Aqueous Solutions Of Poly Research Articles

Optical limiting properties of in situ reduced graphene oxide/polymer nanocomposites

Reduced graphene oxide/polymer nanocomposites are prepared by the in situ reduction of graphene oxide in the polymer matrix. Graphene oxide is dispersed in an aqueous solution of poly(vinyl alcohol) and is chemically reduced within the polymer matrix followed by solution casting to form the composite films. The nonlinear absorption characteristics and the optical limiting behaviour of the composite films are studied using z-scan technique. The composites exhibit excellent optical limiting behaviour along with improved thermal characteristics. The nonlinear absorption characteristics and the optical limiting properties are found to increase with increasing concentration of reduced graphene oxide in the polymer matrix. This clearly provides an opportunity to tune the optical limiting behaviour to attain a desired limiting threshold intensity by adjusting the concentration of the filler and hence these composites can find practical applications in many devices as potential optical limiters.

Top-down synthesis of polyaspartamide morphogens to derive platinum nanoclusters

Metallic nanoparticles are widely used in various applications, and their successful uses depend on the size and stability. In this study, we present a method to synthesize platinum nanoparticle clusters with tunable size and spatial organization. These nanoparticle clusters were synthesized by conducting sol-gel polymerization of platinum precursors in aqueous solution of poly(amino acid)s' derivative substituted with both particle precursor-binding amine groups and particle-binding thiol groups. Control experiments displayed that poly(amino acid)s' derivative tuned the morphology of nanoparticles and also induced organized association between the particles. Therefore, this study serves to provide novel method to synthesize a wide array of nanoparticles and clusters along with novel polymers to tune morphology and organization of the nanoparticles.

Counterion Binding in Aqueous Solutions of Poly(vinylpyridines) as Assessed by Potentiometric Titration

The extent to which counterions bind to polyelectrolytes influences a variety of polymer-based applications, including polyelectrolyte enhanced ultrafiltration and forward osmosis using polyelectrolytes as draw agents. Potentiometric titrations of poly (2-vinylpyridine) (P2VP), poly (3-vinylpyridine) (P3VP), and poly (4-vinylpydine) (P4VP) were performed using HBr, HCl, HNO3, and HClO4 in both the presence and absence of added NaCl. Because of the systematic differences among the three polyelectrolytes, titration results provide insight into the role of polymer structure in the relative extents to which various counterions bind. Titration data reveal that ionization properties vary as functions of polymer investigated, titrant used, degree of protonation, and added salt concentration. Acid dissociation constants of the pyridinium moieties were found to generally increase with increasing degree of protonation, though appreciable differences were exhibited among the three polymers investigated. For all three polymers, Cl- demonstrated the lowest affinity for the charged pyridinium residues, while the affinities associated with Br- and NO-3 were nearly identical to each other. The relative extent of binding for CIO-4 varied across the polymers investigated, and was greatest for P4VP.

Waterborne physically crosslinked antimicrobial nanogels

Aqueous solutions of poly(ethylene imine) functionalized with decyl- and azetidinium groups form physically cross-linked antimicrobial nanogels.

Free surface electrospinning of aqueous polymer solutions from a wire electrode

The production of nanofibers from an aqueous solution of poly(vinyl alcohol) by the method of free surface electrospinning from a wire electrode has been examined. The results are interpreted in terms of a previously reported model that was based on the production of fibers from polymeric solutions in ethanol by the same method. Differences in behavior were observed between the processing of aqueous and ethanolic solutions, arising from the more viscoelastic nature of the aqueous solution, the higher surface tension, the fewer number of droplets jetting simultaneously from the wire, and the different electrical current profile observed for jetting from a single droplet. These differences necessitated changes in equipment design, operation of the process, and modeling of productivity. The result is a more robust model for the productivity of fibers by free surface electrospinning from a wire electrode.

FeCl3-catalyzed tandem condensation/intramolecular nucleophilic addition/C–C bond cleavage: a concise synthesis of 2-substitued quinazolinones from 2-aminobenzamides and 1,3-diketones in aqueous media

A concise approach for the synthesis of 2-substituted quinazolinones using an iron-catalyzed tandem reaction of 2-aminobenzamides with acyclic or cyclic 1,3-diketones via condensation, intramolecular nucleophilic addition, C–C bond cleavage in an aqueous solution of poly(ethylene glycol) under oxidant-free conditions has been developed.

