Langmuir (LANGMUIR)

Publications in this journal

• Article: Supramolecular Organization in Organic–Inorganic Heterogeneous Hybrid Catalysts Formed from Polyoxometalate and Poly(ampholyte) Polymer

  Gijo Raj, Colas Swalus, Alain Guillet, Michel Devillers, Bernard Nysten, Eric M. Gaigneaux
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  ABSTRACT: Hybridization of polyoxometalates (POM) via the formation of an organic-inorganic association constitutes a new route to develop heterogeneous POM catalyst with tunable functionality imparted through supramolecular assembly. Herein, we report on strategies to obtain tunable well-defined supramolecular architectures of an organic-inorganic heterogeneous hybrid catalyst formed by the association of a hydrophobically substituted polyampholyte copolymer (poly N, N-diallyl-N-hexylamine-alt-maleic acid), and phosphotungstic acid (H3PW12O40) POM. The self-assembling property of the initial polyampholyte copolymer matrix is modulated by controlling the pH of the hybridization solution. When deposited on a mica surface, isolated, long and extended polymer chains are formed under basic conditions (pH 7.9), while globular or coiled structures are formed under acidic conditions (pH 2). The supramolecular assembly of the POM-polymer hybrid is found to be directed by the type and quantities of charges present on the polyampholyte copolymer, which themselves depend on the pH conditions. The hypothesis is that the Keggin type [PW12O40]3- anions, which have a size of ~1nm, electrostatically bind to the positive charge sites of the polymer backbone. The hybrid material stabilised at pH 5.3 consists of POM decorated polymer chains. Statistical analysis of distances between pairs of POM entities show narrow density distributions suggesting that POM entities are attached to the polymer chains with a high level of order. Conversely, under acidic conditions (pH 2), the hybrid shows the formation of a core-shell type structure. The strategies reported here, to tune the supramolecular assembly of organic-inorganic hybrid materials, are much valuable for the design, and a more rational utilisation of POM heterogeneous catalysts in several chemical transformations.
  Langmuir 03/2013;
• Article: Benzene- and Anthracene-Mediated Assembly of Gold Nanoparticles at the Liquid−Liquid Interface

  Ashavani Kumar, Saikat Mandal, Suju P. Mathew, P. R. Selvakannan, A. B. Mandale, Raghunath V. Chaudhari, Murali Sastry
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  ABSTRACT: The organization of gold nanoparticles at the liquid−liquid interface between the gold hydrosol and benzene as well as anthracene in chloroform is described. Vigorous stirring of the biphasic mixture results in almost complete transfer of the gold nanoparticles from the aqueous to the benzene phase and the subsequent assembly of the gold nanoparticles at the liquid−liquid interface. In the case of anthracene in chloroform, the gold nanoparticles assembled directly at the interface forming an extremely flexible membrane. The gold nanoparticle films formed at the interface in both cases could be transferred onto different solid supports and were analyzed by a host of techniques. The films show reasonable two-dimensional ordering of the gold nanoparticles over large length scales. It was observed that the benzene and anthracene molecules are strongly bound to the gold particle surface, presumably through cation−π interactions between the aromatic molecules and nanoparticle surface-bound Au+ ions, thus opening up a hitherto unexplored avenue for the assembly of gold nanoparticles.
  Langmuir 02/2013;
• Article: Computer Simulations of Evaporation of Pinned Sessile Droplets: Influence of Kinetic Effects

  Sergey Semenov, Victor M. Starov, Ramon G. Rubio, Manuel G. Velarde
  Langmuir 11/2012; 28(43):16724–16724.
• Article: Cationic Poly(N-isopropylacrylamide) Block Copolymer Adsorption Investigated by Dual Polarization Interferometry and Lattice Mean-Field Theory.

