Strong Interphase Research Articles

A novel chemical technique for compatibility of ethylene-propylene-diene monomer rubber and styrene-butadiene rubber in their blends

The market for commercial polymer blends has grown steadily. A good blend should have strong interphases between different parts of the constituted polymers. Lack of strong interphases is a classical problem of the blend industry. Ethylene-propylene-diene monomer rubber (EPDM)/styrene-butadiene rubber (SBR) blends have a very good aging resistance and good compression sets. However, these rubbers are partially miscible. To improve the miscibility of EPDM and SBR in their blends, a Lewis acid, AlCl3, was used to form EPDM–g–SBR copolymer through Friedel–Crafts reactions. The existence of covalent bonds between EPDM and SBR macromolecules was studied by the cure traces of the blends, that is, ΔTorque, Fourier transform infrared spectrums, differential scanning calorimetry (DSC) heat flow curves, thermogravimetric analysis curves, and scanning electron (SEM) micrographs. Subsequently, several blends with EPDM/SBR ratio of 40/60 and with various AlCl3 amounts were prepared and after curing, their mechanical properties were measured and compared. The results showed covalent bonds formed between SBR–EPDM and SBR–SBR macromolecules. An exothermic change in heat flow in the DSC curve was observed around 111.28°C, which can be attributed to the formation of carbocations in Friedel–Crafts reactions. Adding 2 phr AlCl3 had an efficient effect on EPDM–SBR and or SBR–SBR linkages. The mechanical properties of the cured blends, that is, tensile strength were lower when compared with corresponding values for prepared compound with SBR. Excellent compatibility between the two polymers and strong interphases were observed in SEM micrograph of the cured blend with 1 phr AlCl3.

Development of simplified Tandon‐Weng solutions of Mori‐Tanaka theory for Young's modulus of polymer nanocomposites considering the interphase

ABSTRACTThe known Tandon‐Weng model originated from Mori–Tanaka theory commonly underestimates the Young's modulus of polymer nanocomposites containing spherical nanofillers. This phenomenon is attributed to disregarding the nanoscale interfacial interaction between polymer and nanoparticles, which forms a different phase as interphase in polymer nanocomposites. In this paper, the simplified Tandon‐Weng model is developed assuming interphase and the predictions of the developed model are compared with the experimental data. The calculations of the developed model completely agree with the experimental results at reasonable levels of interphase properties. Additionally, the effects of main material and interphase properties on the predictions of modulus are evaluated. The developed model predicts that a high‐content, thick, and strong interphase creates a high modulus in polymer nanocomposites. These logical observations demonstrate the correctness of the developed model for Young's modulus of polymer nanocomposites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43816.

Modeling the yield strength of polymer nanocomposites based upon nanoparticle agglomeration and polymer–filler interphase

In this paper, some models for yield strength of polymer nanocomposites are developed to determine the properties of interphase and agglomerated nanoparticles. In this regard, “Bagg” parameter is defined assuming the agglomerates size (Dagg) and interphase properties. Additionally, the influences of “Bagg” and “Dagg” on the thickness and strength of interphase are evaluated by the developed equations.The agglomeration of nanoparticles causes contradictory effects on interphase properties in samples with different levels of interfacial bonding. Also, “Bagg” more depends to interphase properties compared to “Dagg”. It is found that upon increasing in “Bagg” and “Dagg”, the strength of interphase improves and reaches the most level at the highest values of “Bagg” and “Dagg”. Therefore, controlling the levels of “Bagg” and “Dagg” is crucial to obtain a strong interphase.

Effect of nanofiller shape on viscoelasticity of rubber nanocomposite investigated by FEA

Abstract Based on the micromechanical theory, the effect of the shapes of nanofillers on the viscoelasticity of rubber nanocomposites was evaluated by the finite element analysis. The shapes of nanofillers we discussed included sphere, cylinder, tube, plate, ring, and spring. Two types of interphase – “bonding interphase” and “frictional interphase” – which represented the strong interphase and the weak interphase respectively were assumed to discuss the effect of interphase on the viscoelasticity of rubber nanocomposites. The dissipation and loss factors were calculated and discussed. The predicted results show that the shapes of nanofillers have great effect on the viscoelasticity of rubber nanocomposite. Including the spring nanofillers in the rubber matrix can greatly decrease the loss factor of the nanocomposite when the interphase is a “bonding interphase,” while including the ring nanofillers in the rubber matrix can greatly increase the loss factor of the nanocomposite when the interphase is a “frictional interphase.”

