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Query: UMLS:C1832588 (PSS)
 2,979 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The conformation of poly(styrene sulfonate) (PSS) layers physisorbed from 1 M NaCl is determined by force measurements and imaging on two length scales. With colloidal probe technique steric forces as predicted for neutral grafted brushes are observed. On decrease and increase of the NaCl concentration, the grafting density remains constant, yet the brush thickness swells and shrinks reversibly with the salt concentration with an exponent of -0.3. At low salt conditions, the brush length amounts to 30% of the contour length, a behavior known for polyelectrolyte brushes and attributed to the entropy of the counterions trapped in the brush. Between a PSS layer and a pure colloidal silica sphere, the same steric forces are observed, and additionally at large separations (beyond the range of the steric repulsion) an electrostatic force is found. A negatively charged AFM tip penetrates the brush--a repulsive electrostatic force between the tip and surface is found, and single chains can be imaged. Thus, with the nanometer-sized AFM tip, the flatly adsorbed fraction of the PSS chains is seen, whereas the micrometer-sized colloidal probe interacts with the fraction of the chains penetrating into solution.
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PMID:Conformation of poly(styrene sulfonate) layers physisorbed from high salt solution studied by force measurements on two different length scales. 1862 Apr 52

The electrostatically driven binding dynamics of a polyelectrolyte multilayer (PEMU) film was investigated in real-time using dual-beam polarization interferometry (DPI) and independently supported by quartz crystal microbalance with dissipation monitoring (QCM-D) studies. Multilayer assemblies of the polyanions poly[1-[4[(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl sodium salt] (PAZO) and poly(styrene sulfonate) (PSS) were respectively constructed with the polycation poly(ethylenimine) (PEI) on anionic functionalized substrates using the layer-by-layer electrostatic self-assembly method. DPI measurements indicate that polyelectrolyte adsorption occurs in three distinct stages. In the first stage, for approximately 5 s, coil-like segments of polyanion partially tether to the surface of the oppositely charged PEI. In the second stage, these coils unfurl over a period of approximately 10 s to cover the surface resulting in an increase in average density of the film. During the final adsorption step, the surface-bound polyelectrolyte diffuses into the multilayer assembly, exposing the surface to further deposition. This last step occurs over a much longer time period and results in a highly interpenetrated film containing a charge-overcompensated region at the film surface.
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PMID:Dual-beam polarization interferometry resolves mechanistic aspects of polyelectrolyte adsorption. 1878 89

Compression of the polyelectrolyte multilayers has been found previously when they were pressed by a poly(dimethylsiloxane) (PDMS) stamp under a small pressure (Macromolecules 2004, 37, 8836). In this work, we further found that the pattern formation of the poly(diallyldimethylammonium chloride) (PDADMAC) containing multilayers is dependent on the drying time of the multilayers prior to compression. After the poly(4-styrenesulfonic acid-co-maleic acid) sodium salt (PSSMA)/PDADMAC multilayers were dried at 70% relative humidity and room temperature for 2, 6, and 12 h, compression of the multilayers by a PDMS stamp with linear patterns obtained double strips, high ridges and linear patterns on the multilayers, respectively. These phenomena were independent of the layer number and salt concentration and could be applied to other PDADMAC containing multilayer systems such as poly(styrene sulfonate) sodium salt (PSS)/PDADMAC and poly(acrylic acid, sodium salt) (PAA)/PDADMAC. A model was suggested to depict the process, and the influence of the water content on the multilayer structure and properties was discussed. The stability experiments revealed that the strips and high ridges obtained at shorter drying time could be erased by incubation in water for 5 h, while the compression created patterns were very stable.
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PMID:Influence of drying time of polyelectrolyte multilayers on the compression-induced pattern formation. 1905 63

The attenuation of endothelium-dependent nitric oxide (NO) mediated vasodilation is a consistent finding in both conduit and resistance vessels during dietary copper (Cu) deficiency. Although the effect is well established, evidence for the mechanism remains circumstantial. This study was designed to determine the relative amount of NO produced in and released from the vascular endothelium. Using the fluorescent NO indicator, 4-amino-5-methylamino-2',7'-difluorofluorescein (DAF-FM), we now demonstrate the effect of a Cu-deficient diet on the production of NO from the endothelium of resistance arterioles. In one group of experiments, control and Cu-chelated lung microvascular endothelial cells (ECs) were used to assay NO production and fluorescence was observed by confocal microscopy. Weanling Sprague-Dawley rats were fed purified diets that were either Cu adequate (6.3 micrograms Cu per gram of food) or Cu deficient (0.3 micrograms Cu per gram of food) for 4 weeks. In the second series of experiments, first-order arterioles were microsurgically isolated from the rat cremaster muscle, cannulated, and pressurized with (3[N-morpholino]propanesulfonic acid) physiologic salt solution (MOPS-PSS). DAF-FM (5 micromol.L-1) was added in the lumen of the vessel to measure NO release. Baseline DAF-FM fluorescence was significantly lower in Cu-chelated ECs than in controls. In response to 10-6 mol.L-1 acetylcholine, fluorescent intensity was significantly less in chelated ECs and in the lumen of Cu-deficient arterioles. The results suggest that production and release of NO by the vascular endothelium is inhibited by a restriction of Cu. This inhibition may account for the attenuated vasodilation previously reported in Cu-deficient rats.
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PMID:Endothelial cell-derived nitric oxide mobilization is attenuated in copper-deficient rats. 1908 64

