Nonionic latices in aqueous media part 1. Preparation and characterization of polystyrene latices

A series of non-ionic polystyrene latices in aqueous media containing particles with a narrow size distribution have been prepared using a nonyl phenol poly(ehylene glycol) condensate as the surfactant, methoxy poly(ethylene glycol methacrylate) as the comonomer/stabilizer, and ascorbic acid/hydrogen peroxide as the initiator system. As a control synthesis for comparison with the above latex, a charge stabilized polystyrene latex was prepared, using an anionic surfactant and potassium persulphate as the initiator. Latices employing a combination of charge plus steric stabilization mechanisms were also prepared, in order to investigate the effect of the non-ionic surfactant and the comonomer/stabilizer. The particle size of the latices was measured by transmission electron microscopy, the surface charge density by conductimetric titration and the glass transition temperature of the polymer by differential scanning calorimetry. The latex prepared using non-ionic ingredients, showed no titratable charge and exhibited a profound lowering of the glass transition temperature, with respect to the charge stabilized latex. On the basis of these results, schematic models for the polymerization mechanism and the morphology of the latex particles are proposed.     

Investigation of the nonspecific interaction between quantum dots and immunoglobulin G using Rayleigh light scattering

Quantum dots (QDs) have been used as a new class of bioprobes in medical imaging in recent years. The study of interaction between QDs and biomacromolecules is important for interpreting biological data. In this work, Rayleigh light scattering (RLS) was employed to investigate the nonspecific interaction between mercaptoacetic acid modified CdSe/ZnS quantum dots (MAA-QDs) and human immunoglobulin G (IgG). The conjugation processes between QDs and IgG in different conditions including addition sequence, pH were carefully studied. The addition of IgG to QDs solution was found to form a fixed size of QDs-IgG conjugate, with the QDs-to-IgG ratio of ∼13, while the addition of QDs to IgG solution resulted in a gradually increased conjugate size, with variable QDs-to-IgG ratio till the binding saturation was reached.     

On the factors affecting the enhanced resonance light scattering signals of the interactions between proteins and multiply negatively charged chromophores using water blue as an example

Electrostatic interactions of proteins, including bovine serum albumin (BSA), human serum albumin (HSA), γ-globulin (γ-IgG), α-chymotrypsin (Chy), lysozyme (Lys) and cellulase (Cel), with multiply negatively charged chromophores were investigated based on the measurements of the enhanced resonance light scattering (RLS) signals. Using triply negatively charged water blue (WB) as an example, the factors were discussed that affect the enhanced resonance light scattering signals of the interactions between proteins and the negatively charged chromophores. It was found that the enhanced RLS signals with the maximum light scattering peak at 346.0 nm in these interacting systems are strongly dependent on the isoelectric points of proteins and show adverse linear relationships with increasing ionic strength depending on the positive charges of the inorganic metal ions used to control the ionic strength of the medium, sufficiently disclosing that the electrostatic attraction performs an important role in the combination of proteins with WB. Linear responses were discovered between the enhanced RLS signals and the protein molecular weights (M_w), displaying the dimensions of scattered particles formed by proteins and WB make a key contribution to the RLS enhancements. An empirical equation is proposed which possibly displays the factors affecting the enhanced RLS signals of the interactions between proteins with negatively charged chromophores.     

Small-angle x-ray scattering of isotactic polystyrene

Isothermal crystallization process of isotactic polystyrene at 167°C has been studied by smallangle x-ray scattering. The observed SAXS intensities consist of the twophase lamellar structure component, the density fluctuation, and the foreign particle components. The profile of lamellar structure component remains unchanged during crystallization while its intensity increases with crystallization. The lamellar structure of isotactic polystyrene is investigated on the basis of the interface distribution function. An interface distribution function is obtained from the lamellar structure component after correcting the effect of the finite thickness of boundary regions between crystalline and amorphous phases. In order to obtain the structure parameters, the Gaussian correlation model is used, in which the correlation between the distributions of neighboring crystal and amorphous thicknesses is taken into account. Agreement is satisfactory between the experimental results and the calculations. The structure parameters of isotactic polystyrene are determined for isothermal crystallization at 167°C as follows: the average and the standard deviation of crystal thickness are 40 A and 10 A, respectively, those of amorphous thickness are 70 A and 23 A, and the standard deviation of long period is 31 A.     

