Volume transition and internal structures of small poly(N‐isopropylacrylamide) microgels

Monodispersed poly(N‐isopropylacrylamide) (PNIPAM) nanoparticles, with hydrodynamic radius less than 50 nm at room temperature, have been synthesized in the presence of a large amount of emulsifiers. These microgel particles undergo a swollen–collapsed volume transition in an aqueous solution when the temperature is raised to around 34 °C. The volume transition and structure changes of the microgel particles as a function of temperature are probed using laser light scattering and small angle neutron scattering (SANS) with the objective of determining the small particle internal structure and particle–particle interactions. Apart from random fluctuations in the crosslinker density below the transition temperature, we find that, within the resolution of the experiments, these particles have a uniform radial crosslinker density on either side of the transition temperature. This result is in contrast to previous reports on the heterogeneous structures of larger PNIPAM microgel particles, but in good agreement with recent reports based on computer simulations of smaller microgels. The particle interactions change across the transition temperature. At temperatures below the transition, the interactions are described by a repulsive interaction far larger than that expected for a hard sphere contact potential. Above the volume transition temperature, the potential is best described by a small, attractive interaction. Comparison of the osmotic second virial coefficient from static laser light scattering at low concentrations with similar values determined from SANS at 250‐time greater concentration suggests a strong concentration dependence of the interaction potential. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 849–860, 2005     

Thioamides: Versatile Bonds To Induce Directional and Cooperative Hydrogen Bonding in Supramolecular Polymers

The amide bond is a versatile functional group and its directional hydrogen‐bonding capabilities are widely applied in, for example, supramolecular chemistry. The potential of the thioamide bond, in contrast, is virtually unexplored as a structuring moiety in hydrogen‐bonding‐based self‐assembling systems. We report herein the synthesis and characterisation of a new self‐assembling motif comprising thioamides to induce directional hydrogen bonding. N,N′,N′′‐Trialkylbenzene‐1,3,5‐tris(carbothioamide)s (thioBTAs) with either achiral or chiral side‐chains have been readily obtained by treating their amide‐based precursors with P₂S₅. The thioBTAs showed thermotropic liquid crystalline behaviour and a columnar mesophase was assigned. IR spectroscopy revealed that strong, three‐fold, intermolecular hydrogen‐bonding interactions stabilise the columnar structures. In apolar alkane solutions, thioBTAs self‐assemble into one‐dimensional, helical supramolecular polymers stabilised by three‐fold hydrogen bonding. Concentration‐ and temperature‐dependent self‐assembly studies performed by using a combination of UV and CD spectroscopy demonstrated a cooperative supramolecular polymerisation mechanism and a strong amplification of supramolecular chirality. The high dipole moment of the thioamide bond in combination with the anisotropic shape of the resulting cylindrical aggregate gives rise to sufficiently strong depolarised light scattering to enable depolarised dynamic light scattering (DDLS) experiments in dilute alkane solution. The rotational and translational diffusion coefficients, D_trans and D_rot, were obtained from the DDLS measurements, and the average length, L, and diameter, d, of the thioBTA aggregates were derived (L=490 nm and d=3.6 nm). These measured values are in good agreement with the value L_w=755 nm obtained from fitting the temperature‐dependent CD data by using a recently developed equilibrium model. This experimental verification validates our common practice for determining the length of BTA‐based supramolecular polymers from model fits to experimental CD data. The ability of thioamides to induce cooperative supramolecular polymerisation makes them effective and broadly applicable in supramolecular chemistry.     

