Copper sols stabilized by poly(ethylene glycol-600-monolaurate) and its complexes with poly(acrylic acid)

Copper sols stabilized by a polymer-colloid complex are studied via dynamic light scattering and transmission electron microscopy. It is shown that the polymer-colloid complex including poly(acrylic acid) and the nonionogenic polymeric surfactant poly(ethylene glycol-600-monolaurate) is an effective protector of copper nanoparticles formed via the reduction of Cu²⁺ ions in an aqueous medium. The sizes of sol particles of the nanocomposite consisting of the polymer-colloid complex and copper nanoparticles depend on the method of preparation of the nanocomposite. The incorporation of the copper nanoparticles being formed (an average diameter of 5 nm) into particles of the polymer-colloid complex leads to an insignificant change in the sizes of the complex particles. The same sizes are typical for particles of the nanocomposite formed during the introduction of surfactant micelles in the copper sol formed in the solution of poly(acrylic acid). The interaction of copper nanoparticles formed in an aqueous medium with surfactant micelles entails their aggregation; as a result, these nanoparticles turn out to be incorporated into large aggregates with equivalent radii of up to 100 nm. When poly(acrylic acid) is incorporated into this sol, the sizes of its particles insignificantly change apparently because of the low rate of structural rearrangements accompanying the formation of the polymer-colloid complex.     

Mutual enhancement of the complexing properties of components in tertiary systems containing copper nanoparticles, poly(acrylic acid), and poly(ethylene glycol)

It is shown that nonstoichiometric interpolymer complexes composed of high-molecular-mass poly( acrylic acid) and PEG of various molecular masses are more efficient stabilizers of copper sols than each component of the complex taken separately. This conclusion is based on comparison of dimensions of copper nanoparticles in sols formed via reduction of copper(II) ions in solutions of poly (acrylic acid), PEG, and their blends and on the enhanced stability of sols protected by the interpolymer complex against aggregation and oxidation of metal particles. Much shorter PEG chains than those necessary for formation of corresponding interpolymer complexes in the absence of nanoparticles can be involved in formation of tertiary complexes including copper nanoparticles, poly(acrylic acid), and PEG. On the basis of the experimental data, it is inferred that the mutual enhancement of the complexing behavior of components occurs in tertiary complexes containing copper nanoparticles and both polymers.     

Effect of complexation of poly(acrylic acid) with Cu2+ ions on the size of copper nanoparticles prepared via reduction in aqueous solutions

Sols of zero-valence copper are prepared via the chemical reduction of Cu(II) ions by hydrazine borane in aqueous solutions of high-molecular-mass poly(acrylic acid), which forms stable complexes with copper ions at 20°C in a wide pH range. The study of the composition of coordination centers, the ligand surrounding of metal ions, and the character of distribution of copper ions over poly(acrylic acid) coils in a wide range of solution compositions and pH values shows that the size of copper nanoparticles in the sols can be controlled by varying the ratio between ligand groups (carboxylate anions in poly(acrylic acid)) and copper ions in the reaction system during the synthesis of sols. This effect can be accomplished either by variation in the initial composition of solution or change in pH (the degree of ionization of the initial poly(acrylic acid) in the presence of copper ions).     

Amphiphilic polymers as pseudotemplates in the synthesis of metal sols

The effects of poly(ethylene glycol) and its amphiphilic polymers on the products of copper ion reduction in aqueous solutions are studied. Whereas coarse metal dispersions are formed in poly(ethylene glycol) solutions, stable sols of metal nanoparticles with diameters of 2 nm and above are produced in the presence of poly(ethylene glycol monolaurate) and poly(ethylene glycol monostearate). A poly(ethylene glycol)-poly(propylene glycol) block copolymer (Pluronic) also stabilizes copper nanoparticles; however, the interaction product of this copolymer with nanoparticles forms a precipitate. According to the electron microscopy data, sol particles comprise polymer micelles containing included copper nanoparticles.     

