Controlled formation of ag nanoparticles by means of long-chain sodium polyacrylates in dilute solution

A new tool is presented to control formation of Ag nanoparticles. Small amounts of silver ions were added to dilute solutions of long-chain sodium polyacrylates (NaPA). Four NaPA samples covering a molar mass regime of 97 kD < or = Mw < or = 650 kD have been used. With amounts of added Ag(+) as low as 1-2% of the COO(-) groups of the polyanionic chains, significant changes could already be induced in the NaPA coils with 650 kD. If the NaPA concentration was kept below 0.1 g/L, the coils with 650 kD exhibited a significant coil shrinking in stable solutions. At larger NaPA concentrations, addition of Ag+ initiates an aggregation of the polyacrylate coils toward compact structures. Coil shrinking and aggregation was revealed by means of time-resolved static light scattering. If exposed to UV-radiation, small Ag particles formed within the shrunken anionic polyacrylate coils. The Ag nanoparticles were identified by means of an enhanced light scattering and a characteristic plasmon absorption band around 410 nm. No such Ag particle formation could be observed even at 5 times larger concentrations of Ag(+) and NaPA if the two smallest polyacrylate samples have been used under otherwise equal conditions. This molar mass sensitive response of NaPA to Ag(+)-addition suggests an interesting phenomenon: if the coil size of the NaPa chains, which act as Ag(+) collectors, is large enough, local Ag(+) concentration in these coil-shaped Ag(+) containers exceeds a critical value, and irradiation with UV generates Ag nanoparticles.     

Time-resolved SAXS study of the effect of a double hydrophilic block-copolymer on the formation of CaCO3 from a supersaturated salt solution

The effect of a double hydrophilic block-copolymer additive (made of polyaspartic acid and polyethyleneglycol, pAsp(10)-b-PEG(110)) on the initial formation of calcium carbonate from a supersaturated salt solution has been studied in situ by means of time-resolved synchrotron small-angle X-ray scattering (SAXS). A stopped-flow cell was used for rapidly mixing the 20 mM aqueous reactant solutions of calcium chloride and sodium carbonate. In reference measurements without polymer additive the very rapid formation of primary, overall spherical CaCO(3) particles with a radius of ca. 19 nm and a size polydispersity of ca. 26% was observed within the first 10 ms after mixing. A subsequent, very rapid aggregation of these primary particles was evidenced by a distinct upturn of the SAXS intensity at smallest angles. During the aggregation process the size of the primary particles remained unchanged. From an analysis of the absolute scattering intensity the mass density of these particles was determined to 1.9 g/cm(3). From this rather low density it is concluded that those precursor particles are amorphous, which has been confirmed by simultaneous wide-angle X-ray diffraction measurements. Upon adding 200 pm of the block-copolymer no influence on the size, the size polydispersity and morphology of the primary particles, nor on the kinetics of their formation and growth, was found. On the other hand, the subsequent aggregation and precipitation process is considerably slowed down by the additive and smaller aggregates result. The crystalline morphology of the sediment was studied in situ by WAXS ca. 50 min after mixing the reactants. Several diffraction rings could be detected, which indicate that a transformation of the metastable, amorphous precursor particles to randomly oriented vaterite nanocrystallites has taken place. In addition, a few isolated Bragg spots of high intensity were detected, which are attributed to individual, oriented calcite microcrystals that nucleated at the wall of the capillary.     

Synthesis and characterization of new chiral liquid crystalline polyacrylates from L-isoleucine

The synthesis of chiral side chain liquid crystalline polyacrylates with a two-stereogenic centre from L-alpha-aminoacid is described. The chiral tail is 2-chloroalcohol obtained from L-isoleucine and the spacer group has either four or eleven methylene units. The mesogenic moiety is derived from phenyl benzoate. The stereochemistry of the key intermediate (2 S ,3 S )-(+)-4- [1-(2-chloro-3-methyl)pentyloxy]phenyl benzoate ( 6 ) obtained by a Mitsunobu reaction was established by single crystal X-ray analysis. This result indicates that the nucleophilic displacement of chiral diazonium salts proceeds with overall retention of configuration. The liquid crystalline behaviour of polyacrylates P 13 and P 14 was investigated by DSC, optical microscopy, small angle X-ray scattering and depolarized light scattering. The polyacrylate P 13 , with eleven methylene units in the spacer, exhibits a chiral smectic A phase whereas the polyacrylate P 14 , with a spacer containing four methylene units, displays a chiral nematic phase.     

