pinecone/core-2020-05-10-deduplication huggingface dataset:
Equilibrium Statistics of Weakly Slip-Linked Gaussian Polymer Chains

We calculate the free energy and the pressure of a weakly slip-linked
Gaussian polymer chains. We show that the equilibrium statistics of a
slip-linked system is different from one of the corresponding ideal chain
system without any constraints by slip-links. It is shown that the pressure of
a slip-linked system decreases compared with the ideal system, which implies
that slip-linked chains spontaneously form aggregated cluster like compact
structures. These are qualitatively consistent with previous theoretical
analyses or multi chain simulations. We also show that repulsive potentials
between chains, which have been phenomenologically utilized in simulations, can
cancel the artificial pressure decrease.Comment: 24 pages, 3 figures, to appear in J. Polym. Sci. B: Polym. Phy
Why is Understanding Glassy Polymer Mechanics So Difficult?

In this Perspective, I describe recent work on systems in which the
traditional distinctions between (i) unentangled vs. well-entangled systems and
(ii) melts vs. glasses seem least useful, and argue for the broader use in
glassy polymer mechanics of two more dichotomies: systems which possess (iii)
unary vs. binary and (iv) cooperative vs. nonccoperative relaxation dynamics. I
discuss the applicability of (iii-iv) to understanding the functional form of
glassy strain hardening. Results from molecular dynamics simulations show that
the "dramatic" strain hardening observed in densely entangled systems is
associated with a crossover from unary, noncooperative to binary, cooperative
relaxation as strain increases; chains stretch between entanglement points,
altering the character of local plasticity. Promising approaches for future
research along these lines are discussed.Comment: Results and conclusions same but manuscript extensively edited for
  clarity. Accepted for publication in J. Polym. Sci. - Polym. Phy
Development of internal fine structure in stretched rubber vulcanizates

Small-angle X-ray scattering (SAXS) pattern and tensile stress during relaxation of stretched rubber vulcanizates (synthetic polyisoprene) were measured simultaneously at room temperature and at 0 °C. The samples were quickly stretched to the prefixed strain and then allowed to relax for 1 h. In every SAXS pattern, the intensity distribution was elongated along the equator, indicating the formation of structures elongated in the stretching direction. The so-called two-spots pattern corresponding to the long period of stacked lamellar crystals did not appear even when the critical strain to induce crystallization was exceeded. On the other hand, even below the critical strain, additional development of equatorial streaks was detected in the differential SAXS patterns. This result suggests the growth of the density fluctuation elongated in the stretching direction, which is not directly related to strain-induced crystallization
Rheological and electrical analysis in carbon nanofibre reinforced polypropylene composites

Two different types of carbon nanofibers (CNF) were incorporated in the same polypropylene
(PP) matrix by twin-screw extrusion. The electrical characterization of both CNFs / PP
composites as a function of volume fraction show different electrical performance:
conducting and non-conducting. The objective of this work is to study the rheological
behaviour of both composites with the aim of relating it to the electrical behaviour. The
results indicate that the rheological behaviours are different, suggesting that rheology
differentiates the microstructural variations responsible for the electrical performance.
Furthermore, the main rheological parameters were correlated to the electrical conductivity.
The results show that G´/ G´´ and G´ are the most sensitive parameters when compared to the
onset of electrical percolation. Finally, in spite of the intrinsic measuring differences between
electrical and rheological analysis, the two calculated thresholds are very similar: ~ 0.5 for
the rheological and ~ 0.4 for the electrical.Financial support for this work has been provided by Consellería de Educación e Ordenación
Universitaria, Xunta de Galicia through grant CN2011/008
The effect of mixing methods on the dispersion of carbon nanotubes during the solvent-free processing of multiwalled carbon nanotube/epoxy composites

