Memory effects in nanoparticle suspensions
Researchers uncover how memory effects arise in electrically aligned nanoparticles in suspension and use this understanding to accelerate relaxation The post Memory effects in nanoparticle suspensions appeared first on Physics World .
In the field of physics, equilibrium is typically achieved when a system experiences a change, a process known as relaxation. Predicting the system's future state relies on its present condition and external factors. However, certain polymers exhibit memory-like behavior, where the system's evolution depends not only on the current state but also on past states, a phenomenon called the Kovacs effect.
This study delves into the Kovacs effect in a suspension of rod-like nanoparticles. By introducing an electric field, the particles align, altering the liquid's optical anisotropy, or birefringence, which can be quantified as the light polarization change. The greater the birefringence, the more aligned the particles. Interestingly, nanoparticles display varying relaxation speeds due to their polydispersity and size differences, aligning at distinct rates.
Adjusting the electric field strength causes faster and slower particles to become desynchronized. As a result, the system's subsequent behavior hinges on its hidden historical record, which is masked by the overall birefringence measurement; this is the Kovacs effect. Utilizing the Smoluchowski equation, researchers modeled the nanoparticles' orientation dynamics, revealing that relaxation is not dictated by a single timescale or relaxation mode.
When some modes are fast while others are slow, memory effects surface. The Kovacs effect is significant because it demonstrates that simply applying a robust electric field before transitioning to the desired field may not accelerate relaxation. Due to memory effects resulting from particles relaxing at different velocities, the system overshoots the target state, curbing the anticipated speed enhancement.
To mitigate this, researchers devised enhanced two- and three-step protocols that suppress the slowest relaxation modes instead of merely aligning with the average birefringence. These protocols diminish the memory effect, facilitate a smoother approach to equilibrium, and expedite relaxation, albeit the additional switching steps' benefit wanes progressively.
This research enhances our understanding of memory effects in intricate systems and offers a pragmatic approach to controlling nanoparticle dynamics more swiftly and efficiently.
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