Different Polymers (different + polymer)

Distribution by Scientific Domains

Selected Abstracts

Processing of transmission electron microscope images for quantification of the layer dispersion degree in polymer-clay nanocomposites

Amir H. Navarchian
Abstract Quantification of the layered silicates dispersion level is necessary to more accurately evaluate the performance in polymer/clay nanocomposites. In this article, a new approach is developed to quantify the degree of exfoliation, intercalation, and immiscibility of layered silicates in polymer matrix, based on bright-dark pixel measurement (BDPM) in transmission electron microscope (TEM) images. Several examples of exfoliated, intercalated, and immiscible composites with different polymer and clay systems were examined. The method is capable of estimating the percent contribution of all morphologies present in the image. Comparing with X-ray diffraction (XRD) evidences, it is indicated that as a rule of thumb, the exfoliated structure is dominant whenever the exfoliation percent calculated by BDPM methodology is over 65%, no matter what kind of clay or polymer matrix is used. The intercalated structure can be ascribed to the images with exfoliation level less than 65%, but with the intercalation degree over 28%. Application of this method can facilitate the modeling or correlation of various nanocomposite properties with respect to exfoliation degree. A quantified relation is also possible between XRD and TEM using this approach. 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source]

Glass bead grafting with poly(carboxylic acid) polymers and maleic anhydride copolymers

H. Zengin
Abstract Glass beads were etched with acids and bases to increase the surface porosity and the number of silanol groups that could be used for grafting materials to the surfaces. The pretreated glass beads were functionalized using 3-aminopropyltriethoxysilane (APS) coupling agent and then further chemically modified by reacting the carboxyl groups of carboxylic acid polymers with the amino groups of the pregrafted APS. Several carboxylic acid polymers and poly(maleic anhydride) copolymers, such as poly(acrylic acid) (PAA), poly(methacrylic acid) (PMA), poly(styrene-alt-maleic anhydride) (PSMA), and poly(ethylene-alt-maleic anhydride) (PEMA) were grafted onto the bead surface. The chemical modifications were investigated and characterized by FT-IR spectroscopy, particle size analysis, and tensiometry for contact angle and porosity changes. The amount of APS and the different polymer grafted on the surface was determined from thermal gravimetric analysis and elemental analysis data. Spectroscopic studies and elemental analysis data showed that carboxylic acid polymers and maleic anhydride copolymers were chemically attached to the glass bead surface. The improved surface properties of surface modified glass beads were determined by measuring water and hexane penetration rates and contact angle. Contact angles increased and porosity decreased as the molecular weights of the polymer increased. The contact angles increased with the hydrophobicity of the attached polymer. The surface morphology was examined by scanning electron microscopy (SEM) and showed an increase in roughness for etched glass beads. Copyright 2007 John Wiley & Sons, Ltd. [source]

Capillary electrophoresis using copolymers of different composition as physical coatings: A comparative study

Guillaume L. Erny
Abstract In this work, a comparative study on the use of different polymers as physically adsorbed coatings for CE is presented. It is demonstrated that the use of ad hoc synthesized polymers as coatings allows tailoring the EOF in CE increasing the flexibility of this analytical technique. Namely, different polymers were synthesized at our laboratory using different percentages of ethylpyrrolidine methacrylate (EpyM) and N,N -dimethylacrylamide (DMA). Thus, by modifying the percentage of EpyM and DMA monomers it is possible to manipulate the positive charge of the copolymer, varying the global electrical charge on the capillary wall and with that the EOF. These coated capillaries are obtained by simply flushing a given EpyM,DMA aqueous solution into bare silica capillaries. It is shown that by using these coated capillaries at adequate pHs, faster or more resolved CE separations can be achieved depending on the requirements of each analysis. Moreover, it is demonstrated that these coated capillaries reduce the electrostatic adsorption of basic proteins onto the capillary wall. Furthermore, EpyM,DMA coatings allow the reproducible chiral separation of enantiomers through the partial filling technique (PFT). The EpyM,DMA coated capillaries are demonstrated to provide reproducible EOF values independently of the pH and polymer composition with%RSD values lower than 2% for the same day. It is also demonstrated that the coating procedure is reproducible between capillaries. The compatibility of this coating protocol with CE in microchips is discussed. [source]

Surface Patterning: Spatiotemporal Control over Molecular Delivery and Cellular Encapsulation from Electropolymerized Micro- and Nanopatterned Surfaces(Adv.

