Affinity Of Polymer Research Articles

Surfactant-Assisted Hydrothermal Synthesis of Water-Dispersible Hafnium Oxide Nanoparticles in Highly Alkaline Media

Hafnium oxide nanoparticles were synthesized via a short-duration (10 min) hydrothermal reaction. The reaction was found to produce three differently shaped nanoparticles: flower-like nanostructures (20 nm diameter), polycrystalline nanoagglomerates (25 nm diameter), and water-dispersible single nanoparticles (4 nm diameter). The mechanisms by which these different shapes form were then investigated by examining the effects of precursor alkalinity and the presence of an organic capping agent. The synthesized water-dispersible nanoparticles showed a very high affinity for water-soluble polymers, thus demonstrating their potential for fabrication of transparent nanocomposite films.

Dynamic Interaction of the Escherichia coli Cell Division ZipA and FtsZ Proteins Evidenced in Nanodiscs

The full-length ZipA protein from Escherichia coli, one of the essential components of the division proto-ring that provides membrane tethering to the septation FtsZ protein, has been incorporated in single copy into nanodiscs formed by a membrane scaffold protein encircling an E. coli phospholipid mixture. This is an acellular system that reproduces the assembly of part of the cell division components. ZipA contained in nanodiscs (Nd-ZipA) retains the ability to interact with FtsZ oligomers and with FtsZ polymers. Interactions with FtsZ occur at similar strengths as those involved in the binding of the soluble form of ZipA, lacking the transmembrane region, suggesting that the transmembrane region of ZipA has little influence on the formation of the ZipA·FtsZ complex. Peptides containing partial sequences of the C terminus of FtsZ compete with FtsZ polymers for binding to Nd-ZipA. The affinity of Nd-ZipA for the FtsZ polymer formed with GTP or GMPCPP (a slowly hydrolyzable analog of GTP) is moderate (micromolar range) and of similar magnitude as for FtsZ-GDP oligomers. Polymerization does not stabilize the binding of FtsZ to ZipA. This supports the role of ZipA as a passive anchoring device for the proto-ring with little implication, if any, in the regulation of its assembly. Furthermore, it indicates that the tethering of FtsZ to the membrane shows sufficient plasticity to allow for its release from noncentral regions of the cytoplasmic membrane and its subsequent relocation to midcell when demanded by the assembly of a division ring.

A first principles approach to identifying polymers for use in two-phase partitioning bioreactors

BACKGROUND: Two-phase partitioning bioreactors (TPPBs) employ an immiscible phase to partition toxic substrates/products to/away from cells to reduce cytotoxicity and improve bioprocess performance. Initially, immiscible organic solvents were used as the sequestering phase, and their selection included consideration of solute–solvent affinity, which can be predicted through first principles consideration of solute activity and phase equilibrium thermodynamics. Polymers can replace organic solvents in such systems, however, their selection has largely been via heuristic means, and a more fundamental approach is necessary for future success in rational polymer identification. RESULTS: Material properties (polymer crystallinity, solubility parameter, and glass transition temperature Tg) were examined across several polymers and polyaromatic hydrocarbons as target solutes. All were shown to influence solute–polymer affinity. CONCLUSION: This first attempt at identifying physical/chemical properties that affect solute–polymer partitioning has been able to demonstrate some clear trends, and has allowed us to formulate a polymer selection guide, based on first principles, to facilitate the selection of solute–polymer pairs for solid–liquid TPPB applications. Copyright © 2012 Society of Chemical Industry

Synthesis and characterization of luminescent poly(ester-imide) derivatives constituted of alternating spirobifluorene moiety

