A novel dynamic constitutive micromechanical model to predict the strain rate dependent mechanical behavior of glass/epoxy laminated composites

In the present research, a novel dynamic constitutive micromechanical (DCM) model was developed to predict the strain rate dependent mechanical behavior of laminated glass/epoxy composites. The present model is an integration of the generalized strain rate dependent constitutive model as a constitutive model for the neat polymer, the plasticity model of Huang as a micromechanical model, and dynamic progressive failure criteria. This model is able to predict the longitudinal and transverse tensile and in-plane shear behaviors of unidirectional glass/epoxy composites with arbitrary fiber volume fractions at arbitrary strain rates. The present model can also predict the stress-strain behavior of laminated composites with different layups and fiber volume fractions at arbitrary strain rates. A comparison between the results predicted by the present model and the available experimental data showed that the model predicts the strain rate dependent mechanical behavior of glass/epoxy composites with very good accuracy.     

Surface active properties of polyoxyethylene macromonomers and their role in radical polymerization in disperse systems

Conventional dispersion polymerization and copolymerization of low-molecular weight (conventional) unsaturated monomers allows preparation of monodisperse and micronsize polymer particles. A similar behavior can be found in the surfactant-free dispersion polymerization of non-traditional vinyl monomers, unsaturated macromonomers. The latter systems allow preparation of random, comb-like, star-like and graft copolymers as well. An interesting alternative arises with the use of amphiphilic reactive macromonomers that contain a polymerizable group and aggregate into an organized structure -- a micelle. Under such conditions the high rate of polymerization and ultrafine (microparticles) polymer dispersions are generated. Thus, the surface-active macromonomers promote the formation of micelles and polymer growth within the main reaction loci -- polymer particles. Furthermore, the surface-active compounds can be formed during the copolymerization of hydrophilic macromonomer and hydrophobic low-molecular weight comonomer. The reactive surface-active oligomeric radicals are incorporated into the polymer matrix or the particle surface layer, which prevents them from subsequent migration. Besides, the covalently bound surface-active groups at the particle surface strongly increase the colloidal stability of final polymer dispersion. This article presents a review of the current literature in the field of the surfactant-free dispersion polymerization of the polyoxyethylene unsaturated macromonomers. Besides a short introduction into some kinetic aspects of radical polymerization of traditional monomers in homogeneous and disperse systems, we mainly focus on the organized aggregation of amphiphilic polyoxyethylene macromonomers, the characterization of amphiphilic graft copolymers and their aggregation properties, and radical copolymerization of polyoxyethylene macromonomers. We discuss the birth and growth of chains, the transfer of reaction loci from the continuous phase to polymer particles, the diffusion-controlled termination, association of amphiphilic reaction by-products, the particle growth by agglomeration, the particle nucleation, the deactivation of polymer chain growth and the colloidal stability. Effects of initiator type and concentration, the surface activity of macromonomer, the macromonomer type and concentration, temperature, additives and the type of continuous phase on the kinetics of polymerization, and colloidal parameters of the reaction system are also evaluated. Variation of the polymer coil density, the polymer-polymer interaction, and polymer-solvent interaction with the molecular weight, diluent and method (light scattering, the size exclusion, etc.) are discussed. Polymerization of macromonomers provides regularly branched polymers with varied branching density. Since both the degree of polymerization and the length of branches may be varied, polymeric materials with specific properties can be prepared.     

Epoxy polymer coating to prevent the corrosion of aluminum nanoparticles

Aluminum nanoparticles were coated by epoxy polymer in order to prevent the corrosion reaction. The coverage of the epoxy polymer film was controlled from 0% to 100%, which changed the corrosion rate of nanoparticles quantitatively. The surface of the polymer coating was investigated by transmission electron microscopy (TEM) and atomic force microscopy (AFM), and the corrosion resistance of these nanoparticles was estimated by the wet/dry corrosion test on platinum (Pt) plate with a NaCl solution. From a TEM analysis, 10 mass% polymer‐coated Al particles in the synthesis were almost 100% covered on the surface by a polymer film of 10 nm thick. On the other hand, 3 mass% polymer‐coated Al was partially covered by a film. In the AFM–Kelvin force microscopy, the potential around the Al particles had a relatively low value by the polymer coating, which indicated that the conductivity of the Al was isolated from Pt plate by the polymer. Both the corrosion and H₂ evolution reaction rates were quantitatively reduced by the mass% of polymer coating. In the case of 10 mass% coated sample, there was very little corrosion of Al nanoparticles. This fact suggested that the electrochemical reaction was suppressed by the polymer coating. Thus, it was found that the corrosion reaction rate of Al nanoparticles could be quantitatively suppressed by the mass% of epoxy coating. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and Characterization of Surface-Active Ionic Liquids Used in the Disruption of Escherichia Coli Cells

