Constructing robust and functional micropatterns on polystyrene surfaces by using deep UV irradiation

Polystyrene Pocket Lithography: Sculpting Plastic with Light

Tissue-culture-ware polystyrene is the gold standard for in vitro cell culture. While microengineering techniques can create advanced cell microenvironments in polystyrene, they require specialized equipment and reagents, which hinder their accessibility for most biological researchers. An economical and easily accessible method is developed and validated for fabricating microstructures directly in polystyrene with sizes approaching subcellular dimensions while requiring minimal processing time. The process involves deep ultraviolet irradiation through a shadow mask or ink pattern using inexpensive, handheld devices followed by selective chemical development with common reagents to generate micropatterns with depths/heights between 5 and 10 µm, which can be used to guide cell behavior. The remarkable straightforwardness of the process enables this class of microengineering techniques to be broadly accessible to diverse research communities.

Hierarchical, Self-Assembled Metasurfaces via Exposure-Controlled Reflow of Block Copolymer-Derived Nanopatterns

Nanopatterning for the fabrication of optical metasurfaces entails a need for high-resolution approaches like electron beam lithography that cannot be readily scaled beyond prototyping demonstrations. Block copolymer thin film self-assembly offers an attractive alternative for producing periodic nanopatterns across large areas, yet the pattern feature sizes are fixed by the polymer molecular weight and composition. Here, a general strategy is reported which overcomes the limitation of the fixed feature size by treating the copolymer thin film as a hierarchical resist, in which the nanoscale pattern motif is defined by self-assembly. Feature sizes can then be tuned by thermal reflow controlled locally by irradiative cross-linking or chemical alteration using lithographic ultraviolet light or electron beam exposure. Using blends of polystyrene-block-poly(methylmethacrylate) (PS-b-PMMA) with PS and PMMA homopolymers, we demonstrate both self-assembled PS grating and hexagonal hole patterns; exposure-controlled reflow is then used to reduce the hole diameter by as much as 50% or increase the PS grating linewidth by more than 180%. Transferring these nanopatterns, or their inverse obtained by a lift-off approach, into silicon yields structural colors that may be prescriptively controlled based on the nanoscale feature size. Furthermore, patterned exposure enables area-selective feature size control, yielding uniform structural color patterns across centimeter square areas. Electron beam lithography is also used to show that the lithographic resolution of this selective-area control can be extended to the nanoscale dimensions of the self-assembled features. The exposure-controlled reflow approach demonstrated here takes a pivotal step toward fabricating complex, hierarchical optical metasurfaces using scalable self-assembly methods.

Degradation of primary nanoplastics by photocatalysis using different anodized TiO2 structures

In recent years, plastic pollution has become an environmental problem requiring urgent attention. Recently, the release of nano-sized plastics (<1 µm) into the environment has raised concern due to the possible adverse effects that their small size can have on the trophic web. Advanced oxidation processes are efficient at removing organic pollutants such as dyes and pharmaceuticals, making them a viable approach for treating these hazardous materials. This study proposes the use of photocatalysis as an alternative for removing polystyrene nanoparticles (PS-NPs) from aqueous media. A comparative study was carried out to determine the photocatalytic activity of three different TiO₂ photocatalysts synthesized by anodization. Elimination and degradation were monitored by turbidimetry, TOC, FTIR, and GC/MS, and the presence of carbonyl groups and intermediate products was recorded to confirm PS-NP degradation. Statistical analysis revealed that PS-NP elimination using TiO₂/T and TiO₂/M as photocatalysts was more efficient than with photolysis. The results indicate that the mixed structure (nanotubes/nanograss) reduces the concentration of PS-NPs in dispersion 2 times more efficiently than photolysis with UV light does. Despite the challenges posed by nanoplastic contamination, this study provides a useful remediation approach; a technique that, to date, has received little attention.

Rapid Processing of Bottlebrush Coatings through UV-Induced Cross-Linking

Bottlebrush polymers can be used to introduce novel surface properties including hydrophilicity, stimuli-responsiveness, and reduced friction forces. However, simple, general, and efficient approaches to cross-linking bottlebrush polymer films and coatings are limited. Here, we report that bottlebrush polymers with an unsaturated polynorbornene backbone and thiol-terminated side chains can be cross-linked on demand by UV irradiation to produce uniform and insoluble bottlebrush polymer coatings. To quantify the kinetics and efficiency of cross-linking by UV exposure (254 nm), we measured the normalized residual thickness (NRT) of bottlebrush and linear polymer films after UV exposure and solvent washing. For bottlebrush polymers with thiol-terminated polystyrene (PS) side chains, the NRT exceeded 60% for a UV dose of 1.0 J/cm², while unfunctionalized linear PS required a dose of 7.9 J/cm² to achieve similar NRT values. Rapid UV-induced cross-linking of the bottlebrush PS was attributed to the thiol-ene coupling of the thiol-terminated side chains with the unsaturated polynorbornene backbones, as demonstrated through FTIR measurements and control studies involving bottlebrush polymers with saturated backbones. To establish the broader applicability of this approach, UV-induced cross-linking was demonstrated for thin films of bottlebrush polymers with thiol-terminated poly(methyl acrylate) (BB-PMMA-SH) side chains and those with poly(ethylene glycol) (BB-PEG) and poly(lactic acid) (BB-PLA) side chains which do not contain thiol end groups. UV-induced cross-linking of BB-PEG and BB-PLA films required the use of a multifunctional thiol additive. Finally, we demonstrated that bottlebrush polymer multilayers can be fabricated through sequential deposition and UV-induced cross-linking of different bottlebrush polymer chemistries. The cross-linking process outlined in this work is simple, general, and efficient and produces solvent-resistant coatings that preserve the unique properties and functions of bottlebrush polymers.

