The phenomenological analysis of the pressure-temperature $\mathrm{}(P-T)\mathrm{}$ phase diagram of ${\left[\mathrm{N}\right(\mathrm{C}\mathrm{H}}_3{)}_4{]}_2{\mathrm{CuCl}}_4$ (TMATC-Cu) crystals is presented. It is shown that serious disagreement between the experimental results and theory may be removed assuming that the coefficient of the Landau free energy expansion $\kappa$ at the gradient term ${\mathrm{}(dq/dz)(dq}^{*}/dz)$ changes the sign in the experimental range of pressures. The phase diagram in the $\alpha -\kappa$ phase plane is characterized by infinite Lifshitz point (at $\overrightarrow{\kappa }\infty )$ in which both lines of the phase transitions into the incommensurate phase merge together, whereas the incommensurate wave vector approaches its zero value. The triple point ${(P}_K\approx 55\mathrm{MPa},$ $T_K\approx 304\mathrm{K})$ observed in these crystals may be considered as an artificial point, which results from the limitation of experimental resolution. Therefore, even above $P_K$ there still exist two very close (unresolved) lines of the incommensurate phase transitions.

We report on the capillary rise of water in three-dimensional networks of hydrophilic silica pores with 3.5 nm and 5 nm mean radii, respectively (porous Vycor monoliths). We find classical square root of time Lucas-Washburn laws for the imbibition dynamics over the entire capillary rise times of up to 16 h investigated. Provided we assume two preadsorbed strongly bound layers of water molecules resting at the silica walls, which corresponds to a negative velocity slip length of $-0.5\text{nm}$ for water flow in silica nanopores, we can describe the filling process by a retained fluidity and capillarity of water in the pore center. This anticipated partitioning in two dynamic components reflects the structural-thermodynamic partitioning in strongly silica bound water layers and capillary condensed water in the pore center which is documented by sorption isotherm measurements.

To clarify the inconsistencies in existing elastic constant data of ${\mathrm{SrTiO}}_3$ in the vicinity of the 105 K phase transition we have studied the temperature dependence of the Young’s modulus of ${\mathrm{SrTiO}}_3$ crystals. Dynamic mechanical analysis at 10–140 K and 10–45 Hz has been used for the experiments. We found two remarkable features: a giant elastic softening (superelasticity) below the cubic $\to$ tetragonal phase transition, and elastic anomalies in the quantum paraelectric region between about 25 K and 45 K. The giant elastic softening is caused by domain-wall motion: it can be suppressed with uniaxial compression and does not occur in the [111] direction. Elastic anomalies observed in the quantum paraelectric region display nonlinear elastic behavior. We relate these nonlinear elastic anomalies with the appearance of polarization clusters. Our data can be consistently described assuming a freezing of the dynamical polar clusters below 25 K.

During spontaneous imbibition, a wetting liquid is drawn into a porous medium by capillary forces. In systems with comparable pore length and diameter, such as paper and sand, the front of the propagating liquid forms a continuous interface. Sections of this interface advance in a highly correlated manner due to an effective surface tension, which restricts front broadening. Here we investigate water imbibition in a nanoporous glass (Vycor) in which the pores are much longer than they are wide. In this case, no continuous liquid–vapor interface with coalesced menisci can form. Anomalously fast imbibition front roughening is experimentally observed by neutron imaging. We propose a theoretical pore-network model, whose structural details are adapted to the microscopic pore structure of Vycor glass and show that it displays the same large-scale roughening characteristics as observed in the experiment. The model predicts that menisci movements are uncorrelated, indicating that despite the connectivity of the network the smoothening effect of surface tension on the imbibition front roughening is negligible. These results suggest a new universality class of imbibition behavior, which is expected to occur in any matrix with elongated, interconnected pores of random radii.

The optical birefringence of rodlike nematogens (7CB, 8CB), imbibed in parallel silica channels with 10 nm diameter and 300 $\mu$m length, is measured and compared to the thermotropic bulk behavior. The orientational order of the confined liquid crystals, quantified by the uniaxial nematic ordering parameter, evolves continuously between paranematic and nematic states, in contrast to the discontinuous isotropic-to-nematic bulk phase transitions. A Landau–de Gennes model reveals that the strength of the orientational ordering fields, imposed by the silica walls, is beyond a critical threshold, that separates discontinuous from continuous paranematic-to-nematic behavior. Quenched disorder effects, attributable to wall irregularities, leave the transition temperatures affected only marginally, despite the strong ordering fields in the channels.