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International audience; We proposed recently a theoretical description for hydrodynamic flows in inhomogeneous liquids in the vicinity of solid interfaces, consistent with current theoretical descriptions of the thermodynamical equilibrium of liquids in the vicinity of solid surfaces and with the Onsager formalism for linear response theory in out-of-equilibrium liquids. We showed that these equations allow for describing diffusio-osmosis along a capillary and also wetting/dewetting dynamics of liquids on a solid substrate. We now apply this physical model to the wetting/dewetting dynamics of nano-particles in polymer blends, showing how they reach equilibrium at the interface between two liquids at rest and how they migrate from the non-preferred polymer to the preferred one under applied flow.

We measure the center-of-mass diffusion of silica nanoparticles (NPs) in entangled poly(2-vinylpyridine) (P2VP) melts using Rutherford backscattering spectrometry. While these NPs are well within the size regime where enhanced, nonhydrodynamic NP transport is theoretically predicted and has been observed experimentally (2RNP/dtube ≈ 3, where 2RNP is the NP diameter and dtube is the tube diameter), we find that the diffusion of these NPs in P2VP is in fact well-described by the hydrodynamic Stokes–Einstein relation. The effective NP diameter 2Reff is significantly larger than 2RNP and strongly dependent on P2VP molecular weight, consistent with the presence of a bound polymer layer on the NP surface with thickness heff ≈ 1.1Rg. Our results show that the bound polymer layer significantly augments the NP hydrodynamic size in polymer melts with attractive polymer–NP interactions and effectively transitions the mechanism of NP diffusion from the nonhydrodynamic to hydrodynamic regime, particularly at high mole...

Nanorod diffusion in polymer melts is faster than predicted by the continuum model (CM). Rutherford backscattering spectrometry is used to measure the concentration profile of titanium dioxide (TiO2) nanorods (L = 43 nm, d = 5 nm) in a polystyrene (PS) matrix having molecular weights (M) from 9 to 2000 kDa. In the entangled regime, the tracer diffusion coefficients (D) of TiO2 decrease as the M–1.4, whereas the CM predicts DCM ∼ M–3.0 using the measured zero-shear viscosity of TiO2(1 vol %): PS(M) blends. By plotting D/DCM versus M/Me, where Me is the entanglement molecular weight, diffusion is enhanced by a factor of 10–103 as M/Me increases. The faster diffusion is attributed to decoupling of nanorod diffusion from polymer relaxations in the surrounding matrix, which is facilitated by the nanorod dimensions (i.e., L greater than and d less than the entanglement mesh size, 8 nm).

International audience; Thermosets are frequently toughened by a high-T g thermoplastic (TP). Blend morphologies, obtained by curing induced phase separation with scales of a few hundreds of nanometers are relevant for highperformance applications, but no quantitative description for obtaining these morphologies exist yet. We propose such a quantitative approach for predicting and controlling the final morphology. The key is the degree of curing and the corresponding T g of the blend and of both phases when phase separation takes place. It is controlled by the Flory interaction parameter  of the constituents and their respective T g 's. We show that if phase separation takes place too early during curing, the T g is too low and morphologies grow to reach sizes of a few micrometers, or more. Our study of different systems allows us to propose the relevant range of Flory interaction parameter  and temperature window T-T g for which the sizes of interest may be obtained. Our work opens the way for devising thermoplasticsthermosets couples with the appropriate affinity and T g s in order to make blends with tailored morphologies.

Correction for ‘Migration of nanoparticles across a polymer–polymer interface: theory and simulation’ by Nigel Gibbions et al., Soft Matter, 2021, 17, 7294–7310, https://doi.org/10.1039/D1SM00671A.

Using tools from morphological image analysis, we characterise spinodal decomposition microstructures by their Minkowski functionals, and search for a correlation between them and data from scattering experiments. To do this, we employ machine learning in the form of Gaussian process regression on data derived from numerical simulations of spinodal decomposition in polymer blends. For a range of microstructures, we analyse the predictions of the Minkowski functionals achieved by four Gaussian process regression models using the scattering data. Our findings suggest that there is a strong correlation between the scattering data and the Minkowski functionals.

