Confined polymer dynamics on clay platelets

The structure and dynamics of poly(ethylene oxide) adsorbed on dispersed clay platelets are investigated by small-angle neutron scattering and neutron spin-echo spectroscopy. The intermediate scattering function has a mobile contribution described by the Zimm theory and an immobile contribution that is constant within the time window. The immobile fraction as a function of the scattering vector Q is described by a Lorentz function, from which a localization length is determined. The relaxation rates grow with polymer concentration in agreement with dielectric measurements but contrary to pure polymer gels.     

Molecular motion in polymer networks and concentrated solutions from photon correlation spectroscopy

The dynamics of well-characterised polymer networks have been studied from Rayleigh light scattering linewidth measurements using photon correlation spectroscopy. The linewidth dependence on scattered wave-vector and on the degree of chemical cross-linking can be described by a model of whole molecule diffusion which is restricted by certain sites along it being cross-linked into the network. Linewidths of uncross-linked polymer solutions of similar concentrations have been found to be smaller by about a factor of two.     

Coupling of concentration fluctuations to viscoelasticity in highly concentrated polymer solutions

Photon correlation spectroscopy in the polarized geometry has been used to systematically investigate the complex dynamics of a highly concentrated entangled polymer solution in a nominally good solvent, poly(butylacrylate) in dioxane. In addition to the well known fast cooperative diffusion process, a slow virtuallyq-independent mode is detected, whereq is the scattering wavevector, in agreement with previous experimental works on semidilute solutions. This mode is attributed to the viscoelastic nature of the transient physical network, formed by the entanglements, which relaxes its elastic stress induced by the concentration fluctuations, as confirmed by small amplitude oscillatory shear measurements; the latter reveal a terminal relaxation time comparable to the characteristic time of the slow relaxation process. Results, especially in terms of concentration and temperature dependence, are evaluated and discussed in view of the existing theoretical treatments in the field, predicting the existence of the slow viscoelastic relaxation. The relationship between dynamic light scattering and mechanical spectroscopy is established.     

荧光关联光谱在高分子单链研究中的应用

荧光关联光谱(fluorescence correlation spectroscopy,FCS)是一项用于研究体系动力学性质的统计光谱技术,随着它被引入材料与化学研究领域,近年来取得了大量全新的研究成果.该技术在高分子科学研究中也逐渐发挥出越来越大的作用,特别是在聚合物结构和动力学方面,这表明它在高分子领域的巨大潜力.本文将从FCS的基本原理、实验技巧以及在一些具有挑战性体系中的应用等方面展开,着重介绍它在高分子溶液,如聚电解质溶液、高分子混致不溶现象,以及不同的表界面体系中取得的新成果,展示FCS区别于其他传统技术的特点和优势.     

Structure and activity assay of nanozymes prepared by the coimmobilization of practically useful enzymes and hydrophilic block copolymers on gold nanoparticles

Enzyme/polymer/gold nanoparticle hybrids, called "nanozymes", were prepared and structurally analyzed by dynamic light scattering (DLS), ultraviolet-visible spectroscopy, and zeta-potential and transmission electron microscopy (TEM) measurements, which showed that the nanozyme particles were mainly composed of a single gold nanoparticle, on whose surface the enzyme and polymer were coimmobilized. This kind of structure resulted in the high dispersion stability of the nanozyme under various conditions, accompanied by improved thermal stability of the enzyme.     

Interaction between the conjugated polyelectrolyte poly{1,4-phenylene[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} copolymer and the lecithin mimic 1-O-(l-Arginyl)-2,3-O-dilauroyl-sn-glycerol in aqueous solution

In this paper, the interaction between the water-soluble conjugated polyelectrolyte poly{1,4-phenylene[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} copolymer and the amino acid glyceride conjugate 1-O-(L-arginyl)-2,3-O-dilauroyl-sn-glycerol dichlorohydrate (a mimic for the phospholipid lecithin) has been studied in aqueous solution by electronic spectroscopy (absorption and fluorescence) and small-angle neutron scattering (SANS). A significant increase in the polymer fluorescence and blue shift in its emission are observed on association with the surfactant. This is suggested to be due to breakup of polymer aggregates. In addition, the spectroscopic and photophysical data suggest this is followed by the vesicle to ribbon transition characteristic of this surfactant, leading to incorporation of single chains of the polymer within mixed polymer-surfactant aggregates. Support for this comes from preliminary SANS measurements, from which evidence for polymer dissolution and formation of two-dimensional structures has been obtained.     

Polyethyleneglycol-pepsin interaction and its relationship with protein partitioning in aqueous two-phase systems

The interaction between the acidic protein, pepsin, and the non-charged polyethyleneglycol polymer was studied by dynamic light scattering, fluorescence spectroscopy and measurements of the protein thermal stability at neutral pH. Polyethyleneglycol of average molecular mass 1450 showed a higher interaction capacity with the protein than polyethyleneglycol of average molecular mass 8000. Polyethyleneglycol of average molecular mass 1450 showed a molecular mechanism where the interpolymer interaction led to the complex formation. This fact can be explained taking into account that the extended form on this polymer molecule favours the interaction with the protein, which is highly dependent of the polymer total concentration. Polyethyleneglycol of average molecular mass 8000 showed a cooperative interaction between the polymer and protein molecules which was independent of the PEG concentration.     

