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Understanding the effect of mixed crowding is of prime importance with regards to addressing the manner in which the crowded cellular interior influences the structure, function and dynamics of proteins. In this study we have used the internal dynamics of the multidomain serum protein, bovine serum albumin (BSA), labeled with the solvation probe 7-diethylamino-3–4-maleimidophenyl-4-methylcoumarin (CPM), as a sensor for binary crowding mixtures. Both synthetic (Ficoll 70, Dextran 70, Dextran 40 & PEG 8000) and protein based (unlabeled BSA) crowders have been used. The ‘BSA + Ficoll 70’ mixture had the maximum retardation effect on the protein dynamics with the average solvation time being more than that of the sum of the individual crowding agents. On the contrary, all other binary mixtures had the reverse effect with the excluded volume induced in their presence being lesser than that of the component crowders taken together. Further support was obtained from the overall protein dynamics based on the acrylamide quenching of emission of the tryptophan residues of BSA. Our results have been discussed in the light of the compatibility and lack in thereof, of the individual components of the mixtures, an aspect that has been further supported by excess viscosity ( η E ) estimations based on our time resolved anisotropy data. Till date, crowding induced excluded volume has been sensed mostly through diffusion-based experiments or FRET based sensors. As shown in this study, internal protein dynamics can also add another dimension to the manner in which the degree of macromolecular congestion can be sensed, with the possibility of mapping site-specific response along the polypeptide backbone.

Statistical-thermodynamic analysis for the calculation of chemical equilibrium in the case of dimerization of hard-sphere monomer species of different sizes into an asymmetric dumbbell was considered. The description of the dimerization was carried out within two models: a) the simplest yet analytical description of the van der Waals type in order to take into account excluded volume effects, and b) the approach of the Largo and Solana type for more accurate description of hard-body mixtures with the effective form factor. Deviations of dimerization equilibrium from ideality depending on the ratio of the reacting monomers' diameters and their overlapping in the dimer were analyzed. It was shown that the reduction in entropy of the resulting hard-body mixture is more noticeable with a larger difference in the diameters but with less fusion of spheres in the dimer.

We consider a low-density assembly of identical spherical colloids, on which one has grafted f linear chains from an initial polymer solution of volume fraction, Φ0. Once the grafting process is accomplished, the clothed colloids are immersed in a good solvent. We assume that the lengths of the grafted chains are randomly distributed around the core of the clothed particles. For simplicity, we suppose that the clothed particles are small enough to be considered as polydisperse star-polymers. The purpose is the computation of the effective force between polydisperse star-polymers, which is caused by the excluded volume interaction between monomers. More precisely, we are interested in a quantitative investigation of the influence of the grafting mode on the force expression. To compute the latter, we first study the structure of the polymer-layer around each particle, depending on the grafting nature (from a melt, dilute or semi-dilute solutions). Second, thanks to the obtained size distribution, we determine the expected force versus the center-to-center distance. When the grafting is realized from a semi-dilute solution, we show the existence of distance-regimes, where the force expression is not the same. In any case, we find that the force decays according to a power law in the interparticle distance, with amplitudes that explicitly depend on the number of arms per star-polymer, f, and the volume fraction of the initial solution, Φ0. The main conclusion is that, the induced force is more significant only when the grafting is realized exposing the clothed colloidal particles to more concentrated initial solutions. Finally, the obtained results are compared to those relative to the situation when the grafting is accomplished rather from a polymer melt.

The electrophoretic mobility of a spherical colloid particle immersed in a binary electrolyte is studied by using the Primitive Model Electrophoresis formalism, in combination with the Modified Poisson-Boltzmann equilibrium theory. This approach differs from the classical descriptions of electrophoresis, based on the Poisson-Boltzmann equation for point ions, in that the Primitive Model Electrophoresis theory takes into account consistently the ionic correlations and excluded volume contributions due to the finite size of the ions. Using the equilibrium radial distribution functions of the Modified Poisson-Boltzmann, the primitive model electrophoresis theory predicts a non-universal behavior of the reduced mobility, as a function of the reduced ζ -potential, in contrast to the universal behavior exhibited by the well-known treatment of Wiersema, O’Brien and White. The primitive model electrophoresis mobilities calculated with the Modified Poisson-Boltzmann theory compare favorably with the previously reported mobilities obtained through the hypernetted-chain/mean spherical approximation equilibrium theory. The agreement between these two theories is very good, both quantitatively and qualitatively for univalent electrolytes. For 2:2 electrolytes they qualitatively agree. In particular, the Modified Poisson-Boltzmann mobilities confirm the occurrence of reversed electrophoretic mobilities. Overall the results presented here show the adequacy of the Modified Poisson-Boltzmann equilibrium theory to calculate the electrophoretic mobility of colloidal particles.

