Laser light scattering as a probe for structure and dynamics in bulk polymers: Polystyrene

Summary We begin with an outline of a theory of density fluctuations in the glassy state based on a partial freeze-in of an ordering parameter, as derived from previous equation of state investigations. Then laser light scattering studies of glasses formed by atactic polystyrene are described. Photon correlation analysis indicates two relaxation mechanisms. A slow process dominates aboveT _g , has a wide asymmetric distribution of relaxation times and is evidently related to the glass transition phenomenon. A small-amplitude fast decay with a narrow relaxation spectrum is also observed. BelowT _g , this mode is shown to be dependent on scattering angle and is evidently a diffusion mechanism, which may be related to the-relaxation process. Relative integrated intensities are presented for isotropic and depolarized scattering from glasses densified by pressurization in the melt, followed by isobaric cooling to 25°C and depressurization. The depolarized scattering for the glass formed at atmospheric pressure has a value consistent with a completely disordered glass. However, a small increase in depolarized scattering appears to occur on densification. This result may reflect a small increase in intersegmental ordering in glassy polystyrene upon densification. The isotropic scattering shows a large systematic increase in the densified glass. This is apparently the result of an inhomogeneous density change during the depressurization step.

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Zusammenfassung Wir beginnen mit dem Umriß einer allgemeinen Theorie der Dichteschwankungen im glasigen Bereich. Sie beruht auf der Annahme despartiellen Einfrierens eines Struktur-Parameters, wie aus vorherigen Untersuchungen der Zustandsgleichung gefolgert wird. Sodann werden Versuche mit ataktischem Polystyrol beschrieben. Die zeitliche Korrelationsfunktion der Photonenstreuung zeigt zwei Relaxationsmechanismen an. OberhalbT _g herrscht ein langsamer Prozeß vor, der durch eine breite, assymetrische Verteilungsfunktion von Relaxationszeiten charakterisiert ist. Dieser Prozeß hängt offensichtlich mit dem Glasübergang zusammen. Ein zusätzlicher, viel rascherer Prozeß mit einer geringen Amplitude und einem schmalen Relaxationsspektrum ist auch beobachtbar. UnterhalbT _g wird dieser Prozeß vom Streuwinkel abhängig, stellt einen Diffusionsvorgang dar, und sollte mit dem ß-Prozeß zusammenhängen. Weiter untersuchen wir die relativen totalen Intensitäten der isotropen und der depolarisierten Streuungskomponente für eine Reihe von verdichteten Gläsern. Diese wurden durch Druckanwendung in der Schmelze, nachherige isobarische Abkühlung zu 25 °C, und schließliche Druckentlastung erzeugt. Die depolarisierte Streuungskomponente im Glase, welches bei atmosphärischem Druck hergestellt wurde, ist mit einem System ohne sichtliche Ordnungszustände vereinbar. Ein schwacher Anstieg dieser Streuung wird jedoch im verdichteten System bemerkbar, welcher möglicherweise einen geringeren Ordnungsprozeß der Kettensegmente anzeigt. Die isotropische Streuung wächst systematisch mit der glasigen Verdichtung an. Offensichtlich ist dies die Folge einer inhomogenen Dichteänderung während der Druckentlastung.

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Dedicated to Professor Dr. G. Rehage on the occasion of his 60th birthday.

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With 7 figures and 1 table     

曙红Y共振光散射探针测定盐酸丙米嗪

在弱酸性介质中,盐酸丙米嗪与曙红Y依靠静电引力和疏水作用力形成离子缔合物,使曙红Y溶液的吸收光谱、荧光光谱和共振光散射光谱发生变化。其中以共振光散射法灵敏度最高。据此,建立了使用曙红Y作为共振光散射探针测定盐酸丙米嗪的新方法。研究了体系的吸收光谱、荧光光谱和共振光散射光谱特征。在最大散射峰364 nm处,测得盐酸丙米嗪的线性范围为0.025～2.5μg/mL,检测限为5.32 ng/mL,并将方法用于药物中盐酸丙米嗪含量的测定。     

Melting behavior of shear-induced crystals in dense emulsions as investigated by time-resolved light scattering