Specific features of nonstoichiometric interpolymer complexes of poly(acrylic acid) and poly(ethylene glycol) as protectors of copper nanoparticles in aqueous sols

Advantages of interpolymer complexes for use as amphiphilic protectors of nanoparticles during the formation and stabilization of sols are considered. The effects of the ratio of poly(acrylic acid) and poly(ethylene glycol) and the molecular mass of poly(ethylene glycol) on the mean size and size distribution of copper nanoparticles in sols formed via the reduction of divalent copper ions in mixed aqueous solutions of these polymers are investigated. It is shown that sols of metal nanoparticles with small sizes and narrow size distributions are formed even when poly(ethylene glycols) with chain lengths below the “critical” chain length and a small PEG-to-PAA base-molar ratio are used. This is evidence for efficient protection of the formed copper nanoparticles by the interpolymer complex PEG-PAA under conditions of its instability and for self-organization of oligomeric PEG chains in complex macromolecular shields of nanoparticles.     

Interaction of copper nanoparticles with liposomes

The reduction of copper(II) ions in an aqueous dispersion of positively charged liposomes results in the formation of stable sols of a complex of copper nanoparticles with the surface of liposomes. The mean size (7 nm) and the narrow size distribution of metal nanoparticles are similar to those observed in the case of metal sol formation in polymer solutions. The labile character of bonds between nanoparticles and liposomes makes the latter able to compete with a linear polymer (poly-N-vinylpyrrolidone) in binding to nanoparticles. This ability is manifested in the independence of an almost even distribution of nanoparticles between these competitors from the sol preparation mode in a system including both poly(N-vinylpyrrolidone) macromolecules and liposomes. The evenness of the distribution indicates an approximately identical stability of complexes of copper nanoparticles with both competitors. The replacement of liposomes with poly(N-vinylpyrrolidone) macromolecules in the protective shields of nanoparticles is accompanied by the detachment of the nanoparticles from the surface, thereby allowing the measurement of their size and size distribution in the case where such measurements are impossible because of a high density of nanoparticles on the liposome surface.     

Hydrogen-bonding-driven self-assembly of PEGylated organosilica nanoparticles with poly(acrylic acid) in aqueous solutions and in layer-by-layer deposition at solid surfaces

PEGylated organosilica nanoparticles have been synthesized through self-condensation of (3-mercaptopropyl)trimethoxysilane in dimethyl sulfoxide into thiolated nanoparticles with their subsequent reaction with methoxypoly(ethylene glycol) maleimide. The PEGylated nanoparticles showed excellent colloidal stability over a wide range of pH in contrast to the parent thiolated nanoparticles, which have a tendency to aggregate irreversibly under acidic conditions (pH < 3.0). Due to the presence of a poly(ethylene glycol)-based corona, the PEGylated nanoparticles are capable of forming hydrogen-bonded interpolymer complexes with poly(acrylic acid) in aqueous solutions under acidic conditions, resulting in larger aggregates. The use of hydrogen-bonding interactions allows more efficient attachment of the nanoparticles to surfaces. The alternating deposition of PEGylated nanoparticles and poly(acrylic acid) on silicon wafer surfaces in a layer-by-layer fashion leads to multilayered coatings. The self-assembly of PEGylated nanoparticles with poly(acrylic acid) in aqueous solutions and at solid surfaces was compared to the behavior of linear poly(ethylene glycol). The nanoparticle system creates thicker layers than the poly(ethylene glycol), and a thicker layer is obtained on a poly(acrylic acid) surface than on a silica surface, because of the effects of hydrogen bonding. Some implications of these hydrogen-bonding-driven interactions between PEGylated nanoparticles and poly(acrylic acid) for pharmaceutical formulations are discussed.     

