We present a neutron and X-rays scattering study of the phase transitions of 4-n-octyl-4 ′-cyanob... more We present a neutron and X-rays scattering study of the phase transitions of 4-n-octyl-4 ′-cyanobiphenyl (8CB) confined in unidirectional nanopores of porous alumina and porous silicon (PSi) membranes with an average diameter of 30 nm. Spatial confinement reveals a rich polymorphism, with at least four different low temperature phases in addition to the smectic A phase. The structural study as a function of thermal treatments and conditions of spatial confinement allows us to get insights into the formation of these phases and their relative stability. It gives the first description of the complete phase behavior of 8CB confined in PSi and provides a direct comparison with results obtained in bulk conditions and in similar geometric conditions of confinement but with reduced quenched disorder effects using alumina anopore membranes. PACS. 61.05.fg Neutron scattering (including small-angle scattering) – 64.70.mj Experimental studies of liquid crystal transitions – 61.30.Pq Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems
Physical chemistry chemical physics : PCCP, Jan 14, 2015
We report dielectric relaxation spectroscopy experiments on two rod-like liquid crystals of the c... more We report dielectric relaxation spectroscopy experiments on two rod-like liquid crystals of the cyanobiphenyl family (5CB and 6CB) confined in tubular nanochannels with 7 nm radius and 340 micrometer length in a monolithic, mesoporous silica membrane. The measurements were performed on composites for two distinct regimes of fractional filling: monolayer coverage at the pore walls and complete filling of the pores. For the layer coverage a slow surface relaxation dominates the dielectric properties. For the entirely filled channels the dielectric spectra are governed by two thermally-activated relaxation processes with considerably different relaxation rates: a slow relaxation in the interface layer next to the channel walls and a fast relaxation in the core region of the channel filling. The strengths and characteristic frequencies of both relaxation processes have been extracted and analysed as a function of temperature. Whereas the temperature dependence of the static capacitance ...
On connaît peu l'effet des éléments fins sur la floculation des fibres, et par conséquent sur la ... more On connaît peu l'effet des éléments fins sur la floculation des fibres, et par conséquent sur la formation de feuille. A l'aide du capteur de floculation du CTP, nous avons mesuré la tendance à floculer de suspensions fibreuses avec des taux d'éléments fins variables, en présence d'un système de rétention composé d'amidon cationique et de polyacrylamide anionique. Il apparaît qu'un taux d'éléments fins ajouté de 40% provoque une augmentation de la floculation fibreuse de 18%, dans des conditions de rétention usuelles. Nous avons estimé qu'une telle fraction d'éléments fins pouvait être observée en caisse de tête pour une rétention totale de 63%. Il est donc probable que l'effet néfaste des éléments fins sur la floculation soit amplifié sur machine à papier. Ainsi, il semble souhaitable de maintenir un bon niveau de rétention des éléments fins pour optimiser la formation de feuille.
We report filling-fraction dependent dielectric spectroscopy measurements on the relaxation dynam... more We report filling-fraction dependent dielectric spectroscopy measurements on the relaxation dynamics of the rod-like nematogen 7CB condensed in 13 nm silica nanochannels. In the film-condensed regime, a slow interface relaxation dominates the dielectric spectra, whereas from the capillary-condensed state up to complete filling an additional, fast relaxation in the core of the channels is found. The temperature-dependence of the static capacitance, representative of the averaged, collective molecular orientational ordering, indicates a continuous, paranematic-to-nematic (P-N) transition, in contrast to the discontinuous bulk behaviour. It is well described by a Landau-de-Gennes free energy model for a phase transition in cylindrical confinement. The large tensile pressure of 10 MPa in the capillary-condensed state, resulting from the Young-Laplace pressure at highly curved liquid menisci, quantitatively accounts for a downward-shift of the P-N transition and an increased molecular mo...
