Ch4 - part 2

Question 1

What are some unit operations

Answer 1

Particle sorting (eg. separation using diffusion, pinched flow fractionation, inertial particle ordering, dean flow particle separators, Aqueous two phase systems ATPSs, dielectrophoretic separation)

droplet generation (Flow focusing, T-function, coaxial droplets)

Question 2

Explain separation using diffusion

Answer 2

• laminar flow
  -mass transfer by diffusion
• separate particles on the basis of their diffusion coefficient.

diffusion coefficient scales roughly with the inverse of the size of the molecule and on the shape of the molecules.
–> smaller molecules have higher diffusion coefficients and will move a longer average distance per time.

Question 3

Explain pinched flow fractionation

Answer 3

1. in pinched portion of the channel, particles are pushed to the sidewall
2. center of mass of smaller particles is closer to the wall
3. when the channels broaden, the particles travel different paths

Question 4

Explain inertial particle ordering

Answer 4

velocity gradient causes shear induced lift force that pushes particles away from centerline

wake of a particle near the wall causes wall induced lift force, which pushes particles away from wall

she literally doesn’t explain how it separates the particles

Question 5

Explain the dean flow particle separators

Answer 5

in inertial particle ordering in a rectangular channel, particles to settle at 4 equilibrium positions

when drag due to dean vortex in curved channel, equilibrium position changes to 1.

separation based on size

Question 6

Explain Aqueous two phase systems

Answer 6

2 incompatible additives are above critical concentration which allow for phase separation of an aqueous mixture

Question 7

explain dielectrophoretic separation

Answer 7

particles separated based on electrophoretic mobility, which is the solutes response to an applied electric field.

dependent on type of medium, electrical properties of the particle, shape and size of the particles

Question 8

what are the advantages of droplet generation using a microfluidic platform?

Answer 8

1. narrow size distribution
2. high frequency of droplet generation
3. control of droplet morphology (double emulsions)

Question 9

why double emersions?

Answer 9

• serve as a template for polymer capsules, core-shell particles, and non-spherical particles.
• ## being developed as delivery vehicles for active compounds

Question 10

what is the best method for forming double emulsions with controlled structure

Answer 10

coaxial flow focusing

Question 11

what is a micrototal analysis system?

Answer 11

device that automates and includes all necessary steps for the chemical analysis of a sample

Question 12

what are external power sources/field or actuators used for active microfluidics

Answer 12

peristaltic pumps
syringe pumps
electrokinetic pumps
centrifugal pumps (lab on a disc)

Question 13

What are some passive microfluidic mechanisms

Answer 13

finger pressure-driven
osmosis
capillary
permeation/diffusion

Question 14

explain the advantages of using the electrokinetic phenomena

Answer 14

minimal space requirements
no moving parts
low cost