Twelve surface-active ionic liquids (SAILs) and surface-active derivatives, based on imidazolium, ammonium, and phosphonium cations and containing one, or more, long alkyl chains in the cation and/or the anion, were synthetized and characterized. The aggregation behavior of these SAILs in water, as well as their adsorption at solution/air interface, were studied by assessing surface tension and conductivity. The CMC values obtained (0.03–6.0 mM) show a high propensity of these compounds to self-aggregate in aqueous media. Their thermal properties were also characterized, namely the melting point and decomposition temperature by using DSC and TGA, respectively. Furthermore, the toxicity of these SAILs was evaluated using the marine bacteria Aliivibrio fischeri (Gram-negative). According to the EC₅₀ values obtained (0.3–2.7 mg L⁻¹), the surface-active compounds tested should be considered “toxic” or “highly toxic”. Their ability to induce cell disruption of Escherichia coli cells (also Gram-negative), releasing the intracellular green fluorescent protein (GFP) produced, was investigated. The results clearly evidence the capability of these SAILs to act as cell disruption agents.     

Synthesis and characterization of hyperbranched polymer with epoxide-terminated group and application as modifier for epoxy/polyamide system

Hyperbranched polymer with epoxide-terminated group was synthesized through end-capping reaction between hyperbranched polymer with hydroxyl-terminated group and epichlorohydrin. The chemical structure of the synthesized polymer was characterized by ATR-IR and ¹H NMR spectroscopy. The influence of hyperbranched polymer content on the mechanical properties and fracture toughness of epoxy/polyamide systems was investigated. The toughening mechanism was discussed basing on observing the fracture surface morphologies of epoxy/polyamide/ hyperbranched polymer system.     

环氧树脂/玻璃纤维复合界面的电子能谱化学分析

采用化学分析用电子能谱技术分别对机械剥离后的玻璃纤维布和短切玻璃纤维增强环氧树脂试样的玻璃纤维面作了对比分析,发现树脂残留物表面上有富裕的环氧基,证明剥离不是发生在树脂／玻璃纤维（布）粘结界面上,而是发生在粘结界面附近的树脂层里;环氧树脂／玻璃纤维布界面比环氧树脂／短切玻璃纤维界面有更强的界面增强效应。     

Insights into phthalonitrile/epoxy blends modification system from non-competitive cure system based on alicyclic anhydride

A series of polymer blends were prepared from 1,3-bis(3,4-dicyanophenoxy)benzene (3BOCN) and epoxy resin with methyl tetrahydrophthalic anhydride as curing agent.The curing behavior and curing kinetics of the blends were studied by differential scanning calorimetry.The apparent activation energy of the blends with various contents of 3BOCN was higher than that of the blends without 3BOCN.A model experiment suggested that there is no obvious reaction between phthalonitrile and epoxy.The thermal and mechanical properties of the polymer blends were evaluated.The polymer blends exhibit high storage modulus and char yield compared with the neat epoxy.The polymer blends show ductile fracture morphology by scanning electron microscopy (SEM) images.     

A model for simulating the dynamic surface tension behavior of aqueous surfactant dispersions

A dynamic adsorption model for surface-active materials at air/liquid interfaces with the consideration of aggregate dissolution effect was developed to investigate the dynamic surface tension behavior of aqueous surfactant dispersions. Two catanionic surfactants, cetylpyridinium dodecylsulfate (CP-DS) and dodecyltrimethylammonium dodecylsulfate (DTMA-DS), with low critical aggregation concentrations were chosen as model systems. Dynamic surface tensions of aqueous CP-DS and DTMA-DS systems were measured by a drop volume tensiometer. A model with diffusion-controlled or mixed-kinetic dynamic adsorption mechanisms considering the dissolution effect of dispersed aggregates was developed to simulate the dynamic surface tension data. An analysis by comparing the model predictions with experimental data demonstrated that the dynamic surface tension behavior of aqueous CP-DS and DTMA-DS dispersions could be described with a diffusion-controlled dynamic adsorption model taking the aggregate dissolution effect into account.     

Combined effect of zeolite and boric acid on thermal behavior of epoxy composites

The particles of natural zeolite in combination with boric acid were incorporated into the epoxy resin ED-20 in order to improve the thermal stability of epoxy polymer. Epoxy resin was cured using polyethylenepolyamine. Characterization of the epoxy composites was carried out by using Fourier transform infrared spectrometry, thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) under flow of air and argon. The thermal behavior of the zeolite/boric acid-based epoxy composites (total percentage 15 mass%) were compared with that of 15 mass% boric acid-based epoxy system and the neat epoxy resin. TG and DSC results revealed that the combination of 5 mass% zeolite and 10 mass% boric acid significantly increased the mid-point temperature and residue, and decreased the maximum decomposition rate of the epoxy composites at the heating.     

