calonmetry (DSC) The mixture loaded with curing agent was a single-phase system in the early stage of curing.When the cure reaction proceeded,phase separation took place via the spinodal decomposition induced by polymerization of epoxy resin.This was supported by the characteristic change of light scattering profile with curing time.Cure reaction plays an important role in the progress of phase separation.The bigger the cure reaction rate is,the longer periodic distance will be.The overall two-phase structure was basically locked in when the conversion approached 80% estimated by DSC,and finally the co-continuous two-phase structure was successfully obtained.     

Selective solvation effects in phase separation in aqueous mixtures

Selective solvation can be crucial in phase separation in polar binary mixtures (water–oil) with a small amount of hydrophilic ions or hydrophobic particles. They are preferentially attracted to one of the solvent components, leading to a number of intriguing effects coupled to phase separation. For example, if cations and anions interact differently with the two components, an electric double layer emerges at a liquid–liquid interface. The main aim of this paper is to show that a strongly hydrophilic (hydrophobic) solute induces precipitation of water-rich (oil-rich) domains above a critical solute density n_p outside the solvent coexistence curve.     

The morphology and dynamics of polymerization-induced phase separation

The morphology and dynamics of polymerization-induced phase separation in the initially homogeneous solution of a non-reactive component in reactive monomers are investigated by incorporating the reaction kinetics into the Cahn-Hilliard equation. Analytical results show that there is a reduction of the initial length scale in the early stage of phase separation. The reason is the increase of the molecule weight of emerging polymer, independent of the fact whether the system goes through the metastable region or not. The numerical results are in good agreement with theoretical prediction quite well.     

Phase separation behavior of epoxy resin modified with crosslinked rubber

Low molecular weight liquid rubber (ATBN = amine terminated butadiene acrylonitrile copolymer or CTBN = carboxyl terminated butadiene acrylonitrile copolymer)–DGEBA (diglycidyl ether of bisphenol A) blends indicated upper critical solution temperature (UCST) behavior. The phase separation behavior of the neat and crosslinked rubber (ATBN, CTBN)–epoxy blends was analyzed by a laser light scattering experiment. Lauryl peroxide (LPO) was employed to crosslink the rubber during the initial annealing stage. The onset point of the phase separation in the crosslinked ATBN–epoxy system occurred later than in the case of the neat ATBN–epoxy system. However, the onset point of the phase separation process started earlier in the case of the crosslinked CTBN–epoxy system. The domain correlation length of the crosslinked rubber-added system was smaller than that of the neat rubber-added system.     

Modelling the influence of nanoparticles in the phase behaviour of an epoxy/polystyrene mixture

The cloud point temperatures of four series of epoxy/polystyrene blends have been experimentally determined as a function of polymer mass and system composition. The phase diagrams show an UCST behaviour, increasing incompatibility as the molar mass increases. The Flory-Huggins theory with a concentration-dependent interaction parameter has been developed to study the compatibility of two polymers in presence of spherical nanoparticles. This theory has been first compared with the experimental cloud point curve in absence of nanoparticles, and secondly it has been used to predict the thermodynamic behaviour in presence of different volume fraction of nanoparticles. Nanoparticles coated with two types of functional groups have been tested. It can be concluded that the inclusion of nanoparticles increases compatibility. Moreover concentration-dependent interaction parameters have been obtained in these systems for the first time.     

Kinetics of phase separation at the early stage of spinodal decomposition in epoxy resin modified with PEI blends

The behavior at the early stage of spinodal decomposition (SD) for polyetherimide (PEI)/epoxy blends was investigated. It was found that the phase separation of PEI/epoxy blends took place by SD mechanism. The development of molar mass in the epoxy resin was gradual and then the three blends could still be considered as concentrated solutions of thermoplastic. The kinetics at the early stage of phase separation for these blends could be described by the Cahn–Hilliard–Cook linearized theory.     

Chemically induced phase separation in the preparation of porous epoxy monolith

A methodology for preparing porous epoxy monolith via chemically induced phase separation was proposed. The starting system was a mixture of an epoxy precursor, diglycidyl ether of bisphenol‐A (DGEBA), a curing agent, 4,4′‐diaminodiphenylmethane (DDM), and a thermoplastic polymer, polypropylene carbonate (PPC). As DGEBA was cured with DDM, the system became phase‐separated having PPC particles dispersed in epoxy matrix. After PPC particles were removed by thermal degradation, a porous structure was obtained. The phase separation mechanism was determined by the initial composition and illustrated by a pseudophase diagram. The pore size increased with increasing the concentration of PPC and raising the curing temperature. The intermediate and final morphologies of the system were studied using optical and scanning electron microscopy, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

流变学方法测定共混物相图及其分辨尺度探讨

应用小振幅振荡剪切(SAOS)和小角激光散射(SALS)测定了苯乙烯-马来酸酐共聚物/聚甲基丙烯酸甲酯(SMA/PMMA)共混体系相分离温度,并分析了动态储能模量对频率响应的敏感程度以及不同测试方法在相分离判据方面的差别.认为前者是造成由不同的测试频率得到的相边界之间存在差异的原因,而SAOS与SALS得到的相边界不同则缘于后者;通过评估不同温度下分散相的尺度,发现选择合适的测试频率进行SAOS测试可以得到比SALS法更小的分辨尺度.     