Fluorescence and viscometry study of complexation of poly(acrylic acid) with poly(acrylamide) and hydrolysed poly(acrylamide)

Interpolymer complexation of poly(acrylic acid) with poly(acrylamide) and hydrolysed poly(acrylamide) was studied by fluorescence spectroscopy and viscometry in dilute aqueous solutions. Changes in chain conformation and flexibility due to the interpolymer association are reflected in the intramolecular excimer fluorescence of pyrene groups covalently attached to the polymer chain. Both poly(acrylamide) and hydrolysed poly(acrylamide) form stable complexes with poly(acrylic acid) at low pH. The molecular weight of poly(acrylic acid) and solution properties such as pH and ionic strength were found to influence the stability and the structure of the complexes. In addition, the polymer solutions mixing time showed an effect on the mean stoichiometry of the complex. The intrinsic viscosity of the solutions of mixed polymers at low pH suggested a compact polymer structure for the complex.     

Limiting stability temperatures for copper sols stabilized by poly(<Emphasis Type="Italic">N</Emphasis>-vinyllactams)

It has been shown that stable copper sols cannot be prepared through the reduction of copper ions in aqueous solutions of poly(N-vinyllactams) in the presence of poly(N-vinylpyrrolidone) in the temperature range 50–70°C, while in the presence of poly(N-vinylcaprolactam), the said sols cannot be prepared at temperatures below ～12°C. This tendency is related to the thermodynamic instability of complexes formed via noncovalent interactions of copper nanoparticles with polymer macromolecules in corresponding temperature ranges. Stable sols synthesized in the presence of the above polymers at other temperatures rapidly lose stability in the said temperature ranges, and this effect is accompanied by the aggregation of metal particles. The experimental results provide evidence that there is a relationship between the stability of complexes macromolecules-metal nanoparticles and the thermodynamic quality of the solvent.     

Stabilization of copper nanoparticles prepared by reduction from solutions of poly(acrylic acid) complexes with Cu2+ ions and poly(ethylene glycols)

Copper sols are prepared via the reduction of copper ions with hydrazine borane in dilute aqueous solutions of mixtures of the PAA-Cu²⁺ complex and poly(ethylene glycols) of various molecular masses at PEG: PAA = 0.25 base-mol/base-mol and PAA: Cu²⁺ = 10 base-mol/mol in the pH range 4.0–7.0. The stability of sols against oxidation (dissolution) or aggregation (enlargement) of metal nanoparticles is much higher than that of sols prepared in the absence of PEG. With an increase in the initial pH or a decrease in the molecular mass of PEG, the formed copper nanoparticles are much larger (no less than 20 nm in diameter) than copper nanoparticles occurring in the sol prepared in a solution of the PAA double complex with Cu²⁺ ions and high-molecular-mass PEG at a low initial pH (3–10 nm in diameter). Copper nanoparticles in sols prepared in solutions of complexes based on the high-molecular-mass PEG do not aggregate during exposure, thereby indicating the high stability of polymer screens on their surfaces.     

Interpolymer complexes of copolymers of vinyl ether of diethylene glycol with poly(acrylic acid)

 The complex formation reactions of poly(vinyl ether of diethylene glycol) as well as vinyl ether of diethylene glycol–vinyl butyl ether copolymers with poly(acrylic acid) have been studied in aqueous and alcohol solutions. The formation of interpolymer complexes which were stabilized by hydrogen bonds was shown. The effects of molecular weight of poly(acrylic acid) and the nature of the nonionic polymer on the composition and stability of interpolymer complexes were clarified. The critical pH values of complexation were determined for different systems with various molecular weights and hydrophobic–hydrophilic balances. The stability of the interpolymer complexes formed in aqueous and alcohol solutions with respect to dimethylformamide addition was evaluated. The role of hydrophobic interactions and the presence of active groups on stability of the interpolymer complexes is discussed. Received: 23 July 2001 Accepted: 27 September 2001     

非共价键自组装制备聚对苯撑乙炔/聚丙烯酸水溶性荧光纳米粒子及其光物理行为研究

通过功能化聚对苯撑乙炔(含羟基与氨基)和聚丙烯酸之间的非共价键自组装制备了一系列含共轭聚合物的水溶性荧光纳米粒子, 并进行了相关结构和光学性质表征. 研究表明, 纳米粒子的大小和聚丙烯酸/聚对苯撑乙炔质量比直接相关. 光物理性质研究表明, 形成水溶性纳米粒子后, 疏水的聚苯撑乙炔链在纳米粒子中易于形成π-链间聚集, 其光物理性质与其在薄膜态时相似.     

