1 research outputs found
Modifying the Properties of Microemulsion Droplets by Addition of Thermoresponsive BAB* Copolymers
Oil-in-water (O/W) microemulsions (ME) typically feature
a low
viscosity and exhibit ordinary viscosity reduction as a function of
temperature. However, for certain applications, avoiding or even reverting
the temperature trend might be required. This can be conceived by
adding thermoresponsive (TR) block copolymers that induce network
formation as the temperature increases. Accordingly, various MEāpolymer
mixtures were studied for which three different block copolymer architectures
of BAB*-, B2AB*-, and B(AB*)2-types were employed.
Here, āBā represents a permanently hydrophobic, āAā
a permanently hydrophilic, and āB*ā a TR block. For
the TR-block, three different poly(acrylamide)s, namely poly(N-n-propylacrylamide) (pNPAm), poly(N,N-diethylacrylamide) (pDEAm), and poly(N-isopropylacrylamide) (pNiPAm), were used, which all exhibit
a lower critical solution temperature. For a well-selected ME concentration,
these block copolymers lead to a viscosity enhancement with increasing
temperature. At a polymer concentration of about 22 g Lā1, the most pronounced enhancement was observed for the pNPAm-based
systems with factors up to 3, 5, and 8 for BAB*, B2AB*,
and B(AB*)2, respectively. This phenomenon is caused by
the formation of a transitory network mediated by TR-blocks, as evidenced
by the direct correlation between the attraction strength and the
viscosity enhancement. For applications requiring a high hydrophobic
payload, which is attained via ME droplets, this kind of tailored
temperature-dependent viscosity control of surfactant systems should
therefore be advantageous