Evaluation of light scattering models to characterize concentrated polymer particles embedded in a solid polymer matrix

This work deals with the application of the static light scattering (SLS) model of Vrij (VM) for the characterization of a spherical polydisperse concentrated polymer particle system. This model is the exact solution for the SLS of such mixture of particles in the Percus–Yevick approximation. The analyzed polymer particle samples are obtained by solution polymerization of isobornyl methacrylate in polyisobutylene. At the end of the polymerization, as a result of phase separation, a particle system of micrometer sized particles with a moderate distribution of sizes and a volume fraction between 5 and 10% is formed. The SLS data were also analyzed using the local monodisperse approximation (LMA), a well‐known approximation to the model of Vrij. As expected, the estimations with the VM gave better results than those performed with the LMA model for the parameters related to the shape of the particle size distribution as compared with independent determinations of these quantities obtained from scanning electron microscopy micrographs. However, the main motivation to use the more rigorous model seems to be the fact that the volume fraction of particles can be extracted from the data even when relative SLS measurements are used. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 958–963, 2010     

Strong diffuse scattering and lamellar morphologies of syndiotactic polystyrene: Polymorphic effects

Syndiotactic polystyrene (sPS) samples melt‐crystallized into neat α″‐ hexagonal and β′‐orthorhombic modifications were prepared at various temperatures thoroughly for extensive morphological studies. The lamellar morphologies of the as‐prepared sPS samples were investigated with small‐angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM). For SAXS measured at 25°C, a barely observed scattering hump was detected for β′‐form sPS, whereas no discernible scattering feature was found for α″‐form sPS because of a small difference in the electron density between the crystalline and amorphous phases. For increased scattering contrast and strength, SAXS was carried out at 150°C so that more reliable morphological parameters would be obtained. In addition to the enhanced scattering peak relevant to the lamellar features, strong diffuse scattering near the beam stop was observed for both α″‐ and β′‐form sPS samples. The contribution of the diffuse scattering at low q regions (where q is the scattering vector) was rather prominent, obscuring the precise position of the scattering peak. On the basis of the Debye–Bueche theory, the strength and inhomogeneity length were derived to render the diffuse scattering. After the subtraction of the diffuse scattering from the observed intensities, scattering intensities exclusively associated with the lamellar features were obtained. Lamellar thicknesses were further derived from the one‐dimensional correlation function of the modified intensities, and a good agreement was reached in comparison with TEM results. From exhaustive TEM observations on the RuO₄‐stained samples, long and parallel lamellae were readily observed in β′‐form sPS. However, relatively irregular packing of lamellar stacks with short lateral dimensions was detected in the as‐prepared α″‐form sPS, leading to the absence of spherulitic birefringence under polarized optical microscopy. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2457–2469, 2003     

Glucose detection at attomole levels using dynamic light scattering and gold nanoparticles

Glucose is directly related to brain activity and to diabetes.Therefore,developing a rapid and sensitive method for glucose detection is essential.Here,label-free glucose detection at attomole levels was realized by detecting the average diameter change of gold nanoparticles(AuNPs)utilizing dynamic light scattering(DLS).Single-strand DNA(ssDNA)adsorbed into the AuNPs’surfaces and prevented them from aggregating in solution that contained NaCl.However,ssDNA cleaved onto ssDNA fragments upon addition of glucose,and these fragments could not adsorb onto the AuNPs’surfaces.Therefore,in high-salt solution,AuNPs would aggregate and their average diameter would increase.Based on monitoring the average diameter of AuNPs with DLS,glucose could be detected in the range from 15 pmol/L to 2.0 nmol/L,with a detection limit of 8.3 pmol/L.Satisfactory results were also obtained when the proposed method was applied in human serum glucose detection.     

An abnormal resonance light scattering arising from ionic-liquid/DNA/ethidium interactions

In the aqueous phase, ethidium bromide (EB) intercalates into the double helix structure of dsDNA (ds=double-stranded) with a notable enhancement in fluorescence and resonance light scattering (RLS). However, when dsDNA was extracted into an ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF(6)), an abnormal RLS arising from the interactions of IL-DNA-EB was observed, with a substantial decrease of the recorded RLS. The cationic Bmim(+) groups of BmimPF(6) intercalate into the DNA helix structure, in which they interact with the P-O bonds of phosphate groups in DNA strands and result in a reduction of the base-pair interstice along with transformation of DNA conformations that consequently prohibits the intercalation of EB with DNA. Thus, in the IL phase, the interactions between ethidium and DNA were dominated by electrostatic interactions and hydrogen bonding, leading to a congregation of EB entities around the DNA strands that results in an increase of absorption by ethidium, and consequently the inner filter effect leads to a reduction of the RLS. The present observation has been applied to the direct quantification of DNA in an ionic-liquid phase after DNA from human whole blood was extracted into BmimPF(6).     