This frontispiece image shows a multicomponent chip inspired by a vaccine node for specific T-cell stimulation, as described by Stern et al. on page 2888. The chip is functionalized with two different polymers (silver and black) as shown in the clockwise fabrication steps in the corners, each of which presents and releases different molecules necessary for stimulation. T-cells are stained red and dendritic cells are stained green. The inset image shows the reverse polymer pattern. [source]

Coupled-perturbed Hartree,Fock theory for quasi,one-dimensional periodic systems: Calculation of static and dynamic nonlinear optical properties of model systems

A. Martinez
Abstract An alternative method to solve the coupled-perturbed Hartree,Fock (CPHF) equations for infinite quasi,one-dimensional systems is presented. The new procedure follows a proposal made by Langhoff, Epstein, and Karplus to obtain perturbed wavefunctions free from arbitrary phase factors in each order of perturbation. It is based on the intermediate orthonormalization of the perturbed wavefunctions (which is different from the usual one) and a corresponding selection of the Lagrangian multipliers. In this way it is possible to incorporate the orthonormalization conditions into the set of CPHF equations. Moreover, a new, advantageous procedure to determine the derivatives of the wavefunction with respect to the quasimomentum k is presented. We report calculations of the dipole moment, the polarizability ,, and the first hyperpolarizability , for different polymers (poly-HF, poly-H2O, trans-polyacetylene, polyyne, and polycarbonitrile) for different frequencies. These results are extensively compared with oligomer calculations. 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 251,268, 2003 [source]

Polymer-acid solutions: Their use for the enhancement of oil reservoir stimulation

Mohammed M. Amro
Abstract A reduction in permeability occurring around the wellbore resulting from drilling, completion and/or workover fluids increases the flow resistance to the petroleum reservoir fluids and is defined as formation damage. Acidizing process removes near-wellbore damage and enhances hydrocarbon production from producing wells. This study investigates the effect of adding polymer as a retarding agent to acid solutions to slow and control the reaction in matrix acidizing treatment of carbonate rocks. Two different polymers, polyacrylamide (PAA) and polysaccharide (xanthan) and two different acids, acetic acid and formic acid, were used through this study. The results revealed that the presence of PAA did not change the viscosity of the acid solution significantly, while the viscosity of xanthan-acid solutions was decreased with increasing the acid concentration. Additionally, the reaction of polymer-acid solutions with the rock material was monitored under microscope. Original rock samples obtained from Saudi reservoirs containing mainly carbonate were used in the reaction. The PAA-acid solution did not show any decrease in the reaction rate compared to that of acid solution. Thus, the PAA solution applied in this study is not recommended as a retarder. However, xanthan-acid solutions showed a significant decrease in the reaction time. Therefore, xanthan was selected to perform further investigations in Rotating Disk Reactor at different pressures. Scanning electronic microscopy (SEM) was conducted on pretreated and posttreated rock samples. This provides the opportunity to perform a detailed description of the rock surface and facilitates the identification of the changes occurring due to polymer-acid treatment. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

A solid-state approach to enable early development compounds: Selection and animal bioavailability studies of an itraconazole amorphous solid dispersion

David Engers
Abstract A solid-state approach to enable compounds in preclinical development is used by identifying an amorphous solid dispersion in a simple formulation to increase bioavailability. Itraconazole (ITZ) was chosen as a model crystalline compound displaying poor aqueous solubility and low bioavailability. Solid dispersions were prepared with different polymers (PVP K-12, K29/32, K90; PVP VA S-630; HPMC-P 55; and HPMC-AS HG) at varied concentrations (1:5, 1:2, 2:1, 5:1 by weight) using two preparation methods (evaporation and freeze drying). Physical characterization and stability data were collected to examine recommended storage, handling, and manufacturing conditions. Based on generated data, a 1:2 (w/w) ITZ/HPMC-P dispersion was selected for further characterization, testing, and scale-up. Thermal data and computational analysis suggest that it is a possible solid nanosuspension. The dispersion was successfully scaled using spray drying, with the materials exhibiting similar physical properties as the screening samples. A simple formulation of 1:2 (w/w) ITZ/HPMC-P dispersion in a capsule was compared to crystalline ITZ in a capsule in a dog bioavailability study, with the dispersion being significantly more bioavailable. This study demonstrated the utility of using an amorphous solid form with desirable physical properties to significantly improve bioavailability and provides a viable strategy for evaluating early drug candidates. 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:3901,3922, 2010 [source]

Versatile ,-end group functionalization of RAFT polymers using functional methane thiosulfonates

Peter J. Roth
Abstract Five different polymers, poly[methyl methacrylate] (PMMA), poly[lauryl methacrylate] (PLMA), poly[diethylene glycol methacrylate] (PDEGMA), poly[N -isopropylacrylamide] (PNIPA), and poly[styrene] (PS) prepared by the RAFT process and thus terminated with dithioesters were aminolyzed in the presence of S -3-butynyl methane thiosulfonate (MTS), which was synthesized in two steps. Analysis of the polymers by 2D NMR, UV,vis absorbance, and gel permeation chromatography revealed them to quantitatively carry acetylene end groups connected with disulfide bridges, indicating that functional MTS reagents can be employed for end group functionalization of RAFT polymers. This versatile method is of advantage compared with conjugations with functional maleimides, where isolation of terminal thiols is often required but inexpedient for poly[(meth)acrylates] because their terminal thiols may undergo backbiting and thus avoid conjugation. The acetylene-terminated polymers were bound to an azide functionalized glass surface in a Cu(I) catalyzed cycloaddition. The modified surfaces exhibited water contact angles corresponding to the polarity of the attached polymers. In the case of the stimulus responsive polymers PNIPA and PDEGMA, the surfaces showed temperature-dependent contact angles. The disulfide bond connecting the polymers to the surface could be selectively cleaved and resulted in all surfaces having the same contact angle, independent of the nature of the polymer prior attached to the surface. 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3118,3130, 2009 [source]

