Adsorption of poly(ethyleneglycol) and poly(amidoamine)dendrimer from their mixtures on alumina/water and silica/water interfaces

Colloidal particles in competition for stabilizer: a solvent relaxation NMR study of polymer adsorption and desorption

The competitive adsorption of poly(vinylpyrrolidone) onto silica and alumina-modified silica particles was studied using solvent relaxation nuclear magnetic resonance. The additive nature of the measured relaxation rate enabled predictions to be made of the relaxation rate in different polymer adsorption scenarios. Preferential adsorption of the poly(vinylpyrrolidone) onto the unmodified silica particles occurred when there was insufficient polymer in the system to coat the entire available surface area. Desorption was also found to occur when the polymer was initially adsorbed upon the alumina-modified particle and silica particles were added.

Silica-coated La0.75Sr0.25MnO3 nanoparticles for magnetically driven DNA isolation

Magnetic La(0.75)Sr(0.25)MnO(3) nanoparticles possessing an approximately 20-nm-thick silica shell (LSMO(0.25)@SiO(2) ) were characterised and tested for the isolation of PCR-ready bacterial DNA. The results presented here show that the nanoparticles do not interfere in PCR. DNA was apparently reversibly adsorbed on their silica shell from the aqueous phase system (16% PEG 6000-2 M NaCl). The method proposed was used for DNA isolation from complex food samples (dairy products and probiotic food supplements). The isolated DNA was compatible with PCR. The main advantages of the nanoparticles tested for routine use were their high colloidal stability allowing a more precise dosage and therefore high reproducibility of DNA isolation.

Poly(ethylene oxide) (PEO) and poly(vinyl pyrolidone) (PVP) induce different changes in the colloid stability of nanoparticles

The phase behavior of model polymer-colloid mixtures is measured for solutions approaching the "protein limit", that is, when the radius of gyration of the polymer (R(g)) is greater than or approximately equal to the radius of the colloid (R). Cationic nanoparticles are mixed with poly(ethylene oxide) (PEO) or poly(vinyl pyrolidone) (PVP) at size ratios of R(g)/R = 0.7 and 1.8. The addition of PEO to stable nanoparticle dispersions leads to depletion flocculation in both deionized water and buffer solutions. The instability mechanism for the PVP-nanoparticle system depends on the suspension medium. In water, bridging occurs below the saturation adsorption of PVP, whereas depletion phase separation is evident at concentrations exceeding those necessary to saturate the particle surface. In acidic buffer, PVP addition results in depletion phase separation. The difference between bridging and depletion is distinguished by both visual appearances and rheological measurements. There is no trend (within error bars) in the polymer concentration required to induce instability with increasing R(g)/R in contrast with theoretical predictions. This is most likely due to adsorption of polymer onto the particle surface.

Calorimetric study of the adsorption of poly(ethylene oxide) and poly(vinyl pyrrolidone) onto cationic nanoparticles

The adsorption of two polymers, poly(ethylene oxide) (PEO) and poly(vinyl pyrrolidone) PVP, onto cationic nanoparticles suspended in both water and a buffer solution is studied via isothermal titration calorimetry (ITC). These are model systems studied previously to understand polymer-induced phase separation and bridging flocculation in the protein limit. ITC measurements provide critical information for rationalizing the effects of polymer type and added buffer solution on the loss of stability of nanoparticle-polymer solutions. For PEO, weak segmental adsorption energies of approximately 0.2k(B)T for PEO in water and buffer are consistent with depletion phase separation. For PVP in water, segmental adsorption energies on the order of approximately 1.6k(B)T support the observed bridging flocculation, whereas a weaker adsorption energy of approximately 0.7k(B)T for PVP in buffer is consistent with depletion phase separation. Multilayer adsorption is observed in buffer solutions, which corroborates a measured increase in the hydrodynamic size of the polymer-nanoparticle complexes with added buffer. The entropy of adsorption is calculated from equilibrium constants determined by combining ITC and adsorption isotherms.

Colloidal stability dependence on polymer adsorption through disjoining pressure isotherms

The disjoining pressure of polymers confined by colloidal walls was computed using dissipative particle dynamics simulations at constant chemical potential, volume, and temperature. The polymers are able to adsorb on the surfaces according to two models. In the so-called surface-modifying polymers, all monomers composing the chains have the same affinity for the substrate, whereas for the end-grafted polymer only the monomer at one of the ends of the polymer molecule adsorbs on the colloidal surface, resembling the behavior of dispersing agents. We find that these adsorption models yield markedly different disjoining pressure isotherms, which in turn predict different stability conditions for the colloidal dispersion. Our results show that for end-grafted polymers, a larger degree of polymerization at the same monomer concentration leads to better stability than for the surface-modifying ones. But also the unbound monomers of the surface-modifying type dominate over both kinds of polymers at large surface distances. The origin of these differences when the chemical nature of monomers is the same, and molecular weight and polymer concentration are used to characterize colloidal stability, is found to be mainly entropic.

