Polymer Mass Research Articles

Influence of Branching on the Configurational and Dynamical Properties of Entangled Polymer Melts

We probe the influence of branching on the configurational, packing, and density correlation function properties of polymer melts of linear and star polymers, with emphasis on molecular masses larger than the entanglement molecular mass of linear chains. In particular, we calculate the conformational properties of these polymers, such as the hydrodynamic radius R h , packing length p, pair correlation function g ( r ) , and polymer center of mass self-diffusion coefficient, D, with the use of coarse-grained molecular dynamics simulations. Our simulation results reproduce the phenomenology of simulated linear and branched polymers, and we attempt to understand our observations based on a combination of hydrodynamic and thermodynamic modeling. We introduce a model of “entanglement” phenomenon in high molecular mass polymers that assumes polymers can viewed in a coarse-grained sense as “soft” particles and, correspondingly, we model the emergence of heterogeneous dynamics in polymeric glass-forming liquids to occur in a fashion similar to glass-forming liquids in which the molecules have soft repulsive interactions. Based on this novel perspective of polymer melt dynamics, we propose a functional form for D that can describe our simulation results for both star and linear polymers, covering both the unentangled to entangled polymer melt regimes.

Size-Dependent Photophysical Behavior of Low Bandgap Semiconducting Polymer Particles.

The photophysics of water and propan-1-ol suspensions of poly [N-9”-heptadecanyl-2,7-carbazole-alt−5,5-(4,7-di-2-thienyl-2′,1′,3′- benzothiadiazole)] (PCDTBT) nanoparticles and mesoparticles has been studied by ultrafast spectroscopy. High molar mass polymer (HMM > 20 kg/mol) forms nanoparticles with around 50 nm diameter via mini-emulsion post-polymerization, while low molar mass (LMM < 5 kg/mol) polymer prepared by dispersion polymerization results in particles with a diameter of almost one order of magnitude larger (450 ± 50 nm). In this study, the presence of excited-states and charge separated species was identified through UV pump and visible/near-infrared probe femtosecond transient absorption spectroscopy. A different behavior for the HMM nanoparticles has been identified compared to the LMM mesoparticles. The nanoparticles exhibit typical features of an energetically disordered conjugated polymer with a broad density of states, allowing for delayed spectral relaxation of excited states, while the mesoparticles show a J-aggregate-like behavior where interchain interactions are less efficient. Stimulated emission in the red-near infrared region has been found in the mesoparticles which indicates that they present a more energetically ordered system.

Effect of a Competitive Solvent on Binding Enthalpy and Chain Intermixing in Hydrogen-Bonded Layer-by-Layer Films

This work is focused on the effect of a small-molecule/hydrogen-bonding competitor on the heat of complexation of hydrogen-bonding polymers in aqueous solutions, as well as on deposition of these molecules within layer-by-layer (LbL) films. Specifically, binding between poly(methacrylic acid) (PMAA) and poly(vinylpyrrolidone) (PVP) under acidic conditions in the presence of dimethyl sulfoxide (DMSO) has been explored. Isothermal titration calorimetry showed that with increasing concentration of DMSO in aqueous solution, the positive enthalpy of formation of PMAA/PVP complexes decreased and switched sign at ∼25 vol % DMSO. This change is interpreted as a transition from endothermal association between PMAA and PVP in water, driven by release of solvation water molecules, to exothermic association driven by the enthalpy of interpolymer hydrogen bonding. This switch is interpreted as destruction of polymer hydration shells by DMSO molecules. The content of DMSO also strongly impacted the growth of LbL films. With an increase in DMSO concentration from 0 to 60 vol %, polymer mass deposited within the bilayer increased, while larger DMSO concentrations suppressed film deposition. The effect of DMSO was also revealed in neutron reflectometry measurements, which showed enhanced interpenetration of deuterated PMAA chains within a hydrogenated LbL matrix at increasing concentration of DMSO. The dependence of film intermixing on DMSO content was strongly history dependent. While assembly of LbL films in aqueous solutions followed by exposure to a mixed solvent post-assembly did not significantly influence the internal film structure, the effect of DMSO on film intermixing was strongest when DMSO was present in the film deposition solutions.

