NMR Provides Checklist of Generic Properties for Atomic-Scale Models of Periodic Mesoporous Silicas

Shenderovich, Ilya G.; Mauder, D.; Akcakayiran, Dilek; Buntkowsky, Gerd; Limbach, Hans−Heinrich; Findenegg, Gerhard H.

doi:10.1021/jp073682m

Cited by 65 publications

(75 citation statements)

References 51 publications

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“…The smoothness of the interface is in line with the data reported for MCM-41 silica pores in Ref. 32. Nevertheless, the hydrophilic pore wall of the present work is not designed to reproduce the properties of a silica pore but a simpler-more ideal case-in which the interaction of water with the surface moieties is identical to that of water with other water molecules.…”

Section: Introductionsupporting

confidence: 83%

Water filling of hydrophilic nanopores

Llave

Molinero

Scherlis

2010

The Journal of Chemical Physics

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Phase diagram of supercooled water confined to hydrophilic nanopores J. Chem. Phys. 137, 044509 (2012) Molecular dynamics simulations of water in cylindrical hydrophilic pores with diameters of 1.5 and 3 nm were performed to explore the phase behavior and the nucleation dynamics of the confined fluid as a function of the percentage of volume filled f. The interactions of water with the pore wall were considered to be identical to the interactions between water molecules. At low water contents, all the water is adsorbed to the surface of the pore. A second phase consisting of a liquid plug appears at the onset filling for capillary condensation, f onset = 27% and 34% for the narrow and wide pores, respectively. In agreement with experimental results for silica pores, the liquid phase appears close to the equilibrium filling f eq in the 1.5 nm pore and under conditions of strong surface supersaturations for the 3 nm pore. After condensation, two phases, a liquid plug and a surface-adsorbed phase, coexist in equilibrium. Under conditions of phase coexistence, the water surface density ⌫ coex was found to be independent of the water content and the diameter of the pore. The value of ⌫ coex found in the simulations ͑ϳ3 nm −2 ͒ is in good agreement with experimental results for silica pores, suggesting that the interactions of water with silica and with itself are comparable. The surface-adsorbed phase at coexistence is a sparse monolayer with a structure dominated by small water clusters. We characterize the density and structure of the liquid and surface phases, the nucleation mechanism of the water plug, and the effect of surface hydrophilicity on the two-phase equilibrium and hysteresis. The results are discussed in light of experiments and previous simulations.

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Section: Introductionsupporting

confidence: 83%

Water filling of hydrophilic nanopores

Llave

Molinero

Scherlis

2010

The Journal of Chemical Physics

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“…Since the three samples of Lys-Sil were synthesized from the same reaction mixture, and particle size was tuned solely by the stirring rate and a weak temperature increase (see Table 4.1), we believe that the surface density of lysine and silanol groups was independent of particle size. This is in line with earlier published results on similar silica particles [27], where the surface density of lysine on the Lys-Sil particles was estimated to be 0.5 nm −2 , and a value 3 nm −2 was adopted for the surface density of silanol groups as reported previously by Shenderovich et al [34] From these values the fraction of silanol groups blocked by lysine was estimated to be 15 %. This then implies that the surface density of free silanol groups at the Lys-Sil particles will be lower than for pure Stöber-type or Ludox-type silica.…”

Section: Effect Of Lysine On Binding Strength Of Surfactantsupporting

confidence: 90%

Surfactant Adsorption and Aggregate Structure at Silica Nanoparticles

Bharti

2014

Adsorption, Aggregation and Structure Formation in Systems of Charged Particles

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Surfactant adsorption onto colloidal particles is of eminent importance to technological processes in which colloidal stability or detergency plays a role [1][2][3][4][5]. Surfactant adsorption onto hydrophilic surfaces can be regarded as a surface aggregation process, reminiscent of micelle formation in solution [6][7][8][9][10][11][12][13][14]. When the anchoring of the surfactant heads to the surface is weak, as in the case of nonionic surfactants at oxide surfaces, the morphology of surface aggregates may depend both on the anchoring strength [15,16] and on the curvature of the adsorbing surface [17][18][19][20][21][22][23]. For instance, for the surfactant penta (ethyleneglycol) monododecylether (C 12 E 5 ) it was recently found that discrete surface micelles are formed on silica nanoparticles [19,21], although flat bilayers aggregates are preferred at planar silica surfaces [11,12]. At even weaker anchoring energies, surface micelles may be disfavored against micelles in solution, implying that little or no adsorption occurs, as in the case of dodecyl maltoside (β-C 12 G 2 ) at silica nanoparticles [19].Here, we study the influence of particle size and surface modification on the adsorption of the surfactant C 12 E 5 at silica nanoparticles. The particles were synthesized by a modified Stöber method [24] yielding particles of narrow size distribution down to the 10 to 50 nm size range which was of interest in this study. In this method, the basic amino acid lysine is used instead of ammonia as the catalyst for the hydrolysis of the silica precursor. For the resulting Lys-Sil particles [24] it was found that the adsorption isotherm of C 12 E 5 exhibits a pronounced dependence on particle size. To assess the influence of lysine on the surface energy and the adsorption of the surfactant at the silica particles we also investigated the adsorption of lysine on pure siliceous silica nanoparticles (Ludox-TMA) and

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“…, and a value 3 nm À2 was adopted for the surface density of silanol groups as reported previously by Shenderovich et al 26 From these values the fraction of silanol groups blocked by lysine was estimated to be 15%. This then implies that the surface density of free silanol groups at the LysSil particles will be lower than for pure St€ ober-type or Ludoxtype silica.…”

Section: à2mentioning

confidence: 99%

Surfactant adsorption and aggregate structure at silica nanoparticles: Effects of particle size and surface modification

et al. 2012

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The influence of particle size and a surface modifier on the self-assembly of the nonionic surfactant C 12 E 5 at silica nanoparticles was studied by adsorption measurements and small-angle neutron scattering (SANS). Silica nanoparticles of diameter 13 to 43 nm were synthesized involving the basic amino acid lysine. A strong decrease of the limiting adsorption of C 12 E 5 with decreasing particle diameter was found. To unveil the role of lysine as a surface modifier for the observed size dependence of surfactant adsorption, the morphology of the surfactant aggregates assembled on pure siliceous nanoparticles (Ludox-TMA, 27 nm) and their evolution with increasing lysine concentration at a fixed surfactant-to-silica ratio was studied by SANS. In the absence of lysine, the surfactant forms surface micelles at silica particles. As the concentration of lysine is increased, a gradual transition from the surface micelles to detached wormlike micelles in the bulk solution is observed. The changes in surfactant aggregate morphology cause pronounced changes of the system properties, as is demonstrated by turbidity measurements as a function of temperature. These findings are discussed in terms of particle surface curvature and surfactant binding strength, which present new insight into the delicate balance between the two properties.

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NMR Provides Checklist of Generic Properties for Atomic-Scale Models of Periodic Mesoporous Silicas

Cited by 65 publications

References 51 publications

Water filling of hydrophilic nanopores

Water filling of hydrophilic nanopores

Surfactant Adsorption and Aggregate Structure at Silica Nanoparticles

Surfactant adsorption and aggregate structure at silica nanoparticles: Effects of particle size and surface modification

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