Diffusion and phase relaxations within the interphase domain of polymer blendlike particles

A single-photon counting technique in conjunction with a direct energy transfer (DET) method was used to study the diffusion of small dye molecules within the interphase domain of anthracene (An)- and/or phenanthrane (Phe)-labeled poly(methyl methacrylate) (PMMA) particles sterically stabilized by polyisobutylene (PIB). Mean lifetimes of fluorescing donor molecules were measured during diffusion. A Fickian model for diffusion was employed to fit the experimental data and diffusion coefficients were found to be around 10⁻¹⁹ and 10⁻¹⁶ cm^2/s at room and above glass transition temperatures (T_g) for the corresponding samples, respectively. A reversed Gaussian distribution was detected for the PMMA phase density at the interphase domain. An increased amount of self-quenching of naphthalene (N) dyes labeled to the PMMA phase was investigated against annealing temperature above T_g and the results were attributed to phase relaxations at the interphase domain. © 1996 John Wiley & Sons, Inc.     

ESR studies of molecular motions at the interphase region of a blendlike polymeric material

The molecular motions of spin probes at the interphase region of poly(methyl methacrylate) particles sterically stabilized by polyisobutylene (PIB) were studied by ESR spectroscopy. The correlation times (τ) were measured by using the methods of Freed and Kivelson. Activation energies for different modes of motion were calculated at wide temperature range between ?140 and 140°C. Viscosities were estimated in methanol saturated PIB channels in the polymer particles. © 1994 John Wiley & Sons, Inc.     

Compositional variation within the epoxy/adherend interphase

At a polymer-solid interface, an inorganic adherend may influence the structure and/or chemistry of the polymer in the near-interface region. This region between the adherend and the homogeneous polymer is referred to as the interphase. While there is general agreement that interphases exist, extensive debate revolves around the characteristic length scale of the interphase and its composition and structure. The present study examines the size and composition of the epoxy-aluminum interphase using spatially resolved electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). Aliphatic bis(p-aminocyclohexyl)methane (PACM20) curing agent and aromatic diglycidyl ether of bisphenol-A (DGEBA) epoxy resin were selected as a model system. Spatially resolved π - π ^*, carbon, and thickness profiles were measured using EELS in the epoxy region immediately adjacent to the interface between the bulk epoxy and the nanoporous oxide on the aluminum adherend surface. These profiles systematically show deviations in the spectral intensities characteristic of carbon and aromaticity over distances extending 90±15 nm from the oxide surface. Simulations of such data indicate that these fluctuations cannot be accounted for by variations in specimen thickness but rather result from changes in epoxy composition near the oxide surface. The results show that this epoxy- aluminum interphase is enriched in curing agent, as indicated by a gradual compositional change from 25 ± 5 vol% PACM20 in the bulk epoxy to 80 ± 15 vol% PACM20 at the epoxy/oxide interface. This chemical segregation may have important implications on the properties and performance of epoxy-aluminum adhesive joints.     

Electrical conductivity of interphase zone in polymer nanocomposites by carbon nanotubes properties and interphase depth

In this work, carbon nanotubes (CNT) properties and interphase depth define the interphase conductivity in polymer CNT nanocomposites (PCNT). In addition, the operative CNT length and volume portion are linked to the conductivity transportation between CNT and insulated polymer medium to propose a simple model for conductivity. The significances of various terms on the interphase conductivity and conductivity of PCNT are justified and the model's predictions are examined using the experimental outputs of certain examples. Thin CNT and dense interphase obtain the extraordinary conductivity transportation, while CNT length and conductivity are ineffective. Moreover, thin, small, and high-conductive CNT as well as dense interphase introduce the high interphase conductivity. The estimations of conductivity appropriately follow the experimental data authorizing the established model. This model is capable to substitute the conventional models owing to the assumption of innovative nanocomposite's terms.     

Dependence of morphological changes of polymer particles on hydrophobic/hydrophilic additives

