Charge reversal of moisturous porous silica colloids by take-up of protons

Boon, Niels; Roij, René van

doi:10.1016/j.jcis.2012.06.048

Cited by 12 publications

(14 citation statements)

References 23 publications

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“…The availability of the microporous structure of Stöber spheres for water filling (and emptying) under usual humidity conditions has barely been studied, although it will surely affect e.g. their mechanical 25 properties, individual 50 and collectively, 83 charge state 62,63 or optical performance of Stöbercomposed colloidal crystals. 68 Our findings of unambiguous and notable water uptake in the micropores, together with previous evidence of fast dynamics related to water sorption in Stöber spheres, 65,84 may also raise questions about the ability of water to easily, and rapidly, adsorb and desorb in such strongly confined environment.…”

Section: Discussionmentioning

confidence: 99%

Direct Measurement of Microporosity and Molecular Accessibility in Stöber Spheres by Adsorption Isotherms

et al. 2018

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The microporous nature of monodisperse Stöber silica spheres is demonstrated in the literature, although usually via indirect evidence. Contradictorily, there also exist numerous reports of nonporosity based on conventional N 2 adsorption isotherms, leading to a confusing scenario and questioning the evaluation methodology. Thus, there is the strong need of straight measure of microporosity in Stöber spheres, at best by available adsorption techniques, which must be further directly confronted with the standard nitrogen method. Here, for the first time, microporosity detection by N 2 and CO 2 adsorption are compared in Stöber spheres. We demonstrate that CO 2 isotherms at 273 K allows direct detection and quantification of the microporosity (about 0.1 cm 3 /g in our samples), while N 2 at 77 K cannot probe adequately the internal volume. We also show that a large amount of water fills the micropores under usual ambient conditions, also revealing the presence of small mesoporosity. Thus, the porous nature of Stöber spheres is investigated by a simple combination of adsorption isotherms, and the different accessibility of N 2 , CO 2 and H 2 O molecules are discussed. We emphasize the inadequacy of standard N 2 isotherms for micropore detection in Stöber silica, as the access of nitrogen molecules at cryogenic temperatures is kinetically restricted and may lead to erroneous 2 conclusions. Instead, we propose CO 2 isotherms as a simple and direct means for evaluation of microporosity.

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Section: Discussionmentioning

confidence: 99%

Direct Measurement of Microporosity and Molecular Accessibility in Stöber Spheres by Adsorption Isotherms

et al. 2018

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“…Therefore, it depends also on their local spatially-dependent concentration. In this sense, our collective description of the CR macroions differs significantly from other approaches based on the cell model approximation [31,32], as these latter approaches do not fully capture the collective effect of the macro-ions.…”

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confidence: 94%

Complex fluids with mobile charge-regulating macro-ions

Markovich¹,

Andelman²,

Podgornik³

2017

EPL

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We generalize the concept of charge regulation of ionic solutions, and apply it to complex fluids with mobile macro-ions having internal non-electrostatic degrees of freedom. The suggested framework provides a convenient tool for investigating systems where mobile macroions can self-regulate their charge (e.g., proteins). We show that even within a simplified chargeregulation model, the charge dissociation equilibrium results in different and notable properties. Consequences of the charge regulation include a positional dependence of the effective charge of the macro-ions, a non-monotonic dependence of the effective Debye screening length on the concentration of the monovalent salt, a modification of the electric double-layer structure, and buffering by the macro-ions of the background electrolyte.

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“…These studies disregarded the real physical mechanisms defining ionic concentrations in a porous system, even though they are well aware that EDL overlaps dominates surface charging 21 . There are some numerical studies dedicated to calculating inner surface charge using extended PB equation with CR, but they either ignored overlap effects 28,48 , only focused on ionic distributions/conductance 49–51 or solved some specific cases and remain far from providing a general explanation 52 . For such a case, a proper consideration of combined effects of the pore throat EDL overlap and the so-called “pore to throat connectivity” in a mesoporous system as a function of the structural porous parameters is needed to determine the surface charging mechanisms, which does not exist in literature.…”

Section: Introductionmentioning

confidence: 99%

Internal surface electric charge characterization of mesoporous silica

Şen

Barışık

2019

Sci Rep

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Mesoporous silica is an emerging technology to solve problems of existing and to support projected revolutionary applications ranging from targeted drug delivery to artificial kidney. However, one of the major driving mechanisms, electric charging of internal mesoporous surfaces, has not been characterized yet. In the nanoscale confinements of mesoporous structures made of pore throats and pore voids, surface charges diverge from existing theoretical calculations and show local variation due to two occurrences. First, when the size of pore throat becomes comparable with the thickness of ionic layering forming on throats’ surfaces, ionic layers from opposite surfaces overlap so that ionic concentration on the surface becomes different than Boltzmann distribution predicts, and there will no longer be an equilibrium of zero electric potential at pore throat centers. Second, when this non zero potential inside throats becomes different than the potential of pore voids, ionic diffusion from void to throat creates axial ionic variation on surfaces. For such a case, we performed a pore level analysis on mesoporous internal surface charge at various porosities and ionic conditions. Pore parameters strongly affected the average internal charge which we characterized as a function of overlap ratio and porosity, first time in literature. Using this, a phenomenological model was developed as an extension of the existing theory to include nano-effects, to predict the average mesoporous internal surface charge as a function of EDL thickness, pore size and porosity.

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Charge reversal of moisturous porous silica colloids by take-up of protons

Cited by 12 publications

References 23 publications

Direct Measurement of Microporosity and Molecular Accessibility in Stöber Spheres by Adsorption Isotherms

Direct Measurement of Microporosity and Molecular Accessibility in Stöber Spheres by Adsorption Isotherms

Complex fluids with mobile charge-regulating macro-ions

Internal surface electric charge characterization of mesoporous silica

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