Ion exchange in carboxylated latices — AUC studies using sedimentation and density gradient techniques

Crosslinked highly carboxylated acrylic latices with narrow particle size distributions were prepared by emulsion polymerization and characterized carefully by different AUC techniques (particle size distributions and particle density measurements). The acid form of those latices was neutralized with metal oxides like MgO, CaO, ZnO, or PbO in order to obtain the corresponding salt form of the latices which again were characterized carefully. The kinetics of the ion exchange between latex particles were studied by mixing, for example, the acid and the salt form of the latices monitoring the density distribution of the latex particles by density gradient ultracentrifugation. With all latices the hydrogen-metal ion exchange tends to be a complete one provided this process is given a sufficiently long exchange time. Theoretical models are provided which yield a qualitative explanation of the experimental data.     

Speckle reduction in the small-angle light scattering technique using sample vibration

Experimental patterns obtained using the small-angle light scattering technique for thin-film polymer studies are fraught with speckles arising from the effect of interspherulitic interference. The presence of speckles hampers efforts in characterizing the spherulitic structure. Using a divergent beam increases the number of scattering sites and results in a reduction of the degree of speckling. Nevertheless, this decimates the ability of analyzing the pattern at low-scattering angles. Employing an expanded collimated beam produces the same effect but necessitates the use of specially designed optical components. This article outlines a novel technique that involves simple vibration of the polymer sample. Experimental results confirm its efficacy in reducing speckles without limiting the ability for analysis at low-scattering angles. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 937–943, 1997     

Light scattering near and from interfaces using evanescent wave and ellipsometric light scattering

The broad range of interface light scattering investigations in recent years shows the power and the versatility of these techniques to address new and open questions in colloid and interface science and the soft condensed matter field. Structural information for polymers, liquid crystals, or colloids close to planar or spherical colloidal interfaces are either captured with long range light scattering resolution, or in a complementary approach by high resolution ellipsometric techniques. Of special interest is the dynamic behavior close to or in interfaces, since it determines material properties and responses to external fields. Due to the broad dynamical range and the high scattering contrast for visible light, interface light scattering is a key to elucidate soft matter interfacial dynamics. This contribution reviews experimental and related theoretical approaches for interface light scattering and further gives an overview of achievements based on such techniques.     

Morphology development during the polymerization of styrene within a polyurethane network: Investigations by small-angle X-ray and light scattering

Phase separation that takes place during the formation of semi-interpenetrating polymer networks based on crosslinked polyurethane and linear polystyrene was studied by small-angle X-ray scattering and light scattering. The kinetics of the chemical reactions was followed by Fourier transform infrared spectroscopy. The occurrence of broad peaks in the X-ray scattering curves was interpreted in terms of distances between the urethane crosslinks. Small modulations on these curves were assigned to sphere-like structures with a diameter of around 5 nm which might be related to the urethane crosslink regions. Small modulations on the light-scattering curves at the beginning of styrene polymerization were assigned to spheres with diameters of around 4.5 μm, which can be related to the polystyrene-rich phase. These modulations disappear with time, which might indicate an increasing polydispersity of the domain sizes. The final morphology was found to depend on the time at which polymerization of styrene is initiated with respect to the time of gelation of polyurethane.     

聚苯乙烯稀溶液的小角激光弹性和准弹性光散射

随着激光技术的发展,近年来出现了与散射光频加宽相应的光子相干光谱即准弹性光散射。于是,利用光散射(也称弹性光散射)法不仅能获得高聚物的各种物性参数如分子量(?),第二维利系数A_2和均方旋转半径(),而且还能得到大分子在溶液中的动态参数,即扩散系数D_0。由D_0求得流体力学半径R_H。本文只涉及小角度准弹性光散射(1°<θ<7°)对稀溶液范围的平动扩散系数的测定。与文献比较,表明方法是成功的。     

共振光散射光谱研究噻嗪红R与牛血清白蛋白的作用及其分析应用

研究了噻嗪红R(Thiazine red R,TR)与牛血清蛋白(BSA)作用的共振光散射(RLS)光谱特征。考察了各种影响因素,并计算出了BSA与TR的结合比(质量之比)为1.25。结果表明,在优化条件下体系的RLS强度与蛋白质浓度在一定范围内具有良好的线性关系,据此建立了一种蛋白质测定的新方法。在最佳实验条件(TR,2.0×10-5mol/L;pH2.36)下,BSA的线性范围是0.01~5.0μg/mL,检出限为1.4ng/mL。该方法已用于合成样品及尿液的测定。     

Liposomal structure: A comparative study on light scattering and chromatography techniques

Liposomes play an important role in medical and pharmaceutical science as, nanoscale drug carriers. One of the most important features is their size and size distribution, influencing both their bio-distribution and their targeting efficiency to tumors and also therapeutic activity of liposomal antitumor drugs. In this study, the effect of preparation method and molecular interaction on size and shape of liposome was studied. The size and shape characterization of liposomes was performed by asymmetrical flow field-flow fractionation coupled online with multi-angle light scattering (AF4-MALS). The size distributions obtained by AF4-MALS were compared to mean particle sizes and size distribution measured with other standard method such as Photon Correlation Spectroscopy (PCS). Furthermore, the effect of molecular interaction (hydrophilic and hydrophobic model drugs) on liposomal structure was assessed.     

