Hydrogen-Bonded Supramolecular Liquid Crystal Polymers: Smart Materials with Stimuli-Responsive, Self-Healing, and Recyclable Properties.

Hydrogen-bonded liquid crystalline polymers have emerged as promising "smart" supramolecular functional materials with stimuli-responsive, self-healing, and recyclable properties. The hydrogen bonds can either be used as chemically responsive (i.e., pH-responsive) or as dynamic structural (i.e., temperature-responsive) moieties. Responsiveness can be manifested as changes in shape, color, or porosity and as selective binding. The liquid crystalline self-organization gives the materials their unique responsive nanostructures. Typically, the materials used for actuators or optical materials are constructed using linear calamitic (rod-shaped) hydrogen-bonded complexes, while nanoporous materials are constructed from either calamitic or discotic (disk-shaped) complexes. The dynamic structural character of the hydrogen bond moieties can be used to construct self-healing and recyclable supramolecular materials. In this review, recent findings are summarized, and potential future applications are discussed.

Smectic Liquid Crystalline Polymer Membranes with Aligned Nanopores in an Anisotropic Scaffold.

Bottom-up methods for the fabrication of nanoporous polymer membranes have numerous advantages. However, it remains challenging to fabricate nanoporous membranes that are mechanically robust and have aligned pores, that is, with a low tortuosity. Here, a mechanically robust thin-film composite membrane was fabricated consisting of a two-dimensional (2D) porous smectic liquid crystalline polymer network inside an anisotropic, microporous polymer scaffold. The polymer scaffold allows for relatively straightforward planar alignment of the smectic liquid crystalline mixture, which consisted of a diacrylate cross-linker and a dimer forming benzoic acid-based monoacrylate. Polymerized samples displayed a smectic A (SmA) phase, which formed the eventual 2D porous channels after base treatment. The aligned 2D nanoporous membranes showed a high rejection of anionic solutes bigger than 322 g/mol. Cleaning and reusability of the system were demonstrated by intentionally fouling the porous channels with a cationic dye and subsequently cleaning the membrane with an acidic solution. After cleaning, the membrane properties were unaffected; this, combined with numerous pressurizing cycles, demonstrated reusability of the system.

Optical Patterns on Drawn Polyethylene by Direct Laser Writing.

Optical patterns are produced on the surface of drawn linear polyethylene containing 2-(2H-benzotriazol-2-yl)-4,6-ditertpentylphenol (BZT), a photothermal dye, by direct laser writing. The photothermal dye absorbs the UV light and dissipates heat in the polyethylene film. This heat locally results in the melting, shrinking, and recrystallization of PE and the loss of the fibrillar crystalline morphology which is typical for these materials. By using this writing method, an optical image can be obtained by controlling the local UV irradiation dose with a pulsed UV laser. The optical image is visible with the naked eye but also between crossed polarizers giving an overt and covert authentication verification that might be interesting for anti-counterfeit applications.

Surface Micropatterning of Uniaxially Oriented Polyethylene Films Using Interference Holography for Strain Sensors.

A new procedure is presented for direct generation of surface micropatterns on uniaxially oriented polyethylene (PE) films using interference holography with a nanosecond pulsed laser. An ultraviolet absorber, 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (BZT) is incorporated into PE prior to stretching to generate absorption at the wavelength of the laser. Illumination with an interference pattern in the absorption band of BZT leads to an obvious height variation in the exposed regions and consequently relief gratings are generated. The height in the exposed regions is strongly dependent on the angle between the grating direction and the film orientation direction. This phenomenon is attributed to a combination of events such as melting, entropic contraction, recrystallization, thermal evaporation of BZT, and anisotropic thermal conductivity. It is shown that the relief height increases with increasing BZT concentration and exhibits a linear dependence on the energy dose above a certain threshold. Additionally, the oriented PE films with the surface micropatterns are explored for strain sensors. The results demonstrate that small strains below 10% are monitored accurately in tensile deformation of the micropatterned, oriented PE films which makes these films potentially useful as strain sensors.