Title:Neuromorphic features from microfluidic memristors of aqueous electrolytes

Time: May 14, 2024 (Tuesday) 9:00-10:00

Venue: Guangzhou International Campus C3-c204

All students and faculties are welcome to join this lecture.

Abstract: 

In this talk we will discuss recent advances in our understanding of the physics of cone-shaped microfluidic channels under static and pulsatile voltage- and pressure drops. On the basis of Poisson-Nernst-Planck-Stokes equations for transport of aqueous electrolytes through channels carrying a surface charge, we will provide a theoretical explanation for the experimentally observed diode-like current rectification of these channels in terms of salt depletion (accumulation) at steady forward (backward) electric driving [1], which also explains the observed pressure-sensitivity of the electric conductance. An extension towards an applied AC voltage predicts these channels to be tunable between diodes at low frequencies ωτ<<1, memristors (resistors with memory) at intermediate frequencies ωτ ~ 1, and Ohmic resistors at high frequency ωτ>>1, with a characteristic (memory retention) time τ proportional to the square of the channel length [2]. We predict that Hodgkin-Huxley-inspired iontronic circuits of short (fast) and long (slow) conical channels yield neuromorphic responses akin to (trains of) action potentials [2] and several other neuronic spiking modes [3]. Next, we show theoretically and experimentally that a tapered microfluidic channel filled with an aqueous nearly close-packed dispersion of colloidal charged spheres is a much stronger memristor [4]. Upon applying a train of positive (negative) voltage pulses, with pulse durations τ/8 and representing a binary “1” (“0”), we map a binary bit string on the channel conductance, which offers opportunities for reservoir computing -we give a proof of principle for the case of recognizing hand-written digits [4]. Finally, if time permits, we will also discuss recent and ongoing work on iontronic information processing. We exploit the mobility of the medium (water) by considering simultaneously applied pulsatile pressure and voltage signals to increase the bandwidth [5]. Finally, the versatile ionic nature of the charge carriers allows for Langmuir-like ionic exchange reaction kinetics on the channel surface [6]. We show that this can give rise to direct iontronic analogues of synaptic long-term potentiation and coincidence detection of electric and chemical signals [7], which are both ingredients for brain-like (Hebbian) learning.

[1] W.Q. Boon, T. Veenstra, M. Dijkstra, and R. van Roij, Pressure-sensitive ion conduction in a conical channel: optimal pressure and geometry, Physics of Fluids 34, 101701 (2022).

[2] T.M. Kamsma, W.Q. Boon, T. ter Rele, C. Spitoni, and R. van Roij, Iontronic Neuromorphic

Signaling with Conical Microfluidic Memristors, Phys. Rev. Lett. 130, 268401 (2023).

[3] T.M. Kamsma, E. A. Rossing, C. Spitoni, and R. van Roij, Advanced iontronic spiking modes with multiscale diffusive dynamics in a fluidic circuit, Neuromorph. Comput. Eng. 4 024003 (2024).

[4] T.M. Kamsma, J. Kim, K. Kim, W.Q. Boon, C. Spitoni, J. Park, and R. van Roij, Brain-inspired computing with fluidic iontronic nanochannels, PNAS 121, e23202242121 (2024).

[5] A. Barnaveli, T.M. Kamsma, W.Q. Boon, and R. van Roij, Pressure-gated microfluidic memristor for pulsatile information processing, arXiv 2404.15006.

[6] W.Q. Boon. M. Dijkstra, and R. van Roij, Coulombic Surface-Ion Interactions Induce Nonlinear and Chemistry-Specific Charging Kinetics, Phys. Rev. Lett. 130, 058001 (2023).

[7] T.M. Kamsma, M. Klop, W.Q. Boon, C. Spitoni, and R. van Roij, manuscript in preparation.

Brief Biography：

René van Roij is a tenured professor at the Center for Theoretical Physics at Utrecht University in the Netherlands. He obtained his PhD in Physics from the University of Amsterdam in 1996, followed by postdoctoral research at the École Normale Supérieure in Lyon and the University of Bristol. He returned to Utrecht University in 200. Professor van Roij's research interests include classical (dynamic) density functional theory, equilibrium and non-equilibrium electric double layers, nanoscale transport of diffusion-convection reactions, blue energy, liquid crystals, self-assembly, and capillary phenomena.