Adsorption Of Poly Research Articles

Electrophoretic deposition of silicon-substituted hydroxyapatite/poly(ε-caprolactone) composite coatings

Silicon-substituted hydroxyapatite/poly(epsilon-caprolactone) composite coatings were prepared on titanium substrate by electrophoretic deposition in n-butanol and chloroform mixture. The effect of the concentration of poly(epsilon-caprolactone) in suspension on the morphology and the microstructure of coatings were investigated, furthermore, the thermal behavior and in vitro bioactivity were also investigated. The results show that the coarse and accidented silicon-substituted hydroxyapatite/poly(epsilon-caprolactone) composite coatings were obtained by electrophoretic deposition when the concentration of poly(epsilon-caprolactone) in suspension was 6-16 g/l. The adsorption of poly(epsilon-caprolactone) on the surface of Si-HA particles hinders the electrophoretic deposition of Si-HA. The shear-testing experiments indicated that the addition of poly(epsilon-caprolactone) in suspension is in favor of improving the bonding strength of the coatings. After immersion in simulated body fluid for 8 days, silicon-substituted hydroxyapatite/poly(epsilon-caprolactone) composite coatings have the ability to induce the bone-like apatite formation.

Adsorption of Poly(rA) on the Carbon Nanotube Surface and its Hybridization with Poly(rU)

Adsorption of poly(rA) on a single-walled carbon nanotube surface in aqueous suspension and the subsequent hybridization of this polymer with free poly(rU) is studied. A comparison of the temperature dependence of the absorbance of free poly(rA) and poly(rA) adsorbed on the nanotube surface [poly(rA)(NT)] at nu(max)= 38,500 cm(-1) shows that the thermostability of the adsorbed polymer is higher. Molecular dynamics simulations demonstrate that more than half of the adenines are not stacked on the tube surface and some of them undergo self-stacking. After addition of a complementary poly(rU) to the poly(rA)(NT) suspension, a double-stranded polymer is formed as confirmed by the characteristic S-like form of its melting curve. However, the melting temperature of this polymer is lower than that of the free poly(rA)poly(rU) duplex. This result indicates that poly(rU) hybridization with poly(rA)(NT) occurs with defects along the whole length of the polymer because of pi-pi stacking between nitrogen bases and the nanotube surface, which hinders the usual hybridization process. Computer modeling demonstrates different possible structures of hybridized polymers on the nanotube surface.

Preparation and characterization of a dye–ligand adsorbent for lysozyme adsorption

Abstract Dye–ligand macroreticular poly(styrene- co -divinylbenzene) microparticles with different pore properties have been obtained and used as adsorbents of proteins. To do so, plain microparticles were first coated with poly(vinyl alcohol) to shield the hydrophobic polymer surface from non-specifically adsorbing protein. The poly(vinyl alcohol) coating was then chemically cross-linked with glutaraldehyde to obtain a stable layer. Following this, Cibacron Blue F3GA, which was chosen as the dye affinity ligand, was immobilized on these microparticles to obtain specific protein adsorption. After each modification step, the pore size distributions of the microparticles were determined, observing that the adsorption of poly(vinyl alcohol) clogged micropores and low-interval mesopores, and that only microparticles with a high pore volume, basically due to high-interval mesopores and macropores, largely continued to exhibit these pores. The batch adsorption properties of the functionalized microparticles were studied using lysozyme as a model protein, observing that the existence of high-interval mesopores and macropores was essential in the adsorption of the protein. In fact, it was only possible to evaluate the adsorption characteristics in the case of microparticles that largely continued to display this kind of pores after their functionalization. Adsorption equilibrium was found to be described well by the Sips model, with a maximum adsorption capacity of 100.8 mg g −1 dry adsorbent. With regard to adsorption kinetics, both pore-diffusion and solid-diffusion models were used to estimate the diffusion coefficients, with the observation that the simplified solid-diffusion model was reliable for describing the experimental kinetic data, with a diffusion coefficient of 1.4 × 10 −9 cm 2 s −1 . The non-specific adsorption of lysozyme on the functionalized microparticles was found to be 2.6 mg g −1 dry adsorbent. Finally, regarding desorption of the protein, it was observed that more than 73% of the lysozyme adsorbed was readily desorbed in a desorption medium containing 1.0 mol L −1 NaCl at pH 7.3.

