Confinement effects on phase behavior of soft matter systems

Binder, Kurt; Horbach, Jürgen; Vink, R. L. C.; Virgiliis, Andrés De

doi:10.1039/b802207k

Cited by 126 publications

(168 citation statements)

References 134 publications

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“…Computer simulations on LCs in thin film and pore geometry can give here important complementary insights [13,24,[41][42][43][44][45][46][47][48][49][50]. These studies indicate pronounced spatial heterogeneities, in particular interface-induced molecular layering and radial gradients both in the orientational order and reorientational dynamics in cylindrical pore geometry [51].…”

Section: Fig 1: (Color Online)mentioning

confidence: 99%

“…Thus confinement plays here a similar role as an external magnetic field for a spin system [18,29]: The strong first order I-N transition is replaced by a weak first order or continuous paranematic-to-nematic (P-N ) transition at a temperature T P N and may also be accompanied by pre transitional phenomena in the molecular orientational distribution [30]. An understanding of these phenomonenologies is of high fundament interest, for it allows to explore the validity (and break-down) of basic concepts of condensed matter science at the nanoscale [3,8,13,15,22].…”

Section: Introductionmentioning

confidence: 99%

“…Both the collective orientational (isotropic-to-nematic) and the translational (smectic-toliquid or smectic-to-nematic) transitions have turned out to be significantly affected by finite size and interfacial (solid-liquid or liquid-liquid) interactions introduced by confining walls [1][2][3][4][5][6] or the geometrical constraints in nanoporous media [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24].…”

Section: Introductionmentioning

confidence: 99%

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Inhomogeneous relaxation dynamics and phase behaviour of a liquid crystal confined in a nanoporous solid

et al. 2015

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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 capillarycondensed 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-deGennes 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 mobility in comparison to the unstretched liquid state of the complete filling. The strengths of the slow and fast relaxations provide local information on the orientational order: The thermotropic behaviour in the core region is bulk-like, i.e. it is characterized by an abrupt onset of the nematic order at the P-N transition. By contrast, the interface ordering exhibits a continuous evolution at the P-N transition. Thus, the phase behaviour of the entirely filled liquid crystal-silica nanocomposite can be quantitatively described by a linear superposition of these distinct nematic order contributions.

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Section: Fig 1: (Color Online)mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Inhomogeneous relaxation dynamics and phase behaviour of a liquid crystal confined in a nanoporous solid

et al. 2015

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“…At the cylinder radius R = D/2 we apply a hard wall, which may overlap with neither colloids nor polymers. This boundary condition at the surface leads to an entropic attraction of the colloidal particles to the wall [40], causing the formation of a precursor of a wetting layer (a true wetting layer can only form in the limit D → ∞, of course [40]). For this model, the polymer fugacity exp(µ p /k B T ) or the related "polymer reservoir packing fraction" η r p = (4πr 3 p /3) exp(µ p /k B T ) plays the role of an inverse temperature like variable, while the colloid packing fraction η c = (4πr 3 c /3)N c /V (N c is the number of colloids in the system of volume V = πR 2 L) is the order parameter density.…”

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confidence: 99%

“…Polymer-colloid overlap (as well as colloid-colloid overlap) is strictly forbidden, while polymers can overlap with no energy cost. The phase diagram of this model in the bulk and for thin films has already been carefully studied [39,40]. At the cylinder radius R = D/2 we apply a hard wall, which may overlap with neither colloids nor polymers.…”

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Rounding of Phase Transitions in Cylindrical Pores

et al. 2010

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Phase transitions of systems confined in long cylindrical pores (capillary condensation, wetting, crystallization, etc.) are intrinsically not sharply defined but rounded. The finite size of the cross section causes destruction of long range order along the pore axis by spontaneous nucleation of domain walls. This rounding is analyzed for two models (Ising/lattice gas and Asakura-Oosawa model for colloid-polymer mixtures) by Monte Carlo simulations and interpreted by a phenomenological theory. We show that characteristic differences between the behavior of pores of finite length and infinitely long pores occur. In pores of finite length a rounded transition occurs first, from phase coexistence between two states towards a multi-domain configuration. A second transition to the axially homogeneous phase follows near pore criticality. PACS numbers: 64.75Jk, 64.60.an, 05.70Fh, 02.70Tt Fluids and fluid mixtures in nano-and microporous materials (pore diameters from 1 nm to 150 nm) play important roles in various industries (extracting oil and gas from porous rocks; use as catalysts or for mixture separation in the chemical and pharmaceutical industry; nanofluidic devices, etc.) [1][2][3]. The interplay of finite size and surface effects strongly modifies the phase behavior of such confined fluids [1,[3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] in comparison with the bulk. The vapor to liquid transition is shifted ("capillary condensation"), as well as critical points [3,4,9,12]. Effects of wetting [20] on phase coexistence give rise to interesting patterns (plugs versus capsules versus tube structures etc. [7]). However, although various phase diagrams (different from the bulk) have been proposed (e.g. [1,3,7,9,12,13,17]), many aspects hitherto are not well understood. E.g., the "critical point" where adsorption/desorption hysteresis vanishes seems to be systematically lower than the critical temperature where the density difference between the vapor-like and liquid-like states vanishes [12], in contrast to what theories have predicted [14].However, a crucial aspect (stressed only in a few pioneering studies [3,8], and in the context of Ising/lattice gas models [21][22][23]) is the rounding of all transitions, caused by the quasi-one-dimensional character of a fluid in a long cylindrical pore with cross-sectional radius R. With the current progress of producing pores of wellcontrolled diameter varying from the nanoscale (carbon nanotubes [23][24][25]) to arrays of pores in silicon wafers [26], up to 150 nm wide and of well-controlled length, experiments become feasible which are not plagued by effects of random disorder, which occur in porous glasses [1,27]. Thus, it is important to understand the phase transitions in pores more precisely, considering both the radius R and the length L of the pore as variables (the important role of L has so far been largely disregarded). In the present Letter, we elucidate the rounding of vaporliquid type transitions in cylindrical pores, based on Monte Carlo sim...

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Nematic and Chiral Nematic Liquid Crystals in Confined Geometries: Elementary Background with Selected Examples

Ravnik

Žumer

2014

Handbook of Liquid Crystals

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Confinement effects on phase behavior of soft matter systems

Cited by 126 publications

References 134 publications

Inhomogeneous relaxation dynamics and phase behaviour of a liquid crystal confined in a nanoporous solid

Inhomogeneous relaxation dynamics and phase behaviour of a liquid crystal confined in a nanoporous solid

Rounding of Phase Transitions in Cylindrical Pores

Nematic and Chiral Nematic Liquid Crystals in Confined Geometries: Elementary Background with Selected Examples

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