Abstract
The shape and interactions between model microemulsion droplets (R = 8.2 nm, polydispersity 20%) either decorated with hydrophilic-hydrophobic diblock (PEO-m: C12H25-(EO)n, MPEO = 5.2 kg/mol), or with telechelic triblock copolymers (PEO-2m: C12H25-(EO)2n-C12H25 , MPEO = 10.4 kg/mol) have been studied by small angle neutron scattering (SANS). The results as a function of droplet and copolymer concentration have been compared to the reference case of the bare microemulsion. Using Porod representations, the average bare droplet size was found to be independent of microemulsion concentration in the range studied here, up to some 13%v. Upon addition of copolymer (from r=0 to 30 hydrophobic stickers per droplet), the average droplet radius was unaffected. The interactions between bare and decorated droplets have been analyzed using the structure factor S(q), at first in a model-free way based on its low-q limit S(q→0). This analysis provides clear evidence on the concentration-dependent repulsive or attractive nature of the contributions to the pair droplet-droplet pair potential of the copolymers. Model pair potentials describing the steric repulsions and attractions by copolymer bridging are used to describe the low-q behavior of the structure factor based on an integral equation approach, giving a quantitative estimate of the range and amplitude of the potentials. Moreover, they provide an explanation for the observed transient clustering in terms of a shallow minimum of the total potential.