Squeezing-out dynamics in free-standing smectic films

Structural, Optical and Dynamic Properties of Thin Smectic Films

“…There are several methods to investigate the coupling between structural and dynamic properties of thin smectic films, both suspended in air or deposited on the solid surface, and molecular structure. A usual route in these studies is provided by a combination of statistical-mechanical theories [7,8,[11][12][13][16][17][18][19][20][21]23,25,26] and optical and calorimetric techniques [1,2,6,9,10,14,15,22,24,[29][30][31][32][33].…”

“…In that case [12,17] ∇P is responsible for the driving out of one or several smectic layer(s) from the N-layer smectic film. The dynamics of the bounding area, which is separated by the layer-thinning transition front, during the layer-thinning transition N → N − 1, will be described by using the conservation laws for mass and linear momentum [17,18], with and without accounting for the coupling between the smectic film and the meniscus.…”

“…The dynamics of the bounding area between the squeezed-out and non-squeezed-out areas in the FSSF has been investigated for the case of the circular shape of the smectic film. This section will generalize the previous case to the case of accounting for the influence of the meniscus [17,18]. In this approach, the mechanism which is responsible for squeezing-out process, is based on the concept of the the disjoining pressure.…”

“…The movement of these phase fronts consists of successive spontaneous layer-by-layer thinning transitions (local transformations of smectic layers into nematic and isotropic phases) of films, when the interior layer(s) is(are) squeezed-out in meniscus. Thinning was observed for different low-temperature smectic systems, such as SmA, SmC, and ferroelectric SmC * , but we will focus here on the review of the structural and dynamic properties of thin free-standing smectic-A films in air or water, as well as deposited on the solid surface.A great variety of phenomena, both structural and dynamic, can be observed in thin FSSFs: layer-thinning transitions [1,2,6], stepwise reduction of heat capacity and reflectivity [1,[6][7][8], sawtooth behavior of the surface tension upon heating the FSSFs above T AI(N) (bulk) [9][10][11][12], dynamics of removal of one or several layers from the N-layer FSSF during the layer-thinning process [13][14][15][16][17][18], et al In particular, it was shown that the AI or AN transitions occurs through a series of layer-thinning transitions, causing the films to thin in a stepwise manner as the temperature is increased above T AI(N) (bulk) [1,2], whereas the film tension, at each thinning, abruptly drops to a lower value and then continues to increase with a smaller slope [9-12]. These transitions have been attributed to the reduction of smectic fluctuations in the bounding layers [7,[19][20][21].…”

“…For description of the layer-thinning transition in FSSFs, several theoretical approaches have been suggested. First of all, it has been suggested that the squeezing-out transition is initiated by a thermally activated nucleation in which a density fluctuation forms a small circular hole (void) of critical radius in the smectic film [17,18], whereas in the second approach, the squeezing-out transition is initiated by spontaneous nucleation of dislocation loops, the growth of which causes a film to thin [15,16].…”