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1. Linear and Nonlinear Dielectric Response of Intrinsically Disordered Proteins

   https://doi.org/10.1021/acs.jpclett.4c00866  

   Sauer, Michael A; Colburn, Taylor; Maiti, Sthitadhi; Heyden, Matthias; Matyushov, Dmitry V (May 2024, The Journal of Physical Chemistry Letters)

   Scholes, Gregory D (Ed.)

   Linear and nonlinear dielectric responses of solutions of intrinsically disordered proteins (IDPs) were analyzed by combining molecular dynamics simulations with formal theories. A large increment of the linear dielectric function over that of the solvent is found and related to large dipole moments of IDPs. The nonlinear dielectric effect (NDE) of the IDP far exceeds that of the bulk electrolyte, offering a route to interrogate protein conformational and rotational statistics and dynamics. Conformational flexibility of the IDP makes the dipole moment statistics consistent with the gamma/log-normal distributions and contributes to the NDE through the dipole moment’s non-Gaussian parameter. The intrinsic non-Gaussian parameter of the dipole moment combines with the protein osmotic compressibility in the nonlinear dielectric susceptibility when dipolar correlations are screened by the electrolyte. The NDE is dominated by dipolar correlations when electrolyte screening is reduced. 

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2. Influence of dielectric inhomogeneities on the structure of charged nanoparticles in neutral polymer solutions

   https://doi.org/10.1039/c8sm00298c  

   Samanta, Rituparna; Ganesan, Venkat (January 2018, Soft Matter)

   We study the structural characteristics of a system of charged nanoparticles in a neutral polymer solution while accounting for the differences in the dielectric constant between the particles, polymer and the solvent. We use a hybrid computational methodology involving a combination of single chain in mean-field simulations and the solution of the Poisson's equation for the electrostatic field. We quantify the resulting particle structural features in terms of radial distribution function among particles as a function of the dielectric contrast, particle charge, particle volume fraction and polymer concentration. In the absence of polymers, charged macroions experience increased repulsion with a lowering of the ratio of particle to solvent dielectric constant. The influence of the dielectric contrast between the particle and the solvent however diminishes with an increase in the particle volume fraction and/or its charge. In the presence of neutral polymers, similar effects manifest, but with the additional physics arising from the fact that the polymer-induced interactions are influenced by the dielectric contrast of the particle and solvent. 

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3. A “hump” in the third-order dielectric response of a highly polar liquid: Now you see it, now you don’t

   https://doi.org/10.1063/5.0248963  

   Thoms, Erik; Richert, Ranko (March 2025, The Journal of Chemical Physics)

   We have measured the linear and nonlinear dielectric responses of S-methoxypropylene carbonate, a highly polar glass-former, for which it has been reported that the “hump,” which is typical of third harmonic susceptibilities, disappears across a 5 K temperature change. To understand this unusual feature, we have measured the responses to high amplitude ac and dc electric fields at the fundamental frequency. The static limits of these results are entered into a model aimed at reproducing nonlinear dielectric susceptibility spectra using the concept of a fictive electric field. This model reproduces the “hump” in the third-harmonic response and its seeming disappearance. It is revealed that the “hump” is predominantly the result of reduced time constants, a consequence of the energy the sample absorbs from the electric field. At elevated temperatures, the “hump” only appears to vanish because its reduced amplitude submerges below the extraordinarily high level of polarization saturation of this liquid. 

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4. Strong increase of correlations in liquid glycerol observed by nonlinear dielectric techniques

   https://doi.org/10.1063/5.0093235  

   Thoms, Erik; Matyushov, Dmitry V.; Richert, Ranko (May 2022, The Journal of Chemical Physics)

   Nonlinear dielectric measurements are an important tool to access material properties and dynamics concealed in their linear counterparts, but the available data are often intermittent and, on occasion, even contradictory. Employing and refining a recently developed technique for high ac field dielectric measurements in the static limit, we ascertain nonlinear effects in glycerol over a wide temperature range from 230 to 320 K. We find that the temperature dependence of the Piekara factor a, which quantifies the saturation effect, changes drastically around 290 K, from ∂ a/∂ T = +1.4 to −130 in units of 10 −18  V 2  m −2  K −1 . These high values of | a| quantify not only elevated dielectric saturation effects but also indicate a temperature driven increase in higher-order orientational correlations and considerable correction terms with respect to the central limit theorem. No signature of this feature can be found in the corresponding low field data. 

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5. Quasi-steady-state modelling and characterization of diffusion-controlled dissolution from monodisperse prolate and oblate spheroidal particles

   https://doi.org/10.1098/rspa.2022.0283  

   Wang, Yanxing; Wan, Hui; Wei, Tie; Nevares, Dominick; Shu, Fangjun (November 2022, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences)

   A quasi-steady-state model of the dissolution of a single prolate or oblate spheroidal particle has been developed based on the exact solution of the steady-state diffusion equation for mass transfer in an unconfined media. With appropriate treatment of bulk concentration, the model can predict the detailed dissolution process of a single particle in a container of finite size. The dimensionless governing equations suggest that the dissolution process is determined by three dimensionless control parameters, initial solid particle concentration, particle aspect ratio and the product of specific volume of solid particles and saturation concentration of the dissolved substance. Using this model, the dissolution processes of felodipine particles are analysed in a broad range of space of the three control parameters and some characteristics are identified. The effects of material properties indicated by the product of specific volume and saturation concentration are also analysed. The model and the analysis are applicable to the system of monodisperse spheroidal particles of the same shape. 

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