Phase behaviour and structure formation

There are basically two topics that need to be addressed regarding the effect of amphiphilic polymers on the physical behaviour of microemulsions. The first topic is related to phase behaviour and structure formation. Amphiphilic polymers can strongly influence phase behaviour because of their impact on the bending rigidity of the surfactant film. For both droplet micro emulsions and bicontinuous microemulsions such phenomena were studied. Especially in droplet microemulsions, amphiphilic polymers were used to interconnect microemulsion domains. This leads to ordering phenomena and can alter the phase behaviour. The second topic again is based on systems where microemulsion domains are connected via polymers. It covers dynamic phenomena with a focus on viscoelastic properties. Important in this area is the formation of transient or permanent networks. 

Amphiphilic polymers can have a strong impact on the phase behaviour of microemulsions already at very low concentrations. The most drastic consequence is that on the emulsification capacity of surfactants. A first work in this respect was carried out using hydrophobically modified ethyl hydroxyethyl cellulose [ 1 ]. This is a comb-shaped polymer, having a water-soluble backbone functionalised with low molecular weight hydrophobic 

The magnitude of the polymer effect - on the bending rigidity for instance - is proportional to the number grafting density and the projected polymer size, the square of 

The difference between PEO being functionalised at one chain end with a hydrophobic sticker and its counterpart containing the hydrophobic units at both chain ends was examined with oil-in-water (o/w) droplet microemulsions [22-24]. Cetyl pyridiniumchlo-ride/octanol or alkylphenol ethoxylate were used as surfactant. The monofunctional polymers were only capable to decorate the oil droplets whereas the difunctional polymers could also bridge them. Experiments were carried out as a function of the droplet volume 

---