Review of Nano Section

7/27/2019 Review of Nano Section

1/103

Semester 1, 2013

Bio-Nano EngineeringCHE 2165Revision


2/103

1. Introduction and conceptmap

2. Electrostatic and van derWaals Forces

3. Colloid: optical properties

4. Colloids basic5. Colloids chemistry

6. Colloids physics

7. Colloids stability

8. Wetting9. Wetting real surfaces

10. Capillary phenomena

11. Surface energy and adhesionpromotion

12. Bio-nano application (1)

13. Bio-nano application (2)

14. Cell overview

15. Biomolecules I

16. Biomolecules II

17. Enzymes

18. Fermentation technology

19. Bioproduct recovery

20. Chromatography andbiomolecular interaction

Unit Schedule


3/103

3

Learning Outcomes (Sunway)

1. Describe the fundamental of colloid science and explainthe basic concepts of cell, biomolecules and enzymes.

2. Solve problems in surface modificationandsurface

engineering by applying surface and interface sciences,and illustrate bioprocess development usingfermentation technology and bioproduct recoverymethods.

3. Be able to prepare literature review by undertakingliterature search, working in a team and applying concisecommunication.


4/103

4

Objectives

Knowledge1) Understand Bio-nano engineering in terms of

biological, colloid, and surface science.

2) Understand the forces involved in colloids and

their effect on colloid stability/coagulation.

3) Understand the different types of cells/

molecules used in biotechnology.


5/103

5

Objectives

Skills1) Colloid stability under the influence of pH and

salt. Control of surface polarities for adhesion

and functionalization purposes.

2) Apply notions of biology, colloids & surfaces

to nanotechnology, biotechnology and

sustainable processes.

3) Improve communication and team work ability

(through a project).


6/103

Semester 1, 2013

Bio-Nano EngineeringCHE 2165

Revision of Physics


7/103

Coulombs law - Electrostatic force

The phenomenonQuantitative measurement

by Coulomb in 1784 1785.


8/103

122

12

21

12r

r

qqkF

2

29

0

1099.84

1

C

mNk

TheCoulombs Law:

+ +1 2

F12

r

2

212

0 1085.8mN

C

q1 q2

+

1

1

+

+

1

+

1

+2

F12

++

2

F12

++2

F12

+

-

2

F12

+ ++

2

F12

A summary of Coulombs

results

Forces between Charged Particles: Coulombs Law

Dielectric constant of vacuum, C2/Nm2

(or permittivity)


9/103

+

q1

-

q2

Electric Field

The line of force originates from a positive charge and ends at a negative

charge.

+

+

+

+

+

--

--

-

Two point electric charges interact with each other in a non-contact

manner in vacuum or a medium.

Electric field is an imaginary concept to help us to understand such

interaction.

Electric field is a vector, like Coulomb force. The line of force is

an imaginary concept to help us to visualize the field.

A useful references: D. Giancoli, Physics, principle with applications, 5 ed.Prentice Hall, NJ, USA,1998. (Electrostatic section)

Concept of electric field


10/103

+

q1

The intensity of the electric field of

the point charge (q1) in vacuum is

Read and think:

An electric charge, q1, generates an electric field around it. Any other charged

particle, e.g. q2(in the previous slide) will feel the existence of q1. q2 will be

either pushed or pulled, depending on the signs of the two charge particles. Thiscan be understood in the following way: q1 fills up the space with a property (a

field). When q2 is placed in this space, it is affected by the property in this space

set by q1. q2consequently feels a force. The magnitude of the force q2 feels is

dependent upon the property of the space (or the intensity of the electric field).

(This simple explanation of electric field can be found in: H.Y. Erbil, Surface chemistry ofsolid and liquid interfaces, Blackwell Publishing, 2006, p. 25)

r

rr

q

E 21

01 4

1

2

1

0

14

1

r

qE

or

Vector form:

Scalar form:

Electric field, E


11/103

Electric field and coulomb force - the link

+

q1

-

q2

Electric field

2

1

0

14

1rqE

If a second point charge q2

is placed at a distance r

away from q1, then q2 will

sense the existence of q1

and experience anelectrostatic force exerted

by q1 on q2.

F12 1

40

q1

q2

r122

2112 qEF 2

121

qFE

r

Electric field generated by q1:

Coulomb force felt by q2in the electricfield by q1 :

The link between the electric field and

the coulomb force:

If we know the electric field intensity, we can calculate coulomb force.

Unit of electric field = N/C.


12/103

D

bbondwater

85.1

)25.52cos(51.12

2cos2

OH

H

d+d+

dO

H d+d

The unit of the dipole moment

is Debye (D) = 3.33810-30 Cm

(Dictionary of Physics, the penguin, 2nd ed, p104)

bb = 104.5bond=1.51 D

d = e (partial charge)e =1.60910-19 (C)l= 10-10 m

ll

l

dd

d

Be careful with thedirection of the

dipole. i.e. to +

- +

Simplified

View of a

Molecular

dipole

Polar covalent bond and bond polarity(Bond Dipole Moment, )

E


13/103

Intermolecular interactions

2

0

2

12,0

2

21,0

4

+

kT2

0

2

2

2

1

43

2

Dipole/dipole

van der WaalsInteractions

Dipole/Induced-dipole

Induced dipole/

induced dipole

-+ +

-

+-+

-

V Cr

6

Keesom

Derby

London

20

2,01,0

21

21

42

3

II

IIh

+

Potential energy


14/103

14

van der Waals forces are very short range

re is of the order of < 1 nmfor molecules and atoms.

