Ordering and Grain Growth in Charged Block Copolymer Bulk Films

Significance 

Recent technological advances have already demonstrated that the morphologies of block copolymer bulk films can be controlled through cautious chemical design and thermal annealing techniques. This has in turn led to sudden interest primarily focusing on how to regulate the orientation of block copolymers nanostructures and minimize the prevalent defects. Presently, thermal processes have been developed in bid to circumvent this shortcoming, however, such processes have been deemed unsuitable for orienting microphase-ordered block copolymers composed of at least one block with charged moieties that can form thermally stable ionic clusters. As a probable solution, solvent-vapor (SV) annealing has been applied to block ionomer bulk films composed of midblock-sulfonated pentablock copolymers. Using this technique, highly ordered morphologies that display evidence of improved in-plane orientation have been achieved. Nonetheless, it is imperative that other similar and yet alternative solvent annealing strategies be assessed.

To this note, Justin J. Ryan (PhD candidate) and Professor Richard J. Spontak at North Carolina State University in collaboration with Dr. Byeongdu Lee at Argonne National Laboratory and Professor Kenneth P. Mineart at Bucknell University compared the effectiveness of three different solvent-related processes and reported the technique that yields the most promising route to morphological ordering and in-plane grain growth. Their work is currently published in the research journal Advanced Materials Interfaces.

The research method employed entailed the application of small-angle X-ray scattering to compare the effectiveness of three solvent-related processes–SV annealing, SV permeation, and SV sorption–on block ionomer ordering and grain growth, and offer explanations for observed differences on the basis of thermodynamic- and transport-related considerations. The methodology employed also involved an in-depth assessment on the influence of the three solvent-related processes in three midblock-sulfonated block ionomers.

The authors observed that, while the SV-permeation approach succeeded, the resultant morphology was not as highly ordered as those generated by either SV-annealing or SV-sorption. In fact, they noted that only SV-annealing yielded highly ordered nanostructural elements that likewise exhibited a moderate degree of orientation with an orientation parameter measuring ≈0.47. According to the authors, the in-plane lamellar grain growth observed could be attributed to the mold-induced lateral constraint with accompanying in-plane epitaxy.

In summary, controlling the orientation of microphase-ordered block copolymers and ionomers is of substantial interest in a variety of nanotechnologies. The study presented a thorough investigation of the influence of SV-annealing, SV-permeation, and SV-sorption on morphological ordering and in-plane grain growth, using three midblock-sulfonated block ionomers. In general, differences in the experimental design of the solvent-related processes were found to affect nanostructural development, as evidenced by the extent of in-plane grain growth. Altogether, insights gleaned from their study provide guidance for the production of block ionomer bulk films requiring anisotropic morphologies that are both highly ordered and oriented, as well as a better understanding of the experimental design of solvent-related processes intended to alter the spatial characteristics of polymer nanostructures.

About the author

Justin J. Ryan completed his undergraduate degree at the Virginia Polytechnic Institute in 2013 and received his Ph.D. in Materials Science & Engineering from North Carolina State University in 2018. In January 2019, he will be joining the Chemistry Division of the Naval Research Laboratory in Washington, DC as a National Research Council Postdoctoral Fellow.

His research interests currently focus on utilizing post-polymerization modification techniques for the strategic development of advanced soft materials and elucidating structure-function relationships governing these systems.

About the author

Kenneth P. Mineart is the C. Graydon and Mary E. Rogers Faculty Fellow and Assistant Professor of Chemical Engineering at Bucknell University. He began this position in the Fall of 2017 following a nearly two-year term as a National Research Council Postdoctoral Fellow at the National Institute of Standards and Technology. Kenneth received his Ph.D. and B.S.E. from North Carolina State University and the University of Iowa, respectively, each in Chemical Engineering. His current research interests include small-angle scattering techniques, multiple self-assembly of surfactants and block polymers, and soft material structure property relationships – specifically diffusion and mechanical behavior.

About the author

Byeongdu Lee received his B.A. in earth science education from Seoul National University in 1998. In 2003, he completed his Ph.D. in polymer physical chemistry with Prof. Moonhor Ree at POSTECH focusing on studies of polymer crystallization and low-k nanoporous materials using SAXS and GISAXS. Since he joined the APS, his research focus has been on the development of scattering methods for studies of nanoparticles and their assemblies. He was awarded the Young Scientist Award from the IUCr small-angle scattering committee in 2006. Currently he is a physicist of Argonne National Laboratory and a fellow of Northwestern-Argonne Institute for Science and Engineering.

About the author

Richard J. Spontak is a Distinguished Professor in the Departments of Chemical & Biomolecular Engineering and Materials Science & Engineering at North Carolina State University. He received his B.S. and Ph.D. degrees in Chemical Engineering from Penn State University and the University of California at Berkeley, respectively. Before launching his academic career, he held post-doctoral appointments at the University of Cambridge (U.K.) and the Institute for Energy Technology (Norway) and was employed at P&G.

His primary research interests relate to the phase behavior and morphology/property development of nanostructured polymers, electron microscopy and stimuli-responsive materials. He received several awards in recognition of his research, including the 2006 American Chemical Society (PMSE Division) Cooperative Research Award in Polymer Science & Engineering, the 2007 German Society for Electron Microscopy Ernst Ruska Prize, the 2008 American Chemical Society (Rubber Division) Chemistry of Thermoplastic Elastomers Award, the 2011 Institute of Materials, Minerals and Mining (IOM3) Colwyn Medal, the 2012 Norwegian University of Science & Technology Lars Onsager Medal, and the 2015 Society of Plastics Engineers International Award. An elected fellow of the American Physical Society, IOM3 and the Royal Society of Chemistry, he is a member of the Norwegian Academy of Technological Sciences.

Reference

Justin J. Ryan, Kenneth P. Mineart, Byeongdu Lee, and Richard J. Spontak. Ordering and Grain Growth in Charged Block Copolymer Bulk Films A Comparison of Solvent-Related Processes. Advanced Materials Interfaces 2018, volume 5, page 1701667.

Go To Advanced Materials Interfaces

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