Light-Induced Nanowetting: Erasable and Rewritable Polymer Nanoarrays via Solid-to-Liquid Transitions

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.

Photo-Healable Fabrics: Achieving Structural Control via Photochemical Solid-Liquid Transitions of Polystyrene/Azobenzene-Containing Polymer Blends

While polymer fabrics are integral to a wide range of applications, their vulnerability to mechanical damage limits their sustainability and practicality. Addressing this challenge, our study introduces a versatile strategy to develop photohealable fabrics, utilizing a composite of polystyrene (PS) and an azobenzene-containing polymer (PAzo). This combination leverages the structural stability of PS to compensate for the mechanical weaknesses of PAzo, forming the fiber structures. Key to our approach is the reversible trans-cis photoisomerization of azobenzene groups within the PAzo under UV light exposure, enabling controlled morphological alterations in the PS/PAzo blend fibers. The transition of PAzo sections from a solid to a liquid state at a low glass transition temperature (Tg ∼ 13.7 °C) is followed by solidification under visible light, thus stabilizing the altered fiber structures. In this study, we explore various PS/PAzo blend ratios to optimize surface roughness and mechanical properties. Additionally, we demonstrate the capability of these fibers for photoinduced self-healing. When damaged fabrics are clamped and subjected to UV irradiation for 20 min and pressed for 24 h, the mobility of the cis-form PAzo sections facilitates healing while retaining the overall fabric structure. This innovative approach not only addresses the critical issue of durability in polymer fabrics but also offers a sustainable and practical solution, paving the way for its application in smart clothing and advanced fabric-based materials.

Guard Cell-Inspired Ion Channels: Harnessing the Photomechanical Effect via Supramolecular Assembly of Cross-Linked Azobenzene/Polymers

Stimuli-responsive ion nanochannels have attracted considerable attention in various fields because of their remote controllability of ionic transportation. For photoresponsive ion nanochannels, however, achieving precise regulation of ion conductivity is still challenging, primarily due to the difficulty of programmable structural changes in confined environments. Moreover, the relationship between noncontact photo-stimulation in nanoscale and light-induced ion conductivity has not been well understood. In this work, a versatile design for fabricating guard cell-inspired photoswitchable ion channels is presented by infiltrating azobenzene-cross-linked polymer (AAZO-PDAC) into nanoporous anodic aluminum oxide (AAO) membranes. The azobenzene-cross-linked polymer is formed by azobenzene chromophore (AAZO)-cross-linked poly(diallyldimethylammonium chloride) (PDAC) with electrostatic interactions. Under UV irradiation, the trans-AAZO isomerizes to the cis-AAZO, causing the volume compression of the polymer network, whereas, in darkness, the cis-AAZO reverts to the trans-AAZO, leading to the recovery of the structure. Consequently, the resultant nanopore sizes can be manipulated by the photomechanical effect of the AAZO-PDAC polymers. By adding ionic liquids, the ion conductivity of the light-driven ion nanochannels can be controlled with good repeatability and fast responses (within seconds) in multiple cycles. The ion channels have promising potential in the applications of biomimetic materials, sensors, and biomedical sciences.

Interface Wetting Driven by Laplace Pressure on Multiscale Topographies and Its Application to Performance Enhancement of Metal-Composite Hybrid Structure

Surface topography reconstruction is extensively used to address the issue of weak bonding at the polymer-metal interface of metal-composite hybrid structure, while enhancement from this approach is seriously impaired by insufficient interface wetting. In this study, the wetting behavior of polymer on aluminum surfaces with multiscale topographies was theoretically and experimentally investigated to realize stable and complete wetting. Geometric dimensions of multiscale surface topographies have a notable impact on interfacial forces at the three-phase contact line of polymer/air/aluminum, and a competition exists between Laplace pressure and bubble pressure in dominating the wetting behavior. Laplace pressure facilitates the degassing of trapped air bubbles in grooves, bringing more robust interfacial wettability to grooves than dimples and grids. Conversely, dimples with excessive dimensions generate interfacial pores, and this intrinsic mechanism is theoretically unraveled. Moreover, different degrees of interface wetting cause variations in bonding strength of polymer-aluminum interface, which changes from ∼18% improvement to ∼17% reduction compared to original strength. Finally, groove topography perfectly achieved complete wetting between polymer and aluminum and consequently improved flexure performance by over 11% for the aluminum-carbon fiber hybrid side impact bar, which verifies the importance of complete wetting at a part scale. This study deepens the understanding of wetting behavior and clarifies the intrinsic correlation between interfacial bonding performance and surface topography.

