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Studies of internal and interfacial energy dissipation mechanisms in thin (50nm-few µm) soft matter films, with well defined interfacial boundary conditions, are of significant scientific and technical interest. In particular, as the confined film thickness gets below 50-100nm one expects that interface related effects become more and more important in comparison to the bulk related physical properties. In this work we present a novel device for extreme confinement of soft matter in one dimension: a nano-sized cell with very large cell-surface to cell-height ratio (up to 107), as an accessory to the Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) sensor. The cell consists of two plates, top and a bottom, separated by appropriate spacers with heights ranging from below 100nm up to 10ìm. The surfaces of both lid and bottom plate can be chemically modified, prior to the assembly of the cell, in order to provide with desired interfacial properties. The cell is mounted on the standard QCM-D sensor, an AT-cut quartz crystal. We illustrate the use of this device for studies of energy dissipation processes in thin liquid crystal films in the vicinity of the nematic-isotropic phase transitions. In our studies thin 5CB liquid crystal films, confined within the cell, with identical boundary conditions on both interfaces, are studied. In particular, we have compared dissipation measurements in thin liquid crystal films consisting of a single domain samples with the director oriented: a) in the shearing direction, b) perpendicular to the shearing direction but in the same plane as the shearing velocity vector, c) perpendicular to the shearing direction and d) samples with a twist. We show that 5CB films, confined within the nanocell, with the director oriented in the shear direction have the same normalized dissipation, as the films of 5CB with the director oriented perpendicular to the two parallel surfaces (homeotropic orientation)1 confining the cell. This result has been predicted theoretically. In addition, the energy dissipation per unit thickness d of the 5CB film is found to scale with 1/d, clearly indicating the increasing importance of the interfacial effects on the viscoelastic properties of the 5CB film. |