Small-Angle Neutron Scattering on a Core−Shell Colloidal System:  A Contrast-Variation Study

Zackrisson, M.; Stradner, Anna; Schurtenberger, Peter; Bergenholtz, Johan

doi:10.1021/la051664v

Cited by 58 publications

(61 citation statements)

References 73 publications

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“…Most probably the structure of the corona, and to a lesser extent the silica core, plays a key role in the liquid-liquid phase transition. 4 Knowledge of these features can be obtained from small angle neutron scattering ͑SANS͒ as has been shown in numerous other investigations on core-shell particles, [11][12][13][14][15] since it can provide us with the desired information by performing contrast variation experiments. However, an unambiguous interpretation of such data is not straightforward.…”

Section: Introductionmentioning

confidence: 99%

Colloidal dispersions of octadecyl grafted silica spheres in toluene: A global analysis of small angle neutron scattering contrast variation and concentration dependence measurements

Kohlbrecher

Buitenhuis

Meier

et al. 2006

The Journal of Chemical Physics

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In this paper we report measurements of the form factor and the structure factor of a sterically stabilized colloidal dispersion consisting of silica spheres coated with octadecane in toluene by small angle neutron scattering ͑SANS͒. The phase diagram of this system shows the liquid-liquid coexistence line and also a jamming transition at higher concentrations, where the jamming line intersects the coexistence line roughly at the critical point. We have performed SANS experiments at a temperature well above the transition temperature and at various volume fractions , spanning from the very dilute regime ͑ = 0.2% ͒ to the critical concentration ͑ =16%͒ and the highly viscous regime ͑ = 39.2% ͒. Except for the very dilute regime, we observe a structure factor S͑q͒ in all other cases. We fitted our data over the whole concentration regime using a global fitting routine with a core-shell model for the form factor P͑q͒, taking into account the structure factor, which we describe with the Robertus model for an adhesive polydisperse core-shell particle. At a volume fraction of = 5% a SANS contrast variation experiment has been performed. From that the product of the volume of the shell and the amount of solvent within the corona of our core-shell particle could be determined. At the most probable shell thickness of 2.3 nm a solvent content of about 50% within the corona was found. Moreover we could conclude that the core is not interpenetrated by solvent molecules. From the contrast variation experiment followed that the structure factor at zero average contrast exhibits a strong q dependence, which is an effect of an inhomogeneous particle in combination with a size distribution.

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Section: Introductionmentioning

confidence: 99%

Colloidal dispersions of octadecyl grafted silica spheres in toluene: A global analysis of small angle neutron scattering contrast variation and concentration dependence measurements

Kohlbrecher

Buitenhuis

Meier

et al. 2006

The Journal of Chemical Physics

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“…Examples are fuzzy-sphere systems consisting of highly porous, cross-linked microgel spheres exhibiting large volume changes as a function of temperature [1,2]. Another experimentally well-studied class of permeable colloids are core-shell-like particles consisting of an impermeable rigid core and a permeable stabilizing layer of some soft material [3,4], such as grafted polymers [5,6]. Despite the importance of permeable particles both from a fundamental viewpoint and in terms of applications, little is known theoretically about transport properties in non-dilute systems, such as self-and collective diffusion coefficients.…”

