Search results for "DYNAMIC LIGHT SCATTERING"
showing 10 items of 211 documents
Mesoscopic gel at low agarose concentration in water: a dynamic light scattering study
1995
Previous work in our laboratory has shown that at very low agarose concentration in water gelation still occurs within mutually disconnected, high concentration regions generated by spinodal demixing. The freely diffusing particles obtained in these conditions are studied in the present work by depolarized dynamic light scattering and probe diffusion experiments. These particles are found to behave as large (in fact, mesoscopic) polymer fibers entangled in a continuously rearranged mesh with scaling parameters typical of partially flexible, neutral chains. The present results allow specifying the notion of mesoscopic gelation. They also reveal that the same symmetry-breaking mechanism that …
Origin of the low-frequency plateau and the light-scattering slow mode in semidilute poly(ethylene glycol) solutions
2019
A low-frequency plateau is often found in the rheological spectra of various kinds of semidilute solutions of polymers and other colloids; also, many such solutions have been reported to show slow-modes in their dynamic light scattering autocorrelation functions. Both these observations may lead to the hypothesis of weak associative network structures built by the dissolved polymer chains or colloidal building blocks. To challenge this hypothesis, we conduct a series of comparative studies on semidilute solutions of poly(ethylene glycol) by using classical rheology as well as passive microrheology based on dynamic light scattering, along with structural studies using static light scattering…
Polyelectrolytes in dilute solution: viscometric access to coil dimensions and salt effects
2015
Copolymers of acrylamide (AM) and diallyldimethylammonium chloride (DADMAC), differing in molar masses M (52.3 to 227 kDa) and degrees of charging y (0.2 to 0.6), were studied with respect to their viscometric behavior in dilute aqueous solutions containing variable amounts of NaCl. Complementary measurements were performed on a Brookhaven 90 plus particle size analyzer. M dominates the intrinsic viscosities [η]. For the viscometric interaction parameters B this is only true for large concentrations of extra salt. [η] and B as a function of solvent salinity follow Boltzmann laws. Coil dimensions, determined either via dynamic light scattering or viscometry, agree well. For low salt contents…
Chain Stiffness of Elastin-Like Polypeptides
2010
The hydrodynamic radii of a series of genetically engineered monodisperse elastin like polypeptides (ELP) was determined by dynamic light scattering in aqueous solution as function of molar mass. Utilizing the known theoretical expression for the hydrodynamic radius of wormlike chains, the Kuhn statistical segment length was determined to be lk = 2.1 nm, assuming that the length of the peptide repeat unit was b = 0.365 nm, a value derived for a coiled conformation of ELP. The resulting chain stiffness is significantly larger than previously reported by force-distance curve analysis (lk < 0.4 nm). The possible occurrence of superstructures, such as hairpins or helices, would reduce the conto…
Highly Defined, Colloid‐Like Ionic Clusters in Solution
2012
Many societal challenges at the beginning of the 21st century lead to an apparent and growing need for functional materials and novel ways of materials synthesis and assembly. Rising to the challenge, the utilization of small, self-assembling building blocks for the bottom-up construction of new types of polymers and nanostructures has enjoyed increasing popularity among materials researchers in the recent past. Supramolecular materials like foldamers, surface films, nanoparticles, etc. are created by exploiting noncovalent forces [1] leading to an ordered arrangement of nanoscale building blocks. [2] In the search for new polymers based on noncovalent molecular forces, we are motivated by …
Porphyrin-Polymer Networks, Worms, and Nanorods: pH-triggerable Hierarchical Self-assembly
2011
In this study, we present a novel, multifaceted pH-triggerable system of self-organized hierarchical nanostructures. The system consists of meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and poly(2-vinylpyridine) cylindrical brushes (PVP brushes) and can yield polymer-porphyrin networks, porphyrin loaded polymer brushes and pure porphyrin nanorods. In addition, the polymer influences the pK(a) and the mutual TPPS stacking geometry. Structures were characterized by AFM, dynamic light scattering using an IR laser, UV-Vis spectroscopy and small-angle neutron scattering (SANS). Supramolecular composite porphyrin structures that can be switched through external triggers have potential in photo…
Functionalized halloysite multivalent glycocluster as a new drug delivery system.
2020
A new design for halloysite nanotube materials was obtained by grafting chemically modified cyclodextrin units onto the nanotube surface. In particular, grafted cyclodextrins were decorated with thiosaccharide pendants, in order to mimic the well-known binding of sugars to proteins and the glyco-cluster effect occurring during cellular recognition events. The obtained materials were characterized by using a combination of varied techniques (FT-IR spectroscopy, thermogravimetric analysis, scanning electron microscopy, dynamic light scattering, turbidimetry), and their potential drug-delivery abilities were tested by studying their interactions with the common naturally occurring anticancer a…
Effects of solvent perturbation on gelation driven by spinodal demixing
1999
We study effects of solvent perturbation on kinetic competition between spinodal demixing and gelation in agarose solutions at a concentration of 5 g/l. Two different cosolutes (tert-butyl alcohol and trimethyl amine N-oxide) known for altering in opposite way solvent-mediated interactions are chosen. By rheometry, static and dynamic light scattering experiments, we show that the cosolute presence shifts the boundary of the instability region of solution leaving unaffected temperature and polymer concentration values required for percolation. Results suggest that an appropriate choice of quenching temperature and solvent allows controlling the gelation time and the gel structural properties.
Composite soy lecithin–decylpolyglucoside vesicles: A theoretical and experimental study
2008
In the present work, vesicles made with soy lecithin and a commercial mixture of alkyl polyglucosides were prepared and characterized. Vesicles with a constant amount of soy lecithin and an increasing amount of a decylpolyglucoside surfactant, (OrNS10), were formulated and their physicochemical properties were studied with the aim to design a drug delivery system suitable for different applications. To this purpose, morphology, size distribution, ζ-potential and apparent viscosity of the prepared vesicles were studied. Vesicles were also characterized by using optical and light polarized microscopy, transmission electron microscopy and photon correlation spectroscopy. A stability study was …
Characterization of Micelles of Polyisobutylene-block-poly(methacrylic acid) in Aqueous Medium
2000
Four amphiphilic block copolymers polyisobutylene-block-poly(methacrylic acid) (IBm-MAAn; m = 70−134, n = 52−228) were synthesized and transferred into aqueous medium at pH 10−12. Their structure in solution was characterized by fluorescence correlation spectroscopy (FCS), static and dynamic light scattering (SLS, DLS), analytical ultracentrifuge (AUC), and by transmission electron microscopy (TEM) with freeze-fracturing and staining techniques. DLS data, AUC sedimentation traces, and TEM images indicate at least two different kinds of particles. TEM shows spherical micelles; however, especially for polymers with larger hydrophobic blocks, additional particles are observed. FCS shows extrem…