Strong Polymer-filler Interactions Research Articles

Vapor phase infiltration of ZnO quantum dots for all-solid-state PEO-based lithium batteries

Composite solid polymer electrolytes (CSPEs) have long been considered as one of the most promising candidates for all-solid-state lithium batteries owing to the merits of easy fabrication and low cost. However, the inorganic fillers physically mixed into the polymer matrix have weak polymer-filler interactions and tend to agglomerate, which limits the further improvement of the ionic conductivity and Li+ transference number of CSPEs. In this work, we demonstrated ZnO quantum dots can be chemically incorporated into the poly(ethylene oxide) (PEO) matrix by vapor phase infiltration (VPI), a special variant of atomic layer deposition (ALD). The ZnO quantum dots have strong chemical interactions with PEO polymer chains, which suppresses the crystallization of PEO and enhances the Li+ conduction. Due to the strong interactions, ZnO quantum dots distribute uniformly in the PEO-based solid electrolyte matrix as well as the top surface, which leads to a significant decrease of interfacial resistance with Li metal. As a result, the NCM811|Li half-cell with the VPI-ZnO/PEO/LiTFSI CSPE exhibit high discharge capacity at 50 ℃ (164.7 mAh g−1 at 0.5 C (1 C = 200 mA g−1), 2.8–4.25 V). This result could potentially serve as a model for a more general approach of using VPI to introduce strong polymer-filler interaction in CSPEs for high-performance lithium metal batteries.

Dispersion and Localization Behavior of Modified MWCNTs in Immiscible Polymer Blends of Polystyrene and Polybutadiene and in Corresponding Nanostructured Block Copolymers

The influence of carbon nanotube (CNT) modification on the dispersion and localization behavior of the CNTs in immiscible blends of polystyrene (PS) and polybutadiene (PB), and in the nanostructured morphology of a star-shaped styrene-butadiene based block copolymer (BCP), was studied to form a basis for the development of functional materials with defined electrical property profiles. Unmodified multi-walled CNTs (MWCNTs) were dispersed in PS, PB and PS/PB blends by solution mixing. Additionally, MWCNTs were functionalized with n-octadecylamine and monoamino-terminated polystyrene to increase the compatibility between the homopolymers and the nanofiller. The MWCNT dispersion and the blend morphology formation were studied using transmission light microscopy and scanning electron microscopy. The MWCNT dispersion could be significantly improved by the modification of the MWCNTs. All MWCNT types were found to preferably localize in the PS phase of the PS/PB blend. However, only blends containing unmodified MWCNTs were electrically conductive. Similar effects were found in BCP/MWCNT composites. The BCP was already electrically conductive with a filler content of 0.1 wt % of unmodified MWCNTs. The stress–strain behavior of the BCP was slightly influenced by MWCNT addition and CNT modification. The dispersability of MWCNTs was significantly improved by CNT functionalization, which indicates a strong polymer-filler interaction.

Preparation and Rheology of Isocyanate Functionalized Graphene Oxide/Thermoplastic Polyurethane Elastomer Nanocomposites

Using monomer-functionalized nanofiller to prepare polymeric nanocomposites is a promising strategy toward achieving enhanced performance. In this study toluene-2,4-diisocyanate (TDI), one of the monomers used for synthesizing polyurethane, was covalently functionalized on graphene oxide (GO) and then the functionalized GO (TDI-GO) was polymerized with polycaprolactone diol (PCL) via in-situ polymerization, leading to chemically linked polyurethane nanocomposites through the covalent bonds between the isocyanate groups on GO and the hydroxyl-terminated PCL. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and dispersion experiments of the nanofillers demonstrated that the TDI was successfully grafted onto the GO. The rheological properties were investigated to establish the structure-property relationships of the nanocomposites. The storage moduli (G’), loss moduli (G”) and complex viscosity (η*) of the samples increased monotonically with TDI-GO content, which is attributed to the strong polymer-filler interactions and the effective dispersion of the nanofillers. Additionally, the tan δ variation with frequency, the intersection of G’ and G”, Han plots, van Gurp-Palmen plots and Cole-Cole plots all showed that the incorporation of TDI-GO decreased the degree of microphase separation and improved the elastic properties of the nanocomposites. We suggest this is related to the enhanced interactions between the polymer and nanofillers, which strongly restricted the mobility and relaxation of the polymer chains.

