It is demonstrated that interactions between nanoparticles and topological defects induce a twist-grain boundary phase in a chiral liquid crystal. The occurrence of this phase, the analogue of the Shubnikov phase in type-II superconductors, is driven by direct interactions between surface-functionalized CdSe quantum dots and screw dislocations. It is shown that, within an adaptive-defect-core-targeting mechanism, nanoparticles of appropriate size and functionalization adapt to qualitatively different cores of topological defects such as disclination lines and screw dislocations. This mechanism enables the effective reduction of the energetically costly, singular defect core volume, while the surrounding phase ordering remains relatively weakly affected. The findings suggest new pathways towards the controlled assembly of superstructures in diverse, symmetry-broken, condensed-matter systems, ranging from nanoparticle-decorated liquid crystals to superconductors.

The phase transition behaviour of the chiral liquid crystal CE6 doped with spherical surface-functionalised CdSe nanoparticles has been examined by means of high-resolution adiabatic scanning calorimetry and polarising microscopy. The addition of nanoparticles results in an essentially stabilised blue phase III. The phase diagram is displayed upon heating and cooling and the enthalpy changes involved in the conversion between the blue phases are determined. The dispersion of functionalised nanoparticles is prominent for the stabilisation of blue phase III, which is potentially useful for applications, especially if applied on liquid crystals that exhibit blue phases close to room temperature.

Liquid-crystalline blue phases are attracting significant interest due to their potential for applications related to tunable photonic crystals and fast optical displays. In this work a brief theoretical model is presented accounting for the impact of anisotropic nanoparticles on the blue phase stability region. This model is tested by means of high-resolution calorimetric and optical measurements of the effect of anisotropic, surface-functionalized ${\mathrm{MoS}}_2$ nanoparticles on the blue phase range of a chiral liquid crystal. The addition of these nanoparticles effectively increases the temperature range of blue phases and especially the cubic structure of blue phase I.

By means of high-resolution ac calorimetry and polarizing optical microscopy, it is demonstrated that surface-functionalized spherical CdSSe nanoparticles induce a twist-grain boundary phase when dispersed in a chiral liquid crystal. These nanoparticles can effectively stabilize the one-dimensional lattice of screw dislocations, thus establishing the twist-grain boundary order between the cholesteric and the smectic-$A$ phases. A Landau–de Gennes–Ginzburg model is used to analyze the impact of nanoparticles on widening the temperature range of molecular organizations possessing a lattice of screw dislocations. We show that in addition to the defect-core-replacement mechanism, the saddle-splay elasticity may also play a significant role.

The structural and thermodynamic phase behavior of the thermotropic liquid crystal dodecylcyanobiphenyl (12CB) confined in controlled-pore glasses (CPGs) has been studied by means of high-resolution calorimetry and small-angle X-ray scattering. Non-treated CPG matrices have been used with a characteristic pore size R ranging from nanometre to micrometre scale. Even in the case of the strongest confinement the isotropic-to-smectic-A (I-SmA) transition was pronounced. Both the smectic pretransitional ordering and the broadening of the specific heat capacity anomaly were relatively weak. This signals the secondary importance of the surface interaction potential and of the disorder upon phase behavior. We claim that the surface interaction is dominated by the coupling between surface-frozen and volume liquid crystal molecules. This coupling is weak due to the flexible long alkyl chains which dominantly influence the phase behavior of 12CB. The depression of the phase transition temperature T_c is dominated by smectic elastic compressibility distortions. The observed anomalous T_c(R) dependence is explained by allowing surface rearrangement processes. In severely-confined samples the 1^st order I-SmA phase transition tends to be replaced by a 2^nd order one. This phenomenon is attributed to a dimensional-crossover which, in 12CB samples, is not masked by surface interactions as it is in case of similar liquid crystals with shorter alkyl chains. The observed behavior is explained using scaling and dimensional analysis within the Landau–Ginzburg–de Gennes mesoscopic approach.