Browsing by Subject "Dynamic light scattering"

Now showing 1 - 4 of 4
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    Aggregation of gold nanoparticles in presence of the thermoresponsive cationic ciblock copolymer PNIPAAM48-b-PAMPTMA6
    (MDPI, 2021-11-23) Herrera Robalino, David; Durán del Amor, María del Mar; Almagro Gómez, Carmen María; Hernández Cifre, José G.; Química Física
    The adsorption of the thermoresponsive positively charged copolymer poly(N-isopropylacr ylamide)-block-poly(3-acrylamidopropyl)trimethylammonium chloride, PNIPAAM48-b-PAMPTMA6(+), onto negatively charged gold nanoparticles can provide stability to the nanoparticles and make the emerging structure tunable by temperature. In this work, we characterize the nanocomposite formed by gold nanoparticles and copolymer chains and study the influence of the copolymer on the expected aggregation process that undergoes those nanoparticles at high ionic strength. We also determine the lower critical solution temperature (LCST) of the copolymer (around 42 ºC) and evaluate the influence of the temperature on the nanocomposite. For those purposes, we use dynamic light scattering, UV-vis spectroscopy and transmission electron microscopy. At the working PNIPAAM48-b-PAMPTMA6(+) concentration, we observe the existence of copolymer structures that trap the gold nanoparticles and avoid the formation of nanoparticles aggregates. Finally, we discuss how these structures can be useful in catalysis and nanoparticles recovery.
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    Chitosan as stabilizing agent for negatively charged nanoparticles
    (Elsevier, 2016-12-24) Collado-González, Mar; García Montalbán, Mercedes; Peña-García, Jorge; Pérez-Sánchez, Horacio; Víllora Cano, Gloria; Díaz Baños, F. Guillermo; Biología Celular e Histología
    Chitosan is a biocompatible polysaccharide with positive Z potential which can stabilize negative charged nanoparticles. Silk fibroin nanoparticles and citrate gold nanoparticles, both with negative Z potential, but they form aggregates at physiological ionic strength. In this work, we study the behavior of chitosan in solution when the ionic strength of the medium is increased and how the concentration of chitosan and the proportion of the two components (chitosan and AuNP or SFN) significantly affect the stability and size of the nanocomposites formed. In addition to experimental measurements, molecular modeling were used to gain insight into how chitosan interacts with silk fibroin monomers, and to identify the main energetic interactions involved in the process. The optimum values for obtaining the smallest and most homogeneous stable nanocomposites were obtained and two different ways of organization through which chitosan may exert its stabilizing effect were suggested.
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    The effect of number of arms on the aggregation behavior of thermoresponsive poly (N-isopropylacrylamide) star polymers
    (Wiley, 2020-06-16) Zhu, Kaizheng; Pamies, Ramón; Al-Manasir, Nodar; Hernández Cifre, José G.; García de la Torre, José; Nyström, Bo; Kjøniksen, Anna-Lena; Química Física
    The thermoresponsive nature of aqueous solutions of poly(Nisopropylacrylamide) (PNIPAAM) star polymers containing 2, 3, 4, and 6 arms has been investigated by turbidity, dynamic light scattering, rheology, and rheo-SALS. Simulations of the thermosensitive nature of the single star polymers have also been conducted. Some of the samples form aggregates even at temperatures significantly below the lower critical solution temperature (LCST) of PNIPAAM. Increasing concentration and number of arms promotes associations at low temperatures. When the temperature is raised, there is a competition between size increase due to enhanced aggregation and a size reduction caused by contraction. Monte Carlo simulations show that the single stars contract with increasing temperature, and that this contraction is more pronounced when the number of arms is increased. Some samples exhibit a minimum in the turbidity data after the initial increase at the cloud point. The combined rheology and rheo-SALS data suggest that this is due to a fragmentation of the aggregates followed by re-aggregation at even higher temperatures. Although the 6-arm star polymer aggregates more than the other stars at low temperatures, the more compact structure renders it less prone to aggregation at temperatures above the cloud point.
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    Volumetric macro- and micro-scale assessment of crystalline lens opacities in cataract patients using long-depth-range swept source optical coherence tomography
    (Optica Publishing Group, 2018-07-24) Grulkowski, Ireneusz; Manzanera, Silvestre; Cwiklinski, Lukasz; Mompeán, Juan; Castro, Alberto de; Marín Sánchez, José María; Artal, Pablo; Oftalmología, Optometría, Otorrinolaringología y Anatomía Patológica
    We demonstrate an optimized optical platform for the three-dimensional (3-D) visualization of crystalline lens opacities in vivo in the eyes of patients with different types and grades of cataracts. We developed a prototype long-depth-range swept source optical coherence tomography (SS-OCT) instrument operating at the speed of 50 kA-scans/second and at the central wavelength of 1 μm to perform high-resolution imaging of the whole anterior segment of the eye. Volumetric data sets of cataractous eyes were acquired and processed to obtain contrast-enhanced high-resolution images of lenticular structures and opacifications. The results showed lens micro- and macro-scale features related to possible cataract development such as cortical spokes, water clefts and enhanced scattering in the lens nucleus. The results demonstrate also the ability of this SS-OCT imaging to locate and characterize opacities quantitatively. The instrument might be a useful tool in the high-resolution preoperative evaluation of crystalline lens opacities in cataract patients.