Generation of Monolayer Gradients in Surface Energy and Surface Chemistry for Block Copolymer Thin Film Studies

Albert, Julie N. L.; Baney, Michael J.; Stafford, Christopher M.; Kelly, Jennifer Y.; Epps, Thomas H.

doi:10.1021/nn900750w

Cited by 60 publications

(99 citation statements)

References 32 publications

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“…The total, dispersive, and polar surface energy components of the bare silica and chlorosilanemodified substrates used in this study are listed in Table 1 and match well with reported measurements found in the literature. 15,16,31,48 Gradient thickness PMMA-PnBA films were coated onto modified substrates via flow coating to determine commensurate and incommensurate thicknesses. 47 Substrate Wetting Behavior Determined by Total Surface Energy.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Decoupling Substrate Surface Interactions in Block Polymer Thin Film Self-Assembly

Shelton

Epps

2015

Macromolecules

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We report a highly predictive approach to capturing the major substrate−polymer interactions that can dominate nanoscale ordering and orientation in block polymer (BP) thin films. Our approach allows one to create designer BP thin films on modified substrates while minimizing the need for extensive parameter space exploration. Herein, we systematically and quantitatively examined the influence of substrate surface energy components (dispersive and polar interactions) on thin film self-assembly, and our analysis demonstrates that although total surface energy plays a dominant role in substrate wetting, individual contributions from the dispersive and polar components of the surface energy influence the composite through-film behavior. Additionally, long-range forces as described by the Hamaker constant are under-recognized factors in thin film assembly and can alter expected wetting behavior by affecting thermodynamic stability. This more inclusive interpretation of surface energy effects, including the Hamaker constant, on BP thin films was supported by studies of interfacial and through-film behavior as gleaned from temporal island/hole measurements via in situ optical microscopy during thermal annealing. The formalism correctly predicted experimental wetting and hole formation sizes over a wide range of substrate surface energies when employing the appropriate relationships based on decoupled dispersive and polar components. Our results indicate a promising and more universal approach for matching desired BP thin film self-assembly with chemically tailored substrate modifications. ■ INTRODUCTIONBlock polymers (BPs) have received significant attention because they can self-assemble into nanostructures (e.g., spheres, cylinders, networks, and lamellae) with periodicities from 5 to 100 nm, which are ideal for thin film applications including nanolithographic masks, nanotemplates, nanoporous membranes, and organic solar cells. 1−7 Although bulk BP selfassembly is dependent largely on the Flory−Huggins interaction parameter (χ), the degree of polymerization (N), and the block volume fractions ( f), thin film self-assembly is influenced by additional confinement parameters such as film thickness (t), substrate surface interactions, and/or free surface interactions. 5,8−12 Furthermore, as the number of potential BP systems continues to increase, 13 experimental investigation of the full parameter space in a given system is no longer feasible and must be replaced by predictive tools that incorporate the nuanced effects of surface interactions and film thickness on nanoscale morphology, ordering, and orientation. 14 Previous studies suggest that substrate−polymer interactions are some of the most influential factors controlling polymer wetting behavior, 15,16 nanostructure orientation, 17−20 nanostructure uniformity through the film, 21−23 and defect density 24,25 in BP thin films. The substrate−polymer interactions typically are quantified by the interfacial energy (Δγ A ) or difference between the substrate (γ S ) and...

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Section: ■ Results and Discussionmentioning

confidence: 99%

Decoupling Substrate Surface Interactions in Block Polymer Thin Film Self-Assembly

Shelton

Epps

2015

Macromolecules

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“…Each contact angle was measured <0.5 s after each droplet first came into contact with the PB surface. 33 A minimum of five contact angles per sample were measured. The average value of these angles was used in the interfacial tension calculations.…”

Section: Methodsmentioning

confidence: 99%

Structural changes in block copolymer micelles induced by cosolvent mixtures

Kelley¹,

Smart²,

Jackson³

et al. 2011

Soft Matter

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We investigated the influence of tetrahydrofuran (THF) addition on the structure of poly(1,2-butadiene-b-ethylene oxide) [PB-PEO] micelles in aqueous solution. Our studies showed that while the micelles remained starlike, the micelle core-corona interfacial tension and micelle size decreased upon THF addition. The detailed effects of the reduction in interfacial tension were probed using contrast variations in small angle neutron scattering (SANS) experiments. At low THF contents (high interfacial tensions), the SANS data were fit to a micelle form factor that incorporated a radial density distribution of corona chains to account for the starlike micelle profile. However, at higher THF contents (low interfacial tensions), the presence of free chains in solution affected the scattering at high q and required the implementation of a linear combination of micelle and Gaussian coil form factors. These SANS data fits indicated that the reduction in interfacial tension led to broadening of the core-corona interface, which increased the PB chain solvent accessibility at intermediate THF solvent fractions. We also noted that the micelle cores swelled with increasing THF addition, suggesting that previous assumptions of the micelle core solvent content in cosolvent mixtures may not be accurate. Control over the size, corona thickness, and extent of solvent accessible PB in these micelles can be a powerful tool in the development of targeting delivery vehicles.

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“…[ 20 , 23 ] Specifi cally, one way to change the surface affi nity is to modify the surface using a polymer brush. [ 20 ] Recently, Albert et al [ 23 ] created a gradient with chemical functionalities that mimics the structures of PS and PMMA, and demonstrated the utility of the fabricated gradient in a PSb -PMMA thin fi lm morphology study in which they identifi ed the expected morphological changes across the gradient. Another approach to tune surface affi nity is based on the use of different solvent vapor treatments.…”

Section: Introductionmentioning

confidence: 99%

Morphology Tailoring of Thin Film Block Copolymers on Patterned Substrates

Edwards

Khomami

2012

Macromol. Rapid Commun.

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It is well known that chemically patterned substrates can direct the assembly of adsorbed layers or thin films of block copolymers. For a cylinder-forming diblock copolymer on periodically spot-patterned substrates, the morphology of the block copolymer follows the pattern at the substrate; however, with different periodic spacing and spot size of the pattern, novel morphologies can be created. Specifically, we have demonstrated that new morphologies that are absent in the bulk system can be tailored by judiciously varying the mismatch between the width of the pattern and the periodic spacing of the bulk block copolymer, the top surface affinity, and spot size. New morphologies can thus be achieved, such as honeycomb and ring structures, which do not appear in the bulk system. These results demonstrate a promising strategy for fabrication of new nanostructures from chemically patterned substrates.

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Generation of Monolayer Gradients in Surface Energy and Surface Chemistry for Block Copolymer Thin Film Studies

Cited by 60 publications

References 32 publications

Decoupling Substrate Surface Interactions in Block Polymer Thin Film Self-Assembly

Decoupling Substrate Surface Interactions in Block Polymer Thin Film Self-Assembly

Structural changes in block copolymer micelles induced by cosolvent mixtures

Morphology Tailoring of Thin Film Block Copolymers on Patterned Substrates

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