Cyphochilus beetle scales are amongst the brightest structural whites in nature, being highly opacifying whilst extremely thin. However, the formation mechanism for the voided intra-scale structure is unknown. Here we report 3D x-ray nanotomography data for the voided chitin networks of intact white scales of Cyphochilus and Lepidiota stigma. Chitin-filling fractions are found to be 31 ± 2% for Cyphochilus and 34 ± 1% for Lepidiota stigma, indicating previous measurements overestimated their density. Optical simulations using finite-difference time domain for the chitin morphologies and simulated Cahn-Hilliard spinodal structures show excellent agreement. Reflectance curves spanning filling fraction of 5-95% for simulated spinodal structures, pinpoint optimal whiteness for 25% chitin filling. We make a simulacrum from a polymer undergoing a strong solvent quench, resulting in highly reflective (~94%) white films. In-situ X-ray scattering confirms the nanostructure is formed through spinodal decomposition phase separation. We conclude that the ultra-white beetle scale nanostructure is made via liquid–liquid phase separation. White beetle scales strongly scatter white light, whilst being very thin. Here, the authors measured the internal scale nanostructure for the beetles, Cyphochilus and L. stigma, and demonstrate that the optical structure can be simulated using liquid–liquid phase separation nanostructures, pointing to this as the formation mechanism.

Nanorod diffusion and polymer dynamics in nanocomposites were investigated by means of molecular dynamics simulations. We show that thin nanorods (spherocylinders) can diffuse much faster than that predicted by a Stokes–Einstein continuum model, similar to experiments, in the dilute nanorod regime. In entangled polymer matrices, nanorod diffusion reaches a plateau region. Increase of the nanorod diameter or aspect ratio (AR) slows its diffusion. The nanorod diffusion, at long time scales, displays a non-Gaussian behavior as is depicted by the several Gaussian peaks present in the self-part of the van Hove function. We also show that the unentangled polymer dynamics decreases in the nanocomposite due to the nanorods interfacial area.

This paper explores radar methods to measure the coordinates (distance and height) of objects on or beside a road. Knowledge of these parameters is essential in the development of autonomous or semi-autonomous cars, as well as to improve driving safety. It is shown that the height is best found by trilateration from sensors at multiple locations on a vehicle. The novelty of the work consists in the formulation of the problem and in its solution using a low-THz radar trilateration approach. The expressions obtained allow calculating the coordinates of targets using a number of different methods of radar trilateration. The influence of the system parameters on the accuracy of measurement using different methods of trilateration has been analyzed. The assumptions made were verified by the experimental system based on a 300-GHz ultra-wideband radar. Experimental results are in good agreement with theoretical calculations; they confirmed the practicality of obtaining high-accuracy height measurements on distributed targets such as pedestrians. The physical basis of the techniques developed would also allow the plan position of a target to be found using the same approach.

Microwave-promoted continuous flow systems have emerged as a game-changer in nanoparticle synthesis. Owing to the excellent compatibility between fast, sustainable microwave heating and one-step, efficient flow chemistry, this promising technology is meant to enhance the synthetic abilities of nanoscientists. This Perspective aims to present a panoramic view of the state of the art in this field. Additionally, the effect of various microwave and flow parameters on the properties of nanoparticles is discussed along with a comparative glance at the features that make flow reactors more practical and sustainable than their batch counterparts. The overview has also analyzed various microwave continuous flow reactors available in the literature, with an acute emphasis on the nanosynthesis route and design features. Moreover, a discussion on the numerical modeling of microwave flow systems has been made a part of this perspective to reiterate its significance and encourage research in this domain. The Perspective also briefly comments on existing challenges and future prospects of this technology.

In this chapter, we focus on the polymer nanoparticle (either spherical, anisotropic or free surface) interface and specifically on polymer dynamics considering attractive interaction with the nanoparticles. We concisely report the main experimental and computer molecular simulation studies regarding the polymer mobility at the interface. We show how changes of the glass transition (\(T_\mathrm{g}\)) are correlated with segmental dynamics and relaxation at the interface.

Polymer core–shell nanoparticles are attractive drug-delivery systems because the drug can be encapsulated inside the core, while the shell properties can be assigned to optimise drug-delivery needs. An elegant approach to such particles is to use polymer gels, which have swelling properties that depend upon conditions such as pH. In this way swelling of the shell, and the drug release, can be targeted to occur at the desired location. We use computer simulations to capture the deformation of polymer core–shell nanoparticles and, subsequently, the drug diffusion from the core of these structures. In particular, we investigate the effects of shell swelling on drug-release rates, where the expanding shell leaves more free space for the drug to diffuse out of the core. Furthermore, we introduce enthalpic interactions and investigate both the physical and chemical barriers to drug release. Therefore, through a combination of structural and fluid simulations we can capture the physics of polymer core–shell nanoparticles and their uses for drug delivery.