  Alexander Shovsky, Stefan Knohl, Andra Dedinaite, Kaizheng Zhu, Anna-Lena Kjøniksen, Bo Nyström, Per Linse, Per M Claesson
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  ABSTRACT: A series of cationic diblock copolymers, poly(N-isopropylacrylamide)(48)-block-poly((3-acrylamidopropyl)trimethylammonium chloride)(X), abbreviated as PNIPAAM(48)-b-PAMPTMA(+)(X) (X = 0, 6, 10, 14, and 20), has been synthesized, and their adsorption onto silicon oxynitride from aqueous solution has been investigated using dual polarization interferometry. The polymer adsorption was modeled by using a lattice mean-field theory, and a satisfactory consistency between theory and experiments was found in terms of surface excess and layer thickness. Both theory and experiments show that the adsorption is limited by steric repulsion for X < X(max) and by electrostatic interactions for X > X(max). Modeling demonstrates that significant surface charge regulation occurs due to adsorption. Both the nonionic and cationic block exhibit nonelectrostatic affinity to silicon oxynitride and thus contribute to the driving force for adsorption, and modeling is used for clarifying how changes in the nonelectrostatic affinity affects the surface excess. The segments of the nonionic and cationic blocks seem less segregated when both have a nonelectrostatic affinity for the surface compared to the case where the segments had no surface affinity. Adsorption kinetics was investigated experimentally. Two kinetic regimes were observed: the adsorption rate is initially controlled by the mass transfer rate to the surface and at higher coverage is limited by the attachment rate.
  Langmuir 08/2012; 28(39):14028-38.
• Article: Structure and Dynamic Properties of Colloidal Asphaltene Aggregates

  Joëlle Eyssautier, Didier Frot, Loic Barre
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  ABSTRACT: The abundant literature involving asphaltene often contrasts dynamic measurements of asphaltene solutions, highlighting the presence of small particle sizes between 1 and 3 nm, with static scattering measurements, revealing larger aggregates with a radius of gyration around 7 nm. This work demonstrates the complementary use of the two techniques: a homemade dynamic light scattering setup adapted to dark and fluorescent solutions, and small-angle X-ray and neutron scattering. Asphaltene solutions in toluene are prepared by a centrifugation separation to investigate asphaltene polydispersity. These experiments demonstrate that asphaltene solutions are made of Brownian colloidal aggregates. The hydrodynamic radii of asphaltene aggregates are between 5 and 10 nm, while their radii of gyration are roughly comparable, between 3.7 and 7.7 nm. A small fraction of asphaltenes with hydrodynamic and gyration radii around 40 nm is found in the pellet of the centrifugation tube. The fractal character of the largest cluste is observed from small angle scattering nearly on a decade length scale. Previous results on aggregation mechanisms are confirmed (Eyssautier, J., et al. J. Phys. Chem. B 2011, 115, 6827): nanoaggregates of 3 nm radius, and with hydrodynamic properties also frequently illustrated in the literature, aggregate to form fractal clusters with a dispersity of aggregation number.
  Langmuir 07/2012; 28:11997−12004.
• Article: The Simple Synthesis of Palladium Nanoparticles, the β- Phase Formation and the Control of Chain and Dipole Orientations in Palladium Doped Poly(vinylidene fluoride) Thin Films

  Dipankar Mandal, a Kap Jin Kim, † Jong Soon Lee‡
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  ABSTRACT: The palladium nanoparticles (Pd-NPs) are prepared by a simple one step procedure when poly(vinylidene fluoride) (PVDF) is used as a polymer stabilizer. The high quality Pd-NPs doped PVDF thin films are fabricated where heat-controlled spin-coating technique is adopted. The effect of Pd-NPs on the crystal modifications and lamellae orientation in PVDF film is investigated using the Fourier-Transform infrared-grazing incidence reflection absorption spectroscopy. The electroactive β-phase and edge-on crystalline lamellae are found to be formed preferentially in Pd-NPs doped PVDF films. As a result, Pd-NPs doped PVDF ultrathin films gave very good discernible contrast between the written and erased data bits, which suggests that they can be used as a scanning probe microscopy based ferroelectric memory device or a ferroelectric gate field effect transistor memory device in future.
  Langmuir 06/2012; accepted(---):-.
• Article: Galvanically Replaced Hollow Au-Ag Nanospheres: Study of Their Surface Plasmon Resonance.

