Iontronics: from fundamentals to ion-controlled devices

Iontronics: from fundamentals to ion-controlled devices 21-23 June 2023 | Edinburgh, UK

Faraday Discussions

Iontronics: from fundamentals to ion-controlled devices 21-23 June 2023 | Edinburgh , UK #FDIontronics Book of Abstracts

Introduction

Iontronics: from fundamentals to ion-controlled devices Faraday Discussion is organised by the Faraday Community for Physical Chemistry of the Royal Society of Chemistry This book contains abstracts of the posters presented at Iontronics: from fundamentals to ion-controlled devices Faraday Discussion. All abstracts are produced directly from typescripts supplied by authors. Copyright reserved. Oral presentations and discussions All delegates at the meeting, not just speakers, have the opportunity to make comments, ask questions, or present complementary or contradictory measurements and calculations during the discussion. If it is relevant to the topic, you may give a 5-minute presentation of your own work during the discussion. These remarks are published alongside the papers in the final volume and are fully citable. If you would like to present slides during the discussion, please let the session chair know and load them onto the computer in the break before the start of the session. Faraday Discussion volume Copies of the discussion volume will be distributed approximately 6 months after the meeting. To expedite this, it is essential that summaries of contributions to the discussion are received no later than Friday 30 June 2023 for questions and comments and Friday 14 July for responses. Posters Posters have been numbered consecutively. The poster session will take place on Wednesday 21 June 2023 after the main sessions have ended. The posters will be available to view throughout the discussion during all refreshment breaks. During the dedicated poster session, authors should stand with their poster to discuss their research with other attendees. Poster prize The Faraday Discussions poster prize will be awarded to the best student poster as judged by the committee. Networking sessions There will be regular breaks throughout the meeting for socialising, networking and continuing discussions started during the scientific sessions.

Scientific Committee

Invited Speakers

Serge Lemay (Co-Chair) University of Twente, Netherlands Sanil Faez (Co-Chair) Utrecht University, Netherlands Monica Olvera de la Cruz Northwestern University, USA

Yan Levin (Introductory lecture) URRGS, Brazil

Lyderic Bocquet (Closing remarks lecture) Ecole Normale Supérieure, Paris, France Martin Bazant Massachusetts Institute of Technology, USA Arianna Marchioro École Polytechnique Fédérale de Lausanne, Switzerland

Susan Perkin University of Oxford, UK

René van Roij Utrecht University, Netherlands

Frieder Mugele University of Twente, Netherlands

Sumita Pennathur University of California, Santa Barbara, USA

Markus Valtiner TU Wien, Austria

Tanja Vidakovic-Koch MPI Magdeburg, Germany Gilad Yossifon Tel-Aviv University, Israel

Faraday Discussions Forum

www.rscweb.org/forums/fd/login.php In order to record the discussion at the meeting, which forms part of the final published volume, your name and e-mail address will be stored in the Faraday Forum. This information is used for the collection of questions and responses communicated during each session. After each question or comment you will receive an e-mail which contains some keywords to remind you what you asked, and your password information for the forum. The e-mail is not a full record of your question. You need to complete your question in full on the forum . The deadline for completing questions and comments is Friday 30 June 2023.

The question number in the e-mail keeps you a space on the forum. Use the forum to complete, review and expand on your question or comment. Figures and attachments can be uploaded to the forum. If you want to ask a question after the meeting, please e-mail faraday@rsc.org. Once we have received all questions and comments, responses will be invited by e-mail . These must also be completed on the forum . The deadline for completing responses is Friday 14 July 2023 Please note that when using the Forum to submit a question or reply, your name and registered e-mail address will be visible to other delegates registered for this Faraday Discussions meeting. Key points: • The e-mail is not a full record of your comment/question. • All comments and responses must be completed in full on the forum Deadlines: Questions and comments Friday 30 June 2023 Responses Friday 14 July 2023

Poster presentations

P01

Ion current rectification and long-range interference in conical silicon micropores Mark Aarts imec, Belgium

P02

Electrical impedance microscopy Sidahmed Abayzeed University of Nottingham, UK

P03

Role of ion transport in silicon-based hydrovoltaic devices Tarique Anwar EPFL, Switzerland Pressure-gated memristor based on a microfluidic channel Alexander Barnaveli Utrecht University, Netherlands

P04

P05

Cation dependence of noise induced by polymer adsorption in nanopores Anna Drummond Young University of Oxford, UK

P06

Nanoelectrochemical detection of single-molecule semiconducting polymers

Daniel Felipe Duarte Sánchez Universiteit Twente, Netherlands

P07

Proton enrichment and surface charge dynamics in pH-responsive nanopores Dominik Duleba University College Dublin, Ireland Material-dependent surface polarization impacts ionic current in strong confinement Ali Ehlen Northwestern University, USA Aprotic solvent accumulation amplifies ion current rectification in conical nanopores Emer Farrell University College Dublin, Ireland

P08

P09

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A capacitive-analogue of semiconductor-based diodes (CAPode) and its fabrication via 3D-printing Christin Gellrich Technical University Dresden, Germany

P11

Forces and structure in ionic liquid mixtures Timothy Groves University of Oxford, UK

P12

Frequency-dependent response of confined electrolytes Minh-Thê Hoang Ngoc CNRS, Sorbonne Université, France

P13

Correlation between electrostatic and hydration forces on silica and gibbsite surfaces: an atomic force microscopy study Siretanu Igor University of Twente, Netherlands DNA volume, topology, and flexibility dictate nanopore current signals Yunxuan Li University of Cambridge, UK Reevaluating concentration polarization: clarifying its meaning, genesis, and consequences Joan Montes de Oca University of Chicago, USA Electrical fluctuations next to an electrode to probe the properties of interfacial electrolytes Swetha Nair CNRS, Sorbonne Université, France Experimental investigation of model reverse electrowetting systems Zaeem Najeeb Imperial College London, UK Frequency-dependent impedance of nanocapacitors from electrode charge fluctuations as a probe of electrolyte dynamics Giovanni Pireddu CNRS, Sorbonne Université, France