Due to their inherently high surface energy, polar end-functionalised polymers do not normally adsorb to the external surfaces of blends. However, adsorption of polar functionalities can be induced rapidly by annealing in a polar environment such as glycerol prior to quenching to a glassy state. Blended films of carboxy end-functionalised deuteriopolystyrene (dPS-COOH) with hydrogenous polystyrene (hPS) were annealed at 150 °C under glycerol. Nuclear reaction analysis was used to quantify the surface excess of dPS-COOH retained at the surface after quenching the films to below the glass transition temperature. Incorporation of multiple COOH groups onto a single chain end greatly increases the affinity of these chains to the interface with glycerol. Here we have shown that even a difunctional material, dPS-2COOH, is much more surface active than either the singly functionalised dPS-COOH or the difunctional ester from which it was prepared. Self-consistent mean field theory yielded thermodynamic ‘sticking energy’ values per functionality at the polystyrene–glycerol surface of 1.3–1.7 kBT for carboxy groups and 0.3 kBT for ester groups.

We report on numerical simulations of late stage undulation growth in Dutcher films. Dutcher films are ultrathin trilayer films consisting of a fluid layer sandwiched in between two solid layers. The van der Waals forces acting across the film can result in the spontaneous formation of surface undulations and corrugations. The complex interplay between the van der Waals forces, the elastic deformation of the solid layers and the fluid dynamics of the sandwiched fluid essentially selects a wavelength of undulation which grows most rapidly. We show how the lateral deformations in the solid layers can be obtained from the elastic stretching free energy as a function of the height variations. Furthermore, these lateral deformations can be shown to contribute to a pressure normal to the film which influences the dynamics of fluctuation growth. By taking into consideration the large-amplitude elastic stretching effects we simulate the late stages of undulation growth including the contact between the upper and lower solid layers. As the area of contact between the solid layers increases the fluid is corralled into isolated pockets. Because our numerical model captures the full elasticity of the solid layers we show how internal forces can be incorporated into the system. As a demonstration, we simulate the effects of thermal mismatch between a small region of the film and the surrounding matrix and show how concentric grooves can be formed in Dutcher films.

We investigate the relationship between the metachronal wavelength of an array of beating cilia and the resulting fluid flow rate through numerical simulations. Our model is based on a hybrid immersed boundary lattice Boltzmann algorithm. Our results suggest that varying the metachronal wavelength of the cilium array affects the fluid flow rate by increasing or decreasing the spread of cilia during their active strokes. We quantify this behaviour by constructing an analytical model of the system and deriving an equation for free area within the cilium array that depends on the metachronal wavelength. We show that there is a strong correlation between free area and fluid flow rate that holds for different values of cilium spacing.

International audience; In order to account for diffusio-osmosis, Derjaguin proposed long ago that there is an excess pressure confined within a layer of typically a few nanometers in the vicinity of a solid surface immersed in a liquid and resulting from the interaction between the liquid and the surface. In the presence of a composition gradient in the liquid a confined pressure gradient parallel to the surface is therefore responsible for the diffusio-osmotic flow. This picture appears in contradiction with the contact theorem of colloidal science according to which such excess pressure does not exist. We propose a theoretical description for calculating hydrodynamic flows in inhomogeneous liquids in the vicinity of solid interfaces which is consistent with the contact theorem. This approach is based on a Gibbs free energy and a virtual work principle for calculating the driving forces in the liquid due to inhomogeneous composition along a capillary and to the interaction with the solid interfaces. Our approach allows us to show that the physics at play is the same in wetting or in diffusio-osmosis experiments, as one can go continuously from the latter to the former by making composition gradients sharper. We obtain an explicit expression for thediffusio-osmotic mobility which depends on the Gibbs free energy density in the vicinity of the interface and its dependance onthe solute concentration in the liquid beyond the interfacial region, and which is inversely proportionnal to the liquid viscosity.

Low-terahertz (THz) (above 150 GHz) radar sensing is one of the promising technologies to provide safe navigation for autonomous cars due to its expected high-resolution imaging capability. It is anticipated that for robust operation at high levels of autonomy the sensor suite should provide a fusion of video and radar data and its efficiency depends on radar ability to deliver a resolution high enough to be compatible with that of the optical image. Performance of low-THz radar, capable to deliver required resolution, is considered in this study, with the focus on reflectivities of pedestrians at frequencies within the low-THz region – 150 and 300 GHz. Backscatter returns are collected in a controlled environment at a number of frequency bands and at different aspect angles. Measurement methodology is presented and several indicators of reflectivities are calculated. Results are compared with values of radar cross-section reported for current automotive frequency standards 24 and 77 GHz. The effect of clothing on reflectivities is also considered in this study.