Developing a dynamic magnetic flux template to guide 1D nanomaterial growth

A dynamic magnetic flux template (DMT) has been developed for preparing 1D nanomaterials efficiently. It can be quickly established and revoked without introducing any pollution. The DMT behaves like a template for guiding the orientation, bearing a 1D structure, activating the nucleation, and providing a driving force for 1D nanomaterial growth.

Designing Rewritable Dual-Mode Patterns using a Stretchable Photoresponsive Polymer via Orthogonal Photopatterning

The fabrication of dual-mode patterns in the same region of a material is a promising approach for high-density information storage, new anti-counterfeiting technologies, and highly secure encryption. However, dual-mode patterns are difficult to achieve because the two patterns in one material may interfere with each other during fabrication and usage. The development of noninterfering dual-mode patterns requires new materials and patterning techniques. Herein, a novel orthogonal photopatterning technique is reported for the fabrication of noninterfering dual-mode patterns on an azopolymer P1. P1 is a unique material that exhibits both photoinduced reversible solid-to-liquid transitions and good stretchability. In the first step of orthogonal photopatterning, patterned photonic structures are fabricated on a P1 film via masked nanoimprinting controlled by photoinduced reversible solid-to-liquid transitions. In the second step, the P1 film is stretched and irradiated with polarized light through a photomask, which generates a chromatic polarization pattern. In particular, the photonic structures and chromatic polarization in the dual-mode pattern are noninterfering. Another feature of dual-mode patterns is that they are rewritable via photo-, thermal, or solution reprocessing, which are useful for recycling and reprogramming. This study opens an avenue for the development of novel materials and techniques for photopatterning.

Developing Anisotropy in Self-Assembled Block Copolymers: Methods, Properties, and Applications

Block copolymers (BCPs) self-assembly has continually attracted interest as a means to provide bottom-up control over nanostructures. While various methods have been demonstrated for efficiently ordering BCP nanodomains, most of them do not generically afford control of nanostructural orientation. For many applications of BCPs, such as energy storage, microelectronics, and separation membranes, alignment of nanodomains is a key requirement for enabling their practical use or enhancing materials performance. This review focuses on summarizing research progress on the development of anisotropy in BCP systems, covering a variety of topics from established aligning techniques, resultant material properties, and the associated applications. Specifically, the significance of aligning nanostructures and the anisotropic properties of BCPs is discussed and highlighted by demonstrating a few promising applications. Finally, the challenges and outlook are presented to further implement aligned BCPs into practical nanotechnological applications, where exciting opportunities exist.

Spindle-Shaped Surface Microstructure Inspired by Directional Water Collection Biosystems to Enhance Interfacial Wetting and Bonding Strength

Unique spindle microstructures with an apex angle of ∼20° bring the ability of directional water collection to various biosystems (i.e., spider silk and cactus stem). This has great potential to solve the insufficient interfacial wetting for mechanical interlocking formation between polymers and substrates. In this study, the bioinspired spindle microstructures were easily fabricated through the deposition of molten materials by a nanosecond laser with an overlap ratio of 21% between laser spots and achieved superior interfacial wetting for commercial epoxy adhesive on aluminum substrates. Detailed analyses show that there are four mechanisms responsible for the superior interfacial wettability of bioinspired spindle microstructures: the Laplace pressure difference, newly formed aluminum oxide, the capillary effect, and no extra pressure from a trapped atmosphere. Consequently, the bioinspired spindle surface microstructures achieve a maximum improvement of ∼16 and ∼39% in interfacial bonding strength before and after water soak exposure compared to the as-received condition. Moreover, the stable interfacial wettability of bioinspired spindle microstructures ensures that the improved joint strength varied little with an increase in surface roughness from ∼1.7 to ∼12.8 μm. However, the interfacial wettability of common dimple microstructures deteriorated with an increase in surface roughness, which is indicated by the decreasing rule in the quadratic polynomial function of the interfacial bonding strength as the surface roughness increases from ∼2.1 to ∼18.2 μm.

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.