Ionization thermodynamics of poly(acrylic acid) in ionic liquids

Ryo KANZAKI¹, Mika SAKO1, Hitoshi KODAMATANI¹, Takashi TOMIYASU¹, Véronique Peyre²

¹Graduate School of Science and Engineering, Kagoshima University, Kagoshima, 890-0065, Japan

²Sorbonne Université, CNRS, Laboratoire PHENIX, Paris, F-75005 France

Presenting author email: kanzaki@sci.kagoshima-u.ac.jp

Ionic liquids, regarded as an extremely condensed electrolyte solvents, are attracting colloidal dispersion media. According to DLVO theory, the addition of electrolytes is generally the primary cause for reduced colloidal stability for charged nanoparticles in water. Therefore, ionic liquids could not be “good” dispersing media of colloids. Even those predictions, techniques to yield stable dispersions of nanoparticles have already been obtained in various ionic liquids. We so far investigated the pH response of the colloidal stability of maghemite magnetic nanoparticles, whose surface is functionalized with polyacrylic acid (pAA), namely coated nanoparticles (CNps). [1,2] In aqueous solutions, CNps aggregate to precipitate in an acidic condition, showing a single threshold pH, while the same CNps aggregate in both acidic and basic conditions and flocculate in the medium pH region in protic ionic liquids (PILs), ethylammonium nitrate (EAN) and N,N-diethylethanolammonium trifluoromethanesulfonate (Et₂HyNH⁺×TfO⁻), showing two switching pHs. In the current study, the ionization thermodynamics of pAA in ionic liquids are studied in order to reveal the role of pAA on the dispersion of CNps.

Figure 1(a) shows the enthalpogram of pAA ionization titration, and Figure 1(b) shows that of CNp in EAN. CNps disperse under the acidic condition (titration ratio < 0), flocculate when the titration ratio exceeds zero, and then redisperse when the titration proceeds (titration ratio > 0.8) to achieve an adequate degree of ionization. These enthalpograms are very similar, indicating that the ionization behavior of the surface pAA on CNp resembles that in the bulk. Interestingly, this works out even in the flocculation pH region, implying that the chemical potential of bulk pH penetrates inside the CNp aggregation to govern the ionization equilibria of the inside pAA. Figure 3(c) shows the pAA titration curve in Et₂HyNH⁺×TfO⁻. Prior to the ionization of the pAA, a heat generation not to be attributed to the ionization was observed. This has also been observed for CNp in the same PIL, [2] which may arise from the condensation of the solvent cation at the vicinity of the surface pAA. Since the entropy of the subsequent ionization was large and negative, further condensation of the solvent cation around CNps may occur with increasing degree of ionization. Thanks to such strong solvations of the surface pAA of the CNps, the pH region of the stable dispersion of the CNp is considered to be wider than that in EAN.

In both PILs, the ionization thermodynamics of CNp resemble those of pAA in each solvent, and thus, the ionization and solvation of pAA are confirmed to contribute to the dispersion stability of CNps. Notably, the dispersion mechanism of CNps in EAN and Et₂HyNH⁺×TfO⁻ is different, even though both are PILs.

Figure 1. Enthalpogram of ionization of pAA and CNp in PILs.

[1] R. Kanzaki, C. Guibert, J. Fresnais, V. Peyre, J. Colloid Interface Sci., 2018, 516, 248.

[2] R. Kanzaki, M. Sako, H. Kodamatani, T. Tomiyasu, C. Guibert, J. Fresnais, V. Peyre, J. Mol. Liq., 2022, 349, 118146.

Swelling clay modeling from the molecular scale

Laurent Brochard

Laboratoire Navier (UMR 8205), École des Ponts ParisTech, Univ. Gustave Eiffel, CNRS,

