90 Aristeidis Papagiannopoulos and Stergios Pispas
NH
COONa
SO 3 Na0. 68 x
0. 32 xScheme 1. The molecular structure of SCPI anionic polyelectrolyte utilized in this
study.
In this study a polyisoprene precursor having molecular weight, Mw =
54,000 g/mol and polydispersity Mw/Mn = 1.05 was used for the
functionalization reaction. The molecular weight of the resulting SCPI
polyelectrolyte is Mw = 154,000 g/mol.A functionalized monomer contains
one strong (푆푂 3 −) and one weak (퐶푂푂−) chargeable unit that offers the
polymer its hydrophillic properties. The acidic groups are accompanied by
푁푎+ as counterion, while 퐶푂푂−can be neutralized by 퐻+ below pH 4.2. The
polyelectrolyte was dissolved in distilled water (pH~7) in the desired
concentration and left overnight to equilibrate.
Dodecyltrimethylammonium bromide (DTMAB) was purchased from
Aldrich and used as received. The surfactant was dissolved in water in a
desired initial stock concentration. The initial stock solution surfactant
concentration was kept below DTMAB critical micellar concentration. For
mixed solutions (complexation experiments) the volume of the polyelectrolyte
solution was kept constant while the volume from the surfactant stock solution
was varied. Distilled water was added to a fixed final volume. The addition of
surfactant was done dropwise (2 drops/min) under stirring. For dilution
studies, the complexes containing mixed solutions were diluted with distilled
water to the desired ratio.
As a hydrophobic probe pyrene was purchased from Aldrich
(recrystallized from ethyl acetate) and used for fluorescence measurements.
Fixed volumes of 1mM pyrene solutions in acetone were introduced to the
aqueous solutions with a micropipette and acetone was allowed to evaporate.
The final concentration of pyrene was lower than 3x10-^7 M.
All experiments were performed at room temperature (25°C).