[show abstract][hide abstract] ABSTRACT: Nanoparticles can be used for decoration and functionalization of single polymer molecules that
have been adsorbed to asolid substrate. Initial attempts to prepare Prussian Blue nanoclusters
by alayer-by-layer deposition technique of hexacyanoferrate anions and ferric cations onto isolated polycation chains in water failed because of the desorption of the
first layer upon deposition of the next one. Asimple method for the preparation of charge-stabilized
Prussian Blue nanoparticles of readily adjustable size is reported. Prussian Blue nanoparticles have
been purified by addition of non-solvents and redispersed in water without aggregation. Thus formed
Prussian Blue nanoparticles are crystalline and display along-range ferromagnetic ordering at
5.1K. Prussian Blue nanoparticles were selectively deposited along single polycation molecules
to form aone-dimensional array or were attached to the surface of carbon nanotubes (CNTs) functionalized
with poly2-vinylpyridine (P2VP). These nanoparticle-based nanostructures might be useful materials
for manufacture of electrooptical devices, or mechanically robust ion-sieving membranes.
[show abstract][hide abstract] ABSTRACT: We investigated the adhesive properties of binary heterogeneous polymer brushes made from end-functionalized polystyrene (PS) and poly(2-vinylpyridine) (P2VP) chains. The molecular organization of the mixed brush could be varied reversibly by exposure to selective solvents for PS (toluene) and for P2VP (acidic water). This exposure results in reversible switching of adhesive and wetting properties. The manner in which the adhesion switching occurs can be tuned by the composition of mixed brushes. However, the outer surface composition could be enriched more effectively in PS after the toluene treatment than in P2VP after the acidic water treatment. As a result, the mixed brush compositions that showed the largest difference in properties between an exposure to toluene and an exposure to water were the P2VP-rich compositions. Adhesive properties, tested against a soft hydrophobic pressure-sensitive adhesive (PSA) using a probe test, always showed smaller differences between solvent treatments than wetting properties with water, suggesting a much higher sensitivity of the hydrophobic/hydrophilic brushes to polar molecules than to nonpolar molecules.
[show abstract][hide abstract] ABSTRACT: We developed the simple contrasting procedure to improve AFM visualization of single positively charged polymer chains via counterion exchange between Cl- anions and bulky hexacyanoferrate anions or negatively charged nanoclusters of Prussian Blue. This method allowed us to increase thickness of the resulting structures up to 10 nm and, consequently, to provide visualization of isolated polymer chains deposited on a glass surface (root-mean-square roughness about 1 nm). In contrast, the contrasting with relatively large PB clusters (more than 10 nm in size) distorts conformations of the molecules and even eventually leads to a fragmentation of polymer chains.
[show abstract][hide abstract] ABSTRACT: Single molecule conformations and associate morphologies for polystyrene/poly(2-vinylpyridine) (PS7−P2VP7) heteroarm star copolymer, formed in controlled environment and deposited onto mica or Si wafers, have been studied by atomic force microscopy (AFM) with molecular resolution. At concentrations below 0.01 mg/mL PS7−P2VP7 exists in the molecularly dissolved state in both selective (acidic water, toluene) and common good (chloroform, tetrahydrofuran) solvents. In acid conditions PS7−P2VP7 forms either unimolecular or multimolecular micelles depending on concentration and pH. The core of the micelles is constituted of the collapsed PS arms surrounded by protonated P2VP shell. PS7−P2VP7 undergoes inverse intramolecular segregation upon addition of toluene. In this case, P2VP arms form the dense core of the micelles embedded in the swollen PS shell. The transition between those two inverse types of micelles is strongly modified by interaction with the mica substrate. The micelles deposited onto mica from acidic water are trapped via P2VP extended arms. Upon treatment of the trapped micelles with toluene the PS core is swollen and PS arms gradually adapt an extended conformation whereas P2VP trapped arms retain their extended conformation due to the strong interaction with the mica substrate. The obtained “squash” structures exhibit a unique conformation that does not exist in any solvent and could not be obtained upon a simple adsorption procedure. Surface-supported metallization of the PS7−P2VP7 on Si wafers improves AFM resolution due to the selective deposition of the Pd clusters along the P2VP chains. Thus, the number of P2VP arms of the unimers as well as the aggregation number of the multimolecular micelles and morphological details of the structures were directly analyzed.
[show abstract][hide abstract] ABSTRACT: We developed a simple contrasting procedure to improve the AFM visualization of single positively charged polymer chains deposited on substrates of a relatively high roughness via the decoration of the molecules with hexacyanoferrate anions or negatively charged clusters of cyanide-bridged complexes.
Journal of the American Chemical Society 10/2003; 125(37):11202-3. · 10.68 Impact Factor
[show abstract][hide abstract] ABSTRACT: Unimolecular micelles constituted from the star-shaped PS7−P2VP7 polysterene/poly(2-vinylpyridine) block copolymer single molecules were studied with molecular resolution using AFM. In selective solvent the unimers show core−shell structures with very pronounced segregation into the collapsed core and the extended shell formed by stretched polymer arms of P2VP and PS in water and toluene, respectively. Metallization of P2VP arms of the copolymer leads to the organic−inorganic nanocomposite with 1−3 nm in diameter palladium clusters localized in the outer shell of unimers, forming starlike structures with metallized arms and improving the contrast to resolve the fine molecular morphology.
