| 1. |
- Mohanty, P. S., et al.
(författare)
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Dielectric spectroscopy of ionic microgel suspensions
- 2016
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Ingår i: Soft Matter. - 1744-683X. ; 12:48, s. 9705-9727
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Tidskriftsartikel (refereegranskat)abstract
- The determination of the net charge and size of microgel particles as a function of their concentration, as well as the degree of association of ions to the microgel backbone, has been pursued in earlier studies mainly by scattering and rheology. These methods suffer from contributions due to inter-particle interactions that interfere with the characterization of single-particle properties. Here we introduce dielectric spectroscopy as an alternative experimental method to characterize microgel systems. The advantage of dielectric spectroscopy over other experimental methods is that the polarization due to mobile charges within a microgel particle is only weakly affected by inter-particle interactions. Apart from electrode polarization effects, experimental spectra on PNIPAM-co-AA [poly(N-isopropylacrylamide-co-acrylic acid)] ionic microgel particles suspended in de-ionized water exhibit three well-separated relaxation modes, which are due to the polarization of the mobile charges within the microgel particles, the diffuse double layer around the particles, and the polymer backbone. Expressions for the full frequency dependence of the electrode-polarization contribution to the measured dielectric response are derived, and a theory is proposed for the polarization resulting from the mobile charges within the microgel. Relaxation of the diffuse double layer is modeled within the realm of a cell model. The net charge and the size of the microgel particles are found to be strongly varying with concentration. A very small value of the diffusion coefficient of ions within the microgel is found, due to a large degree of chemical association of protons to the polymer backbone.
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| 2. |
- Bucciarelli, Saskia, et al.
(författare)
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Unusual dynamics of concentration fluctuations in solutions of weakly attractive globular proteins
- 2015
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185 .- 1089-5639. ; 6:22, s. 4470-4474
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Tidskriftsartikel (refereegranskat)abstract
- The globular protein γB-crystallin exhibits a complex phase behavior, where liquid–liquid phase separation characterized by a critical volume fraction ϕc = 0.154 and a critical temperature Tc = 291.8 K coexists with dynamical arrest on all length scales at volume fractions around ϕ ≈ 0.3–0.35, and an arrest line that extends well into the unstable region below the spinodal. However, although the static properties such as the osmotic compressibility and the static correlation length are in quantitative agreement with predictions for binary liquid mixtures, this is not the case for the dynamics of concentration fluctuations described by the dynamic structure factor S(q,t). Using a combination of dynamic light scattering and neutron spin echo measurements, we demonstrate that the competition between critical slowing down and dynamical arrest results in a much more complex wave vector dependence of S(q,t) than previously anticipated.
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