Synthesis and characterization of new chiral liquid crystalline polyacrylates from L-isoleucine

The synthesis of chiral side chain liquid crystalline polyacrylates with a two-stereogenic centre from L-α-aminoacid is described. The chiral tail is 2-chloroalcohol obtained from L-isoleucine and the spacer group has either four or eleven methylene units. The mesogenic moiety is derived from phenyl benzoate. The stereochemistry of the key intermediate (2S,3S)-(+)-4- [1-(2-chloro-3-methyl)pentyloxy]phenyl benzoate (6) obtained by a Mitsunobu reaction was established by single crystal X-ray analysis. This result indicates that the nucleophilic displacement of chiral diazonium salts proceeds with overall retention of configuration. The liquid crystalline behaviour of polyacrylates P13 and P14 was investigated by DSC, optical microscopy, small angle X-ray scattering and depolarized light scattering. The polyacrylate P13, with eleven methylene units in the spacer, exhibits a chiral smectic A phase whereas the polyacrylate P14, with a spacer containing four methylene units, displays a chiral nematic phase.     

Temperature-induced collapse of alkaline Earth cation-polyacrylate anion complexes

Polyacrylate anions are used to inhibit CaCO3 precipitation and may be a promising additive to control formation of inorganic nanoparticles. The origin of this applicability lies in specific interactions between the alkaline earth cations and the carboxylate functions along the polyacrylate chains. In the absence of CO32- anions, these interactions eventually cause precipitation of polyelectrolytes. Extended investigation of dilute sodium polyacrylate solutions approaching this precipitation threshold revealed a dramatic shrinking of the PA coil dimensions once the threshold is reached (Eur. Phys. J. E 2001, 5, 117). Recent isothermal calorimetric titration experiments by Antonietti et al. (Macromolecules 2004, 37, 3444) indicated that the driving force of this precipitation is entropic in nature. In the present work, we investigated the impact of temperature on the structural changes of dissolved polyacrylate chains decorated with alkaline earth cations. To this end, large polyacrylate chains were brought close to the precipitation threshold by the addition of distinct amounts of Ca2+ or Sr2+ cations. The resulting structural intermediates were then subjected to temperature variations in the range of 15 degrees C 相似文献   

In situ investigation of complex BaSO4 fiber generation in the presence of sodium polyacrylate. 2. Crystallization mechanisms

The formation mechanisms of complex BaSO(4) fiber bundles and cones in the presence of polyacrylate sodium salt via a bioinspired approach at ambient temperature in an aqueous environment are reported. These complex organic-inorganic hybrid structures assemble after heterogeneous nucleation of amorphous precursor particle aggregates on polar surfaces, and the crystallization area can be patterned. In contrast to earlier reports, three different mechanisms based on the oriented attachment of nanoparticles were revealed for the formation of typical fibrous superstructures depending on the supersaturation or on the number of precursor particles. (A) High supersaturation (S > 2): large amorphous aggregates stick to a polar surface, form fiber bundles after mesoscopic transformation and oriented attachment, and then form a narrow tip through polymer interaction. (B) Low supersaturation (S = 1.02-2): only a few fibers nucleate heterogeneously from a single nucleation spot, and amorphous particles stick to existing fibers, which results in the formation of a fiber bundle. (C) Vanishing supersaturation (S = 1-1.02): nucleation of a fiber bundle from a single nucleation spot with self-limiting repetitive growth as a result of the limited amount of building material. These growth processes are supported by time-resolved optical microscopy in solution, TEM, SEM, and DLS.     

Stabilization of Nanostructured Zeolite Particles: The Effect of Sodium Polyacrylate on the Disaggregation Kinetics and Threshold

The influence of sodium polyacrylate on the disaggregation kinetics and threshold of conglomerates of a natural agromineral, zeolite, under ultrasonic dispersion has been studied. It has been demonstrated that the use of sodium polyacrylate as a stabilizing additive has resulted in the reduction of the zeolite particle size, the increase in the content of isolated fractions, and significant decrease in the ultrasonic treatment duration. When the zeolite was dispersed with sodium polyacrylate, the particles achieved an average size of 750.0 nm after the first minute of cavitation treatment, while the dispersion of the agromineral without the additive required a 5-min treatment to achieve the same result. The use of sodium polyacrylate increased the stabilized state period of zeolite particles to half a year.     