A new category of luminescent poly(ester-imide)s derivatives based on spirobifluorene rings in the main chain was synthesized from 2,6-bis(4-hydroxybenzylidine)cyclohexanone (BC) derivatives and diimide-dicarboxylic acid (DIDA) containing spirobifluorene moiety. The structure of the polymer was confirmed by elemental and spectral analyses. The various characteristics of the resulting polymers including optical properties, solubility, thermal analysis, and X-ray diffraction analysis were determined and discussed. The new polymers showed relatively high glass-transition temperatures (about 200°C) and good thermal stability. Two polymers emitted blue-greenish light with photoluminescence (PL) emission maxima around 400–600nm and the electron affinity of new polymers was estimated as 2.75–2.84eV. Cyclic voltammetry displayed that both conjugated polymers had reversible oxidation and irreversible reduction, making them n-type electroluminescent materials. [Display omitted]

Probing the recognition of molecularly imprinted polymer beads

A facile, robust and cost-effective suspension polymerisation methodology for the generation of ibuprofen molecularly imprinted polymers in bead formats was evaluated. Mineral oil was employed as the continuous phase whereby microdroplets of the pre-polymerisation mixture were formed through vigorous agitation, followed by photo-polymerisation resulting in formation of imprinted beads. For comparison purposes, irregular particles were also prepared from monolith polymers. Physical characteristics of the imprinted polymers were investigated using scanning electron microscope, particle size distribution, nitrogen sorption porosimetry and solvent swelling ratios, with subsequent correlation of these parameters to analyte rebinding performance. Overall, an increase in affinity was observed with decreasing the degree of cross-linking, however, specific rebinding was compromised. An inverse relationship between polymer affinity for the template and surface area was identified, while solvent swelling ratios were directly related to polymer affinity. Correlation between pre-polymerisation studies and polymer binding performance highlighted the significance of employing the polymerisation solvent in template rebinding in order to achieve superior recognition capabilities. Additionally, shape selectivity of binding sites was demonstrated by the decreased binding performance of template structural analogues to the imprinted polymer.

The effect of acrylamide-co-vinylpyrrolidinone copolymer on the depression of talc in mixed nickel mineral flotation

Copolymers of acrylamide and vinylpyrrolidinone with varying compositions have been synthesised and employed to depress talc in a model flotation system with process plant operation conditions. Adsorption isotherms indicated that the hydrophilic acrylamide homopolymer has a very low affinity for the hydrophobic talc surface, whereas vinylpyrrolidinone homopolymer strongly adsorbs onto the talc surface. Micro-flotation experiments revealed that the copolymer system can induce stronger talc depression than the homopolymer variants, with the most effective copolymer depressant having 25–30% vinylpyrrolidinone incorporation. The copolymer system is observed to have inherited the strong talc affinity of vinylpyrrolidinone polymer and the strong hydrophilic property from polyacrylamide. This combined effect facilitates the desired strong talc depression in single mineral flotation. However, this copolymer system has similar adsorption affinity on both the talc and pentlandite, hence depressing both talc and pentlandite in the mixed mineral flotation system. This research shows that a sufficient hydrophobic balance on the polymer is necessary for the adsorption and subsequent depression for talc. However, polymer with high adsorption selectivity is required to be a successful synthetic talc depressant for mixed mineral system.

비닐렌기에 플루오르기를 도입한 m-SiP-PPDFV의 합성과 색 안정성에 대한 물성

New electroluminescent polymers with fluoro groups in vinylene units, poly(m-silylphenyl-p-phenylene-difluorovinylene) (m-SiP-PPDFV) have been synthesized by GILCH polymerization. These polymers have been used as the electroluminescent (EL) layers in single layer light-emitting diodes (LEDs) (ITO/PEDOT/polymer/Ca:Al). m-SiP-PPDFV shows PL around = 452 nm and green EL around = 497 nm. The current-voltage-luminance (I-V-L) characteristics of the polymers show turn-on voltages of 4.0 V approximately. Two fluoro groups were introduced on every vinylene units of m-SiP-PPV to give m-SiP-PPDFV in an attempt to increase the electron affinity of the parent polymer, and the devices show an increased color stability even with vinylene units. The color stability is attributed to the electron-withdrawing effect of the fluoro groups, which protect vinylene units from oxidation in PPV derivatives. We believe that fluoro groups can be introduced in vinylene units in order to attain excellent stability of PPV derivatives.