Aqueous Solutions of Poly[2‐(N‐morpholino)ethyl methacrylate]: Learning about Macromolecular Aggregation Processes from a Peculiar Three‐Step Thermoresponsive Behavior

Aqueous solutions of narrowly distributed poly[2‐(N‐morpholino)ethyl methacrylate], a biocompatible multiple stimuli‐responsive polymer, show a peculiar three‐step aggregation behavior upon heating, an effect which has hitherto barely been reported for other polymers. The phenomenon is discussed in terms of mesoglobule formation (first step) as well as by an unusual distinct disruption of hydrophobic hydration (second step) and hydrogen bonding to the hydrophilic aggregate surface (third step). Macroscopic precipitation only takes place after the third step, a behavior which resembles the denaturation and limited aggregation of proteins. Furthermore, the influence of different anions along the Hofmeister series is investigated, identifying salting‐out (kosmotropic) and salting‐in (chaotropic) effects. As an experimental tool to monitor the thermally induced aggregate growth, dynamic light scattering is used. The reported findings might lead to a more detailed understanding of both aggregation behavior of (biological) macromolecules and mechanistic processes involved in thermoresponsivity and salt‐responsivity of water soluble polymers. image

Hofmeister effect on thermo-responsive poly(propylene oxide): Role of polymer molecular weight and concentration

Although a vast amount of research has been dedicated to investigate the Hofmeister effect on the stability of polymer solutions, a clear understanding of the role of polymer properties in this phenomenon is still missing. Here, the Hofmeister effect of NaCl (destabilizing) and NaSCN (stabilizing) salts on aqueous solutions of poly(propylene oxide) (PPO) is studied. Four different molecular weights of PPO were investigated, to determine how the variation in the polymer coil size affects the Hofmeister effect. The investigation was further conducted for different PPO concentrations, in order to understand the effect of inter-chain interactions on the response to addition of salt. The temperature-driven phase separation of the solutions was monitored by differential scanning calorimetry, which provides the precise value of the phase separation temperature, as well as the enthalpy change accompanied with the transition. It was observed that increasing the molecular weight weakens the effect of the both salts, which is interpreted in terms of a scaling law between the molecular weight and the accessible surface area of the polymers. Increasing the PPO concentration further diminished the NaCl effect, but amplified the NaSCN effect. This difference is attributed to an electrostatic stabilization mechanism in the case of NaSCN.

Improved Transversal Relaxivity for Highly Crystalline Nanoparticles of Pure γ‐Fe2O3 Phase

Pure and highly crystalline γ-Fe2O3 nanocrystals (NCs) are obtained when hydrolysis and oxidation of a Fe(II) organometallic precursor are performed in successive steps. Their synthesis in pure alkylamine leads to NCs of about 6 nm. In aqueous solutions of poly(vinyl)pyrrolidone, such pristine NCs form aggregates of about 150 nm that exhibit a high transversal relaxivity (r2 =466 mM(-1) s(-1)) about four times higher than that of a commercial Feridex magnetic resonance imaging (MRI) contrast agent. Consequently, they provide a significant decrease in the NMR signal at very short echo time (8 ms), which is of paramount importance in clinical practice because of the reduced duration of MRI measurements.

Spin probes in micellar and polymer self-associating systems

The results of studies of micellar and self-associating polymer systems by spin probe ESR spectroscopy are summarized. The local dynamics and structures of low-molecular-weight micelles built of cationic surfactants bearing long alkyl chains (from C16 to C22), gels of hydrophobically modified polymers, polymer micelles, micellar complexes of nonionic surfactant (Brij58) with hydrogels based on polyacrylic acid, and associates formed in aqueous solutions of poly(diphenylenesulfophthalide) are discussed. Interest in these systems is caused by prospects of their practical use as carriers in drug delivery, in biotechnology, for the enhancement of oil production, and in other purposes.