Motional heterogeneity and phase separation of functionalized polyester polyurethanes

The polyester polyurethanes, PU based on isophoronediisocyanate, polycaprolactone, and 1,4-butanediol with different amounts of functional groups introduced into the hard segments via second chain extender, 2,2′-bis-(hydroxymethyl) propionic acid, were investigated by electron spin resonance, ESR, spin label method, wide-angle X-ray diffraction, WAXD, optical microscopy and differential scanning calorimetry, DSC. The objective of this study is to clarify the effect of functional groups on the motional heterogeneity, microphase separation and crystallisation of the polyurethanes. The concentration of carboxylic groups varied from 0 to 0.45 mmol g⁻¹. The temperature-dependent ESR spectra of spin labelled PU hard segments chain ends with stable nitroxide radical 2,2,6,6-tetramethyl-4-aminopiperidin-1-yloxyl are sensitive to the amount of functional groups attached to the hard segments. Composite ESR spectra of functionalized PU, with fast and slow component, suggest that PU hard segments are partitioned in two motionally different environments. According to the ratio of fast and slow component motional heterogeneity increases with an increase of functional groups up to 0.35 mmol g⁻¹ and above this concentration slow component decreases indicating higher degree of phase mixing and stronger effect of soft segments. Polarized micrographs and the extent of ordering from WAXD measurements reveal the changes of phase morphology with the carboxylic groups content in a similar way as shown from the motional behaviour of spin label on the segmental level. The degree of crystallinity and the separation of spherulitic rings are decreasing above a certain concentration of functional groups. The effect of functional groups in PU on the hard and soft segment mixing is discussed in terms of additional noncovalent interactions and chain structure which at critical level of interactions lead to a formation of more open hard segment structure accessible to interaction with the soft segment.     

Phase separation during synthesis of polyetherimide/epoxy semi-IPNs

The phase separation behavior and the morphology of polyetherimide (PEI)-modified diglycidyl ether of bisphenol A (DGEBA) epoxy resin were studied using scanning electron microscopy and light scattering. Reaction kinetics, cloud point and onset of gelation were determined by differential scanning calorimeter, optical microscope and physica rheometer, respectively. The mixture of partially cured epoxy and PEI showed bimodal upper critical solution temperature (UCST) behavior. For PEI content smaller than 10 wt%, the blends exhibited a sea-island morphology formed via nucleation and a growth mechanism. Above 25 wt% PEI content, the phase separation proceeded via a spinodal decomposition mechanism and a nodular structure was formed. With PEI content between 15 and 20 wt%, dual phase morphology was observed. This morphology was formed via primary spinodal decomposition and secondary phase separation within the dispersed phases and the matrix phases formed by the primary phase separation. This morphology was presumed to be formed in the reaction-induced phase separation mechanism with the mixture showing bimodal UCST behavior. The curing temperature had an effect on the final morphology, and the modulus of PEI-modified epoxy was influenced by the phase separation.     

Entanglement and phase separation in hyperbranched polymer/linear polymer/solvent ternary blends

Hyperbranched polyethylene (HBPE)/linear polystyrene (PS)/chloroform (CF) solution was selected as a model system to investigate the effect of branching structure on entanglement and phase separation behavior in semi-dilute ternary polymer solutions. All the HBPE materials in this work were found to have similar chain architectures and the critical molecular weight was estimated to be 81.2 kDa. The results obtained by elastic light scattering and intrinsic fluorescence methods suggested that all ternary solutions exhibited UCST transition behavior upon cooling. Also, it was found that the increase in the molecular weight of PS led to increase in the phase separation rate, consistent with de Gennes prediction. However, the increase of molecular weight of HBPE did not monotonously reduce the compatibility of polymer components and the phase separation rate in ternary blends is as follows: medium molecular weight HBPE (HBPE-M) > high molecular weight HBPE (HBPE-H) > low molecular weight HBPE (HBPE-L). This abnormal behavior can be explained by the fact that, (i) for HBPE-L, no entanglements between HBPE chains occurred and the branching effect can be ignored, and (ii) for HBPE-M and HBPE-H, entanglement of HBPE chains can be formed, and the dilution of branches on entanglement of backbones should be taken into consideration, that is, the shorter the branches of HBPE, the higher the possibility of interpenetration of HBPE backbones between neighboring molecules and, consequently, the faster aggregation of HBPE during phase separation. Furthermore, a simple model based on decomposition reaction was proposed to quantitatively describe the phase separation kinetics and the apparent activation energies of phase separation were calculated to be −150.3 and −52.3 kJ/mol for HBPE-M/PS/CF and HBPE-H/PS/CF systems, respectively.     