Fairly uniform microspheres of poly(styrene‐co‐methyl methacrylate) were prepared by employing a microporous glass membrane [Shirasu porous glass (SPG)]. The single‐step SPG emulsification, the emulsion composed mainly of monomers, hydrophobic additives, and an oil‐soluble initiator, suspended in the aqueous phase containing a stabilizer and inhibitor, was then transferred to a reactor, and subsequent suspension polymerization followed. The droplets obtained were polymerized at 75°C under a nitrogen atmosphere for 24 h. The uniform poly(styrene‐co‐methyl methacrylate) microspheres with diameters ranging from 7 to 14 μm and a narrow particle‐size distribution with a coefficient of variation close to 10% were prepared by using SPG membrane with a pore size of 1.42 μm. The effects of the crosslinking agent and hydrophobic additives on the particle size, particle‐size distribution, and morphologies were investigated. It was found that the particle size decreased with a narrower size distribution when the additives were changed from long‐chain alkanes to long‐chain alcohols and long‐chain esters, respectively. Various microspheres with different morphologies were obtained, depending on the composition of the oil phase. The spherical poly(styrene‐co‐methyl methacrylate) particles without phase separation were obtained when using an adequate amount of the crosslinking agent and methyl palmitate as an additive. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1013–1028, 2000     

Electrodeposition of a polymer interphase in carbon-fiber composites

The performance of an electrodeposited interphase of poly(butadiene-co-maleic anhydride) (BMA) in carbon-fiber composites is investigated. Carbon fibers are electrocoated with BMA from an aqueous solution and the coated fibers are fabricated into composite bars for evaluation of mechanical properties. These composites show superior impact strength, but lower interlaminar shear strength, compared to composites made from commercially treated fibers. It is suggested that unsaturation in the butadiene segments of the interphase polymer leads to the formation of a crosslinked layer during electrodeposition and subsequent drying. Inadequate penetration of this interphase by bulky epoxy molecules leads to a weak interphase/matrix interface which is the locus of failure, generating the observed mechanical properties. These conclusions are supported by examination of the fracture surfaces by Scanning Electron Microscopy. Further evidence of lack of matrix penetration into the interphase comes from electron microprobe line scans for bromine performed on cross-sections of single-filament composites, the bromine being introduced into the matrix via a brominated epoxy resin. Appropriate control of the chemical structure and physical characteristics of the interphase polymer is thus indicated, for acieving simultaneous improvements in impact and interlaminar shear strengths.     

The effects of transcrystalline interphase in advanced polymer composites

Surface-induced transcrystallization in fibers has been reported in some advanced polymer composites. It is believed that transcrystalline interphase may affect stress transfer efficiency between the reinforcing fiber and the matrix. In this study, attempts were made to examine the effects of transcrystallinity on composite performance, particularly on fiber-matrix interfacial bond strength, and to investigate possible attributes of transcrystallization. Three polymer resins, poly(etherketoneketone) (PEKK), poly(etheretherketone) (PEEK), and poly(phenylenesulfide) (PPS), and four types of fiber, polyacrylonitrile (PAN)-based AU-4 (untreated AS-4) carbon, pitch-based carbon, poly (p-phenylene terephthalamide) (PPDT) aramid, and E-glass were used. It was found that PPDT aramid and pitch-based carbon fibers induce a transcrystalline interphase in all three polymers because of an epitaxial effect. Under certain conditions, transcrystallization was also observed in PAN-based carbon and E-glass fibers, which may be partially attributed to the thermal conductivity mismatch between the fiber and the matrix. Plasma treatment on fiber surface showed a negligible effect on inducing transcrystallization, whereas solution-coating of PPDT on the fiber surface showed a positive effect. The Microdebonding test, which measures the interfacial bond strength between the fiber and the matrix, consistently showed more than 40% increments for various single filament systems with transcrystalline interphase versus without. However, the effects of transcrystallinity on the interfacial bond strength appeared to decrease as the fiber content increased in composites.     

The viscosity of immiscible polymer blends: influences of the interphase and deformability

The viscosity of immiscible polymer blends has been studied via application of certain aspects of rheology. A symmetric mixture rule was derived, and the deviations from the ‘additivity rule’ have been associated, essentially, with the properties of the interphase, with its influence on the effective volumes of the two polymers constituting the blend and with the deformability of both the interphase and the disperse phase. The rule predicts a positive deviation for a mixture with a disperse-phase viscosity (η_d) greater than that (η_m) of the continuous medium, and a much higher-viscosity interphase, i.e. η_i å η_d ≥ η_m. Negative deviation is to be expected when the interphase has a much lower viscosity than those of the two pure polymers (η_d, η_m å η_i) in the blend. The viscosity and strength of the interphase depend mostly on the specific thermodynamic interactions that led to its creation.     

A comparative study to predict the interphase modulus in polymer nanocomposites

In this study, the interphase modulus (E_i) in polymer nanocomposites is calculated by two methods and the calculated results are compared at different conditions. In the first method, the experimental moduli of samples are applied to Ji model and suitable “E_i” is calculated. In the second method, a multilayered interphase is considered, in which the Young's moduli of layers (E_k) depend to the distance between the nanoparticle surface and the polymer matrix by power function of “Y” parameter. The “E_i” is calculated for multilayered interphase assuming the same and different layer thicknesses (t_k) by Parallel and Series models. Finally, the “E_i” values calculated by the explained methods are compared for two reported samples. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44076.     