Determination of the Rayleigh Ratio with an Uncertainty Analysis by Static Light-Scattering Measurements of Certified Reference Materials for Molecular Weight.

The most important parameter for light-scattering measurements in the Rayleigh scattering region is the Rayleigh ratio, which is necessary to obtain the absolute scattered light intensity from the relative scattered light intensity. The absolute scattered light intensity is directly related to the molar masses of polymers, colloids, biomolecules, and the like. A new Rayleigh ratio was determined by measuring static light scattering from certified reference materials with highly accurate certified values of the molecular weight determined by several other techniques, such as MALDI-TOF mass spectrometry or size-exclusion chromatography. The new Rayleigh ratio can be used for evaluating the uncertainty of the molecular weight of polymers and macromolecules, as measured by light scattering.

Amorphous solid dispersions of ketoprofen and poly-vinyl polymers prepared via electrospraying and spray drying: A comparison of particle characteristics and performance

The purpose of this work was to compare the particle characteristics and dissolution performance of amorphous solid dispersions (ASDs) of ketoprofen and vinyl-pyrrolidone based polymers prepared using electrospraying and spray drying methods. Solution characteristics (surface tension, viscosity and conductivity) were determined for ethanolic solutions containing different vinyl-pyrrolidone based polymers (PVP and PVPVA) and different ketoprofen to polymer mass ratios. The only statistically significant difference in solution properties between PVP and PVPVA systems was electrical conductivity. The higher conductivity in PVP-containing solutions resulted in smaller, more spherical particles than the equivalent formulations prepared with PVPVA when processed via electrospraying. Electrospraying resulted in powders with higher specific surface area, smaller mean particle size, and narrower particle size distribution relative to the spray-dried material. Amorphisation of ketoprofen via both processes was confirmed using pXRD, DSC and FTIR. Although the specific surface area of the electrosprayed powder was higher than the equivalent spray-dried system, this did not translate into a faster dissolution rate at pH 1.2 but did lead to a faster surface moisture adsorption rate at various relative humidities. The flowability of the powder produced via the electrospraying process is poor compared to the equivalent powder produced via spray drying, which may cause challenges in downstream processing. While the ASD powder produced via electrospraying had a smaller particle size and narrower size distribution compared to equivalent spray-dried ASD, further refinement in terms of a final formulation is needed to translate this benefit into an improved dissolution rate in the case of ketoprofen.

The Dispersion Composition of Polymethylmethacrylate Suspensions and Molecular Weights of Polymers Obtained by Suspension Polymerization in the Presence of Acrylic Copolymers as Surfactants

The dispersion composition of polymer suspensions and molecular weights of polymers obtained by suspension polymerization of MMA in the presence of polymer surfactants – methylmethacrylate and methacrylic acid copolymers – were studied. It is shown that a highly dispersed fraction of particles with diameters of 0.02–2.0 µm and a fraction of particles with large diameters (up to 1000 µm) are always present in the polymer suspension. After fractionation of polymer suspensions 3 fractions of particles with different diameters were obtained. For each particle fraction the molecular masses of polymers were determined by viscometry. A significant difference in the values of the molecular masses of polymers obtained as particles of small and large diameters – 105 and 106 Da, respectively – is shown. The presence of a highly dispersed fraction of particles in which a polymer of high molecular weight is formed has a noticeable effect on the average molecular weight of the polymer. In particles of small diameter polymerization takes place according to a mechanism close to the emulsion, due to the fact that the volume of such particles contains a small amount of radicals. The high rate of polymerization leads to the formation of a polymer of high molecular weight, the appearance of a gel effect and a decrease in the termination constant. In most particles, polymerization proceeds by a mechanism close to the solution polymerization, and polymers of low molecular weight are formed. This makes it possible to synthesize polymers of a given molecular weight in drops of certain dispersity.

Multiplexed Charge Detection Mass Spectrometry for High-Throughput Single Ion Analysis of Large Molecules.

