Block copolymers find applications in many fields, including adhesives,plastics, drug delivery and photonics. Several of these rely on the ability of block copolymers to self-assemble into ordered mesophases in solution. One such application of particular interest to our research group is their use as templates in the synthesis of porous silica materials, such as SBA-15 [1]. Because of their highly ordered pores, high surface areas, high functionality and low cost, mesoporous silicas have been of great interest for an increasing variety of applications and research. Understanding the synthesis mechanism for this class of materials, however, models that can predict how block copolymer templates self-assemble in aqueous solution. This study aims to produce an accurate coarse-grained (CG) model of self-assembling block copolymers, including those used in the synthesis of SBA-15 mesoporous silica (i.e., Pluronic surfactants). Such a model will enable us to probe the large time and length scales that are needed to describe the mesostructure formation from solution, thus clarifying the mechanisms by which these materials are formed.
Our approach is based on the established Martini CG force field [2],which has been previously applied to model these systems [3,4]. We have found that existing models are unable to accurately describe micelle aggregation self-assembly of Pluronic surfactants, although they are designed to match single-chain properties. We have thus systematically tested the existing MARTINI parameters against experimental Gibbs free energies of solvation in both water and hexadecane, leading to improved mapping schemes for polymer molecules. In some cases, parameters needed to be adjusted to accurately describe the solvation free energies in both solvents. In the future, we will test these improved parameters against the phase diagram of block copolymer surfactants, in order to effectively replicate the micelle aggregation and formation processes.
[1] J. Thielemann, F. Girgsdies, R. Schlgl, and C. Hess. Pore structure and surface area of silica sba-15: influence of
washing and scale-up. Beilstein Journal of Nanotechnol, 11:110–118, 2011
[2] S. Marrink and P. Tieleman. Perspective on the martini model. Chem. Soc. Rev., 42:6801–6822, 2013
[3] P. Carboneand S. Nawaz. Coarse-graining poly(ethylene oxide)/poly(propyleneoxide)/poly(ethylene oxide) (peo/ppo/peo) block copolymers using themartini force field. J. Phys. Chem. B, 118(6):1648-1659, 2014
[4] G. Rossi, P. F. J. Fuchs, J. Barnoud, and L. Monticelli. A coarse- grained martini model of polyethylene glycol and
of polyoxyethylene alkyl ether surfactants. J. Phys. Chem. B, 116(49):14353–14362, 2012
Advances in molecular simulation , Engineered self-assembly