Adsorption and disjoining pressure isotherms of confined polymers using dissipative particle dynamics

The adsorption and disjoining pressure isotherms of polymers confined by planar walls are obtained using Monte Carlo (MC) simulations in the Grand Canonical (GC) ensemble in combination with the mesoscopic technique known as dissipative particle dynamics (DPD). Two models of effective potentials for the confining surfaces are used: one with both an attractive and a repulsive term and one with a purely repulsive term. As for the polymer, seven-bead linear model of polyethylene glycol (PEG) dissolved in water is used. The results indicate remarkably good agreement between the trends shown by our adsorption isotherms and those obtained from experiments of PEG on oxide surfaces. Additionally, the disjoining pressure isotherm of water shows oscillations, while those of PEG display the same trend for both wall models. Moreover, it is found that the disjoining pressure isotherms are in qualitative agreement with those from experiments on confined linear polymers.

Inverse gas chromatography as a tool for investigation of nanomaterials

Inverse gas chromatography (IGC) is presented as a representative tool for the investigation of nanomaterials: Aerosil200V and two iron oxides (nanohematite and nanogoethite). IGC was used for characterization of the surface properties of materials. Parameters describing their surface properties are calculated from the retention data of test solutes injected into a column filled with the solid of interest. It is possible to determine the surface activity and the Hamaker constants of different nanomaterials.

Isolation of polymerase chain reaction-ready bacterial DNA from Lake Baikal sediments by carboxyl-functionalised magnetic polymer microspheres

Carboxyl group-containing magnetic nonporous poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate) (P(HEMA-co-EDMA)) microspheres were used for the isolation of polymerase chain reaction (PCR)-ready DNA from samples of Baikal sediments. DNA was isolated using the phenol extraction method or the Soil DNA Isolation Kit. The occurrence of false-negative results in PCR caused by the presence of extracellular inhibitors in DNA samples was solved using solid phase reversible DNA immobilisation. PCR-ready DNA was reversibly adsorbed to the microspheres in the presence of 8.0% (w/v) poly(ethylene glycol) (PEG 6000) and 2.0M sodium chloride concentrations. The adsorbed DNA was released from the microspheres in a low ionic strength TE buffer. The quality of isolated DNA was checked by PCR amplification.

Isolation of microbial DNA by newly designed magnetic particles

Carboxyl group-containing magnetic nonporous poly(2-hydroxyethyl methacrylate-co-glycidyl methacrylate) (P(HEMA-co-GMA)) microspheres and cobalt ferrite nanoparticles modified with alginic acid (natural carboxylic polysaccharide) were used for isolation of microbial DNA of lactic acid bacteria (LAB) from dairy products, lyophilised cell cultures, and bacterial colonies grown on hard media, and Trichophyton fungi DNA from lyophilised cells. DNA from the samples with lysed cells was reversibly adsorbed to the particles in the presence of high poly(ethylene glycol) (PEG 6000) and sodium chloride concentrations. The optimal final PEG and NaCl concentrations were 9.1 wt.% and 2.0 M, respectively. The adsorbed DNA was released from the particles in low ionic strength TE buffer. The quality of isolated DNA was checked by PCR amplification. Moreover, PCR amplicons were isolated on cobalt ferrite nanoparticles modified with alginic acid and checked by restriction analysis.

Surface chemical studies on the competitive adsorption of poly(ethylene glycol) and ammonium poly(methacrylate) onto alumina

The adsorption of poly(ethylene glycol) (PEG) and ammonium poly(methacrylate) (APMA) onto alumina has been examined both individually and in combination. The adsorption density of APMA was found to be higher than that of PEG onto alumina. The adsorption isotherms of PEG and APMA for alumina exhibited a Langmuirian behavior. The adsorption density of PEG was significantly reduced in the presence of APMA, but the reverse was not true. About 60% desorption of PEG from alumina was achieved, while in the case of APMA the amount desorbed was only 10% in the pH range of 3-6. The zeta potential values of alumina were decreased and the isoelectric point (i.e.p.) values were shifted toward acidic pH values, proportional to the concentration of APMA added. However, such changes in the electrokinetic behavior were not observed by the addition of PEG. The dispersion behavior of alumina in the combined presence of PEG and APMA essentially followed the trends obtained for the alumina-APMA system, corroborating the electrokinetic measurements. Coprecipitation tests confirmed complexation between aluminum species and APMA in the bulk solution, but not with PEG. The interaction between alumina and PEG is primarily governed by hydrogen-bonding forces, while both hydrogen bonding and chemical interaction are involved in the case of the alumina-APMA system. FTIR spectroscopic studies provided evidence in support of the interaction mechanisms proposed.

