Phase Behavior and Dimensional Scaling of Symmetric Block Copolymer−Homopolymer Ternary Blends in Thin Films

Abstract

The phase behavior and dimensional scaling of symmetric ternary blends composed of poly(styrene-block-methyl methacrylate) block copolymers and the corresponding polystyrene and poly(methyl methacrylate) homopolymers in thin films were investigated as a function of χN (the product of the Flory−Huggins interaction parameter and the overall degree of polymerization of the block copolymer), α (the ratio of the degree of polymerization of the homopolymers to that of the block copolymer), and ϕH (the volume fraction of homopolymers in the blends). The phase transitions were characterized by three methods: disappearance of high-order peaks in the fast Fourier transform (FFT) spectra from scanning electron microscopy (SEM) images, application of the amphiphilicity factor determined from the FFTs, and, in the case of thicker films, the appearance of either microphase- or macrophase-separated domains in SEM images. Above the order−disorder transition (ODT) in the χN−ϕH phase diagram, the symmetric ternary blends transitioned from lamellae to a microemulsion and then to macrophase-separated domains as ϕH increased. The phase transitions depended weakly on χN and α in the range of 12.7 ≤ χN ≤ 36.7 and 0.20 ≤ α ≤ 0.99. The periods of swollen lamellae and microemulsions (L B) were determined as a function of ϕH and α and were well described empirically with L B = L 0/(1 − ϕH)β, where L 0 is the natural period of pure block copolymer and β is a parameter that depends linearly on α with values ranging from ∼0.5 to 1.5.

Integration of Density Multiplication in the Formation of Device‐Oriented Structures by Directed Assembly of Block Copolymer–Homopolymer Blends

“…However, while the previous work used a ternary blend with w H ¼ 0.4, we used a blend w H ¼ 0.2 in an effort to ensure the success of density multiplication in these structures. [22,23] The combination of the low w H and the low M n of the homopolymers relative to the block copolymer (PS-b-PMMA, M n ¼ 52-b-52 kg mol À1 ; PS, M n ¼ 6 kg mol À1 ; PMMA M n ¼ 6 kg mol À1 ) reduced the likelihood of the formation of a microemulsion structure in the blend [37] while retaining the capacity for density multiplication previously observed in pure block copolymers. [17,28,30] We spin-coated the ternary blend onto the chemical pattern and annealed it to direct the assembly of the polymer domains into the desired structures, based on the www.afm-journal.de www.MaterialsViews.com Figure 1.…”

“…Smaller feature dimensions could be achieved by decreasing the molecular weights of the blend components, as shown by the scaling behavior of block copolymer blends determined previously. [37,38] First we examined our ability to direct the assembly of the blend with density multiplication to form discrete pattern regions, controlling both the location and the dimensions of the interpolated domains. Figure 2 shows the directed assembly of ternary blends into parallel lines with 50-nm pitch in desired areas by using a chemical pattern on a PS preferential brush.…”

“…The natural period of PS-b-PMMA was measured to be 47.7 nm by small angle X-ray scattering (SAXS) of the bulk sample and fast Fourier transform of the SEM images of the block copolymer thin film annealed on a neutral brush [37]. PMMA (M n ¼ 950 kg mol À1 ) photoresist was www.MaterialsViews.com www.afm-journal.de Experimental Procedure: A silicon wafer was treated in an oxygen plasma for 5 min to remove any organic residue and ensure the presence of a thin layer of silicon oxide.…”

Thin film confinement reduces compatibility in symmetric ternary block copolymer/homopolymer blends

“…The phase behavior of ternary blends consisting of a lamellae‐forming symmetric diBCP and corresponding homopolymers is influenced by the ratio of homopolymer to BCP length (given by α = N H /N BCP ) and the overall volume fraction of homopolymer (Φ H ) in the blend . The ternary blend system can be examined by adding homopolymer (Φ H ) into the BCP such that overall composition of the blend remains the same as that of the pristine BCP.…”

“…The ternary blend system can be examined by adding homopolymer (Φ H ) into the BCP such that overall composition of the blend remains the same as that of the pristine BCP. In this scenario, the addition of homopolymers swells the lamellar domains until a morphology transition to a bicontinuous microemulsion phase and eventually macrophase separation occurs . The extent of domain swelling depends on the distribution of homopolymer within lamellar domains and is quantified by , where L 0 is the domain spacing of the pristine BCP and the empirical exponent β depends on α and describes how the homopolymer is distributed within the domains .…”