Abstract: Polyelectrolyte multilayers of poly(acrylic acid) (PAA) and polyacrylamide (PAAm) were prepared via hydrogen-bonding interactions. These multilayers as assembled were stable at low pH but dissolved quickly in neutral pH water. We developed methods for stabilizing these multilayers to high pH through cross-linking by heating or UV-irradiation. Thermal treatment of the multilayers, which resulted in a partial imidization between carboxylic acid and amide groups, gave the multilayer good stability at high pH. In addition, we introduced photoreactive groups in the multilayer, which rendered the film insoluble after UV irradiation. Using these selective stabilization approaches, we have succeeded in micropatterning these films by ink-jet printing and photolithography to create subtractive patterns.

Abstract: Alternating adsorption of polyethyleneimine−metal ion complexes and polyanions results in the formation of multilayered polyelectrolyte films. Postdeposition reduction of the metal ions by heating or exposure to NaBH4 then yields composite films containing metal nanoparticles. UV/visible spectroscopy and transmission electron microscopy confirm the formation of well-dispersed nanoparticles with sizes (4−30 nm) that depend on the concentration of metal ions initially in the film. These films are effective as both catalysts and antimicrobial coatings.

Abstract: The size of in situ prepared silver nanoparticles and the overall metal concentration within poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) multilayer films are systematically co...

Abstract: The layer-by-layer deposition method to prepare multilayers of polyelectrolytes of alternating charge has been followed in situ by means of optical reflectometry experiments. It turns out that in solutions containing both polyelectrolyte and appropriate salts up to a certain concentration, the regular build up of multilayers is modified and becomes an adsorption/redissolution process. We explain this by taking into account (i) that during the regular multilayer formation process the macromolecules cannot equilibrate, (ii) that the added salt plasticizes the multilayer to a state where the molecules are sufficiently mobile to enable them to equilibrate between the layer and the surrounding solution, and (iii) that the presence of excess polyelectrolyte brings the system to a one-phase region of the polyelectrolyte complex phase diagram, implying that polyelectrolyte complexes must dissolve under these conditions.

Abstract: The influence of poly(lysine) and poly(arginine) on silicate solutions and silica sols has been investigated. In both cases, solid formation could be observed that appeared to depend on the polymer chain length. Polyelectrolytes induced gelation of diluted sodium silicate solutions. Studies of the silicic acid content using the colorimetric molybdosilicate method suggested that polymers act as gelating agents of silica oligomers via electrostatic interactions that favor condensation. In the case of silica sols, quasi-elastic light scattering measurements indicate that particles are first adsorbed on the polymer chain to form aggregates that then flocculate in the presence of additional peptides. Structural characterizations of the solids obtained in both cases were consistent with the proposed models. These results are discussed in the frame of biogenic silica formation at the protein/silica interface.

Abstract: We examine the influence of the charge density along a polyelectrolyte chain on the buildup of multilayer films formed by the sequential adsorption of alternating layers of polyanions and polycations (the layer-by-layer technique). Model random copolymers of diallyldimethylammonium chloride (DADMAC) and N-methyl-N-vinylacetamide (NMVA) having matched molecular weights and varying percentages (24−100%) of the cationic DADMAC component are alternated with polyanionic polystyrene sulfonate (PSS). Multilayer buildup is monitored by UV−vis and FTIR spectroscopies, and with a quartz crystal microbalance (QCM) and is correlated with structural information obtained using atomic force microscopy. When films are deposited from polyelectrolyte solutions containing added salt, a critical charge density limit (between 75% and 53%), below which no significant layer growth is possible, becomes apparent. Below the critical charge density, addition of the polyanion leads to almost complete removal of the previously deposi...