The article of record as published may be found at: http://dx.doi.org/10.1002/polb.23225Several solvent-free processing methods to disperse multiwalled carbon nanotubes (MWCNTs) in bisphenol F-based epoxy resin were investigated, including the use of a microfluidizer (MF), planetary shear mixer (PSM), ultrasonication (US) and
combinations. The processed mixture was cured with diethyl toluene diamine. Three complimentary techniques were used to
characterize the dispersion of the MWCNTs in cured composite samples: optical microscopy, micro Raman spectroscopy, and scanning electron microscopy (SEM). For sample MF þ PSM, optical micrographs and Raman images showed reduced agglomeration and a homogeneous distribution of MWCNTs in the
epoxy matrix. SEM analysis of fractured specimen after tensile testing revealed breakage of nanotubes along the fracture surface of the composite. A comparison of the MWCNT dispersion in the epoxy samples processed using different methods showed that a combination of MF and PSM processing yields a more homogeneous sample than the PSM or US þ PSM processed samples. Mechanical testing of the composites showed about 15% improvement in the tensile strength of samples processed by the MF þ PSM method over other methods. Thermogravimetric analysis (TGA) results showed a small decrease in the onset degradation temperature for poorly dispersed samples produced by PSM compared with the well-mixed samples (MF þ PSM). These
results strongly suggest that the MF þ PSM processing method yield better-dispersed and stronger MWCNT/epoxy composites
Surface engineering the cellular microenvironment via patterning and gradients

Cell organization, proliferation, and differentiation are impacted by diverse cues present in the cellular microenvironment. As a result, the surface of a material plays an important role in cellular function. Synthetic surfaces may be augmented by physical as well as chemical means. In particular, patterning and interfacial gradients may be utilized to mitigate the cellular response. Patterning is advantageous as it affords control over a range of feature sizes from several nanometers to millimeters. Gradients exist  in vivo , for instance in stem cell niches, and the ability to create interfacial gradients  in vitro  can provide valuable insights into the influence of a series of minute surface changes on a single sample. This review focuses on fabrication methods for generating micro‐ and nanoscale surface patterns as well as interfacial gradients, the impact of these surface modifications on the cellular response, and the advantages and challenges of these surfaces in  in vitro  applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys., 2013    The influence of patterning and interfacial gradients on the cellular response has numerous applications in tissue engineering and basic cell science. Various methods for fabricating small‐scale patterns and interfacial gradients as well as their potential and limitations are described. Furthermore, the impact of patterns and gradients on cellular function for numerous cell types and the use of these techniques to address biological questions in  in vitro  environments are illustrated. Future perspectives are also provided
Micromechanical characterization of the interphase layer in semi-crystalline polyethylene

The interphase layer in semi-crystalline polyethylene is the least known constituent, compared to the amorphous and crystalline phases, in terms of mechanical properties. In this study, the Monte Carlo molecular simulation results for the interlamellar domain (i.e. amorphous+ interphases), reported in (Macromolecules 2006, 39, 439–447) are employed. The amorphous elastic properties are adopted from the literature and then two distinct micromechanical homogenization approaches are utilized to dissociate the interphase stiffness from that of the interlamellar region. The results of the two micromechanical approaches match perfectly. Interestingly, the dissociated interphase stiffness lacks the common feature of positive definiteness, which is attributed to its nature as a transitional domain between two coexisting phases. The sensitivity analyses reveal that this property is insensitive to the non-orthotropic components of the interlamellar stiffness and the uncertainties existing in the interlamellar and amorphous stiffnesses. Finally, using the dissociated interphase stiffness, its effective Young's modulus is calculated, which compares well with the effective interlamellar Young's modulus for highly crystalline polyethylene, reported in an experimental study. This satisfactory agreement along with the identical results produced by the two micromechanical approaches confirms the validity of the new information about the interphase elastic properties in addition to making the proposed dissociation methodology quite reliable when applied to similar problems
Fabrication of zinc oxide nanowires/polymer composites by two-photon polymerization

We present an approach to fabricate ZnO nanowires/ polymer composite into three-dimensional microstructures, based on two-photon polymerization direct laser writing, a fabrication method that allows submicrometric spatial resolution. The structural integrity of the structures was inferred by scanning electron microscopy, while the presence and distribution of ZnO nanowires was investigated by energy dispersive X-ray, Raman spectroscopy, and X-ray diffraction. The optical properties of the produced composite microstructures were verified by imaging the characteristic ZnO emission using a fluorescence microscope. Hence, such approach can be used to develop composite microstructures containing ZnO nanowires aiming at technological applications.FAPESPCAPESCNPqDFG (FOR1616 - project Vo1265-6
Characterization of two- and three-photon absorption of polyfluorene derivatives