Adsorption of polyanions on nanostructured polypyrrole submonolayer grafted on semiconducting transparent support

Polypyrrole submonolayers are formed on three different supports: indium oxide (In2O3), indium tin oxide (ITO) and tin oxide (SnO2). It is seen that this formation is a function of the nature of the substrates. Nanometric film scale has been checked by AFM measurements. These polypyrrole submonolayers allowed self-assembling with polyoxometalate \( {\text{SiMo}}_{{{\text{12}}}} {\text{O}}^{{{\text{4}} - }}_{{{\text{40}}}} \) and played a determining role in the adsorption characteristics.

The adsorption of poly (vinyl alcohol) on the hydroxylated β-cristobalite

The adsorption of poly (vinyl alcohol) with different chain lengths on a hydroxylated β-cristobalite (100) surface is studied via molecular simulations. The relative dielectric constant is selected to be 1 and 78 to mimic in vacuum and in solution environment, respectively. Different configurations and dynamic properties are found in the two absolutely different environments, showing that the solvent condition plays an important role in the process of chain adsorption and diffusion on a surface. In equilibrium, the chain possesses (partial) ordered configuration in vacuum condition.

Selective Hydrogenation of Monosubstituted Alkenes by Pd Nanoparticles Embedded in Polyelectrolyte Films

Pd nanoparticles embedded in multilayer polyelectrolyte films can be easily prepared through layer-by-layer adsorption of poly(acrylic acid) (PAA) and poly(ethyleneimine)-Pd2+ (PEI-Pd(II)) complexes followed by reduction of Pd(II) with NaBH4. Transmission electron microscopy confirms the formation of Pd particles with diameters of 1-3 nm. Remarkably, [PAA/PEI-Pd(0)]3PAA films catalyze the hydrogenation of monosubstituted alkenes with turnover frequencies that are as much as 100-fold higher than turnover frequencies for hydrogenation of multiply substituted double bonds. Selectivities in the hydrogenation of monosubstituted over multisubstituted double bonds are higher than those of Wilkinson's catalyst. Moreover, the turnover frequency for the hydrogenation of allyl alcohol did not change when the catalyst was recycled three times. Intramolecular selectivity for the hydrogenation of monosubstituted alkenes also occurs when substrate molecules contain both mono and multiply substituted double bonds. The combination of the encapsulating polyelectrolyte film and small nanoparticles apparently results in hindered access of multiply substituted double bonds to catalytic sites.

Fabrication and Elimination of PTAA/P4VP Layer-By-Layer Films

Layer-by-layer (LBL) ultra-thin films have been assembled by alternate adsorption of poly(3-thiophene acetic acid) (PTAA) and poly(4-vinyl-pyridine) (P4VP) on planar quartz slides via hydrogen-bonding interaction. Subsequently, the multilayers can be controllably removed by changing the pH values of the aqueous solutions used for film immersion. Our present study is an attempt to reveal the mechanisms of the multilayer film with two-dimensional (2D) ultraviolet-visible (UV-vis) correlation spectroscopy. UV-vis spectroscopy is primarily employed here to monitor the buildup and removal of the ultra-thin films. 2D correlation analysis is performed on the basis of the corresponding spectra for further studies. The morphology of the multilayer film is characterized by atomic force microscopy (AFM). When eliminated in alkaline and acidic aqueous solutions, the polymers in the films show diverse phenomena mainly due to the different extents of dissociation of PTAA and protonation of P4VP at different pH values. In alkaline solution, the elimination of PTAA takes place before P4VP, while in acid solution, the removal of these two polymers adopts a reverse order.