P14

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P19

Designing with Iontronic logic gates - from a single polyelectrolyte diode to an integrated ionic circuit Barak Sabbagh Technion−Israel Institute of Technology, Israel Stochastic single-entity biosensing using CMOS-based nanocapacitor arrays Mohammad Saghafi University of Twente, Netherlands Molecular insights into the ion-solvation and dynamics in a diglyme-based sodium-ion battery electrolyte Ardhra Shylendran Indian Institute of Science Education and Research (IISER), Pune, India Trapping and actuation of a single nanoparticle using nano- dielectrophoresis and label-free read-out Jacco Ton Leiden University, Netherlands Capacitance behaviour of ionic liquids at the semi-metallic interface Jing Yang University of Manchester, UK

P20

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P24

Iontronic circuit-based logic gating of molecules Zhenyu Zhang Tel Aviv University, Israel

Ion current rectification and long-range interference in conical silicon micropores M. Aarts 1 , W. Q. Boon 2 , B. Cuenod 1 , M. Dijkstra 3 , R. van Roij 2 and E. Alarcon-Llado 1 1 Center for Nanophotonics, Netherlands, 2 Institute for Theoretical Physics, Utrecht University, Netherlands, 3 Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Netherlands Fluidic devices exhibiting ion current rectification (ICR), or ionic diodes, are of broad interest for applications including desalination, energy harvesting, and sensing, amongst others. For such applications a large conductance is desirable, which can be achieved by simultaneously using thin membranes and wide pores. Here, we demonstrate ICR in micrometer sized conical channels in a thin (2 μm) silicon membrane with pore diameters comparable to the membrane thickness but both much larger than the electrolyte screening length. We show that for these pores the entrance resistance is key not only to Ohmic conductance around 0 V but also for understanding ICR, both of which we measure experimentally and capture within a single analytic theoretical framework. The only fit parameter in this theory is the membrane surface potential, for which we find that it is voltage dependent and its value is excessively large compared to the literature. From this we infer that surface charge outside the pore strongly contributes to the observed Ohmic conductance and rectification by a different extent. We experimentally verify this hypothesis in a small array of pores and find that ICR vanishes due to pore−pore interactions mediated through the membrane surface, while Ohmic conductance around 0 V remains unaffected. We find that the pore−pore interaction for ICR is set by a long-ranged decay of the concentration which explains the surprising finding that the ICR vanishes for even a sparsely populated array with a pore−pore spacing as large as 7 μm. 1 References Aarts, M. et al. Ion Current Rectification and Long-Range Interference in Conical Silicon Micropores. ACS Appl. Mater. Interfaces 14 , 56226–56236 (2022).

P01

Electrical impedance microscopy Sidahmed Abayzeed University of Nottingham, UK

This abstract presents a novel optical technique that is capable of accurate microscopic measurements of electrical current and impedance. This technique offers a remarkable sensitivity demonstrated by detecting electrical current as low as 0.1pA on a 0.5 micrometre scale [1] . Measurements are performed using plasmonic sensors [2] that can be described as electrodes with optical readout. The poster demonstrates the ability to perform quantitative imaging of heterogenous surface capacitance at the gold-electrolyte interface. The method promises advanced capabilities in studying microscale ionic currents with wide-ranging applications in surface science, energy storage, and life science. References 1. Abayzeed, Sidahmed A. "Plasmonic-based impedance microspectroscopy of optically heterogeneous samples." Biomedical Optics Express 11.11 (2020): 6168-6180. 2. Abayzeed, Sidahmed A., et al. "Sensitive detection of voltage transients using differential intensity surface plasmon resonance system." Optics express 25.25 (2017): 31552-31567.

P02

Role of Ion transport in silicon-based Hydrovoltaic devices Tarique Anwar and Giulia Tagliabue EPFL, Switzerland Evaporation driven fluid flow in porous or nanostructured materials has recently opened a new paradigm for converting thermal energy from the ambient into electrical energy, via an electrokinetic pathway [1] . Although many recent studies have shown that ion transport is the governing phenomenon in these so- called Hydrovoltaic devices, there is a lack of fundamental understanding as to how the solid-liquid interfacial parameters, confinement size, and liquid properties can modulate the overall performance. In this work, we leverage nanofabrication techniques to realize ordered arrays of Silicon nanopillars and we carefully study their hydrovoltaic response. In particular, we change in a controlled manner both the geometrical parameters and the liquid properties (ion type and concentration), to correlate their effect to the open circuit voltage and power output. Importantly, by combining experiments with numerical modelling we can provide deeper insight into the relevant governing parameters that modulate the electrokinetic response of hydrovoltaic devices. Overall, our controlled nanostructuring approach, which lies in between single nanochannel studies and macro-scale porous system characterization, offers critical insight into how to enhance the energy conversion performance of evaporation- driven hydrovoltaic devices. The three main experimental techniques we employ are a direct measurement of open circuit voltage (OCV), I-V characteristics, and electrochemical impedance spectroscopy (EIS). These measurements were carried out for the series of devices with different geometrical parameters and a wide range of electrolyte concentrations for different cationic and anionic components of the simple salts. The study of concentration dependence on OCV was carried out by sweeping concertation up to 4M starting from 0.1 μM. We observe non-monotonic behavior, which can be attributed to the increase in charge screening effect at high concentrations due to ion adsorption at the stern plane of the electrical double layer and ion-ion correlation [2] . Furthermore, the effect of geometrical parameters on OCV was due to the change in the streaming of ions and the associated ionic resistance. We quantify the effective surface charge by determining correlations from our simulation results. For determining the output power, we measured the I-V characteristics for the series of geometrical parameters in various electrolyte concentrations. From moderate-to-high concentration, an increase in power can be attributed to the increase in the advection of ions. At lower concentrations, a slight increase in power output was a consequence of electrical double-layer overlap. The nature of the dependence of output power on the geometrical parameters was similar to the OCV. The EIS measurements were carried out to investigate the effect of ion diffusion and the associated resistive and capacitive elements in the equivalent electrical circuit model of our system [3] . Overall, this study highlights the importance of electrokinetic parameters and nanofabrication process parameters on the performance of hydrovoltaic devices made of uniform array nanostructured silicon. References 1. Chem.Int.Ed.2020,59,10619–10625 2. Rev. Lett. 119 , 026002 3. Langmuir 2014, 30, 36, 10950–10961