Interactions between brushlike polyacrylic acid side chains on a polyacrylate backbone in dioxane-water.

Densely grafted polyacrylic acids (d-PAAs) with overcrowded PAA side chains on the polyacrylate main chains were synthesized and characterized. Acryloyl poly(tert-butyl acrylate) macromonomer [M-P(tert-BA)] was prepared with a definite chain length (n=29) by atom-transfer radical polymerization (ATRP), then homopolymerization was carried out to produce densely grafted P(tert-BA)s with polyacrylate main chains of two different lengths (m=27 and 161). The two d-PAAs were obtained by hydrolyzing d-P(tert-BA)s in the presence of trifluoroacetic acid (TFA). The d-PAAs exhibit intermolecular and intramolecular hydrogen bonding between the carboxylic groups of PAA side chains in dioxane and pyridine; both were investigated using proton nuclear magnetic resonance (1H NMR) spectroscopy. The intermolecular hydrogen bonding was found to be dependent on polymer concentration, temperature, and water content. The intramolecular association between the PAA side chains was found to produce a contraction of the hydrodynamic volume of the d-PAA. Intermolecular hydrogen bonding produces aggregates, as demonstrated by dynamic light scattering (DLS). The clusters were found to shrink as the overall water concentration decreased, and this effect is tentatively explained by considering the gradient in chemical potential of water inside the clusters in comparison with the solvent phase.     

Synthesis and characterization of emulsifier-free trilayer core–shell polysilsesquioxane/polyacrylate/poly(fluorinated acrylate) hybrid latex particles

The trilayer core–shell polysilsesquioxane/polyacrylate/poly(fluorinated acrylate) (PSQ/PA/PFA) hybrid latex particles are successfully prepared, using functional PSQ latex particles with reactive methacryloxypropyl groups synthesized by the hydrolysis and polycondensation of (3-methacryloxypropyl)trimethoxysilane in the presence of a reactive emulsifier as seeds. Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and dynamic light scattering (DLS) confirm that the resultant hybrid latex particles have evident trilayer core–shell structure and a narrow size distribution. The Fourier transform infrared (FTIR) spectra show that fluorinated acrylate monomers are effectively involved in the emulsion copolymerization and formed the fluorine-containing hybrid latex particles. XPS analysis of the obtained hybrid latex film reveals that the intensity of fluorine signal in the film–air interface is higher than that in the film–glass interface. In addition, compared with pure polyacrylate latex film, the obtained fluorine-containing hybrid film shows higher hydrophobicity and thermal stability, and lower surface free energy.     

New phosphate fluorosurfactants for carbon dioxide

Anionic phosphate fluorosurfactants were shown to self-assemble into water-in-carbon dioxide microemulsions. The surfactants, having either two fluorinated chains or one fluorinated chain and one hydrocarbon chain, facilitated significant water uptake in CO2. Small angle neutron scattering (SANS) measurements of surfactant/water/CO2 solutions confirmed the presence of nanometer-scale aggregates, indicative of microemulsion formation.     

Effect of temperature on the reentrant condensation in polyelectrolyte-liposome complexation

Interactions of oppositely charged macroions in aqueous solution give rise to intriguing aggregation phenomena, resulting in finite-size, long-lived clusters, characterized by a quite narrow size distribution. Particularly, the adsorption of highly charged linear polyelectrolytes on oppositely charged colloidal particles is strongly correlated and some short-range order arises from competing electrostatic interactions between like-charged polymer chains (repulsion) and between polymer chains and particle surface (attraction). In these systems, in an interval of concentrations around the isoelectric point, relatively large clusters of polyelectrolyte-decorated particles form. However, the mechanisms that drive the aggregation and stabilize, at the different polymer/particle ratios, a well-defined size of the aggregates are not completely understood. Nor is clear the role that the correlated polyion adsorption plays in the aggregation, although the importance of "patchy interactions" has been stressed as the possible source of attractive interaction term between colloidal particles. Different models have been proposed to explain the formation of the observed cluster phase. However, a central question still remains unanswered, i.e., whether the clusters are true equilibrium or metastable aggregates. To elucidate this point, in this work, we have investigated the effect of the temperature on the cluster formation. We employed liposomes built up by DOTAP lipids interacting with a simple anionic polyion, polyacrylate sodium salt, over an extended concentration range below and above the isoelectric condition. Our results show that the aggregation process can be described by a thermally activated mechanism.     

