Dynamic wrinkling of freely floating smectic films

Abstract

We demonstrate spontaneous wrinkling as a transient dynamical pattern in thin freely floating smectic liquid-crystalline films. The peculiarity of such films is that, while flowing liquid-like in the film plane, they cannot quickly expand in the direction perpendicular to that plane. At short time scales they therefore behave in two dimensions like quasi-incompressible membranes. Such films can develop a transient undulation instability or form bulges in response to lateral compression. Optical experiments with freely floating bubbles on parabolic flights and in ground lab experiments are reported. The characteristic wavelengths of the wrinkles are in the submillimeter range. We demonstrate the dynamic nature of the pattern formation mechanism and develop a basic model for the wavelength selection and wrinkle orientation. arXiv:1809.08082v2 [cond-mat.soft]

Mechanically induced Helfrich-Hurault effect in a confined lamellar system with finite surface anchoring

“…In particular [18,19] explored the case of non-linear undulations where the instability show a transition from sinusoidal to a chevron structure. Napoli and Nobili [20], extended the classical results valid for infinitesimal imposed strain (see equation 40) to the most general case valid for an imposed finite dilatative strain (see equation 391 ), capable therefore to cover cases were the specimen thickness d can be comparable to the characteristic length λ. Analogous observed instabilities are reported in [21,22]. The former refers to active cholesteric liquid crystals where buckling can be induced by both extensile or contractile applied stresses.…”

“…with q ζ given as solution of (35) and q ξ given by (37) 2 and where the amplitude A is still an unknown of the problem. Following the proposed scheme in [13] and [32], in order to compute A, we impose to the total energy (22) The minimization of the fourth order term in ǫ of (42) with respect to A, allows to find the unknown amplitude A = 0 which is a solution of the following second order equation…”

“…The former refers to active cholesteric liquid crystals where buckling can be induced by both extensile or contractile applied stresses. Whilst the latter concerns freely floating smectic liquid crystalline films [22] where spontaneous wrinkling can appear in order to compensate lateral compressions.…”

Structural Landscapes in Geometrically Frustrated Smectics

“…Furthermore, scenarios where partial smectic order exists, such as during the transition from the nematic to the smectic phase, may exhibit very complicated pretransitional structures [37,38,44,45], and few studies have addressed the connection between pattern formation and the peculiar critical behavior of liquid crystals at the nematicsmectic transition [46]. Dynamical phenomena-such as time-varying layer spacing [47], interactions between embedded particles [31], and the evolution of smectic films and bubbles [48][49][50]-also present difficult problems that appear to require numerical modeling.…”

Smectic free-standing films under fast lateral compression

“…In principle, one can also induce wrinkles in thin layers of sufficiently viscous fluid, when the time scale of local compression by external forces is substantially shorter than the time scale on which the film thickness can increase. Examples are collapsing surface bubbles on a pool [12][13][14] or closed bubbles of smectic liquid crystal films 15,16 .…”