Applications of charge detection mass spectrometry (CDMS) for measuring the masses of large molecules, macromolecular complexes, and synthetic polymers that are too large or heterogeneous for conventional mass spectrometry measurements are made possible by weighing individual ions in order to avoid interferences between ions. Here, a new multiplexing method that makes it possible to measure the masses of many ions simultaneously in CDMS is demonstrated. Ions with a broad range of kinetic energies are trapped. The energy of each ion is obtained from the ratio of the intensity of the fundamental to the second harmonic frequencies of the periodic trapping motion making it possible to measure both the m/ z and charge of each ion. Because ions with the exact same m/ z but with different energies appear at different frequencies, the probability of ion-ion interference is significantly reduced. We show that the measured mass of a protein complex consisting of 16 protomers, RuBisCO (517 kDa), is not affected by the number of trapped ions with up to 21 ions trapped simultaneously in these experiments. Ion-ion interactions do not affect the ion trapping lifetime up to 1 s, and there is no influence of the number of ions on the measured charge-state distribution of bovine serum albumin (66.5 kDa), indicating that ion-ion interactions do not adversely affect any of these measurements. Over an order of magnitude gain in measurement speed over single ion analysis is demonstrated, and significant additional gains are expected with this multi-ion measurement method.

Quantitative characterization of the concentration-dependent interaction between molecules of Dextran 70 in aqueous solution: Measurement and analysis in the context of thermodynamic and compressible sphere models.

The static light scattering and sedimentation equilibrium of solutions of Dextran 70 were measured as functions of concentration up to 100 g/L in pH 7.4 phosphate-buffered saline at temperatures between 5 and 37 °C. The concentration dependence of scattering intensity and the apparent molar mass obtained from sedimentation equilibrium were found to be nearly independent of temperature over this range to within the uncertainty of measurement. Global analysis of the concentration dependence of both properties yielded a reliable estimate of the concentration-dependent thermodynamic activity coefficient, a quantitative measure of the free energy of self-interaction. The self-interaction between Dextran molecules is compared with that of a globular protein (BSA) and a highly crosslinked polymer of similar molar mass (Ficoll 70). The observed concentration dependence of the free energy of Dextran self-interaction may be quantitatively accounted for by a semi-empirical model in which the polymer molecule is represented by a compressible sphere.

Signature of Reptation in the Long-Time Behavior of the Simulated Free Induction Decay in High Molecular Mass Polymer Melt

The comparison of the recently obtained experimental [Polymer 142 (2018) 310] and simulated FID is first represented for an entangled polymer melt far from the glass transition temperature. The FIDs resulting from only the intra-segmental dipolar interaction have been simulated by two independent methods. First, the FID was modeled with the help of the mean square displacement for the middle primitive segments of the chain. Second, the FID was designed by means of the reduced FID theoretical definition, which takes into account only the residual dipolar coupling of the middle or all Kuhn segments of the chain.

Dynamics of water and xanthan chains in hydrogels studied by NMR relaxometry and their influence on drug release

The dynamic properties of water and polymer molecules in xanthan hydrogels at different polymer mass fractions were investigated through the combination of conventional and fast-field cycling NMR relaxation to obtain the information about dynamics in different time scales. The results showed that water dynamics were faster in diluted than in concentrated hydrogels. However, the type of polymer-chain dynamics did not change for xanthan fractions from 0.1 to 0.5, although they slowed at higher xanthan fractions as the system approached transition to the glass state. The addition of the nonionic small drug molecules pentoxifylline did not change the dynamics in the hydrogels, but they were affected by the medium pH. The water and polymer-chain dynamics were faster in the hydrogels for the neutral than the acid medium. These differences resulted in slower swelling and thinner and more rigid hydrogel layer of the matrix tablet in the acid medium that was less susceptible to erosion. Consequently, pentoxifylline release from xanthan tablets in acid medium is dominated by drug diffusion. At neutral pH, the molecular mobility is greater, which resulted in rapid and extensive swelling of the hydrogel, leading to erosion-dominated drug release.