P03

Pressure-gated memristor based on a microfluidic channel Alexander Barnaveli , Tim Kamsma, Willem Boon and René van Roij Utrecht University, Netherlands We theoretically study cyclic voltammetry of a microfluidic conical channel filled with an aqueous electrolyte (Fig.1) under the influence of an externally applied time-dependent voltage and pressure. It was recently demonstrated in our group [1] that a conical channel exhibits memristive properties if it is solely driven by an AC voltage; this is due to an enhanced/reduced salt concentration (and hence conductivity) during different phases of the driving period. We also showed already that the conductivity of conical channels is extremely sensitive to an applied static pressure drop [2] , i.e. conical channels are transistors gated by pressure rather than by voltage. In this poster we present the results of employing simultaneously applied time-dependent voltages and pressures to study the suppression or enhancement of the memristive properties of conical channels by pressure. Such an additional control over memristive effects introduces a completely new (hydraulic) way of manipulating neuromorphic circuits based on conical pores. One of the interesting consequences of having two control mechanisms in such circuits is the increased bandwidth, since electric and hydraulic signaling is possible in parallel. References 1. Kamsma, T. M., W. Q. Boon, T. ter Rele, C. Spitoni, and R. van Roij. "Iontronic neuromorphic signalling with conical microfluidic memristors." arXiv preprint arXiv:2301.06158 (2023). 2. Boon, Willem Q., Tim E. Veenstra, Marjolein Dijkstra, and René van Roij. "Pressure-sensitive ion conduction in a conical channel: Optimal pressure and geometry." Physics of Fluids 34, no. 10 (2022): 101701.

P04

Cation dependence of noise induced by polymer adsorption in nanopores Anna M. Drummond Young , Stuart F. Knowles, Alice L. Thorneywork University of Oxford, United Kingdom Nanopores underpin single molecule sensing techniques at the cutting edge of biotechnological measurement. In these techniques, a nanopore is immersed in an electrolyte and a potential difference is applied across the pore so that a current flows through it. Understanding and controlling transport properties in these systems, including fluctuations or noise in the current, is central to the further development of nanopore technologies. Polymers are often added to nanopore systems to improve pore functionality, for example by modifying electrokinetic effects or passivating surfaces. It has previously been observed that for potassium chloride solutions the addition of polyethylene glycol (PEG) creates excess noise in the current trace, which has a characteristic shape and frequency range [1] . This excess noise has been attributed to the process of PEG adsorption and desorption from the walls of the nanopore; the shape of the noise spectrum has been used to infer details of the adsorption potential. Here, we investigate how the choice of group 1 cation used in the electrolyte in quartz glass nanopores affects fluctuations in the ionic current linked to polymer adsorption. Noise in the current was measured with and without PEG for four different group 1 chlorides: sodium chloride, lithium chloride, caesium chloride, and rubidium chloride, and the noise was quantified by calculation of its power spectral density. In NaCl, LiCl, and CsCl, excess noise with the same shape and frequency range as KCl was observed, but no excess noise was observed in the case of RbCl. Previous studies have suggested that PEG adsorption [2] and electro-osmotic flow in conical nanopores [3] is cation dependent, although these studies do not single out differences with rubidium. Our findings suggest that while for Na + , Li + , and Cs + PEG adsorption in glass nanopores is comparable to K + , in the case of Rb + there are qualitatively different fluctuations in the current resulting from the adsorption or desorption of PEG from the surface. References 1. Knowles, S. F. et al. Current fluctuations in nanopores reveal the polymer-wall adsorption potential. Phys. Rev. Lett. 127, 137801 (2021). 2. Chai, L., Goldberg, R., Kampf, N. & Klein, J. Selective adsorption of poly (ethylene oxide) onto a charged surface mediated by alkali metal ions. Langmuir 24, 1570–1576 (2008) 3. Mc Hugh, J., Andresen, K. & Keyser, U. F. Cation dependent electroosmotic flow in glass nanopores. Appl. Phys. Lett. 115, 113702 (2019).

