Rheology of interfacial layers

Miller, R.; Ferri, James K.; Javadi, Aliyar; Krägel, J.; Mucic, N.; Wüstneck, R.

doi:10.1007/s00396-010-2227-5

Cited by 231 publications

(137 citation statements)

References 89 publications

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“…The rheological characterization of the catalyst support precursor dispersion in water was studied using the oscillating pendant drop technique [23] before dissolving the catalyst precursor nitrate salt in the dispersion. The precursor support dispersion, despite its high silica loading, is a clear transparent liquid with relatively low constant simple shear viscosity (10 cp) due to the coating of the dispersed silica particles which reduces silica network formation [27].…”

Section: Rheological Characteristics Of the Catalyst Support Precursomentioning

confidence: 99%

“…It was observed that although a bubble could be generated, during data acquisition, it become unstable and hence the data is confined to the first minute of bubble generation. From this data, the interfacial tension, elastic (storage) modulus (E') and viscous (loss) modulus (E") are evaluated as a function of frequency of oscillations using well established theories [23]. The oscillatory variation of the fluid volume and the computed interfacial tension is shown in Figure 1.…”

Section: Rheological Characteristics Of the Catalyst Support Precursomentioning

confidence: 99%

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Co-Assembled Supported Catalysts: Synthesis of Nano-Structured Supported Catalysts with Hierarchic Pores through Combined Flow and Radiation Induced Co-Assembled Nano-Reactors

Akay

2016

Catalysts

106

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Abstract:A novel generic method of silica supported catalyst system generation from a fluid state is presented. The technique is based on the combined flow and radiation (such as microwave, thermal or UV) induced co-assembly of the support and catalyst precursors forming nano-reactors, followed by catalyst precursor decomposition. The transformation from the precursor to supported catalyst oxide state can be controlled from a few seconds to several minutes. The resulting nano-structured micro-porous silica supported catalyst system has a surface area approaching 300 m 2 /g and X-ray Diffraction (XRD)-based catalyst size controlled in the range of 1-10 nm in which the catalyst structure appears as lamellar sheets sandwiched between the catalyst support. These catalyst characteristics are dependent primarily on the processing history as well as the catalyst (Fe, Co and Ni studied) when the catalyst/support molar ratio is typically 0.1-2. In addition, Ca, Mn and Cu were used as co-catalysts with Fe and Co in the evaluation of the mechanism of catalyst generation. Based on extensive XRD, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) studies, the micro-and nano-structure of the catalyst system were evaluated. It was found that the catalyst and silica support form extensive 0.6-2 nm thick lamellar sheets of 10-100 nm planar dimensions. In these lamellae, the alternate silica support and catalyst layer appear in the form of a bar-code structure. When these lamellae structures pack, they form the walls of a micro-porous catalyst system which typically has a density of 0.2 g/cm 3 . A tentative mechanism of catalyst nano-structure formation is provided based on the rheology and fluid mechanics of the catalyst/support precursor fluid as well as co-assembly nano-reactor formation during processing. In order to achieve these structures and characteristics, catalyst support must be in the form of silane coated silica nano-particles dispersed in water which also contains the catalyst precursor nitrate salt. This support-catalyst precursor fluid must have a sufficiently low viscosity but high elastic modulus (high extensional viscosity) to form films and bubbles when exposed to processing energy sources such as microwave, thermal, ultra-sound or UV-radiation or their combination. The micro-to-nano structures of the catalyst system are essentially formed at an early stage of energy input. It is shown that the primary particles of silica are transformed to a proto-silica particle state and form lamellar structures with the catalyst precursor. While the nano-structure is forming, water is evaporated leaving a highly porous solid support-catalyst precursor which then undergoes decomposition to form a silica-catalyst oxide system. The final catalyst system is obtained after catalyst oxide reduction. Although the XRD-based catalyst size changes slightly during the subsequent heat treatments, the nano-structure of the catalyst system remains substantially unaltered as evaluated through TEM images. Howev...