Resummed thermodynamic perturbation theory for central force associating potential is extended and applied to study the properties of shielded attractive shell model of polymerizing hard spheres of different sizes. The model is represented by the two-component mixture of hard spheres with additional square-well interaction treated in the sticky limit and located inside the hard-core region and acting only between particles of different species. The theory self-consistently takes into account the changes in the excluded volume of the system due to bonding of the particles. Theoretical predictions for the pressure and fraction of the particles in different bonding states at different temperatures and densities are compared against computer simulation predictions. The theory appears to be very accurate in description of the dimerizing and trimerizing versions of the model. For the model, which allows chain polymerization the theory is slightly less accurate, in particular for low temperatures and high densities.

10 pags., 5 figs. --Open Access funded by Creative Commons Atribution Licence 4.0, There is a growing interest in the properties of ionic liquids (ILs) and IL-solvent mixtures at metallic interfaces, particularly due to their applications in energy storage. The main focus so far has been on electrical double layers with ILs far from phase transitions. However, systems in the vicinity of their phase transformations are known to exhibit some remarkable features, such as wetting transitions and capillary condensation. Herein, we develop a mean-field model suitable for the IL-solvent mixtures close to demixing, and combine it with the Carnahan-Starling (CS) and lattice-gas expressions for the excluded volume interactions. This model is then solved analytically, using perturbation expansion, and numerically. We demonstrate that, besides the well-known camel and bell-shaped capacitances, there is a bird-shaped capacitance, having three peaks as a function of voltage, which emerge due to the proximity to demixing. In addition, we find that the camel-shaped capacitance, which is a signature of dilute electrolytes, can appear at high IL densities for ionophobic electrodes. We also discuss the differences and implications arising from the CS and lattice-gas expressions for excluded volume interactions in the context of our model., This work was supported by the European Unions Horizon 2020 research and innovation programmes under the Marie Skłodowska-Curie grant agreement no. 711859 to C.C and no. 734276 to A.C.and S.K. Additional funding was received from the Ministry of Science and Higher Education of Poland for the project no. 734276in the years 2017–2020 (agreement no. 3854/H2020/17/2018/2)and for the implementation of the international co-financed project no. 711859 in the years 2017–2021.

International audience; Very fine molecular arrangement of cholesteric liquid crystal (CLC), can be compressed by applying an external electric field in the liquid crystal cell geometry. This enables very fine tuning of the wavelength of the reflected light. The compression of the periodic dielectric molecular arrangement continues till the chiral energy density meets its repulsive-type excluded volume interaction and hence the corresponding resonant wavelength jumps back to the original spectral position. Experimentally, the tuning range is observed to be highly affected by the concentration of the chiral dopant in the mixture. Analytically, it is shown that, use of chiral molecules with higher helical twisting power (HTP) can reduce the concentration of the chiral dopant for a desired pitch length in visible range and hence, the spectral tuning can be exploited over the entire visible range.

Liquid–liquid equilibrium (LLE) data for N-butylpyridiniumtetrafluoroborate ([BPy]BF 4 ) + sulfate salt + H 2 O systems have been determined experimentally at T = (298.15, 308.15, and 318.15) K. The binodal curves agree with an empirical nonlinear expression developed by Merchuk, while the tie-line data are described by the Othmer–Tobias, Bancroft, two-parameter, and Setschenow-type equations. Factors, such as salts, that affect the binodal curves are also studied. The effective excluded volume (EEV) values obtained from the bimodal models for the two systems were determined, and the salting-out capabilities of different salts follow the order of Na 2 SO 4 > (NH 4 ) 2 SO 4 , which may be related to the Gibbs free energy of hydration of the ions (△G hyd ). Furthermore, the tie line is also discussed to evaluate the phase separation capabilities of the investigated systems. These reported data provide a significant contribution to the further study of extraction processes using ionic liquids (ILs).

