Effective static and high-frequency viscosities of concentrated suspensions of soft particles

We obtain an analytic expression that allows to determine the static η and high-frequency η(∞) viscosities as function of the volume fraction φ of a concentrated suspension of soft spherical particles in a liquid of viscosity η(0). The particles consist of a hard core of radius a covered by a porous layer of thickness d. Suspensions of hard spheres and homogeneous porous particles are limiting cases of the model. The proposed expression incorporates the results for the intrinsic viscosity obtained on the basis of a cell model [H. Ohshima, Langmuir 26, 6287 (2010)] into a recently obtained relation for the effective viscosity of concentrated colloidal suspensions [C. I. Mendoza and I. Santamari?a-Holek, J. Chem. Phys. 130, 044904 (2009); J. Colloid. Interface Sci. 346, 118 (2010)]. In this model, the correlations between the particles due to crowding effects are introduced through an effective volume fraction φ(eff) which is then used as integration variable in a differential effective medium procedure. The final expression is simple, accurate, and allows to collapse all the data in a universal master curve that is independent of the parameters characterizing the system. The only difference between the static and high-frequency cases is that in the later case φ(eff) also incorporates hydrodynamic interactions arising from the so-called relaxation term. We have tested the accuracy of our model comparing with experimental results for spherical polymeric brushes and simulations for the high-frequency viscosity of homogeneous porous particles. In all cases the agreement with the data is extremely good.     

A purely geometric derivation of the scaled particle theory formula for the work of cavity creation in a liquid

A very simple statistical geometric approach is devised that allows the derivation of a formula for the work to create a spherical cavity in a liquid consisting of spherical molecules in the small cavity size limit. This formula exactly corresponds to the general expression for the work of cavity creation provided by scaled particle theory. The origin of the success of the present statistical geometric approach needs further insight.     

Modeling of oxygen transport and cell killing in type-II photodynamic therapy

Photodynamic therapy (PDT) provides an effective option for treatment of tumors and other diseases in superficial tissues and attracts attention for in vitro study with cells. In this study, we present a significantly improved model of in vitro cell killing through Type-II PDT for simulation of the molecular interactions and cell killing in time domain in the presence of oxygen transport within a spherical cell. The self-consistency of the approach is examined by determination of conditions for obtaining positive definitive solutions of molecular concentrations. Decay constants of photosensitizers and unoxidized receptors are extracted as the key indices of molecular kinetics with different oxygen diffusion constants and permeability at the cell membrane. By coupling the molecular kinetics to cell killing, we develop a modeling method of PDT cytotoxicity caused by singlet oxygen and obtain the cell survival ratio as a function of light fluence or initial photosensitizer concentration with different photon density or irradiance of incident light and other parameters of oxygen transport. The results show that the present model of Type-II PDT yields a powerful tool to quantitate various events underlying PDT at the molecular and cellular levels and to interpret experimental results of in vitro cell studies.     

A New Version of the Cell Method of Determining the Suspension Viscosity

The spherical cell method was used to describe the rotational motion of suspension particles with fixed centers of mass. This provided a more natural matching of the symmetry of hydrodynamical flows in the system to the shape of the cell. The question of choosing an optimal radius of the cell was considered. It was shown that, in the framework of the new approach, experimental data on the average viscosity of suspensions are reproduced with a high degree of accuracy up to the value of the specific volume of particles equal to 0.45.     

Inverse Filtering and Linear Prediction as New Analytical Approaches to Analyze the Change of Absorbance Spectra in Visible Spectroscopy: in vivo Study of Protochlorophyll(ide) Phototransformation

Abstract— The common approach of analyzing spectra by derivation is known to be inadequate for kinetic studies in visible spectroscopy (R. I. Sharger, Photochem. Photobiol. 38, 615-617, 1983) because the side-lobes height introduces artifacts and reduces readability in three-dimensional graphic representation. In this study we present for the first time a parametric method that enables the use of inverse filtering and linear prediction for kinetic investigation in visible spectroscopy in cell biology studies. The protochlorophyll(ide) phototransformation at room temperature (295 K) was used to demonstrate the performance of this analytical approach. The change of absorption spectra in etiolated barley leaves was analyzed after being illuminated by a 50 ms flash.     