Abstract: The aim of this study was to develop new biocompatible coatings for bone implants by the alternating deposition of oppositely charged polyelectrolytes. Polyelectrolyte films were built up with different terminating layers on which SaOS-2 osteoblast-like cells and human periodontal ligament (PDL) cells were grown. The terminating layer was made of one of the following polyelectrolytes: poly(ethylene imine) (PEI), poly(sodium 4-styrenesulfonate) (PSS), poly(allylamine hydrochloride) (PAH), poly(L-glutamic acid) (PGA), or poly(L-lysine) (PLL). Cell adherence, viability, stability of osteoblast phenotype, and inflammatory response were studied. Adherence and viability were good on all terminating layers except the PEI-terminating layer, which was cytotoxic. Maintenance of osteoblast phenotype marker expression was observed on PSS- and PGA-terminating films for both cell types, whereas downregulation, associated with the induction of Interleukin-8 (IL-8) secretion, was detected on PEI and PAH for both cell types and on PLL for PDL cells. These results suggested a good biocompatibility of PSS- and PGA-ending films for PDL cells and of PSS-, PGA-, and PLL-terminating films for SaOS-2 cells. As a result, polyelectrolyte multilayer films could emerge as new alternatives for implant coatings.

Abstract: We characterize the structures of various polyelectrolyte block copolymer micelles in dilute aqueous solution as a function of pH and ionic strength. The block copolymers carry a common core block, 2-(diethylamino)ethyl methacrylate (DEAEMA), and one of three coronal blocks, 2-(dimethylamino)ethyl methacrylate (DMAEMA), poly(ethylene oxide) (PEO), and DMAEMA, whose side chain amine groups are selectively quaternized with benzyl chloride (Q-DMAEMA). The PEO−DEAEMA, DMAEMA−DEAEMA, and Q-DMAEMA−DEAEMA copolymers form micelles with electrostatically neutral, weakly charged, and highly charged coronae, respectively. We adjust the fractional charge α on the DEAEMA and DMAEMA blocks by adjusting the solution pH. For DMAEMA−DEAEMA micelles increasing the fractional charge α swells the micelle corona while decreasing the aggregation number due to electrostatic repulsions. The decrease in aggregation number is also observed with increasing α for the PEO−DEAEMA and Q-DMAEMA−DEAEMA micelles, due to electrostatic repu...

Abstract: Polyelectrolyte adsorption onto an oppositely charged interface is determined by electrostatic and secondary interactions. Since polyelectrolytes precipitate at elevated temperatures, the secondary interactions are presumably temperature dependent. This idea is tested for poly(allylamine) hydrochloride/polystyrene sulfonate (PAH/PSS) films adsorbed from aqueous KCl solution (high salt conditions) at temperatures between 5 and 40 °C. KCl was chosen because the films were thicker than those obtained from NaCl or CsCl solutions indicating strong specific binding between K and PSS. The film thickness increases continuously with the adsorption temperature; the changes amount to 20−40%, depending on salt conditions. Furthermore, the roughness is increased, up to a factor of 5. The latter is attributed to the decreased percentage of strong electrostatic bonds within the polyelectrolyte multilayer. Another path to increased roughening is using low-weight polymers with a contour length similar to the thickness of ...

Abstract: The influence of thermal treatment on the permeability of polyelectrolyte multilayer capsules is studied via confocal fluorescence microscopy of individual microcapsules. For the specific most frequently used example, capsules made of poly(styrenesulfonic acid) and poly(allylamine hydrochloride), the penetration of fluorescein is shown to be reduced by 3 orders of magnitude on heating at 80 °C. The data show that holes formed during preparation may be annealed in a predictable way.

Abstract: A new approach to create chemically patterned surfaces utilizing polymers and copolymers is introduced. In this approach, chemical patterns are achieved by the direct stamping of functional polymers onto a surface containing complementary functional groups. The resulting pattern is then used as a template for the further deposition of materials on the surface. This concept can be applied to various functional polymer and substrate systems as well as different thin film deposition techniques. This approach is demonstrated with the direct stamping of polystyrene−poly(acrylic acid) block copolymers (PS−PAA) to create alternating hydrophobic/hydrophilic regions and polyelectrolytes to create alternating positively and negatively charged regions. This approach has been used for patterning surfaces and templating materials deposition. When a patterned polyelectrolyte film is used as the base layer or substrate in this process, functionality can be incorporated in the underlying layer, making this approach parti...

Abstract: We show that hydrophobic flexible polyelectrolyte molecules of poly(2-vinylpyridine) and poly(methacryloyloxyethyl dimethylbenzylammonium chloride) are trapped and frozen due to adsorption on the mica surface, and the observed AFM single molecule structures reflect the molecular conformation in solution. An increase of the ionic strength of the solution induces the cascade of abrupt conformational transitions due to the intrachain segregation from elongated coil to compact globule conformations through intermediate pearl necklace-globule conformations with different amounts of beads per chain. The length of the necklaces and the number of beads decrease, while the diameter of beads increases with the increase of ionic strength. Coexistence at the same time of extended coils, necklaces with different amounts of beads, and compact globules indicates the cascade of the first-order-type phase transitions.

