Controlled copolymer structures via anionic/insertion polymerization of cyclic carbonates

Cyclic carbonates are polymerized in a ring-opening fashion by means of anionic and insertion type initiatiors. Different hexacyclic carbonates are copolymerized in a random way when both monomers are added to the initiator simultaneously. Block copolymers are obtained when the monomers are added in sequential way. With anionic initiators cyclic carbonates are polymerized preferentially as compared with lactones while insertion initiators are less selective. A special case is the preparation of copolymers of carbonates with lactams. When the polycarbonate is formed first the lactam unit is inserted into carbonate bond to form urethane and ester bonds. Thus, eventually an alternating polyesterurethane is formed with negligible amount of carbonate, amide, and urea units. Moreover, the anionic ring-opening polymerization of cyclic carbonates may be combined with vinyl polymerization. In the case of group transfer polymerization a transformation of the active site to the non-metallic anionic initiation of the cyclic carbonate occurs.     

5MeV electron beam facilities in Japan

There are 3 facilities with 5MeV electron beam processing machines in Japan and another one is planned to start operation in 1998. 2 of them are installed by Nissin-High Voltage and the other are by Sumitomo Heavy/Radiation Dynamics. In this report are introduced 2 facilities which we have installed and are operating satisfactorily. The first one was: installed at Radia Industry for irradiation services and the second one for in-house use in a factory of a pharmaceutical plastic container manufacturer, Shinko Chemical. And the second one is available for contract irradiation. The machine in Radia Industry has a comprehensive conveyor system with a turn-over equipment to shoot from the top and the bottom of materials with e-beam and X-ray, and has been successfully operated for many years. The machine in Shinko Chemical is equipped with a unique conveyor system with two conveyor lines under the beam window and the motion of the lines are opposite each other. This conveyor system also has a turn-over equipment like other machines but the direction of turning-over is designed to give the irradiated materials more uniform dose.     

Spot-test detection of aryl hydrazines, hydrazones, osazones, oximes and aromatic amines

Arylhydrazines are detected by oxidation with N-bromosuccinimide and coupling with resorcinol to form azo-dyes which are intensely coloured in alkaline media. Hydrazones and osazones are hydrolysed to form the arylhydrazines, which are then tested for 4-Nitro- and 2,4-dinitrophenylhydrazines are tested for by forming their hydrazone with salicylaldehyde and adding alkali to produce a violet colour. The hydroxylamine formed by the hydrolysis of oximes is oxidized by iodine monochloride in the presence of sulphanilic acid; coupling with 8-hydroxyquinoline forms a dye that is red in alkali. Intense colours are immediately produced when primary, secondary and tertiary aromatic amines are mixed with diacetoxyiodobenzene. All the tests are sensitive and appear to be specific.     

Formation of different gold nanocrystal core-resin shell structures through the control of the core assembly and shell polymerization

The formation of different Au nanocrystal core-resin shell structures through the control of the nanocrystal assembly and shell polymerization is investigated. 4-Mercaptophenol is employed together with formaldehyde as the resin monomers. 4-Mercaptophenol molecules bond to the surface of Au nanocrystals so that the resultant phenolic resin can intimately encapsulate Au nanocrystals. The morphologies of the obtained structures are determined by the nanocrystal assembly and the monomer polymerization behaviors, which are controlled by the solution pH as well as the monomer amounts. At pH = 8-9, Au nanorods are assembled and fused together under hydrothermal conditions in a preferential end-to-end manner. The fused structures are coated with a layer of resin, with the thickness controlled by the supplied amounts of the monomers. At pH = ～10, Au nanorods are coated with resin of controllable thicknesses and separated from each other. The resin-coated Au nanorods are stable in both aqueous and nonaqueous solutions. At pH = ～12, Au nanorods are coated with a thin layer of resin and assembled together in a side-by-side manner. A similar assembly and resin coating behavior is also observed with Au nanopolyhedrons. Moreover, plasmonic-fluorescent bifunctional structures are readily produced by incorporating CdTe nanocrystals in the resin shell that is coated on Au nanocrystals, owing to the presence of a number of thiol groups in the resin shell.     