Fluorene-based polymer derivatives are promising materials for organic electronic devices because of their photoluminescence and electroluminescence, good film-forming ability, and favorable chemical and thermal properties. Although optical properties of polyfluorene have already been reported, most of the studies focused on the linear optical properties, whereas nonlinear optical characteristics have only recently received more detailed attention. Here, we report on two polyfluorene derivatives, poly(9,90-n-dihexyl-2,7-fluorenediyl) (LaPPS 10) and poly(9,90-n-dihexyl-2,7-fluorene-diyl-vinylene) (LaPPS 38), which present intense nonlinear absorption and fluorescence. Two-photon absorption cross-section properties of both polymers were characterized in the spectral range from 500 nm up to 900 nm, reaching peak values around 2000 Göppert Mayer units. Optical limiting behavior and two-photon-induced fluorescence of both polymers have also been investigated. Furthermore, the first molecular hyperpolarizability of the polymers was also studied using hyper-Rayleigh scattering. In addition, the three-photon absorption (3PA) spectra of both materials were also investigated, and 3PA crosssection values in the order of 1 x '10 POT. -78' cm6 s2 photon-2 were observed.FAPESPCNPqCAPESEmbrapa-Rede Agronan
Stretchable and transparent hydrogels as soft conductors for dielectric elastomer actuators

A soft ionic conductor can serve as an artificial nerve in an artificial muscle. A polyacrylamide hydrogel is synthesized containing a hygroscopic salt, lithium chloride. Two layers of the hydrogel are used as ionic conductors to sandwich a dielectric elastomer and fabricate a highly stretchable and transparent actuator. When the two layers of the hydrogels are subject to a voltage, the actuator reduces its thickness and expands. An areal strain of 134% is demonstrated. The voltage-strain curves are calculated by using a model that accounts for the elastic constraint of the hydrogel and the inhomogeneous deformation of the actuator. For actuators fabricated with the hydrogel of various thicknesses and with the dielectric elastomer of various prestretches, excellent agreements are found between experimental data and theoretical predictions.Engineering and Applied Science
High strain-rate response of spiropyran mechanophores in PMMA

The article of record as published may be found at http://dx.doi.org/10.1002/polb.23569We report the high strain-rate response of a spiro-pyran (SP) mechanophore in poly(methylmethacrylate). Previ-ous work on this system has demonstrated a reversible bondscission in the SP under local tensile force, converting it to afluorescent merocyanine form. A Hopkinson bar was used toapply fast compressive loads at rates from 102to 104s21,resulting in significant activation of the SP near fracture surfa-ces. However, comparison with a similar thermochromic SPreveals that much of the observed activation likely arises fromthermal effects during high-rate fracture. These results showthe importance of a thermally active control system in distinguishing mechanochromic response during high-rate loading.
Microscale fluorescence mapping of the fracture surfaces using
a confocal Raman microspectrometer suggests that some dis-
tinct mechanical activation may be occurring in craze-like
regions during fibril rupture. The thermal response of the SP is
useful in its own right for characterizing plastic heating regions
during dynamic fracture
Fluorescent PMMA/MEH-PPV electrospun nanofibers: investigation of morphology, solvent, and surfactant effect

Electrospinning is a powerful technique to produce nanofibers of tunable diameter and morphology for medicine and biotechnological applications. By doping electrospun nanofibers with inorganic and organic compounds, new functionalities can be provided for technological applications. Herein, we report a study on the morphology and optical properties of electrospun nanofibers based on the conjugated polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and poly(methylmethacrylate) (PMMA). Initially, we investigate the influence of the solvent, surfactant, and the polymer concentration on electrospinning of PMMA. After determining the best conditions, 0.1% MEH-PPV was added to obtain fluorescent nanofibers. The optical characterizations display the successful impregnation of MEH-PPV into the PMMA fibers without phase separation and the preservation of fluorescent property after fiber electrospinning. The obtained results show the ability of the electrospinning approach to obtain fluorescent PMMA/MEH-PPV nanofibers with potential for optical devices applications.FAPESPCNPqCAPESMCTIEMBRAP
Effect of the graft ratio on the properties of polythiophene-g-poly(ethylene glycol)

