Liquid crystals (LCs) are a successful example of how the control of self-assembling [1,2] and self-organization [3] via chemical design [4] leads to novel applications. These are mostly based on bulk (quasi-)equilibrium properties related to long-range molecular ordering and anisotropy. Here we present a new application of LCs based on local, non-equilibrium properties: a logic pattern, which is also able to record the thermal history of the system as a time-temperature integrator. The multifunctionality of discotic LCs (DLCs) [5] is the result of lithographic control of the self-assembling. [6] DLCs domains, whose alignment differs from that of the surrounding dominant phase, are patterned into a logic ''checker-board'' where each domain codes for one bit of a binary information. When the temperature overcomes the phase transition temperature T r-h between columnar rectangular and hexagonal mesophases, the individual domains progressively reorient into the dominant phase and their information is erased. The time spent above T r-h is monitored from the irreversible change of the local birefringence. Since T r-h can be tuned by chemical design, a new application of non-equilibrium LC patterns as time-temperature integrators coupled to information storage media can be envisioned.
LCs are central to many industrial applications such as flat-panel displays, and lately have been extensively explored as active materials for organic field effect transistors, [7] photovoltaics, [1] sensors, [8] holographic data storage, [9] and others. [10] Their technological success stems from the enhanced self-assembling properties, which allow the formation and control of a variety of molecularly-ordered bulk mesophases but also the creation of organized structures [11] in low-dimensional mesoscopic and nanoscale-sized environments. [12] Among several classes of LCs, DLCs consist of columnar superstructures formed by stacking of disk-like molecules. Molecular structure (Fig. 1a) exhibits a rigid aromatic core and highly flexible external chains, which provide solubility and improve the rheology of liquid crystalline phases. [13] Different thermodynamic phases emerge from the spatial arrangement of columns. The frequently observed phases, including the DLC used in this work, are columnar rectangular COMMUNICATION www.advmat.de
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