Phase behavior of polyion-surfactant ion complex salts: effects of surfactant chain length and polyion length

The aqueous phase behavior of a series of complex salts, containing cationic surfactants with polymeric counterions, has been investigated by visual inspection and small-angle X-ray scattering (SAXS). The salts were alkyltrimethylammonium polyacrylates, CxTAPAy, based on all combinations of five surfactant chain lengths (C6, C8, C10, C12, and C16) and two lengths of the polyacrylate chain (30 and 6 000 repeating units). At low water contents, all complex salts except C6TAPA6000 formed hexagonal and/or cubic Pm3n phases, with the hexagonal phase being favored by lower water contents. The aggregate dimensions in the liquid crystalline phases changed with the surfactant chain length. The determined micellar aggregation numbers of the cubic phases indicated that the micelles were only slightly aspherical. At high water contents, the C6TAPAy salts were miscible with water, whereas the other complex salts featured wide miscibility gaps with a concentrated phase in equilibrium with a (sometimes very) dilute aqueous solution. Thus, the attraction between oppositely charged surfactant aggregates and polyions decreases with decreasing surfactant chain length, and with decreasing polyion length, resulting in an increased miscibility with water. The complex salt with the longest surfactant chains and polyions gave the widest miscibility gap, with a concentrated hexagonal phase in equilibrium with almost pure water. A decrease in the attraction led to cubic-micellar and micellar-micellar coexistence in the miscibility gap and to an increasing concentration of the complex salt in the dilute phase. For each polyion length, the mixtures for the various surfactant chain lengths were found to conform to a global phase diagram, where the surfactant chain length played the role of an interaction parameter.     

"Like-charge attraction" between anionic polyelectrolytes: molecular dynamics simulations

"Like-charge attraction" is a phenomenon found in many biological systems containing DNA or proteins, as well as in polyelectrolyte systems of industrial importance. "Like-charge attraction" between polyanions is observed in the presence of mobile multivalent cations. At a certain limiting concentration of cations, the negatively charged macroions cease to repel each other and even an attractive force between the anions is found. With classical molecular dynamics simulations it is possible to elucidate the processes that govern the attractive behavior with atomistic resolution. As an industrially relevant example we study the interaction of negatively charged carboxylate groups of sodium polyacrylate molecules with divalent cationic Ca2+ counterions. Here we show that Ca2+ ions initially associate with single chains of polyacrylates and strongly influence sodium ion distribution; shielded polyanions approach each other and eventually "stick" together (precipitate), contrary to the assumption that precipitation is initially induced by intermolecular Ca2+ bridging.     

TEMPO-mediated, room temperature synthesis of pure CoO nanoparticles

Treatment of dicobalt octacarbonyl with TEMPO in THF at room temperature, in the presence of oleic acid as the sole additive, leads to the formation of monodisperse nanoparticles (ca. 3.0 nm diameter) of CoO; the particles agglomerate in solution at room temperature into aggregates, and this property has been used for the controlled preparation of hybrid materials.     

Calcium-induced volume transition in polyacrylate hydrogels swollen in physiological salt solutions

Osmotic and small-angle neutron-scattering measurements are performed to study the volume transition that occurs in sodium polyacrylate gels swollen in sodium chloride solutions when calcium ions are introduced. In the presence of calcium ions, the osmotic pressure depends sensitively on the sodium chloride concentration, indicating that calcium preferentially replaces condensed sodium ions. This substitution modifies the effective attractive interaction between polymer chains. Analysis of the osmotic data in terms of the Flory–Huggins theory reveals a sharp increase in the third-order ternary thermodynamic interaction parameter upon introduction of calcium ions. The neutron-scattering response at low scattering vectors q displays power-law behavior with a slope of approximately −3.6, consistent with scattering from surfaces of large objects. These results are in agreement with the development of dense polymer-rich regions dispersed in a soft polymer matrix. At larger q, a region with slope −1 is observed, characteristic of rigid linear structures.

Small-angle neutron-scattering spectra of polyacrylate hydrogels swollen by 40 mM sodium chloride solutions containing different amounts of CaCl₂ (+: 0.5 mM , ○: 0.85 mM , ×: 1.7 mM ). The dashed curve shows the least squares fit of the 0.85 mM CaCl₂ data to Equation ( 5 ) in which the first term is replaced by Equation ( 8 ), and the second term is approximated by a simple power law.     