Anatomical Exploration of the Tympanic Cavity Using Virtual and Printed 3D Models of the Human Petrous Bone

The tympanic cavity is, from a gross anatomical perspective, both small and complex. Scaling the anatomy of the tympanic cavity to a larger size, while maintaining accuracy with regard to detail, could improve the understanding of the anatomy. Therefore, the purpose of this study was to create an accurate 3D computer model of the tympanic cavity and materialize it, in a larger scale, via 3D printing. The 3D virtual model of the tympanic cavity was created from serial micro‐CT scans of a normal temporal bone and converted into stereolithography files dedicated for 3D printing. Micro‐CT scanning of the petrous bone was performed with aid of the Nanotom 180N device with a slice thickness of 15 μm. To obtain the 3D virtual model of the tympanic cavity, automatic image segmentation was performed with CT‐An software, which generated the mesh of triangles that approximated the geometry of the tympanic cavity. To create a polymer mass from the digital model, the Da Vinci 1.0 printer (nozzle diameter = 0.4 mm), which utilized prototyping technology based on fused filament fabrication, was employed in order to build the model with the acrylonitrile butadiene styrene at the layer height = 0.3 mm. The study demonstrated the possibility of building accurate models of the tympanic cavity that expose anatomical details including the oval window, round window, promontory, pyramidal evidence, subiculum, ponticulus, and sinus tympani— structures with dimensions in the range of only a few millimeters. Both 3D virtual and large‐scale printed models may improve the understanding of the complex anatomy of the tympanic cavity and spatial relationships between the ear components. Enlarged 3D virtual and printed models of the tympanic cavity facilitate demonstration and observation of the tympanic cavity anatomy in comparative studies.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Promising techniques and open challenges for microplastic identification and quantification in environmental matrices.

Microplastics are observed ubiquitously and in different environmental compartments ranging from marine waters and sediments to freshwater and terrestrial ecosystems including biota. Over the last decade, several methods have been applied and advanced to monitor and quantify microplastics, to identify the polymer material and to describe the particle properties, such as size, shape or colour. In most cases, the overarching aim is to elucidate patterns of occurrence that might result from (micro)plastic emissions and environmental fate. But the applied methods are subject to uncertainties and boundary conditions, be it spatial resolution that excludes the smallest microplastics or limitations in distinguishing microplastic particles from natural particles. This critical review provides an overview of the state-of-the-art procedures in microplastic analysis, gives examples of potential ways ahead and remaining challenges and classifies available methods according to the underlying research question. The resulting decision tree for the selection of analytical methods starts with a common research question and takes specificities of the environmental matrix into account. The procedural range consequently ranges from fast screening methods based on visual identification to a highly sophisticated combination of analytical methods that provide information on polymer type, particle number or mass and eventually particle size but are very time-consuming and expensive. Standardization of microplastic analytical methods on the basis of the research aim will help to make study results comparable and obtain a more comprehensive picture of microplastic abundance and fate in the environment. Graphical abstract.

Development of a physicochemical method to quantify the extracellular liquid volume: Application to the transformation of cassava into gari

In fresh vegetal materials, liquid is mostly located in cells. During processing, this liquid is distributed in the entire vegetal matrix volume including exctracellular volume. According to its location, it will be more or less available for physico-chemical mechanisms that takes place during processing of vegetal matrices. This availability greatly influences the quality of the final products. This work consisted in developing a method for determining the quantity of extracellular liquid in a cell-component food matrix. The method developed is spectrophotometric-based and consists in adding a known mass of polymer (poly(4-styrenesulfonate) sodium salt, PSS) to a rasped vegetal material and defining its concentration in the supernatant separated from the solid phase. The PSS molar mass prevents it from penetrating into plant cells. The PSS concentration measured makes it possible to calculate the extracellular liquid volume. The method validation and its application to rasped and processed (fermentation, pressing) cassava makes it possible to obtain results in agreement with those obtained with other methods.

Application of Plasmon-Induced Lithography for Creation of a Residual-Free Pattern and Simple Surface Modifications.

