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Sökning: WFRF:(Kjoniksen Anna Lena)

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1.
  • Dédinaité, Andra, et al. (författare)
  • Friction in aqueous media tuned by temperature-responsive polymer layers
  • 2010
  • Ingår i: SOFT MATTER. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 6:11, s. 2489-2498
  • Tidskriftsartikel (refereegranskat)abstract
    • An atomic force microscope colloidal probe technique has been employed to probe normal and friction forces between silica surfaces coated with adsorbed layers of a diblock copolymer of the composition poly(N-isopropylacrylamide)(48)-block-poly(3-acrylamidopropyl)trimethyla mmonium chloride)(20), abbreviated PNIPAAM(48)-b-PAMPTMA(+)(20). The interactions between the PNIPAAM(48)-b-PAMPTMA(+)(20)-coated surfaces across a 0.1 mM NaCl (pH 6) solution at 25 degrees C are purely repulsive, due to a combination of steric and electrostatic double-layer forces. However, when the temperature is increased to 35 degrees C, and subsequently to 45 degrees C, an attractive force develops at short separations due to the unfavourable PNIPAAM-water interaction at these temperatures. The temperature-dependent polymer-water interaction has implications for the friction force between the layers. At 25 degrees C a frictional force that increases linearly with increasing load is observed once the surfaces are brought into close contact. At higher temperatures significantly higher friction forces appear as a consequence of attractive segment-segment interactions. Further, a clearly expressed hysteresis between friction forces encountered on loading and unloading is detected. Our results demonstrate that both normal and friction forces between surfaces can be controlled by temperature changes when temperature-responsive polymers are employed, and friction forces can be adjusted as required from low to high.
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2.
  • Maleki, Atoosa, et al. (författare)
  • Effect of pH on the association behavior in aqueous solutions of pig gastric mucin
  • 2008
  • Ingår i: Carbohydrate Research. - : Elsevier BV. - 1873-426X .- 0008-6215. ; 343:2, s. 328-340
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, dynamic light scattering (DLS), turbidity, and rheo-small angle light scattering (rheo-SALS) methods have been utilized to examine the impact of pH (1 <= pH <= 7) on aqueous solutions of noncommercial purified pig gastric mucin. The asymmetric flow field-flow fractionation (AFFFF) measurements established that the mucin sample has a high molecular weight and is polydisperse. DLS measurements on dilute solutions of mucin disclosed large interchain aggregates at pH 2, where the polymer has a low charge density or is uncharged. At lower or higher values of pH, mucin is charged and the tendency of forming interpolymer complexes is affected. In the semidilute concentration regime, pronounced junction zones (`lumps' of polymer) are evolved and a heterogeneous connected network is formed at pH 2, whereas the association structures are disintegrated (smaller `lumps') at lower or higher pH values due to electrostatic repulsive interactions, and a more homogeneous network is evolved. The DLS and viscosity results at pH 1 indicate the development of a fragmented network, composed of contracted chains that are decorated by some positive charges. The effect of shear flow on the structure of semidilute solutions of mucin was investigated with the aid of rheo-SALS methods. The scattered intensity revealed a strong upturn at low values of the wave vector (q) for mucin solutions at pH 2 and pH 4, which suggests the evolution of large association domains. At these pH values, a flow-induced anisotropy in the 2D SALS patterns in the form of elliptical shapes was observed at high shear rates.
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4.
  • Pamies, Ramon, et al. (författare)
  • Temperature-Induced Flocculation of Gold Particles with an Adsorbed Thermoresponsive Cationic Copolymer
  • 2010
  • Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:50, s. 21960-21968
  • Tidskriftsartikel (refereegranskat)abstract
    • In this article, we report a study of the adsorption of a charged thermoresponsive poly(N-isopropylacrylamide)-block-poly(3-acrylamidopropyl)trimethylammon ium chloride) [abbreviated as PNIPAAM(24)-b-PAMPTMA(+)(18)] block copolymer onto gold nanoparticles by means of dynamic light scattering (DLS), zeta-potential measurements, cryo-TEM, rheology small-angle light scattering (rheo-SALS), and UV-visible absorbance spectroscopy. At low surface coverage, the cationic copolymer was found to mediate flocculation of the particles at elevated temperatures, whereas at higher polymer concentration, the gold particles were stabilized by the adsorbed copolymer layer. The DLS results showed that the adsorbed polymer was compressed prior to flocculation at elevated temperatures and that the flocs coexisted with single particles. The latter finding was confirmed by cryo-TEM. Rheo-SALS measurements revealed that shear flow disrupted the large flocs formed at higher temperatures. UV-visible absorbance measurements demonstrated that the temperature-induced flocculation process gives rise to a red shift of the localized surface plasmon resonance (LSPR) peak, together with the appearance of a second peak at higher wavelengths.
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  • Resultat 1-4 av 4

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