Statics and Dynamics of Strongly Charged Soft Matter

TL;DR

This paper reviews the static and dynamic behaviors of strongly charged soft matter, including interactions, charge effects, and electric field responses, with implications for biological and technological applications.

Contribution

It provides a comprehensive analysis of charge effects in soft matter, combining theoretical, simulation, and experimental insights into static and dynamic phenomena.

Findings

Like-charged bodies can attract in the presence of multivalent counterions.

Charge distribution and surface corrugation significantly influence counterion behavior.

Strong electric fields can unfold and orient highly charged polymers.

Abstract

Soft matter materials, such as polymers, membranes, proteins, are often electrically charged. This makes them water soluble, which is of great importance in technological application and a prerequisite for biological function. We discuss a few static and dynamic systems that are dominated by charge effects. One class comprises complexation between oppositely charged objects, for example the adsorption of charged ions or charged polymers (such as DNA) on oppositely charged substrates of different geometry. The second class comprises effective interactions between similarly charged objects. Here the main theme is to understand the experimental finding that similarly and highly charged bodies attract each other in the presence of multi-valent counterions. This is demonstrated using field-theoretic arguments as well as Monte-Carlo simulations for the case of two homogeneously charged bodies. Realistic surfaces, on the other hand, are corrugated and also exhibit modulated charge distributions, which is important for static properties such as the counterion-density distribution, but has even more pronounced consequences for dynamic properties such as the counterion mobility. More pronounced dynamic effects are obtained with highly condensed charged systems in strong electric fields. Likewise, an electrostatically collapsed highly charged polymer is unfolded and oriented in strong electric fields. At the end of this review, we give a very brief account of the behavior of water at planar surfaces and demonstrate using ab-initio methods that specific interactions between oppositely charged groups cause ion-specific effects that have recently moved into the focus of interest.