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Query: HUMANGGP:040202 (PSS)
 2,978 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effect of solvent conditions on the growth of polyelectrolyte (PE) multilayer films comprising poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate sodium salt) (PSS) on planar substrates was investigated by means of surface plasmon resonance spectroscopy (SPRS), quartz crystal microbalance (QCM), and atomic force microscopy techniques. The solvent quality was varied by the addition of ethanol to the PE solutions used for deposition of the layers, thus tuning the relative strength of electrostatic and secondary intermolecular and intramolecular interactions. Experiments were performed with PE solutions both without added electrolyte and containing 0.5 M NaCl. Decreasing the solvent quality (i.e., increasing the amount of ethanol in the adsorption solution) resulted in a marked increase of both the multilayer film thickness and mass loading, as determined from the SPRS spectra and QCM frequency shifts, respectively. With the solution composition approaching the precipitation point, thick PAH/PSS films were formed due to the screening of the electrostatic intra- and interchain repulsions and enhanced hydrophobic interactions between the polyelectrolyte chains. However, the films formed from water/ethanol mixtures remained stable upon subsequent exposure to water or salt-containing solutions: no significant film desorption occurred after up to 24 h of exposure to water or 0.5 M NaCl solutions. In addition, the effect of postdeposition exposure to water/ethanol mixtures was investigated for PE multilayers assembled from aqueous solutions. In this case, the optical thickness of the films was determined during exposure to water/ethanol mixtures, and instead of swelling, the polyelectrolyte films collapse to the surface as a result of the unfavorable segment-solvent interactions.
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PMID:Influence of solvent quality on the growth of polyelectrolyte multilayers. 1577 11

The adsorption and complexation of polystyrene sulfonate (a highly charged anionic polyelectrolyte) and a series of cationic surfactants, alkyltrimethylammonium bromide, CnTAB, n = 8-16, at the air-water interface has been studied by combining surface tension and ellipsometry measurements. We find that increasing the chain length of the surfactant from 8 to 10 carbons leads to a sharp increase in adsorption of PSS/CnTAB complexes. When the surfactant tail length is further increased to 12 and 14 carbons, surface adsorption becomes less favored than macroscopic phase separation, resulting in a partial surface depletion. Furthermore, we find that when surface tensions are plotted against surfactant/monomer molar concentration ratio, all data collapse to a single curve. This result shows that the surfactant-polymer molar ratio, s/p, is a key parameter for tuning the surface activity of the complexes formed.
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PMID:Interfacial microgels formed by oppositely charged polyelectrolytes and surfactants. Part 2. Influence of surfactant chain length and surfactant/polymer ratio. 1598 75

We consider the interaction of multivalent counterions with spherical polyelectrolyte brushes (SPB). The SPB result if linear polyelectrolyte (PE) chains (contour length: 60 nm) are densely grafted to colloidal spheres of 116 nm in diameter. Dispersed in water, the surface layer consisting of chains of the strong PE poly(styrene sulfonic acid) (PSS) will swell. We demonstrate that successive addition of trivalent ions (La3+) leads to a collapse in which the surface layer is shrinking drastically. All findings are discussed on the base of a theoretical mean-field approach using the Donnan equilibrium. The ion exchange and a strong binding of trivalent ions by PE chains is followed up by a drop in the osmotic pressure inside the brush. This reduction is the driving force for the collapse. The strong ion-chain correlation is discussed with results obtained from molecular dynamics simulations.
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PMID:Collapse of spherical polyelectrolyte brushes in the presence of multivalent counterions. 1715 65

