A molecular dynamics investigation of the conformation and hydration of polymer brushes

Abbott, Helen Elizabeth (2023). A molecular dynamics investigation of the conformation and hydration of polymer brushes. University of Birmingham. Ph.D.

Preview

Abbott2023PhD.pdf
Text - Accepted Version
Available under License All rights reserved.
Download (5MB) | Preview

Abstract

The unique architecture of polymer brushes (PBs), combined with their ability to respond to external stimuli, have led to numerous applications, for example in biomechanical devices. A thorough understanding of their responsiveness to external stimuli is required to optimise PBs for use in these practical applications. It is well-known that the hydration levels and structural properties of PBs can be modulated by the addition of different types of electrolyte solutions, depending on the categorisation of electrolyte ions within the Hofmeister series.

Atomistic molecular dynamics (MD) simulations have been used to characterise the levels of hydration and conformational behaviour of two different types of PB: (i) strong polyelectrolyte brushes consisting of poly (2-(methacryloyloxy) ethyl trimethylammonium chloride) (PMETAC) and (ii) polyzwitterionic brushes consisting of poly (sulfobetaine methacrylate) (PSBMA) in a range of electrolyte solutions. The chosen atomic parameters successfully reproduced subtle differences in the conformational responses of both types of studied PBs in the presence of highly concentrated chaotropic anions, ClO\(_{4}^{−}\) and SCN\(^{−}\). The responsiveness of the studied PBs has been linked to the formation of ion pairs. The frequency and size of ion pairing and clustering species have been proposed to influence the hydration and structure of PMETAC and PSBMA brushes.

The presence of strongly kosmotropic anions, SO\(_{4}^{2−}\) anions, caused no discernible change in the properties of the simulated PMETAC and PSBMA brushes. The chosen atomistic parameters, while accurate for the studied PBs with the chaotropic anions, do not seem to appropriately describe specific-ion interactions involving SO\(_{4}^{2−}\) anions.

Chapter 7 is a stand-alone study using basin-hopping global optimisation techniques. Alkyl-dicarboxylate di-anions and alkyl-diammonium di-cations, in which the two distinct charge centres are separated by a flexible alkyl (CH\(_{2}\))\(_{m}\) chain were investigated in differently solvated conditions. For each di-ion investigated, a conformational transition from linear to folded is observed at a critical hydration number.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):