Polyethyleneglycol–pepsin interaction and its relationship with protein partitioning in aqueous two-phase systems

The interaction between the acidic protein, pepsin, and the non-charged polyethyleneglycol polymer was studied by dynamic light scattering, fluorescence spectroscopy and measurements of the protein thermal stability at neutral pH. Polyethyleneglycol of average molecular mass 1450 showed a higher interaction capacity with the protein than polyethyleneglycol of average molecular mass 8000. Polyethyleneglycol of average molecular mass 1450 showed a molecular mechanism where the interpolymer interaction led to the complex formation. This fact can be explained taking into account that the extended form on this polymer molecule favours the interaction with the protein, which is highly dependent of the polymer total concentration. Polyethyleneglycol of average molecular mass 8000 showed a cooperative interaction between the polymer and protein molecules which was independent of the PEG concentration.     

Multiple glass-transition temperatures in thin supported films of isotactic PMMA as revealed by enhanced Raman scattering

The glass-transition temperature, Tg, of isotactic PMMA thin films has been measured for four thicknesses by enhanced Raman spectroscopy and ellipsometry. This was made possible by inserting a silica spacer layer between the film and the substrate. The use of such a spacer drastically improves the sensitivity of Raman scattering measurements. The improvement in the sensitivity allows us to study phenomena involving changes in molecular dynamics, such as the phase transition, and to probe the existence in very thin films of several thickness-dependent transition temperatures, Tg(h). This in turn is interpreted as the occurrence in the film of a layered structure. The influence of the polymer concentration on the conformation of the surface adsorbed polymer layer and therefore on Tg(h) is discussed.     

Viscosity reduction in polymer nanocomposites: Insights from dynamic neutron and X-ray scattering

The addition of nanoparticles to a polymer matrix can in certain cases induce a reduction in viscosity, with respect to the pure matrix, in the resulting composites. This counterintuitive phenomenon cannot be explained using the most common rheological models. For this reason, it has been chosen as a good example in this paper to demonstrate the value and methods of dynamic X-ray and neutron scattering techniques for the investigation of polymer nanocomposites. An overview of the main results on this topic is presented together with an introduction to the basic concepts relating to X-ray photon correlation spectroscopy, neutron backscattering, and neutron spin echo measurements.     

Electrochemical characterization of ionically conductive polymer membranes

Cation conductive membranes, especially highly proton conductive membranes, are of interest not only for chlor-alkali electrolysis but for polymer electrolyte fuel cells as well. The very challenge for electrochemical characterization in this case is the low specific resistance of the polymer required for such applications, which in turn makes resistance measurements a non-trivial problem. We investigate the different possibilities to characterize such membranes. The present part of our work deals with the adequate conditioning and equilibration of membranes designed especially for direct methanol fuel cell applications, with the measurement of the conductivity and with the determination of apparent transport numbers in the membrane. The usefulness of the respective leaching investigations, impedance spectroscopy measurements and concentration potential measurements for the case of membranes made from sulfonated poly(phenylene oxide) is discussed.     

Preparation of magnetic polystyrene latex via the miniemulsion polymerization technique

Magnetic iron oxide (magnetite, Fe₃O₄) nanoparticles were encapsulated with polystyrene to give a stable water‐based magnetic polymer latex, using the miniemulsion polymerization technique. The resulting magnetic latexes were characterized with transmission electron microscopy (TEM), dynamic light scattering (DLS), vibrating sample magnetometer measurements (VSM), and ⁵⁷Fe Mössbauer spectroscopy measurements. TEM revealed that all magnetite nanoparticles were embedded in the polymer spheres, leaving no empty polystyrene particles. The distribution of magnetite particles within the polystyrene spheres was inhomogeneous, showing an uneven polar appearance. The DLS measurements indicated a bimodal size distribution for the particles in the latexes. According to our magnetometry and Mössbauer spectroscopy data, the encapsulated magnetite particles conserve their superparamagnetic feature when they are separated in the polymer matrix. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4802–4808, 2004     

Swelling and scattering investigations on chemically cross-linked poly(vinyl alcohol) hydrogels

Swelling and scattering measurements are reported from chemically cross-linked polyvinyl alcohol) hydrogels and the corresponding semi-dilute polymer solutions. The mixing free energy in the swollen network is found to be significantly smaller than that of the corresponding polymer solution at identical concentration. Static light scattering and small-angle neutron scattering measurements indicate the presence of large-scale static structures in the solution. Reasonable agreement is found between the osmotic moduli obtained from light scattering measurements and macroscopic osmotic observations.     

Studies of gaseous molecules by Raman spectroscopy

Raman spectroscopy of gaseous molecules, while not a routine technique, can provide a useful means of probing selected processes: for example, molecular conformation studies and combustion systems. The Raman trace scattering spectrum, obtainable from a suitable combination of the polarized components of the scattered light, is especially well suited for quantitative measurements.     