P05

Nanoelectrochemical detection of single-molecule semiconducting polymers Daniel Felipe Duarte Sánchez , Serge G. Lemay Universiteit Twente, Netherlands

Despite the high attention that semiconducting polymers have received due to their impact in the evolution of organic electronics technologies, there is little insight into the electrical behavior of their constituting units (single polymer chains) as well as their potential applications as electrical labels for biochemical assays. Here we introduce an amperometry-based detection technique for electrolyte-gated single semiconducting polymer chains. 10 nm nanogap sensors were fabricated using standard microfabrication techniques and interfaced with fA-level current readout instrumentation. During each measurement, the current across the nanogap was recorded for several hours while being exposed to a polymer solution. A Pt reference/gate electrode set the solution potential so as to electrochemically dope the semiconducting molecules upon contact with the nanogap electrodes. When both electrodes were contacted by a molecule, sharp current steps were observed. This was followed by equally abrupt returns to the baseline current level once the polymer chains had diffused away. Time-varying, multi-step features also occurred, which we interpret as resulting from fluctuations in the internal conformation of the polymer chains. We have statistically evaluated the duration, current and noise levels of stochastic conduction events for three different alkyl-thiophenes to both characterize them as electrical labels and to assess their semiconducting properties. To achieve this we have developed an analysis technique based on the wavelet decomposition denoising of the current signals on the three (source, drain and gate) electrodes, thus enabling the detection of conduction events in a manner that is agnostic towards the SNR and background drift while also allowing the quasi-automated recognition of time overlapped events. Finally, we studied the coupled electronic-ionic transport occurring during the polymer doping process caused by electrochemical gating. This employed thin polymer films that are formed in the presence of higher concentrations of polymers in solution. The doping level and its variation in time were inferred from the source-drain conductivity, which could be disentangled from the charging current by simultaneously monitoring the liquid gate current. This revealed a doping process different from the intuitive “rolling-carpet" concept and that is dominated by the bulk resistance of the electrolyte solution. This may help optimize the design of electrolyte-gated devices. References 1. Chung, A. Khot, B. M. Savoie and B. W. Boudouris, ACS Macro Lett , 2020, 9 , 646–655. 2. Fahlman, S. Fabiano, V. Gueskine, D. Simon, M. Berggren and X. Crispin, Nature Reviews Materials 2019 4:10 , 2019, 4 , 627–650. 3. Abbasi, L. Bennet, A. J. Gunn and C. P. Unsworth, Int J Neural Syst , , DOI:10.1142/S0129065719500138. 4. H. Lee, D. W. Chang, J. Kim and J. Lee, Journal of the Korean Physical Society , 2023, 82 , 491–496.Roy, X. Chen, M. H. Li,

Y. Peng, F. Anariba and Z. Gao, J Am Chem Soc , 2009, 131 , 12211–12217. 5. N. Hooge and P. A. Bobbert, Physica B Condens Matter , 1997, 239 , 223–230.

P06

Proton enrichment and surface charge dynamics in pH-responsive nanopores Dominik Duleba and Robert Johnson University College Dublin, Ireland

The acid-disassociation of surface groups is crucial in nanopores as it generates the surface charge that drives fundamental nanoscale ion transport behaviors such as ion current rectification. The disassociation of surface groups is influenced by the local proton concentration which itself is dictated by the enrichment and depletion of ions in the conical nanopore as the voltage is changed. 1, 2 Despite this, most models of ion transport in conical nanopore systems assume a fixed surface charge and ignore localized pH changes. To study the dynamic interplay between the magnitudes and distributions of ion concentrations, pH distributions and surface charges, and its influence on the ion-current rectification as a function of electrolyte concentration, a finite element model that calculates the surface charge based on surface site density and local pH values was developed. This model additionally includes the water auto-ionization reaction and the subsequent shifting of the acidity constants at different positions within the nanopore geometry. The surface charge density was found to be non-linear across the nanopore and highly asymmetric between the different applied potentials, as well as highly influenced by the bulk pH and electrolyte concentrations. We demonstrate that our model qualitatively predicts experimental measurements of ion current rectification for different bulk pH values at the low electrolyte concentration regime. References 1. Yeh, L.-H.; Zhang, M.; Qian, S. Ion transport in a pH-regulated nanopore. Analytical chemistry 2013 , 85 (15), 7527-7534. 2. Atalay, S.; Yeh, L.-H.; Qian, S. Proton enhancement in an extended nanochannel. Langmuir 2014 , 30 (43), 13116-13120.

P07

Material-dependent surface polarization impacts ionic current in strong confinement Ali Ehlen 1 , Alexandre dos Santos 4 , Felipe Jímenez-Ángeles 2 , Monica Olvera de la Cruz 1,2,3 1 Northwestern University, USA 2 Department of Materials Science and Engineering, Northwestern University, USA

3 Department of Physics and Astronomy, Northwestern University, USA 4 Instituto de Física, Universidade Federal do Rio Grande do Sul, Brazil

To properly predict and design devices that incorporate ion flow in strong confinement, careful consideration must be taken to account for the effect of the confining surfaces on ion behavior. Here, we focus on the electrostatic response of the surfaces to the presence of ions. We look at ions confined by metallic, dielectric, and non-polarizable surfaces and show the importance of accounting for material-dependent surface polarization charge when studying ion-ion electrostatic interactions. We demonstrate that metallic surfaces and those with a high dielectric constant enhance ionic current by screening electrostatic attraction between opposite charges. Finally, we examine the impact of solvent and how it mediates ion-ion correlations. This work underscores a need to incorporate surface effects when designing iontronics devices in mixed environments.

P08

Aprotic solvent accumulation amplifies ion current rectification in conical nanopores Emer Farrell, Dominik Duleba, Robert P. Johnson University College Dublin, Ireland Electrochemical phenomena in asymmetric glass nanopores, including ion current rectification (ICR), are highly reported in aqueous electrochemical systems and sensors, 1, 2 but lack exploration in organic systems, due to the additional complexity introduced through the use of aprotic solvents. ICR in aprotic electrolyte reportedly arises due to the formation of an effective positive surface charge, through solvent dipole alignment on the nanopore surface. 3, 4 Inspired by prior reports, we present a detailed experimental and theoretical study on rectification ratio (RR) as a function of electrolyte concentration in highly polar and mildly polar organic electrolyte. 5 To explain our surprising experimental results, we present a novel phenomenon: the formation of a double-junction diode inside the nanopore due to solvent enrichment/depletion effects. 5 Understanding the complex ion transport processes that arise in aprotic nanopore systems is essential in the development of nanopore sensors which can operate in organic solvents, facilitating a wider range of industrial applications than that for which such aqueous sensors are currently developed. 2

References 1. D. Duleba, P. Dutta, S. Denuga and R. P. Johnson, ACS Meas. Sci. Au , 2022, 2 , 271-277. 2. D. Duleba and R. P. Johnson, Curr. Opin. Electrochem. , 2022, 34 , 100989.