Micellization of triblock copoly(ethyleneoxide/tetrahydrofuran/ ethylene oxide)

 The association behaviour of triblock copoly(ethylene oxide/tetrahydrofuran/ethylene oxide), in particular E₁₀₀T₂₇E₁₀₀, in aqueous solutions has been investigated by means of static and dynamic light scattering, nuclear magnetic reso-nance (NMR) and surface tension techniques. On raising the polymer concentration at room temperature, the copolymer aggregates to form micelles with an aggregation number of about 105 (R _G, mic≈15 nm and R _H, mic≈13 nm, as revealed by light scattering and FT-PGSE NMR measurements, respectively). The micelles are kinetically quite stable, the micellar lifetime is shown to be more than 1 h. The residence time of a single unimer in a micelle is more than 140 ms. The apparent radius of gyration R _G, mic is fairly independent of concentration, but large effects are observed on varying the temperature. Raising the temperature initially results in an increase of the apparent micellar size, followed by a maximum at an intermediate temperature (≈45 °C). At higher temperatures a contraction of the micelles is observed. The shape of the micelles also appear to vary in this temperature interval. The interactions responsible for these phenomena are discussed in terms of, e.g., the temperature-dependent solubility of the alkylene oxide segments in water and polydispersity effects. Received: 29 January 1996 acccepted : 4 November 1996     

Gelation mechanism and microstructure of organogels formed with various types of gelators

The small‐angle neutron scattering (SANS) and dynamic light scattering (DLS) investigation were carried out for organogels in toluene, formed by organogelators, to elucidate the relationship between the chemical structure and the gelation mechanism as well as the physical properties of the gels. Three different organogelators, that is cyclo(L ‐β‐3,7‐dimethyloctylasparaginyl‐L ‐phenylalanyl) (CPA), trans‐(1R,2R)‐bis(undecylcarbonylamino)cyclohexane (TCH), and N^ε‐lauroyl‐N^α‐stearylaminocarbonyl‐L ‐lysine ethyl ester (LEE), were chosen for comparison. The SANS intensity functions of toluene solutions of these gelators could be reduced with the concentration and were described with a scattering function for thin rods. This indicates that the gels consist of noncorrelated, rod‐like elements aggregated to each other. The characteristic features of the gelation properties, such as the critical gelation concentration, C_gel, the gelation temperature, T_gel, the gel structure, and the gelation mechanism, were different from each other. CPA had the lowest C_gel and became a gel gradually as the temperature decreased, while TCH and LEE had higher C_gels and underwent a sharp sol–gel transition. We conclude that the gelation mechanisms between the CPA and TCH solutions are different. The “CPA type” gelators form a gel by a linear extension of hydrogen‐bonded plane, while the “TCH type” gelators form a twisted wire, because of its strong helicity and crystallizability. In addition, in the latter type, a next generation of fibrils easily stacks on top of the previous ones to form larger fibrils. These models well explain the DLS results and the mechanical properties. That is, the fibrillar stems in CPA gels are rather mobile and fragile, while those in TCH and LEE are frozen and brittle. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3567–3574, 2005     

Evidence for hydrophobic attraction between latex particles in aqueous systems as investigated by turbidimetry

We report the evidence for attractive interaction of latex particles which are covered by poly(ethylene oxide) chains. These particles are suspended in aqueous solutions of ammonium sulfate. The interaction is probed by measurements of the turbidity of the suspensions up to 70 g/l. Turbidity is insensitive to multiple scattering and allows the static structure factor, S(q) [q=(4πn ₀/λ₀)sin(θ/2), where θ is the scattering angle, n₀ is the refractive index of the medium and λ₀ is the wavelength in vacuo], to be determined at small q values. The analysis of S(q) at small q values yields information about possible attraction of the particles. The analysis of the turbidity data furthermore shows that no aggregation took place in these systems. A weak but long-range attractive interaction was found at ammonium sulfate concentrations of 0.01 and 0.1 M. The relation of this attractive force to hydrophobic forces is discussed. Received: 9 March 2000/Accepted: 28 June 2000     

Structure formation of surfactants in concentrated sulphuric acid: a light scattering study