Solvent vapor mediated polymer adsorption in thin films

The effectiveness of a "solvent annealing" process was investigated for thin (approximately 150 nm) polystyrene films, in which the diffusion and reorganization of polymer chains were mediated by the controlled absorption of cyclohexane vapor. Results were compared with conventional "thermal annealing" of films under vacuum above the glass transition temperature. Elastic recoil detection analysis (ERDA) was used to determine the surface excesses of fluorocarbon end-capped polystyrene (hPSF) and poly(styrene-b-dimethylsiloxane) (hPS-PDMS) in deuterated polystyrene (dPS) films. Both annealing methods enabled diffusion of the surface-active polymers; however, only thermal annealing gave rise to a surface excess in hPSF/dPS films. The inhibition ofhPSF adsorption under solvent annealing was due to the low surface tension of cyclohexane. In contrast, hPS-PDMS, having a larger surface-active group than that of hPSF, was found in excess at the air surface under solvent annealing, and surface excesses were consistent with the formation of saturated monolayers in blended films. The mixing of hPS-PDMS with dPS was inhibited by the unfavorable interaction between the PDMS block of the copolymer and the homopolymer. The slow interdiffusion of hPS-PDMS in dPS is consistent with the formation of micelles, and the formation of an excess layer at the air surface may be kinetically inhibited by the rate of dissociation of hPS-PDMS micelles.     

Nukleophile Substanzen zur Entgiftung von Phosphorestern

A series of N-substituted hydroxylamine derivatives was synthesized as a potential substitute for calcium hypochlorite. Like calcium hypochlorite, these compounds are highly P(V)-nucleophilic with respect to toxic phosphorus esters.Incorporating surface-active structural elements into the compounds can enhance their reactivity to phosphorus esters on the one hand (micelle catalysis); on the other hand aqueous solutions of these compounds wet polymer surfaces easily, thus ensuring that they can be well applied. The effectiveness of the compounds in the detoxification of phosphorus esters was examined using diisopropyl fluorophosphate (DFP) as a model substance.

     

Graphene–Epoxy Flexible Transparent Capacitor Obtained By Graphene–Polymer Transfer and UV‐Induced Bonding

A new approach is reported for the preparation of a graphene–epoxy flexible transparent capacitor obtained by graphene–polymer transfer and UV‐induced bonding. SU8 resin is employed for realizing a well‐adherent, transparent, and flexible supporting layer. The achieved transparent graphene/SU8 membrane presents two distinct surfaces: one homogeneous conductive surface containing a graphene layer and one dielectric surface typical of the epoxy polymer. Two graphene/SU8 layers are bonded together by using an epoxy photocurable formulation based on epoxy resin. The obtained material showed a stable and clear capacitive behavior.

     

Polyimide incorporated cyanate ester/epoxy copolymers for high-temperature molding compounds

The rapid development of high-power devices has driven the requirement for high-temperature stable epoxy molding compounds. In this work, a designed polymer blend system consisting of cyanate ester/epoxy copolymers modified by polyimide (CE/EP-PI) has been studied. Polyimide used in this study has shown excellent dispersity in the cyanate ester and epoxy copolymer network (CE/EP), exhibiting homogeneous phase with a denser polymer network structure. With this polymer blend structure, CE/EP-PI system was proved to have a glass transition temperature as high as ~270 °C, increased modulus, and largely enhanced fracture toughness up to 2.06 MPa m^1/2. CE/EP-PI resins showed outstanding long-term stability at high temperature with low mass loss and increased fracture toughness after aging at 200 °C. This work provides a novel insight into the development of molding compounds based on polymer blends system with excellent high-temperature properties. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2412–2421     

Surface Properties of the Solutions of Phase-Forming Oligomers in Diglycidyl Ether of Bisphenol A

Temperature and concentration dependences of the surface tension were measured for solutions of several phase-forming oligomers in diglycidyl ether of bisphenol A by modified Wilhelmy method. Contact angles were determined upon wetting of a cured epoxy resin by oligo(oxypropylene glycols) with different terminal groups. All the oligomers were shown to demonstrate surface-active properties. A thermodynamic compensation effect was disclosed: the surface tensions of all studied systems were almost equal at T 340 K.     