Block copolymer-mediated synthesis of silver nanoparticles from silver ions in aqueous media

Abstract We report here on the silver (Ag) nanoparticle synthesis in aqueous solutions of poly(ethylene oxide)-poly(propylene oxide) (PEO–PPO) block copolymers in the absence of any additional agents. In particular, we examined the effect of reaction temperature, molecular weight of PEO–PPO block copolymer and PEO–PPO block copolymer concentration on the reduction of silver ions (Ag + ) and the resulting formation of Ag nanoparticles in aqueous PEO–PPO block copolymer solutions. We found that Ag nanoparticles were formed from aqueous silver nitrate (AgNO 3 ) solutions containing PEO–PPO block copolymer above 100 °C. This is most likely due to the dehydration of Ag + caused by thermal motion of water molecules in higher-temperature aqueous solution at high vapor pressure. We also found that the formation of Ag nanoparticles in aqueous PEO–PPO block copolymer solutions was enhanced with larger molecular weight of PEO–PPO block copolymer and with increase in the concentration of PEO–PPO block copolymer in aqueous solutions.

Stability and rheological properties of nanofluids containing ZnO nanoparticles, poly(propylene glycol) and poly(vinyl pyrrolidone)

In this work, polymer based nanofluids have been prepared by dispersing the ZnO nanoparticles in base fluid of poly(propylene glycol), PPG, aqueous solution of PPG, aqueous solution of poly(vinyl pyrrolidone), PVP, and mixture of these two polymers. Stability and particle size distribution of these nanofluids have been studied by result analysis of UV–vis spectroscopy, zeta potential and dynamic light scattering. Viscosity values of ZnO–PPG and ZnO–PPG–H2O nanofluids have been measured at 293.15, 298.15, 308.15 and 318.15K. The Eyring-NRTL and Eyring-mNRF models have successfully been used for correlating the viscosity values of the nanofluids investigated with temperature dependency considered. The performance of Einstein, Brinkman, Lundgren and Batchelor models in the prediction of viscosity values of ZnO–PPG nanofluid has also been tested. Rheological behavior of investigated nanofluids has been investigated over volumetric solid concentrations (φ1=0, 0.5, 4.5%) and shear rates (γ=0.01–1000s−1) at 298.15K. The nanoparticle suspensions generally exhibited a pseudoplastic flow behavior, indicating an existence of particle aggregations in the liquid medium. Bingham plastic and Herschel–Bulkley models were used to evaluate the shear stress–shear rate dependency. The colloid yield stress was determined from these models.

Phase transition of poly(vinyl alcohol) hydrogel filled with micro-fibrillated cellulose

Aqueous solution of poly(vinyl alcohol) (PVA) forms hydrogels by freezing and thawing. In this study, micro-fibrillated cellulose (MFC) was mixed with PVA aqueous solution. Thermal properties of PVA–MFC composite hydrogels were investigated in a wide range of water content by differential scanning calorimetry (DSC). On DSC heating curves, glass transition, exothermic peak due to cold crystallization and endothermic peak attributed to melting of water were observed. Phase diagrams of PVA–MFC composite hydrogels were established based on transition temperatures. The amount of non-freezing water increased when MFC is introduced into hydrogels. Glass transition temperature of amorphous ice restrained by PVA–MFC composite hydrogel is restricted by the presence of MFC. Results obtained by DSC suggest that gelation occurs in adjacent PVA molecules due to compartmentalization in the presence of MFC molecules.

Chemical networks of poly(vinyl alcohol)-Si hybrid films and the thermodynamics of their interaction with water

Organic-inorganic hybrid polymer films are prepared through the sol-gel method via the hydrolytic condensation of tetraethoxysilane in a 4% aqueous solution of poly(vinyl alcohol). The films are polymer networks containing O-Si-O bonds between chains formed via the interaction of OH groups of alcohol and Si-OH groups of the products of hydrolysis of tetraethoxysilane. The films contain 10.8–26.2 wt % Si in the polymer matrix. Isotherms of water-vapor sorption by the films are determined and used to calculate the molecular mass of polymer-chain fragments between crosslink-junction points in terms of the Flory-Rehner theory. For hybrid polymer networks, the products of sol-gel synthesis, this calculation is performed for the first time. The molecular mass of chain fragments between crosslink-junction points decreases from 9000 to 180 with an increase in the content of Si in the films. Poly(vinyl alcohol)-Si hybrid films are active during the separation of components of organic-aqueous media (a solution of tetrahydrofuran in water). The selectivity of the films increases as the molecular mass of chain fragments between crosslink-junction points decreases, that is, as the density of the chemical network increases.