Theoretical study of vibration-phonon coupling of H adsorbed on a Si(100) surface

In this paper a perturbation-theory study of vibrational lifetimes for the bending and stretching modes of hydrogen adsorbed on a Si(100) surface is presented. The hydrogen-silicon interaction is treated with a semiempirical bond-order potential. Calculations are performed for H-Si clusters of different sizes. The finite lifetime is due to vibration-phonon coupling, which is assumed to be linear or bilinear in the phonon and nonlinear in the H-Si stretching and bending modes. Lifetimes and vibrational transition rates are evaluated with one- and two-phonon processes taken into account. Temperature effects are also discussed. In agreement with the experiment and previous theoretical treatment it is found that the H-Si (upsilon(s) = 1) stretching vibration decays on a nanosecond timescale, whereas for the H-Si (upsilon(b) = 1) bending mode a picosecond decay is predicted. For higher-excited vibrations, simple scaling laws are found if the excitation energies are not too large. The relaxation mechanisms for the excited H-Si stretching and the H-Si bending modes are analyzed in detail.     

Hydrodynamics of a bounded vertical film with nonlinear surface properties

The drainage of a thin liquid film with an insoluble monolayer down a vertical wall is studied. Lubrication theory is used to develop a model where the film is pinned at the top with a given thickness and the film drains into a bath at the bottom. A nonlinear equation of state is used for the surface tension and the surface viscosity is a nonlinear function of the surfactant concentration; these are appropriate for some aqueous systems. The three partial differential equations are solved via discretization in space and then the resulting differential algebraic system is solved. Results are described for a wide range of parameters, and the conditions under which the free surface is immobilized are discussed.     

Microfabricated reactors for on-chip heterogeneous catalysis

Microfabricated devices constructed from glass and polydimethylsiloxane with integral heaters are described, which can be used for heterogeneous catalysis reactions. Sulfated zirconia is used as the catalyst in an open channel reactor, with either a syringe pump or electroosmotic flow being used to deliver the reactants. The results clearly demonstrate that very high conversion efficiencies are possible, however, the thermodynamics of the reactions are the same as in bulk systems. Ethanol and hexanol are dehydrated to ethene and hexene, respectively, with conversion efficiencies approaching 100%, and the esterification of ethanol is investigated. Yields of approximately 30% ethyl acetate are obtained by gas chromatographic analysis. This is the first time such a method for fabricating a catalyst micro reactor has been reported, yet it demonstrates sufficient robustness and resistance to leakage. The use of electroosmotic flow in a heated catalyst reactor is a significant advancement in reactor design.     

Determination of arsenite, arsenate and monomethylarsonic acid in aqueous samples by gas chromatography of their 2,3-dimercaptopropanol (bal) complexes

Procedures are described for the determination of arsenite, arsenate and monomethylarsonic acid in aqueous samples. The arsenicals (after reduction of arsenic to the tervalent state) readily react with 2,3-dimercaptopropanol (BAL) to yield their BAL complexes. The products are extracted with benzene and introduced into a gas Chromatograph equipped with a flame-photometric detector for sulphur. One aliquot of sample is treated with stannous chloride solution and potassium iodide solution to reduce arsenate and monomethylarsonic acid, then BAL is added and the complexes are extracted with benzene. The extract is analysed for total inorganic As plus monomethylarsonic acid. Magnesia mixture and phosphate solution are added to another aliquot to remove arsenate by co-precipitation with magnesium ammonium phosphate. The precipitate is filtered off and arsenite determined in the filtrate. The detection limits are 0.02 ng of As for arsenate and arsenite and 0.04 ng of As for monomethylarsonic acid.     