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confidence: 99%

Dynamics of permeable particles in concentrated suspensions

et al. 2010

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We calculate short-time diffusion properties of suspensions of porous colloidal particles as a function of their permeability, for the full fluid-phase concentration range. The particles are modeled as spheres of uniform permeability with excluded volume interactions. Using a precise multipole method encoded in the HYDROMULTIPOLE program, results are presented for the hydrodynamic function, H(q), sedimentation coefficient, and self-diffusion coefficient with a full account of manybody hydrodynamic interactions. While self-diffusion and sedimentation are strongly permeability dependent, the wavenumber dependence of the hydrodynamic function can be reduced, by appropriate shifting and scaling, to a single master curve, independent of permeability. Generic features of the permeable sphere model are discussed.Suspensions of solvent-permeable colloidal particles can be found in a great variety of synthesized materials. Examples are fuzzy-sphere systems consisting of highly porous, cross-linked microgel spheres exhibiting large volume changes as a function of temperature [1,2]. Another experimentally well-studied class of permeable colloids are core-shell-like particles consisting of an impermeable rigid core and a permeable stabilizing layer of some soft material [3,4], such as grafted polymers [5,6]. Despite the importance of permeable particles both from a fundamental viewpoint and in terms of applications, little is known theoretically about transport properties in non-dilute systems, such as self-and collective diffusion coefficients. The calculation of transport properties is a challenging problem since one has to cope with manybody hydrodynamic interactions (HIs) by accounting for the fluid flow inside the porous particles relative to their skeletons. A better control on diffusion and viscoelastic properties for industrial processing of concentrated colloids requires a deeper understanding of the influence of the HIs.Theoretical and simulation work on diffusion and sedimentation of porous particles was primarily concerned so far with dilute systems. Chen and Cai [7] calculated the sedimentation velocity in a suspension of uniformly porous spheres to first order in the volume fraction φ, demonstrating that sedimentation is quite sensitive to direct interactions and permeability. Mo and Sangani [8] used a multipole expansion method for hydrodynamically interacting porous spheres to obtain numerical results for the average drag force per particle in random and in bcc fixed-bed arrays.Clearly, there is a strong demand on exploring generic HIs effects in concentrated porous particle systems where pairwise additivity approximations are bound to fail. In this letter, we describe a comprehensive simulation study of short-time diffusion properties for systems of permeable non-overlapping spheres. Our study covers the whole fluid-phase regime including concentrated systems with strong many-body HIs. The considered permeability range from fully impermeable to strongly permeable particles. Numerical results are presented f...

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“…[1][2][3][4][5] However, solvent quality usually changes with temperature, so the stabilizing effects may be reduced or lost upon heating or cooling the system. [6][7][8][9][10][11][12] For instance, many polymer solutions display a lower critical solution temperature, LCST, and when such polymers are grafted onto particles, one may anticipate a decreased stabilization, as the temperature is increased.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Predictions of Temperature-Induced Gelation in Aqueous Dispersions Containing PEO-Grafted Particles

2016

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In this work we utilize classical polymer density functional theory (DFT) to study gelation in systems containing colloidal particles onto which polymers are grafted. The solution conditions are such that the corresponding bulk system displays a lower critical solution temperature (LCST). We specifically compare our predictions with experimental results by Shay et al., who investigated temperature response in aqueous dispersions containing polystyrene particles (PS), with grafted 45-mer poly(ethylene oxide) (PEO) chains. Our DFT treatment is based on a model for aqueous PEO solutions that was originally developed by Karlström for bulk solutions. In this model, monomers are assumed to be in either of two classes of states, labelled A and B, where B is more solvophobic than A. On the other hand, the degeneracy of B exceeds that of A, causing the population of solvophobic monomers to increase with temperature. In agreement with experimental findings by Shay et al., we locate gelation at temperatures considerably below T Θ , and far below the LCST for such chain lengths. This gelation occurs * To whom correspondence should be addressed 1 also without any dispersion interactions between the PS particles. Interestingly, the polymerinduced interaction free energy displays a non-monotonic dependence on the grafting density.At high grafting densities, bridging attractions between grafted layers take place (considerably below T Θ ). At low grafting densities, on the other hand, the polymers are able to bridge across to the other particle surface. Shay et al. conducted their experiments at very low ionic strength, using de-ionized water as a solvent. We demonstrate that even minute amounts of adsorbed charge on the surface of the particles, can lead to dramatic changes of the gelation temperature, especially at high grafting densities. Another interesting prediction is the existence of elongated (chain-like) equilibrium structures, at low particle concentrations. We emphasize that our model does not rely upon any temperature-dependent interactions.

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Small-Angle Neutron Scattering on a Core−Shell Colloidal System: A Contrast-Variation Study

Cited by 58 publications

References 73 publications

Colloidal dispersions of octadecyl grafted silica spheres in toluene: A global analysis of small angle neutron scattering contrast variation and concentration dependence measurements

Colloidal dispersions of octadecyl grafted silica spheres in toluene: A global analysis of small angle neutron scattering contrast variation and concentration dependence measurements

Dynamics of permeable particles in concentrated suspensions

Theoretical Predictions of Temperature-Induced Gelation in Aqueous Dispersions Containing PEO-Grafted Particles

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