Small-angle light scattering studies of dense AOT-water-decane microemulsions

Summary We have performed extensive studies of a three-component microemulsion system composed of AOT-water-decane (AOT=sodium-bis-ethylhexyl-sulfosuccinate is an ionic surfactant) using small-angle light scattering (SALS). The small-angle scattering intensities are measured in the angular interval 0.001–0.1 radians, corresponding to a Bragg wave number range of 0.14 μm⁻¹<Q<<1.4 μm⁻¹. The measurements were made by changing temperature and volume fraction ϕ of the dispersed phase (water + AOT) in the range 0.05<ϕ<0.75. All samples have a fixed water-to-AOT molar ratio,w=[water]/[AOT]=40.8, in order to keep the same average droplet size in the stable one-phase region. With the SALS technique, we have been able to observe all the phase boundaries of a very complex phase diagram with a percolation line and many structural organizations within it. We observe at the percolation transition threshold, a scaling behavior of the intensity data. This behavior is a consequence of a clustering among microemulsion droplets near the percolation threshold. In addition, we describe in detail a structural transition from a droplet microemulsion to a bicontinuous one as suggested by a recent small-angle neutron scattering experiment. The loci of this transition are located several degrees above the percolation temperatures and are coincident with the maxima previously observed in shear viscosity. From the data analysis, we show that both the percolation phenomenon and this novel structural transition are derived from a large-scale aggregation between microemulsion droplets.     

Aggregation Behavior of Copolymer Containing Sulfobetaine Structure in Aqueous Solution

Copolymers containing sulfobetaine (P(AM/DMAPS)) were synthesized by aqueous copolymerization of acrylamide with 3-[N-(2-methacroyloylethyl)-N,N- dimethylammonio]-propane sulfonate. Aggregation and disaggregation of P(AM/ DMAPS) copolymer in aqueous solution as a function of copolymer concentration, added salts, and temperature were studied by dynamic laser light scattering. P(AM/DMAPS) copolymers exist as a mixture of individual chains and interchain aggregation in deionized water. At low copolymer concentrations (below 1.0 g L^?1), the intrachain aggregation is dominant. With increasing copolymer concentration, the interchain aggregation is enhanced. The addition of a small amount of salts (C_NaCl < 0.1 mol L^?1; C_MgCl2/CaCl2 < 0.05 mol L^?1) leads to the disaggregation of the intra- and interchain aggregation. Further addition of salts results in the enhancement of interchain aggregation. The influence of various cations (Na⁺, Ca²⁺, Mg²⁺) on the aggregation behavior increases in the order Na⁺ < Ca²⁺ < Mg²⁺. The increase of temperature from 25°C to 60°C facilitates the breakup of intrachain aggregation and the enhancement of interchain aggregation.     

Synthesis and Investigation of Double Stimuli-Responsive Behavior of N-Isopropylacrylamide and Maleic Acid Copolymer in Solutions

Poly(N-isopropylacrylamide-co-maleic acid) [poly(NIPAAm-co-MA)] linear copolymer with comonomer molar ratio NIPAAm:MA = 94:6 was synthesized by free-radical copolymerization. The molar mass, M_sD = 28,000 Da, of poly(NIPAAm-co-MA) was determined using hydrodynamic methods. The self-assembly of poly(NIPAAm-co-MA) in aqueous solution at a concentration of 0.015 g cm^?3 within the pH interval from 1.8 to 10.6 and the temperature interval from 22 to 60°C was investigated by static and dynamic light scattering. The copolymer showed a double temperature and pH responsiveness. Three types of particles, namely, macromolecules (or unimers), micellar-like structures, and loose aggregates existed in the poly(NIPAAm-co-MA) aqueous solutions. The fraction of dissolved entities and the hydrodynamic radii of the micellar-like structures and loose aggregates depended considerably on temperature and pH. The temperature of the phase separation and the width of the phase separation interval increased with pH. An influence of pH on kinetic processes in poly(NIPAAm-co-MA) solutions was observed.     