Impacts of interfacial interaction on properties of melamine formaldehyde microsphere/rubber: I. filler dispersion and curing dynamic

ABSTRACTMelamine formaldehyde microsphere (MF) was incorporated into nitrile butadiene rubber (NBR) and styrene butadiene rubber (SBR), respectively. The interaction between MF and rubber and effects of interfacial interaction on the dispersion of filler in rubber matrix, dynamic mechanical analysis, vulcanisation characteristics and kinetics were studied. The results showed that MF interacted with NBR through hydrogen bonds while there had no observed interaction between MF and SBR. The parameter b of MF/NBR calculated by the ratio of modulus and strains increased significantly, which demonstrated further the strong interaction between MF and NBR. For MF/SBR system, however, the parameter b changed slightly with little polymer–filler interaction. The Scanning Electron Microscope images released that strong polymer–filler interaction caused the uniform dispersion of MF in NBR matrix. The vulcanisation of MF/rubber was fitted by Ghoreishy’s model, and the addition of MF increased the rate of curing, shear modulus of compound and activity energy.

Mechanical and Electrical Properties of Elastomer Nanocomposites Based on Different Carbon Nanomaterials

Carbon nanostructures including carbon black, carbon nanotubes, graphite or graphene have attracted a tremendous interest as fillers for elastomeric compounds. The preparation methods of nanocomposites that have a strong impact on the state of filler dispersion and thus on the properties of the resulting composites, are briefly described. At a same filler loading, considerable improvement in stiffness is imparted to the host polymeric matrix by the carbon nanomaterials with regard to that provided by the conventional carbon black particles. It is mainly attributed to the high aspect ratio of the nanostructures rather than to strong polymer-filler interactions. The orienting capability of the anisotropic fillers under strain as well the formation of a filler network, have to be taken into account to explain the high level of reinforcements. A comparison of the efficiency of the different carbon nanostructures is carried out through their mechanical and electrical properties but no clear picture can be obtained since the composite properties are strongly affected by the state of filler dispersion.

Mechanical Properties and Thermal Resistance of Natural Rubber Nanocomposite Reinforced with Quaternized Polyvinyl Alcohol/Silica Nanoclusters

Quaternized polyvinyl alcohol (QPVA) was synthesized and used as an intermedium to improve dispersion of silica (SiO2) in natural rubber (NR). QPVA/SiO2 nanoclusters reinforced NR nanocomposite was prepared by latex compounding via electrostatic interaction. TEM micrographs demonstrated QPVA/SiO2 nanoclusters were distributed around NR particles, forming shell-core structure. The mechanical properties and thermal ageing resistance of NR-QPVA/SiO2 were significantly improved compared with that of neat NR. The tensile strength of NR-QPVA/SiO2 film was improved by 60%, when the SiO2 content is 3%. SEM pictures indicated SiO2 was homogenous dispersed throughout NR matrix in the presence of QPVA. It also demonstrated that SiO2 could enhance thermal stability of NR, as NR-QPVA/SiO2 had best surface morphology after 72 hours thermal ageing at 100 °C. The thermal decomposition temperature and glass transition temperature of NR-QPVA/SiO2 film increased to a higher temperature due to strong polymer–filler interaction, which also indicated that all the ingredients were compatible and homogenous.