Adsorption of poly(acrylic acid) onto the surface of titanium dioxide and the colloidal stability of aqueous suspension

The adsorption of poly(acrylic acid) (PAA) in aqueous suspension onto the surface of TiO(2) nanoparticles was investigated. FTIR spectroscopic data provided evidence in support of hydrogen bonding and chemical interaction in the case of the PAA-TiO(2) system. Adsorption isotherms demonstrated that part of the PAA initially added to the suspension was adsorbed onto the TiO(2) surface, after which there was a gradual attainment of an adsorption plateau. The adsorption density of PAA was found to increase with an increase of PAA molecular weight, while it decreased with an increase of pH. The thickness of the PAA adsorption layer was calculated based on measurements of suspension viscosities in the absence and presence of PAA. It was shown that the thickness of the adsorption layer increased with the increase of pH, PAA molecular weight, and its concentration. The surface charge density, the diffuse charge density, and the zeta potential of TiO(2) varied distinctly after PAA adsorption. The shift of pH(iep) toward a lower pH value was observed in the presence of PAA. PAA was found to stabilize the suspension of TiO(2) nanoparticles through electrosteric repulsion. The influence of factors such as PAA molecular weight and its concentration on the colloidal stability of the aqueous suspension was also investigated.

Magnetic hydrophilic methacrylate-based polymer microspheres for genomic DNA isolation

Carboxyl groups containing magnetic and non-magnetic microspheres were used in solid-phase reversible immobilization (SPRI) of genomic DNA. Magnetic non-porous poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate)--P(HEMA-co-EDMA), poly(glycidyl methacrylate)--PGMA and P(HEMA-co-GMA) microspheres with hydrophilic properties were prepared by dispersion copolymerization of the respective monomers in the presence of colloidal iron oxides. DNA from chicken erythrocytes and DNA isolated from bacterial cells of Bifidobacterium longum was used for testing of adsorption/desorption properties of magnetic microspheres. The occurrence of false negative results in polymerase chain reaction (PCR) caused by the presence of extracellular inhibitors in DNA samples has been solved using SPRI. The P(HEMA-co-EDMA) and P(HEMA-co-GMA) microspheres were used for isolation of DNA from different dairy products followed by PCR identification of Bifidobacterium strains.

Chemistry of alumina, reactions in aqueous solution and its application in water treatment

Due to the presence and significance of alumina in the natural aquatic environment and its increasing application in drinking and wastewater purification, the knowledge of the structure of alumina and its possible interactions with organic and inorganic compounds in water are of great importance. This is of particular importance in both the understanding of natural aquatic environment processes and efficient industrial applications. The chemistry of alumina reactions in water is complex. The adsorption ability of alumina towards organic and inorganic compounds might be influenced by several factors such as: surface characteristics of the adsorbent (surface area, density, pore volume, porosity, pore size distribution, pH(PZC) as well as mechanical strength and purity), pH of the solution, ionic strength, composition of water and the physicochemical properties of adsorbates. The aim of this paper is to give a brief review of the properties of alumina and its reactivity with organic and inorganic compounds present in aqueous solutions. It also summarises the usage of alumina and alumina supported phases in water treatment technology.

Direct force measurements between adlayers consisting of poly(amidoamine) dendrimers with primary amino groups or quaternary ammonium groups

Adsorption of poly(amidoamine) generation 3 (PAMAM G3) dendrimer with surface amino groups or PAMAM G0 dendrimer with quaternary ammonium groups (C8qbG0) onto glass has been studied by colloidal probe atomic force microscopy. The adlayer-adlayer interactions for these adsorbates are quite different despite the fact that they are almost equal in the hydrodynamic radius. In aqueous PAMAM G3 dendrimer solutions the electrostatic repulsion is predominant. The conformation of the adsorbed layer is flat and the protrusion of the individual dendrimers is negligible. On the other hand, C8qbG0 behaves as a surfactant and the layered structure of C8qbG0 is expected to be a patchy bilayer. Dispersion stability of silica suspensions with the adsorption of these dendrimers can be correlated with the force data obtained.