On the influence of cylindrical sub-micrometer confinement on heptyloxycyanobiphenyl (7OCB). A dynamic dielectric study

Dielectric relaxation in bulk and cylindrically confined octylcyanobiphenyl (8CB)

“…In recent work regarding 7OCB a similar effect was also observed by means of calorimetric studies [9]. At this point we have to say that our measurements in the 10 2 -10 6 Hz frequency range did not reveal additional relaxations to those mentioned above, as similarly reported by Leys et al [8] and even by ourselves [10] when the same kind of confinement was considered. Nevertheless, in addition to the relaxational bulk-like modes, new relaxational modes were found from dielectric measurements, when these liquid crystals and other related materials were confined to strongly restricted random porous media [3,7,8,27].…”

“…Although n-alkylcyanobiphenyls are perhaps the most widely studied liquid crystals from a dielectric point of view [1,10,[21][22][23] some aspects of their behaviour are still not clear. For example most authors fit the dielectric data in the I phase to only one broad relaxation [3,8,22].…”

“…However, some basic problems concerning the interpretation of the experimental results are still the source of controversy [2]. Recently, much attention has been paid to the effect of confinement of liquid crystals in porous matrices, with calorimetric and dielectric techniques very useful to analyse the changes in dynamic and static properties [3][4][5][6][7][8][9][10]. In this work we report a study on 8CB confined in untreated and treated cylindrical pores of Anopore membranes.…”

Dispersion of γ-Alumina Nano-Sized Spherical Particles in a Calamitic Liquid Crystal. Study and Optimization of the Confinement Effects

“…In some cases, the spontaneous arrangement of calamitics in untreated metallic cells tends to be planar or nearly planar [43,44], though this is not always true and, sometimes, the cell surfaces must be treated with some surfactant in order to achieve the desired planar alignment of the molecules [25]. Fluidity of the nematic phase induces an average disorder of the molecules and, therefore, of the global nematic director, which translates in an inhomogeneous alignment of the sample, as is the case of the bulk 4O.8 sample.…”

“…On the other hand, ω 1 jumps down clearly in frequency when going from I to N and its activation energy is higher than that corresponding to the ω 2 mode. The validity of the fitting of ω 2 , although limited, can be taken as optimal as its tendency is typical of these kind of relaxation modes in rod-like molecules [ 25 , 26 , 28 , 43 ], as can be seen from the Arrenius plot in Figure 7 .…”