Adsorption and Dimerization Studies of Rhodamine 6G

Understanding the mechanism of adsorption of Rhodamine 6G (R6G) to various crystal structures of silica nanoparticles (SNPs) is important to elucidate the impact of the dye size when measuring the size of the dye-SNP complex via the time-resolved fluorescence anisotropy method.

We are using MD simulations to get an insight into the R6G adsorption process, which cannot be observed using experimental methods. It was found that α-Quartz structured SNPs are more suitable for R6G adsorption at high pH, than α-Cristobalite ones. Furthermore, it was found that stable adsorption can occur only when the R6G xanthene core is oriented flat with respect to the SNP surface, indicating that the dye size does not contribute significantly to the measured size of the dye-SNP complex. The requirement of correct dipole moment orientation indicates that only one R6G molecule can adsorb on any size SNP and the R6G layer formation on SNP is not possible. Moreover, we also investigate the competing processes of R6G dimerization and adsorption and we have found that the highest stable R6G aggregate is a dimer, in this form R6G does not adsorb to the SNPs. The other material’s SNPs and surfaces are currently studied to elucidate the role of material properties, its size and curvature as well as pH of the system. The binding energy of R6G dimers and R6G adsorption energy is studied using SMD and DFT methods, both reporting consistent data when compared with other aromatic molecules.

For more information about the project contact Dr Karina Kubiak-Ossowska (karina.kubiak@strath.ac.uk) High Performance Computing Knowledge Exchange Associate, ARCHIE-WeSt, University of Strathclyde or Daniel Doveiko (daniel.doveiko@strath.ac.uk), PhD candidate at the Department of Physics at the University of Strathclyde.

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