Adsorption of poly( N-isopropylacrylamide- co-4-vinylpyridine) onto core–shell poly(styrene- co-methylacrylic acid) microspheres

Adsorption of the thermoresponsive copolymer of poly( N-isopropylacrylamide- co-4-vinylpyridine) (PNIPAM- co-P4VP) onto the core–shell microspheres of poly(styrene- co-methylacrylic acid) (PS- co-PMAA) is studied. The core–shell PS- co-PMAA microspheres are synthesized by one-stage soap-free polymerization in water. The copolymer of PNIPAM- co-P4VP is synthesized by free radical polymerization of N-isopropylacrylamide and 4-vinylpyridine in the mixture of DMF and water using K 2S 2O 8 as initiator. Adsorption of PNIPAM- co-P4VP onto the core–shell PS- co-PMAA microspheres results in formation of the composite microspheres of PS/PMAA–P4VP/PNIPAM. The driven force to adsorb the copolymer of P4VP- co-PNIPAM onto the core–shell PS- co-PMAA microspheres is ascribed to hydrogen-bonding and electrostatic affinity between the P4VP and PMAA segments. The resultant composite microspheres of PS/PMAA–P4VP/PNIPAM with surface chains of PNIPAM are thermoresponsive in water and show a cloud-point temperature at about 33 °C.

Adsorption of Poly(amido amine) (PAMAM) Dendrimers on Silica: Importance of Electrostatic Three-Body Attraction

Adsorption of poly(amido amine) (PAMAM) dendrimers to silicon oxide surfaces was studied as a function of pH, ionic strength, and dendrimer generation. By combining optical reflectometry and atomic force microscopy (AFM), the adsorbed layers can be fully characterized and an unequivocal determination of the adsorbed mass becomes possible. For early stages, the adsorption process is transport limited and of first order with respect to the dendrimer solution concentration. For later stages, the surface saturates and the adsorbed dendrimers form loose but correlated liquidlike surface structures. This correlation is evidenced by a peak in the pair correlation function determined by AFM. The maximum adsorbed amount increases with increasing ionic strength and pH. The increase with the ionic strength is explained by the random sequential adsorption (RSA) model and electrostatic repulsion between the dendrimers. The adsorbing dendrimers interact by the repulsive screened Coulomb potential, whose range decreases with increasing ionic strength and thus leads to increasing adsorbed densities. The pH increase is interpreted as an effect of the substrate and is quantitatively explained by the extended three-body RSA model. This model stipulates the importance of a three-body interaction acting between two adsorbing dendrimers and the charged substrate. The presence of the charged substrate weakens the repulsion between the adsorbing dendrimers and thus leads to higher surface densities. This effect can be interpreted as an additional attractive three-body interaction, which acts in addition to the usual two-body repulsion and originates from the additional screening of the Coulomb repulsion by the counterions accumulating in the diffuse layer.

Multilayer polyelectrolyte films as nanofiltration membranes for separating monovalent and divalent cations

Alternating adsorption of polyanions and polycations on porous supports provides a convenient way to prepare ion-selective nanofiltration membranes. This work examines optimization of ultrathin, multilayer polyelectrolyte films for monovalent/divalent cation separations relevant to water softening. Membranes composed of five bilayers of poly(styrene sulfonate)/poly(allylamine hydrochloride) (PSS/PAH) on porous alumina supports allow a solution flux of 0.85 m 3/(m 2 day) at 4.8 bar, and exhibit 95% rejection of MgCl 2 along with a Na +/Mg 2+ selectivity of 22. Similar results were obtained in Na +/Ca 2+ separations. PSS/poly(diallyl-dimethylammonium chloride) (PDADMAC) films permit higher fluxes than PSS/PAH systems due to the higher swelling of films containing PDADMAC, but the Mg 2+ rejection by PSS/PDADMAC membranes is less than 45%. However, capping PSS/PDADMAC films with a bilayer of PSS/PAH yields Mg 2+ rejections and Na +/Mg 2+ selectivities that are typical of pure PSS/PAH membranes. Separation performance can be optimized through control over deposition conditions (pH and supporting electrolyte concentration) and the charge of the outer layer since Donnan exclusion is a major factor in monovalent/divalent cation selectivity. Streaming potential measurements demonstrate that the magnitude of positive surface charge increases with increasing concentrations of Mg 2+ in solution or when the outer polycation layer is deposited from a solution of high ionic strength.

