The solubilisation behaviour of some dichloroalkanes in aqueous solutions of PEO-PPO-PEO triblock copolymers: a dynamic light scattering, fluorescence spectroscopy, and SANS study

The aggregation behaviour of PEO-PPO-PEO triblock copolymers in water and in water + chlorinated additive mixtures was studied by means of fluorescence spectroscopy, dynamic light scattering (DLS), and small-angle neutron scattering (SANS). The copolymers were chosen such as to investigate the effects of molecular architecture (L35 and 10R5) and molecular weight by keeping constant the hydrophilic/hydrophobic balance (F88 and F108). 1,2-Dichloroethane was used as a prototype of water basins contaminants. The hydrodynamic radius of the block copolymer aggregates (R(h,M)) and the intensity ratio of pyrene of the first and the third vibrational band (I(1)/I(3)) were determined as a function of temperature (10-45 degrees C) and concentration. The copolymer architecture essentially does not affect R(h,M) in the entire range of temperature and concentration investigated. At a given temperature, increasing macromolecular size leads to a decrease of R(h,M). With rising temperature R(h,M) also decreases. According to the DLS results, the I(1)/I(3) change with temperature clearly detects the aggregation only for F88 and F108. The presence of 1,2-dichloroethane, at concentrations close to its solubility in water, does not lead to changes in the distribution of hydrodynamic radii for L35 and 10R5. Larger quantities of additive induce the formation of quite polydisperse mixed aggregates for L35 and of networks for 10R5. In the case of F88 and F108, low concentrations of additive lead to formation of mixed aggregates with smaller R(h,M). The SANS results corroborate the DLS and fluorescence findings proving enhancement of the copolymer aggregation through the presence of 1,2-dichloroethane. The DLS findings combined with those from the fluorescence spectroscopy provide some insight into the site of solubilisation of the additive in the aggregates.