Rheology of aqueous carbon black dispersions

The interaction of carbon black with an acrylic resin has been investigated by rheology. Two carbon blacks, with similar particle size and surface characteristics but quite different particle morphologies, have been examined. These are somewhat arbitrarily denoted as "spherical" and "fractal" as shown by small-angle neutron scattering (SANS) and ultrasonic spectroscopy studies. In the absence of polymer, stable aqueous dispersions could not be obtained. Stable dispersions could be obtained, however, upon addition of polymer to a level corresponding to a ratio of 50 mg of polymer per 13 m2 (+/- m2) of surface area (i.e., 15 wt% particles). These stable dispersions exhibit flow typical of concentrated dispersions-Newtonian behavior up to some apparent "yield" or critical value, above which pronounced shear thinning is observed. The critical stress increases with increasing polymer concentration. When a significant amount of nonadsorbed polymer is also present, a second Newtonian plateau is superimposed on the shear-thinning behavior. This feature is observed for both particle types but is more pronounced for the fractal particle. When there is little or no nonadsorbed polymer, the viscosity of the fractal particle dispersions is greater than the viscosity of the spherical particle dispersions. At low polymer concentrations, the dispersions are predominantly viscous at low shear stresses. The phase angle decreases significantly over a narrow shear stress range and the rheology tends to more elastic behavior. At higher shear stresses, the dependence on particle morphology is weak.     

球胶体颗粒之间相互作用能的求解

根据线性迭加近似方法,定义了一个修正电位项,较详细地推导出用于中等电位条件下球形胶体颗粒相互作用能和力的公式,该公式较为简单、实用,然而,对其所做的改进主要是针对相互作用能而不是力,对其原因也作了简单的讨论.     

Role of Joule heating in dispersive mixing effects in electrophoretic cells: convective-diffusive transport aspects

This contribution addresses the problem of solute dispersion in a free convection electrophoretic cell for the batch mode of operation, caused by the Joule heating generation. The problem is analyzed by using the two-problem approach originally proposed by Bosse and Arce (Electrophoresis 2000, 21, 1018-1025). The approach identifies the carrier fluid problem and the solute problem. This contribution is focused on the latter. The strategy uses a sequential coupling between the energy, momentum and mass conservation equations and, based on geometrical and physical assumptions for the system, leads to the derivation of analytical temperature and velocity profiles inside the cell. These results are subsequently used in the derivation of the effective dispersion coefficient for the cell by using the method of area averaging. The result shows the first design equation that relates the Joule heating effect directly to the solute dispersion in the cell. Some illustrative results are presented and discussed and their implication to the operation and design of the device is addressed. Due to the assumptions made, the equation may be viewed as an upper boundary for applications such as free flow electrophoresis.     

Rotational viscosity of viscoelastic magnetic fluid

The influence of a magnetic field on the viscosity of dilute dispersion of spherical magnetohard particles in viscoelastic matrix, the Maxwell liquid with a single relaxation time, is studied. Calculations are performed on the basis of the equation of rotational diffusion derived previously by the authors. It is shown that the effective viscosity of magnetic fluid decreases in the presence of a field. This unexpected result is clearly explained in physical terms.     

Engineering strength, porosity, and emission intensity of nanostructured CdSe networks by altering the building-block shape

The effect of primary particle shape on the porosity, mechanical strength, and luminescence intensity of metal chalcogenide aerogels was probed by comparison of CdSe aerogels prepared from spherical and rod-shaped particles. Rod-shaped particles yield aerogels with polymeric morphologies in contrast to the colloidal morphology obtained from spherical particles. Relative to the colloidal analogues, the polymeric CdSe aerogels exhibit twice the surface area, a doubling of the complex viscosity for 5 wt % aerogel-PDMS composites, and a 25-fold increase in emission intensity. Altering the shape of the building block from which nanostructured networks are assembled is an effective way to tune the basic properties of metal chalcogenide semiconducting aerogels.     