Multilayer PVA adsorption onto hydrophobic drug substrates to engineer drug-rich microparticles

Despite the availability of numerous crystal engineering techniques, generating drug-rich microparticles with a predetermined size, morphology and crystallinity still represents a significant challenge. A microparticle manufacturing method has recently been developed that attempts to ‘shield’ the physicochemical properties of micronised drugs by the application of a microfine polymer coating. The aims of this study were to investigate the nature of the drug–polymer interactions and determine the effects of this manufacturing strategy upon release of the drug from the microparticles. The adsorption of poly(vinyl alcohol) (PVA) on the micronised hydrophobic drug surface was found to reach equilibrium between 23 and 27 h. The Freundlich isotherm model was shown to give the most accurate fit to the experimental data and thus multilayer adsorption was assumed. The adsorptive capacity (1/ n) was specific to the substrate and PVA grade. An increase in the PVA (%) hydrolysis value caused 1/ n to increase from 0.76 to 1.05 using budesonide and from 0.31 to 0.79 when betamethasone valerate (BMV) was used. Increasing the molecular weight of the adsorbing polymer caused a reduction in the strength of PVA–adsorbate interaction when budesonide was used as the substrate (from 0.76 to 0.59), whereas a three-fold increase (from 0.31 to 0.86) was achieved when the BMV substrate was employed. A proportion of the adsorbed polymer was shown to remain associated with the substrate during the spray-drying process and the polymer coating resulted in a significantly higher ( p < 0.05, ANOVA) amount of drug release in 60 min (ca. 100%) compared to budesonide alone.

Laser reflectometry to investigate adsorption–desorption of poly(styrene sulfonate) onto polyamide 6.6

The adsorption of poly(styrene sulfonate) (PSS) on polyamide 6-6 was investigated using fixed angle laser reflectometry. The appropriate polyamide film thickness for an accurate analysis was first determined theoretically. Polyamide films were further prepared at controlled thickness using dip-coating processes and characterized. The adsorption of PSS was measured at pH 3 on dip-coated films as a function of time and polymer concentration. The adsorption rate at very low polymer coverage revealed diffusion limited adsorption. At and above pH 10, the PSS adsorption/desorption was difficult to evaluate. At and above pH 11.5, the hydrolysis of polyamide produced artifacts that prevent any meaningful measurements. This work showed that reflectometry is an interesting analytical tool in the in situ study of the functionalization of organic materials and to investigate the stability of the films produced.

Facile and controllable synthesis of polyoxometalate nanorods within polyelectrolyte matrix

Well dispersed polyoxometalate nanorods have been selectively and controllably synthesized within the polyelectrolyte (PE) films via a layer-by-layer (LbL) adsorption–precipitation method. The PE matrix was fabricated by LbL self-assembly technology and then the multilayer films containing polyoxometalate nanorods were constructed by repetitive adsorption of polyanions and subsequent precipitation with counter ions-tetraethylammonium bromide (TEAB). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) was used to observe the variation of size and morphology of the nanorods. The growth process and composition of the multilayer films containing nanorods were also studied.