Effect of pyrene treatment on the properties of graphene/epoxy nanocomposites

Graphene is a two-dimensional nanocarbon that is currently being investigated for applications in a variety of areas. Graphene has unusual properties including a large surface area of 2,600 m·g, high thermal conductivity of ~3,000 W m·K, high electrical conductivity of ~550 S·cm, a high modulus of ~1 TPa, and a high aspect ratio of several hundreds. Aksay et al. recently reported that graphene sheets can be produced in bulk by the thermal expansion of sufficiently oxidized graphite oxide (GO). These exfoliated sheets are called functionalized graphene sheets (FGSs) because some of the oxygen containing groups such as epoxy groups remain after thermal treatment. FGSs have an affinity for polar solvents and polymers, as well as have a high electrical conductivity of about 10 S·cm. Polymers such as epoxy resin are generally good electrical insulators. However, an improvement in electric conductivity is necessary for applications that require electrostatic dissipation or electromagnetic radiation shielding. Nanocarbons with high conductivity and a large aspect ratio can be effectively utilized in the preparation of conductive polymer nanocomposites. Recent studies have demonstrated the emergence of FGS as fascinating conductive nanofillers with low percolation thresholds. In nanocomposites, nanofiller dispersion and interfacial interactions with the matrix polymer can be significantly enhanced through chemical or non-covalent physical modification of the nanofiller surface character. Many researchers have reported that polycyclic aromatic hydrocarbons such as pyrene or perylene are strongly adsorbed onto graphene sheets or carbon nanotubes through π-π interactions. We observed that the dispersibility of FGSs in the epoxy resin matrix was improved when the FGSs were treated with pyrene. This paper describes the effect of pyrene treatment on the dispersion, electric, and rheological properties of FGS/epoxy nanocomposites.

In situ growth of gold colloids within alginate films

Gold–alginate bionanocomposite films were prepared by impregnation of alginate films withHAuCl4 followed by reduction with glucose. The mannuronate over guluronate ratio (M/G) of the polymer as well as the initial polymer concentration wereshown to influence the film thickness, the amount of trappedAu3 + ions, and the volume fraction of Au(0) nanoparticles but not the size of these colloids(about 4 nm). The homogeneity of the gold colloid dispersion within the alginate gels wasstudied by transmission electron microscopy (TEM) and confirmed by simulation of thesurface plasmon resonance (SPR) spectra using the Maxwell–Garnett model. Thecalculated spectra also provided fruitful information about the gold colloid/alginateinterface. Overall, the whole process is controlled by the balance between theM/G ratio, defining the polymer affinity for Au(III) species, and the solution viscosity,controlling the diffusion phenomena.

Gas permeation related to the moisture sorption in films of glassy hydrophilic polymers

AbstractThe purpose of this article is to elucidate the effect of integral sorption of moisture on gas permeation in glassy hydrophilic polymers. The oxygen and the simultaneous moisture sorption into various hydroxypropyl methylcellulose (HPMC) films were measured under a wide range of relative humidities using sorption analyzer equipment. Correspondingly, the oxygen permeability at different ambient conditions was measured using an oxygen detector. The solubility of oxygen in the HPMC film was found to be affected by the amount of water and therefore by the water state. At low moisture content, the water molecules are present as bound water, which promotes the sorption of oxygen in the HPMC films. At moisture content higher than 5%, water clusters are rapidly formed, which increase the affinity of HPMC polymer towards water rather than towards oxygen molecules, resulting in a decrease of oxygen solubility in the polymer. This was found to be the governing factor for the reduction in the oxygen permeability in glassy HPMC films at high water activity. This proposes a specific interaction between moisture sorption and oxygen transport in coating films like HPMC, which is of important aspect in the coating design and formulation. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

