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Electrostatically tuned self-assembly of branched amphiphilic peptides

Journal of Physical Chemistry B

Ting, Christina L.; Frischknecht, Amalie L.; Stevens, Mark J.; Spoerke, Erik D.

Electrostatics plays an important role in the self-assembly of amphiphilic peptides. To develop a molecular understanding of the role of the electrostatic interactions, we develop a coarse-grained model peptide and apply self-consistent field theory to investigate the peptide assembly into a variety of aggregate nanostructures. We find that the presence and distribution of charged groups on the hydrophilic branches of the peptide can modify the molecular configuration from extended to collapsed. This change in molecular configuration influences the packing into spherical micelles, cylindrical micelles (nanofibers), or planar bilayers. The effects of charge distribution therefore have important implications for the design and utility of functional materials based on peptides. © 2014 American Chemical Society.

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TYPE Journal Article YEAR 2014
ScopusOSTIDOI

Dynamics of model ionomer melts of various architectures

Macromolecules

Hall, Lisa M.; Stevens, Mark J.; Frischknecht, Amalie L.

Ion-containing polymers have potential as single-ion conducting battery electrolyte materials. Their conductivity is often too low for such applications due to the low dielectric polymer backbone and resulting strong aggregation of ions. We simulate coarse-grained ionomer melts (with explicit counterions) of various polymer architectures to understand the effect of polymer connectivity on the dynamics. We report on the polymer and counterion dynamics as a function of periodically or randomly spaced charged groups, which can be placed in the backbone or pendant to it. The spacer length is also varied. The simulations reveal the mechanism of ion transport, the coupling between counterion and polymer dynamics, and the dependence of the ion dynamics on polymer architecture. Within the ionic aggregrates, ion dynamics is rather fluid and relatively fast. The larger scale dynamics (time and length) depends strongly on the large scale morphology of the ionomer. Systems with percolated clusters have faster counterion diffusion than systems with isolated clusters. In the systems with isolated clusters counterions diffuse through the combination, rearrangement, and separation of neighboring clusters. In this process, counterions move from one cluster to another without ever being separated from a cluster. In percolated systems, the counterions can move similarly without the need for the merging of clusters. Thus, the ion diffusion does not involve a hopping process. The dynamics also depends significantly on the details of the polymer architecture beyond the aggregate morphology. Adding randomness in spacing of the charges can either increase or decrease the ion diffusion, depending on the specific type of random sequence. © 2012 American Chemical Society.

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TYPE Journal Article YEAR 2012
ScopusOSTIDOI

Effect of polymer architecture and ionic aggregation on the scattering peak in model ionomers

Physical Review Letters

Hall, Lisa M.; Stevens, Mark J.; Frischknecht, Amalie L.

We perform molecular dynamics simulations of coarse-grained ionomer melts with two different architectures. Regularly spaced charged beads are placed either in the polymer backbone (ionenes) or pendant to it. The ionic aggregate structure is quantified as a function of the dielectric constant. The low wave vector ionomer scattering peak is present in all cases, but is significantly more intense for pendant ions, which form compact, discrete aggregates with liquidlike interaggregate order. This is in qualitative contrast to the ionenes, which form extended aggregates. © 2011 American Physical Society.

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TYPE Journal Article YEAR 2011
ScopusOSTI

Molecular dynamics simulations of ionic aggregates in a coarse%3CU%2B2010%3Egrained ionomer melt

Hall, Lisa M.; Stevens, Mark J.; Frischknecht, Amalie L.

Ionomers--polymers containing a small fraction of covalently bound ionic groups--have potential application as solid electrolytes in batteries. Understanding ion transport in ionomers is essential for such applications. Due to strong electrostatic interactions in these materials, the ions form aggregates, tending to slow counterion diffusion. A key question is how ionomer properties affect ionic aggregation and counterion dynamics on a molecular level. Recent experimental advances have allowed synthesis and extensive characterization of ionomers with a precise, constant spacing of charged groups, making them ideal for controlled measurement and more direct comparison with molecular simulation. We have used coarse-grained molecular dynamics to simulate such ionomers with regularly spaced charged beads. The charged beads are placed either in the polymer backbone or as pendants on the backbone. The polymers, along with the counterions, are simulated at melt densities. The ionic aggregate structure was determined as a function of the dielectric constant, spacing of the charged beads on the polymer, and the sizes of the charged beads and counterions. The pendant ion architecture can yield qualitatively different aggregate structures from those of the linear polymers. For small pendant ions, roughly spherical aggregates have been found above the glass transition temperature. The implications of these aggregates for ion diffusion will be discussed.

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TYPE Conference YEAR 2010
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Results 1–25 of 40