1,721,113 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 textTuning the Gelation of Aqueous Laponite Dispersions by means of Block Copolymers and their Homopolymers
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
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
Get PDFThe 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
Nanocomposites based on block copolymers and inorganic nanoparticles. Structural and thermal properties
No full textEffect on the block copolymer self-assembling in water of block selective cyclodextrin addition
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