The capability to pattern polymer surfaces at different length scales is an important goal in different research fields, including display technologies, microelectronics, optics, as well as biorelated and medical science. However, the ability to optically and dynamically manipulate topography is a key feature enabling remote control of associated effects/processes mediated by the surface. Azopolymers are largely investigated to this aim based on their sensitivity to optical fields and reconfigurability capabilities. In this work, surface relief formation induced by polarization patterns on an amorphous azopolymer structurally engineered to have large photoinduced birefringence has been investigated both experimentally and theoretically. Based on the different light polarization patterns, depth and shape of the relief grating can be controlled. An optically induced gradient force model that includes both the spatial distribution and the anisotropy of the material permittivity has been theoretically analyzed. The proposed approach is able to explain the experimental results and to overcome the limitation of existing models.

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/macp.201800318. AzopolymersA series of side-chain polymers with a bifunctional repeating unit are prepared by post-polymerization functionalization of poly(propargyl methacrylate) (PPMA) with several azides derived from bis(hydroxymethyl) propionic acid (bis-MPA). The azide incorporates one photoresponsive 4-cyanoazobenzene unit and one photoinert promesogenic moiety at each repeating unit. Both the effect of the photoinert (4-cyanobipheynyl vs 4-cyanotolane) and of the linking group (ester vs carbamate) on the liquid crystalline properties and the generation of optical anisotropy, linear or circular birefringences are explored.

The capability to optically control surface structuration of azopolymer films is an important goal in different research fields, enabling remote activation and tuning of associated processes mediated by the surface. In this work, two amorphous azopolymers, structurally engineered in order to exhibit linear and circular photoinduced optical anisotropies, have been investigated, with the aim to design complex light-reconfigurable topographical structures. Different intensity and polarization patterns were generated by two-or four-beams interferometry and inscribed on the polymer films. Relief depths in the range of hundreds of nanometers have been produced, mediated by the bulk photoinduced anisotropies of the materials. It is shown that, on the basis of the kind of light patterns (intensity and/or polarization), depth and shape of the relief grating can be tuned. Polymers with higher photoinduced birefringences enable one to produce deeper reliefs. Bidimensional light polarization patterns generate complex surface structures, even with chiral features, envisaging the possibility to engineer large area opto-controllable surfaces and platforms.

potential in applications such as additive manufacturing, civil engineering, and biomedicine. [1][2][3][4][5][6] Among them, azobenzene-based materials, due to their unique photo-responsive features, have attracted great attention for the remote and flexible control of materials properties via light stimulation. [7,8] The light response is triggered by photoisomerization of the azobenzene units using UV or visible irradiation, [9] providing the basis for a variety of photonic applications such as energy storage, [10,11] holographic recording, [12][13][14] soft robotics, [15,16] dynamic control of surface topology in liquid crystalline elastomers [17] and nonlinear optics [18,19] where, in particular, photoinduced reorientation allows for all-optical poling. [20] As one striking example, by controlling the impinging light configuration, the photoinduced processes in azobenzene-containing thin films invoke material mass migration that leads to the formation of topographic surface patterns, a prominent example being surface-relief grating (SRG) formation upon irradiation with a light interference pattern. [21][22][23][24] SRGs show great promise as diffractive photonic elements, [25,26] biosensing substrates, [27] or as nano-/microfabrication templates. [28][29][30] The micron-scale periodicity of SRGs renders them an excellent fit for biological systems, many of which are composed of cells that are extremely sensitive to mechanical and topographic features of the surrounding microenvironment. [31,32] Hence, there is a growing interest in the use of azobenzene-based materials as smart bio-interfaces for cell culture. [33][34][35] The native extracellular matrix (ECM) of soft tissue is composed of entangled fibrous proteins, [36,37] as reproduced also in many synthetic ECM products. [38] Furthermore, ECM is continuously remodeled by the cells in physiological and pathological conditions. [39] Sinusoidal SRGs and embossed pillars in azobenzene thin films have been used for mimicking the ECM texture and controlling cellular directional migration in single and multiple cells, [40][41][42] directing axonal extension, [43,44] and determining stem cell fate. [45] The most exciting characteristic provided by azobenzenebased systems lies in the reversibility of the photoinduced processes. It is well known that SRGs recorded in thin films can be erased by heating the sample above the glass transition temperature (T g ). [46,47] SRGs can be also efficiently erased and re-inscribed optically by using single-beam irradiation [24,48,49] or Azobenzene-based light-responsive thin films are emerging as appealing candidates for smart cell-culture substrates. Their attraction lies in the fact that they can be reversibly photo-patterned, providing a route for dynamically mimicking the remodeling of the extracellular matrix. However, since the cells need to be cultured in aqueous environment, a key parameter in the layout of any biological application is the stability of the surface underwater. In this work, the authors perform a detail...

Photochromic liquid crystalline block copolymers (PLCBCs) are currently playing a significant role as light‐responsive materials because of their light controllable features over multiple length scales. Herein, a study of the photoinduced optical anisotropy derived by the combination of orientation phenomena at molecular and supramolecular levels in a novel kind of side‐chain PLCBCs with mesogenic phenyl benzoate groups and pyridine units that is hydrogen bonded with azobenzene‐containing phenol is reported. Based on the polymeric architectures and composition, the supramolecular configuration self‐organizes in different microphases that affect the material response to the external stimuli. Simple, 1D, polarization holograms are recorded to evaluate the photoinduced birefringence. The first step, light patterning, involves the orientation of the azobenzene units and precedes a thermal treatment that amplifies the induced anisotropy through the cooperative orientation of the mesogenic units. By selective extraction, the azobenzene units can be removed, making the material transparent to the visible light. Excellent photostability of the material birefringence is obtained, whose final value is strongly affected by the block copolymer's architecture. The versatility in the molecular design, the fine control of the photoinduced features by external parameters, and, finally, the possibility to achieve photostability make these materials of great potential for developing optical and photonic devices.