Graft copolymers formed by anchoring poly(ethylene glycol) (PEG) chains to conjugated polythiophene have been prepared by copolymerizing two compounds: unsubstituted -terthiophene (Th-3) and a thiophene-derived macromonomer having an -terthiophene conjugated sequence and one Th-3 bearing a PEG chain with molecular weight of 2000 as substitute at the 3-position of the central heterocycle (Th-3-PEG(2000)). The grafting ratio of the resulting copolymers (PTh3*-g-PEG), which were obtained using 75:25 and 50:50 Th-3-PEG(2000):Th-3 weight ratios, is significantly smaller than that of copolymers derived from polymerization of macromonomers consisting of a -pentathiophene sequence in which the central ring bears a PEG chain of M-w = 2000 (PTh5-g-PEG). The electroactivity and electrochemical stability of PTh3*-g-PEG is not only higher than that of PTh5-g-PEG but also higher than that of PTh3, the latter presenting a very compact structure that makes difficult the access and escape of dopant ions into the polymeric matrix during the redox processes. Furthermore, the optical -(*) lowest transition energy of PTh3*-g-PEG is lower than that of both PTh5-g-PEG and PTh3. These properties, combined with suitable wettability and roughness, result in an excellent behavior as bioactive platform of PTh3*-g-PEG copolymers, which are more biocompatible, in terms of cellular adhesion and proliferation, and electro-compatible than PTh5-g-PEG. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 239-252Peer ReviewedPostprint (author’s final draft
Tailoring poly(vinylidene fluoride-co-chlorotrifluoroethylene) microstructure and physicochemical properties by exploring its binary phase diagram with dimethylformamide

Poly(vinylidene fluoride-co-chlorotrifluoroethylene), PVDF-CTFE, membranes were prepared by solven
casting from dimethylformamide, DMF. The preparation conditions involved a systematic variation of 
polymer/solvent ratio and solvent evaporation temperature. The microstructural variations of the 
PVDF-CTFE membranes depend on the different regions of the PVDF-CTFE/DMF phase diagram, 
explained by the Flory-Huggins theory. The effect of the polymer/solvent ratio and solvent evaporation
temperature on the morphology, degree of porosity, β-phase content, degree of crystallinity, 
mechanical, dielectric and piezoelectric properties of the PVDF-CTFE polymer were evaluated. In this 
binary system, the porous microstructure is attributed to a spinodal decomposition of the liquid-liquid
phase separation.  For a given polymer/solvent ratio, 20 wt%, and  higher evaporation solvent 
temperature, the β-phase content is around 82% and the piezoelectric coefficient, d33, is - 4 pC/N.This work is funded by FEDER funds through the “Programa Operacional Factores de Competitividade – COMPETE” and by national funds from FCT – Fundação para a Ciência e a Tecnologia, in the framework of the strategic project Strategic Project PEST-C/FIS/UI607/2014 and PEST-C/QUI/UI0686/2013). The authors also thank funding from Matepro –Optimizing Materials and Processes”, ref. NORTE-07-0124FEDER-000037”, co-funded by the “Programa Operacional Regional do Norte” (ON.2 – O Novo Norte), under the “Quadro de Referência Estratégico Nacional” (QREN), through the “Fundo Europeu de Desenvolvimento Regional” (FEDER), and grant SFRH/BD/68499/2010 (C.M.C.). The authors thank Solvay for kindly supplying the high quality materials and the Departmento de Química Física, Facultad de Ciencia y Tecnología, Universidad del País Vasco UPV/EHU, Spain, for hosting a research stay in which the theoretical work was performed
Gas permeation and positron annihilation lifetime spectroscopy of poly(ether imides) containing main chain ethylene oxide segments

