Hofmeister Effects Shine in Nanoscience

Abstract

Hofmeister effects play a crucial role in nanoscience by affecting the physicochemical and biochemical processes. Thus far, numerous wonderful applications from various aspects of nanoscience have been developed based on the mechanism of Hofmeister effects, such as hydrogel/aerogel engineering, battery design, nanosynthesis, nanomotors, ion sensors, supramolecular chemistry, colloid and interface science, nanomedicine, and transport behaviors, etc. In this review, for the first time, the progress of applying Hofmeister effects is systematically introduced and summarized in nanoscience. It is aimed to provide a comprehensive guideline for future researchers to design more useful Hofmeister effects-based nanosystems.

Keywords: Hofmeister effect; hydrogel engineering; ion-responsive nanosystems; nanotechnology; supramolecular chemistry.

Figure 1

Nonlinear rheology of PIC gels with different sodium salts added. a) The differential modulus K′ as a function of the applied stress σ for gels with different sodium salts at a salt concentration of 0.5 m and T = 37 °C. Chaotropic anions decrease the linear modulus of the gel but increase the sensitivity toward applied stress, while kosmotropic anions increase the linear modulus and decrease the sensitivity toward stress. Note that all gels behave similarly at high stress. b) The plateau modulus G₀ (squares) and the critical stress σ _c (open circles) for gels with different anions plotted versus the entropy of hydration of the anions. The colors correspond to the legend of the panel a). c) The plateau modulus G₀ (squares) and the critical stress σ _c (open circles) for gels with different anions plotted versus the surface tension increments of the anions. The colors correspond to the legend of the panel a). Both G₀ and σ _c show a remarkably good correlation for both chaotropic and kosmotropic anions. The solid lines represent fits with Equation (3). Reproduced with permission.^{[ 20 ]} Copyright 2015, Wiley‐VCH.

Scheme 1

Modern version for Hofmeister series of anions and cations.

Figure 2

a) Freezing‐assisted salting‐out fabrication procedure of the HA‐PVA hydrogels. Structural formation and polymer chain concentration, assembly, and aggregation during the freezing‐assisted salting‐out fabrication process. b) Macroscopic view of real tendon and of the HA‐5PVA hydrogel. Scale bar, 5 mm. c–e) SEM images showing the microstructure c) and nanostructure d,e) of the HA‐5PVA hydrogel. Scale bars, 50 µm c); 1 µm d); 500 nm e). f) Molecular illustration of polymer chains aggregated into nanofibrils. Reproduced with permission.^{[ 21 ]} Copyright 2022, Springer Nature.

Figure 3

a–c) SEM image of printed Au using inks with NaCl concentrations of 0, 25, and 50 g L⁻¹, respectively. d) Porosity as a function of Cl⁻ anion concentrations. e) Particle sizes as a function of Cl⁻ anion concentrations. f) Thickness and conductivity as a function of Cl⁻ anion concentrations. g) Porosity of samples with different anions. h) Particle sizes of samples with different anions. i) Thickness/conductivity of samples with different anions. Data represent mean ± standard deviation, n = 5, significance determined by one‐way ANOVA test. Scale bar: 200 nm for a–c). Reproduced with permission.^{[ 23 ]} Copyright 2022, Wiley‐VCH.

Figure 4

Impact of Hofmeister effects on the AV‐based organohydrogels: a) Schematic illustration of the simplified anionic Hofmeister series, b) SEM images, c) Stress and strain values, and d) Conductivity comparison of various sodium salt‐based AV organohydrogels. Reproduced with permission.^{[ 25 ]} Copyright 2022, Wiley‐VCH.

Figure 5

Tensile mechanical properties of CNF biofibers. a) Representative stress‐strain curves of fibers prepared at pH 2 and 2.5 of the gel initiators and 0.3 wt.% CNF concentration. Young's modulus as a function of b) pH of the gel initiator and, c) CNF concentration for HCl. d) Toughness and e) ultimate strength of fibers prepared with different gel initiators at pH 2 and 2.5. The different acids are referred to by the color and shape of the data points. Error bars are 90 % confidence intervals based on at least 10 different measurements for each type of sample. All the measurements are done at 50 % RH. Reproduced with permission.^{[ 29 ]} Copyright 2019, Wiley‐VCH.