Quartz crystal microbalance and cyclic voltammetry are used to investigate the influence of the supporting salt of polyelectrolyte solutions on the buildup and the structure of PSS/PAH polyelectrolyte multilayers (PSS: poly(4-styrene sulfonate); PAH: poly(allylamine hydrochloride)). This film constitutes a model polyelectrolyte multilayer system. The supporting electrolytes were sodium salts where the nature of the anion was changed by following the Hofmeister series from cosmotropic to chaotropic anions (F-, Cl-, NO3-, ClO4-). For all the investigated anions, the film thickness increases linearly with the number of deposition steps.Wefind that chaotropic anions lead to larger thickness increments per bilayer during the film buildup than cosmotropic ones, confirming results found on PSS/PDADMA multilayers (PDADMA:poly(diallyldimethylammonium)). Films constituted by more than nine PSS/PAH bilayers are still permeable to hexacyanoferrate(II) ions, Fe(CN)(6)4-, whatever the nature of the supporting salt anion. On the other hand, these films are impermeable to ruthenium(II) hexamine ions, Ru(NH3)(6)2+, after the third PAH layer in the presence of NaF, NaCl, or NaNO3. These results are explained by the presence of an excess of positive charges in the film, which leads to a positive Donnan potential. We find that this potential is more positive when more chaotropic anions are used during the film buildup. We also find that a film constructed in the presence of chaotropic anions swells and becomes more permeable to Fe(CN)(6)4- ions when the film is brought into contact with a solution containing more cosmotropic anions. All our experimental findings can be explained by a strong interaction between chaotropic anions with the NH3+groups of PAH that is equivalent, as far as the multilayer buildup and electrochemical response is concerned, to a deprotonation of PAH as it is observed when the film is constructed at a higher pH. We thus arrive to a coherent explanation of the effect of the nature of the anions of the supporting electrolyte on the polyelectrolyte multilayer. We also find that great care must be taken when investigating polyelectrolyte multilayer films by electrochemical probing because electrochemical reactions involving the probes can appreciably modify the multilayer structure.
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PMID:Effect of the supporting electrolyte anion on the thickness of PSS/PAH multilayer films and on their permeability to an electroactive probe. 1912 5

Layer-by-Layer (LbL) technology recently turned out to be a versatile tool for the encapsulation of bioactive entities. In this study, the factual potential of this technology to encapsulate synthetically valuable biocatalysts, that is enzymes and whole cells expressing a specific catalytic activity, was investigated. The biocatalysts were embedded into a polyelectrolyte multilayer system involving poly(allylamine) hydrochloride (PAH) and poly(styrene sulfonate) sodium salt (PSS). The enzymes were adsorbed to CaCO3 or DEAE-cellulose previous to encapsulation. A slight increase (32%) of the catalytic performance was observed for lipase B from Candida antarctica when four layers of polyelectrolytes were applied. On the whole, however, the residual activity of the investigated enzymes after encapsulation was rather low. Similar results were obtained with whole-cell biocatalysts. It was found that the activity decrease can be attributed to mass transfer restrictions as well as direct interactions between polyelectrolytes and catalytically active molecules. Both effects need to be understood in more detail before LbL technology can be advanced to technically efficient biocatalysis.
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PMID:Encapsulation of synthetically valuable biocatalysts into polyelectrolyte multilayer systems. 1920 47

