Orientation specific deposition of mesoporous particles

Kjellman, Tomas; Bodén, Niklas; Wennerström, Håkan; Edler, Karen J.; Alfredsson, Viveka

doi:10.1063/1.4897282

Cited by 5 publications

(9 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In a final step, the organic polymer material is removed by calcination producing a silica material with ordered pores of diameter 6 nm as the final product. During the thermal treatment there is some sintering of the 7-mer particles, but when the product is redispersed in water, the sintering bonds can be broken by ultrasonic treatment and one can obtain reasonably monodisperse flat hexagonal particles of width 1.0 μm (typically the width varies from 0.75 to 1.25 μm), and the height appears constant at 400 nm (±10%) as shown in Figure a. , The uniform size and chemical homogeneity of the pores is also reflected in the step-like capillary condensation of water occurring at the relative humidity (RH) of RH = 70% as shown in Figure b.…”

Section: Details On the Formation Stagesmentioning

confidence: 99%

The Dynamic Association Processes Leading from a Silica Precursor to a Mesoporous SBA-15 Material

Alfredsson

Wennerström

2015

Acc. Chem. Res.

Self Cite

View full text Add to dashboard Cite

During the last two decades, the synthesis of silica with an ordered mesoporous structure has been thoroughly explored. The basis of the synthesis is to let silica monomers polymerize in the presence of an amphiphilic template component. In the first studies, cationic surfactants were used as structure inducer. Later it was shown that pluronic copolymers also could have the role. One advantage with the pluronics copolymers is that they allow for a wider variation in the radius of pores in the resulting silica material. Another advantage lies in the higher stability resulting from the thicker walls between the pores. Mesoporous silica has a very high area to volume ratio, and the ordered structure ensures surface homogeneity. There are a number of applications of this type of material. It can be used as support for catalysts, as templates to produces other mesoporous inorganic materials, or in controlled release applications. The synthesis of mesoporous silica is, from a practical point of view, simple, but there are significant possibilities to vary synthesis conditions with a concomitant effect on the properties of the resulting material. It is clear that the structural properties on the nanometer scale are determined by the self-assembly properties of the amphiphile, and this knowledge has been used to optimize pore geometry and pore size. To have a practical functional material it is desirable to also control the structure on a micrometer scale and larger. In practice, one has largely taken an empirical approach in optimizing reaction conditions, paying less attention to underlying chemical and physicochemical mechanisms that lead from starting conditions to the final product. In this Account, we present our systematic studies of the processes involved not only in the formation of the mesoporous structure as such, but also of the formation of structures on the micrometer scale. The main point is to show how the ongoing silica polymerization triggers a sequence of structural changes through the action of colloidal interactions. Our approach is to use a multitude of experimental methods to characterize the time evolution of the same highly reproducible synthesis process. It is the silica polymerization reactions that set the time scale, and the block copolymer self-assembly responds to the progress of the polymerization through a basically hydrophobic interaction between silica and ethylene oxide units. The progression of the silica polymerization leads to an increased hydrophobicity triggering an aggregation process resulting in the formation of silica-copolymer composite particles of increasing size. The particle growth occurs in a stepwise way caused by intricate shifts between colloidal stability and instability. By tuning reaction conditions one can have an end product of hexagonal prism composite particles with single crystal 2D hexagonal order.

show abstract

Section: Details On the Formation Stagesmentioning

confidence: 99%

The Dynamic Association Processes Leading from a Silica Precursor to a Mesoporous SBA-15 Material

Alfredsson

Wennerström

2015

Acc. Chem. Res.

Self Cite

View full text Add to dashboard Cite

show abstract

“…13,14 An alternative strategy is to use the deposition on a substrate of micron size mesoporous particles with a perfectly controlled morphology. 15 Such particles can be obtained by standard methods of precipitation in solution. 16 For example, the deposition of particles with a platelet morphology would give rise to a true macroscopic orientation of the channels, all perpendicular to the surface of the substrate.…”

Section: Introductionmentioning

confidence: 99%

“…Indeed, monolith growth , or thin film deposition strategies give assemblies of microdomains for which the direction of the pores is different from one microdomain to another. What is more, if the mesoporous material is grown directly on the surface, one typically obtains a parallel orientation of the pores. , An alternative strategy is to use the deposition on a substrate of micron size mesoporous particles with a perfectly controlled morphology . Such particles can be obtained by standard methods of precipitation in solution .…”

Section: Introductionmentioning

confidence: 99%

“…Such particles can be obtained by standard methods of precipitation in solution . For example, the deposition of particles with a platelet morphology would give rise to a true macroscopic orientation of the channels, all perpendicular to the surface of the substrate . For such a strategy, it is necessary to know how to control the morphology of the particles during their synthesis, and this is the aim of the present study.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Outset of the Morphology of Nanostructured Silica Particles during Nucleation Followed by Ultrasmall-Angle X-ray Scattering

et al. 2016

Self Cite

View full text Add to dashboard Cite

Nucleation and growth of SBA-15 silica nanostructured particles with well-defined morphologies has been followed with time by small-angle X-ray scattering (SAXS) and ultrasmall-angle X-ray scattering (USAXS), using synchrotron radiation. Three different morphologies have been compared: platelets, toroids, and rods. SEM observations of the particles confirm that two key physical parameters control the morphology: the temperature and the stirring of the solution. USAXS curves demonstrate that primary particles with a defined shape are present very early in the reaction mixture, immediately after a very fast nucleation step. This nucleation step is detected at 10 min (56 °C) or 15 min (50 °C) after the addition of the silica precursor. The main finding is that the USAXS signal is different for each type of morphology, and we demonstrate that the difference is related to the shape of the particles, showing characteristic form factors for the different morphologies (platelet, toroid, and rod). Moreover, the size of the mesocrystal domains is correlated directly with the particle dimensions and shape. When stirred, aggregation between primary particles is detected even after 12 min (56 °C). The platelet morphology is promoted by constant stirring of the solution, through an oriented aggregation step between primary particles. In contrast, toroids and rods are only stabilized under static conditions. However, for toroids, aggregation is detected almost immediately after nucleation.

show abstract

“…We assume that the water molecules remaining in solution with the P123 molecules are in the liquid-like state, and are linked by H-bonds to the EO groups of the copolymer. 11 The equilibrium between these two phases is fixed by the chemical potential of the water molecules, which is imposed by the ice phase and depends only on temperature. Note that we verified that the freezing-point depression temperature due to the presence of P123 in solution is small, typically of −0.5 °C.…”

mentioning

confidence: 99%