Self-assembly of polymer brushes in the presence of a surfactant: A system of strands

This theoretical study is focused on the formation of a cylindrical microstructure in a planar polymer brush in the presence of a surfactant. It is assumed that the brush may be nonuniform in the direction along the grafting plane and that there are regions with constant concentrations of monomer units and regions occupied only by the surfactant. The surfactant molecule is simulated by a dimer whose parts interact in a different manner with the monomer units of the polymer. At the interface between these regions, dimer molecules are oriented mainly perpendicularly to this interface and the surface tension is reduced. If the surface energy becomes negative, the formation of a structured brush is more favorable in terms of energy than that of a uniform brush. As a result, there may appear a cylindrical microstructure in which grafted macromolecules are united into strands perpendicular to the grafting plane. The stretching of macromolecules and their interaction with the solvent within the strands are described by the Alexander-de Gennes model, whereas the surface energy is calculated with allowance for the surface curvature of strands at a high degree of amphiphilicity of the surfactant molecules. It is shown that the arising strands have radii of the order of the surfactant-molecule length, while the number of macromolecules per strand is proportional to the surface density of their grafting. With an increase in the grafting density, the strand length increases initially, while the volume fraction of the polymer in a strand remains constant. Furthermore, strands start to shorten and their density grows. Structural characteristics are calculated as a function of the parameter characterizing the degree of amphiphilicity of the solvent molecules, their sizes, and their average energy of interaction with monomer units.     

Recent progress in reactive surfactants in emulsion polymerisation

In the synthesis of latexes for use in waterborne coatings, the benefits of using reactive surfactants are now well known. Improvements are obtained in the stability of the latexes, due to the fact that they are not desorbed from the particle surface. The film properties are also better, chiefly if the films are exposed to humidity, where the water rebound is decreased significantly. This lecture summarises some recent progress obtained in that field through a European programme, including the participation of 10 academic and industrial laboratories. Four topics are considered. The first one is dealt with a series of anionic surmers (polymerizable surfactants) prepared upon reacting a polymerisable alcohol with either maleic, or succinic, or sulfosuccinic anhydride. One of these products, resulting from the addition of Hydroxyethylmethacrylate on maleic anhydride is now available commercially, From maleic anhydride one get bifunctional surfmers with 2 polymerisable groups, while the two other anhydride lead to monofunctional surfmers. All these products are engaged in seeded core-shell polymerisations, resulting in film-forming latexes quite stable during and after the polymerisation. However, because they are simply anionic, they do not provide steric stabilization and the latexes flocculate upon addition of strong electrolytes or in freezing tests, except if they are engaged in miniemulsion polymerisations initiated with KPS. The second topic is concerned with a series of nonionic block copolymer surfmers. A hydrophilic sequence of ethylene oxide units, produced upon ring opening living anionic polymerisation, is followed by a hydrophobic sequence of propyleneoxide, and the living polymer is killed with a polymerisable group attached on a reactive halogen atom. A variety of polymerisable groups have been used: styrenic, methacrylic, vinylic, allylic and maleic. The HLB balance is controlled through the lentgh of the hydrophilic and hydrophobic sequences. The more reactive, associated with an adequate HLB balance allows to prepare core-shell latexes with an excellent steric stabilisation at solid contents up to 40%. It is not the case for the less reactive maleic or allylic, the behaviour of which is close to that of a non reactive surfactant with the same structure. Transurfs, with an addition-fragmentation mechanism, is the subject of the third topic. A first study was carried out by the group of Eindhoven, who produced a new surfactant on the basis of a MMA dimer condensed on a long chain bromoalcohol and then sulfonated. This transurf was engaged in a MMA emulsion polymerisation, and compared with SDS; the polymerisation rate was lower and the molecular weight was broader. Optimisation of the incorporation of the transurf was achieved upon using starved feed conditions. We have carried out styrene miniemulsion using controlled RAFT process with a surfactant belonging to the first family reported above together with a RAFT agent. Finally we have used a RAFT agent derived from the nonionic block copolymer surfactants.     