3. T. Plett, W. Q. Shi, Y. H. Zeng, W. Mann, I. Vlassiouk, L. A. Baker and Z. S. Siwy, Nanoscale , 2015, 7 , 19080-19091. 4. X. H. Yin, S. D. Zhang, Y. T. Dong, S. J. Liu, J. Gu, Y. Chen, X. Zhang, X. H. Zhang and Y. H. Shao, Anal. Chem. , 2015, 87 , 9070-9077. 5. E. B. Farrell, D. Duleba and R. P. Johnson, J. Phys. Chem. B , 2022, 126 , 5689-5694.

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A capacitive-analogue of semiconductor-based diodes (CAPode) and its fabrication via 3D-printing Christin Gellrich , Yannik Bräuniger, Dr. Julia Grothe, Prof. Stefan Kaskel Technical University Dresden, Germany The CAPode is a highly asymmetric capacitor with unidirectional charging characteristics based on the size regulation of pores and ions and was firstly proposed in 2019 by the Kaskel’s group. [1] In particular, the CAPode consists of an ultramicroporous and mesoporous carbon as well as an electrolyte with cations and anions of different size. Due to the defined small pore size of the ultramicroporous carbon the bulky cations can be effectively blocked outside of the sub-nanometer pores while small anions can be accommodated leading to a high current rectification ratio. This can be especially interesting for possible future applications like AC- rectification and simultaneous grid-stabilization, but also in ion-based logic circuits for low-energy computing. While current research has mainly focused on expanding the unidirectional charging behavior to both bias directions and increasing the rectification ratio by the usage of new electrode materials, [2][3] the CAPode design is still limited to thin film electrodes in a macroscopic scale which is hindering the miniaturization of the CAPode and its implementation in a planar electrical circuit. To fabricate the desired interdigital in-plane CAPodes a suitable versatile micro-fabrication method is decisive. The three-dimensional (3D) printing technique provides several advantages such as high degree of freedom in design and geometry which is especially crucial for the assembly and logic connection of multiple electrode arrays. [4] Herein, we give a general overview about the concept of the CAPode and present possible printing strategies to fabricate in-plane, interdigital CAPodes. References 1. E. Zhang, N. Fulik, G. P. Hao, H. Y. Zhang, K. Kaneko, L. Borchardt, E. Brunner, S. Kaskel, Angew. Chemie - Int. Ed. 2019 , 58 , 13060–13065. 2. J. Feng, Y. Wang, Y. Xu, H. Ma, G. Wang, P. Ma, Y. Tang, X. Yan, Adv. Mater. 2021 , 33 , 1–8. 3. P. Tang, W. Tan, F. Li, S. Xue, Y. Ma, P. Jing, Y. Liu, J. Zhu, X. Yan, Adv. Mater. 2023 , 2209186 , 1–10. 4. Y. Z. Zhang, Y. Wang, T. Cheng, L. Q. Yao, X. Li, W. Y. Lai, W. Huang, Chem. Soc. Rev. 2019 , 48 , 3229–3264.

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Forces and structure in Ionic liquid mixtures Timothy Groves 2 and Susan Perkin 1 1 University Of Oxford Chemistry Department, UK, 2 University of Oxford, UK

Ionic liquids, salts that are liquid at or near to room temperature, are often thought of as ‘designer solvents’; they can be optimized by choosing a cation and an anion, or by mixing liquids, in order to select for specific properties [1] . In light of this, much work has been done to understand the properties of these liquids. In particular, ionic liquids have been shown to adopt layered structures at charged interfaces, with the nature of the structure depending on features within the ions such as the alkyl chain length [2] . We have investigated structural forces of mixtures of short- and long-chain ionic liquids using the surface force balance. We find that the pure liquids can be described using a simple decaying oscillatory force law, however we observed more complex behaviour with liquid mixtures. We interpret these forces as arising from contributions from the pure liquids, and by combining contributions from the pure liquids are able to obtain fits of the forces in the mixtures. These results will be important in the further design of ionic liquids and in the interpretation of liquid mixture behaviour [3] . References 1. H. Niedermeyer, J. P. Hallett, I. J. Villar-Garcia, P. A. Hunt, T. Welton, Chem. Soc. Rev., 41 , 7780-7802 (2012) 2. S. Perkin, L. Crowhurst, N. Niedermeyer, T. Welton, A. M. Smith, N. N. Gosvami, Chem. Commum., 47 , 6572-6574 (2011) 3. R. Kjellander, Phys. Chem. Chem. Phys. , 22 , 23952-23985 (2020)

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Frequency-dependent response of confined electrolytes Minh-Thê Hoang Ngoc 1 , Benjamin Rotenberg 1 , Gabriel Stoltz 2 1 CNRS, Sorbonne Université, France 2 CERMICS, Ecole des Ponts, Marne-la-Vallée, France