Here, we propose a plasmon-induced redistribution of a thin polymer layer as a unique way for a residual layer-free lithographic approach. In particular, we demonstrate an ultrafast area-selective fabrication method using a low-intensity visible laser irradiation to direct the polymer mass flow, under the plasmon-active substrates. Plasmon-supported substrates were created by thermal annealing of Ag thin films and covered by thin polystyrene layers. Then, laser beam writing (LBW) was applied to introduce a surface tension gradient through the local plasmon heating. As a result, polystyrene was completely removed from the irradiated place, without any residual layer. The proposed approach does not require any additional development steps, such as solvent or plasma treatment. To demonstrate the advantages of the proposed technique, we implemented the LBW-patterned structures for further spatially selective surface functionalization, including the metal deposition, spontaneous thiol grafting, and electrochemical deposition of ordered polypyrrole array.

Effect of Physical Factors during the Preparation of a Reaction Mixture in Turbulent Flows on the Rate of Butadiene Polymerization in the Presence of TiCl4-Al(i-C4H9)3 and Molecular Mass Characteristics of Butadiene Rubber

Butadiene polymerization was used as a model of diene polymerization in the presence of micro-heterogeneous Ziegler-Natta polycentric catalytic systems (TiCl4-Al(i-C4H9)3 catalytic system, toluene solvent, temperature 298 K). It was found that an increase in the rate of feeding of the reaction mixture into a tubular turbulent apparatus of diffuser-confuser design, the ratio of diffuser to confuser diameters, and diffuser opening angle led to a local increase in the kinetic energy and dissipation rate of turbulence; as a consequence, the most probable equivalent radius of the catalyst particles and the average molecular mass of the polymer decreased, while the polymerization rate increased. It was also found that a change in the section length to diffuser diameter ratio when the former or latter was constant and a change in the number of sections of the tubular turbulent apparatus from four to eight did not affect the polymerization rate and the molecular mass characteristics of the polymer.

The locally columnar model for clay/polymer systems: Connections to scattering experiments

A tight connection of scattering to thermodynamic models is missing for clay systems. A new approach called “locally columnar model” gives an attempt for making this connection. The scattering model assumes an up-lining of clay particles with strong paracrystalline order and refers to a chemical potential/distance dependence. The thermodynamic model assumes a bidisperse distance distribution and gives input to the scattering model. Experimentally, polymer/clay systems with many molecular polymer masses were studied showing all very similar scattering curves. While the dominating bulk phase shows only the same weak tendency to stack formation for all molecular polymer masses, one coexisting phase with stronger stack formation was identified. The latter sample was used to determine the thickness of the clay platelets with adsorbed polymer that was then used to model the dominating bulk phase. The comparisons to the theory revealed that (a) most polymers are tightly bound to the clay, and (b) an agreement between the modeling and the theory was achieved. The main result of the experiments is the fraction of free polymers of 1:2400 that are not tightly bound to the clay particles.

Robust Hydrophobic and Hydrophilic Polymer Fibers Sensitized by Inorganic and Hybrid Lead Halide Perovskite Nanocrystal Emitters.

Advances in the technology and processing of flexible optical materials have paved the way toward the integration of semiconductor emitters and polymers into functional light emitting fabrics. Lead halide perovskite nanocrystals appear as highly suitable optical sensitizers for such polymer fiber emitters due to their ease of fabrication, versatile solution-processing and highly efficient, tunable, and narrow emission across the visible spectrum. A beneficial byproduct of the nanocrystal incorporation into the polymer matrix is that it provides a facile and low-cost method to chemically and structurally stabilize the perovskite nanocrystals under ambient conditions. Herein, we demonstrate two types of robust fiber composites based on electrospun hydrophobic poly(methyl methacrylate) (PMMA) or hydrophilic polyvinylpyrrolidone (PVP) fibrous membranes sensitized by green-emitting all-inorganic CsPbBr3 or hybrid organic-inorganic FAPbBr3 nanocrystals. We perform a systematic investigation on the influence of the nanocrystal-polymer relative content on the structural and optical properties of the fiber nanocomposites and we find that within a wide content range, the nanocrystals retain their narrow and high quantum yield emission upon incorporation into the polymer fibers. Quenching of the radiative recombination at the higher/lower bound of the nanocrystal:polymer mass ratio probed is discussed in terms of nanocrystal clustering/ligand desorption due to dilution effects, respectively. The nanocomposite's optical stability over an extended exposure in air and upon immersion in water is also discussed. The studies confirm the demonstration of robust and bright polymer-fiber emitters with promising applications in backlighting for LCD displays and textile-based light emitting devices.