Birefringence in solutions and films of poly(N-methyl-N-vinylacetamide) macromolecules

The flow birefringence of aqueous solutions of poly(N-methyl-N-vinylacetamide) macromolecules for samples of various molecular masses is studied. It is found that the sign of birefringence changes from positive to negative with a decrease in molecular mass in accordance with the manifestation of the macroform effect on condition that the value of the inherent optical anisotropy of macromolecules is negative. With the use of the macroform-effect theory in the Maxwell phenomenon of polymer solutions, the inherent optical anisotropy of the repeating polymer unit is estimated as (a ‖−a ⊥) = −(5 ± 1) × 10−25 cm3. In turn, the value of (a ‖−a ⊥) makes it possible to separate structural and orientational contributions to the effect of spontaneous birefringence for films of various thicknesses that are cast from aqueous solutions of poly(N-methyl-N-vinylacetamide). The parameter of orientational order of chain fragments for this polymer in the near-surface layers of the films is −(0.05 ± 0.01).

Drying dissipative patterns of aqueous solution of poly(methacrylic acid) and its salt neutralized half

Drying patterns of poly(methacrylic acid) (HPMA) and its salt neutralized half with sodium hydroxide (NaHPMA) were studied on a cover glass, a watch glass, and a glass dish. The patterns of HPMA and NaHPMA are compared with the previous observation of sodium salt of poly(methacrylic acid), NaPMA (Okubo et al. Colloid Polym Sci 287:1155–1165, 2009). HPMA and especially NaHPMA are hygroscopic, and only the macroscopic patterns were observed. However, microscopic patterns were not observed clearly especially for NaHPMA in the room atmosphere. The hygroscopy of the dried films was in the order NaPMA NaHPMA > NaPMA. The magnitude of S values of NaPMA was similar to that of poly(ethylene glycol) (PEG). HPMA, NaHPMA, and NaPMA were grouped into E, A, and A, respectively, among six groups of solutes A to F.

Hydration and Hydrogen Bond Network of Water during the Coil-to-Globule Transition in Poly(N-isopropylacrylamide) Aqueous Solution at Cloud Point Temperature.

Aqueous solutions of poly(N-isopropylacrylamide), P-NIPAAm, exhibit a noticeable temperature responsive change in molecular conformation at a cloud point temperature (Tcp). As the temperature rises above Tcp, the extended coil-like P-NIPAAm structure changes into a swollen globule-like conformation as hydration levels decrease and hydrophobic interactions increase. Though water plays an important role in this coil-to-globule transition of P-NIPAAm, the behavior of water molecules and the associated hydrogen-bond (HB) network of the surrounding bulk water are still veiled in uncertainty. In this study, we elucidate changes in the hydration state and the dynamical structure of the water HB network of P-NIPAAm aqueous solutions during the coil-to-globule transition by analyzing the complex dielectric constant in the terahertz region (0.25-12 THz), where bulk water reorientations and intermolecular vibrations of water can be selectively probed. The structural properties of the water HB network were examined in terms of the population of the non-HB water molecules (not directly engaged in the HB network or hydrated to P-NIPAAm) and the tetrahedral coordination of the water molecules engaged in the HB network. We found the hydration number below Tcp (≈10) was decreased to approximately 6.5 as temperature increased, in line with previous studies. The HB network of bulk water becomes more structured as the coil-to-globule phase transition takes place, via decreases in non-HB water and reduction in the orderliness of the tetrahedral HB architecture. Together these results indicate that the coil-to-globule transition is associated with a shift to hydrophobic-dominated interactions that drive thermoresponsive structural changes in the surrounding water molecules.