Tailoring of dual-interface in high tenacity PP composites – Toughening with positive hybrid effect

The study proves the feasibility of manufacturing injection moulded polypropylene composites reinforced with short rayon cellulose fibres of two selectively tailored fibre–matrix interfaces. The originally developed method relies on selective chemical grafting of two different polymer waxes onto the surface of cellulose fibres in order to obtain two different strengths of fibre–matrix interfaces in one composite. This selective tailoring of a dual-interface is meant to improve the notched impact strength without deteriorating of its flexural strength. Compatibilised fibres have a strong interphase, which conditions the transfer of strain from the matrix to fibres during deformation. Fibres tailored for a weak interface more efficiently hinder the crack propagation at crash. A 32% improvement of composite notched impact strength was achieved with merely a 5% deterioration of its flexural strength. Its specific properties are on the level or better than those of polypropylene counterpart reinforced with the same content of glass fibres.

Luminescent Properties of Nanocomposites on the Basis of Isotactic Polypropylene and Zirconium Dioxide Nanoparticles

At the paper studied luminescent properties of nanocomposites on the basis isotactic polypropylene and zirconium dioxide nanoparticles. Shown that change of nanocomposite colour and maximum amplitude of UV spectres depend on ZrO2 nanoparticles sizes in polypropylene. Found that mean-square roughness of PP +1% ZrO2 composition surface in dependence of cooling rate β changes, i.e. for the samples at regime β1=20 deg/min the roughness is 40-60 nm, whereas for the samples prepared at β2=2 deg/min the roughness is 150-220 nm. Shown that polypropylene matrix works as chemically stable preservative of nanoparticles, preserving its spectral peculiarities. Sufficiently strong interphases interactions between PP matrix and ZrO2 nanoparticles change its luminescent properties.

Mechanical properties and structure of solvent processed novolac resin/layered silicate: development of interphase region

It was shown that the solution mixing method is able to disperse natural and organically modified clays in novolac resin efficiently. Development of a strong interphase region around the silicate layers was also explored.

Influence of interphase properties on the effective behaviour of a starch-hemp composite

Elasticity behaviour of a fully biopolymer composite is studied using both numerical and experimental approaches. Hemp fibre-starch composite is thermomoulded using a varied content of hemp fibres. On one end, mechanical testing reveals loss of stiffness due to limited load transfer with the increase of fibre content. On the other end, two-phase theories predict a reinforcement trend due to contrast of phase properties. In order to meet both ends, a numerical study is performed to study sensitivity of the predicted mechanical response to geometrical and mechanical considerations. Filler content, arrangement and interphase properties are some of the major studied effects. Interphases are accounted numerically to exhibit the mismatch of load transfer due to imperfect interface behaviour. Finite element results are discussed based on geometrical and mechanical considerations using a sensitivity analysis. Identification of interphase parameters for the tested experimental conditions is attempted successfully. The three-phase model is able to detect where the two-phase system approximation is valid. In addition, strong interphase properties are identified despite the apparent loss of stiffness. Such loss turns to be related to fibre clustering, which makes thermomoulding processing not suitable to achieve fibre volume contents above 10% if not combined with an energetic mixing stage.

Enhanced electrochemical performance of MnO nanowire/graphene composite during cycling as the anode material for lithium-ion batteries

Generally, the capacity of lithium-ion batteries (LIBs) will fade gradually during cycling especially under large current densities because of the structural collapse of electrode materials. Herein, dramatic and favorable electrochemical performance enhancement was observed in a simply achieved MnO nanowire/graphene composite during long-term cycling when utilized as the anode material for LIBs. Characterized by high-resolution transmission electron microscopy, X-ray diffraction and Fourier-transfer infrared spectroscopy, the MnO nanowires were gradually collapsed to nano-spindles and further nanoparticles but these newly formed nanoparticles are still stably anchored on the graphene lamellas. Correspondingly, the specific capacity of the MnO nanowire/graphene electrode exhibited a significant enhancement with a durable life after a slight decrease in the first several cycles. The reason for the self-enhancement could be ascribed to the strong interphase interaction between MnO and graphene flakes. Our work provides a new understanding and insight for the electrochemical behavior of composite electrodes in LIBs and is helpful for the fabrication of high-performance anode materials.