Absorbency and adsorption of poly(acrylic acid‐co‐acrylamide) hydrogel

AbstractPoly(acrylic acid‐co‐acrylamide) (PAAAM) hydrogels have been prepared from partly neutralized acrylic acid (AA) and acrylamide (AM) by solution polymerization, and their absorbency and adsorption in both CuCl2 and FeCl3 solutions have been investigated. PAAAM hydrogels and their complexes with Cu2+ or Fe3+ have been characterized by FTIR. The absorbency of PAAAM in both CuCl2 and FeCl3 solutions increases initially and then decreases as the absorbing time increases. The adsorption of PAAAM in both CuCl2 and FeCl3 solutions can be described by the pseudo‐second order chemisorption kinetics proposed by Ho and McKay, and the equilibrium uptake of Cu2+ on PAAAM can well be fit with the Langmuir adsorption isotherm. However, the equilibrium uptake of Fe3+ on PAAAM increases as the initial Fe3+ concentration increases for Fe3+ concentration smaller than 5.625 × 10−3 mol/L, and then decreases with Fe3+ concentration. The largest uptakes for Cu2+ and Fe3+ are 247 and 173 mg/g, respectively. The results also show that the uptake of Cu2+ and Fe3+ on PAAAM increases remarkably when pH of the solution is changed from 2.3 to 4.2 and from 1.0 and 2.1, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Adsorption of poly(ethylene oxide) with different molecular weights on the surface of silica nanoparticles and the suspension stability

Adsorption of poly(ethylene oxide) (PEO) with different molecular weights (Mws) in aqueous suspension on the surface of silica nanoparticles and the stability of suspension dispersion were studied. Adsorption isotherms demonstrate that the plateau-adsorbed amount of polymer is related to Mw. Results of infrared analysis indicate that PEO is adsorbed on silica through a hydrogen bonding between –SiOH and ether oxygen of PEO molecule. The change in |ζ| of silica suspensions after adsorption varies distinctly with different Mw, and the main factors responsible for the changes and the stability mechanisms of suspension were discussed. Using the appropriate Mw PEO, a highly stabilized dispersion can be achieved at a certain concentration.

Ion Distribution in Polyelectrolyte Multilayers with Standing-Wave X-ray Fluorescence

Absolute ion concentration and its profile across polyelectrolyte multilayer films were studied. The films were prepared by alternating adsorption of polyanions and polycations from aqueous solution. Standing-wave X-ray fluorescence was used to map the ion profile. The well-studied multilayer system PSS/PAH was investigated, and bromide ions were used as probe entities. The results show that the sign of the charge of the outermost layer and the washing procedure after finishing the preparation have a decisive effect on the ion concentration and the ion profile. Multilayers with PSS as the outermost layer contain fewer bromide ions than the PAH-terminated multilayers. Exposure to water washes the ions out, but even after 6 h of washing, not all of the bromide ions had been removed.

Adsorption of poly(ethylene oxide)– block–polylactide copolymers on polylactide as studied by ATR-FTIR spectroscopy

In this study, the adsorption of amphiphilic poly(ethylene oxide)– block–polylactide (mPEO–PLA) copolymers from a selective solvent onto a polylactide surface was studied as a method of polylactide surface modification and its effect on nonspecific protein adsorption was evaluated. A series of well defined mPEO–PLA copolymers was prepared to investigate the effect of copolymer composition on the resulting PEO chain density and on the surface resistance to protein adsorption. The copolymers contained PEO blocks with molecular weights ranging between 5600 and 23,800 and with 16–47 wt% of PLA. The adsorption of both the copolymers and bovine serum albumin was quantified by attenuated total reflection FTIR spectroscopy (ATR-FTIR). In addition to the adsorbed copolymer amount, its actual composition was determined. The PEO chain density on the surface was found to decrease with the molecular weight of the PEO block and to increase with the molecular weight of the PLA block. The adsorbed copolymers displayed the ability to reduce protein adsorption. The maximum reduction within the tested series (by 80%) was achieved with the copolymer containing PEO of MW 5600 and a PLA block of the same MW.