석조문화재를 위한 아크릴계 보존처리제의 무기친화성 개선

Applying acrylic silane monomer for determent of weathering damage of stone cultural assets from various sources was investigated to improve inorganic affinity of polymer impregnated to the stone for conservation treatment using impregnation of acrylic polymers under pressure. Radical polymerization was carried out with various mixture ratios of methacrylate (MMA), as the base monomer, and vinyl trimethoxy silane (VTMS). Subsequently, according to the changes of glass transition temperatures, average molecular weights, and storage moduli of the obtained copolymers, the case of adding 1 wt% of benzoyl peroxide, polymerization for 8 hrs, and mixing 5 mol% of VTMS to MMA was the optimum condition of monomer ratio and polymerization. Practically, fresh granites collected in domestic site and weathered stones were treated by following the obtained result above, and then, the moisture absorption, impact, acid resistance, and adhesion properties of the treated stones were compared to those of the corresponding stones treated with MMA only. It was found that those properties of the stones treated with PMV5 were considerably improved.

Mesoscale Molecular Dynamics Simulations of the Force between Surfaces with Grafted Poly(ethylene oxide) Chains Derived from Atomistic Simulations

The force between parallel surfaces with grafted poly(ethylene oxide) chains was calculated using molecular dynamics simulations. First, a single chain surrounded by water molecules was simulated with full atomistic detail. On the basis of that, a coarse-grained model with implicit solvent was developed. The force between surfaces with grafted coarse-grained chains was calculated as a function of surface separation (3−18 nm), chain length (12−20 repeat units), grafting density (Γ = 0.01−2.04 chains/nm2), and interactions between surface and polymer. Results showed that the force was mainly repulsive and increased monotonically as distance decreased. Chain length had a stronger influence on the force than Γ. For purely repulsive interactions between polymer and surfaces, chains had extended conformations, leading to higher repulsive forces between surfaces. For surfaces with higher affinity for polymer, adsorption took place. The force between surfaces was significant only for high Γ because chains then ac...

High yield expression and purification of HIV-1 Tat 1−72 for structural studies

The HIV-1 transactivator of transcription (Tat) is a protein essential for virus replication. Tat is an intrinsically disordered RNA-binding protein that, in cooperation with host cell factors cyclin T1 and cyclin-dependent kinase 9, regulates transcription at the level of elongation. Tat also interacts with numerous other intracellular and extracellular proteins, and is implicated in a number of pathogenic processes. The physico-chemical properties of Tat make it a particularly challenging target for structural studies: Tat contains seven Cys residues, six of which are essential for transactivation, and is highly susceptible to oxidative cross-linking and aggregation. In addition, a basic segment (residues 48–57) gives the protein a high net positive charge of +12 at pH 7, endowing it with a high affinity for anionic polymers and surfaces. In order to study the structure of Tat, both alone and in complex with partner molecules, we have developed a system for the bacterial expression and purification of 6 × Histidine-tagged and isotopically enriched (in N 15 and C 13 ) recombinant HIV-1 Tat 1−72 (BH10 isolate) that yields large amounts of protein. These preparations have facilitated the assignment of 95% of the backbone NMR resonances. Analysis by mass spectrometry and NMR demonstrate that the cysteine-rich Tat protein is unambiguously reduced, monomeric, and unfolded in aqueous solution at pH 4.

Temperature-induced adsorption and optical properties of an amphiphilic diblock copolymer adsorbed onto flat and curved silver surfaces

Temperature-induced adsorption of a thermoresponsive amphiphilic copolymer, containing poly(N-isopropylacrylamide), on citrate-capped silver nanoparticles and planar silver surfaces has been studied with the aid of quartz crystal microbalance with dissipation monitoring (QCM-D) and dynamic light scattering (DLS). The results clearly show that both the amount of adsorbed copolymer and thickness of the adsorbed layer increase strongly at temperatures above the lower critical solution temperature (LCST). These findings are ascribed to enhanced hydrophobicity of the polymer and higher affinity for polymer adsorption at elevated temperatures and formation of intermicellar structures of the copolymer. The values of the layer thickness calculated from QCM-D data are practically identical to the values for the hydrodynamic thickness from DLS. This result suggests that the adsorbed layer is compact with few tails protruding out into the bulk. The surface plasmon peak for silver is observed at all temperatures, and the maximum is red-shifted with increasing temperature, which is attributed to an increase of the localized refractive index as more polymer chains are adsorbed onto the silver particles.