Surface activity and emulsification properties of hydrophobically modified dextrans

Neutral polymeric surfactants were synthesized by covalent attachment of hydrophobic groups (aromatic rings) onto a polysaccharide backbone (dextran). By changing the conditions of the modification reaction, the number of grafted hydrophobic groups per 100 glucopyranose units (substitution ratio) was varied between 7 and 22. In aqueous solution, these polymers behaved like classical associative polymers as demonstrated by viscometric measurements. The associative behavior was more pronounced when the substitution ratio increased. The surface-active properties of the modified dextrans were evidenced by surface tension (air/water) and interfacial tension (dodecane/water) measurements. In each case the surface or interfacial tension leveled down above a critical polymer concentration, which was attributed to the formation of a dense polymer layer at the liquid-air or liquid-liquid interface. Dodecane-in-water emulsions were prepared using the polymeric surfactants as stabilizers, with oil volume fractions ranging between 5 and 20%. The oil droplet size (measured by dynamic light scattering) was correlated to the amount of polymer in the aqueous phase and to the volume of emulsified oil. The thickness of the adsorbed polymer layer was estimated thanks to zeta potential measurements coupled with size measurements. This thickness increased with the amount of polymer available for adsorption at the interface. The dextran-based surfactants were also applied to emulsion polymerization of styrene and stable polystyrene particles were obtained with a permanent adsorbed dextran layer at their surface. The comparison with the use of an unmodified dextran indicated that the polymeric surfactants were densely packed at the surface of the particles. The colloidal stability of the suspensions of polystyrene particles as well as their protection against protein adsorption (bovine serum albumin, BSA, used as a test protein) were also examined.     

Structure of association in surface films

Association complexes which from on the polar groups of surface-active compounds during the spreading process on surfaces are described. In the hydration complexes of the interface 1, 2, 4, 9, 16 etc. water molecules surround the hydrophilic group. With the compression of a monolayer spread on water, complexes of higher water contents, out of which the water is pressed, are in thermodynamic equilibrium with the complexes of lower content thus formed.The association equilibrium described apply both to monomear and to polymer compounds, as is shown using the example of polydimethylsiloxane. The principles of the surface structures are discussed with the aid of surface tension, film pressure, space requirement, contact angle and heats of association.     

表面起伏光栅形成速率的影响规律 Ⅰ.偶氮生色团种类和官能度的影响

设计并合成了含有不同生色团以及不同官能度的环氧树脂基偶氮高分子 ,系统研究了偶氮生色团的种类和官能度对光栅形成速率的影响规律 .实验结果表明 ,偶氮苯对位是羧基的聚合物的光栅形成速率明显快于偶氮苯对位是硝基的聚合物 ,光栅形成速率随偶氮生色团官能度的增加而加快 .这两类聚合物都可以形成规整的可擦式表面起伏光栅     

A novel procedure able to predict the rheological behavior of trifunctional epoxy resin/hyperbranched aliphatic polyester mixtures

A hyperbranched polymer (HBP), based on a highly branched polyester, was added to a trifunctional triglycidyl-p-aminophenol (TGAP) epoxy resin as a possible route to increase the toughness of the resin. Different amounts of the HBP, up to 26.5% wt. of resin, were dispersed in the TGAP resin. The rheological behavior of the formulations produced was studied as function of the shear rate and the filler content using a cone and plate rheometer. The rheological behavior of the TGAP resin, initially Newtonian, was modified displaying a pseudo-plastic trend when the hyperbranched polymer was added. An increase in the viscosity of the resin was observed with increasing volume fraction of the filler. The Cross equation was used to predict the viscosity of each formulation as a function of the shear rate. A novel procedure was developed to predict the viscosity of each mixture as a function of the filler volume fraction. This could be employed to provide quantitative information on the filler volume fraction in epoxy/HBP systems, necessary to achieve the characteristic viscosity values corresponding to the typical shear rates for a specific processing technology.     

Fabrication of mesoporous silica/polymer composites through solvent evaporation process and investigation of their excellent low thermal expansion property

We fabricate mesoporous silica/epoxy polymer composites through a solvent evaporation process. The easy penetration of the epoxy polymers into mesopores is achieved by using a diluted polymer solution including a volatile organic solvent. After the complete solvent evaporation, around 90% of the mesopores are estimated to be filled with the epoxy polymer chains. Here we carefully investigate the thermal expansion behavior of the obtained mesoporous silica/polymer composites. Thermal mechanical analysis (TMA) charts revealed that coefficient of linear thermal expansion (CTE) gradually decreases, as the amount of the doped mesoporous silica increases. Compared with spherical silica particle without mesopores, mesoporous silica particles show a greater effect on lowering the CTE values. Interestingly, it is found that the CTE values are proportionally decreased with the decrease of the total amount of the polymers outside the mesopores. These data demonstrate that polymers embedded inside the mesopores become thermally stable, and do not greatly contribute to the thermal expansion behavior of the composites.