Polymer diffusion is enhanced when nanorods (NRs) in a polymer nanocomposite are mobile relative to nanocomposites containing immobile NRs. NR mobility is tuned by varying the molecular weight of the matrix polymer and the NR concentration, and diffusion of deuterated polystyrene (dPS) tracers with varying molecular weight is studied using elastic recoil detection. When dPS diffuses faster than the NRs such that the NRs are “immobile” on the time scale of dPS, the tracer diffusion coefficient (D) monotonically decreases as the nanorod concentration increases; we interpret these results as though the nanorods provide additional topological constraints that slow diffusion of dPS. When the tracer diffusion is slow relative to NR diffusion (i.e., “mobile” NRs), diffusion is enhanced relative to the immobile NR case. This enhanced diffusion is captured by a slip-link model with two populations of topological constraints: one fixed population attributed to the PS matrix, and a second population of constraints w...

Given the exceedingly high interfacial area-to-volume ratios in polymer nanocomposites and the ability to manipulate the polymer/nanoparticle interfacial interactions, manipulating the chain dynamics at these interfaces has immense potential for impacting macroscopic properties. There, the polymer center-of-mass tracer diffusion coefficient (D) from attractive (hydroxyl-terminated) and athermal (phenyl-terminated or polymer-grafted) substrates was measured over a range of temperatures and tracer molecular weights using elastic recoil detection. The tracer polymer diffusion slows significantly relative to the bulk when polymers are in direct contact with an attractive substrate and exhibits a weaker molecular weight dependence, D ∼ M–1.4. For polymers without direct contacts on the attractive substrates and for athermal substrates, the diffusion coefficients are similar to the bulk case. The temperature dependence of these diffusion coefficients indicates that the slower diffusion at the interfaces is coup...

The polymer center-of-mass tracer diffusion coefficient in athermal polymer nanocomposites (PNCs) composed of polystyrene and phenyl-capped, spherical silica nanoparticles was measured over a range of temperatures and nanoparticle concentrations using elastic recoil detection. The polymer tracer diffusion coefficient in the PNC relative to the bulk decreases with increasing nanoparticle concentration and is unexpectedly more strongly reduced at higher temperatures. This unusual temperature dependence of polymer diffusion in PNCs cannot be explained by the reptation model or a modified version incorporating an effective tube diameter. Instead we show that our results are consistent with a mechanism based on nanoparticle-imposed configurational entropy barriers.

Over the past two decades polymer nanocomposites have received tremendous interest from industry and academia due to their advanced properties comparative to polymer blends. Many computational studies have revealed that the macroscopic properties of polymer nanocomposites depend strongly on the microscopic polymer structure and conformations. In this article we review computer simulation studies of the fundamental problem of homopolymers structure and dimensions in nanocomposites containing bare or grafted spherical or rod nanoparticles. Experimentally, there is controversy over whether the addition of nanoparticles in a polymer matrix can perturb the polymer chains.

In this paper, we compare the common remote sensing technologies in terms of their application for road surface classification. The presence of surface classification system in a vehicle will increase the safety of driving, especially in adverse weather conditions, as well as when driving offroad. The paper presents an overview of the application of optical, laser, ultrasonic, and microwave sensors for surface classification. From the analysis it follows that sensor data fusion allows obtaining more accurate and reliable results.

Exploiting graphene’s exceptional physical properties in polymer composites is a significant challenge because of the difficulty in controlling the graphene conformation and dispersion. Reliable processing of graphene polymer composites with uniform and consistent properties can therefore be difficult to achieve. We demonstrate distinctive regimes in morphology and nanocomposite properties, achievable through systematic control of shear rate and shear history. Remarkable changes in electrical impedance unique to composites of graphene nanoplates (GNPs) are observed. Low shear rates ≤ 0.1 s-1 break up the typical GNP agglomerates found in graphene composites, exfoliate the GNPs to fewer graphene layers and reduce orientation, enhancing electrical conductivi-ty in the composite materials. Whereas, at higher shear rates GNP orientation increases and the conductivity reduces by four orders of magnitude, as the graphene filler network is broken down. The structure of the composite continues to evolve, reflected in fur-ther changes in conductivity, after the shear force has been removed and the process temperature maintained. This work provides critical insights for understanding and controlling GNP orientation and dispersion within composites and will have important consequences in the industrial processing of graphene polymer composites via the informed design and choice of processing conditions.

