Optical Deformation and Manipulation of Ferrofluid: Principles, Properties, and Applications

<jats:p>Ferrofluid, a composite liquid of paramagnetic nanoparticles suspended in petroleum oil, exhibits a unique combination of thermomagnetic properties and strongly temperature-dependent surface tension. Its distinct dark appearance makes it ideal for laser-induced localized heating, enabling non-contact studies of fluid dynamics through photothermal effects. This chapter reviews recent advances in the optical deformation and actuation of ferrofluid, focusing on underlying mechanisms, key properties, and emerging applications. We begin by examining light-induced surface deformations without magnetic fields, such as giant depressions and upward fluid fountains. These phenomena are governed by the opto-thermocapillary effect, which is analyzed in terms of its fundamental principles, key parameters, and its contrast with magnetically induced deformation. Subsequent sections explore ferrofluid-laser interactions under magnetic fields, revealing new effects such as magnetic field-enhanced Marangoni convection, surface thermomagnetic convection, and the laser-driven Tesla thermal engine. The implications of these effects for advanced heat transport systems are also discussed. The chapter concludes by introducing the concept of synergistic control—integrating optical and magnetic effects to achieve enhanced manipulation of ferrofluid behavior. This dual-control strategy opens new avenues for fundamental research and transformative applications in microfluidics, thermal management, and next-generation energy systems.</jats:p>