Abstract: Because micro-ions accumulate around highly charged colloidal particles in electrolyte solutions, the relevant parameter to compute their interactions is not the bare charge, but an effective (or renormalized) quantity, whose value is sensitive to the geometry of the colloid, the temperature or the presence of added-salt. This nonlinear screening effect is a central feature in the field of colloidal suspensions or polyelectrolyte solutions. We propose a simple method to predict effective charges of highly charged macro-ions, that is reliable for monovalent electrolytes (and counterions) in the colloidal limit (large size compared to both screening length and Bjerrum length). Taking reference to the non linear Poisson–Boltzmann theory, the method is successfully tested against the geometry of the macro-ions, the possible confinement in a Wigner–Seitz cell, and the presence of added salt. Moreover, our results are corroborated by various experimental measures reported in the literature. This approach provid...

Abstract: We report the formation of poly(acrylic acid) (sodium salt) (PAA) and poly(allylamine hydrochloride) (PAH) multilayers on polystyrene (PS) and melamine formaldehyde (MF) colloid particles by the layer-by-layer (LbL) assembly technique. The use of different solution processing conditions (e.g., pH and ionic strength) was found to have a pronounced effect on film growth, with the degree of dissociation of both polyelectrolytes (PEs) playing an important role for regular PAA/PAH multilayer growth. To retain colloidal stability during the sequential adsorption of PEs, it was essential to deposit the PE layers from adsorption solutions where the PEs are in a highly charged state, the degree of which was regulated by varying the pH. Thicker PAA/PAH coatings were obtained when the pH value of the PAA deposition solution was close to the pKa value of PAA in solution. The presence of salt in the deposition and rinsing solutions also promoted the formation of thicker PAA/PAH coatings. The ζ-potential of the particl...

Abstract: Titania nanoshells with an external diameter of 10–30 nm and a wall thickness of 3–5 nm were prepared by dissolving the silver cores of Ag@TiO2 nanoparticles in a concentrated solution of ammonium hydroxide. The nanoshells were assembled layer-by-layer (LBL), with negatively charged poly(acrylic acid) (PAA) to produce coatings with a network of voids and channels in the interior of the film. The diameter of the channels in the titania shells was comparable to the thickness of the electrical double layer in porous matter (0.3–30 nm). The prepared nanoparticulate films demonstrated strong ion-sieving properties due to the exclusion of some ions from the diffuse region of the electrical double layer. The permeation of ions could be tuned effectively by the pH and ionic strength of a solution between “open” and “closed” states. The ion-separation effect was utilized for the selective determination of one of the most important neurotransmitters, dopamine, on a background of ascorbic acid. Under physiological conditions, the negative charge on the surface of TiO2 facilitated the permeation of positively charged dopamine through the LBL film to the electrode, preventing the access of the negatively charged ascorbic acid. The deposition of the nanoshell/polyelectrolyte film resulted in a significant improvement to the selectivity of dopamine determination. The prepared nanoshell films were also found to be compatible with nervous tissue secreting dopamine. Although the obtained data demonstrated the potential of TiO2 LBL films for implantable biomedical devices for nerve tissue monitoring, the problem of electrode poisoning by the by-products of dopamine reduction has yet to be resolved.

Abstract: The interactions between the cationic surfactant dodecyl trimethylammonium bromide (C12TAB) and the anionic polymer sodium poly(styrene sulfonate) (NaPSS) have been studied using surface tension an...