Semiconducting nanowires made of discotic columnar liquid crystals can be obtained by impregnatio... more Semiconducting nanowires made of discotic columnar liquid crystals can be obtained by impregnation into solid nanoporous templates, and provide new oportunities to tailor devices for organic electronics with promising charge carriers transport properties. These properties are tightly related to the self-assembly and molecular dynamics of the discotic columns inside the nanowires. We recently studied and rationalized the formation of different nanostructures in the columnar phase of pyrene derivative discotics nanoconfined in anodic alumina and porous silicon templates (Cerclier et al., The Journal of Physical Chemistry C 116, 18990 (2012), Kityk et al., Soft Matter 10, 4522 (2014)). We now present the study of the molecular dynamics of nano-confined pyrene derivative mesogenic phases by incoherent quasielastic neutron scattering over a broad range of correlation times. The combination of backscattering and time of flight techniques has allowed to describe the nature of the molecular motions at play on the ps-to-ns time scale The dynamics of the columnar phase is dominated by fluctuations of the lateral chains, while the onset of larger amplitude motions like whole-body reorientations and slow center-of-mass translational diffusion occurs at high temperature in the isotropic phase. Interestingly, nano-confinement does not qualitatively alter the nature of the molecular dynamics, but essentially blocks the long range translational motions and induces broader distributions of correlation times of the fastest local relaxations.
We study water adsorption-induced deformation of a monolithic, mesoporous silicon membrane traver... more We study water adsorption-induced deformation of a monolithic, mesoporous silicon membrane traversed by independent channels of 8 nm diameter. We focus on the elastic constant associated with the Laplace pressure-induced deformation of the membrane upon capillary condensation, i.e. the pore-load modulus. We perform finite-element method (FEM) simulations of the adsorption-induced deformation of hexagonal and square lattices of cylindrical pores representing the membrane. We find that the pore-load modulus weakly depends on the geometrical arrangement of pores, and can be expressed as a function of porosity. We propose an analytical model which relates the pore-load modulus to the porosity and to the elastic properties of bulk silicon (Young's modulus and Poisson's ratio), and provides an excellent agreement with FEM results. We find good agreement between our experimental data and the predictions of the analytical model, with the Young's modulus of the pore walls slightly lower than the bulk value. This model is applicable to a large class of materials with morphologies analogous to mesoporous silicon. Moreover, our findings suggest that liquid condensation experiments allow one to elegantly access the elastic constants of a mesoporous medium.
We report a high-resolution dielectric study on a pyrene-based discotic liquid crystal (DLC) in t... more We report a high-resolution dielectric study on a pyrene-based discotic liquid crystal (DLC) in the bulk state and confined in parallel tubular nanopores of monolithic silica and alumina membranes. The positive dielectric anisotropy of the DLC molecule at low frequencies (in the quasi-static case) allows us to explore the thermotropic collective orientational order. A face-on arrangement of the molecular discs on the pore walls and a corresponding radial arrangement of the molecules is found. In contrast to the bulk, the isotropic-to-columnar transition of the confined DLC is continuous, shifts with decreasing pore diameter to lower temperatures and exhibits a pronounced hysteresis between cooling and heating. These findings corroborate conclusions from previous neutron and X-ray scattering experiments as well as optical birefringence measurements. Our study also indicates that the relative simple dielectric technique presented here is a quite efficient method in order to study the thermotropic orientational order of DLC based nanocomposites.
N-2 and CO condensed into nanoporous glasses have been investigated by vapor pressure measurement... more N-2 and CO condensed into nanoporous glasses have been investigated by vapor pressure measurements and a-ray diffraction as a function of temperature and fractional filling. The pore material is stable with respect to bulk condensation for any fractional filling. The adsorbate on the pore walls has to be distinguished from the capillary condensate in the center of the pores. This distinction can be made not only in the Liquid, but also in the solid state. The solid capillary condensate is quasi-hcp at higher temperatures. N-2 remains in this state down to the lowest temperatures, even in pores as large as 130 Angstrom diameter, whereas CO transforms into the orientationally ordered Pa3 phase. On heating an orientationally disordered intermediate phase with a fec center-of-mass lattice is observed.