Thin adsorbed films of a strong cationic polyelectrolyte on silica substrates

The adsorption of poly(diallyldimethyl ammonium chloride) (DADMAC) on planar silica substrates was examined as a function of ionic strength and pH. The study was carried out with reflectometry in an impinging-jet cell and complemented by atomic force microscopy (AFM) and ellipsometry investigations. The adsorption process is initially transport limited, whereby the adsorption rate increases somewhat with increasing ionic strength. This effect is caused by a simultaneous decrease of the hydrodynamic radius of the polymer. After a transient period, the adsorption process saturates and leads to an adsorption plateau. The plateau value increases strongly with increasing ionic strength. This increase can be explained by progressive screening of the electrostatic repulsion between the adsorbing polyelectrolyte chains, as can be rationalized by a random sequential adsorption (RSA) model. The adsorbed amount further increases with increasing pH, and this effect is probably caused by the corresponding increase of the surface charge of the silica substrate.

Control of Specific Attachment of Proteins by Adsorption of Polymer Layers

This study concerns the design of protein-resistant polymer adsorbed layers for the control of surface binding of biospecific recognition entities. Polymer surface layers were prepared using the adsorption of poly(allylamine hydrochloride) (PAH), poly(l-lysine) (PL), and branched and linear polyethyleneimine (PEI) and further modified by the covalent attachment of biotin for specific avidin attachment. The adsorption of PAH, PL, and PEI on silicon substrates was studied as a function of pH and ionic strength using ellipsometry. Average dry layer thicknesses of approximately 10, approximately 5, approximately 9, and approximately 3 A (+/-1 A) were obtained when polymer adsorption occurred from solutions at pH 9.5 that contained 0.5 M NaCl for PAH, PL, branched PEI, and linear PEI, respectively. These polymers showed significant differences in their efficiency to suppress nonspecific avidin adsorption. At low ionic strength, avidin adsorption occurred on all polymer-coated surfaces at basic pH values, despite the same positive electrostatic charge for protein globules and the surface. Though the net electrostatic repulsion between avidin molecules and branched PEI was efficiently screened in a protein solution of pH 7 and 0.15 M NaCl, branched-PEI coatings of high molecular weight were unique in their ability to provide avidin-resistant surfaces as a result of steric hindrance from the branched architecture of adsorbed polymer chains. All polymers studied were effective in suppressing avidin adsorption at pH 3 as a result of protonation of the avidin surface functional groups at this pH. Branched-PEI-coated surfaces were also effective for the suppression of smaller positively charged proteins such as lysozyme and ribonuclease A at pH 7 and 0.15 M NaCl. They were also resistant to the adsorption of negatively charged proteins such as BSA and fibrinogen at pH 7 and 0.75 M NaCl. Furthermore, by using PEI-modified protein-repellent surfaces, selective binding of avidin was achieved to surface-bound silver nanoparticles, which should provide a promising application for the label-free detection of biological species using surface-enhanced Raman scattering (SERS).

Study of the Influence of Temperature and the Ionic Strength of the Solution on the Adsorption and Conformation of Poly(Acrylic Acid) Macromolecules on the ZrO2Surface

The influence of temperature and the ionic strength of the solution on the adsorption of poly(acrylic acid) (PAA) and the structure of the corresponding adsorbed layers on a zirconium dioxide surface were studied. All measurements (spectrophotometric, electrokinetic, viscosity and potentiometric titrations) were carried out within the temperature range 15–40°C. The methods used allowed the amount of polymer adsorbed, the surface charge and diffuse layer charge of the ZrO2 particles in the absence and presence of the polymer, as well as the thickness of the polymer adsorption layers, to be determined.The adsorption measurements demonstrated the occurrence of a minimum in PAA adsorption over the temperature range 25–30°C caused by conformational changes of the polymer macromolecules. In addition, an increase in polymer adsorption and a decrease in the thickness of the polymer adsorption layers were observed as the ionic strength of the solution increased. This was due to the fact that the repulsion interact...