Supermolecular structures and flow birefringence in polymer solutions

Experimental studies of supermolecular structures and localized flow birefringence in solutions of high-molecular weight polymer are described. Advantage is taken of poly(ethylene oxide) and polyisobutylene. Supermolecular structures are examined with the aid of optical microscopy using freeze-dried samples of the polymer solutions. Birefringence is investigated that arises in planar elongational flow in a cross-slot cell. Flow velocities at which the onset of the localized birefringence occurs are determined. Then these velocities are correlated with viscoelastic characteristics of the solutions. The presence of a liquid-crystalline fibrillar network in the polymer solutions exhibiting flow birefringence is ascertained. The fibrils are birefringent objects. The fibrils are birefringent objects. The localized birefringence phenomenon is explained in term of the orientation of the fibrils in elongational flow. It has been shown that the onset of localized birefringence occurs at a critical Weissenberg number, the value of which is close to unity.     

Ion beam sputtering techniques for high-resolution concentration depth profiling with glancing-incidence X-ray fluorescence spectrometry

The application of ion beam sputtering in combination with glancing-incidence X-ray fluorescence spectrometry for high-resolution concentration depth profiling is presented. Two new techniques are described: first, in the “bevel-etching technique”, the sample depth profile is uncovered on the sample surface either by sputter etching with a gradient of the ion beam intensity or by varying the sputtering time by moving a shutter in front of the sample; second, in the “deposition technique”, samples are etched uniformly and the sputtered material is deposited on a moving substrate. The bevelled sample and also the material deposited on the substrate are characterized (laterally resolved) by glancing incidence X-ray fluorescence spectrometry. The apparatus and techniques are described in detail. Typical experiments showing the advantages of and problems with the two techniques are discussed. The achievable depth resolutions, 1.5 nm with the bevel-etching technique and 1.4 nm with the deposition technique, are comparable with the best results from other depth profiling methods.     

Fragment-Based Ab Initio Molecular Dynamics Simulation for Combustion

We develop a fragment-based ab initio molecular dynamics (FB-AIMD) method for efficient dynamics simulation of the combustion process. In this method, the intermolecular interactions are treated by a fragment-based many-body expansion in which three- or higher body interactions are neglected, while two-body interactions are computed if the distance between the two fragments is smaller than a cutoff value. The accuracy of the method was verified by comparing FB-AIMD calculated energies and atomic forces of several different systems with those obtained by standard full system quantum calculations. The computational cost of the FB-AIMD method scales linearly with the size of the system, and the calculation is easily parallelizable. The method is applied to methane combustion as a benchmark. Detailed reaction network of methane reaction is analyzed, and important reaction species are tracked in real time. The current result of methane simulation is in excellent agreement with known experimental findings and with prior theoretical studies.     

Quantitative inorganic paper chromatography direct determination of cobalt by a scanning method

Cobalt can be determined in the presence of other elements by chromatography followed by photometric scanning. The chromatographic solvent used is a mixture of acetone, n-butanol, hydrochloric acid and acetylacetone, and the cobalt spot is made visible by spraying with a solution of rubeanic acid. The filter paper is cut in strips which are scanned along their length either in a Beckman DU spectrophotometer or a Photovolt densitometer Mod. 525 at 422 mμ. The absorbance curves are plotted and the Co concentration is calculated from the area under the peaks. Chromatograms with 8 spots, each containing 0.4 — 2 μg Co, of which 4 are standards, are convenient. The coefficient of variation for the mean of a single chromatogram is 6 %. Alloys containing as little as 0.2 % Co can be analysed with an accuracy of 5 % or better.     

Review paper: Design of a mass and ion kinetic energy spectrometer for organic chemical work

The design of a mass spectrometer for the determination of the structural formulae of organic compounds is discussed. The ion-optical characteristics of electric and magnetic sectors and also of quadrupole mass analysers are considered and the additional information that can be gleaned when such components are combined in various ways is listed. The advantages of using collision cells for inducing fragmentation of selected ion species are listed including those that result when the collision cell is floated at an electrical potential different from that of the incident ion beam. Important performance characteristics are the resolution with which a particular ion may be selected and the resolution with which daughter ions formed from it can be separated. It is concluded, that for instruments comprising three analysing units together with the appropriate collision cells, the most versatile combinations and those with the highest performance are an arrangement consisting of a magnetic sector followed by an electric sector, this being followed either by a further magnetic sector or a quadrupole. The properties of these two systems are compared in detail.     