Dielectric relaxation of conductive carbon black reinforced ethylene‐octene copolymer vulcanizates

The dielectric relaxation behavior of different conducting carbon black‐filled ethylene‐octene copolymer (EOC) vulcanizates prepared by melt‐mixing method has been studied as a function of frequency (100 Hz–5 MHz) over a wide range of temperatures (25–100°C). The effect of filler loading and frequency on AC conductivity, dielectric permittivity, impedance, and dielectric loss tangent (tanδ) has been studied. The nature of variation of the dielectric permittivity with the filler loadings was explained on the basis of interfacial polarization of the filler in the polymer matrix. The effect of filler loading on the real and complex part of the impedance was explained by the relaxation dynamics of the polymer chains in the vicinity of the fillers. The effect of filler and temperature on dielectric loss tangent, dielectric permittivity, AC conductivity, and Nyquist plot was also reported. The bound rubber (BR) value increases with increase in filler loading suggesting the formation of strong interphase, which is correlated with dielectric loss. Thermal activation energy (Ea) was found to be decreasing with the temperature, which follows the Arrhenius relation: τb = τ0 exp(−Ea/KBT) where τb is the relaxation time for the bulk material. From the plot of lnτb versus inverse of absolute temperature (1/T), the activation energies (Ea) were found to be 0.37 and 0.44eV, respectively. The percolation threshold was observed with 40 phr carbon black loading. POLYM. COMPOS., 37:342–352, 2016. © 2014 Society of Plastics Engineers

An Effective Electrolyte Additive Achieving Dendrite-Free Lithium during Electrochemical Deposition

Lithium (Li) dendrite formation during repeated charging-discharging cycles is one of the critical challenges for the development of next-generation rechargeable Li metal batteries.[1] The dendrites will penetrate through the separator, causing internal short circuit and even thermal runaway of the battery, which is not acceptable for commercial applications. To address this issue, a widely used approach is to create a strong interphase layer between the electrolyte and the Li metal anode in the form of a protective ion-permeable film, also known as a solid-electrolyte interphase (SEI) film.[2] A stronger and more uniform SEI film makes ion conduction more homogeneous, which decreases protuberant tip formation and thus suppresses Li dendrite growth. These approaches include using different electrolyte solvents, salts and additives in electrolytes, which have been shown to effectively enhance the Li deposition behavior.[3-6] Here we introduce a new electrolyte additive A that acts as an effectively SEI formation agent to suppress the Li dendrite growth. This additive can be in-situ electrochemically reduced to form a proactive layer on Cu substrate at a high potential prior to Li deposition. This thin SEI layer can allow Li ion to pass while prevent the electrolyte erosion with the fresh deposited Li metal, thereby a dendrite-free Li film can be obtained.Figure 1 gives the voltage-time profiles of Li deposition process in 1M LiPF6/PC electrolyte without and with additive A. In the control electrolyte (black line), the voltage curve drops quickly from OCV to about 1.0 V vs. Li/Li+, followed by two short slopes between 1.0 V and 0 V which can be attributed to the reduction of PC solvent and salt anion on the substrate surface to form SEI film. Below 0 V, a long Li plating plateau occurs, corresponding to Li deposition reaction. In the electrolyte with additive A (red line), a high voltage plateau occurred at about 2.0 V, which can be ascribe to electrochemical reduction of the additive A to form a proactive layer on Cu substrate at this potential. This layer is supposed to favor the Li deposition of dendrite-free behavior. Figure 2 compares the morphologies (obtained by optical microscope) of the deposited Li films on Cu substrates using electrolytes without and with additive A. The Li film deposited in the control electrolyte is loose and dendritic (Figure 2a), and the Cu substrate surface is not completely covered by Li clusters. In contrast, the electrolyte with additive A shows significant improvement in the Li film surface quality with the elimination of dendrite formation. The Li deposition is smooth and dense, even reflecting blue metallic luminescence. Detailed electrochemical characterization and study of the working mechanism of this additive A will be discussed in the presentation. Acknowledgements This work was supported by the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the Basic Energy Sciences, Office of Science of the U.S. DOE. References F. Ding, W. Xu, G. L. Graff, J. Zhang, M. L. Sushko, X. Chen, Y. Shao, M. H. Engelhard, Z. Nie, J. Xiao, J. Am. Chem. Soc., 135, 4450-4456 (2013).D. Aurbach, E. zinigrad, Y. Cohen, and H. Teller, Solid state ionics, 148, 405-416 (2002).F. Ding, W. Xu, X. Chen, J. Zhang, M. H. Engelhard, Y. Zhang, B. R. Johnson, J. V. Crum, T. A. Blake, X. Liu, J.-G. Zhang, J. Electrochem. Soc. 160, A1894-A1901 (2013).H. Ota, X. M. Wang, E. Yasukawa, J. Electrochem. Soc., 151, A427-A436 (2004).R. Mogi, et al., J. Electrochem. Soc., 149, A1578-A1583 (2002).K. Kanamura, H. Tamura, S. Shiraishi, Z.-i. Takeha, J. Electroanal. Chem., 394, 49-62 (1995).

