196,198 research outputs found
Effect of Block Copolymers and their Homopolymers on the Gelation Kinetics of Aqueous Laponite Dipsersions. Rheology and Dynamic Light Scattering Studies
No full textThe solubilisation behaviour of some dichloroalkanes in aqueous solutions of PEO-PPO-PEO triblock copolymers: a dynamic light scattering, fluorescence spectroscopy, and SANS study
No full textThe aggregation behaviour of PEO–PPO–PEO triblock copolymers in water and in water þ
chlorinated additive mixtures was studied by means of fluorescence spectroscopy, dynamic light
scattering (DLS), and small-angle neutron scattering (SANS). The copolymers were chosen such
as to investigate the effects of molecular architecture (L35 and 10R5) and molecular weight by
keeping constant the hydrophilic/hydrophobic balance (F88 and F108). 1,2-Dichloroethane was
used as a prototype of water basins contaminants. The hydrodynamic radius of the block
copolymer aggregates (Rh,M) and the intensity ratio of pyrene of the first and the third vibrational
band (I1/I3) were determined as a function of temperature (10–45 1C) and concentration. The
copolymer architecture essentially does not affect Rh,M in the entire range of temperature and
concentration investigated. At a given temperature, increasing macromolecular size leads to a
decrease of Rh,M. With rising temperature Rh,M also decreases. According to the DLS results, the
I1/I3 change with temperature clearly detects the aggregation only for F88 and F108. The
presence of 1,2-dichloroethane, at concentrations close to its solubility in water, does not lead to
changes in the distribution of hydrodynamic radii for L35 and 10R5. Larger quantities of additive
induce the formation of quite polydisperse mixed aggregates for L35 and of networks for 10R5.
In the case of F88 and F108, low concentrations of additive lead to formation of mixed
aggregates with smaller Rh,M. The SANS results corroborate the DLS and fluorescence findings
proving enhancement of the copolymer aggregation through the presence of 1,2-dichloroethane.
The DLS findings combined with those from the fluorescence spectroscopy provide some insight
into the site of solubilisation of the additive in the aggregates
Selectivity of cyclodextrins as a parameter to tune the formation of pseudorotaxanes and micelles supramolecular assemblies. A systematic SANS study
No full textDieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.We studied the formation of polypseudorotaxanes formed with cyclodextrins (CDs) threading a copolymer chain that forms self-assembled structures in water. The size of the CD cavity was chosen such that it is block selective with respect to the formation of inclusion complexes and therefore in terms of altering the structure of the copolymer self-assemblies in a systematic fashion. Small angle neutron scattering (SANS) experiments provide a direct and clear picture of the shape and interactions of the copolymer micelles in the absence and the presence of various CDs. Moreover, the dissolution of copolymer micelles by CD addition was clearly described by a simple model which provides a tool for quantitative predictions. This study suggests the possibility of designing materials with tunable aggregation abilities in water, where the extent of aggregate formation is determined by the amount and type of added cyclodextrin.EC/FP7/226507/EU/Integrated Infrastructure Initiative for Neutron Scattering and Muon Spectroscopy/NMI
Tuning the Gelation of Aqueous Laponite Dispersions by means of Block Copolymers and their Homopolymers
No full textPhysico-chemical investigation of inorganic salt nanoparticles confined in dry reversed micelles
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Quantitative description of temperature induced self-aggregation thermograms determined by differential scanning calorimetry
No full textA novel thermodynamic approach for the description of differential scanning calorimetry (DSC) experiments on self-aggregating systems is derived and presented. The method is based on a mass action model where temperature dependence of aggregation numbers is considered. The validity of the model was confirmed by describing the aggregation behavior of poly(ethylene oxide)-poly(propylene oxide) block copolymers, which are well-known to exhibit a strong temperature dependence. The quantitative description of the thermograms could be performed without any discrepancy between calorimetric and van 't Hoff enthalpies, and moreover, the aggregation numbers obtained from the best fit of the DSC experiments are in good agreement with those obtained by light scattering experiments corroborating the assumptions done in the derivation of the new model
