Spontaneous breaking of symmetry in liquid crystal (LC) films often reveals itself as a microscopic pattern of molecular alignment. In a smectic-A LC, the emergence of positional order at the transition from the nematic phase leads to periodic textures that can be used as optical microarrays, templates for soft lithography, and ordering matrices for the organization and manipulation of functional nanoparticles. While both 1d and 2d patterns have been obtained as a function of the LC film thickness and applied fields, the connection has not been made between pattern formation and the peculiar critical behavior of LCs at the nematic–smectic transition, still eluding a comprehensive theoretical explanation. In this article, we demonstrate that an intense bend distortion applied to the LC molecular director while cooling from the nematic phase produces a frustrated smectic phase with depressed transition temperature, and the characteristic 1d periodic texture previously observed in thin films and under applied electric fields. In light of De Gennes’ analogy with the normal-superconductor transition of a metal, we identify the 1d texture as the equivalent of the intermediate state in type I superconductors. The bend distortion is analog to the magnetic field in metals and penetrates in the frustrated phase as an array of undercooled nematic domains, periodically intermixed with bend-free smectic-A domains. Our findings provide fundamental evidence for theories of the nematic–smectic transition, highlighting the deep connection between phase frustration and pattern formation, and perspectives on the design of functional smectic microarrays. Significance Microscopic patterns of molecular alignment are easily obtained in smectic LCs subject to conflicting alignment conditions and provide a promising route to the rapid bottom-up fabrication of ordered materials, notably for the organization and manipulation of nanoparticles. A convenient but puzzling feature is that the pattern type can be switched between 1d and 2d by varying the film thickness or applying an electric field. We devised a simple experiment to show that 1d patterns are due to frustration of the smectic phase under a strong distortion of the molecular director field, leading to a mixed nematic–smectic phase. Our finding confirms the long-standing prediction of an “intermediate” LC state based on an analogy with superconductors.

Studies of temperature behavior of the mean refractive index, ordinary and extraordinary refractive indices, and birefringence have been carried out for three nematogens. The thermo-morphologic properties of the biphasic regions of the direct nematic-isotropic liquid and reverse isotropic liquid-nematic phase transitions have been investigated. The 4-n-alkyl-4′-oxycyanobiphenyls (n = 5, 6, 7) were objects of our study. Studies have been carried out for the circular cycle as the heating-cooling. Temperature behavior of the order parameter in nematic mesophase and at the nematic-isotropic liquid and isotropic liquid-nematic phase transition is discussed.

We report on the temperature-dependent measurements of dielectric permittivity, birefringence, elastic constants and rotational viscosity for 4-propoxy-biphenyl-4-carbonitrile in the nematic region. The temperature dependence of the three elastic constants was determined from studies of the Freédericksz transition. The thermal dependence of elastic constants shows features similar to the literature (bend > splay > twist). Elastic constants are proportional to the square of the order parameter. Temperature-dependent dielectric characterisation was carried out at a frequency of 10 kHz. The compound shows positive dielectric anisotropy in the nematic phase. The rotational viscosity is found to be relatively low. Temperature dependence of order parameter is estimated using Haller’s method. The figure of merit was also calculated as a function of temperature.