Ion separation and ion selectivity inside spherical cavities are studied within the framework of the density functional theory. Results show that, at lower electric potentials and depending on cavity size, counter ions accumulate at the wall to form a shell around the co ions that prefer to aggregate in the middle of the cavity. This gives rise to the formation of separated phases of co ions and counter ions inside the spherical cavity. Depending on cavity size, these phases convert to a nearly single phase of counter ions with increasing electric potential. In this situation, small spherical cavities could be exploited as a counter ion selector tool. Our study also shows that counter ion selectivity readily occurs at lower, rather than higher, concentrations of electrolytes. For electrolytes with monovalent co ions, the (+1: −1) electrolytes exhibit a better selectivity than the (+1: −2) ones at low electric potentials. Also the selective counter ion adsorption occurs at lower electric potential when the difference between size of counter ions and co ions becomes larger. The observed selectivity is the result of confinement effect, electrostatic interaction, and excluded volume. Our study of the average cavity density versus electric potential shows an intersection for different plots related to cavities of different sizes. This intersection point reveals two different behaviors of average cavity density with cavity size on the two sides of the intersection point. In other words, average cavity density increases (decreases) with cavity size for those electric potentials which are lower (higher) than that of the intersection point but it becomes independent of cavity size for the electric potential of the intersection point.

The equivalence of the thermodynamic description of a system comprised of interacting particles by a collection of non-interacting clusters of these particles has been a long-standing issue in statistical mechanics since the pioneering work of Frenkel, Band, and Mayer. Woolley derived the association constants for the postulated chemical reactions of individual particles (monomers) to dimers, trimers, and so on, by matching the pressure of the mixture of non-interacting clusters of different sizes to the virial expansion of the interacting (but non-associating) original particles. The association constants determined in this way, however, turn out to become negative in certain temperature ranges, leading to negative concentrations of clusters. Hill subsequently resolved this problem by introducing the additional requirement that the kinetic energy had to be less than the potential energy in order to have a bound state; with this definition of a cluster, association constants remain strictly positive. Here, we present an alternative approach to avoid negative association constants by correctly incorporating the excluded volume of a cluster that results in a reduction of the space available to the non-interacting clusters of particles, without the need to define bound states. For concreteness, we study the cases of square-well fluids in one, two, and three dimensions. The mass-action laws that govern the association reactions among ideal gases formulated by Woolley are thus augmented by activity coefficients for hard rods, disks, and spheres, respectively, which account for the residual interactions caused by the excluded volume of the particles. We thereby identify the condition for obtaining a formally exact theory of geometrical clusters.

Liquid–liquid equilibrium (LLE) data for quaternary systems containing ethanol + 2-propanol + salt [(NH 4 ) 2 SO 4 /Na 2 SO 4 ] + water were experimentally determined at 308.15, 318.15 and 328.15 K. Binodal curves were fitted to four empirical nonlinear equations, whereas tie-lines were fitted to the Setschenow-type equation and its temperature-dependent expression as well as another two-parameter equation. All of the models were successfully correlated with the experimental data. Factors affecting the phase-forming abilities of the investigated systems were also studied, such as the temperature, mass fraction of ethanol in the alcohol mixture and type of salt. The effective excluded volume values for the studied systems also were determined to evaluate the phase separation abilities of investigated systems. These data can be used for the development and design of extraction processes utilizing such systems.

In water, poly(N-isopropylacrylamide) (PNIPAM) is in a soluble coil state below the lower critical soluble temperature (LCST) but in an insoluble globule state above LCST. Namely, as the temperature decreases, PNIPAM exhibits a globule-to-coil transition at LCST~305 K. We generate structural ensembles of coil and globule states by all-atom molecular dynamics simulations conducted at 273 and 323 K, respectively. We then calculate a variety of energetic and entropic components of thermodynamic quantities of the two states at the two temperatures using our recently developed, accurate statistical-mechanical method for solute hydration where molecular models are employed for water and the PNIPAM structure is taken into account at the atomic level. We identify the physical factors driving or opposing the transition and evaluate their relative magnitudes and temperature dependences. The presence of PNIPAM generates an excluded volume (EV) which is inaccessible to the centers of water molecules in the entire system. The presence of a water molecule also generates an EV for the other water molecules with the result that all of the water molecules are entropically correlated, causing water crowding. The globule state, where the EV is smaller and water crowding is less significant, is more favored in terms of the translational, configurational entropy of water. This effect always opposes the globule-to-coil transition. At low temperatures, however, this effect becomes significantly weaker, yielding to the factors driving it. The mechanism of the transition is physically the same as that of cold denaturation of a protein.