The crystal growth of dense and almost monodisperse colloids has been investigated during recent years, but less is known about the melting behavior. The current study thus focuses on this topic. Monodisperse hard spheres were found to crystallize for certain concentrations (49-58 vol %), after sufficiently long times. The characteristics of the crystal growth change when the colloidal particles are polydisperse. Finally, when the size distribution function of the particles is broad enough, the crystallization no longer took place. Dense oil-in-water emulsions with polydispersities of around 10% were successfully produced, and in a first approximation, these emulsions behaved like hard spheres. The polydispersity of the emulsions was sufficiently high to avoid crystallization in equilibrium but low enough to induce a disorder-to-order transition under shear. The formed crystals started to melt once the shear was discontinued. The melting behavior of these "oil droplet crystals" was investigated by means of time-resolved static light scattering experiments, and it was found that crystallization could be induced in a concentration regime between 46 and approximately 74 vol %. The melting behavior of these crystals depended strongly on the concentration. The typical melting times ranged from a few seconds to several hours or days when the concentration was increased. It was speculated that this phenomenon could be explained by the strong dependence of the mobility of the oil droplets on the volume fraction, as verified by dynamic light scattering experiments on oil-in-water emulsions in a similar concentration regime.     

Interface composition of multiple emulsions: rheology as a probe

We have investigated the dynamic rheological properties of concentrated multiple emulsions to characterize their amphiphile composition at interfaces. Multiple emulsions (W1/O/W2) consist of water droplets (W1) dispersed into oil globules (O), which are redispersed in an external aqueous phase (W2). A small-molecule surfactant and an amphiphilic polymer were used to stabilize the inverse emulsion (W1 in oil globules) and the inverse emulsion (oil globules in W2), respectively. Rheological and interfacial tension measurements show that the polymeric surfactant adsorbed at the globule interface does not migrate to the droplet interfaces through the oil phase. This explains, at least partly, the stability improvement of multiple emulsions as polymeric surfactants are used instead of small-molecule surfactants.     

Dynamic light scattering,a probe of brownian particle dynamics

The principles and techniques of dynamic light scattering (DLS) are outlined and its application to the study of suspensions of interacting colloidal particles is discussed. We show how, under appropriate conditions, DLS can measure long-time collective and self-diffusion coefficients as well as study short-time motions (characterized by the cumulants). These theoretical considerations are illustrated by experimental data. Finally, we discuss the relevance of certain characteristic timescales to theories of the diffusion of interacting particles.     

荧光镓-SDS共振瑞利散射法测定蛋白质的研究

在pH 2.21的B-R缓冲溶液中, 蛋白质的加入导致荧光镓共振瑞利散射信号增强, 基于此, 建立了一种测定蛋白质的新方法. 表面活性剂SDS的加入显著提高了体系的灵敏度, 牛血清白蛋白的浓度在0～4.5 μg/mL之间与体系的散射强度呈线性关系, 检出限为8.14 ng/mL. 方法已应用于人血清样品中蛋白质含量的测定. 同时, 利用分光光度法测定了其不同温度下的结合数、结合常数. 利用热力学方程研究发现荧光镓与蛋白质之间的主要作用力为静电引力.     

结晶紫探针瑞利光散射技术测定安乃近

在弱碱性条件下,结晶紫与安乃近相互作用后,导致瑞利光散射增强,建立了一种简便、快速、灵敏及选择性好的测定安乃近的分析方法。在390 nm处的ΔIRLS最大,增强的瑞利散射光与0.06~0.40 mg·L-1范围的安乃近呈良好的线性关系,方法的检出限(3Sb/S)为0.017mg·L-1。该法用于市售安乃近药物中安乃近含量的测定,结果满意。     

Light scattering as a probe of liquid surfaces and interfaces

The field of quasi-elastic light scattering from thermally excited capillary waves at liquid surfaces is reviewed, with particular attention to scientific advances since 1992. These include surface-induced freezing in molecular fluids, the cross-over from capillary to elastic Rayleigh waves on the surfaces of gelling polymer solutions, the experimental demonstration of mixing of capillary and dilatational surface modes and the observation of effects due to processes tending to reduce the stability of the dilatational waves on surfactant solutions. The potential of this technique for surface and interface science is discussed.     