Volume changes upon heating of aerosol particles from biomass burning using transmission electron microscopy

The responses of aerosol particles to heating are important for measurements of their chemical, physical, and optical properties, classification, and determination of origin. However, the thermal behavior of organic aerosol particles is largely unknown. We provide a method to analyze such thermal behavior through heating from room temperature to >600°C by using a heating holder within a transmission electron microscope (TEM). Here we describe in-situ shape and size changes and variations in the compositions of individual particles before and after heating. We use ambient samples from wildland and agricultural biomass fires in North America collected during the 2013 Biomass Burning Observation Project (BBOP). The results indicate that individual tar balls (TB; spherical organic material) from biomass burning retained, on average, up to 30% of their volume when heated to 600°C. Chemical analysis reveals that K and Na remain in the residues, whereas S and O were lost. In contrast to bulk sample measurements of carbonaceous particles using thermal/optical carbon analyzers, our single-particle results imply that many individual organic particles consist of multiple types of organic matter having different thermal stabilities. Beyond TBs, our results suggest that because of their thermal stability some organic particles may not be detectable by using aerosol mass spectrometry or thermal/optical carbon analyzers. This result can lead to an underestimate of the abundance of TBs and other organic particles, and therefore biomass burning may have more influence than currently recognized in regional and global climate models.

Copyright © 2018 American Association for Aerosol Research     

Dynamic stress/strain response of the interphase in polymer matrix composites

The interphases of various sized E‐glass‐fiber/epoxy‐amine systems were tested at displacement rates in the range of 230 to 2450 fxm/sec using a new experimental technique (dynamic micro‐debonding technique). The fiber systems include unsized, epoxy‐amine compatible sized, and epoxy‐amine incompatible sized glass fibers. A data reduction scheme was developed to relate the force vs. displacement response obtained from the dynamic micro‐debonding technique to interphase shear stress/strain response. The stress/strain curves and interphase shear modulus values were obtained from these composite systems under average shear strain rates (ASSR) in the range of 215–3278 (1/s). The results showed that the magnitude of the interphase shear modulus was sizing and strain rate dependent. In all cases, the shear modulus was found to be more compliant than the bulk matrix. The two sized fiber systems exhibited the highest strain rate sensitivity, with modulus increasing about threefold over the range studied. In addition, the rate dependent behavior of the model interphase materials were determined using the dynamic mechanical analysis (DMA) technique. The model interphase materials closely resemble the interphase that forms on unsized and compatible sized fibers. Master curves relating the flexural storage modulus to strain rate were constructed based on the time‐temperature superposition principle from DMA frequency sweep measurements. The DMA measured results are consistent with the dynamic micro‐debonding test results, providing confidence in the test method as a reliable technique for characterizing the high strain rate properties of the interphase in composites.     

Correlation between mechanical damping and interphase content in interpenetrating polymer networks

Recently, some interpenetrating polymer networks with good mechanical damping properties have been synthesized. However, the effect of morphology on this property has not yet been clearly elucidated. Herein, two polystyrene–polyurethane interpenetrating polymer networks, which were grafted using TMI [benzene‐1‐(1‐isocyanato‐1‐methyl ethyl)‐3‐(1‐methylenyl)] and HEMA (2‐hydroxyethyl methacrylate), respectively, have been investigated, as model samples, by modulated‐temperature differential scanning calorimetry and by dynamical mechanical thermal analysis. The results indicate that there is a correlation between mechanical damping and both interphase content and the distribution of composition in the interphase region. The findings should provide valuable information for the design of future damping materials. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2439–2442, 2001     

Nanoscale characterisation of thickness and properties of interphase in polymer matrix composites

An overview is presented of the properties and effective thickness of the interphase formed between fibres and polymer matrices. Chemical and physical characterization of the interphase is discussed to portray molecular interactions comprising the interphase layers in silane-treated glass-fibre composites. The gap between physico-chemical investigation on one side and bulk material testing on the other side is bridged by implementation of novel techniques, such as nanoindentation, nanoscratch tests, and atomic force microscopy (AFM), which have been successfully used for nanoscopic characterization of the interphase in the past few years. Salient differences are identified between the major findings of these studies in terms of hardness/modulus of the interphase relative to the bulk matrix material. While there is a significant "fibre stiffening" effect that may cause misinterpretation of the interphase hardness very close to the fibre, the formation of both a softer and a harder interphase is possible, depending on the combination of reinforcement, matrix, and coupling agent applied. This is explained by different interdiffusion behaviour, chemical reactions, and molecular conformation taking place at the interphase region in different composite systems. The effective interphase thickness is found to vary from as small as a few hundred nanometers to as large as 10 µm, depending on the constituents, coupling agent, and ageing conditions.     