6-8 avenue Blaise Pascal, 77455 Marne-la-Vallée, France

Clays are geo-materials containing extremely fine mineral grains with peculiar hydro-mechanical behaviors, the most well-known of which being the drying shrinkage. This behavior originates from the adsorption of water in the inter-layer space between nanometric minerals, which induces large deformations. It has been evidenced since the 1950s by X-Ray Diffraction (XRD) [1] that the swelling of clay is ‘crystalline’ at the nanometer scale, i.e., it occurs by sudden changes in the basal spacing. Much progress in the fundamental understanding of clays has been made in the last 30 years, thanks to the development of realistic molecular simulations techniques. The swelling upon humidification remains however specifically hard to evaluate, because the usual grand canonical algorithm is too inefficient. In this work, we set up and implement (LAMMPS) a biased Monte Carlo algorithm inspired by a previous algorithm of Hensen et al. [2], which was adapted to the more recent force field considered here (ClayFF). The hydro-mechanical behavior is obtained by simulations at fixed basal distances, combined with a thermodynamic analysis of the (meta)stability of the various hydration states [3]. This allows establishing at the same time the swelling and the hysteresis under arbitrary external loading. If the first works [3] were limited to 5 different relative humidities and two hydration states (1W et 2W), the present work establishes the most complete stability diagram so far, in the case of a reference (Wyoming) sodium montmorillonite [4]. It covers all the humidity range (from 0.001% to 100%) and all the hydration states (0W, 1W, 2W, 3W, capillary). A major result, easily derived from this diagram, is the accurate prediction of the free crystalline swelling, as it is measured by XRD.

While molecular approaches now provide a quantitative understanding of the mineral layer scale, up-scaling to the clay matrix remains a challenge, in particular because the meso-scale (nm to  m) is hardly accessible to experimental observation, and the microstructure at this scale can only be inferred indirectly (e.g., from small angle scattering). As an alternative to experiments, granular ’meso-scale’ simulations have emerged which aim at taking advantage of the fine understanding obtained at the molecular scale to propose ’coarse-grained’ models at larger scales. The meso-scale physics involves phenomena that are little explored at the molecular scale, in particular the flexibility of the mineral layer and the mechanics of stacks of layers [5]. We propose a meso-scale model for sodium Wyoming montmorillonite, designed specifically to capture the hydration transitions at the layer scale and address the peculiar thermo-hydro-mechanical couplings at conditions representative of geomechanical applications[6].  This meso-scale model is used to investigate in detail the mesostructure and its evolution during mechanical and osmotic loadings.

[1] Mooney et al. (1952) Journal of the American Chemical Society, 74 (6), 1371–1374

[2] Hensen et al. (2001). The Journal of Chemical Physics, 115(7), 3322–3329.

[3] Tambach et al. (2004). The Journal of Physical Chemistry B, 108(23), 7586–7596.

[4] Brochard, L. (2021). The Journal of Physical Chemistry C, 125(28), 15527–15543.

[5] Honorio et al. (2018) Soft Matter, 14 (36), 7354–7367.

[6] Asadi et al. (2022) Soft Matter, 18 (41), 7931–7948.

Non-equilibrium transport along networks: Intracellular traffic rules and molecular crowding by some physical models

Andrea Parmeggiani, Laboratoire Charles Coulomb, University of Montpellier, CNRS

Intracellular organization and dynamics of cargos inside biological cells are non-equilibrium phenomena driven by families of highly specialized molecular machines called motor proteins.
In this seminar, I will introduce some general properties of these systems and show how one can model them from a physico-mathematical perspective. I will present some models of molecular transport of motor proteins along cytoskeletal networks of increasingly complexity: collective (and eventually counterintuitive) physical phenomena of crowding of these nanoscopic shuttles along the cytoskeleton can then occur.

Understanding molecular fluctuations and transport with multiscale experimental models

Prof. Alice Thorneywork,

Physical and Theoretical Chemistry Laboratory, University of Oxford

The effective transport of particles across membranes is essential to the functioning of many systems, from synthetic filters and sensing technologies to biological pores and channels. In nature, this often involves channels or pores which are optimized for transport of a certain species by their size, shape or the inclusion of specific binding sites. Replicating such highly efficient and selective transport in synthetic systems, however, represents an ongoing challenge, in part because unambiguously elucidating transport mechanisms in molecular level experiments is very difficult. Valuable insights can thus be provided by experimental models that display analogous physical behaviour but are experimentally much more accessible. Importantly, such systems allow us to explore not only collective, many particle effects, but also the single particle behaviours and fluctuations that give rise to them.

