Conformational switching of modified guest chains in polymer brushes

• Published in: The Journal of chemical physics Vol. 139; no. 4; p. 044910
• Main Authors: Romeis, D, Sommer, J-U
• Format: Journal Article
• Language: English
• Published: United States 28.07.2013
• Subjects: Molecular Conformation; Nanotechnology; Particle Size; Polymers - chemistry
• ISSN: 1089-7690
• DOI: 10.1063/1.4816125

Using a numerical quasi off-lattice self-consistent field method which describes heterogeneous chains of spherical monomers we study the case of a densely grafted polymer brush with a fraction of free chain ends being replaced by a modified end-group differing in size and solvent selectivity. We can confirm the observation from molecular dynamics simulations that upon changing the solvent conditions, a switching in location of end-groups which are bigger than monomers from a state "exposed" to the solvent (on the top of the brush) to a "hidden" state (inside the brush) takes place. Our numerical method allows a detailed study of the switching effect as a function of the relevant parameters, such as grafting density, chain length, size of end-groups and their volume fraction. We find that the switching effect is enhanced for long chains, low fractions of modified chains, and big end-groups. We consider the case of low fraction of modified chains in more detail using a test chain method. Here, we explore the optimal grafting density as a function of the size of the end-groups, where the switching is most sensitive. These values can be in the experimental range for end-groups which are at least 3-4 times bigger than the monomers. The end-groups can be realized by attaching nano-particles to the last monomer of a brush-chain.