Synthesis of Nickel Nanoparticles by the Reduction of Its Salts Using the Modified Polyol Method in the Presence of Sodium Polyacrylates with Various Molecular Weights

Nickel nanoparticles were synthesized by the reduction of its salts by hydrazine hydrate in a polyol medium in the presence of sodium polyacrylates with molecular weights of 1200, 5100, and 8000. The nanoparticles were characterized by X-ray diffraction, scanning and transmission electron microscopy, IR spectroscopy, and thermogravimetric analysis. The effect of the synthesis conditions, such as temperature, molecular weight of sodium polyacrylate, and polyol and precursor types, on the reduction products were studied. It was shown that the average particle sizes, their aggregation and polydispersity degrees increase as the polymer molecular weight increases.     

Hybrid particles of polystyrene and carboxymethyl cellulose as substrates for copper ions

The synthesis of hybrid particles was carried out by emulsion polymerization of styrene in complexes formed by carboxymethyl cellulose (CMC), a polyanion, and a cationic surfactant, cetyltrimethylammonium bromide (CTAB). CMC chains with variable molecular weights and degrees of substitution were tested. The polymerization condition chosen was that corresponding to CMC chains fully saturated with CTAB and to the onset of pure surfactant micelle formation, namely, at the critical aggregation concentration. The hybrid particles were characterized by zeta potential and light scattering measurements. The period of colloidal stability in the ionic strength of 2.0 mol L(-)(1) NaCl was observed visually. Upon increasing the CMC chain length, the particle characteristics remained practically unchanged, but the colloid stability was increased. The increase in the CMC degree of substitution led to particles with more negative zeta potential values. The adsorption of copper ions (Cu(2+)) on the surface of hybrid particles could be described by the Langmuir model, as determined by potentiometric measurements. The increase in the mean zeta potential values and X-ray absorption near-edge spectra evidenced the immobilization of Cu(2+) ions on the hybrid particles.     

Separation of complex branched polymers by size-exclusion chromatography probed with multiple detection

Size-exclusion chromatography (SEC) separates polymers by hydrodynamic volume (the universal calibration principle). Molecular weights can be determined using viscometry (relying on universal calibration) and light scattering (independent of universal calibration). In the case of complex branched polyacrylates with tetrahydrofuran as eluent, universal calibration is valid, although the separation in term of molecular weight is incomplete: a given elution slice contains a range of molecular weights, described in terms of a 'local polydispersity'. The local polydispersity index decreases when the number of branches per chain increases and complete separation is reached for highly branched chains.     

Characterization of polymeric vesicles of poly(sodium 11-acrylamidoundecanoate) in water

A polysoap poly(sodium 11-acrylamidoundecanoate) was synthesized from sodium 11-acrylamidoundecanoate in water. The molecular weight of the polymer was determined by gel permeation chromatography and static light scattering techniques. Fluorescence probe studies in water have suggested the formation of hydrophobic domains within the same polymer chain. The microenvironment of the hydrophobic domains is highly ordered. The packing of the hydrocarbon chains in the hydrophobic domains formed by intra-chain association increases upon decrease of pH. The transmission electron micrograph revealed large vesicular aggregates in dilute aqueous solution. Temperature-dependent fluorescence anisotropy of the 1,6-diphenyl-1,3,5-hexatriene probe demonstrated stability of the vesicles.     

Laser light scattering and isothermal titration calorimetric studies of poly(ethylene oxide) aqueous solution in presence of sodium dodecyl sulfate

The aqueous solution of poly(ethylene oxide) (PEO) in the presence of different concentrations of sodium dodecyl sulfate (SDS) was examined by laser light scattering and isothermal titration calorimetric techniques. A small fraction of PEO aggregates were found to coexist with unimeric PEO chains in dilute solution. The presence of monovalent salt does not alter the hydrodynamic properties of PEO in aqueous solution. Addition of a monovalent anionic surfactant, such as SDS, induces cooperative binding of surfactant monomers to PEO backbones at SDS concentrations ranging from 4.0 mM (critical aggregation concentration) to 16.5 mM (saturation concentration). The hydrodynamic radius of PEO unimers decreases initially and then increases with SDS concentration, resulting from the structural reorganization of the PEO/SDS complex. Beyond the saturation concentration, the hydrodynamic radii of PEO/SDS complex are independent of SDS concentration.