Pore-space correlations in capillary condensation in Vycor

Abstract

We use ultrasonic attenuation and light scattering to study spatial correlations in the pores of Vycor on filling and draining with hexane. On filling, the hexane initially adsorbs uniformly, but when capillary condensation occurs, vapor microbubbles are formed and persist until the sample is completely full. However, no long-range correlations of the bubbles are observed. By contrast, on drainage, the empty pores exhibit long-range correlations with a fractal dimension of 2.6. This results from the pore connectivity, suggesting that this behavior can be modeled by invasion percolation.

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

“…Their relaxation properties should differ from the molecules located in the core region, since they encounter more heterogeneous surroundings and thus interaction potentials leading to broader distributions of relaxation times. Also the relative number of these molecules increases with decreasing f [39,85,86], in agreement with the increased broadening observed for decreasing f . In order to compare the confined molecular relaxation with the documented molecular dynamics of the bulk LC system, it is instructive to analyse the T -dependence of the relaxation times of the interface and core processes, as displayed in Fig.…”

In situ small-angle neutron scattering study of nitrogen adsorption and condensation in mesoporous silica glass CPG-10-75

“…Adsorptive smoothing has also been observed with benzene [30]. Power law scattering, I (q) ∼ q −2.27±0.05 , is observed at low q, which may indicate that drainage occurs via percolation [4,5,23,27,35,36]. The theoretical value for scattering from a sample spanning cluster in an infinite three-dimensional lattice is D v = 2.53 [37].…”

“…On the one hand molecular simulations, density functional theory, and recent experiments suggest that hysteresis is due to multiple metastable states which are induced by the disorder of the solid matrix [1][2][3]. On the other hand, experiments show, that drainage of n-hexane from Vycor occurs via percolation [4][5][6]. The latter is assumed to be caused by pore blocking: smaller pores retard the drainage of larger pores if the larger pores are connected to the sample surface by the smaller ones only.…”

Thermotropic nematic order upon nanocapillary filling

“…Both regimes can be inferred by light adsorption experiments. Upon onset of capillary condensation or evaporation typically a drastic decrease in optical transmission, lg(I/I 0 ) is observable [25][26][27] (Here I 0 and I are the intensities of incident and transmitted laser light, respectively). The matrix turns milky and the reduction in the transmitted light originates in scattering at the capillary bridges/void structures, which have sizes on the length scale of the wavelength of visible light [28,29].…”