Turbidity Spectra Research Articles

Effect of Polyphenylsulfone and Polysulfone Incompatibility on the Structure and Performance of Blend Membranes for Ultrafiltration.

This study deals with the modification of polyphenylsulfone ultrafiltration membranes by introduction of an incompatible polymer polysulfone to the polyphenylsulfone casting solution to improve the permeability. The correlation between properties of the blend polyphenylsulfone/polysulfone solutions and porous anisotropic membranes for ultrafiltration prepared from these solutions was revealed. The blend polyphenylsulfone/polysulfone solutions were investigated using a turbidity spectrum method, optical microscopy and measurements of dynamic viscosity and turbidity. The structure of the prepared blend flat sheet membranes was studied using scanning electron microscopy. Membrane separation performance was investigated in the process of ultrafiltration of human serum albumin buffered solutions. It was found that with the introduction of polysulfone to the polyphenylsulfone casting solution in N-methyl-2-pyrrolidone the size of supramolecular particles significantly increases with the maximum at (40–60):(60:40) polyphenylsulfone:polysulfone blend ratio from 76 nm to 196–354 nm. It was shown that polyphenylsulfone/polysulfone blend solutions, unlike the solutions of pristine polymers, are two-phase systems (emulsions) with the maximum droplet size and highest degree of polydispersity at polyphenylsulfone/polysulfone blend ratios (30–60):(70–40). Pure water flux of the blend membranes passes through a maximum in the region of the most heterogeneous structure of the casting solution, which is associated with the imposition of a polymer-polymer phase separation on the non-solvent induced phase separation upon membrane preparation. The application of polyphenylsulfone/polysulfone blends as membrane-forming polymers and polyethylene glycol (Mn = 400 g·mol−1) as a pore-forming agent to the casting solutions yields the formation of ultrafiltration membranes with high membrane pure water flux (270 L·m−2·h−1 at 0.1MPa) and human serum albumin rejection of 85%.

Structure of poly(acrylic acid), poly(methacrylic acid) and gelatin solutions

The structure of poly(acrylic acid) (PAA), poly(methacrylic acid) (PMAA), and gelatin solutions are studied using the turbidity spectrum and dynamic light scattering methods. The effect of the polymer concentration and pH value of the solutions on the structure and optical properties of polyelectrolyte solutions are investigated. The size of light scattering particles in different systems is calculated. An increase in size was observed with increasing polymer concentration for the PAA solution. The dependence of the particle sizes on concentration is described by a curve with maxima for the PMAA solution. The sizes of the light scattering particles in solutions are compared with data on quality of solvents. The gelation mechanism of gelatin in water solutions was investigated in the wide range of concentration and at different рН values.

Modeling TiO2׳s refractive index function from bulk to nanoparticles

In recent decades, the use of nanomaterials has become very common. Different nanomaterials are being used in over 1600 consumer products. Nanomaterials have been defined as having at least one dimension in the range of 1−100nm. Such materials often have unique properties. Despite some warnings of applying bulk optical constants for nano size materials, stated already in 1980s, bulk constants are still commonly used in the light scattering measurements of nano size particles. Titanium dioxide is one of the materials that is manufactured and used as an engineered nanomaterial in increasing quantities. Due to the aforementioned facts, it is quite crucial for successful research and production of nanoparticles to find out the dependence of the refractive index function (RIF) of the material on its crystal size. We have earlier performed several ab initio computations for obtaining the dependence of the RIF of TiO2 on the crystal or on the cluster size, for particles of size up to ca. 2nm. Extending the calculations to greater sizes has turned out to be infeasible due to the unbearable increase in computational time. However, in this study we show how the crystal-size-dependent-RIF (CS-RIF), for both rutile and anatase can be modeled from measured extinction or turbidity spectra of samples with varying crystal and particle sizes. For computing the turbidity spectrum, we constructed a model including primary crystals whose distributions were parameterized by mean and standard deviation, and also including aggregates consisting of mean sized primary particles, parameterized just by mean aggregate size. Mainly because of the long computing times Mie calculation was used in the computation of extinction spectra. However, in practical process applications, the obtained RIF will be used together with the T-matrix method. We constructed the RIFs used in the model using generalized oscillator model (GOM) as expanded to crystal size dependence. The unknown parameters of the model were solved using nonlinear least squares estimation. When the crystal size becomes smaller than the bulk size the shape of the estimated CS-RIFs reveal two distinct regions for both rutile and anatase. In the first region, starting apparently already from ca. 200nm, the height of both the real part and the imaginary part of CS-RIF decreases on crystal diameter. However, the band gap remains constant. In the second region, starting when the crystal diameter is decreased to ca. 3nm, a blue shift starts to increase the band gap. The band gap dependence on crystal size is quite consistent with the existing experimental values. Consequently, it is of great importance to use CS-RIF in light scattering measurements for nanoparticle size determination. Neglecting this, the smaller particles in the size distribution will have too small values, already for sub-micrometer particles, naturally distorting also the mean value. To our knowledge, this is the first time ever that a CS-RIF from bulk to 1nm size is determined for any material.