Rheology of foams and highly concentrated emulsions

We review the state of the art in foam and highly concentrated emulsion rheology, with an emphasis on progress made over the last five years. Since the structures and physico-chemical processes relevant for foams and emulsions are closely analogous, comparing the knowledge recently gained in these two neighboring fields brings fresh insight. In this spirit, we review how the macroscopic mechanical response arises from a coupling between interfacial energy and long range molecular interactions, entropic effects, interfacial rheology, and dynamics at the droplet or bubble scale. We present experiments and models concerning elasticity, osmotic pressure, yielding and flow behavior.     

Determination of methylene blue by resonance light scattering method using silica nanoparticles as probe

A simple and novel method was developed to determine methylene blue(MB) by resonance light scattering(RLS) using silica nanoparticles(SiO_2NPs) as the probe.It was found that MB could enhance the RLS intensity of SiO_2NPs.Moreover,the increase in RLS intensity was linear with the concentration of MB over the range of 0.01-3.0 μg mL~(-1).The limit of detection(LOD) was as low as 4.36 ng mL~(-1)(3σ) and the relative standard deviation(RSD) was 2.4%(n=6).Under the optimum experimental conditions,this proposed method was successfully applied for the determination of MB in aquaculture samples with recoveries between 96.3% and 107%.Possible mechanisms for the RLS enhancement of SiO_2NPs in the presence of MB were also discussed.     

Microdetermination of proteins using m-carboxychlorophosphonazo as detection probe by enhanced resonance light scattering spectroscopy

Proteins can be determined using a common spectrofluorometer to detect the intensity of resonance light scattering (RLS). Under acidic conditions, the reaction between m-carboxychlorophosphonazo (CPA-mK) and proteins enhances the weak light scattering of CPA-mK drastically. This enhanced intensity is proportional to the concentration of proteins. The linear ranges for human serum albumin are 0.5–35.0 μg/mL, with detection limits of 0.104 μg/mL. The method yields results comparable to those of the calorimetric method using Coomassie Brilliant Blue G-250 (CBB) with relative standard deviations of 0.72–2.10% (n = 10). There is almost no interference by amino acids and most of the metal ions.     

孔雀石绿共振光散射法测定饮用水中痕量BrO3-

在pH3.8的HAc-NaAc缓冲液中,BrO3-氧化I-生成I2,I2与过量的I-反应生成I3-,I3-与孔雀石绿(MG)反应形成缔合微粒,导致体系的共振光散射强度急剧增强,最大共振光散射波长位于465nm处,BrO3-浓度在0～120μg/L范围内有较好线性关系,检出限以3σ计算为3.4ng/mL,据此建立了一种测定微量BrO3-的共振光谱新方法.该法用于饮用水中BrO3-的测定,得到了满意的结果.     

Microdetermination of proteins using m-carboxychlorophosphonazo as detection probe by enhanced resonance light scattering spectroscopy

Proteins can be determined using a common spectrofluorometer to detect the intensity of resonance light scattering (RLS). Under acidic conditions, the reaction between m-carboxychlorophosphonazo (CPA-mK) and proteins enhances the weak light scattering of CPA-mK drastically. This enhanced intensity is proportional to the concentration of proteins. The linear ranges for human serum albumin are 0.5-35.0 microg/mL, with detection limits of 0.104 microg/mL. The method yields results comparable to those of the calorimetric method using Coomassie Brilliant Blue G-250 (CBB) with relative standard deviations of 0.72-2.10% (n = 10). There is almost no interference by amino acids and most of the metal ions.     

Surface phase transitions in foams and emulsions

Surface phase transitions in surfactant adsorption layers are known to affect the dynamic properties of foams and to induce surface nucleation in freezing emulsion drops. Recently, these transitions were found to play a role in several other phenomena, opening new opportunities for controlling foam and emulsion properties. This review presents a brief outlook of the emerging opportunities in this area. Three topics are emphasized: (1) the use of surfactant mixtures for inducing phase transitions on bubble surfaces in foams; (2) the peculiar properties of natural surfactants saponins, which form extremely viscoelastic surface layers; and (3) the main phenomena in emulsions, for which the surface phase transitions are important. The overall conclusion from the reviewed literature is that surface phase transitions could be used as a powerful tool to control many foam and emulsion properties, but we need deeper understanding of the underlying phenomena to fully explore these opportunities.     

