Research Description
With photoresponsive surfactants, light can be used to manipulate the surface activity and aggregation state of the
surfactant system. The use of light allows for excellent spatial and temporal control of surfactant-based properties, as
light is easily focused and patterned. These responsive surfactant systems permit in situ and reversible control of both
surface and bulk properties, giving way to a variety of potential applications including controlled spreading and coating
of surfaces, controlled release of substrates from micelles, and surface tension driven (Marangoni) flows.
Many useful fluid phenomena involve the creation of a new interface on the time scales of seconds or less. Thus, in
order to be useful, surfactants used in these processes need to be able to bring about changes in interfacial properties
in comparable time scales. Surface tensions of many surfactant systems typically take minutes or hours to reach their
equilibrium values, so in processes operating on small time scales, the dynamic surface tension is the relevant interfacial
property. The dynamic surface tension is itself governed by several dynamic processes, including the diffusion of
monomeric surfactant to the interface and the kinetics of adsorption/desorption of the surfactant on the interface. For
solutions above the CMC, the interchange of surfactant between its monomeric form and micelles must also be considered.
In a responsive surfactant system, there are also dynamics associated with the photoisomerization kinetics. So, for a
responsive surfactant system, there are no fewer than four dynamic processes that contribute to the overall time-evolution
of interfacial properties. The understanding of each of these dynamic processes (including their relative contributions to
the overall temporal response of the system) is crucial in designing more effective surfactants and finding applications
where they may be useful.
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Magnetic Fluids 