Rheological studies on the phase separation of hydroxypropylcellulose solution systems

Phase behavior of hydroxypropylcellulose (HPC) in a mixed solvent of glycerol and water was investigated by two different rheological methods: rheooptical birefringence measurement in an elongational flow field and viscometric measurement in a shear flow field. The association process of the HPC chain during phase separation observed by the elongational flow birefringence method was also investigated by the shear viscometric method. The temperature dependence of chain rigidity was determined by measuring the intrinsic viscosity, and change in the conformation was investigated by observing elongational flow birefringence over the temperature range from the one‐phase to inside a phase boundary. The results focus on the molecular process of phase separation. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1976–1986, 2001     

Sol-gel polycondensation of methyltrimethoxysilane in ethanol studied by <Superscript>29</Superscript>Si NMR spectroscopy using a two-step acid/base procedure

Sol-gel polymerization of methyltrimethoxysilane (MTMS) in ethanol using a two-step acid/base catalyzed procedure (B2) is followed by ²⁹Si NMR spectroscopy. Analysis of the structural evolution of the B2 system shows that esterification of monomeric and end silicon species is rate-limited while that of linear and cyclic species is able to reach pseudoequilibrium in the second basic step. Condensation reactivity is reduced with increasing network connectivity, however, to a much less degree under B2 conditions than MTMS polymerization under acidic conditions. Steric effects as well as many other factors are attributed to this trend. The concentration of cyclic and polycyclic species of the B2 system is nearly 3 times lower compared to the acid-catalyzed system. The empirical degree of condensation at the gel point is determined to be 0.88. The effects of cyclization and phase separation on MTMS gelation are discussed for both B2 and acid-catalyzed systems. Based on these results it is believed that MTMS-based gels form for B2 and not acid-catalyzed conditions due to reduced cyclization, rapid hydrolysis and condensation, effective use of functional groups, and effective contribution of branched and polycyclic species as crosslinking points to connect polymeric chains in the B2 system.     

Rheological phase synthesis,characterization and magnetic property of a cobalt(II)diphosphonate

A new Co(II) diphosphonate compound, [Co(HEDPH₂)₂] (4,4′-bipyH₂)?·?H₂O (1) has been successfully obtained by a rheological phase reaction at 80°C. Single-crystal diffraction analysis shows a 1-D chain structure and the 1-D chains are assembled via hydrogen bonds into a 3-D supramolecular structure with channels. The protonated 4,4′-bipy molecules are encapsulated in the channels. Magnetic study shows 1 to exhibit antiferromagnetic interaction in the 1D Co--O--P--O--Co chain. Crystal data for 1: monoclinic, space group Cc, a?=?15.754(6)?Å, b?=?14.457(5)?Å, c?=?10.020(4)?Å, β?=?92.024(6)°, V?=?2280.7(14)?ų, Z?=?4.     

Sensitive phase separation behavior of ultra-high molecular weight polyethylene in polybutene

Thermally induced phase separation (TIPS) has prompted a great deal of interest, especially as an effective approach to fabricate ultra-high molecular weight polyethylene (UHMWPE) microporous membranes. However, the existing utilized diluents for the TIPS process of UHMWPE suffer from environmental and health issues. Herein, we utilized low molecular weight polybutene (PB) bearing similar structure with liquid paraffin (LP) but inferior miscibility with UHMWPE relative to UHMWPE/LP blend, as a diluent for the TIPS process of UHMWPE. The phase separation behavior of UHMWPE/PB blends were investigated by the combination of rheological measurements, optical microscopy as well as differential scanning calorimeter (DSC). The results suggest that PB is fully miscible with UHMWPE at elevated temperature, but yielding a more sensitive phase separation behavior in respect to LP in TIPS process, because PB has weaker interaction with UHMWPE. The Jeziorny method analysis indicates that the crystallization mechanism of UHMWPE/LP blends is in line with that of UHMWPE/PB blends, which includes nucleation and growth as well as their dynamic competition. Moreover, compared to those of UHMWPE/LP blends, UHMWPE/PB blends display higher TIPS temperature and faster TIPS rate along with faster overall crystallization rate, further demonstrating that PB can accelerate phase separation rates and enhance the efficiency of TIPS process.