A common cationic surfactant,n-hexadecylammonium hydrogensulphate, dissolved in concentrated sulphuric acid, has been studied by static and dynamic light scattering. Micelle formation has been observed even in this unusual solvent. An apparent molar mass of 45 500±4.5% was found for the aggregates. A translational diffusion coefficientD ₀=5.5×10^–9 cm²/s was measured which gave a hydrodynamically effective radius ofR _h=17.7 nm. The geometric radius of gyration wasR _g=76.2 nm. The ratioR _g/R _h=4.33 is indicative for rodlike structures. Assuming a polydispersity ofL _w/L _n=2 this corresponds to a cylinder ofL _w=152 nm. An axial ratiop _w=(L _w/d)=60.4 nm was estimated which leads to a cylinder diameter of 2.53 nm. At surfactant concentrations higher than 5% (w/vol) the rod-like micelles aggregate to form more globular structures. The time correlation function, recorded by dynamic light scattering, exhibited a two-step decay which indicates a bimodal distribution of particle sizes. The fast motion coincides with that of the micelles at low concentrations while the other is slower than the fast one by three orders of magnitude and corresponds to the translational motion of large clusters.     

Resonance Scattering Spectral Determination of HSA with a New Scattering Enhanced Reagent of K_3[Fe(CN)_6]

Ｐｒｏｔｅｉｎｄｅｔｅｒｍｉｎａｔｉｏｎｉｓｖｅｒｙｉｍｐｏｒｔａｎｔｔｏｂｉｏｃｈｅｍ ｉｓｔｒｙａｎｄｂｉｏａｎａｌｙｔｉｃａｌｃｈｅｍｉｓｔｒｙ ,ａｎｄａｎａｎａｌｙｔｉｃａｌｉｔｅｍｏｆｑｕａｌｉｔｙｃｏｎｔｒｏｌｓｉｎｔｈｅｓｅｐａｒａｔｉｏｎｏｒｐｕｒｉｆｉｃａｔｉｏｎｏｆｂｉｏ ｌｏｇｉｃａｌａｎｄｃｈｅｍｉｃａｌｐｈａｒｍａｃｅｕｔｉｃａｌｓａｎｄｔｈａｔｏｆｆｏｏｄｅｘ ａｍｉｎａｔｉｏｎ .Ｃｏｍｐａｒｅｄｗｉｔｈｃｏｍｍｏｎｓｐｅｃｔｒｏｐｈｏｔｏｍｅｔｒｉｃｍｅｔｈｏｄｓｕｃ…     

Real-Time Observation of Pyoverdine Dissolving Ferric Hydroxide

Pyoverdine is one of the siderphores excreted by Pseudomonas aeruginosa that can help microbe to uptake iron in vitro. To determine the effect of pyoverdine chelating with iron, we purified the free pyoverdine and applied the dynamic laser light scattering (DLS) to detect the interaction between the pyoverdine and ferric hydroxide. The real-time DLS data analysis indicated that pyoverdine can directly combine with Fe(OH)₃ to form complexes and these substances are gradually degraded by themselves then completely disappeared. In our experiment, we have demonstrated that pyoverdine may not only chelate ferric ion but also availably dissolve ferric hydroxide which assists bacteria to survive in iron-deficient environments.     

A Simple and Sensitive Label‐free Immunoassay for Factor B Using Resonance Scattering Spectral Detection

In pH 7.2 Na₂HPO₄‐NaH₂PO₄ buffer solution and in the presence of PEG‐6000, goat‐anti‐human factor B (GABF) was combined with human factor B (BF) specifically, and aggregated to form immune complex particles that exhibited a resonance scattering (RS) peak at 400 nm. The laser scattering indicated that the average diameter of immune complex particles was 1320 nm. BF in the concentration range of 0.04 to 9.60 µg/mL was proportional to the resonance scattering intensity at 400 nm. Its regression equation was ΔI=33.61C+ 1.4, with a correlation coefficient of 0.9969, and a detection limit of 0.01 µg/mL BF. This label‐free resonance scattering spectral (RSS) method has been applied to the determination of BF in serum samples, and the results were in agreement with that of the immunoturbity.     