Synthetic Mimicking of Plant Oils and Comparison with Naturally Grown Products in Polyurethane Synthesis

Stuart R. Coles
Abstract The use of plant oils as industrial feedstocks can often be hampered by their lack of optimization towards a particular process, as well as their development being risky; growing suitable volumes of crops to test can take up to five years. To circumvent this, we aimed to discover a method that would mimic plant oil profiles in the laboratory, and show that they exhibited similar properties to the naturally grown plant oils in a given process. Using the synthesis of polyurethanes as an example, we have synthesized six different polymers and demonstrated that plant oils will produce polymers with similar physical properties to those oils mimicked in the laboratory. The use of this mimicking process can be extended to other types of polymers to obtain a method for predicting the properties of a given material based on the plant oil composition of a crop before it is grown in bulk. [source]

A Physical Method of Fabricating Hollow Polymer Spheres Directly from Oil/Water Emulsions of Solutions of Polymers,

Young Baek Kim
Abstract Summary: A new physical method of fabricating hollow spheres from different polymers has been developed. In this method, emulsions were prepared by mixing organic solutions of polystyrene, poly(D,L -lactide- co -glycolide) (PLGA), and bacterial poly(3-hydroxybutyrate- co -3-hydroxyvalerate) (PHBV), water, and surfactants. The evaporation of solvents at room temperature caused a phase separation that eventually yielded hollow spheres. Molecular weights, concentrations of polymers, and the natures of surfactant and solvent were important aspects of hollow sphere formation and structure. A mechanism for the formation of hollow spheres is proposed based on observations made using an optical microscope equipped with a digital camcorder and using scanning electron microscopy images of hollow spheres obtained under different conditions. A scanning electron microscopy image of a broken smaller hollow sphere prepared using a 7 wt.-% polystyrene solution (diameter of the sphere ,10 micrometers). [source]

Sorption and Swelling of Poly(D,L-lactic acid) and Poly(lactic-co-glycolic acid) in Supercritical CO2

Ronny Pini
Abstract Summary: The equilibrium sorption and swelling behavior in supercritical CO2 of poly(D,L-lactic acid) and poly(lactic-co-glycolic acid) has been studied at a temperature of 35,C and at pressures up to 200 bar. Sorption was measured through a gravimetric technique and swelling by visualization. From these data, the behavior of the different polymers can be compared. In terms of partial molar volume of CO2 in the polymer matrix, all the polymers exhibit a behavior typical of rubbery systems. The experimental results have been modeled using the Sanchez-Lacombe equation of state, which is able to represent the actual behavior of the polymer-CO2 systems with reasonable accuracy. [source]

Visual perception and measurements of texture and gloss of injection-molded plastics

Sofie Ignell
The effect of an imposed texture on the gloss of injection-molded polymeric surfaces was evaluated as well as the way in which these properties are visually perceived. Specimens having small differences in surface topography were produced using two mold cavities with slight differences in texture and three different polymers. The texture and gloss were characterized using laser profilometry, gloss measurements, and by means of psychometric evaluations. The measured surface topography parameters and gloss were determined mainly by the texture of the mold surface and the gloss also by the processing conditions. Variations in surface topography due to differences in the rheological properties of the polymer melts were, in most cases, too small to be reflected in the measurements. The visual assessments of the texture and the gloss of specimens from the same cavity were in fair agreement with the measurements, although the observers could discern differences between some specimens not revealed by the measurements. When the specimens molded in the two cavities differing significantly both in gloss and texture were compared, the agreement between the measured topography parameters and the perceived roughness was poorer. It is suggested that higher gloss of a textured surface enhances the perception of a higher roughness. POLYM. ENG. SCI., 2009. 2008 Society of Plastics Engineers [source]

Vero Cell Growth and Differentiation on Poly(l -Lactic Acid) Membranes of Different Pore Diameters

Arnaldo R. Santos Jr.
Abstract: In the last few years, the demand has increased for research on polymeric materials, which can be used as substitutes for injured tissues and organs or to improve their regeneration. In this work, we studied poly(l -lactic acid) (PLLA) membranes, a resorbable biomaterial, which were either dense or had different pore diameters (less than 45 ,m, between 180 and 250 ,m, and between 250 and 350 ,m), in relation to stimulation of cell adhesion, growth, and differentiation in vitro. We used Vero cells, a fibroblastic cell line, as the biological model of investigation. We found that cells attached slowly to all PLLA membranes studied. On the other hand, once the adhesion occurs, the cells are able to grow and differentiate on the different polymers. The cells grew to form a confluent monolayer and were capable of producing collagen Type IV and fibronectin on different PLLA membranes. This behavior indicates that cells try to create a better environment to stimulate their growth. This also indicates that Vero cells alter their differentiation pattern once they are producing extracellular matrix molecules related to epithelial differentiation. [source]