Editorial on the topical issue of charged species in bulk and at interfaces.

The topical issue titled "Charged Species in Bulk and at Interfaces: Interaction, Mobility, Transport, and Regulation" is based on contributions from speakers at three CECAM workshops held in 2016, 2018, and 2022. In addition, this editorial is also intended to express our sincere appreciation to our senior co-organizers, Prof. Jan K.

Electric field-induced control of protein crystal morphology.

In a previous study (D. Ray, ., , 2024, , 8108-8113), we found that an alternating electric field considerably affects the location of the crystallization boundary and the liquid-liquid phase separation line as well as crystallization kinetics in lysozyme solutions containing sodium thiocyanate (NaSCN).

Electric-field induced modulation of amorphous protein aggregates: polarization, deformation, and reorientation.

Proteins in their native state are only marginally stable and tend to aggregate. However, protein misfolding and condensation are often associated with undesired processes, such as pathogenesis, or unwanted properties, such as reduced biological activity, immunogenicity, or uncontrolled materials properties. Therefore, controlling protein aggregation is very important, but still a major challenge in various fields, including medicine, pharmacology, food processing, and materials science.

Direct visualization of local activities of long DNA strands via image-time correlation.

Bacteriophages with long DNA genomes are of interest due to their diverse mutations dependent on environmental factors. By lowering the ionic strength of a hydrophobic (PPh4Cl) antagonistic salt (at 1 mM), single long T4 DNA strand fluctuations were clearly observed, while condensed states of T4 DNA globules were formed above 5-10 mM salt. These long DNA strands were treated with fluorescently labeled probes, for which photo bleaching is often unavoidable over a short time of measurement.

Solvent-dependent morphology and anisotropic microscopic dynamics of cellulose nanocrystals under electric fields.

Cellulose nanocrystals (CNCs) are interesting for the construction of biomaterials for energy delivery and packaging purposes. The corresponding processing of CNCs can be optimized through the variation of intercellulose interactions by employing different types of solvents, and thereby varying the degree of cellulose hydrogen bonding. The aim of this work is (i) to show how different types of solvents affect the self-assembled morphology of CNCs, (ii) to study the microscopic dynamics and averaged orientations on the CNCs in aqueous suspensions, including the effect of externally imposed electric fields, and (iii) to explore the nonlinear optical response of CNCs.

Equilibrium phase diagram and thermal responses of charged DNA-virus rod-suspensions at low ionic strengths.

The collective behavior of DNA is important for exploring new types of bacteria in the means of detection, which is greatly interested in the understanding of interactions between DNAs in living systems. How they self-organize themselves is a physical common phenomenon for broad ranges of thermodynamic systems. In this work, the equilibrium phase diagrams of charged chiral rods (fd viruses) at low ionic strengths (below a few mM) are provided to demonstrate both replicas of (or self-organized) twist orders and replica symmetry breaking near high concentration glass-states.

Shockwave application enhances the effect of dentin desensitizer.

Objectives: The purpose of this study was to develop a new device that can improve the effect of desensitizer using shockwaves and to verify its efficacy.

Methods: A micro-shockwave generator was developed using a piezoelectric actuator (PIA-1000, piezosystem jena GmbH, Jena, Germany), an Arduino Uno microcontroller (Arduino, Torino, Italy), and a high voltage pulser (HVP-1000, piezosystem jena GmbH) at 700 V (400 A) and 100 μs. The occlusal surfaces of 20 extracted human upper and lower third molars without caries or restoration were reduced to expose the occlusal dentin, and the prepared occlusal surfaces were acid-etched with 32% phosphoric acid to remove the smear layer.

Coupling of long-wavelength density fluctuations to orientations in cellulose nanocrystal suspensions under external fields.

Motivated by the development of cellulose-based functional materials, we investigate the microscopic dynamics of suspensions of cellulose nanocrystals (CNCs) at different ionic strengths, both in the absence and in the presence of AC electric fields and for various temperatures. A concentration of 5 wt % of the CNCs is chosen for which the dispersions are in the full chiral-nematic state at low ionic strengths. Dynamic light scattering is used to characterize the wave vector-dependent decay rates of number-density fluctuations.

Anisotropic Diffusion and Phase Behavior of Cellulose Nanocrystal Suspensions.

In this paper, we use dynamic light scattering in polarized and depolarized modes to determine the translational and rotational diffusion coefficients of concentrated rodlike cellulose nanocrystals in aqueous suspension. Within the range of studied concentrations (1-5 wt %), the suspension starts a phase transition from an isotropic to an anisotropic state as shown by polarized light microscopy and viscosity measurements. Small-angle neutron scattering measurements also confirmed the start of cellulose nanocrystal alignment and a decreasing distance between the cellulose nanocrystals with increasing concentration.

Effect of Gelation on the Colloidal Deposition of Cellulose Nanocrystal Films.

One of the most important aspects in controlling colloidal deposition is manipulating the homogeneity of the deposit by avoiding the coffee-ring effect caused by capillary flow inside the droplet during drying. After our previous work where we achieved homogeneous deposition of cellulose nanocrystals (CNCs) from a colloidal suspension by reinforcing Marangoni flow over the internal capillary flow (Gençer et al. Langmuir 2017, 33 (1), 228-234), we now set out to reduce the importance of capillary flow inside a drying droplet by inducing gelation.

Soft-mode of charged chiral fibrous viruses (fd).

The frictional forces in suspensions vary depending on the size, shape, and the surface of the particles, which are either charged or neutral. For anisotropic particles with no spatial gradient in the order parameter under external parameters, they exhibit either a continuous phase transition or "freezing" of the order parameter fluctuation. They are known as the collective soft-mode, which has a finite cutoff dispersion where the relaxation time diverges.

