Dispersion State Of Nanoparticles Research Articles

Nanoparticle agglomeration in molten salt nanofluids: Free energy landscape and its impacts on thermal transport property degradation

The nanofluids consisting of molten salt and nanoparticles can gain enhanced thermal performance for heat transfer and energy storage processes. Agglomeration of nanoparticles is ubiquitous in this colloidal dispersion, deteriorating the dispersed states of the nanocomposite interiors, and its microscopic mechanisms are unsatisfactorily explored. In this work, molecular dynamics simulations combined with umbrella sampling technique to capture the relative dispersion state of nanoparticles in molten salts effectively were performed to reveal the free energy landscape of agglomeration and its influence on heat transport. The dominant deep minima in the free energy surface demonstrates that the agglomeration of MgO nanoparticles in the molten NaCl salt is principally induced by van der Waals attractions between MgO nanoparticles and aggravated by large surface area. The unstable dispersion of nanoparticles is the most fatal problem for enhanced thermal conductivity during agglomeration, and the relative distance of MgO nanoparticles has less impacts on the thermal conductivity of the melt. The stronger adsorption of ions around nanoparticles can improve their relative dispersion, and utilize interfacial effects to enhance the thermal conductivity. Combined with the benefit of ordered ionic layer on the surface, the MgO nanoparticles of 10 Å diameter (specific surface area of ∼ 938.80 m2/g) become the optimal choice for molten NaCl. With the mechanisms of interfacial microstructures preventing agglomerated nanoparticles and improving heat transfer of molten salts revealed, this work can enlighten the selection or feasible modification for nanoparticles in various high-temperature molten salts, since the mechanisms are universal to other nanofluids, especially for ionic liquid based nanofluids.

Experimental Study on Influence of Multiwalled Carbon Nanotubes on Thermal Behavior of ABS & PETG Hybrid Polymer Composites

Polymer composites with enhanced thermal conductivity not only exhibit impressive heat transfer capabilities comparable to metals and ceramics but also preserve the inherent benefits of polymers, including their lightweight nature, ease of processing, and cost-effectiveness. These composites find extensive applications in aerospace, electronics, medical devices, and various other industries. Polymer-based composites incorporating multiwalled carbon nanotubes (MWCNTs) were created, and the impact of different concentrations on the thermal stability of the resulting hybrid composite was examined. This study examines the way of behaving of PETG and ABS materials fabricated through 3D printing and built up with differing measures of carbon fibers (CF) and multiwall carbon nanotubes (MWCNT). The study aims to shed light on the ways in which these materials improve polymer properties, focusing particularly on the beneficial effect of reinforcement on thermal behavior. Additionally, the influence of temperature on the thermal properties of hybrid polymer composites is briefly addressed. These findings underscore the significance of both the content and dispersion state of nanoparticles in shaping the thermal characteristics of such composites.

Molecular dynamics simulations for interfacial structure and affinity between carboxylic acid-modified Al2O3 and polymer melts.

Controlling the dispersion state of nanoparticles in a polymer matrix is necessary to produce polymer nanocomposites. The surface modification of nanoparticles is used to enable their dispersion in polymers. Moreover, molecular dynamics (MD) simulations are useful for revealing the interfacial properties between nanoparticles and polymers to aid in the design of materials. In this study, the effect of surface coverage, modifier length, and polymer species on the interfacial structure and affinity between surface-modified Al2O3 and polymer melts were investigated using all-atom MD simulations. Hexanoic, decanoic, and tetradecanoic acids were used as surface modifiers, and polypropylene (PP), polystyrene (PS), and poly (methyl methacrylate) (PMMA) were used as polymers. The work of adhesion Wadh and the work of immersion Wimm were selected as quantitative measures of affinity. Wadh was calculated using the phantom-wall approach, and Wimm was calculated by simply subtracting the surface tension of polymers γL from Wadh. The results showed that Wadh and Wimm were improved by surface modification with low coverage, owing to a good penetration of the polymer. The effect of modifier length on Wadh and Wimm was small. Whereas Wadh increased in the following order: PP < PS < PMMA, Wimm increased as follows: PMMA < PS < PP. Finally, the trend of Wadh and Wimm was organized using the Flory-Huggins interaction parameter χ between the modifier and the polymer. This study demonstrates that the interfacial affinity can be improved by tuning the surface coverage and modifier species depending on the polymer matrix.

