Photoinduced Alignment under Solvent Vapor Annealing (PA-SVA): Enhanced Ordering and Patterning in Block Copolymer Films

Abstract

In the past few decades, alignment control and directed self-assembly of block copolymer thin films have been widely investigated. Most approaches, however, require chemically or topographically prepatterned substrates, increasing the processing complexity. In this work, we present a facile strategy to form well-aligned block copolymer thin films by photoinduced alignment under solvent vapor annealing (PA-SVA) without chemically or topographically prepatterned substrates. Polystyrene-block-poly(ethylene oxide) (PS-b-PEO) consisting of two polymer blocks with distinct hydrophilicities and mechanical properties is incorporated with 4-butyl-4′-hydroxy­azobenzene (4AzOH) to achieve the light-assisted self-assembly. Under solvent vapor annealing, the PS-b-PEO chains are swollen and possess mobilities. Upon polarized light irradiations, light-responsive azobenzene molecules undergo trans–cis–trans isomerization and achieve photoinduced alignment. The arrangement of the azobenzene molecules can further induce the alignment of the PS-b-PEO chains through supramolecular interactions between the phenol groups of the 4AzOH and the ether groups of the PEO chains. AFM-IR measurements are applied to characterize the selective blending of the 4AzOH molecules in the PEO segments. With different PA-SVA times, the transitions of the PS-b-PEO phase separation can be observed; the alignment of the PS-b-PEO/4AzOH films is further characterized by orientation analysis. The facile design of the PA-SVA strategy not only enables the manipulation of light-responsive molecules in block copolymer chains but also provides an alternative way for obtaining well-ordered block copolymer thin films.

Solution and Film Self-Assembly Behavior of a Block Copolymer Composed of a Poly(ionic Liquid) and a Stimuli-Responsive Weak Polyelectrolyte

“…During AFM-IR analysis, a pulsed IR laser illuminates the sample at the AFM cantilever tip, producing a photothermal expansion response that is directly proportional to the IR absorption of the material. This allows for collecting simultaneous chemical images with nanoscale spatial resolution at specific wavenumbers or full spectra at specified points in the AFM image. , While AFM-IR has previously been used to provide paired nanostructural and chemical composition characterization of different material systems including block copolymers, proteins, , and nanocomposites, , to the authors’ knowledge, this is the first report of a poly­(ionic liquid) system being characterized with AFM-IR.…”

Reversible Sensing Technologies Using Upcycled TPEE: Crafting pH and Light Responsive Materials towards Sustainable Monitoring

“…[1][2][3] In response to the stimuli, diverse styles of smart sensors are triggered owing to the architecture of self-assembled structures in nanoscale. [4][5][6] Among various kinds of stimuli, lights are the most attractive external sources with diverse advantages, such as no chemical contaminants involved, [7] precise and accurate spatial control, [8] and selectivities in different wavelengths and intensities. [9,10] Moreover, the chemical structure transitions in photo-responsive substances are beneficial in the identification of light stimuli with specific wavelengths.…”