Structure of Crystallizable Polymer Solutions

Visually transparent solutions of crystallizable polymers in wide concentration and temperature ranges contain supramolecular particles which are fragments of the most perfect crystallites of condensed polymer. Though the fraction of these particles is usually with in 0.001-0.1wt % of the total polymer, their presence in a solution of macromolecules severely affects its physicochemical and technological properties (performance) and complicates (or even does not allow) the application of structurally-sensitive research techniques (e.g. lights cattering, dynamic birefringence, etc.). The parameters of the first-level supramolecular particles (just after visual dissolution) depend on the conditions of dissolution, storage, and the preliminary treatment temperature of the polymer. In wide polymer concentration and temperature ranges, a second level of the supramolecular particles ensemble is formed, with characteristic features of crystallization. From the formation rate of the second-level supramolecular particles, a microliquidus curve for them can be plotted. The paper presents data for the poly (vinyl alcohol) + water system which lack the area of liquid-liquid phase separation. Supramolecular particles parameters (average sizes, numerical and mass-volume concentration) were determined by means of the turbidity spectrum method.

Структура растворов кристаллизующихся полимеров

Visually transparent solutions of crystallizable polymers in wide concentration and temperature ranges contain supramolecular particles which are fragments of the most perfect crystallites of condensed polymer. Though the fraction of these particles is usually with in 0.001-0.1wt % of the total polymer, their presence in a solution of macromolecules severely affects its physicochemical and technological properties (performance) and complicates (or even does not allow) the application of structurally-sensitive research techniques (e.g. lights cattering, dynamic birefringence, etc.). The parameters of the first-level supramolecular particles (just after visual dissolution) depend on the conditions of dissolution, storage, and the preliminary treatment temperature of the polymer. In wide polymer concentration and temperature ranges, a second level of the supramolecular particles ensemble is formed, with characteristic features of crystallization. From the formation rate of the second-level supramolecular particles, a microliquidus curve for them can be plotted. The paper presents data for the poly (vinyl alcohol) + water system which lack the area of liquid-liquid phase separation. Supramolecular particles parameters (average sizes, numerical and mass-volume concentration) were determined by means of the turbidity spectrum method.

Analysis of the Stability of Metal Working Fluid Emulsions by Turbidity Spectra

AbstractThe physical stability of emulsions can be related to changes in the droplet size distribution over time. Stability control of emulsions used as metal working fluids is an important factor for the machining industry due to the decreased performance of aged and broken emulsions. Results of turbidimetric spectra measurements of metal working fluids for process control purposes and emulsion stability monitoring are discussed. Metal working emulsions were artificially destabilized by admixing salts which resulted in droplet coagulation. The destabilization process was investigated by measuring the droplet size distribution and the turbidity spectra over time. The results were evaluated based on quantitative criteria proposed in the literature. The applicability of these criteria to evaluate metal working fluids during machining operations is discussed.

