Supramolecular fibers in gels can be at thermodynamic equilibrium : a simple packing model reveals preferential fibril formation versus crystallization

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Ramos Sasselli, Ivan and Halling, Peter J. and Ulijn, Rein V. and Tuttle, Tell (2016) Supramolecular fibers in gels can be at thermodynamic equilibrium : a simple packing model reveals preferential fibril formation versus crystallization. ACS Nano, 10 (2). pp. 2661-2668. ISSN 1936-0851 (https://doi.org/10.1021/acsnano.5b07690)

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Abstract

Low molecular weight gelators are able to form nanostructures, typically fibers, which entangle to form gel-phase materials. These materials have wide-ranging applications in biomedicine and nanotechnology. While it is known that supramolecular gels often represent metastable structures due to the restricted molecular dynamics in the gel state, the thermodynamic nature of the nanofibrous structure is not well understood. Clearly, 3D extended structures will be able to form more interactions than 1D structures. However, self-assembling molecules are typically amphiphilic, thus giving rise to a combination of solvophobic and solvophilic moieties where a level of solvent exposure at the nanostructure surface is favorable. In this study, we introduce a simple packing model, based on prisms with faces of different nature (solvophobic and solvophilic) and variable interaction parameters, to represent amphiphile self-assembly. This model demonstrates that by tuning shape and "self" or "solvent" interaction parameters either the 1D fiber or 3D crystal may represent the thermodynamic minimum. The model depends on parameters that relate to features of experimentally known systems: The number of faces exposed to the solvent or buried in the fiber; the overall shape of the prism; and the free energy penalties associated with the interactions can be adjusted to match their chemical nature. The model is applied to describe the pH-dependent gelation/precipitation of well-known gelator Fmoc-FF. We conclude that, despite the fact that most experimentally produced gels probably represent metastable states, one-dimensional fibers can represent thermodynamic equilibrium. This conclusion has critical implications for the theoretical treatment of gels.

ORCID iDs

Ramos Sasselli, Ivan ORCID logoORCID: https://orcid.org/0000-0001-6062-2440, Halling, Peter J. ORCID logoORCID: https://orcid.org/0000-0001-5077-4088, Ulijn, Rein V. ORCID logoORCID: https://orcid.org/0000-0001-7974-3779 and Tuttle, Tell;
  • Item type:Article
    ID code:56551
    Dates:
    Date
    Event
    23 February 2016
    Published
    29 January 2016
    Published Online
    26 January 2016
    Accepted
    Notes:This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACSNano, © American Chemical Society after peer review. To access the final edited and published work see http://dx.doi.org/10.1021/acsnano.5b07690
    Subjects:Technology > Engineering (General). Civil engineering (General)
    Department:Faculty of Science > Pure and Applied Chemistry
    Depositing user: Pure Administrator
    Date deposited:27 May 2016 13:22
    Last modified:11 Nov 2024 11:22
    Related URLs:
    URI:https://strathprints.strath.ac.uk/id/eprint/56551
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