Capillary filling dynamics of liquid n-tetracosane (n-C24H50) in a network of cylindrical pores w... more Capillary filling dynamics of liquid n-tetracosane (n-C24H50) in a network of cylindrical pores with 7 and 10 nm mean diameter in monolithic silica glass (Vycor) exhibit an abrupt temperature-slope change at Ts approx. 54 degC, 4 deg C above bulk and 16 degC, 8 deg C, respectively, above pore freezing. It can be traced to a sudden inversion of the surface tension’s T slope, and thus to a decrease in surface entropy at the advancing pore menisci, characteristic of the formation of a single solid monolayer of rectified molecules, known as surface freezing from macroscopic, quiescent tetracosane melts. The imbibition speeds, that are the squared prefactors of the observed square-root-of-time Lucas-Washburn invasion kinetics, indicate a conserved bulk fluidity and capillarity of the nanopore-confined liquid, if we assume a flat lying, sticky hydrocarbon backbone monolayer at the silica walls.
Journal of Physics: Condensed Matter 27, 103102 (2015)
Spatial confinement in nanoporous media affects the structure, thermodynamics and mobility of mol... more Spatial confinement in nanoporous media affects the structure, thermodynamics and mobility of molecular soft matter often markedly. This article reviews thermodynamic equilibrium phenomena, such as physisorption, capillary condensation, crystallisation, self-diffusion, and structural phase transitions as well as selected aspects of the emerging field of spatially confined, non-equilibrium physics, i.e. the rheology of liquids, capillarity-driven flow phenomena, and imbibition front broadening in nanoporous materials. The observations in the nanoscale systems are related to the corresponding bulk phenomenologies. The complexity of the confined molecular species is varied from simple building blocks, like noble gas atoms, normal alkanes and alcohols to liquid crystals, polymers, ionic liquids, proteins and water. Mostly, experiments with mesoporous solids of alumina, gold, carbon, silica, and silicon with pore diameters ranging from a few up to 50 nm are presented. The observed peculiarities of nanopore-confined condensed matter are also discussed with regard to applications.
A particular emphasis is put on texture formation upon crystallisation in nanoporous media, a topic both of high fundamental interest and of increasing nanotechnological importance, e.g. for the synthesis of organic/inorganic hybrid materials by melt infiltration, the usage of nanoporous solids in crystal nucleation or in template-assisted electrochemical deposition of nano structures.
Ar condensed into a porous glass matrix has been investigated by simultaneous measurements of ads... more Ar condensed into a porous glass matrix has been investigated by simultaneous measurements of adsorption- desorption isotherms and x-ray diffraction patterns as function of the pore filling above and below the melting point. The chemical-potential–temperature phase diagram has been established. It is consistent with a first- order phase transition between the adsorbate state and the capillary condensed state, above and below the melting temperature. The adsorbate and the capillary condensed state can also be distinguished in the diffrac- tion patterns. A consistent picture of the structure and the thermodynamics is obtained.
We present a neutron and X-rays scattering study of the phase transitions of 4-n-octyl-4 ′-cyanob... more We present a neutron and X-rays scattering study of the phase transitions of 4-n-octyl-4 ′-cyanobiphenyl (8CB) confined in unidirectional nanopores of porous alumina and porous silicon (PSi) membranes with an average diameter of 30 nm. Spatial confinement reveals a rich polymorphism, with at least four different low temperature phases in addition to the smectic A phase. The structural study as a function of thermal treatments and conditions of spatial confinement allows us to get insights into the formation of these phases and their relative stability. It gives the first description of the complete phase behavior of 8CB confined in PSi and provides a direct comparison with results obtained in bulk conditions and in similar geometric conditions of confinement but with reduced quenched disorder effects using alumina anopore membranes. PACS. 61.05.fg Neutron scattering (including small-angle scattering) – 64.70.mj Experimental studies of liquid crystal transitions – 61.30.Pq Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems
Physical chemistry chemical physics : PCCP, Jan 14, 2015
We report dielectric relaxation spectroscopy experiments on two rod-like liquid crystals of the c... more We report dielectric relaxation spectroscopy experiments on two rod-like liquid crystals of the cyanobiphenyl family (5CB and 6CB) confined in tubular nanochannels with 7 nm radius and 340 micrometer length in a monolithic, mesoporous silica membrane. The measurements were performed on composites for two distinct regimes of fractional filling: monolayer coverage at the pore walls and complete filling of the pores. For the layer coverage a slow surface relaxation dominates the dielectric properties. For the entirely filled channels the dielectric spectra are governed by two thermally-activated relaxation processes with considerably different relaxation rates: a slow relaxation in the interface layer next to the channel walls and a fast relaxation in the core region of the channel filling. The strengths and characteristic frequencies of both relaxation processes have been extracted and analysed as a function of temperature. Whereas the temperature dependence of the static capacitance ...