For macrobodies (colloidal

particles), it can be in the

order of 10 nm.

For macrobodies (such as colloidal particles), however, van der Waals interactions can

have longer range of up to 10 nm. This is because that a macrobody has manymolecules.

The interaction range becomes longer as we need to add all pairs of molecular

interactions between the two macrobodies together. In future lectures we will re-visit

van der Waals forces between macrobodies (colloidal particles).


15/103

Semester 1, 2013


Optical Properties


16/103

hchE

E = energy of the radiation (carried by one photon) (J)

h = Plancks constant (6.626 x 10-34 J s)

(nu) = frequency of the radiation (Hz, or 1/s)

c = velocity of light 2.998x108 (m/s)

= wavelength (m)

What is energy of a blue light of 400 nm wavelength? What is the frequency of

such light?

Eis inversely proportional to

Light as a wave and as a particle


17/103

Light absorption through electron transition

between molecular orbitals

The presence of-electronsystems corresponds to theabsorption of ultraviolet and

visible light.

The energy gap between the* is of the magnitude ofultraviolet and visible light. E

nergy

-bonding

-bonding

*-anti-bonding

*anti-bonding

C=C

O

C

NHO

C

NH

Indigo

Example:

E = hc/


18/103

r

Scattering by molecules or small particles

)cos1(r

8

I

I 224

24

0

+

Condition for small particles (< / 20).

The theory is based on the electromagnetic

theory of light to the scattering by small,

non-absorbing, spherical particles in a gas

medium.

(See D. Shaw, Introduction to colloid and surface chemistry, p. 57)

= scattering angle

I0 = incident of electromagnetic wave intensityI = scattered intensity at an angle

to the incident beam

= wavelength of incident wave

= polarizabilily

r = distance between the scattering particle

and the observation point.

Rayleigh scattering of individual

particles :C

1r2


19/103

Color of nano metal particle suspensions

Metal nanoparticles are extraordinarily efficient at absorbing and scattering light.

Unlike many dyes and pigments, metal nanoparticles have a color that depends

upon the size (and the shape) of the particle.

The strong interaction of metal (such as Au and Ag) nanoparticles with light

occurs because the conduction electrons on the metal surface undergo a

collective oscillation when excited by light at specific wavelengths.

http://sciencegeist.net/the-shape-of-things/


20/103

Principle of visual observation: refractive index difference

and contrast

Picture from: Ben Selinger, Chemistry in the marketplace, 4 th ed. HBJ, NSW, Australia, (1991), p. 339

In order for a particle to be optically visible, there

must be an acceptable difference between its

refractive index and that of its surroundings to

generate a contrast.

An object may visually disappear if immersed in a liquid

of matching refractive index.


21/103

Semester 1, 2013


Basics of colloid


22/103

22

1. Particle size between 1 nm to 10 m (10-9 m to 10-5 m)

2.At least 2 phases:

Dispersed phase in a

continuous phase

3. High surface to volume ratio (S.Area / Vol.)

4.Surface chemistry/charge dominates interactions and

stability

5. Gravity has little effect

* Colloid from the Greek kolla or glue (colle in French)

Definition/criteria of colloids


23/103

P.C. Hiemenz and Raj Rajagopalan (2007) Principles of colloid and surface chemistry, 3rd ed. New York, p.10

Continuousphase

Dispersedphase

Descriptive name

Gas Liquid Fog, mist, aerosol Gas Solid Smoke, aerosol

Liquid Gas Foam

Liquid Liquid Emulsion Liquid Solid Sol, colloidal solution, gel, suspension

Solid Gas Solid foam

Solid Liquid Gel, solid emulsion Solid Solid Alloy

Summary of colloidal systems


24/103

Description of Diffusion at a

Macroscopic Level

Ficks first law of diffusion

Ficks second law of diffusion Concept of gradient

We will not go into the Stokes mathematical treatment, instead,

we only use his law to solve problems in diffusion and

sedimentation.


25/103

Translational diffusion: Ficks first law

dx

Area=A

(dc/dx)

x

Diffusion is the process for molecules to migrate from a region of

high concentration to a region of lower concentration and is a direct

result of Brownian motion.

dc

dx

C1

C2

Plan 1

Plan 2

C1 > C2

massflow

: concentration gradient

25


26/103

Ficks second law describes the concentration change at any

point during diffusion.

dc

dt

Dd2c

dx

2

d2c

dx2

dc

dx

describes the change in concentration gradient along

the x direction and how fast the driving force changes

with x.

is not a constant, it is still the driving force of the

diffusion process.

