Location, Location, Location… How charge placement can control a self-assembled structure.

September 10, 2019

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The position of a charged monomer (blue dots) along a polymer chain impacts the final structures (structures 1, 3, and 5 from the sequence library) following assembly into micelles (bottom).
The position of a charged monomer (blue dots) along a polymer chain impacts the final structures (structures 1, 3, and 5 from the sequence library) following assembly into micelles (bottom).
Image courtesy of authors (see “Publications”)

The Science

New, complex materials could lead to better tech to purify water or recover oil. Creating the right materials (often polymers) is difficult. For years, scientists have formed polymers using the interaction of charges on molecular chains to determine the shape, geometry, and other properties. Now, a team achieved precise and predictable control of molecular chains by positioning charges. Their method leads to particles with reproducible sizes.

The Impact

This study helps scientists design polymers. Specifically, it helps them predict how to create certain materials by knowing where to place charged groups in molecular assemblies. Tuning the final structure and properties through precise charge placement could lead to smart polymers. Potential uses for such materials include water purification, oil recovery, and drug delivery.

Summary

The hallmark of polymers is that the control of chemical sequence dictates their structure and function. The current study demonstrated that by encoding electrostatic interactions in the sequence of a polymer chain, control of the structure of the resultant micellar assemblies is achieved. Specifically, a class of bio-inspired peptide-like materials, known as polypeptoids that have precisely positioned single or triple charges, form micelles in dilute water solutions. The position and numbers of charges along the chain dictate the structure of the micelles in a predictable manner. The micelle size becomes increasingly larger as a single charge is placed farther away from the junction of the water-attracting and water-repelling polypeptoid segments. Scaling analysis revealed a quantitative relationship between the micellar structure and position of the charges. This general principle may potentially guide fine-tuning of the structures of a variety of weakly charged soft matter assemblies for and the design of smart, stimuli-responsive polymeric materials.

Contact

Donghui Zhang
Louisiana State University
dhzhang@lsu.edu

Funding

Department of Energy (DOE), Office of Science (SC), through the Established Program to Stimulate Competitive Research and use of the Spallation Neutron Source, High Flux Isotope Reactor, and the Molecular Foundry, Office of Science user facilities, with additional support from the Louisiana Board of Regents. The work also made use of expertise and facilities at the Biological Small-Angle Neutron Scattering Instrument supported by the DOE, SC, Office of Biological and Environmental Research.

Publications

G.L. Sternhagen, S. Gupta, Y. Zhang, V. John, G. Schneider, and D. Zhang, “Solution self-assemblies of sequence-defined ionic peptoid block copolymer.” Journal of the American Chemical Society 140, 4100 (2018). [DOI: 10.1021/jacs.8b00461]