Solvent effects on the formation of nanoparticles and multilayered coatings based on hydrogen-bonded interpolymer complexes of poly(acrylic acid) with homo- and copolymers of N-vinyl pyrrolidone

The formation of hydrogen-bonded interpolymer complexes between poly(acrylic acid) and poly(N-vinyl pyrrolidone) as well as amphiphilic copolymers of N-vinyl pyrrolidone with vinyl propyl ether has been studied in aqueous and organic solutions. It was demonstrated that introduction of vinyl propyl ether units into the macromolecules of the nonionic polymer enhances their ability to form complexes in aqueous solutions due to more significant contribution of hydrophobic effects. The complexation was found to be a multistage process that involves the formation of primary polycomplex particles, which further aggregate to form spherical nanoparticles. Depending on the environmental factors (pH, solvent nature), these nanoparticles may either form stable colloidal solutions or undergo further aggregation, resulting in precipitation of interpolymer complexes. In organic solvents, the intensity of complex formation increases in the following order: methanol < ethanol < isopropanol < dioxane. The multilayered coatings were developed using layer-by-layer deposition of interpolymer complexes on glass surfaces. It was demonstrated that the solvent nature affects the efficiency of coating deposition.     

Precipitation-redispersion of cerium oxide nanoparticles with poly(acrylic acid): toward stable dispersions

We exploit a precipitation-redispersion mechanism for complexation of short chain polyelectrolytes with cerium oxide nanoparticles to extend their stability ranges. As synthesized, cerium oxide sols at pH 1.4 consist of monodisperse cationic nanocrystalline particles having a hydrodynamic diameter of 10 nm and a molecular weight of 400 000 g mol(-1). We show that short chain uncharged poly(acrylic acid) at low pH when added to a cerium oxide sols leads to macroscopic precipitation. As the pH is increased, the solution spontaneously redisperses into a clear solution of single particles with an anionic poly(acrylic acid) corona. The structure and dynamics of cerium oxide nanosols and their hybrid polymer-inorganic complexes in solution are investigated by static and dynamic light scattering, X-ray scattering, and chemical analysis. Quantitative analysis of the redispersed sol gives rise to an estimate of 40-50 polymer chains per particle for stable suspension. This amount represents 20% of the mass of the polymer-nanoparticle complexes. This complexation adds utility to the otherwise unstable cerium oxide dispersions by extending the range of stability of the sols in terms of pH, ionic strength, and concentration.     

Interaction of aluminum polyhydroxochloride sol and poly(4-vinylbenzene sulfonic acid) sodium salt

The interaction of aluminum polyhydroxochloride sol and poly(4-vinylbenzene sulfonic acid) sodium salt is studied. It is found that, in dilute aqueous solutions at pH 4.6, aluminum polyhydroxochloride sol and poly(4-vinylbenzene sulfonic acid) sodium salt form insoluble polymer-colloid complexes of steady compositions. Potentiometric titration data show that the interaction between particles of aluminum polyhy-droxochloride sol and linear macromolecules of the polyelectrolyte occurs via salt bonds formed between unlikely charged groups on the surface of particles and units of the linear polyelectrolyte. The composition of the polymer-colloid complex is determined, and the degree of conversion for the reaction of aluminum poly-hydroxochloride sol and poly(4-vinylbenzene sulfonic acid) sodium salt is estimated. The influence of various polyelectrolytes on the stability of the polymer-colloid complex is studied.     