Translational diffusion: Ficks second law


27/103

Brownian motion

Einsteins equation (connects Browniandisplacement with diffusion coefficient)

The link between Ficks first law and theEinsteins equation

Thermal fluctuation of molecules that drivesthe movement of colloidal particles

Description of Diffusion at a

Microscopic Level


28/103

Brownian motion and diffusion of colloids

Description of diffusion at a microscopic level

Robert Brown1773-1858

X

_

(X1

2 + X22 + ...+ X

n

2)

n

Kinetic random motion

dominates the behaviour ofsmall particles.

Kinetic energy preventssettling. Fines suspensionscan be completely stable.

x

n : the number of movement

Random walk and

mean Brownian

displacement_

X
http://upload.wikimedia.org/wikipedia/commons/4/43/Brown.robert.jpg


29/103

The Einsteins Equation

The link between the Brownian motion andthe diffusion constant.

Einsteins

equation

X

_

2Dt

Distance a colloid particle

moved in x-direction in time

t driven by diffusion only

Diffusion coefficient D

and time t

f

kT

r

kTD

6

k - Boltzmann constant

- viscosity

rradius of spherical particles


30/103

The significance of energy kT

Lets consider the random movement of

a particle submerged in a liquid. It isdriven by the random thermal

fluctuation of the liquid molecules

around it.

The thermal fluctuation of molecules

causes the density of molecules at any

location in the liquid varies with time

and at any time varies with locations.

The molecular densities fluctuation

pushes the particle submerged in theliquid.

Such movements have been studied

microscopically and are called Brownian

motion after Robert Brown, a British

biologist who described them in 1828.

kT is a reflection of the thermal

energy that drives the Brownian

motion of the particles, therefore

diffusion coefficient is related to

it.

k : Boltzmanns constant (1.381

x 10-23 J/K)

T : temperature (K)

kT has an energy unit (1 kT =

4.12 x 10-21 J at 298 K )


31/103

31

3 fundamental forces acting on dispersed solid

particles in medium (such as water):

1. Gravitational Forces

Settles or raises particles depending of density relative to thesolvent.

2. Viscous Drag

Arises as a resistance to motion. Fluid has to be forced apart asthe particle moves through it.

3. Kinetic EnergyCauses Brownian motion of particles.

Nature of colloidal suspensions


32/103

Semester 1, 2013


Colloid Chemistry

A comparison of solid surface in vacuum and


33/103

A solid particle carrying a positive

charge in vacuum or in air

A solid particle carrying a

positive charge in water.

The situation cannot be

described by Coulombs

law developed in vacuum

Follow Coulomb law Dont follow Coulomb law

A comparison of solid surface in vacuum and

in water

The behavior of a charged

solid particle in vacuum or in

air can be very well predicted

using the Coulomb law we

reviewed in lecture 2.

Nothing in the

surrounding in

vacuum

S lid f i ( li i i )


34/103

(surface charge is developed via several possible mechanisms)

Solid surface in water (qualitative picture)

Diffuse double layer Bulk solution

(electro neutrality)(charged layer)

When a solid surface develops charges in water, electric neutrality must still be obeyed.

However, in water, the charge distribution at a solid surface is very different from a charged

solid surface in vacuum.

Co-ion

Counter-ion

Co-ion: ion carries

charge of the samesign

Counter-ion: ion

carries charge of

the opposite sign

A solid uncharged

particle in water

Most of the time we

simplify the surface of

a charged particle in

water as a flat surface

Diff l G Ch d l


35/103

35

We want to calculate the charge as a

function ofdistance from the surface

Electrostatic effect at longer distances

Lets define:

o = electric potential at the surface (V)

(x) = electric potential at a distancexfrom the surface in the

electrolyte solution

n+ / n- = number of positive or negative charges per unit volume

where the potential is

Question: The unit of n+ is ions/m3, how can we express the ion concentration in c with

the unit of mol/m3?

Diffuse layer Gouy-Chapman model

o

O

1/ Distance

(x)

Electric

potentia

l

Electric

potential ofthe medium

is 0

Diff l G Ch d l


36/103

36

Simplified equation:

At low potentials (), the potential decreases exponentially with

distance.

Not valid close to the surface because potential is high (Debye-

Huckel approximation is not valid)

-At the surface, the potential will decrease at a greater than exponential rate

x = 1/ (diffuse layer thickness) is defined as the distance overwhich the potential drops by an exponential decay (63%)

Diffuse layer Gouy-Chapman model

0ex

We have achieved what we wanted to

achieve (i.e. a relationship of the electric

potential distribution around a colloid

surface as a function of distance (x).

Check this point, compare the electric potentials

for x = 0 vs. x = 1/ to see if it decay by 63%

Diff l hi k (1/)


37/103

37

The diffuse layer thickness is given by the Debye

length defined as 1/. (The Debye length is aconvenient way to characterize the thickness of the ion atmosphere near a

surface.)

1/ is the distance over which the potential decreases by 63%. The intensity of the diffuse charge decreases (at

least) exponentially from the surface.

Ions (salt) compress the Debye length over which

the charge extends.