An efficient numerical framework for fiber spinning scenarios with evaporation effects in airflows

In many spinning processes, as for example in dry spinning, solvent evaporates out of the spun jets and leads to thinning and solidification of the produced fibers. Such production processes are significantly driven by the interaction of the fibers with the surrounding airflow. Faced with industrial applications producing up to several hundred fibers simultaneously, the direct numerical simulation of the three-dimensional multiphase, multiscale problem is computationally extremely demanding and thus in general not possible. In this paper, we hence propose a dimensionally reduced, efficiently evaluable fiber model that enables the realization of fiber-air interactions in a two-way coupling with airflow computations. For viscous dry spinning of an uni-axial two-phase flow, we deduce one-dimensional equations for fiber velocity and stress from cross-sectional averaging and combine them with two-dimensional advection-diffusion equations for polymer mass fraction and temperature revealing the radial effects that are observably present in experiments. For the numerical treatment of the resulting parametric boundary value problem composed of one-dimensional ordinary differential equations and two-dimensional partial differential equations we develop an iterative coupling algorithm. The solution of the advection-diffusion equations is implicitly given in terms of Green's functions and leads for the surface values to Volterra integral equations of second kind with singular kernel, which we can solve very efficiently by the product integration method. For the ordinary differential equations a suitable collocation-continuation procedure is presented. Compared with the referential solution of a three-dimensional setting, the numerical results are very convincing. They provide a good approximation while drastically reducing the computational time. This efficiency allows the two-way coupled simulation of industrial dry spinning in airflows for which we present results for the first time in literature.

Milligram Size Rheology of Molten Polymers

During laboratory practice, it is often necessary to perform rheological measurements with small specimens, mainly due to the limited availability of the investigated systems. Such a restriction occurs, for example, because the laboratory synthesis of new materials is performed on small scales, or can concern biological samples that are notoriously difficult to be extracted from living organisms. A complete rheological characterization of a viscoelastic material involves both linear and nonlinear measurements. The latter are more challenging and generally require more mass, as flow instabilities often cause material losses during the experiments. In such situations, it is crucial to perform rheological tests carefully in order to avoid experimental artifacts caused by the use of small geometries. In this paper, we indicate the drawbacks of performing linear and nonlinear rheological measurements with very small amounts of samples, and by using a well-characterized linear polystyrene, we attempt to address the challenge of obtaining reliable measurements with sample masses of the order of a milligram, in both linear and nonlinear regimes. We demonstrate that, when suitable protocols and careful running conditions are chosen, linear viscoelastic mastercurves can be obtained with good accuracy and reproducibility, working with plates as small as 3 mm in diameter and sample thickness of less than 0.2 mm. This is equivalent to polymer masses of less than 2 mg. We show also that the nonlinear start-up shear fingerprint of polymer melts can be reliably obtained with samples as small as 10 mg.

Effect of Ultrasonic Vibration on Interlayer Adhesion in Fused Filament Fabrication 3D Printed ABS.

One of the fundamental issues in the Fused Filament Fabrication (FFF) additive manufacturing process lies in the mechanical property anisotropy where the strength of the FFF-3D printed part in the build-direction can be significantly lower than that in other directions. The physical phenomenon that governs this issue is the coupled effect of macroscopic thermal mechanical issues associated with the thermal history of the interface, and the microscopic effect of the polymer microstructure and mass transfer across interfaces. In this study it was found that the use of 34.4 kHz ultrasonic vibrations during FFF-3D printing results in an increase of up to 10% in the interlayer adhesion in Acrylonitrile Butadiene Styrene (ABS), comparing the printing in identical thermal conditions to that in conventional FFF printing. This increase in the interlayer adhesion strength is attributed to the increase in polymer reptation due to ultrasonic vibration-induced relaxation of the polymer chains from secondary interactions in the interface regions.