Investigation of W/O microemulsion droplets by contrast variation light scattering

Dynamic and static light scattering experiments have been performed at various molar ratios (γ) of water to AOT and temperatures on water-in-oil (W/O) microemulsions dispersed in n-heptane, n-octane, and n-nonane. Size and shape fluctuations of microemulsion droplets are determined with very high precision because polydispersity influences the characteristic features of scattering data as well as the hydrodynamic radius withγ. Self-consistent interpretation of dynamic and static light scattering data using optical properties and packing consideration on the basis of the layered sphere model are obtained. The estimated extent of polydispersity index of 17% is found, whereas the polydispersity is independent of the alkane types. The geometrical parameters, e.g., hydrodynamic radius, area per head group of the surfactant molecule and thickness of the surfactant layer of microemulsion droplets are also estimated and compared in three different n-alkane types. The best interpretation of the temperature dependence of data has shown a transition from spherical droplets to ellipsoid aggregates with increasing temperature. Axial ratio increases with increase of temperature and the longer the alkane the larger is the axial ratio. The parameters describing the polydispersity and shape change are in agreement with theoretical and experimental results found in the literature     

Large‐Scale Fluctuation Behavior Prior to the Crystallization of Poly(ethylene terephthalate) Glass: A Small‐Angle Light Scattering Study

The crystallization processes of amorphous, glassy‐state poly(ethylene terephthalate) (PET) at two temperatures, a low temperature near T _g where PET has a slow crystallization speed and a middle temperature (about 55°C above T _g ) where PET crystallization is rapid, were monitored in situ by a time‐resolved small‐angle light scattering (SALS) device. It was found that large‐scale fluctuations happened prior to the crystallization at both temperatures, but the kind of fluctuation had a temperature dependence: at the middle temperature, pure density fluctuation took place during the induction period, whereas at low temperature, both density fluctuation and orientation fluctuation occurred, but the latter was the dominant factor. Analyses of the kinetics of these two kinds of fluctuation processes demonstrated that the spinodal decomposition (SD) type of phase‐separation character was undistinguishable in the SALS scale, while the nucleation‐growth (NG) type of phase behavior could describe the scattering results as well.     

Determination of Microamounts of Proteins by Resonance Light Scattering with Copper Phthalocyanine Tetrasulfonic Acid

Abstract

Based on the strong enhancement effect of proteins on the resonance light scattering of copper phthalocyanine tetrasulfonic acid, a method for the determination of microamounts of proteins has been developed. Under the experimental conditions (2.0×10^?6 mol/L copper phthalocyanine tetrasulfonic acid, pH 2.60, ionic strength 0.001 mol/L NaCl), the linear range of this assay is 0.06–4.0 µg/mL for bovine serum albumin (BSA), 0.1–2.0 µg/mL for human serum albumin (HSA), 0.0–2.0 µg/mL for human γ‐IgG, and 0.2–6.0 µg/mL for ovalbumin. The detection limits (3δ) are 16.8 ng/mL for BSA, 23.4 ng/mL for HSA, 37.6 ng/mL for human γ‐IgG, and 48.3 ng/mL for ovalbumin, respectively. This method has been applied to the analysis of total proteins in human serum samples collected from the hospital, and the results were in good agreement with those reported by the hospital.     

Structure analysis of multiphase systems by anomalous small-angle X-ray scattering

The theory of small-angle scattering is reviewed with special attention paid to the anomalous scattering and multiphase systems. A general equation is derived that describes the scattering of a multiphase system as a sum of scattering functions of each of the phases, as if it scattered alone in a two-phase system, and interphase interference scattering functions. These scattering functions depend only on the spatial distribution of the phase boundaries, but not on the scattering density. Contrast variation techniques are most rewarding when the scattering density of only one phase can be varied. For anomalous small-angle X-ray scattering (ASAXS), this means the most favourable is the case in which resonant atoms are contained in one phase only. The general equation involves n(p ? 1) unknown partial atomic number density differences, where p is the number of phases and n the number of the different atom types in the sample. These partial atomic number density differences can be found if a suitable structure model is applied to calculate the phase scattering functions. Then, the phase compositions and densities can be calculated by solving a system of linear equations incorporating the atom number conservation law. The partial structure factors formalism is also reviewed. Corresponding equations for a system of n types of atoms and p phases are derived. The number of independent partial structure factors is p(p ? 1)/2 and depends on the number of phases, but not on the number of the types of the atoms in the sample, as in the case of wide-angle scattering.     