Experimentally, the ionic current of confined electrolytes exhibits generic low-frequency fluctuations, yet a full explanation of the microscopic origins of this “1/f” noise remains elusive [1-2] . Understanding the underlying dynamics remains a crucial step to control the transport of water and ions at the nanoscale [3] , and the frequency- dependent conductivity of electrolytes reflects the various timescales governing microscopic dynamics [4] . Using Brownian particles simulations [5] and continuous modeling, we investigate the effects of confinement, adsorption on surfaces and ion-ion interactions on the response of confined electrolyte solutions to oscillating electric fields. Making use of appropriate Green–Kubo relation [6-7] for the electrical conductivity, we highlight the contributions of the underlying thermal fluctuations and of the interactions of the particles between themselves and with external potentials. The frequency-dependent conductivity always decays from a bulk-like behavior at high frequency to a vanishing conductivity at low frequency due to the confinement of the charge carriers by the walls. We discuss the characteristic features of this crossover, and most importantly how the transition frequency depends on the confining distance and the salt concentration, and the fact that adsorption on the walls may lead to significant changes both at high- and low-frequencies. Conversely, our results illustrate the possibility to obtain information on diffusion between walls, charge relaxation and adsorption by analyzing the frequency-dependent conductivity [8] . This work is part of the ERC project SENSES (grant No. 863473). Project website: https://benrotenberg.github.io/erc-senses/ References 1. S.J. Heerema, G.F. Schneider, M. Rozemuller, L. Vicarelli, H.W. Zandbergen, C. Dekker, “1/f noise in graphene nanopores”, Nanotechnology 26 074001 (2015) 2. D.P. Hoogerheide, S. Garaj, J.A. Golovchenko, “Probing Surface Charge Fluctuations with Solid-State Nanopores”, Physical Review Letter 102, 256804 (2009) 3. N. Kavokine, R. R. Netz, L. Bocquet, “Fluids at the Nanoscale: from continuum to sub-continuum transport”, Annual Review of Fluid Mechanics Vol. 53:377-410 (2021) 4. A. Chandra, B. Bagchi, “Frequency dependence of ionic conductivity of electrolyte solutions”,The Journal of chemical physics 112, 1876 (2000) 5. M. Jardat, O. Bernard, P. Turq, G. R. Kneller, “Transport coefficients of electrolyte solutions from Smart Brownian dynamics simulations”, The Journal of chemical physics 110, 7993 (1999) 6. B. Felderhof and R. Jones, “Linear response theory of the viscosity of suspensions of spherical brownian particles”, Physica A: Statistical Mechanics and its Applications 146, 417–432 (1987). 7. R. Joubaud, G. Pavliotis, and G. Stoltz, “Langevin dynamics with space-time periodic nonequilibrium forcing”,Journal of Statistical Physics 158, 1–36 (2014) 8. T. Hoang Ngoc Minh, G. Stoltz, B. Rotenberg “Frequency and field-dependent response of confined electrolytes from Brownian dynamics simulations”, The Journal of chemical physics 158, 104103 (2023)

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Correlation between electrostatic and hydration forces on silica and gibbsite surfaces: an atomic force microscopy study Siretanu Igor, Frieder Mugele, Aram Klaassen, Fei Liu University of Twente, Netherlands The balance between hydration and Derjaguin–Landau–Verwey–Overbeek (DLVO) forces at solid–liquid interfaces controls many processes, such as colloidal stability, wetting, electrochemistry, biomolecular self- assembly, and ion adsorption. Yet, the origin of molecular scale hydration forces and their relation to the surface charge density that controls the continuum scale electrostatic forces is poorly understood. We argue that these two types of forces are largely independent of each other. To support this hypothesis, we performed atomic force microscopy experiments using intermediate-sized tips that enable the simultaneous detection of DLVO and molecular scale oscillatory hydration forces at the interface between composite gibbsite:silica–aqueous electrolyte interfaces. We extract surface charge densities from forces measured at tip–sample separations of 1.5 nm and beyond using DLVO theory in combination with charge regulation boundary conditions for various pH values and salt concentrations. We simultaneously observe both colloidal scale DLVO forces and oscillatory hydration forces for an individual crystalline gibbsite particle and the underlying amorphous silica substrate for all fluid compositions investigated. While the diffuse layer charge varies with pH as expected, the oscillatory hydration forces are found to be largely independent of pH and salt concentration, supporting our hypothesis that both forces indeed have a very different origin. Oscillatory hydration forces are found to be distinctly more pronounced on gibbsite than on silica. We rationalize this observation based on the distribution of hydroxyl groups available for H bonding on the two distinct surfaces. References 1. Klaassen, A., Liu, F., Mugele, F., & Siretanu, I. (2022). Correlation between electrostatic and hydration forces on silica and gibbsite surfaces: An atomic force microscopy study. Langmuir, 38(3), 914-926. 2. Siretanu, I., van Lin, S., & Mugele, F. (2023). Ion adsorption and Hydration Forces: a comparison of crystalline mica vs. amorphous silica surfaces. Faraday Discussions.

P13

DNA volume, topology, and flexibility dictate nanopore current signals Yunxuan Li , Sarah E. Sandler, Ulrich F. Keyser, Jinbo Zhu Cavendish Laboratory, University of Cambridge, UK

Nanopores have developed into powerful single-molecule sensors capable of identifying and characterizing small polymers, such as DNA, by electrophoretically driving them through a nanoscale pore and monitoring temporary blockades in ionic pore current. However, the relationship between nanopore signals and the topology and flexibility of DNA remains only partly understood. Herein, we use a programmable DNA carrier platform with two reference sites and four functional sites to capture carefully designed DNA nanostructures. Controlled translocation experiments through our glass nanopores allow us to disentangle the influence of DNA physical properties on the current blockade signal. We vary DNA topology by changing the length, strand duplications, sequence, unpaired nucleotides, and rigidity of the analyte DNA and find that the ionic current drop is mainly determined by the volume and flexibility of the DNA nanostructure in the nanopore. Finally, we use our understanding of the role of DNA topology to discriminate circular single-stranded DNA molecules from linear ones with the same number of nucleotides using the nanopore signal.