High performance waste-derived filler/carbon black reinforced guayule natural rubber composites

Guayule rubber (GNR) is an alternative source of natural rubber that does not crossreact with Type I latex allergy because it does not contain any proteins which can be recognized by antibodies raised against Hevea brasiliensis allergens. To advance the commercialization of this elastomer and diversify sources of natural rubber, efficient reinforcement of GNR is required to match the physical properties of vulcanized materials made from H. brasiliensise natural rubber in specific products. Superior or comparable reinforcement to that of carbon black N330, was achieved by partial replacement of carbon black with 5 and 10 phr of waste-derived material. Out of several waste-derived fillers tested, micro sized eggshells showed remarkable reinforcing potential for GNR. Hybrid carbon black/micro sized eggshells/GNR composites (up to 20 phr micro sized eggshells), had increased tensile strength, and elongation at break, while maintaining similar values of 300% modulus and hardness to those achieved by carbon black/GNR composites. Hierarchical cluster analysis partitioned the data into six groups of composites having statistically similar properties within each group. Composites containing 5–20 phr of micro sized eggshells were clustered in a separate group due to their unique combination of high tensile strength and flexibility. The superior reinforcement may reflect a combined synergistic reinforcing effect of carbon black particles, which possess a strong polymer-filler interaction, with the formation of a unique network between the GNR and the waste-derived materials, not attained with H. brasiliensis natural rubber.

Effect of a silica nanofiller on the structure, dynamics and thermostability of LDPE in LDPE/silica nanocomposites

Study of molecular interactions and dynamics in LDPE–silica nanocomposites using FTIR spectroscopy.

ELASTOMERIC COMPOSITES BASED ON NANOSPHERICAL PARTICLES AND CARBON NANOTUBES: A COMPARATIVE STUDY

ABSTRACT The reinforcement of elastomeric materials by addition of mineral fillers represents one of the most important aspects in the field of rubber science and technology. The improvement in mechanical properties arises from hydrodynamic effects depending mainly on the amount of filler and the aspect ratio of the particles and also on polymer–filler interactions depending on the surface characteristics of the filler particles and the chemical nature of the polymer. The past few years have seen the extensive use of nanometer-scale particles of different morphologies on account of the small size of the filler and the corresponding increase in the surface area that allow a considerable increase in mechanical properties even at very low filler loading. Among these nanoparticles, spherical particles (such as silica or titania) generated in situ by the sol-gel process and carbon nanotubes are typical examples of materials used as a nanosize reinforcing additive. Specific features of filled elastomers are discussed through the existing literature and through results of the author's research based on poly(dimethylsiloxane) filled with spherical silica or titania particles and on styrene–butadiene rubber filled with multiwall carbon nanotubes. The reinforcing ability of each type of filler is discussed in terms of morphology, state of dispersion (investigated by transmission electron microscopy, atomic force microscopy, small-angle neutron scattering), and mechanical and electrical properties. In addition, the use of molecular spectroscopies provides valuable information on the polymer–filler interface. Spherical silica and titania spherical particles are shown to exhibit two distinct morphologies, two different polymer–filler interfaces that influence the mechanical properties of the resulting materials. The superiority of carbon nanotubes over carbon black for mechanical reinforcement and electrical conduction is mainly attributed to their large aspect ratio rather than to strong polymer–filler interactions. The use of hybrid fillers (carbon nanotubes in addition to carbon black or silica, for example) has been shown to give promising results by promoting an enhancement of mechanical and electrical properties with regard to each single filler.

