Texas A&M University MSEN 410 Exam 3 True or False Review Materials

Roughly speaking, a colloid is a particle with a diameter less than <1 μm, small enough for Brownian motion to dominate over gravity.

both True and False answers were accepted as correct because of difference between particle diameter given in the book and class notes)

If maximum of the potential energy of the interaction (i.e. energy barrier) between particles in dispersion is large, the phenomenon known as flocculation can take place in the dispersion.

False

Above some critical concentration C*, polymer chains in a solution also become entangled and their motion in the solvent becomes further restricted, thus leading to the dramatic rise of the solution viscosity above C*.

True

If all other conditions are the same, having slip casting mold with smaller diameter of the channels/pores will decrease drying time.

True

If all other conditions being the same, the thickness of the cast layer in slip casting will increase with increasing viscosity of the slip (or dispersion).

False

When van der Waals attraction dominates, particles that approach one another in suspensions are
drawn together, forming agglomerates. Over time, more particles join the agglomerates and
eventually, the size of the agglomerates makes them susceptible to sedimentation. To prevent this
spiraling process, repulsive interactions beyond those provided by inner shell electrons, are needed
to prepare a stable suspension. Describe briefly two main approaches that are used to deliberately
build repulsive forces between particles and thus enhance their colloidal stability.

Electrostatic repulsion - make suspension (usually by changing pH and adding salts) so that
the particles gain a surface charge and electrostatic repulsion goes into effect.

Steric repulsion - adsorb a polymer or surfactant on the particle surfaces, creating a steric
layer that presents a repulsive interaction.

List at least 3 different methods for applying liquid coatings onto moving substrates.

(a) dip coating, (b) knife coating, (c) adjustable gap blade coating (doctor blade coating), (d)
slot coating, (e) slide coating, and (f) curtain coating.

Inkjet printing is a method for depositing small amounts of liquid (dispersion or solution) onto surfaces
at precise locations that subsequently dries or cure. What are the two main methods of generation
and depositing droplets in inject printing:

continuous ink jet printing________
drop on demand printing_________

In colloid dispersion of particles in the liquid medium, the motion of the solid particles is affected by gravity and Brownian motion.

True

When Electrostatic forces between particles with same surface charge in the dispersion dominates over van der Waals forces, particles that approach one another are drawn together, forming agglomerates

False

For suspension of particles with isoelectric point is at pH=6, any decrease or increase of pH in this suspension will result in the change of surface potential.

True

Above some critical concentration C, polymer chains in a solution also become entangled and their motion in the solvent becomes further restricted, thus leading to the dramatic rise of the solution viscosity above C.

True

Steric repulsion is one of the ways used to obtain strong Van der Waals forces between particles in colloidal dispersions.

False

Slip casting is one of the methods for applying liquid coatings onto moving substrates.

False

Capillary action draws water into the mold during slip casting, leaving behind a consolidated layer of particles on the mold surface.

True

In "coalescence" stage of during drying latex particle suspensions, surface tension, capillary, and van der Waals forces pulling particles toward each other are strong enough to flatten at particle-particle contact.

False

At all other conditions being the same, the thickness of the cast layer in slip casting will increase with:
a) Increasing viscosity of the slip (or dispersion)
b) Increasing resistance of the cast layer
c) Increasing solid loading of the slip
d) Decreasing difference between pressure at the interface between slip and cast layer and capillary pressure in the cast layer.

c) Increasing solid loading of the slip

List at two most common dispersion and solution additive processes:

(a) Stereolithography (SLA)
(b) Inkjet Printing