改进型溶胶-凝胶法制备粒径可调高染料吸附量TiO2微球及其在染敏电池光散射层中的应用

利用改进型的溶胶-凝胶法, 制得了由锐钛矿相纳米颗粒组成的TiO₂多孔微纳小球。通过调节前驱物浓度, 合成出粒径可控的尺寸分别为100, 175, 225, 475 nm的TiO₂微纳小球, 并通过电泳沉积法将合成出的小球作为光散射层引入到染料敏化太阳电池(DSSC)中。由于这种微纳小球在具备良好的光散射性能的同时也具备较高的染料吸附量, 因此相较于基于纳米颗粒的单层结构的DSSC拥有更高的光电转换效率。通过比较分析, 粒径尺寸为475 nm的微球作为光散射层的DSSC光电转换效率可以达到6.3%, 较之于基于纳米颗粒的DSSC提高了30%。     

Fabrication of Core-Shell Nanocolloids with Various Core Sizes to Promote Light Capture for Green Fuels

Core-shell nanocolloids with tailored physical and chemical merits hold attractive potential for energy-related applications. Herein, core-shell nanocolloids composed of zinc/copper sulfide (ZnS/CuS_x) shells and silica (SiO₂) cores were fabricated by a template-engaged synthetic method. Interestingly, the sizes of SiO₂ cores can be tuned by different sulfurization time. In virtue of the light scattering and reflection on the SiO₂ surface, the efficiencies of light capture by ZnS/Cu₂S shells were highly dependent on the SiO₂ sizes. The as-fabricated SiO₂@ZnS/Cu₂S with a core size of 205 nm exhibited the highest and broadest absorption within a light wavelength of 380–700 nm. In virtue of the structural and componential features of these nanocolloids, maximum photocatalytic hydrogen (H₂) production rates of 2968 and 1824 μmol h⁻¹ g⁻¹ under UV-vis and visible light have been delivered, respectively. This work may provide some evidence for the design and fabrication of core-shell nanomaterials to convert solar energy to green fuels.     

Colloidal crystals made of poly(N-isopropylacrylamide) microgel particles

Poly (N-isopropylacrylamide) microgel particles are found to form colloidal crystals similar to those occurring in typical hard-sphere colloids like poly(methylmethacrylate) beads. Samples made of particles with different cross-linker concentrations are investigated and their deswelling ratio is determined using dynamic light scattering. Small-angle neutron scattering data are also presented and analysed in terms of a face-centred-cubic crystal structure. The characteristic length, a, of the elementary cell is found to be 535 ± 16 and 495 ± 15 nm for the two systems investigated. This leads to particle radii of 189 ± 6 and 175 ± 5 nm, respectively. These values compare well to the radii determined using several different methods. Received: 26 July 1999/Accepted: 21 March 2000     

Growth of silica nanoparticles in methylmethacrylate-based water-in-oil microemulsions

The mechanism of silica particle formation in monomer microemulsions is studied using dynamic light scattering (DLS), atomic force microscopy, small-angle X-ray scattering (SAXS), and conductivity measurements. The hydrolysis of tetraethylorthosilicate (TEOS) in methylmethacrylate (MMA) microemulsions (MMA = methylmethacrylate) is compared with the formation of SiO₂ particles in heptane microemulsions. Stable microemulsions without cosurfactant were found for MMA, the nonionic surfactant Marlophen NP10, and aqueous ammonia (0.75 wt%). In the one-phase region of the ternary phase diagram, the water/surfactant ratio (R _w) could be varied from 6 to 18. The DLS and SAXS measurements show that reverse micelles form in these water-in-oil (w/o) microemulsions. The minimum water-to-surfactant molar ratio required for micelle formation was determined. Particle formation is achieved from the base-catalyzed hydrolysis of TEOS. According to atomic force microscopy measurements of particles isolated from the emulsion, the particle size can be effectively tailored in between 20 and 60 nm by varying R _w from 2–6 in heptane w/o microemulsions. For MMA-based microemulsions, the particle diameter ranges from 25 to 50 nm, but the polydispersity is higher. Tailoring of the particle size is not achieved with R _w, but adjusting the particle growth period produces particles between 10 and 70 nm.     