Time reversible and symplectic integrators for molecular dynamics simulations of rigid molecules

Molecular dynamics integrators are presented for translational and rotational motion of rigid molecules in microcanonical, canonical, and isothermal-isobaric ensembles. The integrators are all time reversible and are also, in some approaches, symplectic for the microcanonical ensembles. They are developed utilizing the quaternion representation on the basis of the Trotter factorization scheme using a Hamiltonian formalism. The structure is similar to that of the velocity Verlet algorithm. Comparison is made with standard integrators in terms of stability and it is found that a larger time step is stable with the new integrators. The canonical and isothermal-isobaric molecular dynamics simulations are defined by using a chain thermostat approach according to generalized Nosé-Hoover and Andersen methods.     

Rheology of liquid-crystalline solutions of hydroxylpropyl cellulose filled with layered silicate particles

The rheological properties of nanocomposites with an anisotropic matrix are systematically studied. As a matrix, a 60% solution of hydroxypropyl cellulose in PEG is used. In accordance with the phase diagram, it demonstrates the LC-isotropic-state transition along the temperature scale. The solution is filled with Na-montmorillonite particles (1.0–7.5%). The rheological characteristics of solutions under steady-state shear flow, periodic (harmonic) oscillations with different amplitudes, and uniaxial extension at the constant stretching rate are investigated. Experiments are performed at various temperatures, and the properties of the system are compared with the phase state of the matrix. The viscoelastic properties of the material are described by a model with a single relaxation time. The abnormal behavior of the storage modulus in the low-frequency range is observed. When the matrix is transformed into the LC state, the yield point becomes well-defined and the shear viscosity abruptly increases with an increase in the content of the LC phase. The above-described effects are discussed in terms of the ideas that two competing structures exist in the system, one of which is formed by the LC domains of solution, while the other structure is based on the nanofiller capable of forming ordered structures. Deformation, especially longitudinal flow, facilitates self-organization of the system.     

Controlled formation of gold nanoparticle dimers using multivalent thiol ligands

Approaches for the controlled formation of gold nanoparticle dimers are investigated. These are based on a locally confined surface modification of gold nanoparticles followed by bridging two particles with an organic linker. A key factor in these approaches is the use of multivalent ligands. Citrate-stabilized gold nanoparticles are immobilized on a glass surface and mono- and multivalent thiol ligands are investigated regarding their ability to inactivate the nanoparticles sites facing away from the glass. A successful locally confined functionalization is only possible if multivalent ligands are used in this step. The application of monovalent ligands results in less stable particles without a permanent regioselective functionalization. This result can be explained by the dynamic equilibrium between bound and free ligands. Subsequently, the sites of the nanoparticles previously bound to the glass surface are functionalized with thiol ligands additionally bearing a reactive group. Approaches using dithiol linkers, diamine linkers, and coupling complementary functionalized particles are investigated. The highest yield of stable dimers is obtained from conditions where nanoparticles which are regioselectively functionalized with an N-hydroxysuccinimide ester are reacted with complementary amino-functionalized particles. The application of nanoparticles with activated carboxyl groups is essential since standard carboxyl activation agents induce an aggregation of the nanoparticles due to a reaction with remaining citrate molecules on the nanoparticle surface which reduces significantly electrostatic stabilization. This versatile approach using complementary regioselective with multivalent ligands functionalized nanoparticles may be also used for the coupling of particles with different size, shape, or composition, as well as a control of the interparticle distance.     

Optimization of St John's Wort flavonoid separation by reversed phase liquid chromatography on a silica-based monolithic column

Summary An optimization procedure for the separation of flavonoids from St John's Wort by reversed-phase high-performance liquid chromatography on monolithic stationary phase is described. Three-component mobile phase systems are studied using experimental design methodology. The starting experimental domain is a triangle, each vertex of which is a pure component. From preliminary isocratic experiments, truncations in the domain are performed leading to a quadrilateral shape working domain with no symmetry. To cope with both separation and analysis time, desirability functions are used. Optimal conditions are finally given by binary systems and the four flavonoids are separated in less than seven minutes.