MUSSEL-MIMETIC ELASTOMERS OF VARIED FUNCTIONALITY DESIGN FOR ELASTOMERIC COMPOSITES

ABSTRACT Bulk viscoelasticity and tensile behavior are examined for cross-linked compounds made of mussel-mimetic elastomers of varied functionality design. During polymerization, the mussel-mimetic functionalities containing the 3,4-dihydroxyphenyl (or catechol) group can be incorporated at the molecule chain head, along the backbone, and/or at the molecule chain tail. The compounds are either unfilled or filled to the same filler volume fraction with a single filler chosen among carbon black (hydrophobic), precipitated silica (hydrophilic), and titanium oxide (hydrophilic). For polymers bearing multiple mussel-mimetic functional groups, the polymer cold flow resistance becomes significantly enhanced, arising from the strong intermolecular hydrogen bonding interactions. Such strong intermolecular hydrogen-bonding interactions also affect the bulk viscoelasticity and tensile behavior for the cross-linked gum compounds. Because the mussel-mimetic functional groups exhibit obvious affinity to all three types of filler particles, the extent of modification to bulk viscoelasticity and reinforcement for the filled compounds is observed to vary with the distribution of such functionalities along a polymer molecule, the chemical groups immediately next to the catechol group, and the specific type of filler. As expected, microscale filler dispersion is improved from the strong polymer–filler interactions.

Correlations between mechanical, structural, and dynamical properties of polymer nanocomposites

We study the structural and dynamical mechanisms of reinforcement of a polymer nanocomposite (PNC) via coarse-grained molecular dynamics simulations. In a regime of strong polymer-filler interactions, the stress at failure of the PNC is clearly correlated to structural quantities, such as the filler loading, the surface area of the polymer-filler interface, and the network structure. Additionally, we find that small fillers, of the size of the polymer monomers, are the most effective at reinforcing the matrix by surrounding the polymer chains and maximizing the number of strong polymer-filler interactions. Such a structural configuration is correlated to a dynamical feature, namely, the minimization of the relative mobility of the fillers with respect to the polymer matrix.

Glass transition and polymer dynamics in silver/poly(methyl methacrylate) nanocomposites

Dynamic mechanical–thermal analysis (DMTA), differential scanning calorimetry (DSC), thermally stimulated depolarization currents (TSDC) and, mainly, broadband dielectric relaxation spectroscopy (DRS) were employed to investigate in detail glass transition and polymer dynamics in silver/poly(methyl methacrylate) (Ag/PMMA) nanocomposites. The nanocomposites were prepared by radical polymerization of MMA in the presence of surface modified Ag nanoparticles with a mean diameter of 5.6 nm dispersed in chloroform. The fraction of Ag nanoparticles in the final materials was varied between 0 and 0.5 wt%, the latter corresponding to 0.055 vol%. The results show that the nanoparticles have practically no effect on the time scale of the secondary β and γ relaxations, whereas the magnitude of both increases slightly but systematically with increasing filler content. The segmental α relaxation, associated with the glass transition, becomes systematically faster and stronger in the nanocomposites. The glass transition temperature T g decreases with increasing filler content of the nanocomposites up to about 10 °C, in good correlation by the four techniques employed. Finally, the elastic modulus decreases slightly but systematically in the nanocomposites, both in the glassy and in the rubbery state. The results are explained in terms of plasticization of the PMMA matrix, due to constraints imposed to packing of the chains by the Ag nanoparticles, and at the same time, of the absence of strong polymer–filler interactions, due to the surface modification of the Ag nanoparticles by oleylamine at the stage of preparation.

Effect of the polymer—filler interaction on the thermo-mechanical response of polyurethane-clay nanocomposites from blocked prepolymer

Thin transparent films of polyurethane—clay nanocomposites were prepared by dispersing different amounts of commercial organo-modified clay in a mixture of cycloaliphatic amines used as chain extender of a blocking prepolymer, in order to investigate the role of the filler content on the thermo-mechanical behavior of the resulting composites. X-ray diffraction measurements evidenced the formation of an intercalated structure, regardless to the clay loading. Furthermore, the optical clarity of the samples was not substantially compromised by the nanofiller addition even at elevated clay amounts. Interestingly, the relatively strong polymer—filler interaction led to a substantial reduction of the matrix crosslinking degree for high clay loadings. Consequently, the relative thermal lifetime was positively affected by the presence of clay up to a filler content of 7 wt%, while uniaxial tensile tests under quasi-static and impact conditions evidenced an increase of the elastic modulus proportional to the clay concentration, without impairing the original tensile properties at break.

