Figure 1. (a) SANS of responsive star PDMAEMA with increasing temperature, the solid lines represent model fitting. (b) Schematic representation of the structural changes for star and linear polyelectrolytes upon heating. (W. Xu, et al. Thermo-Induced Limited Aggregation of Responsive Star Polyelectrolytes, Macromolecules, 2014, 47, 2112)

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Highly Branched Nanostructures and their AssembliesVladimir V. Tsukruk, Georgia Institute of Technology, DMR 1002810

Figure 2. (a) PSnP2VPn star block copolymers, (b) the LbL assembly process, (c) CLSM images of hollow microcapsules (I. Choi, et al. Multicompartmental microcapsules from star copolymer micelles, Macromolecules 2013, 46, 1425). (d) AFM images of PS28P2VP28 star copolymers assembled on graphene oxide flakes (I. Choi, et al, Star Polymer Unimicelles on Graphene Oxide Flakes, Langmuir, 2013, 29, 9761)

This project aims at achieving a fundamental understanding of molecular morphology and responsive behavior of branched star-shaped macro-molecules and their assembly into precisely engineered functional films.

In our recent work, the properties and phase behavior of a dual responsive (to pH and temperature) star polyelectrolyte were studied using in situ small-angle neutron scattering (Figure 1a). Upon heating the core-shell stars first experience a contraction in the loose shell region, and then form limited aggregates in contrast to conventional macrophase separation (Figure 1b).

In another study, the pH-sensitive star-shaped block copolymer were utilized as major component to fabricate microcapsules via layer-by-layer assembly. This microcapsules have the ability to deliver different target molecules. The organized interfacial assembly of amphiphilic star copolymers was observed on graphene oxide flakes (Figure 2d).

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Highly Branched Nanostructures and their AssembliesVladimir V. Tsukruk, Georgia Institute of Technology, DMR 1002810

Photo of Weinan, Petr and Dr. Shevchenko

Results of the project have been incorporated into one course (Soft Nanomaterials) taught by the PI at Georgia Tech. The PI and PhD student (Weinan Xu) have presented the results at different international and local conferences, such as the 246th ACS National Meeting and Layer-by-Layer Assemblies Conference.

Some of the work has been done in close collaboration with Oak Ridge National Lab, the PhD students (Weinan Xu and Ikjun Choi) have travelled to ORNL several times to perform SANS and neutron reflectivity experiments.

Education, Training, and Awards

The PI, Vladimir V. Tsukruk, was elected as an ACS Fellow in June 2014.Weinan Xu, a third year graduate student, participated in the 2013 ACS AkzoNobel student award symposium as a finalist. Dr. Ikjun Choi, after receiving PhD degree in 2014 moved to Cornell as a postdoc. Dr. Rattanon Suntivich, recently got his PhD degree, and moved to an industry, SSG company in Thailand in June 2014. Dr. Petr Ledin, with PhD degree in Chemistry from UGA, joined the group as a postdoc in August 2013. Dr. Valeriy Shevchenko, National Academy of Science in Ukraine, visits the PI’s group in the August 2014.

CollaborationsA. H. E. Müller, Universität Mainz: star polyelectrolytes synthesisF. A. Plamper, RWTH Aachen University: miktoarm star synthesis. C. Tsitsilianis, Univ. Patras: star block copolymer synthesisV. V. Shevchenko, NAS of Ukraine: synthesis of star molecules with azobenzene dye arms Yu. B. Melnichenko, ORNL-HFIR, SANS measurementsW. T. Heller, ORNL-SNS, SANS measurements

From left to right: Dr. V. Shevchenko, Dr. P. Ledin, W. Xu.