Single-Molecule Tracking Studies of Flow-Induced Microdomain Alignment in Cylinder-Forming Polystyrene–Poly(ethylene oxide) Diblock Copolymer Films

Abstract

Flow-based approaches are promising routes to preparation of aligned block copolymer microdomains within confined spaces. An in-depth characterization of such nanoscale morphologies within macroscopically nonuniform materials under ambient conditions is, however, often challenging. In this study, single-molecule tracking (SMT) methods were employed to probe the flow-induced alignment of cylindrical microdomains (ca. 22 nm in diameter) in polystyrene-poly(ethylene oxide) diblock copolymer (PS-b-PEO) films. Films of micrometer-scale thicknesses were prepared by overlaying a benzene solution droplet on a glass coverslip with a rectangular glass plate, followed by solvent evaporation under a nitrogen atmosphere. The microdomain alignment was quantitatively assessed from SMT data exhibiting the diffusional motions of individual sulforhodamine B fluorescent probes that preferentially partitioned into cylindrical PEO microdomains. Better overall microdomain orientation along the flow direction was observed near the substrate interface in films prepared at a higher flow rate, suggesting that the microdomain alignment was primarily induced by shear flow. The SMT data also revealed the presence of micrometer-scale grains consisting of highly ordered microdomains with coherent orientation. The results of this study provide insights into shear-based preparation of aligned cylindrical microdomains in block copolymer films from solutions within confined spaces.

Trajectory-Profile-Guided Single Molecule Tracking for Assignment of One-Dimensional Diffusion Trajectories

“…29,32,48,49,51 Such assessments require the accurate measurement of the inplane orientations of 1D trajectories. Therefore, trajectory angle accuracy also represents an important parameter upon which to judge the efficacy of TPG tracking.…”

Fluorescence Microscopic Investigations of Molecular Dynamics in Self‐Assembled Nanostructures

“…Rhodamine (Figure 2a) [35,49,51] and perylene diimide (PDI) (Figure 2b) [38,40,42,44,46,47] dyes having different net charges and hydrophobicity have been used to investigate the effects of steric, electrostatic, and hydrophobic interactions on their diffusion dynamics. Among them, SRB has permitted us to investigate the morphology and permeability of PEO microdomains in PS‐ b ‐PEO films owing to its selective distribution to these microdomains [39,41,43,45] . PDI molecules are suitable for SMT‐SMEP measurements, because the lowest energy electronic transition of the PDI moiety is well‐polarized along the long molecular axis [44,46,47] .…”

“…We also used SMT to investigate the effects of solvent vapor penetration and shear flow on the elongation and orientation of cylindrical PEO microdomains [39,41] . The degree of microdomain alignment was quantitatively assessed using the ORM from the diffusional motions of single SRB molecules in a thin PS‐ b ‐PEO film sandwiched between a glass slide and coverslip (Figure 7).…”

“…We also examined the shear flow of a precursor PS‐ b ‐PEO solution to align cylindrical PEO microdomains [41] . A droplet of a benzene solution of PS‐ b ‐PEO ( ca .…”

“…Herein, we introduce our approaches to unveiling the detailed dynamics of fluorescent solute molecules in self‐assembled nanostructured materials, including surfactant‐filled silica mesopores (Figure 1a), cylindrical block copolymer (BCP) microdomains (Figure 1b), and bolaamphiphile‐based organic nanotubes (ONTs) (Figure 1c), using advanced fluorescence methods built on SMT and FCS [12,34,35] . We have established a number of measurement and analysis methods including (1) orthogonal regression methods (ORM) for the quantitative analysis of 1D trajectories [36,37] and nanostructure characterization; [38–44] (2) FRAP‐SMT for direct comparison of ensemble and single‐molecule diffusion behavior; [45] (3) SMT with simultaneous single‐molecule emission polarization measurements (SMT‐SMEP) for quantitative measurements of translational and orientational molecular dynamics; [46–48] and (4) two‐color SMT for simultaneous measurements of the distribution and diffusion of single solvatochromic molecules [48] . We also employed imaging FCS for assessing molecular diffusion in individual ONTs [35,49–51] .…”