Evaluation of Properties and Structural Transitions of Poly-L-lysine: Effects of pH and Temperature

Abstract

The structural response to temperature and pH changes of poly-l-lysine (PLL) has been studied by a variety of experimental methods including turbidimetry, dynamic light scattering, and Zeta potential analysis. The experimental results and the molecular dynamics simulations showed that the PLL structural transitions were a result of a competition between electrostatic repulsion, which promotes an extended state, and the hydrophobic effect, which favors a compact state. In fact, as the pH was decreased, the PLL conformation changed from α-helix to the random coil and the hydrophilic volume increases resulted in a transition to spherical micelles which then swelled due to charge-charge repulsions. Following a rise in temperature and/or at high pH, PLL undergoes the α-helix-to-β-sheet transition and reacted more rapidly to form hydrophobic aggregates.     

Step-addition Method for Enhancing the Yield of Gold Nanoparticles in Block Copolymer Solution

Triblock copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) has been used to synthesize gold nanoparticles from hydrogen tetrachloroaureate (III) hydrate (HAuCl₄·3H₂O) salt in aqueous solution at room temperature. Measurements were performed using the triblock copolymer Pluronic P85 (EO₂₆PO₃₉EO₂₆) at a fixed concentration (1 wt%) mixed with varying HAuCl₄·3H₂O concentration in the range of 0.001 to 0.1 wt%. The surface plasmon resonance (SPR) band in UV-visible absorption spectra confirmed the formation of the gold nanoparticles. The maximum yield of the nanoparticles was found at 0.005 wt% of the salt solution. Small-angle neutron scattering (SANS) does not show any significant change in the scattering profile in these suspensions of the nanoparticles. A similar behavior was also observed in dynamic light scattering (DLS) experiments where autocorrelation function was found to be independent of the salt concentration. This can be understood since a high-block copolymer-to-gold ion ratio (r ～ 22) is required in the reduction reaction to produce gold particles. As a result, a very small fraction of the block copolymers were associated with the gold nanoparticles, and hence lead to a very low yield. Both SANS and DLS basically see the micelles of most of these block copolymers, which are not associated with nanoparticles. Based on this explanation, a step-addition method was used to enhance the yield of gold nanoparticles by manifold, where the gold salt is added in small steps to maintain higher value of r (>22), and therefore continuous formation of nanoparticles.     

Solid-state structure of polypeptide-based rod-coil block copolymers: Folding of helices

This work compares the solid-state structures of films made from a polystyrene-poly(Z-L-lysine) (1) and a polystyrene-poly(-benzyl-L-glutamate) (2) block copolymer, both having virtually the same numbers of repeating units and block length ratios. Small-angle X-ray scattering (SAXS) revealed a hexagonal-in-undulated lamellar morphology for both films. The long-period and the thickness of layers obtained for 2 were by a factor of three smaller as compared to 1, indicating that PBLGlu helices were folded twice, whereas PZLLys helices were fully stretched. Another difference shows up in the packing of helices, the level of ordering being considerably lower in 2. This might be due to spatial restrictions in the proper alignment of back-folded helical segments.     

Inelastic light scattering by collective excitations in the fractional quantum Hall regime

We report an inelastic light scattering study of long wavelength collective gap excitations of fractional quantum Hall (FQH) states at ν=p/(2p+1) for . The ν-dependence of the gap energy suggests a collapse of the collective excitation gap near . In a range of filling factors close to , where the FQH gap is believed to collapse, we observe a collective excitation mode that exists only at temperatures below 150 mK.     

Determination of wood grain direction from laser light scattering pattern

Laser light scattering patterns from the grains of wood are investigated in detail to gain information about the characteristics of scattering patterns related to the direction of the grains. For this purpose, wood samples of Scots pine (Pinus sylvestris L.) and silver birch (Betula pubescens) were investigated. The orientation and shape of the scattering pattern of laser light in wood was found to correlate well with the direction of grain angles in a three-dimensional domain. The proposed method was also experimentally verified.     

