posted on 2017-11-06, 15:49authored byMaría Monteserín, Hugh D. Burrows, Artur J. M. Valente, A. A. C. C. Pais, Roberto E. Di Paolo, Antonio L. Maçanita, María J. Tapia
The modulation of
conjugated polyelectrolyte fluorescence response
by nonionic surfactants is dependent on the structures of the surfactant
and polymer, polymer average molecular weight, and polyelectrolyte–surfactant
interactions. In this paper, we study the effect of nonionic n-alkyl polyoxyethylene surfactants (CiEj) with different alkyl chain
lengths (CiE5 with i = 6, 8, 10, and 12) and number of oxyethylene groups (C12Ej with j =
5, 7, and 9) on the photophysics and ionic conductivity of poly{[9,9-bis(6′-N,N,N-trimethylammonium)-hexyl]-2,7-fluorene-alt-1,4-phenylene}bromide (HTMA-PFP) in dimethyl sulfoxide–water
4% (v/v). Molecular dynamics simulations show that HTMA-PFP chains
tend to approach as the simulation evolves. However, the minimum distance
between the polymer centers of mass increases upon addition of the
surfactant and grows with both the surfactant alkyl chain length and
the number of oxyethylene groups, although there are no specific polymer–surfactant
interactions. A significant increase in the polymer emission intensity
has been observed at surfactant concentrations around their critical
micelle concentrations (cmcs), which is attributed to polymer aggregate
disruption. However, an increase in the solution conductivity for
concentrations above the C12E5 cmc has only
been observed for the HTMA-PFP/C12E5 system.
The enhancement of fluorescence emission intensity and conductivity
upon surfactant addition increases with polymer average molecular
weights and seems to be controlled by the polymer–surfactant
proximity, which is maximum for C10E5 and C12E5.