一种快速高选择性检测痕量癌胚抗原的共振散射光谱法

用10 nm的金纳米粒子标记单克隆癌胚抗原抗体制备了检测癌胚抗原（CEA）的共振散射光谱探针（Au-CEAAb）。在pH 6.8 的Na2HPO4- NaH2PO4缓冲溶液中及聚乙二醇-6000存在下, CEA与Au-CEAAb发生免疫反应聚集形成疏水性的、平均粒径为227.0 nm的免疫复合物微粒,并在321 nm、581 nm产生2个共振散射峰。随着癌胚抗原（CEA）浓度的增大,581 nm处的共振散射强度I581nm线性增加,其增加值△I581nm与CEA浓度在1.0～50.0 ng·mL-1范围内呈良好的线性关系,相应的回归方程、相关系数、检出限(3σ)分别为ΔI581nm=1.63 C +5.6、0.9940、0.52 ng·mL-1。该法简便、快速、灵敏且选择性好,用于检测人血清中癌胚抗原（CEA）,结果满意。     

改进型溶胶-凝胶法制备粒径可调高染料吸附量TiO2微球及其在染敏电池光散射层中的应用

利用改进型的溶胶-凝胶法,制得了由锐钛矿相纳米颗粒组成的TiO2多孔微纳小球。通过调节前驱物浓度,合成出粒径可控的尺寸分别为100,175,225,475 nm的TiO2微纳小球,并通过电泳沉积法将合成出的小球作为光散射层引入到染料敏化太阳电池(DSSC)中。由于这种微纳小球在具备良好的光散射性能的同时也具备较高的染料吸附量,因此相较于基于纳米颗粒的单层结构的DSSC拥有更高的光电转换效率。通过比较分析,粒径尺寸为475 nm的微球作为光散射层的DSSC光电转换效率可以达到6.3%,较之于基于纳米颗粒的DSSC提高了30%。     

The effect of salts on the conformation and microstructure of poly(N‐isopropylacrylamide) (PNIPA) in aqueous solution

We present an experimental investigation of the conformation and microstructure of Poly(N‐isopropylacrylamide) (PNIPA) in aqueous solution in the presence of salts. As a model, a strong salting–out salt (Na₂SO₄) and a strong salting–in salt (NaSCN) were chosen. Light scattering measurements show that Na₂SO₄ decreases the radius of gyration of PNIPA compared to its value in water, whereas NaSCN increases it. Moreover, the NaSCN solution was found to be a better solvent for PNIPA compared to water, whereas Na₂SO₄ solution is worse. Small‐angle neutron scattering measurements of semidilute PNIPA solutions, at temperatures well below the phase‐transition temperature, exhibit the behavior predicted by the model of dynamic concentration fluctuations characterized by a single correlation length. Excess scattering at low angles is observed in salt solutions at temperatures that are near, yet below, the phase‐transition temperature. This may indicate intrachain heterogeneities on the scale of 6–8 nm. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3713–3720, 2004     

Quantification of uncertainties involved in the conformational study of polymers by light scattering

Gel permeation chromatography (GPC) combined with a multi-angle light scattering (MALS) is a very powerful characterization technique because it provides both absolute molecular weight (M_w) and the radius of gyration (R_g) throughout the separated slices obtained by GPC. This combination of M_w and R_g, can be used to obtain information about the conformation of polymer chains in solutions and the branching of molecules. Due to the interesting properties obtained for polymers, it is essential to quantify the effect of different error sources in light scattering measurements as well as in the data treatment that highly affect the accuracy of obtained molar mass and radius of gyration. Usually, the results obtained for M_w and R_g in this analysis are dispersed for determined ranges of retention time and to have both reliable R_g and M_w for calculation, only high confidence data points have to be chosen. This range is arbitrarily chosen by the user for the data observation.In this work a new method of calculation to obtain R_g and M_w by means of GPC–MALS technique has been developed. As a first point, a data analysis procedure was set in order to describe both R_g and M_w vs. retention time and to determine the range where experimental data are confident. Several aspects in the data analysis have been studied. The polynomial fit function, the influence of the concentration of the sample, the reproducibility of the experiments and the conformational scaling law have been investigated by statistic technique in order to quantify the uncertainties involved.     