Compatibilizing effect of graphite oxide in graphene/PMMA nanocomposites

The structure of single graphene sheets, which are the basal plane of graphite, can be best visualized by making a longitudinal scission on a single wall carbon nanotube (SWCNT) along the tube axis and flattening the resulting sheet. These sheets have electric conductivity, thermal conductivity, and tensile modulus values similar to SWCNTs, and can be used as alternatives to SWCNTs in various applications. Graphite shows a sharp X-ray diffraction peak at 2θ=26.5 because it has a layered structure composed of graphene sheets and the typical interlayer spacing is 3.35 A. These sheets are one-atom-thick and are composed of hexagonal carbon rings. Graphite oxide (GO), prepared by oxidizing graphite, is a graphite-derived compound with a layered structure. GO has a broad X-ray diffraction peak at lower angles than graphite, normally 2θ=10~15, because polar groups such as hydroxyl, epoxide, ether, and carboxylate groups are present on graphene sheets as a result of oxidation and expand the interlayer spacing. Recently, it has been reported that exfoliation of graphite into a single graphene sheet can be achieved from sufficiently oxidized GO, if inter-graphene spacing associated with native graphite is completely eliminated in the oxidation stage, and if adequate pressure builds up at the gallery between the GO sheets by rapid heating. The pressure results from CO2 evolved by the thermal decomposition of functional groups. This exfoliated graphite, where the inter-graphene spaces associated with GO and graphite are completely excluded after thermal expansion, has an affinity for polar solvents and polymers, as well as good conductivity, because this exfoliated graphite is composed of functionalized graphene sheets (FGSs) having polar functional groups remained even after thermal treatment. Normally, carbon nanotubes need surface treatment if they are to be used as a nanofiller for fine dispersion in a polymer matrix. However, FGS can offer comparable or better electrical conductivity enhancement than carbon nanotubes without further surface treatment, owing to the polar functional groups. Our laboratory has prepared and examined FGS nanocomposites with various polymers. During these studies, we discovered that the fine dispersion of FGS in a polymer matrix can be improved when GO is used as a compatibilizer. This paper reports the compatibilizing effect of GO in FGS/poly(methyl methacrylate) (PMMA) nanocomposites.

Influence of Solute−Membrane Affinity on Rejection of Uncharged Organic Solutes by Nanofiltration Membranes

A simple, analytical method for predicting transport of uncharged organic solutes through nanofiltration (NF) and reverse osmosis (RO) membranes is presented in this paper. The method requires characterization of key solute and membrane parameters-namely, solute size, membrane pore size, and solute-membrane affinity. All three parameters can be experimentally determined from relatively simple permeation tests and contact angle analyses. The parameters are fed into an analytical model of solute transport, which accounts for hindered convection and diffusion of solutes in the membrane pores, as well as the combined effects of steric exclusion and solute-membrane affinity on solute partitioning from the feed solution into the membrane pores. Overall model predictions for organic solute rejection agreed well with experimental data for three different solutes and two different polymeric NF membranes. Further, the model demonstrates the dramatic influence of solute-membrane affinity on organic rejection by NF and RO membranes. Solute transport predictions made assuming only steric exclusion significantly overestimated rejections for solutes with strong affinity for membrane polymers and similarly underestimated rejections for solutes that were strongly repelled by membrane polymers.