Influence of the Graft Length on Nanocomposite Structure and Interfacial Dynamics.

Both the dispersion state of nanoparticles (NPs) within polymer nanocomposites (PNCs) and the dynamical state of the polymer altered by the presence of the NP/polymer interfaces have a strong impact on the macroscopic properties of PNCs. In particular, mechanical properties are strongly affected by percolation of hard phases, which may be NP networks, dynamically modified polymer regions, or combinations of both. In this article, the impact on dispersion and dynamics of surface modification of the NPs by short monomethoxysilanes with eight carbons in the alkyl part (C8) is studied. As a function of grafting density and particle content, polymer dynamics is followed by broadband dielectric spectroscopy and analyzed by an interfacial layer model, whereas the particle dispersion is investigated by small-angle X-ray scattering and analyzed by reverse Monte Carlo simulations. NP dispersions are found to be destabilized only at the highest grafting. The interfacial layer formalism allows the clear identification of the volume fraction of interfacial polymer, with its characteristic time. The strongest dynamical slow-down in the polymer is found for unmodified NPs, while grafting weakens this effect progressively. The combination of all three techniques enables a unique measurement of the true thickness of the interfacial layer, which is ca. 5 nm. Finally, the comparison between longer (C18) and shorter (C8) grafts provides unprecedented insight into the efficacy and tunability of surface modification. It is shown that C8-grafting allows for a more progressive tuning, which goes beyond a pure mass effect.

From Ionic Nanoparticle Organic Hybrids to Ionic Nanocomposites: Structure, Dynamics, and Properties: A Review.

Ionic nanoparticle organic hybrids have been the focus of research for almost 20 years, however the substitution of ionic canopy by an ionic-entangled polymer matrix was implemented only recently, and can lead to the formulation of ionic nanocomposites. The functionalization of nanoparticle surface by covalently grafting a charged ligand (corona) interacting electrostatically with the oppositely charged canopy (polymer matrix) can promote the dispersion state and stability which are prerequisites for property "tuning", polymer reinforcement, and fabrication of high-performance nanocomposites. Different types of nanoparticle, shape (spherical or anisotropic), loading, graft corona, polymer matrix type, charge density, molecular weight, can influence the nanoparticle dispersion state, and can alter the rheological, mechanical, electrical, self-healing, and shape-memory behavior of ionic nanocomposites. Such ionic nanocomposites can offer new properties and design possibilities in comparison to traditional polymer nanocomposites. However, to achieve a technological breakthrough by designing and developing such ionic nanomaterials, a synergy between experiments and simulation methods is necessary in order to obtain a fundamental understanding of the underlying physics and chemistry. Although there are a few coarse-grained simulation efforts to disclose the underlying physics, atomistic models and simulations that could shed light on the interphase, effect of polymer and nanoparticle chemistry on behavior, are completely absent.

On the dispersion and experimental investigation on transverse tensile low-cycle-fatigue behaviour of GFRP nanocomposites filled with CNTs and GNPs

Improvements in the thermo-mechanical properties of nanocomposites (NCs), particularly containing nanoparticles (NPs) in the resin largely depends upon the dispersion state of nanoparticles in the matrix phase. A 3-phased GF-NC-Epoxy composite prepared by such method witnesses a final reduction in the volume fraction of nanoparticles due to overall reduction in the matrix volume fraction. This work explores an effective dispersion method based on rheological behaviour of 2-phased NCs and compares the efficacy of the same in dispersion of 0.5 wt% carbon nanotubes (CNTs), graphene nanoplatelets (GNPs) and their mixture in the ratio of 1:1 (GPNTs). The NPs possess close densities and specific surface area (SSA) of SSACNT = 330 m2/g; SSAGNP = 300 m2/g; ρCNT=0.28g/cm3;andρGNP=0.3g/cm3. The prepared GFRP laminates were tested for their static and dynamic (low cycle fatigue (LCF)) flexure properties and it was observed that the effectiveness of nanoparticles depends upon their final volume fraction in the laminates. A laminate containing higher fiber volume fraction (vf) witnessed large improvement in the static strength post addition of NPs due to improved toughness, but they often witness early failure under fatigue loading owing to limited toughening due to lesser volume of NPs in the matrix phase. It was also observed that once the samples witnessed a crack in the midplane, it requires only few cycling to fail abruptly.

