General solvation motifs of a charged linear macroion in an aqueous droplet

ABSTRACT

We explore the solvation patterns of a charged rigid and semi-rigid linear macroion in an aqueous droplet. The solvation patterns are summarised in an empirical ‘phase diagram’ on the parameter space defined by the length of the macroion and its charge density. In the study, we employ molecular dynamics and atomistic modelling. The macroion is represented by a positively charged carbon nanotube. Linear macroion-solvent interactions in droplets are distinct from those of spherical ions because of the interplay among several factors such as the tendency of the solvent to form spherical droplets in order to minimise the surface energy, the constraint on the charge of a spherical droplet imposed by the Rayleigh limit, the solvation energy of the macroion and its length. The combination of all these factors may lead to a variety of solvent distributions along the rigid rod such as asymmetric solvation of the linear macroion, formation of spiky ‘star’-like distribution of solvent, partial wetting of the rod by a droplet. The study provides insight into the solvation of macroions in droplets with applications in electrosprayed macroions and atmospheric aerosols. We also propose a possible path of generating a sequence of nanoparticles of different shapes (spheres, multi-point stars) along a linear macromolecule by exploiting the various solvation patterns.

GRAPHICAL ABSTRACT

KEYWORDS:

• Charge-induced instability
• droplet deformations
• droplet-macroion interactions
• Rayleigh limit

Acknowledgments

M.I.O. and S.C. acknowledge very insightful discussions with Prof. Daan Frenkel, Department of Chemistry, University of Cambridge and Dr Anatoly Malevanets, University of Western Ontario, concerning the stability of charged droplets. We extend our thankfulness to Prof. D. Frenkel for his suggestion for creating solid nanoparticles out of the ‘star’-shaped droplets via polymerisation and we hope that this idea may also apply to the shapes presented in this manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Styliani Consta  http://orcid.org/0000-0001-8869-4155

Additional information

Funding

S.C. acknowledges an NSERC-Discovery grant, Canada, for funding this research. M.I.O. acknowledges financial support from the Alexander Graham Bell Canada Graduate Scholarships-Doctoral Program (CGS D) of Natural Sciences and Engineering Research Council of Canada (NSERC) [grant number RGPIN-2018-06604], Canada. Sci-Net and Compute Canada are acknowledged for providing the computing facilities to perform this project.