Abstract: The XPS (ESCA) method was employed to quantitatively determine polyelectrolyte adsorption on the mica basal plane from low ionic strength solutions. Particular emphasis was given to the effect of the polyelectrolyte charge density. By combining the results obtained from XPS and surface force measurements it was possible to analyze the cation exchange at the surface that occurs as a result of polyelectrolyte adsorption. AFM-imaging was used to obtain information on the structure of the adsorbed layer when the polyelectrolyte coverage was low. Further, the desorption of preadsorbed polyelectrolyte layers by addition of inorganic salt and by addition of an anionic surfactant was investigated by XPS and some complementary surface force measurements. The results demonstrate that the lower the polyelectrolyte charge density is, the easier it is to remove the polyelectrolyte from the surface. The surfactant, which by itself does not adsorb to the mica surface, is more efficient in this respect than the inorganic salt. This observation can be rationalized by considering that the surfactant and polyelectrolyte form complexes with each other. Thus, the surfactant brings negative charges into the adsorbed layer that reduces the affinity to the surface. However, high-charge-density polyelectrolytes are removed to a very limited degree even when the surfactant concentration is above the critical micellar concentration, which is explainable by the poor solubility of the polyelectrolyte-surfactant complexes formed.

Abstract: Organized multilayers of nanoparticles (9-, 20-, and 45-nm-diameter silica or 12-nm magnetite) and glucose oxidase (GOx) were assembled in alternation with oppositely charged polyelectrolytes on 420-nm latex particles. Stepwise growth of the multilayer films on latex was confirmed by microelectrophoresis and transmission electron microscopy. The inclusion of silica layers on latex yields a higher surface area, resulting in greater GOx adsorption and thereby increasing the catalytic activity of the bioreactor. The bioactivity was proportional to the core surface area and also to the number of GOx layers in the shells. Also, the presence of magnetic nanoparticles allows self-stirring of the nanoreactors with a rotating magnetic field and enhances its productivity. The ensemble of GOx and fluorescent dyes in the shells demonstrated the correlation between Ru-bpy fluorescence and glucose concentration in solution.

Abstract: The design, synthesis and characterization of novel blue emission cationic water-soluble conjugated polymers based on the polyfluorene (PF) derivatives with amino-terminal groups are described. Water solubility was realized through quaternization of the amino group, which permits a control of the cationic degree, which in turn determines the solubility of the polymers in organic solvents and water. Better solubility in polar solvents was accompanied by a spectral blue shift for polymers with a higher quaternization degree. In the presence of a trace amount of some weak organic acids, the neutral polymer also showed a high solubility in water. Instead of forming a quaternized salt, the 1H NMR spectra indicated that only electrostatic interaction existed between the acid and the amino-terminal groups, which increased the affinity of the polymers with those polar solvents. In addition to the special solubility, good thermal stability as well as the intense fluorescence both in solutions and as films endows t...

Abstract: Floating multilayers of polyallylamine/polystyrenesulfonate (PAH/PSS) adsorbed to a dimethyldioctadecylammonium bromide (DODAB) monolayer at the air/water interface (at pH 5.5) are analyzed quantitatively with respect to the internal charge stoichiometry of the polyelectrolytes. To this end the adsorbed amount of polymer is translated into charge per area. It is postulated that the strong acid PSS is fully charged (fully dissociated). The weak polyelectrolyte PAH is also assumed to be fully dissociated. This is vindicated by theoretical considerations and deduced from pH-dependent studies of the isotherms of Langmuir monolayers of negatively charged dimyristoylphosphatidic acid (DMPA) with PAH adsorbed from the subphase. With both polyelectrolytes fully charged the PAH charges significantly overcompensate the PSS charges. The polyelectrolyte charge stoichiometry is not 1:1, and the multilayer must contain some small counterions (Cl-) for charge compensation. It is suggested that this “extrinsic compensati...

Abstract: We used Monte Carlo simulations to study the formation of complexes between a flexible, semiflexible, and rigid polyelectrolyte and an oppositely charged spherical particle. Polyelectrolyte adsorption on a small particle, whose surface curvature effect is expected to limit the amount of adsorbed monomers, was considered. We focused on the effects of the intrinsic polyelectrolyte rigidity and ionic concentration of the solution and investigated the adsorption/desorption limit and conformation of the adsorbed polyelectrolyte. Polyelectrolyte adsorption is controlled by several competing effects such as the electrostatic confinement energy of the chain due to the electrostatic repulsions between the charged monomers, polyelectrolyte intrinsic flexibility, and electrostatic attractive interaction between the polyelectrolyte monomers and the particle. On one hand, rigidity and electrostatic repulsions force the polyelectrolyte to adopt extended conformations and limit the number of monomers that may be attache...