Reproducible and Bendable SERS Substrates with Tailored Wettability Using Block Copolymers and Anodic Aluminum Oxide Templates

Surface properties are essential for substrates exhibiting high sensitivity in surface-enhanced Raman scattering (SERS) applications. In this work, novel SERS hybrid substrates using polystyrene-block-poly(methyl methacrylate) and anodic aluminum oxide templates is presented. The hybrid substrates not only possess hierarchical porous nanostructures but also exhibit superhydrophilic surface properties with the water contact angle ≈0°. Such surfaces play an important role in providing uniform enhanced intensities over large areas (relative standard deviation ≈10%); moreover, these substrates are found to be highly sensitive (limit of detection ≈10^-12 m for rhodamine 6G (R6G)). The results show that the hybrid SERS substrates can achieve the simultaneous detection of multicomponent mixtures of different target molecules, such as R6G, crystal violet, and methylene blue. Furthermore, the bending experiments show that about 70% of the SERS intensities are maintained after bending from ≈30° to 150°.

Formation of High-Density Brush of Liquid Crystalline Polymer Block Associated with Dewetting Process on Amorphous Polymer Film

The understanding of polymer dewetting on solid surfaces is significant in both fundamental polymer physics and practical film technologies. When liquid crystalline (LC) polymers are dewetted, LC ordering is involved in the dewetting process. Here, we report on the characteristic dewetting processes of a diblock copolymer composed of a cyanobiphenyl side chain liquid crystalline polymer (SCLCP) block connected with polystyrene (PS) taking place on a PS base film. Thin films of the block copolymer were prepared by the water-floating method onto the PS film, and the dewetting process is observed in a softened state above the glass transition temperature of the PS. At the smectic A phase temperature of the SCLCP block, the dewetted surface layer generated a flat unique fingering pattern leading to a monolayered (two-dimensional) high-density LC polymer brush through the LC ordering. The important role of the anchoring PS block on the base PS film surface is suggested for the formation of highly stretched LC polymer brush. Above the isotropization temperature, in contrast, ordinary three-dimensional droplet morphologies with smooth round edges were observed. By photo-cross-linking the base PS film, the lateral diffusion rate was significantly reduced. This can be applied to an entropy-driven morphology patterning via dewetting. The polymer brush formation and its spatial controls are expected to provide new opportunities for the modification strategies of polymer surfaces.

Biodegradation of weathered polystyrene films in seawater microcosms

A microcosm experiment was conducted at two phases in order to investigate the ability of indigenous consortia alone or bioaugmented to degrade weathered polystyrene (PS) films under simulated marine conditions. Viable populations were developed on PS surfaces in a time dependent way towards convergent biofilm communities, enriched with hydrocarbon and xenobiotics degradation genes. Members of Alphaproteobacteria and Gammaproteobacteria were highly enriched in the acclimated plastic associated assemblages while the abundance of plastic associated genera was significantly increased in the acclimated indigenous communities. Both tailored consortia efficiently reduced the weight of PS films. Concerning the molecular weight distribution, a decrease in the number-average molecular weight of films subjected to microbial treatment was observed. Moreover, alteration in the intensity of functional groups was noticed with Fourier transform infrared spectrophotometry (FTIR) along with signs of bio-erosion on the PS surface. The results suggest that acclimated marine populations are capable of degrading weathered PS pieces.

UV-solvent annealing of PDMS-majority and PS-majority PS-b-PDMS block copolymer films

The response of polystyrene-block-poly(dimethylsiloxane) (PS-b-PDMS) thin films to UV exposure during solvent vapor annealing is described, in order to improve their applicability in nanolithography and nanofabrication. Two BCPs were examined, one with the PS block as majority (f _PS = 68%, M _n = 53 kg mol^-1), the other with PDMS block as majority (f _PDMS = 67%, M _n = 44 kg mol^-1). A 5 min UV irradiation was applied during solvent vapor annealing which led to both partial crosslinking of the polymer and a small increase in the temperature of the annealing chamber. This approach was effective for improving the correlation length of the self-assembled microdomain arrays and in limiting subsequent flow of the PDMS in the PDMS-majority BCP to preserve the post-anneal morphology. Ordering and orientation of microdomains were controlled by directed self-assembly of the BCPs in trench substrates. Highly-ordered perpendicular nanochannel arrays were obtained in the PDMS-majority BCP.

Patterning of individual Staphylococcus aureus bacteria onto photogenerated polymeric surface structures

This manuscript describes the fabrication of bacterial surface arrays by using photolithographic techniques having in addition some particularly interesting features.

Conjugated poly(fluorene-quinoxaline) for fluorescence imaging and chemical detection of nerve agents with its paper-based strip

Conjugated polymer of poly(fluorene-co-quinoxaline) was synthesized via Suzuki coupling polymerization. The emission color of the polymer can be tuned depending on the concentration of the polymer in solution. A low-energy bandgap is observed both in the concentrated solution and in the solid state, caused by aggregation of the polymer chains, resulting in long wavelength emission from the quinoxaline moiety, while short wavelength emission can be seen in diluted, well-dissolved solution. The presence of quinoxaline units enables us to demonstrate fluorescence switching and imaging. Paper-based strips containing the polymer are prepared via simple immersion of filter paper in the polymer solution for practical use in the detection of nerve agents. The emission of the paper-based strip is quenched upon exposure to diethyl chlorophosphate (DCP), a nerve agent simulant, and the initial emission intensity can be almost restored by treatment with aqueous sodium hydroxide solution, making a possible reversible paper-based sensor.

The photodimerization characteristics of anthracene pendants within amphiphilic polymer micelles in aqueous solution

The photodimerization characteristics of anthracene pendants were comprehensively investigated by various selected narrow bands of light in the UV-vis-NIR region.