Stresses inside critical nuclei

The usual derivation of classical nucleation theory is inappropriate for crystal nucleation. In particular, it leads to a seriously flawed estimate of the pressure inside a critical nucleus. This has consequences for the prediction of possible metastable phases during the nucleation process. In this paper, we reanalyze the theory for crystal nucleation based on the thermodynamics of small crystals suspended in a liquid, due to Mullins (J. Chem. Phys. 1984, 81, 1436). As an illustration of the difference between the classical picture and the present approach, we consider a numerical study of crystal nucleation in binary mixtures of hard spherical colloids with a size ratio of 1:10. The stable crystal phase of this system can be either dense or expanded. We find that, in the vicinity of the solid-solid critical point where the crystallites are highly compressible, small crystal nuclei are less dense than large nuclei. This phenomenon cannot be accounted for by either classical nucleation theory or by the Gibbsian droplet model.     

Rheology of dilute and semidilute suspensions of spherical polyelectrolyte brushes

The viscosity, η, of dilute aqueous suspensions of spherical polyelectrolyte brushes is discussed. The spherical polyelectrolyte brushes consist of a solid polystyrene core of 100-nm diameter onto which linear poly(acrylic acid) chains are grafted. The relative viscosity, η/η_S (η_S is the viscosity of the solvent) of these suspensions is studied as a function of shear rate in the presence of different amounts of added salt. A marked dependence on shear rate is found, in particular when going to higher concentrations. Extrapolation to zero shear rate leads to the relative zero-shear viscosity, η₀/η_S, which can be described in terms of an effective volume fraction, φ_eff, for all salt concentrations under consideration. Moreover, the hydrodynamic radii derived from φ_eff coincide with data obtained by dynamic light scattering in the infinitely dilute regime. Data taken at higher concentrations point to a shrinking of the brush layer owing to mutual interaction.     

Damping by bulk and shear viscosity of confined acoustic phonons for nanostructures in aqueous solution

A nanoparticle in aqueous solution is modeled as a homogeneous elastic isotropic continuum sphere in contact with an infinite viscous compressible Newtonian fluid. The frequencies and damping of the confined vibrational modes of the sphere are calculated for the material parameters of a CdSe nanoparticle in water and a poly(methyl methacrylate) nanosphere in water. Although the effects of viscosity are found to be negligible for macroscopic objects, for nanoscale objects, both the frequency and damping of the vibrational modes are significantly affected by the viscosity of the liquid. Furthermore, both shear viscosity and bulk viscosity play an important role. A model of the spherical satellite tobacco mosaic virus consisting of outer solid layers with a water core is also investigated, and the viscosity of the water core is found to significantly damp the free vibrational modes. The same approach can be applied for nonspherical geometries and also to viscoelastic nanoparticles.     

Bubble shapes and orientations in low Re simple shear flow

We present measurements of shape and orientation of air bubbles in a viscous Newtonian fluid deformed by simple shear. The apparatus is a variation of the "parallel band" device developed by G. I. Taylor. Previous experimental studies on low viscosity ratio, low Reynolds number (Re < 1) bubble deformation have focussed on either small or large deformations (mostly small deformation) and have only qualitatively examined the orientation of bubbles except for small deformations. Our data set spans both the theoretical small deformation and high deformation limits. With these data we confirm theoretical relationships and assess the range of capillary numbers (Ca) over which theoretical relationships for shape and orientation of bubbles are appropriate. We also examine the geometry of deformed bubbles as they relax to a spherical shape once shear stresses are removed. Our data indicate that for extremely small Reynolds numbers and viscosity ratios, the small deformation theoretical relationship first developed by Taylor, is a good approximation for Ca<0.5. The large deformation results for both shape and bubble orientation derived by Hinch and Acrivos agree with our data for Ca>1 and Ca>0.5, respectively.     