Study of PEO—PPO—PEO Copolymers Conformational Changes: Viscosity and Dynamic Light Scattering Measurements

The self-assembly behaviour of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly (ethylene oxide) copolymers, (EO)₁₃(PO)₃₀(EO)₁₃ (Pluronic L64), and (EO)₇₀ (PO)₃₀(EO)₇₀ (Pluronic F68) in water and in p-xylene has been elucidated by using viscosity and dynamic light scattering measurements to investigate the effects of hydrophilic chains length on their conformational changes. The viscosity measurements were performed for a range of temperature varying from 27°C to 60°C and concentration from 4 to 60 mg/ml. The variation of the viscosity and the conformational changes in aqueous solution depends on the kinds of interactions and the balance between excluded volume effects and hydrophobic interactions. Some dynamic light scattering measurements were also performed at room temperature for the same range of concentration to provide more information on the micellar structures in aqueous and organic solution.     

Multicomponent Rayleigh scattering from guanidine hydrochloride solutions

We present results of Brillouin light scattering studies of lysozyme and guanidine hydrochloride solutions in the temperature range 290–350 K. The Brillouin spectra of 6 M guanidine hydrochloride have been found to contain an additional component in Rayleigh scattering that manifests itself as a broad quasi‐elastic scattering line centered at the unshifted frequency and described by a Lorentz function (i.e. a Debye relaxor with relaxation time τ₁ ~ 25 ps at room temperature). The temperature dependence of τ₁ is described by the Arrhenius law with activation energy E_a = 0.11 ± 0.01 eV and prefactor τ₀= 0.33 ± 0.03 ps. The Brillouin spectra of lysozyme denatured by 6 M guanidine hydrochloride exhibit a more complicated structure of the additional contribution into Rayleigh scattering, which is fitted best of all by a sum of two Lorentzians centered at the unshifted frequency (with relaxation times τ₁ ~ 19 ps and τ₂ ~ 180 ps at 339 K). Possible origins of the quasi‐elastic scattering are discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

Phase Structure Characterization by SALS of In Situ Compatiblized Binary Polymer Blends and Its Relation to Rheology

Phase structures of polypropylene (PP)/polystyrene (PS) blends, in situ compatiblized by a Friedel–Crafts alkylation reaction with anhydrous aluminum chloride (AlCl₃) as a catalyst, were investigated by small angle light scattering (SALS). The invariant Q, the content of compatible domain between the two phases, i.e., the interphase volume fraction, and the interphase thickness of the in situ compatiblized binary polymer blends were determined by Rayleigh scattering, as well as the phase structure parameters, such as correlation distance and average chord lengths. The results showed that the obtained blend is a partially compatible system. The invariant Q, the interphase volume fraction, and the interphase thickness all can be used to characterize the in situ interfacial compatiblization of the blends and all showed a nonlinear dependence on the in situ formed copolymer content. Further investigations revealed that the contribution of the interfacial modification to the zero shear viscosity of the in situ compatiblized blends showed exponential decay with the increasing invariant Q and showed exponential growth with the increasing volume fraction and thickness of the interphase in the blends. The nonlinear relations between the three phase structure parameters and the in situ formed copolymer content, as well as the nonlinear relations between the three phase structure parameters and the contribution of the interfacial modification to the zero shear viscosity of the blends, might be closely related to the in situ formation of the copolymer and its effect at the interfacial surface in the blends.     

Morphology of Polystyrene Core–dPoly(ethylene oxide) Shell Arborescent Copolymer Micelles from Small-Angle Neutron Scattering Analysis

Arborescent (dendrigraft) copolymers with a branched polystyrene (PS) core grafted at the chain termini with deuterated poly(ethylene oxide) segments (PS-dPEO) were characterized in benzene and acetone by small-angle neutron scattering measurements using the contrast matching technique. While copolymers incorporating a G1 (twice-grafted) PS core aggregated to some extent, the portion of the scattering curve corresponding to non-aggregated copolymer molecules could still be analyzed to determine the shape and segment radial density profile for core and shell. These were derived from the pair distance distribution function P(r) and the scattering length density contrast profile Δρ(r) = ρ(r) ? ρ(solvent), obtained by the indirect Fourier transformation and deconvolution methods. The profiles obtained for the G1 copolymer are consistent with a well-defined PS core–dPEO shell morphology, only observed previously for upper generation (G4) polymers with deuterated PS (dPS) chains grafted randomly on arborescent PS substrates. Detailed morphological analysis could not be carried out for an analogous G3 arborescent PS copolymer terminally grafted with dPEO segments due to extensive aggregation in both solvents.     

