Toward an equilibrium structure in lamellar diblock copolymer thin films using solvent vapor annealing – An in-situ time-resolved GISAXS study

Abstract

a b s t r a c tSolvent vapor annealing (SVA) is frequently used to improve the ordering in diblock copolymer thin films. An important question is which SVA protocol should be chosen to ensure thermodynamic equilibrium. Here, we investigate two thin films from a low molar-mass, lamellae-forming polystyrene-block-polybutadiene (PS-b-PB) diblock copolymer (28.0 kg/mol). The films are prepared by spin-coating Si wafers from toluene solutions and have film thicknesses of 215 nm and 332 nm. The as-prepared films have mainly the parallel lamellar orientation with a lamellar thickness D lam,par significantly lower than in the bulk. SVA cycles were carried out with cyclohexane, and the structural changes were followed in-situ using time-resolved grazing-incidence small-angle X-ray scattering (GISAXS). Before and after SVA, D lam,par is significantly lower than in the bulk, i.e. the equilibrium value of D lam,par in thin film geometry is different from the bulk value. Whereas the behavior of D lam,par is different for the two films in the early stages of the first swelling, it is very similar in the late stages of swelling and during drying. During the first drying, the lamellae deswell, initially slowly and later, when PS becomes glassy again, affinely. During the second SVA cycle on the thin film, the scaling behavior of the lamellar thickness is identical to the one during the first drying and to the drying behavior of the thicker film. We conclude that one cycle of solvent vapor treatment with a degree of swelling of ca. 1.5 is sufficient to bring the PS-b-PB thin films studied into equilibrium and to create a nearly defect-free lamellar structure.

Hierarchical electrospun nanofibers treated by solvent vapor annealing as air filtration mat for high-efficiency PM2.5 capture

“…A typical SEM image of the nanowrinkled air filtration mat fabricated from a PCL/PEO chloroform solution is presented in Fig. 2, which is similar to examples from previous reports [57,58]. The image in Fig.…”

In situ GISAXS study of a Si-containing block copolymer under solvent vapor annealing: Effects of molecular weight and solvent vapor composition

“…In contrast, cylinders formed with out-of-plane orientation after annealing under 1,4-dioxane, a selective solvent, in which a BCC spherical morphology formed in the swollen state and subsequent drying led to cylinders. 24 In thin films, preferential wetting by one block at the top and bottom surfaces favored the in-plane orientation of lamellae in PS-b-PB 34,39 and cylinders in PS-b-PDMS, 26 while solvent gradients were believed to promote out-of-plane orientation of cylinders in PS-b-PDMS for thick films where surface interactions were less important. 26 Structural transitions induced by the absorption of selective solvents were also studied in situ by GISAXS in a cylinder-forming poly(αmethylstyrene)-block-poly(4-hydroxystyrene) (PαMS-b-PHOST), 33 a lamellar-forming poly(2hydroxyethyl methacrylate)-block-poly(methyl methacrylate) (PHEMA-b-PMMA), 3 and a cylinderforming poly(styrene)-block-poly(lactide) (PS-b-PLA).…”

Micellar‐Mediated Block Copolymer Ordering Dynamics Revealed by In Situ Grazing Incidence Small‐Angle X‐Ray Scattering during Spin Coating

“…The corresponding scanning transmission electron microscopy (STEM) image presented in the Figure C reveals that parallel lamellae with 13 nm are formed within the PDMSB ‐b ‐PMMA thin film after deposition. The parallel orientation of the lamellar structure is also confirmed by the 2D GISAXS pattern presented in Figure D which mainly consists of intensity modulations, referred as diffuse Bragg sheets (DBSs), along the vertical q z direction and strongly focused around q y = 0 nm −1 . This behavior is indicative of a lamellar morphology oriented parallel with respect to the substrate plane .…”