Health & Environmental Research Online (HERO)


Print Feedback Export to File
1296500 
Journal Article 
Unusual behavior of PEG/PPG/Pluronic interfaces studied by a spinning drop tensiometer 
Martin, JD; Velankar, SS 
2008 
Yes 
Journal of Colloid and Interface Science
ISSN: 0021-9797
EISSN: 1095-7103 
322 
2 
669-674 
English 
18440544 
The effects of surfactants on the interfacial tension driven retraction of elongated drops were studied in a spinning drop tensiometer. Experiments were conducted on polypropylene glycol (PPG) drops suspended in polyethylene glycol (PEG), with Pluronic block copolymers as surfactants. Two unusual observations are reported here. In the first, initially-elongated drops generated at high rotational speed were allowed to retract by reducing the rotational speed. Pluronic-laden drops would not retract completely, but would instead maintain strongly nonspherical shapes indefinitely. We attribute such "nonretraction" to an interfacial yield stress induced by the Pluronic surfactant. In the second, drops being heated while spinning at a constant speed would elongate sharply at some temperature, and subsequently breakup. Such "autoextension" and breakup indicate complex nonmonotonic changes in interfacial tension with time during heating. We propose that autoextension occurs because at low temperature, interfacially-adsorbed surfactant is crystallized and hence trapped at the interface at a concentration far above equilibrium.