Solid Polymer Matrix Research Articles

Evaluation of light scattering models to characterize concentrated polymer particles embedded in a solid polymer matrix

This work deals with the application of the static light scattering (SLS) model of Vrij (VM) for the characterization of a spherical polydisperse concentrated polymer particle system. This model is the exact solution for the SLS of such mixture of particles in the Percus–Yevick approximation. The analyzed polymer particle samples are obtained by solution polymerization of isobornyl methacrylate in polyisobutylene. At the end of the polymerization, as a result of phase separation, a particle system of micrometer sized particles with a moderate distribution of sizes and a volume fraction between 5 and 10% is formed. The SLS data were also analyzed using the local monodisperse approximation (LMA), a well-known approximation to the model of Vrij. As expected, the estimations with the VM gave better results than those performed with the LMA model for the parameters related to the shape of the particle size distribution as compared with independent determinations of these quantities obtained from scanning electron microscopy micrographs. However, the main motivation to use the more rigorous model seems to be the fact that the volume fraction of particles can be extracted from the data even when relative SLS measurements are used. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 958–963, 2010

A simplified diamine crosslinking method for PI nanofiltration membranes

Abstract The crosslinking of polyimide membranes is a commonly known process to obtain membranes fit for use in solvent resistant nanofiltration. In this work, an existing crosslinking method, involving a reaction between a polyimide membrane and a diamine in a methanol environment, was modified. Instead of crosslinking the membrane after its formation, the crosslinking reaction was included in the phase inversion process itself by adding the crosslinker to the aqueous coagulation bath, thus eliminating the need of an extra solvent-based production step. The crosslinking efficiency of the new and the earlier method was studied in reactions between different types of diamines and polyimides by stability tests and ATR-FTIR analysis. The crosslinking reaction rate in the original method was influenced by the reactivity of the polyimide and the diamine, the hydrophobicity of the diamine, the steric hindrance of diamine and polyimide, and the interchain space in the solid polymer matrix. In the modified method, the reactivity of the polyimide type was the dominant rate-determining parameter. The reported modified crosslinking method can be regarded as more efficient, especially in reactions with para-xylylenediamine, and as economically and environmentally favourable. Crosslinked polyimide membranes synthesized by the new method are applicable in solvent resistant micro-, ultra- and/or nanofiltration, as exemplified by a Lenzing P84® membrane with a permeability in DMF and NMP of 0.43 and 0.19 l/m2 bar h and a Bengal Rose (1017 Da) rejection of 98%.

Analysis of Responsive Characteristics of Ionic-Strength-Sensitive Hydrogel with Consideration of Effect of Equilibrium Constant by a Chemo-Electro-Mechanical Model

A multiphysics model is presented in this paper for analysis of the influence of various equilibrium constants on the smart hydrogel responsive to the ionic strength of environmental solution, and termed the multieffect-coupling ionic-strength stimulus (MECis) model. The model is characterized by a set of partial differential governing equations by consideration of the mass and momentum conservations of the system and coupled chemical, electrical, and mechanical multienergy domains. The Nernst-Planck equations are derived by the mass conservation of the ionic species in both the interstitial fluid of the hydrogel and the surrounding solution. The binding reaction between the fixed charge groups of the hydrogel and the mobile ions in the solution is described by the fixed charge equation, which is based on the Langmuir monolayer theory. As an important effect for the binding reaction, the equilibrium constant is incorporated into the fixed charge equation. The kinetics of the hydrogel swelling/deswelling is illustrated by the mechanical equation, based on the law of momentum conservation for the solid polymeric networks matrix within the hydrogel. The MECis model is examined by comparison of the numerical simulations and experiments from open literature. The analysis of the influence of different equilibrium constants on the responsive characteristics of the ionic-strength-sensitive hydrogel is carried out with detailed discussion.