Flow instability due to coupling of shear-gradients with concentration: non-uniform flow of (hard-sphere) glasses.

Flow-induced instabilities that lead to non-uniform stationary flow profiles have been observed in many different soft-matter systems. Two types of instabilities that lead to banded stationary states have been identified, which are commonly referred to as gradient- and vorticity-banding. The molecular origin of these instabilities is reasonably well understood.

An electric-field induced dynamical state in dispersions of charged colloidal rods.

The response of concentrated dispersions of charged colloids to low-frequency electric fields is governed by field-induced inter-colloidal interactions resulting from the polarization of electric double layers and the layer of condensed ions, association and dissociation of condensed ions, as well as hydrodynamic interactions through field-induced electro-osmotic flow. The phases and states that can be formed by such field-induced interactions are an essentially unexplored field of research. Experiments on concentrated suspensions of rod-like colloids (fd-virus particles), within the isotropic-nematic phase coexistence region, showed that a number of phases/states are induced, depending on the field amplitude and frequency [Soft Matter, 2010, 6, 273].

Glass transition of repulsive charged rods (fd-viruses).

It has recently been shown that suspensions of long and thin charged fibrous viruses (fd) form a glass at low ionic strengths. The corresponding thick electric double layers give rise to long-ranged repulsive electrostatic interactions, which lead to caging and structural arrest at concentrations far above the isotropic-nematic coexistence region. Structural arrest and freezing of the orientational texture are found to occur at the same concentration.

Spatio-temporal analysis of shrinkage vectors during photo-polymerization of composite.

Objectives: The purpose of this study was to validate a new method to investigate the polymerization shrinkage vectors of composite during light curing and to evaluate the overall utility and significance of the technique.

Methods: An optical instrument was developed to measure the location and direction of the polymerization shrinkage strain vectors of dental composite during light curing using a particle tracking method with computer vision. The measurement system consisted of a CCD color camera, a lens and a filter, and software for multi-particle tracking.

Image time-correlation, dynamic light scattering, and birefringence for the study of the response of anisometric colloids to external fields.

In this paper, a detailed description of equipment is given, specially designed to characterize the response of non-spherical colloids to external fields. To characterize slow structural changes on a large length scale we developed an image correlation method, fast dynamics on the colloidal-particle level is probed by means of a vertically mounted, small angle dynamic light scattering setup, while the orientational order (induced by the external field) is measured with a birefringence setup with off-normal incidence. The performance of this in situ set of instruments is illustrated by experiments on concentrated dispersions of very long and thin, charged colloidal rods (fd-virus particles) in external electric fields.

Constitutive equations for the flow behavior of entangled polymeric systems: application to star polymers.

A semimicroscopic derivation is presented of equations of motion for the density and the flow velocity of concentrated systems of entangled polymers. The essential ingredient is the transient force that results from perturbations of overlapping polymers due to flow. A Smoluchowski equation is derived that includes these transient forces.

Diffusion of spheres in isotropic and nematic networks of rods: electrostatic interactions and hydrodynamic screening.

Translational diffusion of a small charged tracer sphere in isotropic and nematic suspensions of long and thin charged rods is investigated as a function of ionic strength and rod concentration. A theory for the diffusive properties of a small sphere is developed, where both (screened) hydrodynamic interactions and charge interactions between the tracer sphere and the rod network are analyzed. Hydrodynamic interactions are formulated in terms of the hydrodynamic screening length.

Vorticity banding in rodlike virus suspensions.

Vorticity banding under steady shear flow is observed in a suspension of semiflexible colloidal rods (fd virus particles) within a part of the paranematic-nematic biphasic region. Banding occurs uniformly throughout the cell gap within a shear-rate interval (.gamma-, .

Nematic-isotropic spinodal decomposition kinetics of rodlike viruses.

We investigate spinodal decomposition kinetics of an initially nematic dispersion of rodlike viruses. Quench experiments are performed from a flow-stabilized homogeneous nematic state at a high shear rate into the two-phase isotropic-nematic coexistence region at a zero shear rate. We present experimental evidence that spinodal decomposition is driven by orientational diffusion, in accordance with a very recent theory.

Diffusion of spheres in isotropic and nematic suspensions of rods.

Diffusion of a small tracer sphere (apoferritin) in isotropic and nematic networks [of fd virus] is discussed. For a tracer sphere that is smaller than the mesh size of the network, screened hydrodynamic interactions between the sphere and the network determine its diffusion coefficient. A theory is developed for such interactions as well as their relation to the long-time self-diffusion coefficient.

Dynamics of distorted cholesterics in a mesogenic versus isotropic polymer network.

The dynamics of the distorted cholesteric director is studied in a complex matrix, such as mesogenic and istotropic polymer networks, by means of dynamic light scattering. We employ polymer-stabilized cholesteric diffraction gratings as our system to measure thermal fluctuations of the cholesteric director in photostabilized low-molecular-weight polymer networks. The relaxation rates of fast and slow dynamical modes of the distorted cholesteric directors are measured in two scattering geometries, where the scattering vector is either parallel or perpendicular to the helical axis.

Diffusion of spheres in crowded suspensions of rods.

Translational tracer diffusion of spherical macromolecules in crowded suspensions of rodlike colloids is investigated. Experiments are done using several kinds of spherical tracers in fd-virus suspensions. A wide range of size ratios L/2a of the length L of the rods and the diameter 2a of the tracer sphere is covered by combining several experimental methods: fluorescence correlation spectroscopy for small tracer spheres, dynamic light scattering for intermediate sized spheres, and video microscopy for large spheres.