On connaît peu l'effet des éléments fins sur la floculation des fibres, et par conséquent sur la ... more On connaît peu l'effet des éléments fins sur la floculation des fibres, et par conséquent sur la formation de feuille. A l'aide du capteur de floculation du CTP, nous avons mesuré la tendance à floculer de suspensions fibreuses avec des taux d'éléments fins variables, en présence d'un système de rétention composé d'amidon cationique et de polyacrylamide anionique. Il apparaît qu'un taux d'éléments fins ajouté de 40% provoque une augmentation de la floculation fibreuse de 18%, dans des conditions de rétention usuelles. Nous avons estimé qu'une telle fraction d'éléments fins pouvait être observée en caisse de tête pour une rétention totale de 63%. Il est donc probable que l'effet néfaste des éléments fins sur la floculation soit amplifié sur machine à papier. Ainsi, il semble souhaitable de maintenir un bon niveau de rétention des éléments fins pour optimiser la formation de feuille.
We report filling-fraction dependent dielectric spectroscopy measurements on the relaxation dynam... more We report filling-fraction dependent dielectric spectroscopy measurements on the relaxation dynamics of the rod-like nematogen 7CB condensed in 13 nm silica nanochannels. In the film-condensed regime, a slow interface relaxation dominates the dielectric spectra, whereas from the capillary-condensed state up to complete filling an additional, fast relaxation in the core of the channels is found. The temperature-dependence of the static capacitance, representative of the averaged, collective molecular orientational ordering, indicates a continuous, paranematic-to-nematic (P-N) transition, in contrast to the discontinuous bulk behaviour. It is well described by a Landau-de-Gennes free energy model for a phase transition in cylindrical confinement. The large tensile pressure of 10 MPa in the capillary-condensed state, resulting from the Young-Laplace pressure at highly curved liquid menisci, quantitatively accounts for a downward-shift of the P-N transition and an increased molecular mo...
Semiconducting nanowires made of discotic columnar liquid crystals can be obtained by impregnatio... more Semiconducting nanowires made of discotic columnar liquid crystals can be obtained by impregnation into solid nanoporous templates, and provide new oportunities to tailor devices for organic electronics with promising charge carriers transport properties. These properties are tightly related to the self-assembly and molecular dynamics of the discotic columns inside the nanowires. We recently studied and rationalized the formation of different nanostructures in the columnar phase of pyrene derivative discotics nanoconfined in anodic alumina and porous silicon templates (Cerclier et al., The Journal of Physical Chemistry C 116, 18990 (2012), Kityk et al., Soft Matter 10, 4522 (2014)). We now present the study of the molecular dynamics of nano-confined pyrene derivative mesogenic phases by incoherent quasielastic neutron scattering over a broad range of correlation times. The combination of backscattering and time of flight techniques has allowed to describe the nature of the molecular motions at play on the ps-to-ns time scale The dynamics of the columnar phase is dominated by fluctuations of the lateral chains, while the onset of larger amplitude motions like whole-body reorientations and slow center-of-mass translational diffusion occurs at high temperature in the isotropic phase. Interestingly, nano-confinement does not qualitatively alter the nature of the molecular dynamics, but essentially blocks the long range translational motions and induces broader distributions of correlation times of the fastest local relaxations.
