Instructor:

1
Interfacial Phenomena II Spring 2009
Instructor Brij M. Moudgil 205 Particle Science
and Technology Bldg. 846-1194 bmoudgil_at_perc.ufl.ed
u
Micromotors Microfans
2
Industrial Applications of Interfacial Phenomena

• Microelectronics
• Chemical mechanical polishing (CMP)
• Chemical purification/filtration
• Food
• Flowability
• Texture
• Fortification/Delivery of Vitamins, Nutrients
• Pharmaceuticals
• Controlled drug delivery
• Agglomeration of dry powders
• Dispersion in biofluids

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Example of Multilevel Metallization
Source Scientific American, May 1997.
4
CMP Process
pressure
slurry feed
wafer

• s

polishing pad
plate
?p
Chemical actions from aqueous media
Mechanical actions from free abrasives
5
Stability of Particulate Systems

• Food
• Texture
• Structure
• - Creaming
• - Settling

• Paper
• Quality
• Uniformity
• Strength

• Paints
• Opacity
• Color Strength
• Gloss
• Viscosity

• Microelectronics
• Chemical Mechanical Polishing (CMP)

• Stabilization / dispersion of particulate systems
  impact the performance of industrial processes.

6
Industrial Issues on Powder Flow
- Approximately 60 of plants worldwide handle
powders. - Plants handling solids perform poorly
when compared with plants handling
liquids/gases. - Plants handling powders operate
at 50 of design capacity. (1/5)th of these
plants fail to attain more than 20 of the design
capacity. Poor performance mostly attributed to
powder flow problems.
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The challenge of capturing the common salt market

• How can a company differentiate something as
  seemingly trivial as common salt?

Free Flowing Edible grade silica is coated
onto salt. Makes naturally hygroscopic NaCl
highly hydrophobic. Hence, salt does not take
up moisture even in tropical climate and is free
flowing
Measured Iodine Delivery Silica can be used
to encapsulate iodine, which otherwise sublimes
at high cooking temperatures. It however breaks
at acidic pH (stomach), facilitating controlled
release of iodine
Hence, a differentiated product helps beat
competition!
8
Pulsed Laser Deposition Method (PLD)

• PLD coatings control particle adhesion/flow,
  hydration rate/stability, and release-rate.
• Commercialized by Spin-off Company, NanoSphere
  Inc.

Fitz-Gerald, J., Pennycook, S., Gao, H. and
Singh, R. K., Nanostructured Matls., 12, 1167
(1999)
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Nanoscale Coatings for Enhanced Drug Delivery
In Vitro Dissolution Profiles
Dissolution of micronized TA asthma powder with
coating times of 10 minutes ? and 30 minutes ?
vs. uncoated TA powder ?
Fitz-Gerald et al. (2000)Nano-Thin Coatings for
Improved Lung Targeting of Glucocorticoid Dry
Powder In-vitro and In-vivo Characteristics,
Respiratory Drug Delivery VII (1)
10
Microemulsions for Drug Detoxification

• Test Drugs

Amitriptyline (Antidepressant)
Bupivacaine (Local Anesthetic)
Reduction in Amitriptyline-induced cardiotoxicity
by Microemulsions
11
Relative Contribution of Bulk and
Surface Properties in Particulate Processes
Adapted from R.K. Klimpel PST course notes
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Surfaces and Interfaces
A region of space in which the system
undergoes transition from one phase to another
Surface Region between condensed phase (S or
L) and a gas phase
Interface Region between two condensed phases
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Surface Free Energy
Atoms and molecules at interfaces posses
energies and reactivities significantly
different from those of the same species in bulk
Imbalance leads to surface free energy
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Surface Free Energy
Process of creating new surface area
equivalent to separating two half
spaces. Surface Energy (Solid/Gas) ?
0.5?W DW energy change per unit area required
to separate the two new interfaces to
infinity Units mJ/m2
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Surface Tension

• Imbalance of forces at the Gas/Liquid Interface

• For Liquid/Liquid Interface, usually termed
• Interfacial Tension
• Units of force/unit length (mN/m)
• note mN/m mJ/m2

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Surface Energy vs. Surface Tension

• For liquids, Surface Tension Surface Energy
• For solids, the tension depends on the direction
• in the surface, and the exact crystal
  structure of
• the surface ? surface tension is inhomogeneous

Hence, surface tension should be used for
interfaces involving fluid phases, whereas for
interfaces involving solids, surface energy
should be used.
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Solid Surface Free Energy

• New surface formation involves two steps
• Formation of two new surfaces with no
• rearrangement of atoms/molecules
• Rearrangement of molecules/atoms on the
• new surfaces to establish the lowest
• energy state

• In liquids, the rearrangement is very fast
• ? Surface tension is an equilibrium value

• In solids, reduced mobility slows rearrangement
• ? Surface energy is a non-equilibrium,
• non-uniform value

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Solid Surface Free Energy
Surface energy may change dramatically based on
the history of the surface
a
b
Surface Energy (g)
Separation Distance (h)

• New surface in contact with vacuum
• New surface in contact with another interacting
  phase

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Factors affecting Surface Free Energy

• Other factors influencing surface energy
• Surface energy of solids is not only a
  material
• property, it may be significantly influenced
  by the
• environment

• Organic contamination
• Roughness/edges/high energy sites
• Wetting agents
• Humidity
• Crystal plane

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Factors affecting Surface Free Energy

• Contact angle of water on silica changes from
• approximately 10º to 45º with heat treatment.
• Contact angle of water on TiO2 - silicone thin
  film
• changes from 120? to 3? upon irradiation with
  UV

TiO2-Silicone film after UV irradiation
TiO2-Silicone film before UV irradiation
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Surface Energy of Different Material
Surface Energy of Material at different
temperatures
(Israelachvili, J.N, Intermolecular and Surface
Forces, 2nd ed., Academic Press)
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Questions
Is Surface Energy of clean cleaved crystal
surface less or greater than surface of the same
material that has been ground or polished
? Would the adsorption of gases be higher or
lower on high surface energy surfaces ?
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Experimental Determination of Surface Energy (van
der Waals Method)
THE WORK OF COHESION (Wc )

• Energy needed to separate two identical surfaces
  from contact to infinite separation
• Units of energy per unit area (mJ/m2 erg/cm2)

? Surface Free Energy A11 Hamaker
constant (Material Property) HO
Distance of Separation Between Liquid Atoms
0.165 nm Between Solid Atoms 0.3 nm

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The Work of Adhesion

• Energy needed to separate two dissimilar surfaces
  from contact to infinite separation
• Units of energy per unit area (mJ/m2 erg/cm2)

Wa ?1 - ?2 - ?12
?1 ?12 ?2
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Conact Angle, q (Young-Laplace Equation)
?LG
?SG
?
?SL
At equilibrium all tensions must be balanced
?SG ?SL ?Lgcos ? For a
water droplet on a surface 0 lt ? lt 90
hydrophilic , 90 lt ? lt 180, hydrophobic
TiO2-Silicone film after UV irradiation
TiO2-Silicone film before UV irradiation
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Determination of Surface Energy Using Contact
Angle (Zisman Plot)
Contact angle measurement of a solid with
various liquids of known surface tension
Cos ? 1 b(?l - ?c)
Cos ?
? Contact angle b 0.03 0.04 ?l Surface
tension of liquid ?c Critical surface tension
?1
Extrapolate curve to Cos ? 1, obtain ?c ,
characteristic of Surface Energy
(Adamson, 1997)