A theory of thin lamellar eutectic growth with anisotropic interphase boundaries

We present a semiempirical theory of the effects of an orientation dependence of the surface free energy of interphase boundaries (interphase boundary anisotropy) on lamellar eutectic growth in thin samples. We show that, to a good approximation, thin lamellar eutectic patterns with a strong interphase boundary anisotropy travel along the growth front at such a velocity – or, equivalently, at such an inclination angle of the lamellae left behind in the solid – that the surface tension force of the interphase boundary is nearly parallel to the applied thermal gradient. This explains, among other things, the crystallographic locking of lamellar eutectic patterns that occurs in those eutectic grains, which have cusp singularities in the Wulff plot of the interphase boundary. Based on this theory, we show that the rotating directional solidification method, by which a thin sample is rotated with respect to a fixed unidirectional thermal gradient, must yield eutectic lamellae whose trajectories are nearly homothetic to the two-dimensional Wulff form of the interphase boundary. This opens up new possibilities for the experimental study of interphase boundary anisotropy in eutectic alloys.

Intrinsic nanoscale phase separation in miscible mixtures and supramolecular assemblies

A model is used to describe the intrinsic nanoscale phase separation in miscible mixtures and supramolecular assemblies. Phase-separated nanostructures related to size-dependent surface tension, molecular structural factors and strong interphase interactions exist in miscible mixtures and supramolecular assemblies. The intrinsic nanoscale phase separation may exist universally in miscible mixtures.

Effect of interphase interaction within zinc-filled composite coating on the potential of the cathodic protection of steel

The potential of cathodic protection of steel with composite coatings based on polystyrene (PS) filled by highly dispersed powders of zinc (Zn) of different forms and dispersivities is investigated. The potential for all PS/Zn systems with a low content of filler is shown to be less than for pure metal; as some critical value (the percolation threshold) is reached, the negative values of potential increase abruptly and become higher in absolute value than the potential of pure metal. The threshold zinc contents are found to depend on the particle shape and rise from 9 to 30 vol% upon transitioning from spear-shaped to spherical particles. The electrochemical protection properties of a composite coating are correlate with the enthalpy of mixing of filled composites. The enthalpy of mixing in regions of low filling is shown to be negative, indicating strong interphase interaction; that in regions of high filling is positive. The positive enthalpy of mixing corresponds to compositions that generate the potential of cathodic protection. It is found that an increase in the concentration range of positive values of a composition’s enthalpy of mixing occurs symbatically with a decrease in the threshold concentration of metallic zinc within the composition. We conclude that cathodic protection by zinc-filled polymeric composites is due to weak interphase interaction that results in the aggregation of particles of metallic zinc within a polymeric matrix and the appearance of an infinite cluster. In the case of PS/Zn compositions, it is shown that the infinite cluster appears at enthalpies of mixing greater than 0.6 J/g of the composition.