We study water adsorption-induced deformation of a monolithic, mesoporous silicon membrane traver... more We study water adsorption-induced deformation of a monolithic, mesoporous silicon membrane traversed by independent channels of 8 nm diameter. We focus on the elastic constant associated with the Laplace pressure-induced deformation of the membrane upon capillary condensation, i.e. the pore-load modulus. We perform finite-element method (FEM) simulations of the adsorption-induced deformation of hexagonal and square lattices of cylindrical pores representing the membrane. We find that the pore-load modulus weakly depends on the geometrical arrangement of pores, and can be expressed as a function of porosity. We propose an analytical model which relates the pore-load modulus to the porosity and to the elastic properties of bulk silicon (Young's modulus and Poisson's ratio), and provides an excellent agreement with FEM results. We find good agreement between our experimental data and the predictions of the analytical model, with the Young's modulus of the pore walls slightly lower than the bulk value. This model is applicable to a large class of materials with morphologies analogous to mesoporous silicon. Moreover, our findings suggest that liquid condensation experiments allow one to elegantly access the elastic constants of a mesoporous medium.
We report a high-resolution dielectric study on a pyrene-based discotic liquid crystal (DLC) in t... more We report a high-resolution dielectric study on a pyrene-based discotic liquid crystal (DLC) in the bulk state and confined in parallel tubular nanopores of monolithic silica and alumina membranes. The positive dielectric anisotropy of the DLC molecule at low frequencies (in the quasi-static case) allows us to explore the thermotropic collective orientational order. A face-on arrangement of the molecular discs on the pore walls and a corresponding radial arrangement of the molecules is found. In contrast to the bulk, the isotropic-to-columnar transition of the confined DLC is continuous, shifts with decreasing pore diameter to lower temperatures and exhibits a pronounced hysteresis between cooling and heating. These findings corroborate conclusions from previous neutron and X-ray scattering experiments as well as optical birefringence measurements. Our study also indicates that the relative simple dielectric technique presented here is a quite efficient method in order to study the thermotropic orientational order of DLC based nanocomposites.
N-2 and CO condensed into nanoporous glasses have been investigated by vapor pressure measurement... more N-2 and CO condensed into nanoporous glasses have been investigated by vapor pressure measurements and a-ray diffraction as a function of temperature and fractional filling. The pore material is stable with respect to bulk condensation for any fractional filling. The adsorbate on the pore walls has to be distinguished from the capillary condensate in the center of the pores. This distinction can be made not only in the Liquid, but also in the solid state. The solid capillary condensate is quasi-hcp at higher temperatures. N-2 remains in this state down to the lowest temperatures, even in pores as large as 130 Angstrom diameter, whereas CO transforms into the orientationally ordered Pa3 phase. On heating an orientationally disordered intermediate phase with a fec center-of-mass lattice is observed.
Capillary filling dynamics of liquid n-tetracosane (n-C24H50) in a network of cylindrical pores w... more Capillary filling dynamics of liquid n-tetracosane (n-C24H50) in a network of cylindrical pores with 7 and 10 nm mean diameter in monolithic silica glass (Vycor) exhibit an abrupt temperature-slope change at Ts approx. 54 degC, 4 deg C above bulk and 16 degC, 8 deg C, respectively, above pore freezing. It can be traced to a sudden inversion of the surface tension’s T slope, and thus to a decrease in surface entropy at the advancing pore menisci, characteristic of the formation of a single solid monolayer of rectified molecules, known as surface freezing from macroscopic, quiescent tetracosane melts. The imbibition speeds, that are the squared prefactors of the observed square-root-of-time Lucas-Washburn invasion kinetics, indicate a conserved bulk fluidity and capillarity of the nanopore-confined liquid, if we assume a flat lying, sticky hydrocarbon backbone monolayer at the silica walls.