This article reports a study of four poly(ether imide)s with varying ethylene oxide (EO) segments lengths using positron annihilation lifetimes spectroscopy, wide angle X-ray diffraction, and gas transport measurements. The measured properties change with the length of the EO segment. Comparison of the poly(ether imide) containing a single ether linkage with those containing one and three EO units, show progressive changes of the permeability and diffusion coefficient with void size. However, when six EO units are incorporated into the polymer backbone certain of the observed trends are reversed. Incorporation of flexible EO segments in the polymer backbone allows changes in the chain-chain interactions which increases the packing density and changes the void size and influences the solubility coefficients leading to variation of the gas transport characteristics. Differences in the measured solubility parameters reflect the extent to which the gases molecules are able to interact with the polymer matrix. The highest values obtained for the gas separation for carbon dioxide and nitrogen is observed when EO has a value of three. Further increasing of the length of the EO segments in the poly(ether imide) leads to a reduction the gas transport properties and hence the extent to which gas separation would be achieved
Short-Time Elasticity of Polymer Melts: Tobolsky Conjecture and
  Heterogeneous Local Stiffness

An extended Molecular-Dynamics study of the short-time "glassy" elasticity
exhibited by a polymer melt of linear fully-flexible chains above the glass
transition is presented. The focus is on the infinite-frequency shear modulus
$G_\infty$ manifested in the picosecond time scale and the relaxed plateau
$G_p$ reached at later times and terminated by the structural relaxation. The
local stiffness of the interactions with the first neighbours of each monomer
exhibits marked distribution with average value given by $G_\infty$. In
particular, the neighbourhood of the end monomers of each chain are softer than
the inner monomers, so that $G_\infty$ increases with the chain length. $G_p$
is not affected by the chain length and is largely set by the non-bonding
interactions, thus confirming for polymer melts the conjecture formulated by
Tobolsky for glassy polymers.Comment: 18 pages, 6 figure
Dependence on Material Choice of Degradation of Organic Solar Cells Following Exposure to Humid Air

Electron microscopy has been used to study the degradation of organic solar cells when exposed to humid air. Devices with various different combinations of commonly used organic solar cell hole transport layers and cathode materials have been investigated. In this way the ingress of water and the effect it has on devices can be studied. It was found that calcium and aluminium in the cathode both react with water, causing voids and delamination within the device. The use of PEDOT:PSS was found to increase the degradation by easing water ingress into the device. Replacing these materials removed these degradation features.This work was funded by the EPSRC (grant: EP/I029257/1).This is the final published version of the article. It was originally published in the Journal of Polymer Science Part B: Polymer Physics (Glen, T. S., Scarratt, N. W., Yi, H., Iraqi, A., Wang, T., Kingsley, J., Buckley, A. R., Lidzey, D. G. and Donald, A. M., J. Polym. Sci. B Polym. Phys., 2015, doi: 10.1002/polb.23905). The final version is available at http://dx.doi.org/10.1002/polb.2390
Electrospinning of poly(lactic acid): Theoretical approach for the solvent selection to produce defect-free electrospun nanofibres

This is the peer reviewed version of the following article: CASASOLA, R., THOMAS, N.L. and GEORGIADOU, S., 2016. Electrospinning of poly(lactic acid): Theoretical approach for the solvent selection to produce defect-free electrospun nanofibres. Journal of Polymer Science Part B: Polymer Physics, 54(15), pp.1483-1498, which has been published in final form at http://dx.doi.org/10.1002/polb.24042. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.In this study an integrated methodology is proposed for the selection of solvent systems to produce electrospinnable solutions that form defect-free poly (lactic acid) fibres with narrow diameter distributions. The solvent systems are chosen using a thermodynamic approach, combined with electrical and rheological property criteria. More specifically, the three step methodology includes 1) initial choice of solvent by solubility evaluation to meet thermodynamic criteria, 2) electrical properties i.e. conductivity and dielectric constant adjustment by using solvent mixtures to meet electrical property criteria, and 3) critical entanglement concentration (Ce) determination by viscosity measurements, supported by elastic and plastic moduli measurements, followed by concentration adjustment to meet rheological criteria. All three criteria need to be met to ensure defect-free nanofibre morphology. The methodology is demonstrated using poly (lactic acid) solutions that were characterised in terms of thermodynamic properties, conductivity, surface tension and viscosity measurements. These data were analysed and related to the nanofibre morphology and diameter as determined from scanning electron microscopy (SEM). Measurements of the elastic (G’) and the plastic (G’’) moduli of PLA solutions showed a sharp increase of G’ at the chain entanglement concentration