Diffuse layer thickness (1/)

Eff t f lt d bl l


38/103

38

F : Faraday constant (96,500 C/mol)

R : gas constant (8.314 J/K mol ) : r0 = 78.58.8510-12 (in water) (C2 J-1 m-1)

1/2

11-11212

221-1/2

22

298KJ314.8C1085.85.78

c)molC(965002c2F

KmolmJ

z

RT

z

)(mol/Lcwhenm)(10329.0

)(mol/mcwhenm)(1004.1

1-1/2210

3-11/228

cz

cz

T = 25C:

Effect of salt on double layer

For 25C, symmetrical ions

Double layer is about 1 nm for a 10-1 mol/L solution of 1-1 electrolyte (NaCl).

Double layer is about 10 nm for a 10-3 mol/L solution of 1-1 electrolyte.

S lt l ( )


39/103

For NaCl, z =1; CaCl2

, z =2 ; AlCl3

, z = 3

For each mole of AlCl3 added to solution, we indeed

add 3 moles of charges (Cl-).

z is the correction factor that takes in account the

dissociation of salt into charges that canscreen/compete with the charge of the surface.

)(mol/Lcwhenm)cz(10329.0 -11/2210

Salt valency (z)


40/103

Semester 1, 2013


Colloid Physics


41/103

41

1. Inner region includes adsorbed ions.

2. Diffuse region (last lecture)

[] ions are distributes according to

influence of electrical forces and

thermal motion.

Charged interfaces

Electrical double layer is made of 2 parts:

l i d bl l h


42/103

A layer of ion adsorbs at the surface. The effective surface is therefore

further by the diameter of the ion. The potential at the Stern plane is d

d o

A charged layer of some thickness remains bonded to the surface. The effective

plane (surface of shear) of shear is therefore a bit further from the surface.

denotes the potential at this plane of shear. It should be slightly lower than d .

However, we assume = d for convenience.

o

d

O

d 1/ Distance

Electricpotential

Potential change between the particle

surface and the Stern plane is linear

Potential change outside of the Stern plane

follows the Guoy-Chapman model

Electric double layer Stern theory

fi i i f i l


43/103

Zeta potential is the electric potential in the interfacial double layer at

the location of the shear plane (or surface of shear) versus a pointin the bulk fluid away from the interface.

In other words, zeta potential is the potential difference between thedispersion medium and the stationary layerof fluid attached to thedispersed particle.

We need to be clear about this concept,

as we will need to derive the equation

for zeta potential calculation.Assume = d for convenience.

Definition of zeta potential

o

d

O

d 1/ Distance

Electric

potential

Potential change between the particle

surface and the Stern plane is linear

Potential change outside of the Stern planefollows the Guoy-Chapman model

f i l


44/103

Particles in a colloidal suspension or emulsion usuallycarry anelectrical charge, which affects the degree of

dispersionor aggregation.

Zeta potential:The voltage difference between thatsurface and the liquid beyond the double layer.

Zeta potential System stability

44

Importance of zeta potential

l ki i h


45/103

ElectrophoresisMovement of the charged colloid (vE, m/s) relative to stationary liquid

created by an applied electric field.

Electro-osmosis

Movement ofliquid(Q) relative to a stationary charged surface (capillary,

porous plug) by an applied electric field.

Streaming potential

Electric field (V) created when a liquid is made to flow along a stationarycharged surface.

Sedimentation potential

Electric field (V) created when charged particles move relative to a

stationary liquid. 45

Four electrokinetic phenomena

El h i


46/103

2 extreme cases (assumptions and conditions)

a1 Flat surfaces - Smoluchowski equation

a (or [a/(1/)] ) is the ratio of the radius of curvature of the colloid (a) to

the double layer thickness (1/ )

1/

1/

Low ionic strength

Small particles (nano)

Larger colloids (micron)

Medium > Ionic strength

I (cii1

n

zi2)

Space outside of

1/ is the bulk of

the fluid.

thicknesslayerdouble

radiusparticle

1

a

a2a

Electrophoresis

a

El h i bili


47/103

a > 1 Flat surfaces - Smoluchowski equation

47

u

E

uE

3

2

Electrophoretic mobility


48/103

Semester 1, 2013


Colloid Stability

Force-Distance and Potential-Distance curves of 2


49/103

Primaryminimum

- Attraction

+ Repulsion

As a particle approaching to another particle, the

potential energy shows a monotonic decrease.

This will lead to a reversible coagulation,

depending on the depth of the potential energy

well.

At large h, the force (dashed line) is attractive.

When force is in its equilibrium separation (i.e.

neither attractive nor repulsive), the potential

energy reaches the primary minimum.

The derivative of potential energy is force, dV/dh = F

colloid particles with weak charge

This diagram isapplicable to situation

where charge is weak.

The barrier is not very

strong. The force

distance curve follows

the vdW trend

Force-Distance curve of 2 charged colloids


50/103

50

Force-Distance curve of 2 charged colloids

0

energy barrier

In this diagram the particles

carry significant charges, their

interaction curves look differentfrom that in the previous slide.

