References of "Vanhoorne, Pierre"
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See detailLight scattering study of salt-free "polyelectrolyte behaviour" of monotelechelic ionomers in a polar solvent
Kupperblatt, Gary; Hara, Masanori; Vanhoorne, Pierre ULg et al

in Polymer (1996), 37(16), 3741-3744

Salt-free polyelectrolyte behaviour which is typically observed at low polymer concentrations for polyelectrolyte aqueous solutions and random ionomer non-aqueous solutions (in polar solvents) (i.e ... [more ▼]

Salt-free polyelectrolyte behaviour which is typically observed at low polymer concentrations for polyelectrolyte aqueous solutions and random ionomer non-aqueous solutions (in polar solvents) (i.e., negative angular dependence of the reciprocal scattering in static light scattering and an appearance of the fast mode in dynamic light scattering) has been observed for monotelechelic ionomer solutions in a polar solvent. This indicates that only single charge (per chain) is sufficient to produce intermolecular electrostatic interactions, which are responsible for such characteristic behaviour. However, the 'characteristic' behaviour, which is typically observed at higher concentrations for polyelectrolyte and random ionomer solutions (i.e., large positive apparent radius of gyration in static scattering and appearance of the slow mode in addition to the fast mode in dynamic scattering) has not been observed to date for monotelechelic ionomer solutions. The absence of high-concentration characteristics for the monotelechelic ionomer solutions gives additional insight as to the nature and structure of 'heterogeneities' in salt-free polyelectrolyte solutions, which is still controversial. [less ▲]

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See detailTelechelic ionomers studied by light scattering and dynamic mechanical measurements
Chassenieux, Christophe; Johannsson, Ragnar; Durand, Dominique et al

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (1996), 112(2-3), 155-162

The formation of a transient network by sulfonato polyisoprene and sulfonato polystyrene in toluene is studied using static and dynamic light scattering and dynamic mechanical analysis. It is shown that ... [more ▼]

The formation of a transient network by sulfonato polyisoprene and sulfonato polystyrene in toluene is studied using static and dynamic light scattering and dynamic mechanical analysis. It is shown that at low concentrations aggregates are formed with increasing molar mass and polydispersity as the polymer concentration is increased. Above a certain concentration well below the overlap concentration of the polymer chains (C*), a transient network is formed. This is characterised by a plateau modulus at high frequencies and a relatively narrow viscoelastic relaxation time distribution. The intensity auto-correlation function of the transient network shows two relaxational modes: a relatively fast diffusional mode close to the co-operative diffusional mode of semidilute solutions of the unfunctionalised polymers, and a slow broader mode which becomes independent of the scattering angle at concentrations close to C*. The relation between this slow mode and the viscoelastic relaxation is discussed. [less ▲]

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See detailChain end effects and dewetting in thin polymer films
Henn, G.; Bucknall, D. G.; Stamm, Manfred et al

in Macromolecules (1996), 29(12), 4305-4313

The dewetting of thin films of end-functionalized polymers, ω- and α,ω-barium sulfonato polystyrenes, on a silicon substrate has been investigated as a function of initial film thickness, molecular weight ... [more ▼]

The dewetting of thin films of end-functionalized polymers, ω- and α,ω-barium sulfonato polystyrenes, on a silicon substrate has been investigated as a function of initial film thickness, molecular weight, and functionality of the chains. The lower molecular weight monofunctional chains are found to dewet the substrate analogously to normal polystyrene but display an anomalous flow behavior at the surface. Moreover, after dewetting, the entire silicon surface still remains covered by a monolayer of monofunctional chains. The monolayer consists of a polymer brush of densely packed tethered chains, adsorbed via their ionic end groups. The dense packing and special conformations of the chains in the brush prevent interpenetration with other polymer chains, and the unadsorbed macromolecules dewet the brush. When the molecular weight of the monofunctional chains is increased, entanglements between the adsorbed polymer brush and the unadsorbed chains can occur and the dewetting process is retarded. Thin films of the difunctional chains do not dewet regardless of the molecular weight of the chains. The difference between mono- and difunctional materials is attributed to ionic aggregation, which is responsible for thermoreversible cross-linking and stabilization of thicker films by interaction of aggregates with dangling ends. It is suggested to use high molecular weight end-functionalized chains as polymeric additives to retard thin polymer film dewetting. [less ▲]