The effects associated with the migration of charged particles in solution, driven by an external pressure gradient and/or electric field, are known as electrokinetic phenomena. Among these are the electroosmotic volume flux, capillary conductance, streaming potential, and the apparent electroviscosity. In this work we study the electrokinetic properties of an electrolyte solution confined in a slit-like nanopore. The pore is made up of two charged parallel plates and the fluid is considered through the restricted primitive model electrolyte. The hypernetted chain/mean spherical approximation (HNC/MSA) and Poisson–Boltzmann theory are used to obtain the equilibrium ionic concentration profiles inside the nanopore, thus, the electrokinetic coefficients are calculated by means hydrodynamics equations. The considered monovalent electrolytes are characterized by different ionic diameters and they are at fixed molar concentration. It is exhibited that the electrokinetic coefficients are strongly sensitive to the ionic size, especially for small pore widths. Important variations of electrokinetic coefficients are produced for large ionic diameters associated with their enhanced excluded volume. The quantitative differences between HNC/MSA and Poisson–Boltzmann theories are discussed throughout the paper.

In this paper, we highlight the relevance of our renovated method for investigating molecular to diffusion dynamics and static structures of aqueous micellar solutions, in which we combine small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS) with dielectric relaxation spectroscopy (DRS). Our unique SAXS/DLS/DRS approach, applied to aqueous solutions of non-ionic amphiphile, poly(oxyethylene) cholesteryl ether, clarifies how hydrated water molecules, which exhibit ca. 3–4 times slower collective reorientational dynamics than bulk water, contribute to the packing fraction, or the effective volume fraction of the non-ionic micelles. The results demonstrate that the excluded volume of the micelles involving the hydrated water molecules determines the osmotic compressibility of the uncharged systems manifested in the extrapolated structure factor to zero scattering vector, S ( q → 0). The data further prove that the concentration dependence of the collective diffusion constant measured by DLS can fully be explained only when the excluded volume of the hydrated water molecules is properly accounted for.

The particular low-temperature variant of fluctuational EOS with constant excluded volume b and temperature-dependent-coefficient a(T) is applied to water and two imidazolium-based ionic liquids: [bmim][PF6] and [pmmim][Tf2N]. The former demonstrates the regular linear correlations of liquid density ρ(T) (decreasing) and isobaric heat capacity (increasing) at atmospheric pressure P = 101,325 kPa. The latter has some trend to density maxima near the melting point similar to low-temperature density anomaly in water. Such a behavior, if it exists in ionic liquids, implies the reentrant spinodal form with the presence of minimum at negative pressures in the range from triple up to normal boiling point. Only the above input data have been used to predict qualitatively both types (regular and anomal) of a hypothetical gas–liquid phase diagram for ionic liquids and water. To control the quantitative results one needs the thermodynamically consistent choice of the excluded volume coefficient b0. The method developed for this aim can be useful to predict the phase diagram and solubility of low-molecular substances in imidazolium-based ionic liquids.

The Dynamic Lattice Liquid (DLL) model for molecular rearrangements in liquids is discussed in application to both simple supercooled liquids and polymer melts. It is shown, that the model is able to reproduce a broad class of various temperature dependencies of relaxation times, lying between the extremal cases represented by the Arrhenius relation on one and by the Vogel-Fulcher-Tamman (VFT) relation on the other hand. Rates of rearrangements are considered as being controlled by thermal activation with activation energy barriers dependent on local density. Various dependencies of the activation energy barriers on local density are examined. All cases are based on the uniform microscopic picture of cooperative molecular rearrangements operating in a dense system under conditions of the excluded volume and continuity of the system. The model is implemented as a simulation algorithm, which is used to describe dynamic properties of liquids and polymer melts. Simulation results obtained for systems representing simple liquids as well as linear polymers, multiarm star polymers and microgels are presented. An analogy in the dynamic behavior between the low molecular liquids and melts of macromolecules with complex compact architectures is discussed.

The parameters that enter excluded volume theory, namely the persistence length and the excluded volume between segments, depend in a qualitatively obvious way on the polyelectrolyte charge and the solution ionic strength. However, a quantitative understanding is quite difficult to achieve for realistic models of flexible chains. Therefore a simulation of these parameters was performed for small sections of polyelectrolyte chains and the results were incorporated into excluded volume theory. The theory was suitably modified to take into account the fact that a segment is a finite rather than an infinitesimal fraction of the whole chain, as is usually assumed. Excellent agreement was found between the predicted expansions of whole chain dimensions and simulation results.