When charged particles

approaching to each other,

particularly when their double

layers begin to overlap, therepulsive charge-interaction

becomes strong and tends

push them apart. This is barrier

we see in the diagram. The

higher the barrier is the more

stable the colloid system is,

since it would be more difficult

for the approaching particles to

overcome the barrier and get

into the primary minimum.

DLVO th


51/103

DeryaginLandau and Verview & Overbeck

DLVO theory estimates the energy resulting from the overlap of theelectric double layers (usually repulsion) and the London van derWaals energy (usually attraction) in terms ofinterparticle distance.

Total interaction energy in terms of inter-particle distance.

V = VR + VA (1)

V : total interaction potential (V or kT)

VR : repulsive potential (V)

VA : attraction potential (V)

51

DLVO theory

El t t ti l i f (V )


52/103

If the Debye-Huckel assumption is made:

52

E)thermalenergyatic(electrost12

0 kT

ze

Low charges kT/e = 25.6 mV at 25CEquation (2) simplifies to

(3))exp(2 2 HaV dR

Electrostatic repulsive forces (VR)

Van der Waals potential


53/103

The attractive van der Waals forces between two macroscopic colloid

particles shows much slower decay. Instead of following (VA C/r6), it follows

equation (5). For two equal spheres at small interparticle distances, the van

der Waals attractive potential decay follows (VA Aa/12(H))

There is a brief derivation process of eq.(5) in Shaws book

VA Aa12H

(7) a

HThe potential equation applies for situation

when H


54/103

54

122211A VVVV 2+

V11 V22V12 V12

12H

aA

12H

a2A-AAV 121122211

A

+

2212 AAA 11

22211121AAA

Hamaker constant (A)

The potential energy change that accompanies this process is

Attraction potential VA change: An example of coagulation process

of particles with the same radius

Effect of electrolytes on total interaction curve


55/103

D.J. Shaw, Introduction to Colloid and Surface Chemistry, p. 221 (1992) 55

Effect of electrolytes on total interaction curve

1/ = 10-8 m

1/ = 10-9

m

1/ = 510-9 m1/ = 210-9 m

Electrolyte concentration increases, increases, and Debye length 1/ decreases

Schulze hardy rule


56/103

The critical coagulation concentration (CCC) of an

electrolyte sufficient to coagulate a colloid shows:

1. Considerable dependence upon the charge number ofits counter-ion

2. Relative independence of the specific character of ion

concentration of colloids

nature of colloid

CCC z-6 (10)

56

CCC is related to the valence of counter-ions.

Schulze-hardy rule

The Schulze Hardy rule


57/103

CCC value is mainly determined by the valence rather than the type

of the ions with opposite charge sign to the particles.

Ions with the same charge sign than the particles are of secondary

importance.

The higher the valence of the ion, the lower CCC.

57

CCC is proportional to

1

z6




58/103

An experimental appreciation ofC.C.C.

[M+] : [M+2] : [M+3] = 100 : 1.6 : 0.3 (in mmol/L)

=(1/1)6 : (1/2)6 : (1/3)6

Ions of higher charges are more effective in causing coagulationof colloids stabilized by the opposite charge.

The numerical calculation is: (1/1)6 : (1/2)6 : (1/3)6 = 1 : 0.0156 : 0.0014

The Schulze-Hardy rule is an empirical rule.



59/103

Semester 1, 2013

Bio-Nano EngineeringCHE 2165Wetting

Contact angle as a description of wetting


60/103

In case of liquid wets a solidsurface in air, is defined as

the contact angle.

The degree of wetting of a solid by a

liquid is loosely described by the

contact angles as

fully wetting ( 0),

partially wetting (0 <


61/103

The Young s equation

gSV : interfacial free energies of the solidgSL : interfacial free energies of the solid/liquidgLV: interfacial free energies of the liquidFor a liquid, gLV is also the surface tension of the liquid.

ggg cosLVSLSV +

Proposed by Thomas

Young in 1806. Young

proposed, but did not

prove the equation.

gLV

gSL gSV

Liquid drop

ggg cosLSLS +

Air/vapor

Units of surface tension/surface free energy: dyne/cm or erg/cm2 , mN/m or mJ/m2

Tangent on

liquid surfaceHorizontal balance:

Surface tension of a liquid


62/103

Surface tension of a liquid

Surface tension of a liquid is a cohesive or internal force per unit that

resists an external force.

External Force

Surface Tension of Liquid

At Equilibrium ?

Experimental measurements of surface tension


63/103

Experimental measurements of surface tension

2. Wilhelmy Plate1. Capillary Rise

cgr

cos2h

g

rc

w = P gcos

w = 4Rgf

F

R

3. Du Nouy Ring4. Pendant Drop

Molecular interactions and surface free energy


64/103

Molecular interactions and surface free energy

Intermolecular interactions which are responsible for surface and interfacial

tensions include van der Waals forces and may also include hydrogen bondingforce (e.g. in water) and metallic bonding (e.g. in Hg). These interactions are not

appreciably influenced by one another.