Poro-Viscoelastic Behavior of Gelatin Hydrogels Under Compression-Implications for Bioelasticity Imaging

Ultrasonic elasticity imaging enables visualization of soft tissue deformation for medical diagnosis. Our aim is to understand the role of flow-dependent and flow-independent viscoelastic mechanisms in the response of biphasic polymeric media, including biological tissues and hydrogels, to low-frequency forces. Combining the results of confined and unconfined compression experiments on gelatin hydrogels with finite element analysis (FEA) simulations of the experiments, we explore the role of polymer structure, loading, and boundary conditions in generating contrast for viscoelastic features. Feature estimation is based on comparisons between the biphasic poro-elastic and biphasic poro-viscoelastic (BPVE) material models, where the latter adds the viscoelastic response of the solid polymer matrix. The approach is to develop a consistent FEA material model (BPVE) from confined compression-stress relaxation measurements to extract the strain dependent hydraulic permeability variation and cone-plate rheometer measurements to obtain the flow-independent viscoelastic constants for the solid-matrix phase. The model is then applied to simulate the unconfined compression experiment to explore the mechanics of hydropolymers under conditions of quasi-static elasticity imaging. The spatiotemporal distributions of fluid and solid-matrix behavior within the hydrogel are studied to propose explanations for strain patterns that arise during the elasticity imaging of heterogeneous media.

Model for UV induced formation of gold nanoparticles in solid polymeric matrices

UV irradiation of polymeric PMMA films containing HAuCl 4 followed by annealing at 60–80 °C forms gold nanoparticles directly within the bulk material. The kinetics of nanoparticle formation was traced by extinction spectra of nanocomposite film changes vs annealing time. We propose that UV irradiation causes HAuCl 4 dissociation and thus provides a polymeric matrix with atomic gold. The presence of an oversaturated solid solution of atomic gold in the polymeric matrix leads to Au nanoparticle formation during annealing. This process can be understood as a phase transition of the first order. In this paper we apply several common kinetic models of the phase transition for describing Au nanoparticle formation inside the solid polymer matrix. We compare predictions of these models with the experimental data and show that these models cannot describe the process. We propose that the stabilization effect of the matrix on the growing gold nanoparticles is important. The simplest model introducing some probability for the transition from growing nanoparticle to the non-growing, stabilized form is suggested. It is shown that this model satisfactorily describes the experimentally observed evolution of the extinction spectrum of Au nanoparticles forming in a polymer matrix.

Linear size gradient single layers of polymer-dispersed liquid crystal micrometer-sized droplets for diffractive optics

An experimental study of coherent light diffraction by wedge-formed single layers composed of liquid crystal (LC) micro-sized droplets dispersed in a transparent solid polymer matrix is reported. The micrometer-sized polymer-dispersed liquid crystal (PDLC) material contains prolate-ellipsoid-like LC droplets with a linear-gradient size distribution along the wedge slope. The droplet diameter in the films reaches several tens of micrometers, defined by the wedge. Such a droplet organization in a two-dimensional layer provides both spatial and electrical control of the coherent light diffraction by the LC/polymer interface.

Amphibious polymer-functionalized CdTe quantum dots: Synthesis, thermo-responsive self-assembly, and photoluminescent properties

A straightforward strategy is presented to functionalize aqueous-phase synthesized CdTe quantum dots (QDs) with thermo-sensitive poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) via direct surface-initiated oxyanionic vinyl polymerization. The polymer grafting quantity can be facilely controlled in a wide range up to 95.2wt% by adjusting the weight feed ratio of monomer to pristine QDs. The polymer-grafted QDs still retain good fluorescence properties in solution, solid polymer matrix, and on surfaces of silica (SiO2) sphere. The resulting QD@PDMAEMAs show excellent solubility both in water and organic solvents (e.g., chloroform, dichloromethane, dioxane, ethyl acetate, acetone, methanol, and N, N-dimethylformamide). We have called them amphibious QDs. The thermo-sensitive PDMAEMAs make QDs accessible to self-assemble reversibly by adjusting temperature when the grafted polymer content is over a certain value. The self-assembly process and resulting structure were demonstrated by TEM, variable temperature dynamic light scattering (DLS) and UV-vis spectrometer. Because PDMAEMA is a kind of positive polyelectrolyte, QD@PDMAEMAs were used as building blocks in the layer-by-layer self-assembly process on the surface of SiO2 spheres, affording fluorescent SiO2 spheres.

