Solvent Processing and Ionic Liquid-Enabled Long-Range Vertical Ordering in Block Copolymer Films with Enhanced Film Stability

Abstract

Rapid and reliable processing methods for forming ordered block copolymer (BCP) materials with low defect density in a thin film geometry are required for many nanotechnology applications. Vertically aligned BCP structures, in particular, have applications ranging from nanolithography for electronics and photonics applications to nanoporous membranes for water remediation and novel batteries for flexible electronics. However, the attainment of a nearly complete vertical orientational order of the BCP-ordered phase remains challenging. Solvent-based techniques, such as direct immersion annealing (DIA) and solvent vapor annealing (SVA), have immense potential for these applications of BCP films, as it allows for a ‘tuning’ of their thermodynamic, structural, and chain mobility-driven kinetic properties. We first demonstrate that DIA, using a judicious choice of binary solvent mixtures, along with a relatively hydrophobic ionic liquid (IL), induces the rapid vertical ordering in polystyrene-b-poly­(methyl methacrylate) (PS-PMMA) in lamellae-forming block copolymer films. The IL in a binary solvent mixture with toluene and heptane apparently gives rise to a near-neutral solvent for the BCP for itself and the boundary that is useful for attaining the vertical microstructure within the BCP film. Next, we show that an IL can moreover suppress the dewetting of the PS-PMMA films to achieve long-range order using SVA in cylindrical films after long annealing times. Both vertical and horizontal morphologies are attained in these films by selecting different solvent conditions. Attaining enhanced vertical and horizontal BCP structures with long-range defect-free order by tuning solvent quality and using additives like ILs can render them useful for many nanotech applications.

Thickness Dependence of Contact Angles in Multilayered Ultrathin Polymer Films

“…Examples include glass-transition temperature ( T g ), − density, , refractive index, , wetting/dewetting behavior, − and many others. , Among these polymer material properties, the wettability of ultrathin films is less explored, perhaps because of the difficulty of conducting a systematic study on homogeneous ultrathin polymer films, but no less important. The wetting behavior of ultrathin polymer films is critical knowledge for the design of tailored wettability in performance coatings from flexible electronics, water collection, antifouling, to self-healing …”

“…27,28 Among these polymer material properties, the wettability of ultrathin films is less explored, perhaps because of the difficulty 29 of conducting a systematic study on homogeneous ultrathin polymer films, but no less important. The wetting behavior of ultrathin polymer films is critical knowledge for the design of tailored wettability in performance coatings from flexible electronics, 30 water collection, 31 antifouling, 32 to self-healing. 33 Researchers have reported that contact angle, a measure of wettability and surface energy, is dependent on film thickness for a number of polymer brushes 32,34,35 and films, 24,26,36,37 but the origin of such deviations is not fully understood.…”

Hiking down the Free Energy Landscape Using Sequential Solvent and Thermal Processing for Versatile Ordering of Block Copolymer Films

“…These "transition times" are the sequential TA times for the island/hole heights to increase from the DIA (≈L o /2) domain size to that for TA (L o ). 44 The figure also shows annealing times for TA-only treatment (red circles) at 160 °C for M n = 36.5k and 51k, at 180 °C for 66k, and at 200 °C for 89k BCP. Additionally, Figure 3 also shows SVA + TA time for the transition in island/hole heights from SVA-ordered morphology in SM 1 , followed by TA at 160 °C for M n = 51k and at 180 °C for 66k (blue triangles).…”

Facile Entropy-Driven Segregation of Imprinted Polymer-Grafted Nanoparticle Brush Blends by Solvent Vapor Annealing Soft Lithography

“…For PGNPs dispersed in a polymer matrix, there are two different types of PGNP blends encountered: blends for which the outer polymer brush of the PGNP has a different chemistry from the polymer matrix and the case where the brush layer of the PGNP and the polymer matrix has the same chemistry. For the chemically distinct system, extensive research has shown that these PGNP nanocomposites’ morphologies, similar to other polymer systems, − can be controlled through variation of the Flory–Huggins interaction parameter χ, describing the strength of the polymer–polymer interaction. − Schmitt et al revealed that the morphologies of PGNPs having chemically different grafted layers can undergo an upper critical solution temperature phase behavior, as in the corresponding homopolymer blends without NP cores. Wu et al demonstrated that varying the χ between the two different PGNPs by changing the annealing solvent in the direct immersion annealing process can reversibly alternate the morphologies between phase-separated and homogeneous states.…”