Developing skills for searching the patent literature is an essential element of chemical information literacy programs at the university level. The present article creates awareness of patents as a rich source of chemical information. Patent classification is introduced as a key-component in comprehensive search strategies. The free Espacenet patent search interface and classification browser are used in a case study related to the chemistry of graphene. Step-by-step instructions are provided on how to identify search concepts, retrieve classification symbols with keywords, and iteratively refine the chemical concept based search. Instructional material for the use in chemical literature courses is proposed.

Polymer radii of gyration in isotropic single-walled carbon nanotube (SWCNT)/polymer nanocomposites were previously found to increase with increasing SWCNT concentration. Here, the SWCNTs in nanocomposites were aligned by melt fiber spinning, and the polymer chain conformations were found to be anisotropic. Using SAXS and SANS, the anisotropic SWCNT meshes were found to have smaller mesh sizes in the direction perpendicular to the alignment direction than along the alignment direction. At fixed SWCNT orientation, the radius of gyration was probed parallel and perpendicular to the alignment direction, Rgpar and Rgper, respectively, using SANS. With increasing SWCNT concentration, Rgper increases significantly more than Rgpar, such that the extent of anisotropy increases with SWCNT concentration. The anisotropic polymer conformation is larger in the direction perpendicular to the alignment direction, which corresponds to a smaller SWCNT mesh size. Thus, when the SWCNT concentration and alignment combine to ...

We investigate the effect of various spherical nanoparticles on chain dimensions in polymer melts for high nanoparticle loading which is larger than the percolation threshold, using molecular dynamics simulations. We show that polymer chains are unperturbed by the presence of repulsive nanoparticles. In contrast polymer chains can be perturbed by the presence of attractive nanoparticles when the polymer radius of gyration is larger than the nanoparticle radius. At high nanoparticle loading, chains can be stretched and flattened by the nanoparticles, even oligomers can expand under the presence of attractive nanoparticles of very small size.

We measure the center-of-mass diffusion of poly(methyl methacrylate) (PMMA)-grafted nanoparticles (NPs) in unentangled to slightly entangled PMMA melts using Rutherford backscattering spectrometry. These grafted NPs diffuse ∼100 times slower than predicted by the Stokes-Einstein relation assuming a viscosity equal to bulk PMMA and a hydrodynamic NP size equal to the NP core diameter, 2Rcore = 4.3 nm. This slow NP diffusion is consistent with an increased effective NP size, 2Reff ≈ 20 nm, nominally independent of the range of grafting density and matrix molecular weights explored in this study. Comparing these experimental results to a modified Daoud-Cotton scaling estimate for the brush thickness as well as dynamic mean field simulations of polymer-grafted NPs in athermal polymer melts, we find that 2Reff is in quantitative agreement with the size of the NP core plus the extended grafted chains. Our results suggest that grafted polymer chains of moderate molecular weight and grafting density may alter the NP diffusion mechanism in polymer melts, primarily by increasing the NP effective size.

In this paper the practical issues of automotive surface identification system development are considering. The novelty of this work is the combining of different training algorithms, neural network structures and methods to increase the classification accuracy and avoid overfitting of real-world data. The obtained results thereby demonstrate that the use of proposed system architecture and statistical methods allow for reliable discrimination of various road surfaces in real driving condition.

The development of automotive remote surface identification system is an important step in ensuring road safety. In this paper we shall discuss a novel approach which addresses the road surface classification process. This method is based on polarimetric radar and sonar data fusion and surface identification using artificial neural network. A modular artificial neural network, which is considered in the paper, allows an overall increase in classification accuracy in the presence of a large number of surface types and a large number of signal features. We shall discuss the techniques involved and present classification results that have been achieved using modular neural network.

In this paper we shall discuss a novel approach to road surface recognition, based on the analysis of backscattered microwave and ultrasonic signals. The novelty of our method is sonar and polarimetric radar data fusion, extraction of features for separate swathes of illuminated surface (segmentation), and using of multi-stage artificial neural network for surface classification. The developed system consists of 24 GHz radar and 40 kHz ultrasonic sensor. The features are extracted from backscattered signals and then the procedures of principal component analysis and supervised classification are applied to feature data. The special attention is paid to multi-stage artificial neural network which allows an overall increase in classification accuracy. The proposed technique was tested for recognition of a large number of real surfaces in different weather conditions with the average accuracy of correct classification of 95%. The obtained results thereby demonstrate that the use of proposed system architecture and statistical methods allow for reliable discrimination of various road surfaces in real conditions.

