EFFECT OF ADDITION OF POLYMER TO WATER-IN-OIL MICROEMULSIONS ON DROPLET SIZE AND EXCHANGE OF MATERIAL BETWEEN DROPLETS

The effect of addition of polymers to AOT/decane/water/alcohol water-i n-oil microemulsions on the interdroplet attractive interactions has b een investigated by electrical conductivity and by the time-resolved f luorescence quenching (TRFQ) method. Three types of polymers have been used: (i) water-soluble polymers, namely poly(oxyethylene glycol) (PO EG), poly(acrylamide) (PAM), and poly(vinyl alcohol) (PVA); (ii) an oi l-soluble polymer, namely polybutadiene (PBD); and (iii) a polymer whi ch is partitioned between the water and oil phases, namely poly(propyl eneglycol)(PPG). Addition of POEG, PAM, PVA, and PPG decreases the att ractive interactions between droplets, whereas addition of PBD increas es it. Increase of the molecular weight of POEG produces also a decrea se of the attractive interactions between droplets. The mean droplet s ize has been investigated by TRFQ, in the case of POEG. The droplet si ze decreases upon addition of POEG into the water pool and upon increa se of its molecular weight. This decrease in size of the droplet produ ces a decrease of the overlapping of the interfaces of the colliding d roplets which account for the decrease of the interdroplet attractive interactions. Some possible explanations for the decrease of the dropl et size as POEG is added to the water pool are briefly presented. Addi tion of PBD in the oil continuous phase increases, in average, the oil chain length. The increase of the attractive interactions between dro plets as PBD is added to the oil phase is understood in light of the e ffect obtained with increasing oil chain length. Less penetration of t he oil in the interfacial film of the droplet occurs as the oil chain length increases. This leads to an increase of the size of the droplet s and of the overlapping domain of the interfacial films of the collid ing droplets. Finally, PPG has two competitive effects. The PPG molecu les dissolved in the water pools decrease the interactions between dro plets, whereas the PPG molecules dissolved in the oil increase it. Und er the experimental conditions used (PPG molecular weight and concentr ation), it turns out that the second effect dominates the first one.