[show abstract][hide abstract] ABSTRACT: Solvent-induced aggregation of regioregular head-to-tail poly(3-alkylthiophene)s (PATs; alkyl = octyl and hexyl) was studied using AFM and UV-vis spectroscopy. In hexane, which is a good solvent for alkyl side chains but poor for polythiophene backbones, PAT mols. undergo ordered main-chain collapse driven by solvophobic interactions. Well-pronounced concn.-independent red shift of lmax and good resolved fine vibronic structure in the electronic absorption spectra obsd. upon addn. of hexane, indicate that planarization occurs on the single-mol. level. A helical conformation of the main chain of PATs with 12 thiophene rings per each helical turn is proposed. At higher concn. of PATs, collapsed mols. undergo unexpected one-dimensional aggregation. The Length of aggregates varies from several nanometers to several hundreds nanometers and can be easily adjusted by the solvent compn. or concn. of PATs. [on SciFinder (R)]
[show abstract][hide abstract] 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.
Journal of the American Chemical Society 12/2002; 124(45):13454-62. · 10.68 Impact Factor
[show abstract][hide abstract] ABSTRACT: Conformation of a single flexible polyelectrolyte molecule with a hydrophobic backbone in aqueous solution is effected by the interplay of the short-range intramolecular attraction and the long-range Coulomb repulsion. The conformation can be frozen if the molecule is trapped by a solid substrate. With this approach, we prepared the range of single molecule templates from poly(2-vinylpyridine) (P2VP) deposited on the surface of Si-wafer or mica in different conformations from an elongated wormlike coil to compact globule. Pd(+2) was coordinated by P2VP via an ion exchange reaction exposing the samples to palladium acetate acidic aqueous solution. In the next step, Pd(+2) was reduced by dimethylamine borane. This route results in wire-shaped metallic nanoparticle assembles of about 2-5 nm in diameter and 50-700 nm in length. The conformation and size of the underlaying polyelectrolyte molecules determine the dimensions of nanoparticles.
Journal of the American Chemical Society 09/2002; 124(34):10192-7. · 10.68 Impact Factor
[show abstract][hide abstract] ABSTRACT: Here we described simple chemical route to fabricate wire-shaped metallic nanoparticles of about 5 nm in a diameter and of 1000 nm in a length from single synthetic polycations. The preparation is based on the deposition of Pd-clusters on single poly(methacryloyloxyethyl dimethylbenzylammonium chloride) molecules adsorbed on Si-wafers from aqueous solution. The length and the diameter of nanowires are determined by the length and the diameter of the underlying polymer chains.
[show abstract][hide abstract] ABSTRACT: Single flexible polyelectrolyte molecules of poly(2-vinylpyridine) undergo conformational transition from a stretched wormlike coil to a necklace-like globule, and to a compact globule depending on pH and ionic strength in aqueous solution in good agreement with recent theoretical reports. AFM investigations allow the visualization of details of the chain conformation on mica and the extraction of quantitative statistics of molecular dimensions.
Journal of the American Chemical Society 05/2002; 124(13):3218-9. · 10.68 Impact Factor
[show abstract][hide abstract] ABSTRACT: - -Gegenionen durch große Hexacyano- ferrat-Anionen oder negativ geladene Nanoclusters des Preußisch- blaus. Die ursprüngliche Polymerkonformat ion wird durch diese Verfahren nicht
[show abstract][hide abstract] ABSTRACT: We investigated the adhesive properties of mono-component and bi-component polymeric brushes chemically grafted on silicon wafers from end-functionalized hydrophilic and/or hydrophobic chains by using the technically simple `grafting to' method. The charge state and the molecular organization of high Tg brushes could be varied reversibly by exposure to appropriate solvents or by varying the grafting density. Adhesive properties were tested against soft pressure-sensitive-adhesives (hydrophobic & hydrophilic) with a probe method. In the case of low Tg brushes, an increase in contact time could selectively improve the adhesion with the soft hydrophobic or hydrophilic adhesive layer. This is due to reorganization of the interface at the molecular scale leading to the formation of entanglements or favorable interactions between the polymer brush and the polymers in the soft adhesive.
[show abstract][hide abstract] ABSTRACT: We investigated the adhesive and wetting properties of bicomponent polymeric brushes made from end functionalized hydrophilic and hydrophobic polymer chains. The molecular organization of the mixed brush could be varied reversibly by exposure to selective solvents for the two polymers. Adhesive properties were tested by debonding a flat ended probe from soft pressure-sensitive-adhesives (hydrophobic & hydrophilic) and wetting properties were tested by contact angle measurements of water & diiodomethane droplets. The bicomponent brushes were chemically grafted on silicon wafers from end-functionalized chains. Wetting experiments were done directly on the wafers while for adhesion experiments, the wafers were glued on the flat end of the probe prior to the tests. In all cases the organization of the bicomponent brush could be modified reproducibly and reversibly by exposure to selective solvents. Following this strategy we succeeded to create remarkably stable adaptive polymer surfaces that can modify their adhesion and wetting reversibly and also tune them by varying the ratio of the bicomponent brush layer.