藉L-半胱氨酸包覆的ZnS纳米粒子的共振光散射定量分析蛋白质

合成和表征了功能性L-半胱氨酸包覆的ZnS纳米粒子。在pH5．12的NaAc-HAc溶液介质中,L-半胱氨酸包覆ZnS纳米粒子于波长308．0nm处出现共振光散射峰。一定量蛋白质的加入能明显增强体系的共振光散射,且峰强度增加值与蛋白质浓度间存在良好线性关系,据此建立了一种灵敏的测定微量蛋白质的方法。用L-半胱氨酸包覆ZnS纳米粒子作为探针,不仅克服了有机染料可能出现的光漂白等缺点,而且本身不具毒性。该法用于人血清试样中总蛋白的测定,其结果与临床数据一致。     

Food emulsions and foams: Stabilization by particles

Recent advances in the stabilization of emulsions and foams by particles of nanoscale and microscopic dimensions are described. Ongoing research in this highly active field is providing insight into (i) the molecular factors controlling particle wettability and adsorption, (ii) the structural and mechanical properties of particle-laden liquid interfaces, and (ii) the stabilization mechanisms of particle-coated droplets and bubbles. There is much potential for exploiting the emerging knowledge in new food product applications. The preparation of cheap and effective colloidal particles based on food-grade ingredients, especially proteins, is the key technological challenge.     

Formation and stability of food foams and aerated emulsions: Hydrophobins as novel functional ingredients

Foams remain an invaluable part of the food engineer's arsenal. Unfortunately the number of new molecules available to stabilise foams is starting to dwindle. Partially, this is due to the difficulties of finding new species with favourable properties and, in many respects, this trend is led by a commercial need to make food labels ‘green’.Food grade proteins offer a number of potential solutions, as well as some excellent physical properties, when at the air–water interface. This review will use the example of hydrophobins as useful proteins finding applications within the food industry. It will also serve as a case study to examine potential methods to identify other new and potentially useful molecules.     

结晶紫的酶催化共振散射光谱法测定痕量过氧化氢

在pH4.7的HAc-NaAc缓冲溶液中,牛血红蛋白可催化H2O2氧化I-生成I2,I2与过量的I-生成的I3-与带正电荷的结晶紫(CV+)可形成缔合物微粒,导致体系的共振散射光强度增强。在659 nm处,H2O2在2.065×10-7～1.652×10-6mol/L范围内与共振散射光强度的增加值(ΔI)呈良好的线性关系,相关系数r为0.9989,检出限为2.676×10-9mol/L。据此,建立了检测痕量H2O2的共振散射光谱新方法,该方法已用于水样中H2O2含量的测定。     

High-sensitivity detection of polysaccharide using phosphodiesters quaternary ammonium salt as probe by decreased resonance light scattering

Phosphodiesters quaternary ammonium salt (PQAS) displayed quite intense light scattering in aqueous solution under the optimum condition. In addition, the resonance light scattering (RLS) signal of PQAS was remarkably decreased after adding trace amount polysaccharide with the maximum peak located at 391 nm. It was found that the decreased RLS intensity of the PQAS − PPGL system (ΔI_RLS) was in proportion to PPGL concentration in the range of 0.1-30 ng mL⁻¹, with a lower detection limit of 0.05 ng mL⁻¹. Based on this rare decreased RLS phenomenon, the novel method of the determination of purified polysaccharide of Gracilaria Lemaneiformis (PPGL) at nanogram level was proposed in this contribution. The proposed approach was used to determine purified polysaccharide extracted from Gracilaria Lemaneiformis with satisfactory results. Compared with the reported polysaccharide assays, this proposed method has good selectivity, high sensitivity and is especially simple and convenient. Moreover, the mechanism of the reaction between PQAS and polysaccharide was investigated by RLS, fluorescence, and fluorescence lifetime spectra.