  Yoonjung Choi, Soonchang Hong, Lichun Liu, Seong Kyu Kim, Sungho Park
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  ABSTRACT: We synthesized hollow Au–Ag nanospheres (NSs) by employing a galvanic replacement reaction between HAuCl4 and Ag NSs. Uniform Ag NSs with controllable sizes were synthesized as sacrificial templates by a seed-mediated strategy. The atomic ratio of Au to Ag in Au–Ag NSs was tunable by controlling the reagent concentration. UV–vis extinction spectra acquired from well-dispersed colloidal NS solutions were used to investigate the optical properties of the solutions. In addition to a common dipole mode exhibited on most transition metal nanoparticles, we observed a quadrupole plasmon resonance mode when the diameters of the Ag and Au–Ag NSs were larger than 100 nm. The quadrupole and dipole peaks both shifted to longer wavelengths with increased Au content in Au–Ag NSs. The experimental observation of optical properties of hollow Au–Ag NSs was compared with the theoretical simulation using DDA calculation, showing a good agreement.
  Langmuir 04/2012; 28(16):6670–6676.
• Article: Gemini Imidazolium Surfactants: Synthesis and their Bio-Physiochemical Studies

  Raman Kamboj, Sukhprit Singh, Avinash Bhadani, Hardeep Kataria, Gurcharan Kau
  Langmuir 01/2012;
• Article: Electrically Conducting Nanopatterns Formed by Chemical e-Beam Lithography via Gold Nanoparticle Seeds

  Patrick A. Schaal, Astrid Besmehn, Eva Maynicke, Michael Noyong, Bernd Beschoten, Ulrich Simon
  Langmuir 01/2012; 28(5):2448–2454.
• Article: Silver-assisted colloidal synthesis of gold patchy particles with tunable patchiness

  Huixin Bao, Benjamin Butz, Zhou Zhou, Erdmann Spiecker, Martin Hartmann, Robin Klupp Taylor
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  ABSTRACT: Patchy particles possessing heterogeneous surface composition show great promise as self-organizing building blocks for new classes of hierarchical functional structures. A major hurdle is the scalable synthesis of stable patches on nanosized core particles with arbitrarily defined patch number and coverage. So far, few methods have been reported which could be expected to meet these challenges. Recently we described the heterogeneous nucleation and growth of silver patches on silica nanospheres via a template free colloidal route. The patches produced, although tunable in size and number and showing interesting plasmon resonant properties, were rather unstable and degraded rapidly during attempts to process them further. In the present work, therefore, we set out to explore if related approaches can be employed to produce patchy particles involving gold, which is known to be more stable. The differences between typical patch precursors Ag⁺ and [AuCl_x(OH)_4-x]^- and their respective interactions with amorphous silica make this a significant challenge. We show that preformed small silver patches in addition to the presence of a reducing agent are necessary for the formation of gold patches conformal to the silica nanosphere surface. Systematic study of the process parameters and their influence on the patchiness as well as in-depth analytical TEM investigation of the patch composition reveal that patches spread over the silica surface via a cycle of galvanic dissolution and redeposition of silver.The resulting gold patchy particles remain stable during subsequent storage or washing and display tunable plasmon resonances within the visible and near-IR spectrum.
  Langmuir 01/2012;
• Article: Effect of nanoroughness on highly hydrophobic and superhydrophobic coatings

  Mammen L, Deng X, Untch M, Vijayashankar V, Papadopoulos P, Berger R, Riccardi E, Leroy F, Vollmer D
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  ABSTRACT: The effect of nanoroughness on contact angles and pinning is investigated experimentally and numerically for low energy surfaces. Nanoroughness is introduced by chemical vapor deposition of tetraethoxysilane and was quantified by scanning force microscopy. Addition of a root mean square roughness of 2 nm on a flat surface can increase the contact angle after fluorination by a semifluorinated silane by up to 30°. On the other hand, nanoroughness can improve or impair the liquid repellency of superhydrophobic surfaces which were made from assembled raspberry particles. Molecular dynamics simulations are performed in order to gain a microscopic understanding on how the length and the surface coating density of semifluorinated silanes influence the hydrophobicity. Solid-liquid surface free energy computations reveal that the wetting behavior strongly depends on the density and alignment of the semifluorinated silane. At coating densities in the range of experimental values, some water molecules can penetrate between the semifluorinated chains, thus increasing the surface energy. Combining the experimental and numerical data exhibits that a roughness induced increase of the contact angle competes with increased pinning caused by penetration of liquid into nanopores or between neighboring semifluorinated molecules.
  Langmuir 01/2012;