Study on the water‐tree ageing characteristics of polyethylene/organic montmorillonite and crosslinked polyethylene/organic montmorillonite nanocomposites

AbstractThe dispersion state of nanoparticles affects the properties of composites, and the crosslinking process of polymers affects the dispersion state of nanoparticles. In order to investigate the effects of crosslinking behaviour on the water‐tree ageing characteristics of nanocomposite dielectrics at the molecular level, polyethylene/organic‐montmorillonite (PE/organic montmorillonite (OMMT)) and crosslinked polyethylene/organic‐montmorillonite (XLPE/OMMT) nanocomposites were prepared by the melt blending method, after which the accelerated water‐tree ageing experiments were conducted using a needle electrode. Fourier transform infrared spectroscopy, differential scanning calorimetry, successive self‐nucleation annealing and scanning electron microscope (SEM) tests were conducted to characterise the properties of the samples before and after water‐tree ageing. The results indicate that the initiation probability and the length of water trees in XLPE/OMMT are less than those in PE/OMMT. The carbonyl index in the water‐tree area of the two nanocomposites increases, indicating that the water‐tree ageing is the result of electrochemical degradation. The crystallisability of the water‐tree area degrades, decreasing the crystallinity and the lamellar thickness. The growth of water trees destroys molecular chains and crystal structures, which results in local cracks. There are many holes for the water tree growth in the PE/OMMT specimen. However, the crosslinked meshwork not only restricts the movement of macromolecular chains but also increases the stability of the lamellar barrier effect of OMMT. The combination of the two effects significantly improves the water‐tree resistance of the XLPE/OMMT nanocomposite.

Research progress on the correlation between properties of nanoparticles and their dispersion states in polymer matrix

AbstractWhen fabricating polymer nanocomposites (PNCs), it is difficult for nanoparticles to disperse stably in polymer matrix since their high‐surface energy can cause them to attract each other. In this paper, we review the effects of nanoparticle size, surface chemical properties, and thermodynamic parameters on the dispersion state of nanoparticles (including inorganic and organic particles) in PNCs and describe some key measures to promote the nanoparticles dispersion. The ideal nanoparticles dispersion in polymer melt is available when the particle size is smaller than the rotation radius of polymer chains and the particle surface is highly compatible or has interactions with the matrix. In polymer solution, establishing proper thermodynamic parameters is necessary to ensure the balance interactions among particles, solvents, and polymers, leading to the successful preparation of PNCs with ideal structure. These results could supply theoretical suggestions for the design of PNCs. Moreover, the equilibrium dispersion may be unavailable without reasonable kinetic parameters, even if the dispersion process is thermodynamically favorable. Therefore, more studies are required on both thermodynamics and kinetics of the dispersion process.

Investigating Nanoparticle Organization in Polymer Matrices during Reaction-Induced Phase Transitions and Material Processing.

Controlling nanoparticle organization in polymer matrices has been and is still a long-standing issue and directly impacts the performance of the materials. In the majority of instances, simply mixing nanoparticles and polymers leads to macroscale aggregation, resulting in deleterious effects. An alternative method to physically blending independent components such as nanoparticle and polymers is to conduct polymerizations in one-phase monomer/nanoparticle mixtures. Here, we report on the mechanism of nanoparticle aggregation in hybrid materials in which gold nanoparticles are initially homogeneously dispersed in a monomer mixture and then undergo a two-step aggregation process during polymerization and material processing. Specifically, oleylamine-functionalized gold nanoparticles (AuNP) are first synthesized in a methyl methacrylate (MMA) solution and then subsequently polymerized by using a free radical polymerization initiated with azobis(isobutyronitrile) (AIBN) to create hybrid AuNP and poly(methyl methacrylate) (PMMA) materials. The resulting products are easily pressed to obtain bulk films with nanoparticle organization defined as either well-dispersed or aggregated. Polymerizations are performed at various temperatures (T) and MMA volume fractions (ΦMMA) to systematically influence the final nanoparticle dispersion state. During the polymerization of MMA and subsequent material processing, the initially homogeneous AuNP/MMA mixture undergoes macrophase separation between PMMA and oleylamine during the polymerization, yet the AuNP are dispersed in the oleylamine phase. The nanoparticles then aggregate within the oleylamine phase when the materials are processed via vacuum drying and pressing. Nanoparticle organization is tracked throughout the polymerization and processing steps by using a combination of transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). The resulting dispersion state of AuNPs in PMMA bulk films is ultimately dictated by the thermodynamics of mixing between the PMMA and oleylamine phases, but the mechanism of nanoparticle aggregation occurs in two steps that correspond to the polymerization and processing of the materials. Flory-Huggins mixing theory is used to support the PMMA and oleylamine phase separation. The reported results highlight how the integration of nonequilibrium processing and mean-field approximations reveal nanoparticle aggregation in hybrid materials synthesized by using reaction-induced phase transitions.

