First Steps in the Aggregation Process of Copolymers Based on Thymine Monomers: Characterization by Molecular Dynamics Simulations and Atomic Force Microscopy

Abstract

Atomistic molecular dynamic simulations were performed to study thestructure of isolated VBT−VBA (vinylbenzylthymine−vinylbenzyltriethylammoniumchloride) copolymer chains in water at different monomeric species ratios (1:1 and 1:4).The geometric parameters of the structure that the copolymers form in equilibrium together with the basic interactions that stabilize them were determined. Atomic force microscopy (AFM) measurements of dried diluted concentrations of the two copolymers onto highly oriented pyrolytic graphite (HOPG) substrates were carried out to study their aggregation arrangement. The experiments show that both copolymers arrange in fiber-like structures. Comparing the diameters predicted by the simulation results and those obtainedby AFM, it can be concluded that individual copolymers arrange in bunches of two chains, stabilized by contra-ions−copolymer interactions for the 1:1 copolymerization ratio at the ionic strength of our samples. In contrast, for the 1:4 system the individual copolymer chains do not aggregate in bunches. These results remark the relevance of the copolymerization ratio and ionic strength of the solvent in the mesoscopic structure of these materials.