They are assumed to be additive.

pd

ggg +

d - surface tension component

due to van der Waals interactions;mainly nonpolar interactions

gp - surface tension componentdue to polar interactions; mainly

hydrogen bonding

D.J. Shaw, Introduction to colloid and surface chemistry, 4th ed. Chapter 4

Interfacial tension between


65/103

two immiscible liquids

ABBAABW+ ggg

work of adhesion

p

B

p

A

d

B

d

ABAABggggggg ++ 2

d = van der Waals interactions (mainly non-polar part)

p = polar interactions (mainly hydrogen bonding)

Rewrite:

Interfacial tension

Liquid - Liquid interface tension


66/103

q q

ppdd21212112 2 ggggggg ++

van der Waals interactions do not appreciably influence

hydrogen bonding interaction.

These two types of interactions can be considered separately.

dOd

W

p

W

d

W

d

OOWgggggg 2++

020

2

++++

++++

d

W

d

O

d

W

p

W

d

W

d

OOW

p

O

p

W

d

O

d

W

p

W

d

W

p

O

d

OOW

ggggggg

ggggggggg

gdOil gpOil

gdWater

1 oi l phase or O 2 water phase or W

Oil phase does not have H-bonding

Contact angle measurements


67/103

b

h

b

h2tan2 1

b

h2

2tan

Inverse tanAssumption:

The liquid drop on solid surface is a part of a sphere.

Simple math is required to prove the validity of the equation.

Tangent on

liquid surface

Contact angle measurements

This method assumes the liquid drop on solid surface

is a part of a sphere.

Many simple contact angle instruments use this

assumption.


68/103

Semester 1, 2013


Wetting of real surfaces

Youngs equation from last lecture


69/103

Young s equation from last lecture

gLV

gLS

gSV

gSV, gSL and gLVare theinterfacial free energies of

the solid, solid/liquid andliquid, respectively.

Sessile drop

Youngs equation itsapparent simplicity is highly

deceptive.

(Principle of colloid and surface

chemistry, 3rd ed. P.C. Hiemenz and

R. Rajagopalan, p 266)

ggg cosLVSLSV

+

LV

SLSVcosg

gg

ggg cosLVSLSV

Conditions of Youngs equation:

liquid and solid have molecular contact.

the solid surface must be smooth.

Contact angle on wood surfaces


70/103

g

In reality, surfaces are most likely rough

Drop on projected area

Drop on real area

Projected area and real area


71/103

(real area)

(projected area)= 1.27

An atomic force

microscopic image

of an anodized Alsurface.

Tlvslsv cosggg

Rlvslsv cosggg r is a roughness rat io which must be 1.When r = 1: Youngs equation.

r =

r

Summary: Wenzel equation


72/103

y q

Smooth or true surface:

Rlvslsv cosr ggg

Tlvslsv cosggg

Rough surface:

RT coscosr

Areal : the real or actual area of a rough surface

Aprojected : the projected area of the rough surfaceRorrough : the observed contact angle on a rough surfaceT

ortrue

: the true or intrinsic contact angle on a smooth surface of the same material

1projected

real

A

Ar

Wenzel state:

The drop interface follows the

contours of surfaces.

Ratio:

Wetting of chemically heterogenous surfaces


73/103

Cassie equation

obs : the observed contact angle1 : the contact angle of liquid with area 12 : the contact angle of liquid with area 2f1 : the area fraction of material 1

f2 : the area fraction of material 2

Cassie A.B.D., S. Baxter, Trans. Faraday Soc., 1944, 40, 546

2211 cosfcosfcos

obs+

121 + ff

2111

2211

1

cos)f(cosf

cosfcosfcos:areastwoforobs

+

+

Contact angle on composite surfaces


74/103

g p

Youngs equation:

gs1

gs1L

gs2L

gs2

lv

slsvcosg

gg

+

lv

2sl2sv2

lv

1sl1sv1obs ffcos

g

gg

g

gg

Cassie or Cassie-Baxter state:

The drop is situated on top of an effective

composite surface consisting of peaks of the

rough surface and air.

Contact angle hysteresis:


75/103

advancing and receding contact angles

Dettre & Johnson, J. Phys. Chem. 69 (1965) 1507.

Contact angle hysteresis of glass coated with Ti.

H = (A - R ): contact angle hysteresis

equivalent to

adding liquid

equivalent to

removing

liquid

Contact angle hysteresis on rough surfaces


76/103

Figures from: J.D. Miller et al. Polym. Eng. Sci, 36 (1996) 1849

** This diagram uses the Wenzels model, liquid penetrates

into the troughs.

H =A -R= 2

Advancing to a

maximum angle

Receding to a minimum

angle

+ 0A 0R

Superhydrophobicity and liquid-solid contact


77/103

fraction: Cassie model

1)1(coscos 11)( + fCassieobv

211)( coscos ffCassieobv Cassie equation on

screen or woven.1 is the intrinsiccontact angle of water

on micro-pillar surface.

Superhydrophobic

surfaces have a very

small fraction of

contact area.

1ff 21 +


78/103

Semester 1, 2013


Capillary Phenomena

Anycurved liquid-gas interfacemust havea


79/103

pressuredifferencePcrossit.