Flexible Low-Density Polyethylene–BaTiO3 Nanoparticle Composites for Monitoring Leakage Current in High-Tension Equipment

Polymer–nanoparticle composites prepared using a low-density polyethylene (LDPE) matrix with BaTiO3 nanoparticle compositions of 6, 9, 12, and 15 wt % have shown insulating behavior and are evaluated for their applicability as flexible strain sensors. With increasing percentage of the nanoparticles, the LDPE crystallinity decreased from 38.11 to 33.79% and the maximum electrical displacement response was seen to increase from 2.727 × 10–4 to 4.802 × 10–4 C/cm2. The maximum current, remnant current, and coercive field, all increased with the increasing nanoinclusion loading. Furthermore, the interaction radius values derived from the three-dimensional (3D) model of the nanoparticle dispersion state in polymer–nanoparticle composites were found to be correlated with its key properties. The interaction radius values from the simulated 3D model gave a clear basis for comparing the electrical properties of the samples with the effect of the nanoparticles’ functionalization on the dispersion state in the context of the increased NP loading and giving the values of 275, 290, 310, and 300 nm, respectively. The 12 wt % nanoparticulate-loaded sample demonstrates the best overall trade-off of key parameters studied herein. Overall, the results demonstrate that these flexible polymer–nanoparticle composites could be used for strain-based sensors in the high-tension applications.

Insulating MgO–Al2O3–LDPE Nanocomposites for Offshore Medium-Voltage DC Cables

A polymer–metal oxide nanocomposite is a key in developing a high-temperature insulation material for power electronics and high-voltage direct current (HVDC) and medium-voltage direct current (MVDC) subsea cables having the capability of transmitting offshore renewable energy with lower losses and higher reliability. To achieve a higher operation voltage level and larger power capacity at a reduced cable size, weight, and volume, the lighter material offering improved electrical insulation at a high operating temperature is required. Addition of metal oxide ceramics in the polymer is shown to improve the insulating properties of the polymer used in the cable and power electronic applications; however, their performance deteriorates at elevated temperatures as thermal energy facilitates the electron injection to the bulk material by following conduction according to the Schottky emission. In this work, the heat insulating Al2O3 nanoparticles are added to the MgO–polyethylene nanocomposite to observe the effect of the interface between mix oxide nanoparticles on current density and breakdown strength of the nanocomposite compared to the MgO–polyethylene nanocomposite at room and elevated temperatures (90 °C). The concentrations of the MgO and MgO + Al2O3 mixture were varied from 1 to 12 wt % to find out that the nanocomposite containing MgO showed the best response than MgO + Al2O3 at elevated and room temperatures. There was no unified trend observed in the leakage current density and breakdown strength results for the MgO + Al2O3 nanocomposite, indicating the absence of the interface formation between MgO and Al2O3. The decrease in the interaction radius, calculated using numerical simulation of the nanoparticle dispersion state, resulted in the high breakdown strength. Addition of 12 wt % MgO helped achieving the highest breakdown strength, but overall breakdown strength for the MgO + Al2O3 nanocomposite improved at elevated temperatures. All nanocomposites showed improved electrical insulating properties compared to virgin low-density polyethylene (Pure LDPE) .

Revisiting stress-strain behavior and mechanical reinforcement of polymer nanocomposites from molecular dynamics simulations.