Novel water-soluble fluorescent polymer containing recognition units: Synthesis and interactions with PC12 cell

New water-soluble fluorescent poly(N-vinylpyrrolidone) (PVP) containing carbonylhydrazide recognition units was synthesized by free radical polymerization of N-vinylpyrrolidone in the presence of mercaptoacetic acid as chain transfer agent and then being modified by 1-pyrenebutyric acid hydrazide. FT-IR, ¹H NMR, gel permeation chromatography-multi-angle laser light scattering and fluorescence spectroscopy were used to characterize these polymers. Results of fluorescence measurements show that these polymers have a good affinity for deoxyribonucleic acid (DNA). The interactions with PC12 cell results indicated that the polymer with suitable molecular weight could penetrate into PC12 cell and emit fluorescence. This water-soluble polymer with recognition units and high luminescence can be used as a promising fluorescent probe for measurements of biomacromolecules and cells.     

Fabrication of nanoaggregates of poly(ethylene oxide)-b-polymethacrylate by complex formation with chitosan or methylglycolchitosan

Nanoaggregate formation of poly(ethylene oxide)-b-polymethacrylate (PEO-b PMA) is induced by chitosan (Ch) or methylglycolchitosan (MGC). The nanoaggregates are basically obtained by electrical charge neutralization of the anionic PMA block of the PEO-b-PMA polymer with cationic Ch or MGC, which results in insolubilization of the PMA block to form the core of the aggregates. Formation of the nanoaggregates was confirmed by dynamic light scattering, fluorescence spectroscopy, atomic force microscopy and zeta-potential measurements. The properties of the nanoaggregates depend upon the concentration of the polymer as well as the concentration of Ch or MGC. The significance of these aggregates is their ability to incorporate ionic species, leading them to potential applications as drug carriers and nanoreactors.     

Properties of cellulose acetate in solution. II. Light scattering and elasticity measurements on gels in benzyl alcohol

Kinetic studies are reported for the light scattering and elasticity of thermally reversible gels of cellulose acetate in benzyl alcohol over a range of temperature and polymer concentration. The small-angle light scattering data are found to be described by exponential correlation functions, and it is concluded that the scattering has its origin in the nonrandom character of the crosslinking in the gels studied. The elasticity is discussed in terms of the density of crosslinks in the gels. Thus, the kinetics studied by light scattering and elasticity measurements are independently related to temperature and polymer concentration.     

Structure and size of spontaneously formed aggregates in Aerosol OT/PEG mixtures: effects of polymer size and composition

Dynamic light scattering and Cryo-TEM measurements have allowed us to obtain the size and structure of spontaneous aggregates formed by mixtures of Aerosol OT, AOT, and ethylene glycol polymers of different molecular mass. The results presented in this work show that small unilamellar vesicles predominate in pure Aerosol OT solutions and in dilute polymer solutions mixed with AOT. In the latter case, elongated micelles coexist with unilamellar vesicles. When polymer concentration increases above a certain concentration, the small vesicles disappear and the size of the elongated micelles decreases to a radius compatible with spherical micelles. For PEG concentrations above the overlapping ones, spherical micelles coexist with very large aggregates probably formed by large rod like micelles or by superstructures of elongated micelles embedded in a polymer network. This behavior is consistent with theoretical models based in molecular mean-field theory [M. Rovira-Bru, D.H. Thompson, I. Szleifer, Biophys. J. 83 (2002) 2419]. The properties of the different types of aggregates are obtained by fluorescence spectroscopy and electrophoretic mobility measurements.     

Dilute solution properties and phase separation of branched low-density polyethylene

Viscosity, light scattering, and precipitation temperature measurements on dilute solutions of high-density and low-density polyethylene fractions have been carried out and a theory by Flory for phase equilibrium of linear polymers has been extended to branched polymer. From the results, it is shown that the entropy parameter ψ, depends on branching; a method for the determination of long-chain branching in polymer fractions is proposed combining precipitation temperature and molecular weight measurements. The method has been applied to the evaluation of long-chain branching in low-density polyethylene.     

A new attempt to study biomineralised silica bodies in Dactylis glomerata L

The accumulation process of inorganic compounds in animals and plants by biomineralisation is not well understood nowadays, though it may be the key to an environmental-compatible production of modern materials in future. In this paper a new attempt will be made on the investigation of silica accumulation in grasses (especially Dactylis glomerata L.). The silicic acid agglomerates in Dactylis glomerata L. were studied by means of scanning electron microscopy in combination with energy dispersive X-ray spectrometry as well as infrared and micro-RAMAN spectrometry.In particular blades were prepared by critical point drying or shock-freezing for anatomical studies of silica cells and bristles in the plant tissue. SEM imaging and EDX microanalysis for elemental composition were done in the cryostage as well as under variable pressure. The localized silica bodies were examined for their structural properties by means of IR and micro RAMAN spectroscopy. The results are comparable to SiO(2) polytypes such as high disperse silica and opal.