Dual turn-on fluorescent chemosensor for Cu2+ and Hg2+ in aqueous medium based on a water-soluble polyacrylamide containing rhodamine

An acrylic monomer bearing rhodamine 6G group, salicylaldehyde rhodamine 6G hydrazone acrylate (AR6GHS), was synthesized from salicylaldehyde rhodamine 6G hydrazone (R6GHS) and acryloyl chloride in the presence of triethylamine in dry dichloromethane (CH2Cl2) at room temperature. The poly(acrylamide- salicylaldehyde rhodamine 6G hydrazone acrylate) (poly(AM-AR6GHS)) was synthesized by a combiation of AR6GHS and a hydrophilic comonomer acrylamide (AM) with 2,2′-azobis(2-methylpropionitrile) (AIBN) as a thermal initiator in tetrahydrofuran (THF). The resultant AR6GHS and poly(AM-AR6GHS) were identified by FTIR and 1H NMR spectra. The fluorescent characteristic of the poly(AM-AR6GHS) in the aqueous solutions were investigated both in varied pH and in the presence of metal cations. It was found that the copolymeric sensor exhibited “off-on” recognition toward Cu2+ and Hg2+ over a wide range of tested metal ions with remarkably enhanced fluorescent intensities. The poly(AM-AR6GHS) had a good linear response between the relative fluorescence intensity and Cu2+ or Hg2+ concentration. In addition, upon the addition of Cu2+ or Hg2+ into the aqueous solution of poly(AM-AR6GHS), the color changes occurred from colorless to pale pink or pink under visible light, and the emission color of the sensor solution turned from dark to bright greenish yellow or orange yellow under the UV light at 365 nm.

Effect of kappa-carrageenan on the properties of poly(vinyl alcohol) hydrogel prepared by application of gamma radiation

Synthesis of hydrogels from aqueous solution of poly(vinyl alcohol) (PVA) and kappa-carrageenan (KC) has been performed with radiation processing technology using Co-60 gamma source. As investigation on the influence of radiation dose and concentration of KC on gel content, swelling properties, and thermal behaviors of hydrogel has been performed. Gel content obtains a maximum value at 25 kGy radiation dose. Equilibrium water content of hydrogel decreases with increased radiation dose but it increases with increased concentration of KC. The water absorption of hydrogel is fast up to 5 hours and it becomes a maximum value at 24 hours. It increases with increased concentration of KC in the feed solution. The water absorption of hydrogel increases from 210 to 410% for the increment of KC content from 0 to 2.0% at the radiation dose 25 kGy. Thermo-gravimetric analysis (TGA) and dynamic mechanical analysis (DMA) showed that thermal degradation reduces with increased concentration of KC in PVA hydrogel. Scanning electron microscopy (SEM) was used to investigate the surface morphology of PVA/KC blend hydrogel. The hydrogel was applied to absorb dye (methyl violet) from aqueous solution. Langmuir and Freundlich models were applied to study the dye adsorption pattern.

The Effect of Hydrophilic Bentonite Nanoclay on the Thermogelation Properties of Poly(N-isopropylacrylamide)-poly(ethylene glycol)-poly(N-isopropylacrylamide) Triblock Copolymer Aqueous Solutions

The effect of hydrophilic bentonite addition on the thermogelation properties of aqueous solutions of poly(N-isopropylacrylamide)–poly(ethylene glycol)–poly(N-isopropylacrylamide) (PNIPAM-PEG-PNIPAM) triblock copolymers of various compositions and molecular weights was investigated. Dynamic rheometry and differential scanning calorimetry (DSC) measurements showed that increasing concentrations of clay added to 20 wt.% polymer aqueous solutions caused a decrease of the temperature at which the viscosity starts increasing, while the temperature corresponding to the maximum endothermic effect due to the PNIPAM chain dehydration remained practically unchanged. The storage modulus, G′, increased with clay concentration for shorter PNIPAM chain triblock copolymers, while an opposite situation occurred in the case of the block copolymer with the longest PNIPAM block. For bentonite concentrations above 1 wt.%, G′ was larger than the viscous modulus, G″, at temperatures higher than the phase separation temperature, indicating a predominantly elastic character of the resulting composite hydrogels. These findings were explained through the presence of polymer–clay interactions occurring mainly through the PEG blocks.