اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدInfluence of solvent granularity on the effective interaction between charged colloidal suspensions
198
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We study the effect of solvent granularity on the effective force between two charged colloidal particles by computer simulations of the primitive model of strongly asymmetric electrolytes with an explicitly added hard sphere solvent. Apart from molecular oscillating forces for nearly touching colloids which arise from solvent and counterion layering, the counterions are attracted towards the colloidal surfaces by solvent depletion providing a simple statistical description of hydration. This, in turn, has an important influence on the effective forces for larger distances which are considerably reduced as compared to the prediction based on the primitive model. When these forces are repulsive, the long-distance behaviour can be described by an effective Yukawa pair potential with a solvent-renormalized charge. As a function of colloidal volume fraction and added salt concentration, this solvent-renormalized charge behaves qualitatively similar to that obtained via the Poisson-Boltzmann cell model but there are quantitative differences. For divalent counterions and nano-sized colloids, on the other hand, the hydration may lead to overscreened colloids with mutual attraction while the primitive model yields repulsive forces. All these new effects can be accounted for through a solvent-averaged primitive model (SPM) which is obtained from the full model by integrating out the solvent degrees of freedom. The SPM was used to access larger colloidal particles without simulating the solvent explicitly.
قيم البحث
اقرأ أيضاً
Based on primitive model computer simulations with explicit microions, we calculate the effective interactions in a binary mixture of charged colloids with species $A$ and $B$ for different size and charge ratios. An optimal pairwise interaction is o
btained by fitting the many-body effective forces. This interaction is close to a Yukawa (or Derjaguin-Landau-Verwey-Overbeek(DLVO)) pair potential but the $AB$ cross-interaction is different from the geometric mean of the two direct $AA$ and $BB$ interactions. As a function of charge asymmetry, the corresponding nonadditivity parameter is first positive, then getting significantly negative and is getting then positive again. We finally show that an inclusion of nonadditivity within an optimal effective Yukawa model gives better predictions for the fluid pair structure than DLVO-theory.
We discuss the peculiarities of the Seebeck effect in stabilized electrolytes containing the colloidal particles. Its unusual feature is the two-stage character, with the linear increase of differential thermopower as the function of colloidal partic
les concentration $n_{odot}$ during the first stage and dramatic drop of it at small $n_{odot}$ during the second one (steady state). We show that the properties of the initial state are governed by the thermo-diffusion flows of the mobile ions of the stabilizing electrolyte medium itself and how the colloidal particles participate in formation of the electric field in the bulk of suspension. In its turn the specifics of the steady state in thermoelectric effect we attribute to considerable displacements of the massive colloidal particles in process of their slow thermal diffusion and break down of their electroneutrality in the vicinity of electrodes
Aqueous suspensions of highly charged polystyrene particles with different volume fractions have been investigated for structural ordering and phase behavior using static light scattering (SLS) and confocal laser scanning microscope (CLSM). Under dei
onized conditions, suspensions of high charge density colloidal particles remained disordered whereas suspensions of relatively low charge density showed crystallization by exhibiting iridescence for the visible light. Though for unaided eye crystallized suspensions appeared homogeneous, static light scattering measurements and CLSM observations have revealed their inhomogeneous nature in the form of coexistence of voids with dense ordered regions. CLSM investigations on disordered suspensions showed their inhomogeneous nature in the form coexistence of voids with dense disordered (amorphous) regions. Our studies on highly charged colloids confirm the occurrence of gas-solid transition and are in accordance with predictions of Monte Carlo simulations using a pair-potential having a long-range attractive term [Mohanty and Tata, Journal of Colloid and Interface Science 2003, 264, 101]. Based on our experimental and simulation results we argue that the reported reentrant disordered state [Yamanaka et al Phys. Rev. Lett. 1998, 80, 5806 and Toyotama et al Langmuir, 2003, 19, 3236] in charged colloids observed at high charge densities is a gas-solid coexistence state.
Thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) particles of different sizes are synthesized by varying the concentration of sodium dodecyl sulphate (SDS) in a one-pot method. The sizes, size polydispersities and the thermoresponsivity of the P
NIPAM particles are characterized by using dynamic light scattering and scanning electron microscopy. It is observed that the sizes of these particles decrease with increase in SDS concentration. Swelling ratios of PNIPAM particles measured from the thermoresponsive curves are observed to increase with decrease in particle size. This observation is understood by minimizing the Helmholtz free energy of the system with respect to the swelling ratio of the particles. Finally, the dynamics of these particles in jammed aqueous suspensions are investigated by performing rheological measurements.
We apply a hybrid Molecular Dynamics and mesoscopic simulation technique to study the steady-state sedimentation of hard sphere particles for Peclet numbers (Pe) ranging from 0.08 to 12. Hydrodynamic back-flow causes a reduction of the average sedime
ntation velocity relative to the Stokes velocity. We find that this effect is independent of Pe number. Velocity fluctuations show the expected effects of thermal fluctuations at short correlation times. At longer times, non-equilibrium hydrodynamic fluctuations are visible, and their character appears to be independent of the thermal fluctuations. The hydrodynamic fluctuations dominate the diffusive behavior even for modest Pe number, while conversely the short-time fluctuations are dominated by thermal effects for a surprisingly large Pe numbers. Inspired by recent experiments, we also study finite sedimentation in a horizontal planar slit. In our simulations distinct lateral patterns emerge, in agreement with observations in the experiments.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