P14

Reevaluating concentration polarization: clarifying its meaning, genesis, and consequences Joan Montes de Oca and Juan J. de Pablo University of Chicago, USA

Concentration polarization (CP) has been a central topic in the literature on ionic transport and is consistently highlighted in discussions related to the performance of selective membranes. In this poster presentation, we aim to elucidate the ambiguities surrounding the concept, particularly in the context of charged nanoporous membranes with pore diameters well above the Debye length. Our study delves into the mechanisms that give rise to CP, its impact on membranes' behavior, and the reasons why it should not always be viewed as a limitation. Furthermore, we investigate the relationship between CP and ionic current rectification properties of bipolar membranes. By offering a renewed perspective on CP, we hope to promote a deeper understanding of its implications and potential applications in selective membrane technology.

P15

Electrical fluctuations next to an electrode to probe the properties of interfacial electrolytes Swetha Nair , Giovanni Pireddu, Benjamin Rotenberg CNRS, Sorbonne Université, France The fluctuations of physical quantities are often considered as noise that should be minimized with respect to a signal. In electrochemical processes, the charge exchange between electrode and electrolyte promotes chemical changes at the interface, and such interfacial electron transfer reactions serve as the foundation for important technologies that combine electrical and chemical energy. In this context, we use molecular simulations to investigate the link between solvent polarization fluctuations around a solute near an electrode and electron transfer kinetics (Marcus theory) and how these fluctuations are reflected in the charge fluctuation of the electrode [1,2,3] . It has also been observed that the metallicity of the electrode, which reflects its electronic structure, affects the electron transfer kinetics [4] . This metallic character can be captured in a simplified description via the so-called Thomas-Fermi screening length within the electrode [5,6] . This quantity can further be introduced in molecular simulations in the constant-potential ensemble [7] , which allowed in particular to uncover its role on the interfacial thermodynamics via the charge distribution within the electrode[8]. In order to understand the charge distribution induced on the surface by a single ion as a function of its distance from the electrode[9], we use classical molecular simulations of an ion in vacuum or water next to a graphite electrode with a tunable metallicity. Based on the 2D and radial distributions of the induced charge, we discuss the effects of the ion-surface distance and of the screening both in the metal (Thomas-Fermi length) and the solvent (described in the continuum picture by its permittivity). By comparing the simulation results with analytical predictions, we analyze the effect of the atomic structure of the electrode. Finally, we also compare analytically and numerically the case of a single ion and that of a periodic lattice of ions, since molecular simulations are done under periodic boundary conditions. This work is part of the ERC project SENSES (grant No. 863473). Project website: https://benrotenberg.github.io/erc-senses/ References 1. Marcus, R. A, J. Chem. Phys. 1965, 43, 3477−3489. 2. L. Scalfi, D. T. Limmer, A. Coretti, S. Bonella, P. A.Madden, M. Salanne, and B. Rotenberg, Phys. Chem. Chem. Phys. 2020, 22, 10480. 3. G. Pireddu and B. Rotenberg, Phys. Rev. Lett. 2023, 130, 098001. 4. Y. Yu, K. Zhang, H. Parks, M. Babar, S. Carr, I. M. Craig, M. Van Winkle, A. Lyssenko, T. Taniguchi, K. Watanabe, V. Viswanathan, D. K. Bediak, Nat. Chem. 2022, 14, 267−273. 5. M. Vorotyntsev and A. A. Kornyshev, Zh. Eksp. Teor. Fiz., 1980, 78(3), 1008–1019. 6. V. Kaiser, J. Comtet, A. Niguès, A. Siria, B. Coasne and L. Bocquet, Faraday Discuss., 2017, 199, 129–158. 7. L. Scalfi, T. Dufils, K. G. Reeves, B. Rotenberg, and M. Salanne, J. Chem. Phys. 2020, 153, 174704.

8. L. Scalfi and B. Rotenberg, Proc. Natl. Acad. Sci. U.S.A, 2021, 118, e2108769118. 9. G. Pireddu, L. Scalfi, and B. Rotenberg, J. Chem. Phys. 2021, 155, 204705.

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Experimental investigation of model reverse electrowetting systems Zaeem Najeeb , Yuan Chen , Jack Dawson, Ehud Haimov, Alexei Kornyshev, Anthony Kucernak Imperial College London, UK Both Yuan and Zaeem will be presenting the poster at separate time intervals. In recent years, ionotronic devices have attracted much attention due to their great potential for applications in energy harvesting. In previous studies, designs based on the effect of double layer charging have been widely explored [1-3]. Several works have proposed systems under the principle of reverse electrowetting utilising electrolytic solution. Those systems are designed to fit into a shoe sole so that electrical current can be harvested simply from walking. This theoretical investigation of new systems was furthered in our recent study, presented in this Faraday Discussion [4], of two proposed, different designs of double layer capacitive-based ionotronic devices. The two designs are, namely, the (i) ‘flat shoe’ design, where a droplet of nonwetting ionic liquid is squeezed between two electrodes, and the (ii) porous sole design, where the nonwetting ionic liquid is being pushed into and out of the pores. Operation of both systems is driven by the periodic pressure exerted on the system while walking. In both cases, the external pressure causes a change in contact area between the liquid and the electrodes, changing the double layer capacitance and thus triggering fluxes of current. The theory predicted promising results with the systems producing power in the order of 0.01 W/dm 2 and 0.05 W/dm 2 accordingly with appropriately chosen parameters. But such systems are yet to be investigated experimentally. The subject of our work was to test those predictions. Therefore, a proof-of-concept study for both the ‘flat shoe’ and ‘porous sole’ design has been carried out with specially prepared electrodes and using 1-butyl-3-methylimidazolium hexafluorophosphate as the electrolyte. We present first results obtained along these lines. References 1. Haimov, E., et al., Theoretical demonstration of a capacitive rotor for generation of alternating current from mechanical motion. Nature Communications, 2021. 12 (1): p. 3678. 2. Kolomeisky, A.B. and A.A. Kornyshev, Current-generating ‘double layer shoe’ with a porous sole. Journal of Physics: Condensed Matter, 2016. 28 (46): p. 464009. 3. Kwon, S.-H., et al., An effective energy harvesting method from a natural water motion active transducer. Energy & Environmental Science, 2014. 7 (10): p. 3279-3283. 4. Haimov, E., et al., Ionotronics for reverse actuation . Faraday Discussions, Manuscript ID: FD-ART-03-2023-000056.R1