Shape fluctuations of microemulsion droplets: a neutron spin-echo study
No full textHellweg T, Gradzielski M, Farago B, Langevin D. Shape fluctuations of microemulsion droplets: a neutron spin-echo study. Colloids and Surfaces A Physicochemical and Engineering Aspects. 2001;183-185:159-169.An alternative approach to the determination of the bending elastic constants of the surfactant film in droplet microemulsions was presented recently, which accounts for the viscosity differences of the liquids forming the microemulsion. In this work the approach will be applied to investigate a C8E3 and C10E4 based microemulsion containing the oil n-decane. The determined values for kappa and )over bar> are compared to results from macroscopic measurements. (C) 2001 Elsevier Science B.V. All rights reserved
Effect of the supramolecular interactions on the nanostructure of halloysite/biopolymer hybrids: A comprehensive study by SANS, fluorescence correlation spectroscopy and electric birefringence
No full textThe structural properties of halloysite/biopolymer aqueous mixtures were firstly investigated by means of combining different techniques, including small-angle neutron scattering (SANS), electric birefringence (EBR) and fluorescence correlation spectroscopy (FCS). Among the biopolymers, non-ionic hydroxypropylcellulose and polyelectrolytes (anionic alginate and cationic chitosan) were selected. On this basis, the specific supramolecular interactions were correlated to the structural behavior of the halloysite/biopolymer mixtures. SANS data were analyzed in order to investigate the influence of the biopolymer adsorption on the halloysite gyration radius. In addition, a morphological description of the biopolymer-coated halloysite nanotubes (HNTs) was obtained by the simulation of SANS curves. EBR experiments evidenced that the orientation dynamics of the nanotubes in the electric field is influenced by the specific interactions with the polymers. Namely, both variations of the polymer charge and/or wrapping mechanisms strongly affected the HNT alignment process and, consequently, the rotational mobility of the nanotubes. FCS measurements with fluorescently labeled biopolymers allowed us to study the aqueous dynamic behavior of ionic biopolymers after their adsorption onto the HNT surfaces. The combination of EBR and FCS results revealed that the adsorption process reduces the mobility in water of both components. These effects are strongly enhanced by HNT/polyelectrolyte electrostatic interactions and wrapping processes occurring in the halloysite/chitosan mixture. The attained findings can be useful for designing halloysite/polymer hybrids with controlled structural properties
Small Angle Neutron Scattering, X-ray Diffraction, Differential Scanning Calorimetry, and Thermogravimetry Studies to Characterize the Properties of Clay Nanocomposites
No full textNanocomposites based on laponite RD and (ethylene oxide)98(propylene oxide)67(ethylene oxide)98 (F127)triblock copolymer or poly(ethylene) glycol 2000 (PEG2000) were prepared by using the melting method.
Small-angle neutron scattering and the X-ray diffraction experiments provided insights into the organization of the laponite RD dispersed in the macromolecular matrix over a wide length scale. SANS data analysis by means of a fractal law evidenced the formation of clusters of laponite RD at long correlation distance. The
single laponite RD particles and the lamellar structure of F127 were described in the shorter length scale.
Finally, the crystalline structure of the macromolecule was observed for very short length scales. Differential scanning calorimetry measurements confirm that the macromolecule anchored to the laponite RD surface is
amorphous, in agreement with the XRD findings, and allowed to determine amount and thickness of the
adsorbed macromolecule layer. The mesoscopic structure of the nanocomposites is straightforwardly correlated with the macroscopic properties (thermal stability, crystallization), which are crucial in the application areas.
Namely, the different effect played by the nanofiller on the thermal stability of F127 and PEG2000 was correlated to the laponite RD cluster size. Accordingly, the thermal stability of the nanocomposites is enhanced if the clusters have a smaller size. As concerns the crystallization, the clusters were invoked as responsible
for the observed retardation of the growth of the crystalline domains due to an increased diffusion energy
barrier that slows down the macromolecule mobility
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