The formation of a complex between an anionic spherical polyelectrolyte brush (SPB) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) is investigated. The SPB consists of long chains of the strong polyelectrolyte poly(styrene sulfonate) (PSS), which are bound chemically to a solid poly(styrene) core of 56 nm in radius. The SPB are dispersed in water, and the ionic strength is adjusted by addition of NaBr. The resulting complexes are investigated in dilute solution by dynamic light scattering, by electrophoretic light scattering, and by cryogenic transmission electron microscopy (cryo-TEM). The formation of the complex between the SPB and the surfactant can be monitored by a strong shrinking of the surface layer when adding CTAB to dilute suspensions (0.01 wt %) and by a decrease of the effective charge of the complexes. Complex formation starts at CTAB concentrations lower than the critical micelle concentration of this surfactant. If the ratio r of the charges on the SPB to the charge of the added surfactant is exceeding unity, the particles start to flocculate. Cryo-TEM images of the complexes at r = 0.6 measured in salt-free solution show that the surface layer composed of the PSS chains and the adsorbed CTAB molecules is partially collapsed: A part of the chains form a dense surface layer while another part of the chains or aggregates thereof are still sticking out. This can be deduced from the cryo-TEM micrographs as well as from the hydrodynamic radius, which is still of appreciable magnitude. The 1:1 complex (r = 1.0) exhibits a fully collapsed layer formed by the PSS chains and CTAB. If the complex is formed in the presence of 0.05 M NaBr, r = 0.6 leads to globular structures directly attached to the surface of the core particles. All structures seen in the cryo-TEM images can be explained by a collapse transition of the surface layer brought about by the hydrophobic attraction between the polyelectrolyte chains that became partially hydrophobic through adsorption of CTAB.
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PMID:Binding of oppositely charged surfactants to spherical polyelectrolyte brushes: a study by cryogenic transmission electron microscopy. 1731 35

We present a study on water-soluble interpolyelectrolyte complexes (IPECs) formed by cationic cylindrical polyelectrolyte brushes (CPBs) and linear anionic poly(sodium styrenesulfonate) (PSSNa) using atomic force microscopy (AFM). The IPECs were prepared by dialysis of salt-containing solutions of the two polymeric components. The morphologies of the IPECs could be tuned by changing the charge ratio between the two polyelectrolytes, Z(-/+). Addition of increasing numbers of short PSSNa chains induced morphology changes of host CPBs from worms through intermediate pearl-necklace structures to fully collapsed spheres. Extremely long guest PSSNa caused the full collapse of the brushes to spheres even at very low charge ratios without intermediate states. In both cases we observe "disproportionation", that is, inhomogeneous distribution of the PSS chains between the CPB for Z(-/+) < 1. Unexpected micrometer-scale core-shell cylindrical objects were found by directly mixing CPBs with long PSSNa, which might be nonequilibrium structures caused by the kinetically controlled IPEC formation.
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PMID:Manipulating the morphologies of cylindrical polyelectrolyte brushes by forming interpolyelectrolyte complexes with oppositely charged linear polyelectrolytes: an AFM study. 2022 89

Atomic force microscopy, AFM, and nanoindentation of polyelectrolyte multilayers, PEMUs, made from poly(diallyldimethylammonium), PDADMA, and poly(styrene sulfonate), PSS, provided new insight into their surface morphology and growth mechanism. A strong odd/even alternation of surface modulus revealed greater extrinsic (counterion-balanced) charge compensation for fully hydrated multilayers ending in the polycation, PDADMA. These swings in modulus indicate a much more asymmetric layer-by-layer growth mechanism than previously proposed. Viscoelastic properties of the PEMU, which may contribute to cell response, were highlighted by variable indentation rates and minimized by extrapolating to zero indentation rate, at which point the surface and bulk equilibrium moduli were comparable. Variations in surface composition were probed at high resolution using force mapping, and the surface was found to be uniform, with no evidence of phase separation. AFM comparison of wet and dry films terminated with PSS and PDADMA revealed much greater swelling of the PDADMA-terminated PEMU by water, with collapse of surface roughness features in dry conditions. Dynamic and static contact angle measurements suggested less rearrangement for the glassy PSS surface.
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PMID:Homogeneity, modulus, and viscoelasticity of polyelectrolyte multilayers by nanoindentation: refining the buildup mechanism. 2248 Mar 7

Macromolecular characteristics and morphology of water-soluble complexes between sodium poly(styrene sulfonate) (PSS) and tetradecyltrimethylammonium bromide have been followed as a function of surfactant-to-polymer charge ratio (S/P) to elicit possible changes in the complexation mechanism. As revealed by light scattering, shorter PSS (30 and 150 repeat units) yield multichain complexes while longer PSS (450 and 5000 repeat units) form single-chain species throughout 0 < S/P < 0.9. Irrespective of PSS chain length, the complexes exist in solution in a swollen coil conformation and undergo a compaction with S/P but never collapse into a globule. Even when the free PSS chain is too short to coil (30 repeat units), the complexes adopt a coiled conformation due to multichain aggregation. Morphological changes (manifested by a hypochromic shift in UV spectra of the complexes at S/P < 0.5 and an increase in the local surfactant mobility observed at S/P > 0.5 by ESR) strongly suggest a change in the formation mechanism of the complexes with a transition near S/P = 0.5.
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PMID:Macromolecular and morphological evolution of poly(styrene sulfonate) complexes with tetradecyltrimethylammonium bromide. 2299 69