Measurement of thermal diffusivity in polymer melts using forced Rayleigh light scattering

Thermal diffusivity measurements on three polymer melts were made using the Forced Rayleigh Light Scattering technique. The polymers, which were tested at room temperature where they are in the molten state, included a polydimethylsiloxane and two polyisobutylenes. The optical setup and procedures developed in this study to conduct thermal Forced Rayleigh Light Scattering experiments are shown to be capable of producing thermal diffusivity data with a high degree of accuracy and precision. From measurements on a reference fluid (ethanol), experimental error was estimated to be no greater than 2%, and could be reduced to less than 1% by appropriate design of a series of experiments. Discrepancies of 4 and 14% in thermal diffusivity data on the polymer samples between measured values and those found in the literature were observed. It is suggested that these deviations are attributable to either sample variations or to errors in the techniques used in previous investigations. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1069–1078, 1999     

Dynamic light scattering and small-angle neutron scattering studies on organogels formed with a gelator

Small-angle neutron scattering (SANS) and light scattering studies were carried out on an organogel consisting of a gelator, coded P-1, and dimethyl sulfoxide (DMSO). The gelator was made of an oligosiloxane stem and about eight branches of an amino acid derivative combined with a long alkyl chain. The amino acid part, N-n-pentanoyl-L -isoleucylaminooctadecane, was responsible for intermolecular association via hydrogen bonding between amide groups. After the complete dissolution of P-1 in DMSO at 85 °C, the solution was cooled, and the variations of the scattered light intensity were monitored as a function of the temperature. The scattered intensity increased drastically at about 40 °C when the P-1 concentration (C) was 3.5 g/L, and this indicated gel formation. The SANS results showed that the scattering intensity function was a monotonically decreasing function, regardless of C. A master relationship of the scattering intensity was obtained with respect to C. These scattering studies disclosed the following facts. First, gelation could be monitored as an abrupt increase in the intensity. Second, the gel was composed of randomly oriented bundlelike clusters. Third, the structure factor could be reduced by the gelator concentration, and this indicated the presence of a self-similar structure across the gelation threshold. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1841–1848, 2004     

On-line measurement of molecular weight and radius of gyration of polystyrene in a good solvent and in a theta solvent measured with a two-angle light scattering detector

On-line two-angle (15° and 90°) light scattering measurements with a gel permeation chromatography for linear and branched polystyrene in tetrahydrofuran (a good solvent) and in trans-decalin (a theta solvent) were made and compared with data from a multi-angle light scattering detector and literature values. Theoretically, weight-average molecular weight and the radius of gyration R_g can be determined accurately in the range where R_g²k² is less than 1.2 (rod)∼1.7 (random coil); here, k is the absolute value of the scattering vector for a right angle detector with the Berry square root method. Molecular weight dependence of the radius of gyration obtained from the two-angle light scattering detector for linear and branched polystyrenes under different thermodynamic conditions were measured and found to be almost the same as values measured with a multi-angle light scattering detector and literature values in the appropriate range of molecular weight.     

Attractive interactions in critical scattering from non-ionic micelles

We have studied the temperature-dependent critical scattering of both light and neutrons from aqueous solutions ofn-octyl pentaoxyethylene glycol monoether (C₈E₅). We show that the assumption of a short-ranged temperature-dependent attractive pair potential between approximately spherical micelles of constant size permits a quantitative analysis of the neutron scattering data. The analysis, which is undertaken using current liquid-state theory and is in analytic form, contains only one free parameter, the depth of the attractive potential. We find that a potential with a range of only a fraction of a nm is sufficient to generate spatial correlations over tens of nm as the attractive potential deepens on approaching the critical temperature. The analysis also provides a semi-quantitative understanding of the light scattering data as a function of concentration and temperature, and leads to a qualitative prediction of the form of the phase diagram. Numerical values obtained are consistent with the hypothesis that the primary effect of raising the temperature is to lower the degree of structure of water near the micelle surface, allowing increased van der Waals attraction due to closer contact.