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Section: Rheological Characteristics Of the Catalyst Support Precursomentioning

confidence: 99%

Section: Rheological Characteristics Of the Catalyst Support Precursomentioning

confidence: 99%

Co-Assembled Supported Catalysts: Synthesis of Nano-Structured Supported Catalysts with Hierarchic Pores through Combined Flow and Radiation Induced Co-Assembled Nano-Reactors

Akay

2016

Catalysts

106

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“…The first experiment at an interface was performed 25 years later by Plateau, who compared the dumping of an oscillating magnetic needle on bare and surfactant-laden interfaces (3). He discovered that the needle was better immersed when a surfactant was present, but he could not explain why.…”

Section: Interfacial Rheology: Theory and Available Measuring Techniquesmentioning

confidence: 99%

“…Shear interfacial rheological methods involve inducing shear in the adsorbed film without changing the area. These methods provide information on the structures formed at the interface (3,8,19). These techniques are most commonly used for the adsorption layers of protein or combinations of protein and low-molecular-weight surfactants and can be divided into direct and indirect methods.…”

Section: Shear Measuring Techniquesmentioning

confidence: 99%

“…only affect the stability of foams and emulsions but also influence a variety of technological processes, such as electrospinning (2), mass transfer, foaming, emulsification, oil-recovery and high-speed coating (3). Numerous reports dealing with the effects of incorporated surfactants on dispersion stability in correlation with rheological parameters can be found in the literature (4)(5)(6).…”

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Interfacial rheology: An overview of measuring techniques and its role in dispersions and electrospinning

Pelipenko¹,

Kristl²,

Rošic³

et al. 2012

Acta Pharmaceutica

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Colloidal disperse systems represent the increasing number of modern delivery systems whose primary characteristic, a large interfacial area, causes thermodynamic instability. Therefore, the foremost challenge in dispersion design is the reduction of interface instability and an understanding of the behaviour of interfaces. Interfacial rheology is one of the most powerful tools for observing occurrences at the interphase. As previously mentioned, the stability of such systems is provided by the formation of a stable interfacial layer of surfactants around each dispersible particle. The stability of these systems can be improved by using more than one surfactant, but it must be kept in mind that different surfactants can have varying mechanisms of stabilisation, some of which can be mutually incompatible. Surfactant selection is therefore crucial and must be based on physicochemical properties, stability of the interfacial film, mobility of the molecules in the interfacial film, HLB, film formation kinetics, compatibility and interactions between molecules on the surface, CMC, etc. Interfacial rheological properties have yet to be thoroughly explored. Only recently, methods have been introduced that provide sufficient sensitivity to reliably determine viscoelastic interfacial properties. In general, interfacial rheology describes the relationship between the deformation of an interface and the stresses exerted on it.Due to the variety in deformations of the interfacial layer (shear and expansions or compressions), the field of interfacial rheology is divided into the subcategories of shear and dilatational rheology. While shear rheology is primarily linked to the long-term stability of dispersions, dilatational rheology provides information regarding short-term stability. Interfacial rheological characteristics become relevant in systems with large interfacial areas, such as emulsions and foams, and in processes that lead to a large increase in the interfacial area, such as electrospinning of nanofibers.

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Emulsions

Schaaf

2017

Ullmann's Encyclopedia of Industrial Chemistry

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Rheology of interfacial layers

Cited by 231 publications

References 89 publications

Co-Assembled Supported Catalysts: Synthesis of Nano-Structured Supported Catalysts with Hierarchic Pores through Combined Flow and Radiation Induced Co-Assembled Nano-Reactors

Co-Assembled Supported Catalysts: Synthesis of Nano-Structured Supported Catalysts with Hierarchic Pores through Combined Flow and Radiation Induced Co-Assembled Nano-Reactors

Interfacial rheology: An overview of measuring techniques and its role in dispersions and electrospinning

Emulsions

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