Reflectometry and quartz crystal microbalance are used to study the response of adsorbed polyelectrolyte monolayers to solutions of variable composition. These techniques respectively yield the dry and wet masses of the adsorbed layer, and by combing these results, one obtains the water content and the thickness of the polyelectrolyte films. The systems investigated are films of adsorbed poly(allyl amine) (PAH) and poly-L-lysine (PLL) on silica and films of poly(styrene sulfonate) (PSS) on amino-functionalized silica. When such films are adsorbed from concentrated polyelectrolyte solutions containing high levels of salt, they are found to swell reversibly up to a factor of 2 when incubated in solutions of low salt. This swelling is attributed to the strengthening of repulsive electrostatic interactions between the adsorbed polyelectrolyte chains. PAH films may also swell upon decrease of pH, and collapse upon a pH increase. This transition shows a marked hysteresis and can be rationalized by the competition of electrostatic repulsions between the chains and their attraction to the surface. The presently observed swelling phenomena are caused by a collective process driven by the electrostatic repulsion between the densely adsorbed polyelectrolyte chains. Such responsive layers are only obtained by adsorption from high polyelectrolyte and salt concentrations. Layers absorbed at low polyelectrolyte and salt concentrations show only minor swelling effects, since the adsorbed polyelectrolytes layers are dilute and the adsorbed polyelectrolyte chains interact only weakly.
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PMID:Response of adsorbed polyelectrolyte monolayers to changes in solution composition. 2317 Dec 42

We have investigated changes in the cation-specific conformational behavior of poly(sodium styrenesulfonate) (PSS) brushes as the solvent changes from water to methanol using a quartz crystal microbalance with dissipation (QCM-D). A solvation to desolvation transition of the grafted chains accompanied by swelling to the collapse transition of the brushes is observed for Na(+). In the case of Cs(+), the brushes undergo solvation to desolvation to resolvation accompanied by swelling to collapse to reswelling transitions. The resolvation and reswelling transitions for Cs(+) are induced by the charge inversion of the brushes via van der Waals interactions between Cs(+) and the brushes. All of the transitions for monovalent cations become less obvious as the methanol content increases. For divalent Ca(2+) and trivalent La(3+), a solvation to desolvation to resolvation transition of the grafted chains accompanied by a swelling to collapse to reswelling transition of the brushes can be observed. The resolvation and reswelling of the brushes for the multivalent cations are induced by the charge inversion of the brushes via charge-image charge interactions. The extent of the transitions for the PSS brushes in the presence of multivalent cations is only slightly influenced by the methanol content.
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PMID:Cation-specific conformational behavior of polyelectrolyte brushes: from aqueous to nonaqueous solvent. 2530 Apr 30

The complex interaction of polyelectrolyte multilayers (PEMs) physisorbed onto end-grafted polymer brushes with focus on the temperature-responsive behavior of the system is addressed in this work. The investigated brush/multilayer composite consists of a poly(styrene sulfonate)/poly(diallyldimethylammonium chloride) (PSS/PDADMAC) multilayer deposited onto the poly(N-isopropylacrylamide-b-dimethylaminoethyl methacrylate) P(NIPAM-b-DMAEMA) brush. Ellipsometry and neutron reflectometry were used to monitor the brush collapse with the thickness decrease as a function of temperature and the change in the monomer distribution perpendicular to the substrate at temperatures below, across and above the phase transition, respectively. It was found that the adsorption of PEMs onto polymer brushes had a hydrophobization effect on PDMAEMA, inducing the shift of its phase transition to lower temperatures, but without suppressing its temperature-responsiveness. Moreover, the diffusion of the free polyelectrolyte chains inside the charged brush was proved by comparing the neutron scattering length density profile of pure and the corresponding PEM-capped brushes, eased by the enhanced contrast between hydrogenated brushes and deuterated PSS chains. The results presented herein demonstrate the possibility of combining a temperature-responsive brush with polyelectrolyte multilayers without quenching the responsive behavior, even though significant interpolyelectrolyte interactions are present. This is of importance for the design of multicompartment coatings, where the brush can be used as a reservoir for the controlled release of substances and the multilayer on the top as a membrane to control the diffusion in/out by applying different stimuli.
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PMID:Temperature responsive behavior of polymer brush/polyelectrolyte multilayer composites. 2661 42


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