We investigated the effect of the feeding formulation (premixed powders of pure components versus solvent-blended mixture) of polystyrene−C60 composites on the dispersion and reagglomeration phenomena developing along the barrel of a twinscrew extruder. The dispersion of C60 in the PS matrix is studied over different length scales using a combination of optical microscopy, spinecho small-angle neutron scattering (SESANS), small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), and wideangle X-ray scattering (WAXS). When a solvent-blended mixture is used as the feeding formulation, the inlet material contains essentially molecularly dispersed C60 as revealed by the nanodomains with very small phase contrast. However, C60 reagglomeration occurs along the extruder, creating a morphology still containing only nanodomains but with much higher phase contrast. In the case of mixed powders, the material evolves from the initial macroscopic mixture of pure polystyrene and C60 into a composite simultaneously containing micro- and nanoaggregates of C60 as well as C60 molecularly dispersed in the matrix. Our results show that the two different initial feeding formulations with widely different initial morphologies converge along the extruder, through opposite morphological pathways, into a similar final nanomorphology which is dictated by the interplay between the thermodynamics of the system and the flow. Correlations between the morphological evolution along the extruder and the thermorheological properties of the composites are identified, NSF Award DMR-0520547, This work was funded by FEDER funds through the COMPETE 2020 Program and National Funds through FCT - Portuguese Foundation for Science and Technology under the Project UID/CTM/50025/2013. Funding from FEDER through the program COMPETE (Project EXPL/CTMPOL/0933/2012) is also acknowledged. SANS data were collected during beam time provided through the user program at the ISIS Neutron and Muon Source, operated by the UK Science & Technology Facilities Council. We thank Chris Duif (TU Delft) for assistance with the SESANS measurements. This work benefited from DANSE software developed under NSF Award DMR-0520547., info:eu-repo/semantics/publishedVersion

The nanoscale mechanical properties of live Staphylococcus aureus cells during different phases of growth were studied by atomic force microscopy. Indentation to different depths provided access to both local cell wall mechanical properties and whole-cell properties, including a component related to cell turgor pressure. Local cell wall properties were found to change in a characteristic manner throughout the division cycle. Splitting of the cell into two daughter cells followed a local softening of the cell wall along the division circumference, with the cell wall on either side of the division circumference becoming stiffer. Once exposed, the newly formed septum was found to be stiffer than the surrounding, older cell wall. Deeper indentations, which were affected by cell turgor pressure, did not show a change in stiffness throughout the division cycle, implying that enzymatic cell wall remodeling and local variations in wall properties are responsible for the evolution of cell shape through division.

Polymer nanocomposites (PNCs) have characteristic length scales associated with both the nanoparticles (i.e., size and interparticle distance) and the polymer molecules (i.e., tube diameter of entanglement and radius of gyration; Rg). When the nanoparticle (NP) and polymer length scales are comparable, the polymer dynamics exhibit contrasting behavior for NPs differing only in size and shape. For spherical NPs and short anisotropic NPs, the polymer diffusion coefficient decreases monotonically with NP concentration. However, for long anisotropic NPs, polymer diffusion slows down at low NP concentration and recovers for NP concentrations above the critical concentration for network formation. By spanning intermediate ranges of nanoparticle size and shape, the role of the NP geometric parameters on the polymer dynamics is substantially advanced, thereby providing new routes toward controlling polymer dynamics and viscoelasticity of PNCs.

Diffusion of deuterated polystyrene (dPS) is probed in PS matrices containing stringlike chained nanoparticles (cNP) grafted with PS. This investigation connects prior diffusion studies in model spherical and cylindrical NP systems and provides insight for technological applications, which typically involve irregularly shaped NPs such as carbon black. We report that the presence of chained NPs in PS matrices induces a minimum in the diffusion coefficient (D) with increasing cNP concentration when the key length scale, 2Rg/L ≤ 1.5, where Rg is the gyration radius of dPS and L is the mean length of the impenetrable core of the chained NPs. When 2Rg/L > 1.5, D decreases monotonically as the NP concentration increases. Note that in all cases 2Rg is larger than the diameter of these short-stringy NPs. The diffusion minimum is attributed to anisotropic diffusion in the vicinity of the chained NPs and requires that the long dimension of the cNP be comparable to or longer than the tracer molecule. Two normalizati...