R1 R2 =

R1

R2 = R1 = R

Cylinder drop Sphere drop,air bubble

According to Young-Laplace equation (more details later):

Soap bubble

1RP

g

R

2P

g

R

22P

g

(two interfaces)

R

(P = inside pressure outside pressure, N/m2)

Summary: Young-Laplace pressure


80/103

1. A spherical surface, R1 = R2 = R

r

cos

RRRP

ggg

2211

21

+

2. Cylindrical and plates, R2 = r

cos

RRRP

ggg

+

121

11

The spherical surface is contacted with solids.

Summary: Young-Laplace pressure


81/103

3. For a spherical soap bubble, R1 = R2= R

R

22PPP outsideinside

g

011

+

gP

Dont have the dimension ofconstrained space.

4. For a planner surface

Inside of a bubble is air and inside of a liquid sphericaldroplet is liquid.

(no curvature), R1 and R2

Surface curvatures


82/103

Positive curvature:

Triangle angles add to more than 1800.

Negative curvature (saddle-shaped surface):

Triangle angles add to less than 1800.

Zero curvature (flat surface):

Triangle angles add to an exact 1800.

Washburn equation


83/103

q

tr

l

g

2

cos

rPc

gcos2

Washburn equation considers the balance of the capillary

driving force ofPc and flow resistance force due toviscosity, Pf.

Laminar flow with

a pressure drop ofP

r

l

2

)(8

r

ldt

dl

Pf

fc PP

2

)(8cos2

r

dt

dll

r

g

Capillary pressure;

driving force

Poiseuille flow friction;

resistance force

Different forms of Washburn equation


84/103

q

tcosr

l

g

2

2 Laminar flow with

Capillary driving force only

r

t

r

dt

dl

g

8

cos

l

r

dt

dl

g

4

cos

Washburn equation predicts that if

the liquid has a contact angle >90,the liquid cannot penetrate the

capillary

rpore radius (m)

gsur face tension (N m-1, kg s-2)

viscosity of liquid (kg s-1m-1)

lpenetration distance (m)

Length form

Speed forms


85/103

Semester 1, 2013


Free energy ofsolid surface

Zisman plot: Critical surface tension (gc)f lid f f li id


86/103

of solid surfaces from liquids

An empirical plot of cosine of

liquid contact angles vs. surfacetensions of liquids.

Liquids with surface tensions

higher than the gc form finitecontact angles; liquids with

surface tensions lower than thegc spread on the surface.

Liquids with known surface tensions are used to test the solid surface

gcFor PTFE

gcFor PE

C LVcos 1 b( ) + g g

Work of adhesion between liquid and solid


87/103

q

SLSVLV

initialFinalSL

WG

ggg

gg

+

S

LG = WSLLS ggg cosLVSLSV +

Workof adhesion

between a solid and a

liquid can be determined

Rewrite a liquidsolid system:

Youngs equation:

g cosW LVSL + 1

We have:

if the liquid

surface tensiongLV

is known

contact angle between the solid

and the liquid

Spreading coefficient


88/103

p g

LLSL WWS

S = spreading coefficient

Sinitial-finalGSVLVSL

+ ggg

)(S LVSLSV ggg +

L

L

LLW SLW

L

Sspreading

from L-L to L-S

spreading areaL V

S

L

V

S

0SWW LLSL Liquids spread over surfaces


89/103

0SWW LLSL Liquids spread over surfaces.

0SWW LLSL Liquids dont spread over surfaces.

)(S LVSLSV ggg +solid-vapor solid-liquid liquid-vapor

Generalized equation for spreading:

A spreading over B:Aas liquid and Bas solid.

Examples:

Oil spreading over water: oil = liquid and water = solid or surface.

Water spreading over oil: water = liquid and oil = solid or surface.

Solid surface energy (gs) measurement


90/103

(Two-liquid approach)

1. Use a liquid (l iquid 1) with van der Waals component, gdL1,ONLYto determine gdsof solids.2. Use another liquid (l iquid 2) with gdL2 andgPL2 to determine

the polar component, gps

of solids.

3. And then gs = gds + gps .

The general equation:

g g g g gl ld

sd

lp

sp( )1 2 2+ +cos

We are in a situation that if we can measure the contact angles of two liquids with known surface

tensions with a solid surface, we can use the below equation to calculate the surface energy of the

solid surface.

Two-liquid approach


91/103

4

12

1

1

L

L

d

S

cosgg

+

Liquid 1 has van der Waals component only, gpL1=0gL1=gpL1+ gdL1, and then gL1=gdL1

Liquid 2 has both polar and van der Waals components,gL2=gpL2+ gdL2.

From liquid 1, van der Waals

component is obtained.

From liquid 2, polar component is obtained.

02cos1 11 ++p

S

d

L

d

SL gggg

p

2L

2d

s

d

2L2L2Lp

S4

2)cos1(

g

gggg

+

For the calculation of solid surface energy from liquid contact angle data on the solid

surface, we need two equations to determine two unknowns, gsd and gi

p

Principle of plasma surface treatment


92/103

In physics and chemistry, a plasma is typically an ionized

gas, and is considered to be a distinct state of matter.(Source of the picture: http://en.wikipedia.org/wiki/Plasma_%28physics%29)

A simplified view of

plasma environment

1. Ionized gas

2. Roughly equal number of

positively and negativelycharged particles.