Through coarse-grained molecular dynamics simulations, the effects of nanoparticle properties, polymer-nanoparticle interactions, chain crosslinks and temperature on the stress-strain behavior and mechanical reinforcement of polymer nanocomposites (PNCs) are comprehensively investigated. By regulating the filler-polymer interaction (miscibility) in a wide range, an optimal dispersion state of nanoparticles is found at moderate interaction strength, while the mechanical properties of PNCs are improved monotonically with the increase of the particle-polymer interaction due to the tele-bridge structures of nanoparticles via polymer chains. Although smaller-sized fillers more easily build interconnected structures, the elastic moduli of PNCs at the percolation threshold concentration where a three-dimensional filler network forms are almost independent of nanoparticle size. Compared with spherical nanoparticles, anisotropic rod-like ones, especially with larger aspect ratio and rod stiffness, contribute exceptional reinforcement towards polymer materials. In addition, the elastic modulus with the strain, derived from the stress-strain curve, shows an analogous nonlinear behavior to the amplitude-dependence of the storage modulus (Payne effect). Such a behavior originates essentially from the failure/breakup of the microstructures contributing to the mechanical reinforcement, such as bound polymer layers around nanoparticles or nanoparticle networking structures. The Young's modulus as a function of the nanoparticle volume fraction greatly exceeds that predicted by the Einstein-Smallwood model and Guth-Gold model, which arises primarily from the contribution of the local/global filler network. The temperature dependence of the Young's modulus is further examined by mode coupling theory (MCT) and the Vogel-Fulcher-Tammann (VFT) equation, and the results indicate that the time-temperature superposition principle holds modestly above the critical temperature on the short-time (small-length) scale of elastic response. This work is expected to provide some guidance on controlling and improving the mechanical properties and nonlinear behavior of PNCs.

Leveraging Nanoparticle Dispersion State To Tune Vanadium Ion Selectivity of Nanophase-Segregated Ionomer Nanocomposites for Redox Flow Batteries

Ionomer nanocomposites provide a promising solution to address ion crossover issues inherent to traditional ion-containing membranes used in batteries for grid-scale energy storage (e.g., vanadium redox flow batteries). Herein, we investigate the impact of nanoparticle surface chemistry on nanoparticle dispersion, membrane morphology, and vanadium ion permeability in a series of Nafion nanocomposites. Specifically, silica nanoparticles (SiNPs) were functionalized with various chemical moieties, seven in total, that electrostatically interact, either attractively or repulsively, with the sulfonic acid groups that coalesce to form the ionic network within Nafion. As seen from electron microscopy analysis of the nanocomposites, SiNPs with sulfonic acid end-functionality were, on average, well dispersed within the ionomer membrane, though increased vanadium ion permeability, as compared to pristine (or unmodified) Nafion, was observed and attributed to changes in the Donnan potential of the system. In contrast, SiNPs with amine end-functionality were, on average, observed to form large aggregates within the ionomer membrane. Surprisingly, nanocomposites containing a higher degree of nanoparticle aggregation demonstrated the lowest vanadium ion permeability. Fractal analysis of the low-Q small-angle neutron scattering data suggests that the interface between the ionomer and the SiNP surface transitions from rough to smooth when the nanoparticle surface is changed from sulfonic acid-functionalized to amine-functionalized.

Poly(lactic acid)/thermoplasticized rice straw biocomposites: effects of benzylated lignocellulosic filler and nanoclay

The physical, viscoelastic, thermal and mechanical properties of poly(lactic acid) (PLA) as a well-known biodegradable plastics were enhanced by incorporating a chemically modified biomass without sacrificing the biodegradability of the matrix. Rice straw after milling was benzylated with NaOH and benzyl chloride solution at reflux temperature for 6 h. The weight gain percentage of benzylated rice straw (BRS) was 145% and some thermoplasticity was induced in the material. The results showed that the chemical modification successfully reduced the glass transition temperature (Tg) of rice straw to about 170 °C. By adding the benzylated rice straw at an optimal loading, the mechanical properties of PLA, i.e., Young’s modulus, tensile strength as well as toughness, were considerably improved as well as Tg, crystallinity and processability. Higher Tg, intensified non-terminal behaviour, and microscopic observations of the resultant PLA green composites demonstrated the strong interactions between PLA chains and the plasticized lignocellulosic polymers. Despite the positive effect of benzylated rice straw in PLA, compounding of the organically modified nanoclay with the biocomposites did not change the latter properties as expected due to the poor dispersion state of nanoparticles in the matrices.

