Entropy and Enthalpy Mediated Segregation of Bottlebrush Copolymers to Interfaces

Journal Article · Wed Nov 13 00:00:00 EST 2019 · Macromolecules

DOI:https://doi.org/10.1021/acs.macromol.9b01801· OSTI ID:1606954

Mei, Hao ^[1]; Laws, Travis S. ^[2]; Mahalik, Jyoti P. ^[3]; Li, Jiabei ^[1]; Mah, Adeline Huizhen ^[4]; Terlier, Tanguy ^[1]; Bonnesen, Peter V. ^[5]; Uhrig, David ^[5]; Kumar, Rajeev ^[6]; Stein, Gila E. ^[2]; Verduzco, Rafael ^[1]

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1. Rice Univ., Houston, TX (United States)
2. Univ. of Tennessee, Knoxville, TN (United States)
3. Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Science (CNMS)
4. Univ. of Houston, TX (United States)
5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Science (CNMS)
6. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Science (CNMS) and Computational Sciences and Engineering Division

The composition of polymer blends near interfaces can differ from the average blend composition because the attraction of each polymer toward surfaces is controlled by its chemistry, size, and architecture. In this work, we studied thin film blends of bottlebrush copolymers and linear homopolymers to understand the enthalpic and entropic effects that drive preferential segregation of one constituent to film interfaces. Bottlebrush copolymers containing polystyrene (PS) and poly(methyl methacrylate) (PMMA) side chains were blended with either linear PS or linear PMMA, and time-of-flight secondary ion mass spectroscopy was used to quantify the distribution of bottlebrushes through the film thickness as a function of homopolymer type, homopolymer molecular weight, and processing conditions. We found that the bottlebrush copolymers segregated to air and substrate interfaces above a critical molecular weight of the linear homopolymer, consistent with an entropic preference for chain ends and shorter chains toward the interfaces. This segregation was used to tailor the surface wettability of blend films using bottlebrush additives as a minority component. Modeling using self-consistent field theory highlighted effects of conformational entropy and enthalpic interactions in driving almost complete segregation from the interior of the films toward interfaces. Furthermore, enthalpic interactions were predicted to cause lateral phase segregation in cases where the homopolymer is preferred over the bottlebrush copolymer at the substrate, an effect that was also observed in experiments. Finally, this study demonstrates that bottlebrush copolymer additives can be designed to spontaneously segregate to surfaces in thermal blends, providing a possible route to decouple surface properties from bulk properties.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Science (CNMS)
• Sponsoring Organization: National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); Welch Foundation
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1606954
• Journal Information: Macromolecules, Journal Name: Macromolecules Journal Issue: 22 Vol. 52; ISSN 0024-9297
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
Copolymers
Interfaces
Organic compounds
Polymers
Silicon