Ordering at diblock copolymer surfaces

Abstract

The temperature dependence of the surface excess of a series of symmetric microphaseseparated diblock copolymers of polystyrene (PS) and poly(methy1 methacrylate) (PMMA) was determined by using X-ray photoelectron spectroscopy. For diblock copolymer systems in the strong segregation limit, under equilibrium conditions, a pure layer of PS was located at the surface, whereas for systems in the weak segregation limit, a layer composed of a mixture of PS and PMMA was located there. The surface excess of PS of a weakly segregated diblock copolymer system was observed to decrease with increasing temperature. We show that the chemical potential difference that favors PS at the surface decreases with increasing temperature. The segmental interactions in the vicinity of the surface are modified such that the surface should order at a temperature above the bulk microphase-separation transition (MST). The length scale over which the segmental interactions in the vicinity of the surface are perturbed is on the order of a statistical segment length. Finally, an estimate of the proximity of the weakly segregated system to the bulk MST is made based on the experimental data.

Studies on the effects of the alkyl group on the surface segregation of poly(n-alkyl methacrylate) end-capped 2-perfluorooctylethyl methacrylate films

“…Instead, the size scale N is an important factor, where N is the number of statistical segments that compose copolymer chain. Russell and co-workers [37,38] investigated a series of symmetric diblocks of PS and poly(methyl methacrylate) (PMMA) and found that at low N values, both PMMA and PS coexisted at the surface. At large N, only PS was at the surface.…”

Apertureless Near‐Field Vibrational Imaging of Block‐Copolymer Nanostructures with Ultrahigh Spatial Resolution

“…The connection between the chemically distinct units in block copolymers restricts the microphase separation of the respective chemical constituents, which results in spatially mesoscopic arrangements with a periodicity on the molecular-block length scale of 10-100 nm. [20,21] The complex microphase behavior has attracted much interest both concerning fundamental aspects [22][23][24] and because of the technological potential of block copolymers as functional materials for nanolithography, waveguides and sensor applications. [25,26] These investigations thus call for a high-resolution chemically specific imaging technique to visualize the spatial and chemical composition of the polymer.…”

Effects of copolymer composition, film thickness, and solvent vapor annealing time on dewetting of ultrathin block copolymer films

“…Generally, spinodal dewetting (SD) and nucleation and growth (NG) mechanisms are widely accepted by researchers. Due to the ordered wetting layers, thin films of block copolymers (BCPs) are more stable than those of homopolymers against dewetting over a wide range of film thickness [19][20][21][22][23][24]. Occasionally, autophobic dewetting may be observed in some BCP films, which is because entropy drives copolymer droplets forming on the dense brush layer anchored to the substrate [23,[25][26][27].…”

“…In the past, studies on dewetting of films mainly focused on the initial stage, like hole growth and rim instability, to confirm how dewetting happens [20,22,24,[31][32][33][34][35]. Lee et al used solvent vapor to induce PS film dewetting and found that instability regime changes from the spinodal dewetting to the hole-nucleation with the increase of film thickness [31].…”