An antitracking varnish for rated electrical application

AbstractWe report on a synthesis, characterization, and thermal evaluation of a pigmented and silicone‐modified medium oil alkyd insulating varnish for antitracking application in rated electrical machines such as traction motors, transformers, and large generators. The varnish is generally applied on the top surface of the main insulation of coils by spray or brush and then baked to remove solvent. The semiconducting pigments entrapped in solid polymer matrix reduces surface corona, flash‐over, and tracking of the main insulation by distributing uneven charges from polar or charged particles deposited on the surface after long time use of the machines. The varnish was thoroughly evaluated by means of electrical and mechanical properties over a temperature range. The temperature class of the antitracking varnish was 191.22°C determined by IEC 60216 methods on helical coil bond strength of the cured films. The dielectric strength, tracking, and arc resistance of the pigmented varnish were exceptionally high and it will save core insulation from the tracking, corona and short‐time flash‐over. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Effective anisotropy field variation of magnetite nanoparticles with size reduction

Size effect on the internal magnetic structure has been investigated on weakly interacting magnetite (Fe3O4) nanoparticles by ferromagnetic resonance experiments at 9.5 GHz as a function of temperature (4–300 K). A set of three samples with mean particle size of 2.5 nm, 5.0 nm and 13.0 nm, respectively, were prepared by chemical route with narrow size distribution (σ < 0.27). To minimize the dipolar interaction, the particles were dispersed in a liquid and a solid polymer matrix at ∼0.6% in mass. By freezing the liquid suspension with an applied external field, a textured was obtained. Thus, both random and textured suspensions were studied and compared. The ferromagnetic resonance experiments in zero-field-cooled and field-cooled conditions were carried out to study the size effect on the effective anisotropy field. The dc magnetization measurements clearly show that the internal magnetic structure was strongly affected by the particle size.

Thermal isomerization of dewarbenzene derivatives

The rates of thermal conversion of seven simple dewarbenzene derivatives to their corresponding benzene isomers were measured. Relatively minor substituent changes were found to have profound effects; isomerization rates increased with the number and strength of electron-withdrawing moieties. Surprisingly, the rate of thermal isomerization for one derivative was the same in fluid solution as in a solid polymer matrix, suggesting that this reaction has a low volume of activation. Other preliminary experiments suggest that the putative intermediate has some polar character. These data may provide some insights into the reaction mechanism.

Determination of Size Distributions of Concentrated Polymer Particles Embedded in a Solid Polymer Matrix

AbstractIn this work we present the results obtained from the size characterization of polymer particles embedded in a solid polymer matrix using Static Light Scattering (SLS) and Scanning Electron Microscopy (SEM). The analyzed samples are the result of the solution polymerization of isobornyl methacrylate (IBoMA) in polyisobutylene (PIB) at complete conversion. Induced by polymerization, the system undergoes phase separation. As a result, spherical micron sized particles rich in PIB are formed. At the end of the polymerization, the particles become trapped in a solid polymer matrix rich in Poly‐IBoMA. Size, concentration, and refractive index, make the resulting particle system scatter light under the Rayleigh‐Debye‐Gans (RDG) regime with interparticle interference. For Light Scattering (LS) characterization the samples are measured with a Flat Cell Static Light Scattering (FCSLS) apparatus, in which the reaction takes place. The resulting SLS spectra are analyzed using the Percus‐Yevick approximation to model the interference effects. The local monodisperse approximation is used to consider polydispersity in the particle sizes. The estimated particle size distributions agree well with the measurements from SEM. In this work a concentrated particle system that naturally scatters light according to the RDG regime has been fully characterized in terms of its particle size distribution. This work, against the opinion of other authors, shows the feasibility of measuring still particles using a one dimensional array of light detectors.