Journal of Physics: Condensed Matter 27, 103102 (2015)
Spatial confinement in nanoporous media affects the structure, thermodynamics and mobility of mol... more Spatial confinement in nanoporous media affects the structure, thermodynamics and mobility of molecular soft matter often markedly. This article reviews thermodynamic equilibrium phenomena, such as physisorption, capillary condensation, crystallisation, self-diffusion, and structural phase transitions as well as selected aspects of the emerging field of spatially confined, non-equilibrium physics, i.e. the rheology of liquids, capillarity-driven flow phenomena, and imbibition front broadening in nanoporous materials. The observations in the nanoscale systems are related to the corresponding bulk phenomenologies. The complexity of the confined molecular species is varied from simple building blocks, like noble gas atoms, normal alkanes and alcohols to liquid crystals, polymers, ionic liquids, proteins and water. Mostly, experiments with mesoporous solids of alumina, gold, carbon, silica, and silicon with pore diameters ranging from a few up to 50 nm are presented. The observed peculiarities of nanopore-confined condensed matter are also discussed with regard to applications.
A particular emphasis is put on texture formation upon crystallisation in nanoporous media, a topic both of high fundamental interest and of increasing nanotechnological importance, e.g. for the synthesis of organic/inorganic hybrid materials by melt infiltration, the usage of nanoporous solids in crystal nucleation or in template-assisted electrochemical deposition of nano structures.
Ar condensed into a porous glass matrix has been investigated by simultaneous measurements of ads... more Ar condensed into a porous glass matrix has been investigated by simultaneous measurements of adsorption- desorption isotherms and x-ray diffraction patterns as function of the pore filling above and below the melting point. The chemical-potential–temperature phase diagram has been established. It is consistent with a first- order phase transition between the adsorbate state and the capillary condensed state, above and below the melting temperature. The adsorbate and the capillary condensed state can also be distinguished in the diffrac- tion patterns. A consistent picture of the structure and the thermodynamics is obtained.
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Papers by Patrick Huber
sudden inversion of the surface tension’s T slope, and thus to a decrease in surface entropy at the advancing pore menisci, characteristic of the formation of a single solid monolayer of rectified molecules, known as surface freezing from macroscopic, quiescent tetracosane melts. The imbibition speeds, that are
the squared prefactors of the observed square-root-of-time Lucas-Washburn invasion kinetics, indicate a conserved bulk fluidity and capillarity of the nanopore-confined liquid, if we assume a flat lying, sticky hydrocarbon backbone monolayer at the silica walls.
A particular emphasis is put on texture formation upon crystallisation in nanoporous media, a topic both of high fundamental interest and of increasing nanotechnological importance, e.g. for the synthesis of organic/inorganic hybrid materials by melt infiltration, the usage of nanoporous solids in crystal nucleation or in template-assisted electrochemical deposition of nano structures.
desorption isotherms and x-ray diffraction patterns as function of the pore filling above and below the melting
point. The chemical-potential–temperature phase diagram has been established. It is consistent with a first-
order phase transition between the adsorbate state and the capillary condensed state, above and below the
melting temperature. The adsorbate and the capillary condensed state can also be distinguished in the diffrac-
tion patterns. A consistent picture of the structure and the thermodynamics is obtained.
sudden inversion of the surface tension’s T slope, and thus to a decrease in surface entropy at the advancing pore menisci, characteristic of the formation of a single solid monolayer of rectified molecules, known as surface freezing from macroscopic, quiescent tetracosane melts. The imbibition speeds, that are
the squared prefactors of the observed square-root-of-time Lucas-Washburn invasion kinetics, indicate a conserved bulk fluidity and capillarity of the nanopore-confined liquid, if we assume a flat lying, sticky hydrocarbon backbone monolayer at the silica walls.
A particular emphasis is put on texture formation upon crystallisation in nanoporous media, a topic both of high fundamental interest and of increasing nanotechnological importance, e.g. for the synthesis of organic/inorganic hybrid materials by melt infiltration, the usage of nanoporous solids in crystal nucleation or in template-assisted electrochemical deposition of nano structures.
desorption isotherms and x-ray diffraction patterns as function of the pore filling above and below the melting
point. The chemical-potential–temperature phase diagram has been established. It is consistent with a first-
order phase transition between the adsorbate state and the capillary condensed state, above and below the
melting temperature. The adsorbate and the capillary condensed state can also be distinguished in the diffrac-
tion patterns. A consistent picture of the structure and the thermodynamics is obtained.