Features of the Structure and Rheology of Nitrocellulose Solutions

The latest methods – rotation viscometry, IR spectroscopy, NMR spectroscopy, gel permeation chromatography, and the turbidity spectrum method – were used to investigate the structural, rheological, and molecular properties of cellulose nitrate solutions. Results clarified the laws governing the structure formation in medium- and semidilute cellulose nitrate solutions.

Influence of Cations on Aggregation Rates in Mg-Montmorillonite

AbstractCritical-zone reactions involve inorganic and biogenic colloids in a cation-rich environment. The present research defines the rates and structure of purified Mg-montmorillonite aggregates formed in the presence of monovalent (K+) and divalent (Ca2+, Mg 2+) cations using light-extinction measurements. Time evolution of turbidity was employed to determine early-stage aggregation rates. Turbidity spectra were used to measure the fractal dimension at later stages. The power law dependence of the stability ratios on cation concentration was found to vary with the reciprocal of the valence rather than the predicted reciprocal of valence-squared, indicating that the platelet structure may be a factor influencing aggregation rates. The critical coagulation concentrations (CCC) (3 mM for CaCl2, 4 mM for MgCl2, and 70 mM for KCl) were obtained from the stability ratios. At a later time and above a minimal cation concentration, turbidity reached a quasi-stable state, indicating the formation of large aggregates. Under this condition, an approximate turbidity forward-scattering correction factor was applied and the fractal dimension was determined from the extinction spectra. For the divalent cations, the fractal dimensions were 1.65 ± 0.3 for Ca2+ and 1.75 ± 0.3 for Mg2+ and independent of cation concentrations above the CCC. For the monovalent cation, the fractal dimension increased with K+ concentration from 1.35 to 1.95, indicating a transition to a face-to-face geometry from either an edge-to-edge or edge-to-face orientation.

Phase Analysis of the Cellulose Triacetate-Nitromethane System

A comprehensive study was made on the cellulose triacetate-nitromethane system to explore its phase separation within ranges 2–25 wt.% and−5÷+80°Cby means of polarization light and electron microscopy, the turbidity spectrum method, differential thermal and X-ray analyses, and rheological techniques. The physical state of the polymer was identified within the phase coexistence boundaries on the phase diagram which included three types of phase separation (amorphous (with a UCST atTcr=57∘Candccr=7.3 wt.%), crystal, and liquid crystal). The boundaries of the regions determining the coexistence of the liquid crystal (LC) and the partly crystal phase were found to be inside the region of amorphous liquid-liquid phase separation. For cellulose ester-solvent systems, this state diagram is the first experimental evidence for the possibility of coexistence of several phases with amorphous, LC, and crystal polymer ordering.

Turbidity Spectroscopy for Characterization of Submicroscopic Drug Carriers, Such as Nanoparticles and Lipid Vesicles: Size Determination

To apply UV/Vis spectrometry for characterization of submicroscopic drug carriers, such as nanoparticles and lipid vesicles. We first investigated theoretically, within the framework of the Rayleigh-Gans-Debye approximation (RGDA), parameters affecting turbidity spectrum, τ(λ), of nanosized light scatterers. We then analyzed, within the framework of the RGDA, experimental turbidity spectra (λ = 400-600 nm) of extruded unilamellar vesicle (70 nm ≤ 2r ≤ 110 nm) suspensions to derive vesicle size, using dynamic light scattering results for comparison. We similarly studied the preparations polydispersity and lamellarity and monitored vesicle size changes. Turbidimetry suffices for accurate, fast, and viscosity-independent characterization of submicroscopic particles. Analysis of turbidity spectra, or more precisely wavelength exponent spectra (derivatives of logarithmic turbidity spectra), yielded similar average radii (r = 54.2 ± 0.2 nm; 46.0 ± 0.2 nm; 35.5 ± 0.1 nm) as dynamic light scattering (r = 55.9 ± 1.5 nm; 46.1 ± 0.4 nm; 36.1 ± 0.4 nm). Both methods also revealed similar suspension polydispersity and cholate-induced vesicle size changes in a few nanometer range. Despite its experimental simplicity, the widely accessible turbidimetric method provides accurate size values and is suitable for (continuous) monitoring size stability, or sameness, of submicroscopic drug carriers.