Polymer–nanoparticle interfacial behavior revisited: A molecular dynamics study

By tuning the polymer-filler interaction, filler size and filler loading, we use a coarse-grained model-based molecular dynamics simulation to study the polymer-filler interfacial structural (the orientations at the bond, segment and chain length scales, chain size and conformation), dynamic and stress-strain properties. Simulated results indicate that the interfacial region is composed of partial segments of different polymer chains, which is consistent with the experimental results presented by Chen et al. (Macromolecules, 2010, 43, 1076). Moreover, it is found that the interfacial region is within one single chain size (R(g)) range, irrespective of the polymer-filler interaction and the filler size, beyond which the bulk behavior appears. In the interfacial region, the orientation and dynamic behaviors are induced by the interfacial enthalpy, while the size and conformation of polymer chains near the filler are controlled by the configurational entropy. In the case of strong polymer-filler interaction (equivalent to the hydrogen bond), the innerest adsorbed polymer segments still undergo adsorption-desorption process, the transport of chain mass center in the interfacial region exhibits away from the glassy behavior, and no plastic-like yielding point appears in the stress-strain curve, which indicates that although the mobility of interfacial polymer chains is restricted, there exist no "polymer glassy layers" surrounding the filler. In addition, it is evidenced that the filler particle prefers selectively adsorbing the long polymer chains for attractive polymer-filler interaction, validating the experimental explanation of the change of the bound rubber (BR). In short, this work provides important information for further experimental and simulation studies of polymer-nanoparticle interfacial behavior.

Conducting carbon black filled NR/ IIR blend vulcanizates: Assessment of the dependence of physical and mechanical properties and electromagnetic interference shielding on variation of filler loading

A series of natural rubber/ butyle rubber NR/ IIR (70/30) loaded with general purpose furnace (GPF) carbon black have been produced on a laboratory scale, and their electrical and mechanical properties were investigated. The percolation threshold concentration has been described using Kirkpatrick and Zallen model. The percolation model gives a suitable explanation, within the experimental data of the studied samples. The thermal stability of composites was also investigated. It was found that the stability of high filler content blend was better than that of low filler content, due to strong polymer-filler interaction at high filler concentrations. Variation of mechanical properties of carbon black-filled compounds with the filler content was also investigated. Electromagnetic interference (EMI) shielding characteristics of these composites were studied. The measurements of shielding effectiveness (SE) were carried out in different frequency ranges from 0.5–5 GHz and it increases with the increase in filler loading. SE values were in the range of 7–30 dB.

A frictional molecular model for the viscoelasticity of entangled polymer nanocomposites

The dynamics of polymer melts and concentrated solutions reinforced with nanoscale rigid spherical particles is analyzed. Nanocomposites with low filler volume fraction and strong polymer-filler interactions are considered. Entanglement effects are represented by requiring the diffusion in the chain contour direction to be more pronounced than in the direction transverse to the chain primitive path. Filler particles are treated as material points. They reduce the polymer mobility in both longitudinal and transverse tube directions due to short-range energetic filler-polymer interactions. Hence, the contribution to chain dynamics and stress production of both filler-polymer and polymer-polymer interactions is considered to be purely frictional in nature. In the model, the strain rate sensitivity is associated with the thermal motion of chains, with the convective relaxation of entanglement constrains and with the polymer-filler attachment/detachment process. The effect of model parameters is discussed and the predictions are compared with experimental data.

Network model for the viscoelastic behavior of polymer nanocomposites

A theoretical network model reproducing some significant features of the viscoelastic behavior of unentangled polymer melts reinforced with well dispersed non-agglomerated nanoparticles is presented. Nanocomposites with low filler volume fraction (∼10%) and strong polymer–filler interactions are considered. The model is calibrated based on results obtained from discrete simulations of the equilibrium molecular structure of the material. This analysis provides the statistics of the network of chains connecting fillers, of dangling strands having one end adsorbed onto fillers, and that of the population of loops surrounding each nanoparticle. The network kinetics depends on the attachment–detachment dynamics of grafted chains of various types and is modeled by using a set of convection equations for the probability distribution functions. The overall viscoelastic response depends strongly on the lifetime of the polymer–filler junctions. The largest reinforcement is observed at low strain rates and low frequency oscillations. A solid like behavior is predicted for systems in which the polymer molecules interact strongly with the nanoparticles, effect which is associated with the behavior of the network of bridging segments.

