Microfluid segment technology

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The microfluidic technology segment is one of the methods of drop-based microfluidics , where many single drops are separated from each other by an inert carrier fluid and can be thus used as individual small reactors. In most cases the fluid segments are formed by an aqueous phase, while a water-immiscible liquid such as e.g. B. oils or liquid perfluoroalkanes form the carrier phase. The fluid segments are created by introducing the aqueous phase into the carrier phase when it is passed through a capillary or a microchannel. By bringing the two immiscible liquids together, the liquid column is segmented. The individual droplet volumes formed are dependent on the channel diameter and are typically in the nanoliter or upper picolitre range.

In contrast to other microfluidic processes, in microfluid segment technology the droplets are guided in an orderly manner, so that they retain their initially obtained order over the entire course of the process. In this way, initial information such as B. get starting concentrations and thus the individuality and addressability of the individual drops. Therefore, the microfluid segment technology is particularly suitable for series of measurements and experiments in which individual samples are processed or in which concentration series or two- and multi-dimensional concentration spaces are examined.

Plug flow and narrow residence time distribution

Since the interfacial tension between the fluid segments and the carrier phase brings about the stability and high integrity of the segments, they are transported as plugs. The result is a practically constant dwell time, ie an ideally narrow dwell time distribution, which ensures a very high degree of homogeneity and reproducibility in the process management, especially with thermal activation, cooling and irradiation. Such process homogeneity is particularly important for time-critical processes, e.g. B. in the nucleation phase in the production of micro- and nanoparticles of great importance.

Fast mixing

By merging two or more liquid streams of the embedded phase, fluids can be mixed. The mixing process is strongly promoted by the forward movement of the segment, as this movement rapidly builds up circular flows in the microchannel or the capillary. This intensive local convection results in a much faster mixing than in homogeneous fluids in which only diffusive mixing is possible due to the laminar flow.

Flow rate controlled concentration programs

By setting certain ratios of the volume flow rates of two fluids to be mixed during segment generation, different concentration ratios can be easily set. By automatically varying the flow rate ratios, concentration programs are automatically generated in a sequence of microfluid segments. Due to the periodic segment formation, a digitization principle works: Even with continuously varied flow rates, there is a graduated variation of the concentrations in the microfluid segment sequence. The gradations can be very fine, so that high-resolution concentration series can be generated. The method can also be used to generate two- and multi-dimensional concentration spaces if a corresponding number of miscible fluids is fed to the segment generator. The principle of automatic concentration gradation by program-controlled flow rates is z. B. used in the synthesis of nanoparticles and in microtoxicology .

Individual evidence

  1. ↑ JM Köhler et al .: Digital reaction technology by micro segmented flow - components, concepts and applications . In: Chemical Engineering Journal . tape 101 , no. 1–3 , 2004, pp. 201-216 , doi : 10.1016 / j.cej.2003.11.025 .
  2. ↑ Shia-Yen Teh, Robert Lin, Lung-Hsin Hung, Abraham P. Lee: Droplet microfluidics . In: Lab on a Chip . tape 8 , no. 2 , January 2008, p. 198-220 , doi : 10.1039 / B715524G .
  3. ^ Helen Song et al .: Reactions in Droplets in Microfluidic Channels . In: Angewandte Chemie . International Edition . tape 45 , no. 44 . Wiley, 2006, ISSN  1521-3773 , pp. 7336-7356 .
  4. ↑ Ilya Shestopalov et al .: Multi-step synthesis of nanoparticles performed on millisecond time scale in a microfluidic droplet-based system . In: LAB on a chip . Miniaturization for chemistry and biology . tape 4 , no. 4 , 2004, ISSN  1473-0197 , p. 316-321 .
  5. ^ Joshua D. Tice: Formation of Droplets and Mixing in Multiphase Microfluidics at Low Values ​​of the Reynolds and the Capillary Numbers . In: Langmuir . The ACS journal of surfaces and colloids . tape 19 , 2003, ISSN  0743-7463 , p. 9127-9133 .
  6. ↑ Jialan Cao et al .: Uncovering toxicological complexity by multi-dimensional screenings in microsegmented flow . Modulation of antibiotic interference by nanoparticles . In: LAB on a chip . Miniaturization for chemistry and biology . tape 12 , no. 3 , 2012, ISSN  1473-0197 , p. 474-484 .