Creation of lateral structures in diblock copolymer thin films during vapor uptake and subsequent drying – Effect of film thickness

Abstract

a b s t r a c tWe have studied the structure formation in compositionally nearly symmetric poly(4-octylstyrene-b-butylmethacrylate) diblock copolymer films during exposure to saturated vapor of n-hexane (a poor solvent for both blocks) and subsequent drying using real-time, in situ grazing-incidence small-angle X-ray scattering (GISAXS). Previous bulk studies revealed a lamellar structure after thermo-annealing; and surface studies on hexane treated samples revealed a lateral surface structure (Č ernoch et al., 2007) [14]. We focus here on the effect of film thickness which is varied between 1.3 and 2.0 times the bulk lamellar thickness. We report on the lateral repeat distance as well as on the correlation length in the film plane. Complex, non-monotonous behavior is observed for both parameters. Upon drying, the lateral structure created during vapor treatment is stable only for the thick film, not for the intermediate and the thin film. The kinetics depends strongly on the film thickness; especially for the thinnest film, it is very slow. For all film thicknesses, we attempt to identify the most stable morphology, occurring when the inner film structure is close to the one in the bulk.

Restructuring in block copolymer thin films: In situ GISAXS investigations during solvent vapor annealing

“…These chambers enabled in-situ imaging of thin BCP films by optical microscopy as well as monitoring the swelling of various homopolymer and BCP thin films during SVA using ellipsometry. For GISAXS, chambers containing liquid solvent in a reservoir have been frequently used [128][129][130][131][132][133][134]. Moreover, the vapor pressure in the chamber may be controlled by an additional flow of dry gas which facilitates stepwise swelling [111,135].…”

“…While the majority of studies using GISAXS on thin diblock copolymer films address the structures resulting from specific treatments, a number of studies have addressed the more complex issue of the mechanisms behind the restructuring processes using real-time in-situ GISAXS [111,120,121,129,131,134,[138][139][140]193,194,[197][198][199].…”

Block copolymer thin films: Characterizing nanostructure evolution with in situ X-ray and neutron scattering

“…As the number of BCP chemistries, architectures, and morphologies grows exponentially [52], results from in situ GISAXS studies, such as those described above, are instrumental in the design of annealing protocols that reduce structural defects and control the through-film uniformity of various nanostructures. Recently, in situ GISAXS during SVA has been used to investigate how factors such as solvent choice [153,154], solvent partial pressure [55,133,139,153,155], swelling/deswelling rates [55,156,157], and film thickness [141,155] affect the restructuring of BCP thin film domains.…”

In situ multi-modal monitoring of solvent vapor swelling in polymer thin films

“…For diblock copolymers, grazing incidence small-angle x-ray scattering (GISAXS) has been used to assess transient nanostructures that arise during swelling. 12,13,[19][20][21][22] While GISAXS can reveal nanostructural motifs present in a swollen film, it cannot describe molecular motions in a spatially resolved manner. Indeed, no study to date has simultaneously assessed film thickness and local structure or dynamics in real time.…”