Competition between polyelectrolyte macromolecules and amphiphilic polymer micelles in interaction with copper nanoparticles

Competition between poly(1,2-dimethyl-5-vinylpyridinium methyl sulfate) polycationic macromolecules and micelles of amphiphilic polymers containing hydrophilic and hydrophobic blocks (polyethylene glycol-600 monolaurate and poly-N-vinylpyrrolidone monostearate) for copper nanoparticles was studied by means of electrophoresis and electron microscopy techniques. It was shown that, irrespective of the formation method, almost all copper nanoparticles were bonded to the polycation in polycation-polyethylene glycol-600 monolaurate mixed solutions but were distributed between the polymers in polycation-poly-N-vinylpyrrolidone monostearate mixtures. It was concluded that the stability of the complex of copper nanoparticles with the polycation is higher than that with polyethylene glycol-600 monolaurate and is comparable with that of the copper particle-poly-N-vinylpyrrolidone monostearate complex.     

Formation of copper–polymer nanocomposite upon copper electrodeposition in the presence of poly(<Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone)

The composition and structure of products formed on a cathode upon electrodeposition of copper from copper sulfate–poly(N-vinylpyrrolidone) mixed solutions have been studied. These products have been shown to be nanocomposites consisting of copper nanoparticles and the polymer. It has been suggested that the composite is formed by a pseudotemplate mechanism via noncovalent interaction between macromolecules and copper particles growing on the cathode. The interaction is accompanied by deceleration of subsequent growth of particles because of their screening by the polymer. This decreases the sizes of copper particles in the reaction product and the rate of metal reduction. The sonication of the reaction system yields a nanocomposite sol containing nanoparticles of copper(I) oxide. The oxide results from rapid oxidation of copper metal particles that have passed to the sol with copper(II) ions.     

Water-soluble iron oxide nanoparticles with high stability and selective surface functionality

The water dispensability and stability of high quality iron oxide nanoparticles synthesized in organic solvents are major issues for biomedical and biological applications. In this paper, a versatile approach for preparing water-soluble iron oxide nanoparticles with great stability and selective surface functionality (-COOH, -NH(2), or -SH) was demonstrated. The hydrophobic nanoparticles were first synthesized by the thermal decomposition of an iron oleate complex in organic solvent. Subsequently, the hydrophobic coatings of nanoparticles were replaced with poly(acrylic acid) , polyethylenimine, or glutathione, yielding charged nanoparticles in aqueous solution. Two parameters were found to be critical for obtaining highly stable nanoparticle dispersions: the original coating and the surfactant-to-nanoparticle ratio. These charged nanoparticles exhibited different stabilities in biological buffers, which were directly influenced by the surface coatings. This report will provide significant practical value in exploring the biological or biomedical applications of iron oxide nanoparticles.     

Effect of copolymer composition on interpolymer complex formation of (co)poly(vinyl ether)s with poly(acrylic acid) in aqueous and organic solutions

The complex formation between vinyl ether of poly(ethylene glycol‐co‐vinyl butyl ether) with poly(acrylic acid) has been considered in aqueous and isopropanol solutions. The effect of copolymer composition on the complex formation process was clarified. It has been shown that the incorporation of hydrophobic fragments into macromolecules enhances the hydrophobic stabilization of polycomplexes in aqueous solutions. In organic media this effect disappears. The stability of polycomplexes formed both in aqueous and in organic solutions in respect to the addition of dimethylformamide has been studied.     

Study of the effect of poly(vinyl alcohol) concentration on the gelation point of poly(vinyl alcohol) poly(acrylic acid) semi‐IPN systems as determined by viscoelastic measurements

We report on the determination of the gelation point of semi‐interpenetrating polymer networks (semi‐IPNs) composed of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAAc) formed by a sequential method. The evolution of the viscoelasticity during the gelation reaction of acrylic acid (AAc) in solutions of PVA has been monitored through the sol‐gel transition with dynamic mechanical experiments. The gelation time of the system increased with PVA concentration; however, the molecular structure of the gel, composed of swollen clusters, is rather independent of the presence of PVA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1944–1949, 2005