Dynamic mechanical properties of pineapple leaf fiber polyester composites

AbstractIn the recent years, lignocellulosic fibers that originate from a renewable source have been found to provide good reinforcement in polymer matrices. Among the natural fibers, pineapple leaf fiber (PALF) exhibits excellent mechanical properties, besides possessing low density, high stiffness, and low cost. The dynamic mechanical properties, storage modulus (E′), and loss tangent of PALF‐reinforced polyester (PER) composites were evaluated at three frequencies 0.1, 1, and 10 Hz and temperatures ranging from 30 to 200°C. Addition of PALF of 30 mm length (aspect ratio 600) was found to increase the storage modulus leading to a maximum value at 40 wt%. The glass transition temperature (Tg) of the composite of 40 wt% showed a positive shift indicating high polymer/fiber interaction. A new relaxation is observed at 40 wt% showing the presence of a strong interphase at all aspect ratios. SEM photographs of fracture surfaces of composites confirm the results obtained from static and dynamic mechanical analysis. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers

Photoluminescence of a 5CB liquid crystal–organomontmorillonite nanoparticle heterocomposite

Photoluminescence (PL) of a heterocomposite, consisting of the nematic liquid crystal (LC) 4-pentyl-4´-cyanobiphenyl (5CB) and anisometric nanoparticles of montmorillonite (MMT) clay, modified by cetyltrimethylammonium bromide (CTAB) has been investigated at 4.2 and 300 K. The incorporation of this organoclay (B4) to 5CB decreases the emission intensity by 7–8 times due to efficient resonant quenching of the exciting energy by the organoclay. The spectrum shifts to a long-wave region, with this effect being considerably larger at low temperatures. Graphical separation of complex bands, corresponding to the bulk 5CB and 5СВ + В4 heterosystem at both temperatures revealed that the presence of the organoclay resulted in a significant growth of LC dimer quantity, shifting spectra towards longer wavelengths. Changes in the 5CB luminescence under organoclay influence can be explained by quite strong interphase interactions specified earlier by infrared spectroscopy between the MMT surface and LC, and by a realisation of more flat conformations of 5CB molecules. Confinement effects prevent full crystallisation of 5CB in the 5CB + B4 composite, and LC dimer structures located in the organoclay near-surface layers on the outer surface of the nanoparticles and inside its galleries remain in a larger amount, at low temperature, when compared to bulk 5CB. The remaining LC crystallises and photoluminescence from the 5CB monomers becomes intense.

Photocatalytic oxidation of benzene derivatives in aqueous suspensions: Synergic effect induced by the introduction of carbon nanotubes in a TiO2 matrix

Nanostructured composite catalysts produced using multi-walled carbon nanotubes (CNT) and titanium dioxide were prepared by means of a modified acid catalyzed sol–gel method. Materials were extensively characterized by XRD, TG, N2 adsorption–desorption isotherms, TEM, UV–vis spectroscopy and TPD. Composite catalysts with different CNT contents were tested in the photo-oxidation of phenol under different irradiation wavelengths. A correlation between CNT content and the changes in the UV–vis absorption properties is observed especially in the visible spectral range. The introduction of CNT into the titanium matrix induced a synergic effect when irradiating in the near-UV to visible spectral range. This effect may be explained in terms of a strong interphase interaction between CNT and TiO2 in the composite catalysts. CNT with different surface chemical groups were used to produce CNT–TiO2 composites. The presence of mild concentrations of oxygen containing surface groups, mainly carboxylic acids and phenols, appears to produce a beneficial effect in the photocatalytic activity of CNT–TiO2 composite catalysts. The photocatalytic oxidation of other monosubstituted benzene derivatives such as, aniline, nitrobenzene and benzoic acid, has been investigated under visible irradiation. The primary intermediates of photocatalytic reaction are single substituted hydroxy derivatives. The photoefficiency of the composite catalyst showed to be affected by the aromatic ring reactivity properties of the substrate.

