How to Make a Surface Act as a Micropump

Bekir, Marek; Sharma, Anjali; Umlandt, Maren; Lomadze, Nino; Santer, Svetlana

doi:10.1002/admi.202102395

Cited by 12 publications

(10 citation statements)

References 50 publications

(76 reference statements)

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“…Similar to the rigid porous particles, we explain this observation by the dissimilar photoisomerization rate of the surfactant inside the microgel and in the bulk, ,, which creates an excess of cis -isomer concentration Δ c C near the microgels in comparison to the bulk soltion. We have demonstrated that the DO flow velocity scales linearly with Δ c C ( t ), where the dependence of Δ c C on time is estimated by solving the equation where k TC , MG and k TC are the rate constants of trans – cis isomerization inside the microgel and bulk solution, respectively, k CT is the rate constant of cis – trans isomerization in the bulk solution, c T,MG is the trans -isomer concentration in the microgel, c T,B and c C,B are the concentrations of trans- and cis- isomers in the bulk, and I is the intensity of the light (an illustration of the process is provided in Figure S3, Supporting Information). In the following, we demonstrate how three experimental parameters, i.e., (1) wavelength of irradiation, (2) amount of charged groups within the gel, and (3) intensity of light, determine the extent of the DO flow generated around and by the microgels.…”

Section: Resultsmentioning

confidence: 87%

“…The gradient in the osmotic pressure is formed near the particle, thus a local -light driven diffusioosmotic ( l -LDDO) flow . Examples of such particles are silica colloids having pores of nanometer size and rough surfaces such as wood, dust, soil, sand, hair, and so on . For spherical particles, the flow is directed radially and results in long-range diffusioosmotic repulsion or attraction (wavelength dependent) in an ensemble of the colloids.…”

Section: Introductionmentioning

confidence: 99%

“…28 Examples of such particles are silica colloids having pores of nanometer size and rough surfaces such as wood, dust, soil, sand, hair, and so on. 29 For spherical particles, the flow is directed radially and results in long-range diffusioosmotic repulsion or attraction (wavelength dependent) in an ensemble of the colloids. The range over which the repulsion is effective is controlled by the irradiation parameters, i.e., wavelength and intensity, and can exceed several tens of the particle radius.…”

Section: ■ Introductionmentioning

confidence: 99%

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Generation of Local Diffusioosmotic Flow by Light Responsive Microgels

et al. 2022

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Here we show that microgels trapped at a solid wall can issue liquid flow and transport over distances several times larger than the particle size. The microgel consists of cross-linked poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM-AA) polymer chains loaded with cationic azobenzene-containing surfactant, which can assume either a trans- or a cis-state depending on the wavelength of the applied irradiation. The microgel, being a selective absorber of trans-isomers, responds by changing its volume under irradiation with light of appropriate wavelength at which the cis-isomers of the surfactant molecules diffuse out of the particle interior. Together with the change in particle size, the expelled cis-isomers form an excess of the concentration and subsequent gradient in osmotic pressure generating a halo of local light-driven diffusioosmotic (l-LDDO) flow. The direction and the strength of the l-LDDO depends on the intensity and irradiation wavelength, as well as on the amount of surfactant absorbed by the microgel. The flow pattern around a microgel is directed radially outward and can be maintained quasi-indefinitely under exposure to blue light when the trans-/cis-ratio is 2/1, establishing a photostationary state. Irradiation with UV light, on the other hand, generates a radially transient flow pattern, which inverts from inward to outward over time at low intensities. By measuring the displacement of tracer particles around neutral microgels during a temperature-induced collapse, we can exclude that a change in particle shape itself causes the flow, i.e., just by expulsion or uptake of water. Ultimately, it is its ability to selectively absorb two isomers of photosensitive surfactant under different irradiation conditions that leads to an effective pumping caused by a self-induced diffusioosmotic flow.