The role of the filler surface chemistry on the dielectric and thermal properties of polypropylene aluminium nitride nanocomposites

In nanocomposites, different surface states of nanoparticles can potentially provide different interactions with the base polymer and in turn change the bulk properties. Aluminium nitride (AlN) nanoparticles were surface functionalised with three different silane coupling agents (SCAs) with varying organofunctional and hydrolysable groups. The effects of the filler surface chemistry on the resulting AlN/polypropylene (PP) nanocomposites were examined and compared with an unfilled reference system. It is observed that different organofunctional groups can provide different nucleating effects and the dispersion states of nanoparticles while the hydrolysable group is not the dominant factor. The dielectric spectroscopy results show the hydrolysable group of SCA will also result in a difference of the interphase since the trimethoxy silane treated systems show much higher imaginary permittivity than the triethoxy silane treated systems when the frequency is below 1 Hz. The grafted organofunctional layer on the particle surface can provide a significant improvement of the thermal conductivity of the composite materials, e.g. 15 % improvement in thermal conductivity was observed when adding 10 wt% methacrylate silanes treated nano-AlN into PP, while the untreated counterpart only has 5 % improvement.

Nondestructive Monitoring of the Dispersion State of Titanium Dioxide Nanoparticles in Concentrated Suspensions Using Magnetic Resonance Imaging.

The purpose of the present study is to demonstrate the applicability of magnetic resonance imaging, especially T2 relaxation time mapping, for nondestructive monitoring of the dispersion state of nanoparticles (NPs) in concentrated suspensions. TiO2 15-nm-diameter NPs, for use in sunscreen lotion products, were examined as a test NP. First, this study investigated whether T2 is sensitive to the NP concentration. In experiments with pulsed nuclear magnetic resonance on TiO2 NP suspensions with different organic solvents (ethanol, acetone, and decamethylcyclopentasiloxane), the T2 of each solvent varied in the suspensions according to the NP concentration. This study also confirmed that T2 mapping was effective for visualizing differences in NP concentration. Subsequently, gravitational sedimentation of the test suspensions was investigated. T2 mapping exhibited better detection sensitivity to sedimentation occurring in concentrated suspensions than visual observation, as it enabled the detection of changes in NP distributions that could not be visible to the naked eye. In addition, measurements of backscattered light enabled the full understanding of the dispersion stability of the TiO2 NPs in each solvent. Finally, the present study evaluated the centrifuge sedimentation of a commercial TiO2 NP suspension. T2 mapping clearly showed the complicated sedimentation behavior induced by the centrifugation treatment. The simulated fluid flow was consistent with the particle distribution in the centrifuged sample; thus, the sedimentation was believed to have developed in accordance with the vorticity generated by the centrifugation.

Investigation of polyvinyl alcohol nanocomposite hydrogels containing chitosan nanoparticles as wound dressing

Polymeric hydrogels, water-swollen 3 D networks of the polymers, have found wide ranges of applications in the medical fields, such as wound care and wound dressing, in order to prevent infections. Prevention from microorganisms transfer in to the wounds is one of the ideal wound dressing duties of polyvinyl alcohol (PVA) hydrogels. In this study, at the start, under optimal conditions, nanoparticles of chitosan using ionotropic gelation method were synthesized and in the next step in order to achieve particles with a minimum size, they were evaluated by scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR). Then after to obtain a wound dressing with preferable properties, nanocomposite hydrogels using a combination of PVA and 5, 10 and 15 wt% chitosan nanoparticles were prepared through freezing-thawing cycles. The necessary features of PVA nanocomposite hydrogels for wound dressing were investigated. The dispersion state of nanoparticles and structure of samples were evaluated by SEM microscopy. The nanoparticle size and the nanoparticle size distribution of chitosan was determined using the dynamic light scattering test at the nanometer scale. The physical behavior of hydrogels such as swelling and gel fraction was studied and their mechanical properties were investigated by compressive test. Finally the antimicrobial test and biocompatibility as cell viability were carried out. The results proved that the PVA nanocomposite hydrogels fulfill the requirements of a good wound dressing with desirable characteristics such as favorable swelling and acceptable strength, excellent barrier against microbial penetration.