Spectroturbidimetric determination of the sizes of poly(ethylene glycol)-induced insoluble immune complex particles

A spectroturbidimetric method adaptable to routine clinical practice is proposed for estimating the sizes of insoluble immune complex particles in poly(ethylene glycol) (PEG)-treated blood serum. In order to determine average particle diameter d from wavelength exponent w (the exponent in the power approximation of turbidity spectra), calibration is performed relative to polystyrene latexes, d (nm) = exp(8.2 − 0.9w). To optimize the method, the influence of PEG concentration and antigen/antibody ratio on the average sizes of formed particles is studied by the example of a model antigen (tetanic toxoid)-antibody (human antitoxoid γ-globulin) system. The optimized procedure is used to analyze human blood serum. It is shown that, in the presence of 3% PEG, the average particle sizes and volumes of the insoluble immune complexes are significantly different in healthy individuals and patients with rheumatoid arthritis. These differences are in significant correlation with the rheumatoid factor level determined in sera through the standard latex agglutination test.

Determination of the Size, Concentration, and Refractive Index of Silica Nanoparticles from Turbidity Spectra

The size and concentration of silica cores determine the size and concentration of silica/gold nanoshells in final preparations. Until now, the concentration of silica/gold nanoshells with Stober's silica core has been evaluated through the material balance assumption. Here, we describe a method for simultaneous determination of the average size and concentration of silica nanospheres from turbidity spectra measured within the 400-600 nm spectral band. As the refractive index of silica nanoparticles is the key input parameter for optical determination of their concentration, we propose an optical method and provide experimental data on a direct determination of the refractive index of silica particles n = 1.475 +/- 0.005. Finally, we exemplify our method by determining the particle size and concentration for 10 samples and compare the results with transmission electron microscopy (TEM), atomic force microscopy (AFM), and dynamic light scattering data.

The Use of an Exact Light‐Scattering Theory for Spheroidal TiO2 Pigment Particles

Titanium dioxide pigments are widely used, e.g., in paints, printing inks, plastics, and papers, because of the excellent and whiteness they provide. As is well known, the opacity and to it related optical properties depend on the pigment's crystal- and particle-size distributions (CSD, PSD). Therefore, the process and quality control of the CSD and PSD are very essential. The development of a straightforward and sophisticated method for process and quality control is presented here. The principal component is a new determination method for the PSD based on an accurate theory of light scattering of spheroidal particles. In this new method, called the turbidity spectrum method (TSM), the whole turbidity spectrum is measured. This spectrum, which is due to the particle-size distribution of the pigment particles, is then solved using the T-matrix method by taking into account the shape of the particles. After that the CSD is extracted from the PSD. The T-matrix method is one of the most powerful and widely used tools for the rigorous computing of electromagnetic scattering by non-spherical particles. The repeatability of the mean PSD (∼200 nm) obtained by the TSM is excellent, with a standard deviation of 0.1 nm (0.05 %). Linear regression models based on TSM results were developed for undertone and tint-reducing power, which are important optical parameters of the pigment. The excellent repeatability of the TSM results was necessary for the production of representative models.

The Use of an Exact Light‐Scattering Theory for Spheroidal TiO2 Pigment Particles

AbstractTitanium dioxide pigments are widely used, e.g., in paints, printing inks, plastics, and papers, because of the excellent and whiteness they provide. As is well known, the opacity and to it related optical properties depend on the pigment's crystal‐ and particle‐size distributions (CSD, PSD). Therefore, the process and quality control of the CSD and PSD are very essential. The development of a straightforward and sophisticated method for process and quality control is presented here. The principal component is a new determination method for the PSD based on an accurate theory of light scattering of spheroidal particles. In this new method, called the turbidity spectrum method (TSM), the whole turbidity spectrum is measured. This spectrum, which is due to the particle‐size distribution of the pigment particles, is then solved using the T‐matrix method by taking into account the shape of the particles. After that the CSD is extracted from the PSD. The T‐matrix method is one of the most powerful and widely used tools for the rigorous computing of electromagnetic scattering by non‐spherical particles. The repeatability of the mean PSD (∼200 nm) obtained by the TSM is excellent, with a standard deviation of 0.1 nm (0.05 %). Linear regression models based on TSM results were developed for undertone and tint‐reducing power, which are important optical parameters of the pigment. The excellent repeatability of the TSM results was necessary for the production of representative models.