Multihydroxyl end functional polyethylenes have been prepared with controlled molecular weight, microstructure, and functionalization. These materials, designed as interfacially active blend additives for polar interfaces, are thermally stable up to 250 °C and to have similar crystallinity and dynamics to their unfunctionalized homopolymer analogues. The polymers segregated strongly to silicon oxide interfaces, with adsorbed layers forming spontaneously at annealed polymer interfaces, having surface excess concentrations approaching 2Rg and a maximum areal density of approximately 0.6 adsorbed chains per nm2. This interfacial activity is achieved almost without detriment to the bulk physical properties of the polymer as evidenced by thermal analysis, quasi-elastic neutron scattering, and small-angle neutron scattering (SANS). SANS experiments show little evidence for aggregation of the dihydroxyl functionalized polymers in blends with PE homopolymers, which is thought to explain why these additives have particularly strong interfacial adsorption, even at relatively high concentrations. A modest level of segregation of the additives to exposed blend surfaces was also seen, particularly when the additive molecular weight was significantly lower than that of the matrix. We attribute this to a combination of the relatively low molecular weight of the additives and the marginally lower surface energy associated with deuterated polymers.

Thin films of cadmium sulphide (CdS) nanoparticle induced polyaniline (PANI) nanocomposites have worked as a better system for application in photovoltaics due to the efficient charge separation and charge transfer. In this communication, we have chosen such a system of varying thickness deposited by the Langmuir–Blodgett (LB) technique in order to study the growth and roughness phenomena by dynamic scaling theory. Different techniques such as X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and X-ray reflectivity (XRR) are used for characterization of these films. In the study, the growth exponent, β, is found to have a correlation with the invariant logarithmic scaling law. A very large value of β = 1.18 ± 0.23 as calculated is a result of the rapid roughening in the multilayer film growth process. We have investigated the dynamic scaling behavior of the multilayer system which shows a difference in the value of the coarsening factor and this confirms the breakdown of self-affinity as a consequence of some nonlocal growth effects. The normal grain formation with deposition at the initial stage and the increase in grain abnormality with increase in thickness is also verified in support of the dynamic scaling ansatz. In the present study the layer-by layer deposition is confirmed by XRR fitting for a 3 layer film whereas the multilayer shows diffusing behavior due to H-bonding or electrostatic interactions.

Chain conformations dictate many of the important physical properties of polymers including their dynamics. Using small angle neutron scattering, we probed chain conformations, specifically the radius of gyration (Rg), in both SWCNT/polystyrene (rSWCNT/Rg ∼ 0.4) and MWCNT/polystyrene (rMWCNT/Rg ∼ 1) nanocomposites. We fit the scattering data using a model that includes an ideal Gaussian chain to describe the polymer conformation and a rod network to describe the carbon nanotube (CNT) network. The scattering contribution from the rod network increases with the CNT concentration in both SWCNT and MWCNT nanocomposites, and the contribution is higher for SWCNT nanocomposites due to the smaller mesh size and higher mesh density. When the SWCNT and MWCNT concentrations are below 2 wt %, there is no significant change in Rg. Above 2 wt %, Rg in the MWCNT nanocomposites decreases slightly, while Rg in the SWCNT nanocomposites increases monotonically as a function of CNT concentration, showing a ∼30% increase at 1...

Diffusion of deuterated poly(methyl methacrylate) (dPMMA) is slowed down in a PMMA matrix filled with hydroxyl-capped spherical silica nanoparticles, from 13 to 50 nm in diameter and at loadings up to 40 vol %. At constant T – Tg = 75 K, the normalized diffusion coefficients (D/D0) collapse onto a master curve, when plotted against the confinement parameter, ID/2Rg, where ID is interparticle distance and 2Rg is probe size. This result suggests that the confinement parameter captures the effect of nanoparticle size, size polydispersity, and volume fraction on polymer dynamics for the PMMA composite. For ID 2Rg, the curve falls in a weakly confined region where D/D0decreases only moderately by up to 15%. Surprisingly, D/D0 is reduced even when ID is 8 times larger than 2Rg. A comparison between the master curves for PMMA and polystyrene nanocomposites indicates that attractive interactions in the ...

We present results of the direct observation, in real-space, of the phase separation of high molecular weight polystyrene and poly(methyl methacrylate) from ortho-xylene using our newly developed technique of high speed stroboscopic interference microscopy. Taking a fixed concentration (3 wt % in o-xylene) at a fixed composition (1:4 by weight) and by varying the rotational rate during the spin-coating process, we are able to observe the formation of a range of phase separated bicontinuous morphologies of differing length-scales. Importantly, we are able to show that the mechanism by which the final phase separated structure is formed is through domain coarsening when rich in solvent, before vitrification occurs and fixes the phase separated structure. The ability to directly observe morphological development offers a route toward controlling the length-scale of the final morphology through process control and in situ feedback, from a single stock solution. © 2013 Wiley Periodicals, Inc.

