Since the discovery 25 years ago, many investigations have reported light-induced macroscopic mass migration of azobenzene-containing polymer films. Various mechanisms have been proposed to account for these motions. This study explores light-inert side chain liquid crystalline polymer (SCLCP) films with a photoresponsive polymer only at the free surface and reports the key effects of the topmost surface to generate surface relief gratings (SRGs) for SCLCP films. The top-coating with an azobenzene-containing SCLCP is achieved by the Langmuir-Schaefer (LS) method or surface segregation. A negligible amount of the photoresponsive skin layer can induce large SRGs upon patterned UV light irradiation. Conversely, the motion of the SRG-forming azobenzene SCLCP is impeded by the existence of a LS monolayer of the octadecyl side chain polymer on the top. These results are well understood by considering the Marangoni flow driven by the surface tension instability. This approach should pave the way toward in-situ inscription of the surface topography for light-inert materials and eliminate the strong light absorption of azobenzene, which is a drawback in optical device applications. Surface morphology generations on azobenzene(Az)-containing polymer films induced by patterned irradiation have been the active area in photofunctional material research. In 1995, Natansohn's 1 and Tripathy's 2 groups independently reported the induction of surface relief gratings (SRGs) on Az amorphous films using interference irradiation of two laser beams. Since then, photoinduced SRG processes have been reported using various photofunctional materials such as amorphous polymers 1-20 , side chain liquid crystalline polymers (SCLCPs) 21-27 , supramolecular systems 24,27-29 , amorphous molecular materials 30. Additionally, SRG formation can be realised using other photoresponsive units 31-35. Various mechanistic models for mass transfer have been proposed: isomerisation pressure due to volume change 7,8 , gradient force 9-11 , mean-field model 12 , directed softening or fluidisation 13-15 , molecular diffusion 16-18,34 , molecular orientation force 19,20 , etc. With regard to Az-containing SCLCPs 21-27 , UV light irradiation leads to a photochemical phase transition between the liquid crystal (LC) and isotropic phases. This phase change plays an important role in highly efficient SRG formation 23,25,26 , which requires an overall dose of much less than 1 J cm-2. Typically mass transport depends on the light irradiation conditions and physicochemical properties. Consequently, a universal explanation about the mechanism has yet to be provided. Recent studies have noted the importance of the surface effect on the mass transfer process. Ambrosio et al. 17,18 proposed an anisotropic light-driven molecular diffusion model for spiral morphology induction under vortexbeam illumination. Their model stressed enhanced molecular diffusion in proximity of the free surface. Ellison et al. 36-39 have proposed microfabrications via the Marangoni flow by photo...

Slight contaminations existing in a material lead to substantial defects in applied paint. Herein, we propose a strategy to convert this nuisance to a technologically useful process by using an azobenzene-containing side chain liquid crystalline (SCLCP) polymer. This method allows for a developer-free phototriggered surface fabrication. The mass migration is initiated by UV-light irradiation and directed by super-inkjet printed patterns using another polymer on the SCLCP film surface. UV irradiation results in a liquid crystal-to-isotropic phase transition, and this phase change immediately initiates a mass migration to form crater or trench structures due to the surface tension instability known as Marangoni flow. The transferred volume of the film reaches approximately 440-fold that of the polymer ink, and therefore, the printed ink pattern acts as a latent image towards the amplification of surface morphing. This printing-aided photoprocess for surface inscription is expected to provide a new platform of polymer microfabrication.

Elastin-like polypeptides (ELPs) are promising candidates for fabricating tissue-engineering scaffolds that mimic the extracellular environment of elastic tissues. We have developed a “double-hydrophobic” block ELP, GPG, inspired by non-uniform distribution of two different hydrophobic domains in natural elastin. GPG has a block sequence of (VGGVG)5-(VPGXG)25-(VGGVG)5 that self-assembles to form nanofibers in water. Functional derivatives of GPG with appended amino acid motifs can also form nanofibers, a display of the block sequence’s robust self-assembling properties. However, how the block length affects fiber formation has never been clarified. This study focuses on the synthesis and characterization of a novel ELP, GPPG, in which the central sequence (VPGVG)25 is repeated twice by a short linker sequence. The self-assembly behavior and the resultant nanostructures of GPG and GPPG were when compared through circular dichroism spectroscopy, atomic force microscopy, and transmission electron microscopy. Dynamic rheology measurements revealed that the nanofiber dispersions of both GPG and GPPG at an extremely low concentration (0.034 wt%) exhibited solid-like behavior with storage modulus G′ > loss modulus G” over wide range of angular frequencies, which was most probably due to the high aspect ratio of the nanofibers that leads to the flocculation of nanofibers in the dispersion.

Large mass transport driven by the difference in the photoisomerization-induced surface tension was demonstrated in ion pairs of anionic azobenzene and a cationic polymer. This material motion enabled the fluorescence...

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