3. High temperature plasma

is based on corona discharge

process.

4. Low temperature plasma are ionized gases generatedunder pressures.
http://en.wikipedia.org/wiki/Image:Plasma-lamp_2.jpg


93/103

http://www.astp.com/plasma-equipment/applications

For example, oxygen plasma contacts with PP surface

Effects of corona treatments of some polymer films


94/103

Su

rfaceenergy(mJ/m2)

Assignment 2


95/103

Assignment 2

31 May 2013 (Friday)

11-12nn


96/103

The online Student Evaluation of

Teaching and Units (SETU)

Is now available for this unitComplete a simple 5 minute online survey and

give us your opinion.

What is SETU?


97/103

9 May 2013 Survey Presentation for Students 97

What is SETU?

An online survey to help the Universitymonitor and improve the teaching and

learning across the university.

Your opportunity to be heard and provideconstructive feedback on your experiences

with a unit and the teaching staff. Have your

say and help improve the quality of unit

offerings and teaching.The primary purpose of the

Student Evaluation of Teaching and Units

is to provide staff with valid and reliable information with which to make informed

decisions about improving student learning outcomes.

How is SETU data used?


98/103


How is SETU data used?

University level - to monitor overall quality of teaching and learning and torequest that faculties provide strategies for responding to units perceived as

needing critical attention or needing improvement.

Faculty/Department level - to monitor the quality of units offered and provide an

opportunity to take action to remedy a problem or congratulate those associated

with outstanding units and to ensure that students are given feedback on survey

outcomes.

Unit coordinator/teaching staff level to monitor the student experience and to

understand and act upon those aspects which are perceived as the units strengths

or weaknesses. Staff also use SETU data in achievement reports supportingapplications for confirmation, promotion or teaching awards.


99/103


The SETU is now available for this unit.

Please complete your survey as soon as possible.

The survey closes on

Friday 7 June** For standard S1-01 units. Refer to SETU timetable for alternate teaching periods :

http://www.opq.monash.edu.au/us/surveys/unit-evaluations/distribution-administration.html
http://www.opq.monash.edu.au/us/surveys/unit-evaluations/distribution-administration.htmlhttp://www.opq.monash.edu.au/us/surveys/unit-evaluations/distribution-administration.htmlhttp://www.opq.monash.edu.au/us/surveys/unit-evaluations/distribution-administration.htmlhttp://www.opq.monash.edu.au/us/surveys/unit-evaluations/distribution-administration.htmlhttp://www.opq.monash.edu.au/us/surveys/unit-evaluations/distribution-administration.htmlhttp://www.opq.monash.edu.au/us/surveys/unit-evaluations/distribution-administration.html


100/103


Login to complete your SETU evaluations within your

my.monash portal(use your standard student Authcate username and password)

http://my.monash.edu.au/study/resources/evalu

ations

1. Select which unit/s you wish to evaluate.

2. Select teaching staff member/s you wish to evaluate.

3. Select your response on a scaleof Strongly Agree to Strongly Disagree or Outstanding to

Very Poor.

4. Provide commentsrelating to the Best aspects of the unit and those Most in need of

improvement. Honest feedback is welcome but please ensure that you respect the UniversitysEqual Opportunity Policy when constructing your feedback*.

*Constructive feedback does notinclude offensive language and is free of all forms of discrimination, harassment, vilification and

victimisation.

Your response is completely


101/103


confidential

Your response is NOT linked to your identity. Reporting of data is in aggregate or summary form.

Departments and teaching staff will NOT have any information that

can identify you or your response unless your specifically mention

something to identify yourself within your comments. Results are not distributed to faculties and teaching staff until

AFTER the release of exam results. For Semester 1, 2013 this will be

: 2 July 2013. Until then faculties only have access to unit level

response rate data.

How to access SETU results for your unit:


102/103


How to access SETU results for your unit:

http://emuapps.monash.edu.au/unitevaluations/index.jsp

This feedback will not identify students, or directly quote your comments only

aggregated quantitative data is available online.

Navigate to your unit by selecting the Administration Period (i.e.. Semester 1, 2013),

Faculty and Unit code. The unit level report will show the distribution of responsesas well as an overall mean/median score to each survey question.

Student comments will be provided to the Associate Dean of Education within your

faculty with very strict procedures relating to the distribution of this data.

In order to protect teaching staff procedures are in place to flag comments referring

to individual teachers or containing offensive comments prior to further distribution.

Reports will be available on 2 July 2013 for Semester 1, 2013 units.


103/103

Please complete your

SETU surveyfor this subject today

Login:http://my.monash.edu.au/study/resources/evaluationsOr click on the link to the survey portal within the reminder emails you receive weekly

during the survey period.

For any queries or issues contact the Surveys team : [email protected]

The University values and acts upon your feedback.
mailto:[email protected]:[email protected]

Review of Nano Section

Documents

Transcript of Review of Nano Section