Building polymer-like clusters from colloidal particles with isotropic interactions, in aqueous solution

Research output: Contribution to journalArticle

Abstract

Hypothesis: Colloidal particles that interact via a long-ranged repulsive barrier in combination with a very short-ranged attractive minimum can “polymerize” to form highly anisotropic structures. Motivated by previous experimental achievements in non-aqueous solvents, and recent theoretical predictions, we hypothesize that it is possible to construct clusters that resemble linear or branched polymers, in aqueous solution. If these clusters are not too large, they may even remain dispersed, but even if they grow large enough to sediment, they may be collected and used in future applications.
Experiments: In this work, we specifically synthesize poly (ethylene glycol) (PEG) chains, grafted onto poly(styrene) (PS) particles in aqueous solution, and adjust the conditions so that strongly anisotropic and isolated polymer-like clusters are formed. These conditions include a very low ionic strength (the particles are weakly charged), a relatively high temperature, and a low particle concentration. An important criterion is that the particle size is large enough to admit structural analyses via confocal laser scanning microscopy (CLSM). We have furthermore utilized Metropolis Monte Carlo (MC) simulation to generate theoretical predictions of these cluster formations. We have conducted such simulations of 3D as well as 2D systems, where the latter is also relevant, given that the clusters sometimes deposit onto the glass surfaces upon imaging. A simplistic particle–particle potential of mean force is adopted for the simulations, but we also invoke a more elaborate theoretical model, to demonstrate that similar interactions can be obtained when the grafted chains are treated explicitly.
Findings: According to our Zeta potential measurements, the particles indeed carry a weak negative charge, presumably due to ion specific adsorption. Furthermore, by ensuring that the ionic strength is very low, with a Debye length similar to the particle size, we could use temperature to control the hydrophobicity of the grafted PEG layer, and thus the strength of the short-ranged attraction. We were indeed able to establish highly anisotropic structures, that resemble linear or branched polymers, which we could image by CLSM. The average degree of polymerization could be adjusted by a variation of the particle concentration.

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Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Theoretical Chemistry
  • Physical Chemistry
  • Polymer Chemistry

Keywords

  • Linear structures, colloidal dispersions, isotropic interactions, poly (ethylene glycol), poly (styrene), core-shell particles
Original languageEnglish
Pages (from-to)669-681
Number of pages13
JournalJournal of Colloid and Interface Science
Volume581
Publication statusPublished - 2021
Publication categoryResearch
Peer-reviewedYes

Bibliographic note

Received 5 June 2020, Revised 31 July 2020, Accepted 31 July 2020, Available online 7 August 2020.