Matched ring diblock and linear triblock copolymers in dilute solution

A unique diblock copolymer ring and its linear triblock copolymer precursor composed of polystyrene and polydimethylsiloxane have been characterized by static and dynamic light scattering in dilute solution. The measurements were carried out with cyclohexane as the solvent over a temperature range of 12–35°C. Cyclohexane has the useful property that it is nearly isorefractive with the PDMS so that the PDMS block segments are invisible to the light-scattering technique and it is a theta solvent for polystyrene at 34.5°C. The block polymers in this work contain 35.1 wt % of styrene as determined by proton NMR. In the linear triblock polymer, the polystyrene is the center block with PDMS blocks on each side. Static light scattering measurements give 4.31 × 10⁴ for the average molecular weight of the whole polymer. Light scattering also shows that the apparent theta temperature for the linear triblock is shifted by 15°C to a value of 20°C at which point the second virial coefficient drops sharply and phase separation begins to induce aggregation. The diblock ring, however, shows a strongly positive second virial coefficient and no aggregation even at 12°C which is the limit of these experiments. The diffusion coefficients of cyclic diblock (D_c) and linear triblock copolymer (D₁) are measured by dynamic light scattering. The ratio of diffusion coefficients of cyclic and linear copolymers at 14.9°C and 30°C are D_c/D_l = 1.13 and 1.107 respectively. These compare well with prediction of 1.18 for this ratio from consideration of the hydrodynamics of matched linear and cyclic polymer chains. Dynamic light scattering quantitatively confirms that the linear copolymer experiences a solvent quality change near 20°C but the cyclic polymer remains in good solvent over the entire experimental temperature range. © 1993 John Wiley & Sons, Inc.     

Characterization of Particle Size and Shape in an Ageing Bismuth Titanate Sol Using Dynamic and Static Light Scattering

The ageing characteristics of a metal-alkoxide solution, used to prepare thin films of ferroelectric bismuth titanate, Bi₄Ti₃O₁₂, were carefully scrutinized using laser light scattering. Dynamic light scattering experiments revealed a bimodal distribution of hydrodynamic diameters, with larger molecular clusters increasing in size from 4 to 68 nm over the course of 60 days ageing in a sealed vial. Static light scattering measured the radius of gyration to be 71 nm. Comparison of these two results suggests that these clusters are approximated as thin cylindrical (or chainlike) structures. Using ellipsoid scattering theory, plots of scattered light intensity versus q (scattering) vector also suggest a long cylindrical type cluster with a length of 350 nm and a diameter of 4 nm. Some deviation of experimental data from the theoretical curves probably is an indication of some flexibility and/or fractal nature of the molecular clusters. Such anisotropy in oligomeric cluster shape apparently has a strong influence on final crystallographic texturing of ceramic thin films made by spin-coating of these solutions on flat substrates.     

Neutron scattering and electrophoresis of dodecyldimethylamine oxide micelles

Small-angle neutron scattering (SANS) measurements were carried out at 25 °C on dodecyldimethylamine oxide solutions under different conditions. In media with no added salt, the micelle aggregation number remained nearly constant (70–78) over the range of the degree of ionization, α_M, between 0 and 0.73 in contrast with the sharp critical micelle concentration increase in a narrow range of α_M from 0.35 to 0.40. This characteristic α_M dependence that deviates markedly from the prediction of the regular solution approach is thus shown to take place without a considerable change with respect to micelle size and shape. The surface electric potential employed to calculate the intermicellar repulsion under the Debye–Hückel approximation was found to be much lower than the actual surface potential determined from hydrogen ion titration. This inconsistency was solved by introducing a rescaled particle size for the hard-sphere interaction part. The surface potential from SANS was rather similar to the zeta potential determined by electrophoretic light scattering. In the range of NaCl concentrations higher than about 0.2 M, micelle growth was observed for both the hemihydrochloride (1:1 complex) and the cationic species and the growth into a cylindrical shape was confirmed. Received: 3 March 1999 Accepted in revised form: 22 April 1999