Polymer tracer diffusion in multiwalled carbon nanotubes (MWCNT)/polystyrene (PS) nanocomposites as a function of MWCNT concentration was measured from 152 to 214 °C. At 170 °C, we previously repor...

We investigate the polymer packing around nanoparticles and polymer/nanoparticle topological constraints (entanglements) in nanocomposites containing spherical nanoparticles in comparison to pure polymer melts using molecular dynamics (MD) simulations. The polymer-nanoparticle attraction leads to good dispersion of nanoparticles. We observe an increase in the number of topological constraints (decrease of total entanglement length Ne with nanoparticle loading in the polymer matrix) in nanocomposites due to nanoparticles, as evidenced by larger contour lengths of the primitive paths. An increase of the nanoparticle radius reduces the polymer-particle entanglements. These studies demonstrate that the interaction between polymers and nanoparticles does not affect the total entanglement length because in nanocomposites with small nanoparticles, the polymer-nanoparticles topological constraints dominate.

We investigate the topological constraints (entanglements) and dynamics of monodisperse polymer melts in the presence of a single wall carbon nanotube (SWCNT) in comparison to inclusion-free polymer melts by molecular dynamics simulations. The SWCNT has an infinite aspect ratio and radius smaller than the polymer radius of gyration. In the presence of SWCNT with or without attractive interactions, the contour length of the primitive path increases indicating more entanglements. We also find that there is a large heterogeneity in the polymer dynamics due to the polymers in contact with the SWCNT. The overall polymer diffusion decreases compared to its melt value and is affected by the enthalpic interaction between monomeric units and SWCNT, and the SWCNT radius. Moreover, the polymer chain diffusivity perpendicular to SWCNT is less than that parallel to the SWCNT in the entangled polymer systems where there is attraction between polymers and SWCNT surface. In the absence of SWCNT-polymer attractions, the p...

A series of chiral bis(urea) compounds based on oligomethylene spacers with S-phenylethyl end groups have been investigated as low molecular weight gelators. The series shows gelation of a variety of liquids and their structural, morphological and rheological properties are reported. The bis(urea) compounds also act as supramolecular hosts for anions such as chloride and acetate and the weakening of the gels by competitive anion complexation on this series of archetypical, low molecular weight gels is reported. Modification of gel properties using gel mixtures is also described and the gelation process studied using a fluorescent napthyl analogue.

We investigate the static properties of monodisperse polymer/single wall carbon nanotube (SWCNT) nanocomposites in comparison to polymer melts by molecular dynamics simulations. The SWCNT has a large aspect ratio and radius smaller than the polymer radius of gyration. We find that although the local chain structure is significantly affected, the overall configuration, as characterized by the radius of gyration, is not perturbed either by the interaction strength between the polymer and the SWCNT or by variations in the SWCNT radius.

We use realistic morphological and charge transport modeling to unambiguously quantify the effect of wetting layers on organic photovoltaic device (OPV) performance. Direct measurements of the blend surface of OPVs commonly reveal surface wetting layers that may hinder charge extraction. However, quantifying the effect of these layers on OPV performance experimentally is extremely challenging due to the conjoined nature of the bulk and surface morphology. We show that wetting layers of both the “wrong” and the “correct” material can adversely affect performance, the latter effect being due to subsurface features. The results are generalized to show that it is the peak composition of “wrong” material en route to an electrode, not the surface composition, which determines the effect of wetting layers. The predictions are in good agreement with available data, suggesting that our model can be used to assess when seemingly ubiquitous wetting layers will adversely affect OPV performance.

Macromolecular motion is reduced in crowded polymer nanocomposites. Tracer diffusion is measured for deuterated polystyrene (dPS) into a polystyrene (PS):silica nanoparticle (NP) matrix using elastic recoil detection. This nanocomposite is ideal for studying diffusion in a crowded system because the interparticle distance (ID) that defines confinement can be varied from much greater than to much less than the size of the dPS chain, which is described by 2Rg, the radius of gyration, and varies from 10 to 40 nm in this study. Diffusion is observed to be significantly slower than that predicted by the Maxwell model. The tracer diffusion coefficient of dPS in the nanocomposite relative to the pure PS matrix (D/D0) plotted against the NP separation relative to probe size (i.e., ID/2Rg) falls on a master curve, indicating that crowding is a property of both the dPS size and confinement in the nanocomposite. Moreover, the normalized diffusion coefficient decreases more rapidly when ID/2Rg is less than ∼1, sugges...