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Phase behavior of nonionic microemulsions with multi-end-capped polymers and its relation to the mesoscopic structure

: Malo de Molina, P.; Ihlefeldt, F.; Prevost, S.; Herfurth, C.; Appavou, M.-S.; Laschewsky, A.; Gradzielski, M.


Langmuir. The ACS journal of surfaces and colloids 31 (2015), Nr.18, S.5198-5209
ISSN: 0743-7463
ISSN: 1520-5827
Fraunhofer IAP ()

The polymer architecture of telechelic or associative polymers has a large impact on the bridging of self-assembled structures. This work presents the phase behavior, small angle neutron scattering (SANS), dynamic light scattering (DLS), and fluorescence correlation spectroscopy (FCS) of a nonionic oil-in-water (O/W) microemulsion with hydrophobically end-capped multiarm polymers with functionalities f = 2, 3, and 4. For high polymer concentrations and large average interdroplet distance relative to the end-to end distance of the polymer, the system phase separates into a dense, highly connected droplet network phase, in equilibrium with a dilute phase. The extent of the two-phase region is larger for polymers with similar length but higher f. The interaction potential between the droplets in the presence of polymer has both a repulsive and an attractive contribution as a result of the counterbalancing effects of the exclusion by polymer chains and bridging between droplets. This study experimentally demonstrates that higher polymer functionalities induce a stronger attractive force between droplets, which is responsible for a more extended phase separation region, and correlate with lower collective droplet diffusivities and higher amplitude of the second relaxation time in DLS. The viscosity and the droplet self-diffusion obtained from FCS, however, are dominated by the end-capped chain concentration.