In this talk, I will discuss some recent examples of how we are using experimental soft matter models to elucidate details of transport processes at the nanoscale and mesoscale. At the nanoscale, we probe the transport of ions through nanopores by measurement of an ionic current. We have recently explored the effect on these currents of passive adsorption of polymers to the pore surface and, excitingly, how this can be linked to details of the polymer adsorption potential [1]. Alongside this, we are developing colloidal models to explore similar aspects of transport and fluctuations in directly observable mesoscale systems. Here, we have previously demonstrated that single particle colloidal dynamics can be directly linked to transport through biological pores [2], and I will share details of our current efforts to now extend these ideas to many-body hard sphere systems [3].

[1] S. F. Knowles, A. L. Thorneywork et al., Phys. Rev. Lett, 127, 137801, (2021)

[2] A. L. Thorneywork et al., Sci. Adv., 6 (18), eaaz4642, (2020)

[3] S. F. Knowles, A. L. Thorneywork et al., J. Phys.: Condens. Matter, 34, 344001, (2022)

Probing multi-scale dynamics in complex fluids and biological systems with differential dynamic microscopy

Roberto Cerbino

Mercredi 8 Mars 2023 32-42 salle 101

Abstract

Complex and biological fluids are often composed of a variety of structures that can exhibit a wide range of dynamic phenomena at different spatial and temporal scales. From the diffusion of individual particles to the collective motion of large ensembles, being able to quantify the dynamics is crucial to understanding the properties and behavior of such systems. To this aim, researchers have developed a variety of experimental techniques, including microscopy, rheology, spectroscopy, and scattering, each with its own advantages and limitations. Among these techniques, differential dynamic microscopy (DDM) has emerged as a flexible and powerful tool to perform a multiscale characterization of the dynamics by analyzing videos of the sample acquired in direct space during microscopy experiments. These videos are analyzed to extract reciprocal space information about the system dynamics (similar to Dynamic Light Scattering or X-Ray Photon Correlation Spectroscopy), and one single DDM experiment can probe simultaneously hundreds to thousands of different wave-vectors. In this talk, we will focus on DDM and its applications in soft matter and biological fluids. We will explore the fundamental principles behind DDM, discuss the experimental setup required for DDM measurements, and highlight the analysis methods used to extract quantitative information from the data. We will also showcase examples of DDM applications, including the study of the dynamics of nanoparticles and the characterization of non-equilibrium behavior, also in active systems.

Abstract

Electrolyte solutions play an important role in many scientific fields, such as electrochemistry, energy research, chemical synthesis, biochemistry and pharmaceutical research [1-4]. The conventional classification of electrolyte solutions as “strong” or “weak” accounts for their charge transport properties, but neglects their mass transport properties, and is not readily applicable to highly concentrated solutions.
Here we use the Onsager transport formalism in combination with linear response theory to attain a more general classification, which is based on a comparison of charge and mass transport [5, 6]. Charge transport is characterized by the ionic conductivity σ??? and mass transport by the neutral salt transport coefficient σ????. Three classes of electrolyte solutions are then distinguished [5,6]: (i) “Strong electrolytes” with σ???≈σ????; (ii) “weak charge transport electrolytes” with σ???≪σ????; and (iii) “weak mass transport electrolytes” with σ????≪σ???. While classes (i) and (ii) encompass the classical “strong” and “weak” electrolytes, respectively, many highly concentrated electrolytes fall into class (iii) and thus exhibit transport properties clearly distinct from classical strong and weak electrolytes.
References:
[1] H.-P. Landolt, S. C. Holst, Science 2016, 352, 517.
[2] Z. Zhang, J. Song, and B. Han, Chem. Rev. 2017, 117, 6834.
[3] M. Watanabe, M. L. Thomas, S. Zhang, K. Ueno, T. Yasuda, K. Dokko, Chem. Rev. 2017, 117, 7190.
[4] M. Li, C. Wang, Z. Chen, K. Xu, J. Lu, Chem. Rev. 2020, 120, 6783.
[5] B. Roling, J. Kettner, V. Miß, Energy Environ. Mater. 2022, 5, 6.
[6] B. Roling, V. Miß, J. Kettner, Energy Environ. Mater. 2022, e12533.
doi: 10.1002/eem.12553