Impact of ultrasonic assisted triangular lattice like arranged dispersion of nanoparticles on physical and mechanical properties of epoxy-TiO2 nanocomposites

Emerging ex-situ technique, ultrasonic dual mixing (UDM) offers unique and hitherto unapproachable opportunities to alter the physical and mechanical properties of polymer nanocomposites. In this study, triangular lattice-like arranged dispersion of TiO2 nanoparticles (average size ∼ 48 nm) in the epoxy polymer has been attained via concurrent use of a probe ultra-sonicator and 4 blades pitched impeller which collectively named as UDM technique. The UDM processing of neat epoxy reveals the generation of triangular lattice-like arranged nanocavities with nanoscale inter-cavity spacing. The UDM processing of epoxy-TiO2 nanocomposites reveals two unique features such as partial and complete entrapping of the nanoparticles by the nanocavities leading the arranged dispersion of particles in the epoxy matrix. Pristine TiO2 nanoparticles were dispersed in the epoxy polymer at loading fractions of up to 20% by weight. The results display that the arranged dispersion of nanoparticles is very effective at enhancing the glass transition temperature (Tg) and tensile properties of the epoxy at loading fractions of 10 wt%. We quantify a direct relationship among three important parameters such as nanoparticle content, cluster size, and inter-particle spacing. Our results offer a novel understanding of these parameters on the Tg and tensile properties of the epoxy nanocomposites. The tensile fracture surfaces revealed several toughening mechanisms such as particle pull-out, plastic void growth, crack deflection, crack bridging and plastic deformation. We show that a strong nanoparticle-matrix interface led to the enhanced mechanical properties due to leading toughening mechanisms such as crack deflection, plastic deformation and particle pull-out. We showed that the UDM has an inordinate prospective to alter the dispersion state of nanoparticles in viscous polymer matrices.

Optical Properties of Blown Films of PA6/MMT Nanocomposites

In this work blown films of polyamide 6 (PA6) nanocomposites were produced at different processing conditions, with the addition of montmorillonite (MMT), pure and surface modified by an organic salt. The films' optical properties were evaluated according to ASTM D-1003 and the results correlated with the degree of crystallinity, nanoparticle's dispersion state and processing conditions. It was observed that the thinner the film, the lower the haze and higher the clarity, due to the presence of less internal scattering structures in the direction of the incident light. The PA6 films with the unmodified MMT had the lowest clarity values, due to nanoparticles' agglomeration. The organic modification of the montmorillonite led to its exfoliating through the PA6 matrix, resulting in an optimization of the films' optical properties (decreased haze and increased clarity) when compared to the pure PA6 films.

Role of Grafting Mechanism on the Polymer Coverage and Self-Assembly of Hairy Nanoparticles.

It is now well-accepted that controlling the spatial dispersion of nanoparticles (NPs), which can be achieved by grafting them with polymers of different chain lengths and grafting densities, is central to optimizing the thermomechanical properties of the resulting polymer nanocomposites. In general, there are two methods for creating such polymer-grafted NPs: "grafting to" and "grafting from". The conventional wisdom is that the "grafting from" mechanism, where monomer-sized initiator/functional groups are attached to the surface followed by growing the chains, allows for higher polymer grafting densities and hence a more uniform polymer coverage of the NP surface. Here, we perform calculations and instead show that the "grafting to" strategy surprisingly leads to a more uniform polymer coverage of the NP surface at a given grafting density since the brush is formed while respecting the excluded volume constraints of the previously grafted chains. This conclusion is especially clear in the limit of low-to-moderate grafting density. Thus, at a given grafting density, the "grafting to" mechanism leads to an enhanced miscibility of the NPs in the matrix (which has the same chemistry as the grafts) and lower propensity to create self-assembled structures. Another important factor is that the dispersity in the number of grafted chains on the NPs is also smaller in the case of "grafting to" systems, thus leading to better defined materials. These two conclusions imply that the "grafting to" mechanism may provide better control over the NP dispersion state and hence the thermomechanical properties of polymer nanocomposites.