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See detailSynthesis and preliminary characterization of model liquid crystalline ionomers
Gohy, Jean-François; Vanhoorne, Pierre ULg; Jérôme, Robert ULg

in Macromolecules (1996), 29(10), 3376-3383

Model liquid crystalline ionomers have been synthesized that consist of low molecular weight linear chains selectively end-capped at one or both end(s) with an ionic mesogenic group. ω- and α,ω ... [more ▼]

Model liquid crystalline ionomers have been synthesized that consist of low molecular weight linear chains selectively end-capped at one or both end(s) with an ionic mesogenic group. ω- and α,ω-carboxylato and sulfonato polystyrene chains have been prepared by living anionic polymerization and associated with mesogenic counterions, the structure of which is a rigid azobenzene moiety attached to a quaternary ammonium halide through a flexible spacer. The thermotropic behavior of the liquid crystalline halato(semi)telechelic polymers (LC H(S)TP's) has been studied by differential scanning calorimetry and optical microscopy. Some of them show smectic mesophases in a large temperature range. Actually, the liquid crystalline properties of the LC H(S)TP's depend on the molecular weight and the nature of the ionic end groups. A model, based on a crystal close packing approach, shows that the bulkiness of the sulfonato end groups can prevent the formation of smectic mesophases. The supramolecular organization of the LC H(S)TP's has also been studied by small angle neutron scattering, which agrees with a microphase separation between the polymer chains and the mesogenic counterions. [less ▲]

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See detailDynamic properties of the transient network formed by telechelic ionomers studied by dynamic light scattering and dynamic mechanical analysis
Johannsson, Ragnar; Chassenieux, Christophe; Durand, Dominique et al

in Macromolecules (1995), 28(25), 8504-8510

Solutions of alpha,omega-sodium sulfonatopolyisoprene (alpha,omega NaPIPS) in toluene are studied using static and dynamic light scattering and dynamic mechanical analysis. At concentrations above 4 g/L ... [more ▼]

Solutions of alpha,omega-sodium sulfonatopolyisoprene (alpha,omega NaPIPS) in toluene are studied using static and dynamic light scattering and dynamic mechanical analysis. At concentrations above 4 g/L, which is well below the overlap concentration of the polymer chains (C*), a transient network is formed characterized by a plateau modulus at high frequencies and a relatively narrow viscoelastic relaxation time distribution. The intensity autocorrelation function of the transient network shows two relaxational modes: a relatively fast diffusional mode close to the co-operative diffusional mode of semidilute solutions of the unfunctionalized polymers and a slow broader mode which becomes independent of the scattering angle at a concentrations close to C*. The relation between this slow mode and the viscoelastic relaxation is discussed. Both the slow mode and the viscoelastic relaxation processes have an Arrhenius temperature dependence with the same activation energy, E(a) = 25 kJ/mol. [less ▲]

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See detailAdsorption behavior of polymers with ionic end groups : mono- and difunctional polystyrenes in toluene
Pankewitsch, T.; Vanhoorne, Pierre ULg; Jérôme, Robert ULg et al

in Macromolecules (1995), 28(20), 6986-6992

The adsorption behavior of mono- and difunctional telechelic polymers, omega- and alpha,omega-sulfonato polystyrenes, from dilute toluene solution on the surface of a silicon wafer is investigated by ... [more ▼]

The adsorption behavior of mono- and difunctional telechelic polymers, omega- and alpha,omega-sulfonato polystyrenes, from dilute toluene solution on the surface of a silicon wafer is investigated by ellipsometry. Polystyrene without ionic end groups does not adsorb, and the attachment of molecules to the silicon dioxide surface proceeds via the functional ionic ends. Already a single ionic group promotes adsorption, and adsorption kinetics at small times is found to be diffusion limited. The approach of an equilibrium adsorbed amount at later times is controlled by the hindered diffusion of chains through the already existing layer. With monofunctional chains a thin stable monolayer at the surface is formed. With difunctional chains there is strong indication for coupling of ionic ends and the formation of additional layers. It is caused by the interaction of dangling ends, when only one end of the chains is adsorbed at the surface. The molecular weight dependence of the grafting density is consistent with scaling predictions, and differences in the adsorbed amount of telechelics with different counterions are explained on the basis of different valencies. [less ▲]