A supramolecular model of hydrophobic interactions in aqueous solutions of acenes

The optical spectra of aqueous suspensions of tetracene (obtained by heating crystals in water) and 9,10-bromoanthracene (obtained by mixing alcoholic solutions of the compound with water) were studied. Both optical pictures were turbidity spectra related to the formation of comparatively large colloidal light scatterers superimposed upon the absorption bands of light hydrophobic ensembles; the absorption bands of free acene molecules were absent. An analysis of the optical spectra and the construction of models with the use of molecular mechanics programs led us to conclude that light hydrophobic ensembles were molecular dimers comparatively stable in the aqueous phase because of the formation of hydration capsules around them. A model of spontaneous dispersion of crystalline tetracene in water under heating was suggested. The model included the stages of the emergence of tetracene molecules from the surface of crystals and their hydration in water layers adjacent to crystals, formation of molecular dimers on the surface of crystals, and diffusion of dimers into the bulk phase, where they experienced clusterization with the formation and sedimentation of fairly large light scattering colloidal particles.

Preparation of Aqueous Colloidal Dispersion of C60 Fullerene

A method for preparing aqueous colloidal dispersions of C60 fullerene free of organic solvents is proposed. The size of dispersed particles is determined using the turbidity spectra. A solvatochromic effect is observed upon the addition of a C60 solution in toluene to a water-acetone mixture.

Turbidity Spectra of Polymeric-Monomeric Particles Formed on Emulsion Polymerization of Acrylates

The possibility of applying the turbidity-spectrum method and the conditions of its application in kinetic investigations of emulsion polymerization are discussed. The necessity of taking into account the spectral dependence of the refractive index of polymeric-monomeric particles and of a dispersion medium and multiple secondary light scattering as well as of using approximating analytical expressions for the characteristic functions of light scattering is noted, because the refractive index of scattering centers depends on the polymerization depth.

A new algorithm for processing turbidity spectra based on multibranch calibrations

A new algorithm for processing turbidity spectra using calibrations several branches or corridors is proposed. The method does not require determination of the wave exponent and makes it possible to estimate the degree of polydispersity of the system under study. Some examples of calibrations for an FEK-56 photoelectrocolorimeter are presented.

A method for studying insoluble immune complexes.

Two variants of a method for determining the average composition of insoluble immune complex particles (IICP) are described. The first variant is based on measuring the specific turbidity (the turbidity per unit mass concentration of the dispersed substance) and the average size of IICP determined from dynamic light scattering (DLS). In the second variant, the slope of the logarithmic turbidity spectrum (wavelength exponent) is used instead of DLS particle size. Both variants allow the average biopolymer volume fraction to be determined in terms of the average refractive index of IICP. The method is exemplified by two experimental antigen+antibody systems: (i) lipopolysaccharide-protein complex (LPPC) of Azospirillum brasilense Sp245+rabbit anti-LPPC; and (ii) human IgG (hIgG)+sheep anti-hIgG. We have found that IICP can be modeled by incompact porous particles that contain about 30% of biopolymer substance and 70% of buffer.

Allowance for instrumental factors in the turbidity and light-scattering spectrum methods

We calculated calibration curves for the turbidity and light-scattering spectrum methods by taking into account the nonmonochromaticity of filters in photoelectrocolorimeters (using the FEK-56 as an example) and nephelometers (using the NFM as an example). The allowance for the nonmonochromaticity was found to have virtually no effect on the calibrations in the former case and to shift them in the latter case. An example of a calibration curve is given for a relative refractive index of 1.12. We touch on the influence of the turbidity of a disperse system on the results of nephelometry.