Thermochromism of Polydiacetylene with a Hysteresis Loop in the Solid State and in Solution

Abstract Partly crystalline polydiacetylene 1, which is soluble in many organic solvents at room temperature, was prepared by the solid-state polymerization of 4-methoxybenzyl 10,12-pentacosadiynoate. We found a reversible change in the UV–vis absorption spectrum of 1 in a solid film, polymer matrix, and solution with a hysteresis loop as a function of temperature.

Hydraulic permeability of a hydrogel‐based contact lens membrane for low flow rates

AbstractHydrogels, widely used for contact lenses, are a class of materials that consists of both fluid and solid components. The aqueous fluid phase is supported by a solid polymer matrix. In this study, we characterize the water transport characteristics of an Etafilcon‐A (copolymer of 2‐hydroxyethyl methacrylate and methacrylic acid) membrane. A flow rate‐controlled permeameter consisting of a syringe pump, membrane holder, pressure transducer, and tubing was developed and used to measure the pressure drop across a flat membrane (average thickness ∼ 686 μm ± 40). The relation between velocity and pressure drop was measured. These data were fit to rigid media and biphasic models of 1‐D flow to determine hydraulic permeability, k = 1.80 × 10−14 m4/N s. The results provide insight into the fluid flow properties of this hydrogel under low flow and low pressure conditions (&lt;3 kPa). Physiological implications of these measured parameters on flow and deformation across the lens due to blinking are discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3730–3735, 2007

Study of PDCLC Materials Using Fabry Perot Scattering Technique

Polymer dispersed cholesteric liquid crystals (PDCLCs) consist of liquid crystal (nematic and Cholesteric) droplets that are dispersed in a solid polymer matrix. PDCLCs are a relatively new class of materials that hold promise for many applications ranging from switchable windows to projection displays. These materials, which are simply a combined application of polymers and liquid crystals, are the focus of extensive research in the display industry.

Direct Assembly of BaTiO3‐Poly(methyl methacrylate) Nanocomposite Films

AbstractSummary: This study examines the use of a PMMA‐mediated assembly of BaTiO3 nanoparticles directly onto Cu electrodes under an electric field. The compatibility of the interface between BaTiO3 nanoparticles and PMMA in a mixed organic solvent system enables the homogeneous dispersion of nanoparticles in a solid polymer matrix. This results in the effective packing of particles, which is desirable from the point of view of achieving a high dielectric constant in the composite. In this study, three‐phase Al/BaTiO3/PMMA nanocomposite films from stable colloidal suspensions containing aluminium nitrate salts were also designed using an electrodeposition process. The simultaneous formation of Al metallic inclusions in the BaTiO3 nanoparticles in the PMMA matrix significantly improved the dielectric constant of nanocomposite films.HRTEM micrographs of BaTiO3 (240 nm)/PMMA and magnified view of BaTiO3 (50 nm)/PMMA/Al(NO3)3 · 9H2O composite particles in each suspension, and FESEM micrograph of electrodeposited three‐phase nanocomposite film.magnified imageHRTEM micrographs of BaTiO3 (240 nm)/PMMA and magnified view of BaTiO3 (50 nm)/PMMA/Al(NO3)3 · 9H2O composite particles in each suspension, and FESEM micrograph of electrodeposited three‐phase nanocomposite film.

Glycidyl methacrylate as a new host material for laser dyes

AbstractThis article reports on the laser action of pyrromethene 597 and pyrromethene 567 doped in the novel solid polymeric matrix glycidyl methacrylate. Mirrorless lasing was observed when samples with diameters of 10 mm and lengths of 20 mm, with different dyes concentrations, were transversely pumped at 532 nm. The influence of the dye concentration on the laser measurements included the peak wavelengths, output energies, conversion efficiencies, and laser gains. Relatively high lasing efficiencies (up to ∼ 60%) were obtained from these new polymeric materials with very good photostability, where a decrease of only 65% in the initial laser output energy was observed after pumping by 60,000 shots of 15 mJ at 10 Hz. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 59–63, 2007