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See detailAggregation behavior of ω- and α,ω-metal sulfonato polystyrene in toluene
Vanhoorne, Pierre ULg; Jérôme, Robert ULg

in Macromolecules (1995), 28(16), 5664-5670

The aggregation behavior of omega- and alpha,omega-metal sulfonato polystyrene in toluene has been investigated by static and dynamic light scattering. Monofunctional chains reversibly associate into ... [more ▼]

The aggregation behavior of omega- and alpha,omega-metal sulfonato polystyrene in toluene has been investigated by static and dynamic light scattering. Monofunctional chains reversibly associate into small reverse micelles. Lithium-based ionic aggregates contain an average of 12 ion pairs, which corresponds to a preferential structure for the ionic cores. When the molecular weight of the chains is increased, polymer-solvent interactions progressively distort the ionic aggregates, and above a critical molecular weight, estimated to be 50000 in toluene, the multiplets collapse into smaller aggregates of an average of 3 ion pairs. Traces of polar solvents do not strongly affect the aggregation number, but do weaken the dipole-dipole interactions. Structure of the ionic cores strongly depends on the nature of the ion pairs, which suggests that this structural feature is a key parameter in the control of the structure-property relationships in ionomers. The aggregation behavior of the difunctional chains is complex, due to the occurrence of a closed association mechanism for the individual multiplets and an open association of reverse micelles into larger aggregates. [less ▲]

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See detailMicrodynamics of reverse micelles of ω- and α,ω-metal sulfonato polystyrene in toluene
Vanhoorne, Pierre ULg; Grandjean, Jean ULg; Jérôme, Robert ULg

in Macromolecules (1995), 28(10), 3553-3561

Reverse micelles of omega- and alpha,omega-metal sulfonato polystyrenes in toluene have been investigated by Li-6, Li-7, and pulsed field gradient NMR. Micelles are found to be of a narrow size ... [more ▼]

Reverse micelles of omega- and alpha,omega-metal sulfonato polystyrenes in toluene have been investigated by Li-6, Li-7, and pulsed field gradient NMR. Micelles are found to be of a narrow size distribution and to consist of roughly spherical ionic cores shielded from the solvent by a polystyrene shell. The nature of the ion pair is found to influence significantly the micellar size. The correlation time characteristic of lithium relaxation is faster than the reorientational correlation time of the aggregates, which means that lithium relaxation essentially takes place within the ionic cores. The effective relaxation mechanism is consistent with a fast exchange of lithium ions between different coordination sites within the aggregates. In concentrated solutions, the equilibrium between aggregated polymer chains and unassociated chains is essentially shifted toward the aggregated species. This tendency is reversed upon dilution. Below a critical micellar concentration of ca. 0.01 g/dL, only ''free'' chains persist in solution. Temperature has no significant effect on the position of the aggregation equilibrium. The aggregates are dissociated by the addition of a polar cosolvent, such as methanol, which solvates the ion pairs. The MeOH/Li+ molar ratio must, however, be higher than 100 to perturb significantly the ion pair aggregation. Up to a MeOH/Li+ ratio of 10 000, part of the chains remain aggregated, and the lithium spin-lattice relaxation is dominated by the aggregates. Above a MeOH/Li+ ratio of 10 000, the aggregates are almost completely disrupted. Self-diffusion coefficients of the difunctional chains are not dramatically smaller compared to the monofunctional counterparts, even when solutions of difunctional compounds form a gel. This behavior might be explained by the percolation model applied to the aggregation process, with the pulsed field NMR experiment probing only the selfdiffusion of the clusters in the sol phase of the gel. [less ▲]

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