Main chain and segmental dynamics of semi interpenetrating polymer networks based on polyisoprene and poly(methyl methacrylate)

Main chain and segmental dynamics of polyisoprene (PI) and poly(methyl methacrylate) (PMMA) chains in semi IPNs were systematically studied over a wide range of temperatures (above and below T g of both polymers) as a function of composition, crosslink density, and molecular weight. The immiscible polymers retained most of its characteristic molecular motion; however, the semi IPN synthesis resulted in dramatic changes in the motional behavior of both polymers due to the molecular level interpenetration between two polymer chains. ESR spin probe method was found to be sensitive to the concentration changes of PMMA in semi IPNs. Low temperature spectra showed the characteristics of rigid limit spectra, and in the range of 293–373 K, complex spectra were obtained with the slow component mostly arising out of the PMMA rich regions and fast component from the PI phase. We found that the rigid PMMA chains closely interpenetrated into the highly mobile PI network imparts motional restriction in nearby PI chains, and the highly mobile PI chains induce some degree of flexibility in highly rigid PMMA chains. Molecular level interchain mixing was found to be more efficient at a PMMA concentration of 35 wt.%. Moreover, the strong interphase formed in the above mentioned semi IPN contributed to the large slow component in the ESR spectra at higher temperature. The shape of the spectra along with the data obtained from the simulations of spectra was correlated to the morphology of the semi IPNs. The correlation time measurement detected the motional region associated with the glass transition of PI and PMMA, and these regions were found to follow the same pattern of shifts in α-relaxation of PI and PMMA observed in DMA analysis. Activation energies associated with the T g regions were also calculated. T 50G was found to correlate with the T g of PMMA, and the volume of polymer segments undergoing glass transitional motion was calculated to be 1.7 nm 3. C-13 T 1ρ measurements of PMMA carbons indicate that the molecular level interactions were strong in semi IPN irrespective of the immiscible nature of polymers. The motional characteristics of H atoms attached to carbon atoms in both polymers were analyzed using 2D WISE NMR. Main relaxations of both components shifted inward, and both SEM and TEM analysis showed the development of a nanometer – sized morphology in the case of highly crosslinked semi IPN.

Interphase Effect on Fiber-Reinforced Polymer Composites

A mathematical model has been developed for the prediction of elastic moduli of three-phase fiber-reinforced composite. This model considers composite materials consisting of three phases, namely, fiber, interphase and matrix, and incorporates the effect of fiber packing. In the present paper, the interphase is assumed to be a homogeneous and isotropic material. The elastic moduli E 11, E 22, G 12 and G 23 have been evaluated and damping coefficients η 11, η 22, η 12and η 23 have been predicted by application of a correspondence principle using this developed model. The effect of interphase volume fraction on loss factors has been evaluated. Prediction of elastic moduli and loss factors has been carried out with a weak and a strong interphase. The calculated results show that the interphase volume fraction and its properties have a very significant effect on loss factor of fiber-reinforced polymer composite. Evaluation of material properties based on the finite element method is presented using representative volume element approach. Results using the developed model are in good agreement with those obtained by FEM and other methods.

The Role of Interfacial Interactions in the Toughening of Precipitated Calcium Carbonate–Polypropylene Nanocomposites

This paper investigates the effect of the interphase properties and the interfacial interactions between matrix and filler on mechanical properties of precipitated calcium carbonate (PCC)–polypropylene nanocomposites. PCC particles were coated with stearic acid (SA). The weight ratio of SA on the particles (w SA) ranged from 0 to 0.135 g SA/g PCC. The introduction of PCC particles resulted in an increase in stiffness and yield stress compared with the pristine polymeric matrix and, at the same time, it increased the impact resistance. The maximum improvement in the impact behaviour was achieved for the composites with w SA =0.045 corresponding to the theoretical monolayer ratio. A decrease in interfacial interactions between monolayer coated PCCs and the matrix with respect to the uncoated particles was observed by using a semi-empirical equation developed by Pukànszky. The low degree of interfacial interactions between particulate filler and matrix allows a matrix–particle debonding phenomenon, as shown by scanning electron microscopy analysis. Extensive plastic deformations were evident as well, promoting an improvement in toughness. The thickness of the interphase between particles and matrix was evaluated by using the Shen–Li model which is based on the hypothesis of a non-homogeneous interphase. It results that the thickness increased in the order uncoated < monolayer coated < 3% SA coated ≅ 13.5% SA coated particles. The thinner and stronger interphase found for the composite with uncoated particles can be explained with the high interaction between matrix and filler and the consequent low mobility of the polymeric chains.