Hierarchical Polymer Structures Using Templates and the Modified Breath Figure Method

Light-Assisted Fabrication of Hierarchical Azopolymer Structures Using the Breath Figure Method and AAO Templates

Hierarchical polymer structures have garnered widespread application across various fields owing to their distinct surface properties and expansive surface areas. Conventional hierarchical polymer structures, however, often lack postfabrication scalability and spatial selectivity. In this study, we propose a novel strategy to prepare light-assisted hierarchical polymer structures using azopolymers (PAzo), the breath figure method, and anodic aluminum oxide (AAO) templates. Initially, the breath figure PAzo films are prepared by dripping a PAzo chloroform solution onto glass substrates in a high-humidity environment. The AAO templates are then placed on the breath figure PAzo film. Upon ultraviolet (UV) light exposure, the azobenzene groups in the azopolymers undergo trans-cis photoisomerization. This process causes the glass transition temperature (Tg) of the PAzo to become lower than room temperature, allowing the azopolymer to enter the nanopores of the AAO templates. The hierarchical azopolymer structures are then formed by using a sodium hydroxide solution to remove the templates. Furthermore, exploring the effects of PAzo concentration and UV light exposure duration on the film morphology reveals optimized conditions for hierarchical structure formation. Additionally, the water contact angles of these polymer structures are measured. The hierarchical PAzo structures exhibit higher hydrophobicity compared with the flat PAzo films and the PAzo breath figure films. Finally, patterned breath figure films can be prepared using designed photomasks, demonstrating the method's capability for spatial selectivity.

Laser-Induced NanoKneading (LINK): Deformation of Patterned Azopolymer Nanopillar Arrays via Photo-Fluidization

Ordered arrays of polymer nanostructures have been widely investigated because of their promising applications such as solar-cell devices, sensors, and supercapacitors. It remains a great challenge, however, to manipulate the shapes of individual nanostructures in arrays for tailoring specific properties. In this study, an effective strategy to prepare anisotropic polymer nanopillar arrays via photo-fluidization is presented. Azobenzene-containing polymers (azopolymers) are first infiltrated into the nanopores of ordered anodic aluminum oxide (AAO) templates. After the removal of the AAO templates using weak bases, azopolymer nanopillar arrays can be prepared. Upon exposure of linearly polarized lights, azobenzene groups in the azopolymers undergo trans-cis-trans photoisomerization, causing mass migration and elongation of the nanopillar along with the polarization directions. As a result, anisotropic nanopillar arrays can be fabricated, of which the deformation degrees are controlled by the illumination times. Furthermore, patterned nanopillar arrays can also be constructed with designed photomasks. This work presents a practical and versatile strategy to fabricate arrays of anisotropic nanostructures for future technical applications.

Honeycomb-like porous chitosan films prepared via phase transition of poly(N-isopropylacrylamide) during water evaporation under ambient conditions

Honeycomb-like porous chitosan (CS) films are attractive tools for developing functional materials for filters, catalyses, adsorbents, biomaterials, etc. A simple method for fabricating honeycomb-like porous CS films without special reagents, facilities, and techniques would make them accessible. Here we introduce an easily available method for fabricating honeycomb-like CS films without a strong acid/base, toxic reagents, or special facilities/techniques. An aqueous solution containing CS and poly(N-isopropylacrylamide) (PNIPAm) was allowed to stand at 25 °C to evaporate water. After 3 days, CS–PNIPAm composite films with homogenously phase-separated PNIPAm particles were obtained. The PNIPAm particles were removed by immersion in methanol, and the resulting films dried under reduced pressure to become honeycomb-like porous CS films. The pore size could be varied in the range of 0.5–3.0 μm by altering the CS concentration and the molecular weight of CS where the pore size was reduced under conditions with stronger interaction between CS molecules. We reveal that the key to success with this system is the decrease of lower critical solution temperature (LCST) of PNIPAm with water evaporation. In addition, we confirmed the removed PNIPAm was recyclable in this system. Furthermore, we found this method was also applicable to alginate. The proposed facile method for fabricating honeycomb-like porous polymeric films could provide various functional porous materials.

A simple method for fabricating honeycomb-like porous chitosan films without special reagents, facilities, and techniques was achieved by using poly(N-isopropylacrylamide).