Use of epoxidized rubber seed oil as a coupling agent and a plasticizer in silica-filled natural rubber compounds

To obtain good reinforcement by silica filler in nonpolar rubbers, it is almost essential to use coupling agents, such as bis(triethoxy silyl propyl) tetrasulfane (TESPT). Chemicals that can interact with the silanol groups on the silica particles and reduce their network formation are also expected to enhance reinforcement. We made a comparative evaluation of TESPT, epoxidized rubber seed oil (ERSO), and their combination as a coupling agent and a plasticizer in silica-filled natural rubber compounds. The results indicate that compounds containing ERSO showed physical and mechanical properties between that of TESPT and naphthenic oil. The action of ERSO in the improvement of the properties was expected to be bifunctional and similar to that of TESPT; that is, it caused the hydrophobation of silica, which increased its degree of dispersion and the formation of chemical bonds with the rubber, thereby ensuring strong polymer–filler interactions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3531–3536, 2004

Use of flow microcalorimetry and dynamic mechanical thermal analysis for probing interphase structure in poly(styrene-b-butadiene-b-styrene)/magnesium hydroxide composites

Interactions between magnesium hydroxide (Mg(OH)2 particles (both untreated and treated with 16-methyl heptadecanoic acid (isostearic acid)) and low molar mass poly(styrene) (PS) and poly(butadiene) (PB) have been studied by flow microcalorimetry (FMC) and have been related to the interphase structure in poly(styrene-b-butadiene-b-styrene) (SBS)/Mg(OH)2 composites using dynamic mechanical thermal analysis (DMTA). The FMC studies revealed that both polymers adsorbed strongly onto an untreated magnesium hydroxide surface though the PB showed greater irreversible adsorption from the heptane carrier fluid. Diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) studies on filler samples removed from the FMC cell after the adsorption-desorption cycle confirmed strong polymer filler interaction. Adsorption of the low molar mass samples of PS and PB onto a pre-adsorbed monolayer of isostearic acid on Mg(OH)2 resulted in a very significant reduction in polymer adsorption activity due to blockage of adsorption sites. DMTA studies revealed that strong adsorption of PS and PB blocks of SBS onto untreated filler in composites containing 60% w/w Mg(OH)2 gave rise to phase mixing that led to an 18 °C reduction in the T g of the PS phase relative to that in the unfilled matrix. However, in equivalent composites based on isostearic acid treated filler a smaller reduction (10 °C) was observed, therefore reflecting reduced filler-matrix interaction and reduced phase mixing.

Electron-beam-modified surface-coated clay: influence on mechanical, dynamic mechanical and rheological properties of ethylene–octene copolymer

Clay filler was surface modified by coating with an acrylate monomer, trimethylolpropane triacrylate (TMPTA) or a silane coupling agent, triethoxyvinyl silane, (TEVS) followed by electron beam irradiation. Both the untreated and the modified fillers, developed by this new technique, were incorporated in an ethylene–octene copolymer. Mechanical, dynamic mechanical and rheological properties of the peroxide as well as electron beam cured unfilled and filled composites were studied in detail. A noticeable improvement in the properties like tensile strength, elongation at break, modulus, tear strength, etc. was observed in the case of surface treated clay-filled rubber vulcanizates. This is more prominent in the silanized clay-filled composite, elucidating strong polymer–filler interaction by the introduction of covalent bonds between the filler surface and the rubber chains. The results obtained from dynamic mechanical thermal analysis further corroborated the above findings. However, the incorporation of the clay filler had marginal influence on the flow properties of the rubber.