Thermal analysis for heat transfer enhancement in electroosmosis-modulated peristaltic transport of Sutterby nanofluids in a microfluidic vessel

Viscosity plays a crucial role in the flow and heat transfer process of nanofluids. To effectively calculate and predict the changing characteristics of nanofluids viscosity, this study presents a theoretical model combining the static interface layer and dynamic Brownian motion mechanisms of spherical nanoparticles for water-based Newtonian nanofluids. The model describes the reasonable dependences of nanofluids viscosity on physical properties of nanoparticles (density, volume fraction, size) and base fluid (temperature, viscosity, density). Taking four kinds of typical water-based Newtonian nanofluids containing spherical oxide nanoparticles (Al₂O₃, CuO, SiO₂ and TiO₂) as examples, the prediction performance of different viscosity models is analyzed in detail. From the comparison studies, it is demonstrated that the new viscosity model developed in this paper can exhibit better prediction performance than many well-known theoretical models and empirical correlations. Not only do the predicted results of model agree well with the experimental data from various studies, but also the effects of different factors are reflected effectively.

     

对球状液滴拉普拉斯公式热力学推导方法的讨论

本文针对球状液滴拉普拉斯公式热力学推导方法进行了讨论分析。首先从界面热力学基本方程的建立方法和界面热力学基本方程中作为偏微分的压强的数学定义两个角度进行分析,得出了液滴界面热力学基本方程中,压强为与之平衡的外界气体压强。另外,从实际发生的物理过程来看,本文所质疑的球状液滴拉普拉斯公式的热力学推导方法采用无外力做功时液滴体积增大d V的过程是明显违反热力学第一定律的。     

Precipitated droplets in-situ cross-linking polymerization and its applications

A novel, green and effective approach to fabricate uniform functional spherical polymer particles remains a huge challenge. Herein, we present a novel one-pot approach superior to traditional precipitation polymerization, called precipitated droplets in-situ cross-linking (PDIC) polymerization, by which uniform particles are fabricated on large scale without any toxic organic solvents or stabilizers. With this approach, functional spherical polymer particles can be fabricated continuously only relying on gravity, and the preparation process is thus super-fast. For example, polyacrylic acid (PAA) hydrogel particles with ultra-high adsorption capacity are fabricated within only 60 s. Moreover, we have successfully fabricated different functional hydrogel particles, including anticoagulant, reinforced and bactericidal particles, based on the monomers of 2-acrylamide-2-methylpropanesulfonic acid (AMPS), acrylamide (AM) and [2-(methacryloyloxy)ethyl]trimethylammonium chloride (DMC), respectively. This approach has several advantages: (i) the technology is green; (ii) the size and porosity of the particles can be well-controlled; (iii) various functional spherical hydrogel particles can be fabricated by using corresponding monomers. More importantly, this approach fits the commercialization of functional hydrogel particles on demand.     

Vapour pressures,densities, and viscosities of the aqueous solutions containing (triethylene glycol or propylene glycol) and (LiCl or LiBr)

In this work, new results for density, viscosity, and vapour pressure of (triethylene glycol or propylene glycol) in H₂O with LiCl or LiBr systems over temperatures ranging from 303.15 K to 343.15 K are presented. For each ternary system, four systems of which (4 to 25) mass% salt mixed with various glycols (50 to 80) mass% were studied. Incorporated with the pseudo-solvent approach, a vapour pressure model based on the mean spherical approximation for aqueous electrolyte solutions was used to represent the measured vapour pressure of the investigated systems. The present density and viscosity results were also correlated as a function of temperature and composition. The correlations yield satisfactory results. Compared to the conventionally used liquid desiccants, the vapour pressures of the systems studied yield smaller values of vapour pressures. The properties presented in this work are, in general, of sufficient accuracy for most engineering-design calculations.     

Cavity ring-down spectroscopy measurement of single aerosol particle extinction. II. Extinction of light by an aerosol particle in an optical cavity excited by a cw laser

The authors present an analytical derivation of the scattered power from a spherical, homogeneous, nonabsorbing particle in a plane standing wave. The scattered power changes significantly with the position of the particle with respect to the peaks and nodes of the standing wave, even for particles whose diameters are many times the wavelength of the light. The analysis is applicable to continuous-wave cavity ring-down spectroscopy on aerosol particles, and the structure of the standing wave is expected to affect both the measured ring-down time and the shape of the ring-down trace. The dependence of the extinction on the phase of the standing wave at the location of the particle is captured in a parameter zeta which connects the current treatment to standard Mie scattering theory. Methods for calculating zeta are presented.