Figure 6

Schematic illustration of the Hofmeister gel iontronic sensor. a) The sandwiching capacitance with hierarchical pyramid electrodes and conductive hydrogel dielectric layer construct the gel iontronic sensor. b) The Hoffmeister effect in the hydrogel manages the gel elasticity modulus of the dielectric layer with the presence of various chemical cosolvents. Reproduced with permission.^{[ 34 ]} Copyright 2023, American Chemical Society.

Figure 7

a) Schematic of PVA sol/gel after weak Hofmeister effects (by acetate) and strong Hofmeister effects (by sulfate) and digital photographs of the corresponding products. b) Mechanisms of proton transfer in free water and PVA without salting‐out; and possible ways that hinder the transfer of H⁺ in PZAS with strong salting‐out effects. Reproduced with permission.^{[ 42 ]} Copyright 2022, Wiley‐VCH.

Figure 8

a) After addition of salts containing various cations (NH₄ ⁺, Na⁺, Mg²⁺, Ca²⁺) and anions (SCN⁻, NO₃ ⁻, Cl⁻, HPO₄ ²⁻, SO₄ ²⁻) into the polymersome solution, the SV shape changed to ellipsoid (ELL), tube, disc, stomatocytes (STO), and large compound vesicles (LCV). The capacity of ions to induce these shape change follows the order of Hofmeister series, as the arrow pointed. b) Shapes obtained from various sodium salts at different concentrations (10^{−2 _} 10⁻⁵ m). The TEM images of SV, ELL, STO, DISC, and LCV (cryo‐TEM image inserted); scale bar (red): 500 nm. c) Shapes obtained from variation of the cations at different the concentration ranging from 10⁻² to 10⁻⁵ m. Reproduced with permission.^{[ 55 ]} Copyright 2020, American Chemical Society.

Figure 9

Hofmeister effects‐driven chemotaxis of nanomotors Reproduced with permission.^{[ 59 ]} Copyright 2019, Springer Nature.

Figure 10

a) Chaotropic anions induce micelle self‐assembly of PEO‐b‐PR copolymers with protonated PR segment, which is a reversed effect (salt‐out) with respect to their ability to solubilize proteins (salt‐in). b) Illustration of FRET design to investigate CA‐induced micelle self‐assembly. Addition of CA results in micelle formation and efficient energy transfer from donor (TMR) to acceptor (Cy5) dyes. c) Chaotropic anion‐induced micelle self‐assembly showing the anti‐Hofmeister trend. Reproduced with permission.^{[ 95 ]} Copyright 2014, Wiley‐VCH.

Figure 11

Summary of anion (1 m) and cation (0.02 m) specific effect on depolymerization kinetics for microcapsules suspended in methanol at [TFA] = 0.01 m as represented by depolymerization half‐life tD50 and depolymerization mol % at 16 h. a) Anion specificity in the coactivation (cation = lithium), showing that only chaotropic anions accelerated the depolymerization rates. The tD50 SO₄ ^2–, F^–, and OAc^– were marked in break columns because these values exceeded the measuring scale and no depolymerization was observed over 48 h. b) Cation specificity in the coactivation (anion = chloride), showing a modulating effect on the depolymerization rates. Reproduced with permission.^{[ 115 ]} Copyright 2017, American Chemical Society.

Figure 12

Hofmeister Effects‐Based T₁–T₂ Dual‐Mode MRI. Reproduced with permission.^{[ 116 ]} Copyright 2019, American Chemical Society.

Figure 13

Chemical Storage and Exocytotic Dynamics Detected Amperometrically Regulated by Hofmeister Anions. Reproduced with permission.^{[ 118 ]} Copyright 2022, American Chemical Society.