The influence of filler particles and polymer structure on the mobility of polymer molecules

The presence of carbon filler has been shown to cause a change in the glass transition temperature of polymers. For poly(vinyl chloride) and two of its copolymers with 10 and 15% vinyl acetate an increase in T_g was observed when Graphon C Carbon was added. The increase was greater when the proportion of vinyl acetate was greater. Polar vinyl acetate units allow stronger adsorption of polymer onto the carbon. Brittle polymers such as polystyrene and poly(methyl methacrylate) showed scattered T_g's when filled with carbon. The changes were not a function of concentration. It is postulated that the thermal stress of these polymers is increased in the presence of filler.     

Viscoelastic effects in the coalescence of polymer particles

A study was made of the coalescence of linear acrylic resins over a much greater dynamic range than previously investigated. The rate of neck growth between a sphere and a flat slab of the same material was measured in situ by optical microscopy and found to exhibit a number of features typical of polymer viscoelastic response. Results are compared with independent measurements of the melt rheology (torsional creep compliance). An analytic approximation is proposed which allows the neck-growth kinetics to be predicted from the recoverable creep compliance and viscosity of the melt. It predicts qualitative trends consistent with the limited data on molecular weight, structure, and particle size variations. This analysis helps resolve some apparent contradictions among earlier studies and implies a qualitative difference in the coalescence mechanisms for large particles (5 μm) and colloids (<0.5 μm). In either case, the ultimate equilibration to homogeneous bulk mechanical properties requires times on the order of the terminal relaxation time, regardless of particle size. Evidence is presented that, in addition to the recognized effects of chain inter-diffusion, stress relaxation may play a role in the equilibration kinetics.     

Preparation and characteristics of ultrafine metal particles immobilized on fine polymer particles

Ultrafine metal particles immobilized on fine copolymer particles were produced by reduction of copolymer particles–metal ion complexes. Submicrometer-size copolymer particles containing nitrogen, prepared by emulsifier-free emulsion polymerization, were applied. Transmission electron microscopy (TEM) observation and X-ray diffraction analysis indicated that ultrafine noble metal particles with diameter below 10 nm were formed and uniformly immobilized on the surface of copolymer particles. © 1995 John Wiley & Sons, Inc.     

高分子胶粘剂与金属粘接的界相理论及其研究进展

在胶粘剂基体和被粘材料之间存在着一个三维转变相区,这一相区被称为界相。在粘接接头中应力通过界相从一侧被粘接体传递到另一侧被粘接体,而且界相最易受环境影响而导致粘接失效,因此界相对粘接接头的性能,如强度、刚度、耐候性等起着非常重要的作用。对界相性能、尺寸大小及形成过程机理的认识有助于控制粘接接头的整体性能。本文介绍了高分子胶粘剂与金属粘接界相形成的相关机理及研究进展。     

Characterization and modeling of sintering of polymer particles

An experimental study of simultaneous sintering of several particles has been carried out using spherical polymer grains. Considering rotational molding condition, coalescence of several grains in contact, happens simultaneously on internal surface of the mould. Theoretical model based on the effect of surface tension and viscosity can accurately predict the coalescence of a pairs of grains. However, it was observed in this study that coalescence rate changes with presence of neighboring grains and their position and the theoretical model proposed for two grains, is not able to predict the coalescence rate of mutli‐grains. Based on this finding, we have modified this model with taking into account the effect of neighboring particles in the sintering rate of multi‐grains. Obtained modified model is capable of predicting the multi‐grains sintering rate observed in this study. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

中空聚合物乳胶粒子的制备

研究了在制备中空乳胶粒子的过程中,复合乳液（苯乙烯（Ｓｔ）－丙烯酸丁酯（ＢＡ）－甲基丙烯醛（ＭＡ））进行种子聚合时,Ｓｔ／ＢＡ的质量比和ＭＡ的用量对胶乳粒子的空径、粒径和表面羧基质量摩尔浓度的影响。实验结果表明,当Ｓｔ／ＢＡ的质量比为１９,ＭＡ质量分数为单体的５．６％时,形成的乳胶粒子的空径最大。