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Section: Resultsmentioning

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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Generation of Local Diffusioosmotic Flow by Light Responsive Microgels

et al. 2022

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“…Feldmann et al [73] could pump tracer particles due to a photosensitive surfactant, which changed from trans to cis state with UV light. The same surfactant was later used by Bekir et al [60] to create a micropump.…”

Section: Applications Of Diffusio-osmosismentioning

confidence: 99%

“…Michelin and Lauga [59] developed a universal optimal geometry to create a pumping wall in a microchannel based on chemically active patches with non-zero phoretic mobility. Bekir et al [60] created a micropump by light-driven diffusio-osmosis, where the surfactant changes from trans to cis states depending on the light wavelength. The surfactant is adsorbed by a particle in the trans state, while the cis state prefers the solution, which creates a strong concentration difference based on adsorption and desorption.…”

Section: Applications Of Diffusio-osmosismentioning

confidence: 99%

Turn on the light: Diffusio-osmosis induced by photocatalytic reactions

Timmerhuis

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Catalysis is widely used in industry, where 90% of the industrial processes uses at least one catalyst in the system. Heterogeneous catalysts are most commonly used (80%) compared to homogeneous catalysts (15%) and biocatalysts (5%). A heterogeneous catalyst is a solid surface with active sites to accelerate a reaction without changing the thermodynamic equilibrium, and the reactant is in gas or liquid phase. The reactant is transported to the surface and active site to be able to convert to products. If the reaction is really fast compared to the mass transport towards the surface, then a boundary layer is formed. This boundary layer limits the effectiveness of the catalyst, as the concentration of reactant vanishes near the surface and conversion mainly depends on the diffusivity of the reactant.The boundary layer can thus be a limiting factor in heterogeneous catalysis. In this study, we aim to create a surface induced flow such that reactant is transported to the surface and product is transported from the surface. The surface flow of interest is diffusio-osmosis, originating from a solute concentration gradient parallel to the surface with which the solute interacts. The interaction of the solute with the wall creates a pressure on the fluid in the interaction layer. This pressure is higher for higher concentrations, so the concentration difference creates an osmotic pressure along the surface. This pressure difference is balanced by a viscous force, creating a flow within the interaction layer along the surface. This flow is defined as the diffusio-osmotic flow.A heterogeneous catalysis process suitable to study diffusio-osmosis involves the oxidation of organic compounds over titanium dioxide. Titanium dioxide is a photocatalyst, meaning that the catalytic properties are activated by light. This process can be used in wastewater treatment systems to remove organic micropollutants from water. An elaboration on this process and a general introduction of diffusio-osmosis are given in Chapter 1.The magnitude of the diffusio-osmotic velocity depends on the concentravii viii Summary ment. This was attributed to the dissociation constants of carboxylic acids, so the ionic gradients were actually lower, decreasing the driving force for diffusiophoretic movement. The H-shaped channel can be used to study diffusiophoretic movement of particles, especially to compare experimental work with theory.The diffusio-osmotic flow induced by a photocatalytic reaction at the surface is studied in Chapter 5. The reaction kinetics measured in Chapter 2 and 3 are used to determine the concentration gradient. The surface ζ-potential of titanium dioxide was measured under reactive and nonreactive conditions, resulting in a potential between 40 and -70 mV for pH 3 to 10. A numerical study showed how diffusio-osmosis can enhance mass transfer especially when the flow is directed from noncatalytic to catalytic surface. The numerical study was also used to determine the diffusio-osmotic velocity for methylene blue, formic acid, acetic ...

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Versatile Microfluidics Separation of Colloids by Combining External Flow with Light‐Induced Chemical Activity

et al. 2023

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Separation of particles by size, morphology, or material identity is of paramount importance in fields such as filtration or bioanalytics. Up to now separation of particles distinguished solely by surface properties or bulk/surface morphology remains a very challenging process. Here a combination of pressure-driven microfluidic flow and local self-phoresis/ osmosis are proposed via the light-induced chemical activity of a photoactive azobenzene-surfactant solution. This process induces a vertical displacement of the sedimented particles, which depends on their size and surface properties . Consequently, different colloidal components experience different regions of the ambient microfluidic shear flow. Accordingly, a simple, versatile method for the separation of such can be achieved by elution times in a sense of particle chromatography. The concepts are illustrated via experimental studies, complemented by theoretical analysis, which include the separation of bulk-porous from bulk-compact colloidal particles and the separation of particles distinguished solely by slight differences in their surface physico-chemical properties.

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How to Make a Surface Act as a Micropump

Cited by 12 publications

References 50 publications

Generation of Local Diffusioosmotic Flow by Light Responsive Microgels

Generation of Local Diffusioosmotic Flow by Light Responsive Microgels

Turn on the light: Diffusio-osmosis induced by photocatalytic reactions

Versatile Microfluidics Separation of Colloids by Combining External Flow with Light‐Induced Chemical Activity

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