Multilayers of sodium salt of poly(4-styrene sulfonate) (PSS) and poly(diallyl dimethyl ammonium) chloride (PDADMAC) have been built layer by layer (LbL) both at the solid/aqueous interface (solid supported) and the air/aqueous interface (liquid supported). For the solid-supported multilayers, the adsorption kinetics and the complex shear modulus were measured using a dissipative quartz crystal microbalance and a null ellipsometer. A bubble tensiometer was used to measure the adsorption kinetics and the elasticity modulus of the liquid-supported multilayers. At the solid/aqueous interface, adsorption kinetics changes with the number of adsorbed layers. However, at the air/aqueous interface, PSS dynamics were the same for all adsorbed layers except the first. Conversely, the adsorption kinetics of PDADMAC at the air/water surface differed between those layers close to the interface and those far from it. Multilayers grow at the air/water interface by an intrinsic-charge-compensation process, whereas, for the same ionic strengths, solid-supported layers deposit by the extrinsic-charge-compensation process. No significant differences were found between the recoverable dilational storage modulus of the liquid-supported multilayers and the real part of the shear modulus of the solid-supported ones built at the same ionic strength. The values of the modulus are in the MPa range, which corresponds to gel-like films. This result is in agreement with the strong hydration degree of the LbL films calculated from ellipsometry measurements.
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PMID:Adsorption kinetics and mechanical properties of ultrathin polyelectrolyte multilayers: liquid-supported versus solid-supported films. 1943 76

Polyelectrolyte multilayer films adsorbed on gold surfaces were studied by combined ellipsometric and electrochemical methods. Multilayers were composed of "synthetic" (poly(4-styrenesulfonic acid) ammonium salt (PSS) and poly(allylamine hydrochloride) (PAH) (PSS/PAH)) and "semi-natural" (carboxymethyl cellulose (CMC) and chitosan (CHI) (CMC/CHI)) polyelectrolytes. It was found that only PSS/PAH Layer-by-Layer (LbL) assembled structures result in dense surface confined films that limit permeability of small molecules, such as ferri-/ferrocyanide. The PSS/PAH assemblies can be envisaged as films with pinholes, through which small molecules diffuse. During the LbL deposition process of these films a number of pinholes quickly decay. A representative pinhole diameter was found to be approximately 20 microm, which determines the diffusion of small molecules through LbL films, and yet remains constant when the film consists of a few LbL assembled polyelectrolyte bilayers. CMC/CHI LbL assemblies at gold electrode surfaces give very low density films, which do not limit the diffusion of ferri-/ferrocyanide between the surface of the electrode and the solution.
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PMID:Polymer multilayer film formation studied by in situ ellipsometry and electrochemistry. 1952 Jun 18

We report a general method for incorporation of nanoparticles into polyelectrolyte multilayer (PEM) thin films by utilizing the excess charges and associated counterions present in the PEMs. Silver ions were introduced directly into multilayers assembled from poly(diallyldimethylammonium chloride) (PDDA) and poly(styrene sulfonate) (PSS), (PDDA/PSS)(n), by a rapid ion exchange process, which were then converted into silver nanoparticles via in situ reduction to create composite thin films. The size and the content of the nanoparticles in the film can be tuned by adjusting the ionic strength in the polyelectrolyte solutions used for the assembly. Spatial control over the distribution of the nanoparticles in the PEM was achieved via the use of multilayer heterostructure containing PDDA/PSS bilayer blocks assembled at different salt concentrations. Because excess charges and counterions are always present in any PEM, this approach can be applied to fabricate a wide variety of composite thin films based on electrostatic self-assembly.
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PMID:Incorporation of nanoparticles into polyelectrolyte multilayers via counterion exchange and in situ reduction. 1952 52

The nanostructure and its transition of in a poly(acrylic acid) (PAA) brush in the water surface monolayers of poly(hydrogenated isoprene)-b-poly(acrylic acid) with different block lengths and block ratios were investigated by X-ray reflectivity as a function of surface pressure (brush density) and salt concentration in the subphase. The PAA brush showed the same behavior after salt addition as did the poly(methacrylic acid) (PMAA) brush, which was investigated previously. The brush chains expanded and then shrunk after passing the maximum with increasing added salt concentration. This behavior could be explained by the change in electric charges on the PAA brush chains as was observed on the PMAA brush. The PAA brush chains showed a critical brush density, where there was a transition between the carpet layer only and carpet + brush layer structures, as did the PMAA and poly(styrene sulfonic acid) (PSS) brushes. The critical brush density was about 0.4 chains nm(-2), which was higher than that of the PSS brush, a strong acid brush, and was close to that of the PMAA brush, a weak acid brush. However, the critical brush density of the PAA brush was independent of the hydrophilic chain length whereas that of the PMAA brush decreased with increasing PMAA chain length. In addition, the PAA brush had a thicker carpet layer than the PSS and PMAA brushes. Hence, the mechanism of PAA brush formation was predicted to be different from that of not only the PSS brush (strong acid brush) but also the PMAA brush.
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PMID:Nanostructure of a poly(acrylic acid) brush and its transition in the amphiphilic diblock copolymer monolayer on the water surface. 1958 29


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