Nanoparticle size characterization by laser light scattering

Spherical semiconductor nanoparticles (ZnS) were specially fabricated by an inexpensive chemical route. The scattering profile of the nanoparticles was investigated by laser light scattering technique. A beam of polarized light from a diode laser (λ ₀ ≈ 630 nm) was allowed to fall on the nanospheres embedded in flexible host matrix Polyvinyl Alcohol (PVA). The light scattered from the samples were detected by means of analyzer mounted photodiode array from 10° to 170° in steps of 1°. Signals from the detectors were interfaced with a high resolution data acquisition system and the whole experiment was carried out in differential mode. Size of the nanoparticles was obtained by using Mie theory and verified by T-matrix approach. The results obtained agree with the XRD and TEM results.      

槲皮素的共振光散射光谱研究

研究了槲皮素(Qu)的共振光散射光谱和吸收光谱,结果表明,pH在3.30～6.50范围内,Qu的共振光散射信号很强且稳定,当pH＞6.50时,共振光散射强度随pH的增大而迅速减小。在pH 4.00的B-R缓冲溶液中,在λ=497 nm处,共振光散射强度在一定浓度范围内与Qu的浓度成线性关系,线性范围为0.0～3.0×10-4 mol·L-1, 相关系数r＞0.999, 检测限为3.1×10-7 mol·L-1。同时运用量子化学计算方法对Qu分子内、分子间氢键进行了计算,理论计算表明: Qu共振光信号增强的原因是Qu分子通过4-4’分子间氢键聚合形成了超分子聚合体, 这一结论和实验得到的光谱数据完全吻合。     

利用Turbiscan多重光散射技术评价pH值与钙离子对脱脂乳的热稳定性的影响

热稳定性直接影响牛乳的加工与感官特性，准确判断牛乳的热稳定性对优化液态乳制品的加工条件具有重要意义。然而，当前液态奶的稳定性评价主要是通过加速实验后肉眼观察分层、沉淀等情况，以及动态光散射等手段，尚无快速可靠以及量化的评价标准，严重制约了热处理工艺的选择效率。Turbiscan多重光技术在测试流体的稳定性时，无需对样品进行前处理，可实时检测样品的背向散射光和透射光的强度，计算出体系内部颗粒的迁移速率、沉淀层的厚度、体系的不稳定指数等参数，因此是评价流体物理特性的有效手段。研究以动态光散射测试结果为对照，利用Turbiscan多重光技术测定了脱脂乳经过80 ℃条件下加热30 min后，分别在pH值6.3，6.5，6.7和6.9，CaCl₂的浓度在0，20，40，60和80 mmol·L-1条件下的热稳定性。结果表明，当CaCl₂添加量为20，40，60和80 mmol·L-1时，脱脂乳的z-平均直径从152.7增加到1 284.4 nm，20 h后的不稳定指数值从0.98增加到17.04，样品顶端的背散射光强变化值从-4.3降低到-37.4，底端的背散射光强变化值从2.2增加到14.7；当样品的pH值分别为6.3，6.5，6.7和6.9时，脱脂乳的z-平均直径分别为148.1，152.7，132.4和122.4 nm，20 h后的不稳定指数值分别为1.32，1.02，0.98和1.41，样品顶端的背散射光强变化值分别为-3.1，-4.7，-4.2和-5.6，底端的背散射光强变化值分别为5.7，3.4，4.1和6.8。结果表明，随着CaCl₂添加量的增加，脱脂乳的热稳定性显著降低，pH值对脱脂乳热稳定性的影响较小。同时发现，与动态光散射技术相比，Turbiscan多重光散射技术可更精确、方便、快捷地获得热处理后的牛乳背散射光强值和体系不稳定指数等牛乳稳定性指标，从而明确热处理导致的乳蛋白分散体系的不稳定性发生的机理。Turbiscan多重光散射技术比动态光散射技术测定更方便快捷，该研究对优化乳制品加工工艺具有重要指导意义。