Influence of Interfacial Layer Between Nanoparticles and Polymeric Matrix on Viscoelastic Properties of Hydrogel Nanocomposites

The viscoelastic properties of nanocomposites are influenced by both the nanoparticle distribution and the nanoparticle−polymer affinity. These two parameters are closely coupled, and evaluation of individual contributions to the mechanical properties is a critical requirement for efficient development of nanocomposites. To decouple these two effects, we utilized charge repulsion among nanoparticles so that we could essentially eliminate particle agglomeration. We then investigated how the nanoparticle−polymer affinity relates to the mechanical properties of the nanocomposite by comparing silica and polystyrene nanoparticles. The surface roughness of the particles and the molecular conformation of the interfacial layer between the polymer and the nanoparticles were characterized by synchrotron small-angle X-ray scattering and quartz crystal microbalance, respectively. On polystyrene particles, the surface roughness was larger, and the polymer adsorbed strongly. Consequently, the mobility of the adsorbed polymer was reduced compared to that on silica particles. This reduced mobility explains a smaller viscoelastic loss for the polystyrene-filled nanocomposite compared to the silica-filled nanocomposite.

Thermodynamics of water interaction with 5-vinyltetrazole copolymers with different hydrophilic-hydrophobic balances

The thermodynamics of interaction with water and the behavior of 5-vinyltetrazole copolymers with comonomers of different chemical natures and hydrophilicities in aqueous media have been studied. It has been shown that the presence of side perfluoroalkyl and disubstituted tetrazole fragments, which ensure a strong self-association of polymer chains in copolymer macromolecules, favors a greater decrease in water affinity of polymers compared to the effect of hydrophobic alkyl substituents.

The role of hydrophobicity in the antimicrobial and hemolytic activities of polymethacrylate derivatives.

We synthesized cationic random amphiphilic copolymers by radical copolymerization of methacrylate monomers with cationic or hydrophobic groups and evaluated their antimicrobial and hemolytic activities. The nature of the hydrophobic groups, and polymer composition and length were systematically varied to investigate how structural parameters affect polymer activity. This allowed us to obtain the optimal composition of polymers suitable to act as non-toxic antimicrobials as well as non-selective polymeric biocides. The antimicrobial activity depends sigmoidally on the mole fraction of hydrophobic groups (f(HB)). The hemolytic activity increases as f(HB) increases and levels off at high values of f(HB), especially for the high-molecular-weight polymers. Plots of HC(50) values versus the number of hydrophobic side chains in a polymer chain for each polymer series showed a good correlation and linear relationship in the log-log plots. We also developed a theoretical model to analyze the hemolytic activity of polymers and demonstrated that the hemolytic activity can be described as a balance of membrane binding of polymers through partitioning of hydrophobic side chains into lipid layers and the hydrophobic collapsing of polymer chains. The study on the membrane binding of dye-labeled polymers to large, unilamellar vesicles showed that the hydrophobicity of polymers enhances their binding to lipid bilayers and induces collapse of the polymer chain in solution, reducing the apparent affinity of polymers for the membranes.

Synthesis and Characterization of Soluble Conjugated Poly(p-phenylenevinylene) Derivatives Constituted of Alternating Pyrazole and 1,3,4-Oxadiazole Moieties

New soluble poly(p-phenylenevinylene) derivatives with 1,3,4-oxadiazole and pyrazole rings along the main chain were synthesized by Heck coupling. The new conjugated polymers are soluble in common organic solvents as a result of the fully conjugated backbone with dodecyloxy side groups. The polymers show relatively high glass-transition temperatures (up to 160°C) and good satisfactory thermal stability. Solutions of the polymers emit blue-greenish light with photoluminescence (PL) emission maxima around 490–500 nm. The PL spectrum of the polymer’s thin films, with a maximum at 515 nm, shows a red-shift (~20 nm), with respect to the solution spectrum. Cyclic voltammetry reveals that both conjugated polymers have reversible oxidation and irreversible reduction, making them n-type electroluminescent materials. The electron affinity of the new polymers was estimated as 2.73–2.74 eV. The weight-average molecular weights (M w) of the new soluble polymers were in the range of 4790–4950.