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Frequency-dependent impedance of nanocapacitors from electrode charge fluctuations as a probe of electrolyte dynamics Giovanni Pireddu and Benjamin Rotenberg CNRS, Sorbonne Université, France The frequency-dependent impedance is one of the most important properties of electrical components, and it is routinely used to characterize energy storage and conversion devices. The frequency-dependence reflects the multiscale dynamics of the charge carriers in these systems. Until recently, there was no direct link between the microscopic mechanisms and the impedance measurements, whose interpretation is often indirect and relies on equivalent circuit models. Building on previous work introducing a fluctuation-dissipation relation between the capacitance to the variance of the electrode charge distribution [1], we show how to compute the full impedance spectrum from the equilibrium dynamical fluctuations of the electrode charge in constant potential molecular simulations [2], with the above- mentioned relation for the capacitance being recovered in the zero-frequency limit. This approach offers a bridge between electrochemical measurements and molecular mechanisms. We illustrate the potential of this approach in the case of nanocapacitors using gold electrodes and pure water or NaCl solutions as a dielectric medium, highlighting how some of the dynamical properties of the electrolyte are reflected in the fluctuations of the electrode charge. We finally show how the electrolyte conductance can be estimated from the impedance results computed from simulations, and compare it with experimental measurements. This work is part of the ERC project SENSES (grant No. 863473). Project website: https://benrotenberg.github.io/erc-senses/ References 1. D. T. Limmer, C. Merlet, M. Salanne, D. Chandler, P. A. Madden, R. van Roij, and B. Rotenberg. Phys. Rev. Lett. 2013, 106102. 2. G. Pireddu and B. Rotenberg, Phys. Rev. Lett. 2023, 130, 098001.

P18

Designing with iontronic logic gates - from a single polyelectrolyte diode to an integrated ionic circuit Barak Sabbagh 1 , Noa Edri Fraiman 2 , Alex Fish 2 , Gilad Yossifon 1,3 1 Faculty of Mechanical Engineering, Technion–Israel Institute of Technology, Israel 2 Faculty of Engineering, Bar-Ilan University, Israel 3 School of Mechanical Engineering, Tel-Aviv University, Israel The work presents the implementation of on-chip iontronic circuits via small-scale integration of multiple ionic logic gates made of bipolar polyelectrolyte diodes 1 . These ionic circuits are analogous to solid-state electronic circuits, with ions as the charge carriers instead of electrons/holes. Nevertheless, there are fundamental differences between fluidic and solid-state devices in that ion transport is much more complicated. Its complexity stems from electrochemical electron-ion exchanges, the significantly lower mobility of ions compared to electrons, the variety of ionic species, the lack of ionic charge recombination, and fluid flow effects 2-3 . On the one hand, based on these unique properties, a rich variety of applications can be realized using ionic diodes, e.g., separation, gating, and sensing of ions4-6. On the other hand, all the mentioned differences are expected to have a major impact on the ability to realize complex iontronic circuits that include multiple stages of operations. Whereas the mechanism underlying the operation of a single diode has been studied extensively 4-9 , we focused on its ability to construct different circuit architectures for in-chip computation. For that purpose, we experimentally characterize the responses of a single fluidic diode made of a junction of oppositely charged polyelectrolytes (i.e., anion and cation exchange membranes). This served to carry out pre-designed logical computations in various architectures by integrating multiple diode-based logic gates, where the electrical signal between the integrated gates was transmitted entirely through ions. The findings shed light on the limitations affecting the number of logic gates that can be integrated, the degradation of the electrical signal, their transient response, and the design rules that can improve the electrical performance of iontronic circuits. Furthermore, the unique advantage of various charge carriers in the ionic environment of these circuits (in contrary to only electrons/holes in solid-state components) was exploited to perform logic operations on the molecule transport on top of the electrical response. References

1. Sabbagh, Barak; et al. ACS Applied Materials and Interfaces. 2023 (Accepted). 2. Chun, H.; Chung, T. D. Iontronics. Annu. Rev. Anal. Chem. 2015, 8, 441–462. 3. Chang, H.-C.; Yossifon, G.; Demekhin, E. Annu. Rev. Fluid Mech. 2012, 44, 401–426. 4. Vlassiouk, I.; Kozel, T. R.; Siwy, Z. S. J. Am. Chem. Soc. 2009, 131 (23), 8211–8220. 5. Huang, X.; et al. Adv. Funct. Mater. 2018, 28 (49). 6. Riza Putra, B.; et al. Electroanalysis 2021, 33 (6), 1398–1418. 7. Cayre, O. J.; Suk, T. C.; Velev, O. D. J. Am. Chem. Soc. 2007, 129 (35), 10801–10806. 8. Han, J. H.; et al. Angew. Chemie - Int. Ed. 2009, 48 (21), 3830–3833. 9. Han, J. H.; et al. Small 2011, 7 (18), 2629–2639.

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