Association of molecules of triphenylmethane dyes in poly(N-epoxypropyl carbazole) and its effect on the sensitizing properties of dyes

The association of triphenylmethane molecules in a poly(N-epoxypropyl carbazole) solid polymer matrix and its effect on the sensitizing properties of dyes were studied. Associates are formed from ion pairs involving triphenylmethane dyes, a process that can cause a decrease in the sensitizing ability of the dyes with respect to of poly(N-epoxypropyl carbazole). The rate of association depends strongly on the type of the counteranion of the cationic dye

Molecular dynamics simulation of polymer dispersed liquid crystal droplets under competing boundary conditions

This paper is devoted to the molecular dynamics simulation of structural organization inside a polydispersed liquid crystal (LC) droplet under competing boundary conditions. The droplet is assumed to be placed at the liquid crystal interface between two different regions of the solid polymer matrix, which accordingly separates the droplet into two hemispheres: the first of these is under radial boundary conditions; the second hemisphere is under bipolar boundary conditions. The droplet is considered as a jagged sphere filled with LC molecules, modelled as classical spins (unit vectors), whose centres of mass are associated with sites of a cubic lattice inside the cavity. The orienting action of the polymer matrix, and hence the resulting boundary conditions, are modelled by the interaction between the internal LC molecules (possessing only orientational degrees of freedom), and those of a delimiting surface layer (a jagged spherical shell), whose orientations are fixed, radial or bipolar, respectively. All interactions are modelled by the short range McMillan pair potential. The molecular orientation inside the LC droplet has been determined for various anchoring strengths of the interaction between internal spins and boundary layers. We have investigated the structure of the spherical defect resulting in the central region of the droplet, as well as of the boojum ‐ like defects existing near the poles of the droplet. It has been found that a change of relative radial and bipolar anchoring strengths can affect both central and boojum ‐ like defects. The effect of an external field on the molecular orientation inside the droplet has also been investigated. It has been found that a sufficiently strong external field increases the radius of the spherical defect placed in the central region of the droplet.

Polymerization of w/o Microemulsions for the Preparation of Transparent SiO2/PMMA Nanocomposites

Reverse w/o microemulsions composed of methyl methacrylate (MMA) forming the oil phase, nonionic surfactants, and water are used for the synthesis of transparent SiO2/PMMA nanocomposites. An inorganic precursor, tetraethoxysilane (Si(OEt)(4), TEOS), is hydrolyzed in the reverse micelles containing aqueous ammonia. During the hydrolysis of TEOS, polymerization of the continuous MMA phase is initiated using AIBN (azobisisobutyronitrile), and after thermal polymerization at 333 K for 12 h, solid blocks of PMMA are obtained in which nanometer-sized silica particles are trapped in the solid polymer matrix. According to small-angle X-ray and dynamic light scattering experiments, the water droplets in MMA microemulsions are 12 nm (R(W) = 13) in diameter, whereas after polymerization of the microemulsion, the SiO2 particles in the transparent SiO2/PMMA composites are 26 nm in diameter. Transmission electron micrographs demonstrate a low degree of agglomeration in the composites. In comparison with materials generated from micelle-free solutions, the particle size distribution is narrow. The reverse micelle-mediated approach produces composites of high transparency comparable with that of pure PMMA.

Optical properties of Sm‐chelate containing methyl methacryate solution and its solid polymer matrix

AbstractFrom optical absorption spectra and using the Judd–Ofelt theory, the phenomenological parameters, Ω2, Ω4, and Ω6 of Sm(DBM)3(TOPO)2 containing methyl methacryate (MMA) solution and solid poly(methyl methacryate) (PMMA) matrix were obtained. The chemical structure of Sm‐chelate accounts for the nearly same Ω2 values in liquid solution and solid polymer matrix. The evaluation of the radiative properties of Sm‐chelate containing PMMA showed that the 4G5/2 → 6H9/2 transition of Sm3+ in polymer matrix is potential to be a laser transition.. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)