SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실

Liquid Interface

Adsorption at Liquid Interfaces

Adsorption at Solid Interfaces

Applications of Surface Active Agents

Electric Properties of Interfaces
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실

Interface
 The boundary between two phases (faces)

Surface
 Ether a gas-solid or a gas-liquid interface
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
Fig. 15-1
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실

Surface tension
 A force pulls the molecules of the interface together
 Unit : dyne/cm

Interfacial tension
 The force per unit length existing at the interface between
two immiscible liquid phases
 Unit : dyne/cm
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
 = f / 2L
Fig. 15-3
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
W =  A
W : The work done or surface free energy (ergs)
  : surface tension (dyne/cm)
 A : The increase in area (cm)

dw
 force  dis tan ce
dw
 f  ds    2 L  ds    dA
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실

Capillary rise method

DuNoüy ring method

Drop weight ….
 Temperature   Surface tension 
 Critical Temperature  Surface Tension = 0
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
2r = r2hg
 = 1/2 rhg
Fig. 15-5
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
dial reading in dynes

 correction,β
2  ring circumference
Fig. 15-6
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
Wa = L + S - LS
Fig. 15-7
w    A
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
Wc = 2L
Fig. 15-8
w    A
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
S = Wa - Wc = (L + S - LS) - 2L
S = S - (L + LS)
 s : 기질액체의
표면장력
 L : 퍼지는 액체의 표면장력
ㅣㄴ : 두 액체 사이의 계면장력
 S > 0 : spreading
 S < 0 : form globules or a floating lens
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실

Surface free energy
 The work that must be done to increase the surface by unit
area

Adsorption
 A phenomenon, where the added molecules are
partitioned in favor of the interface

Absorption
 The liquid or gas being absorbed penetrates into the
capillary spaces of the absorbing medium
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실

Surface-active agent (= surfactant, amphiphile)
 Molecule and ion that are adsorbed at interfaces
 The molecule or ion has a certain affinity for both polar
and nonpolar solvent
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실

An arbitrary scale of
values to serve as a
measure of the
hydrophilic-lipophilic
balance of surface-active
agents
Fig. 15-11
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
Nonionic surfactant
HLB = E/5

E : Percent by weight of nonionic surfactant
Polyhydric alcohol fatty acid esters
 S
HLB  20 1 - 
 A
 S : The saponification number of the ester
 A : The acid number of the fatty acid
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실

The specific HLB that the oil phase of an oil-inwater(O/W) emulsion required
6  s  
Qs 
 4Q 1000
10  0.5 RHLB
 s : The density of the surfactant mixture
  : The density of the dispersed phase
 Q : The percent of the dispersant of the
emulsion
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실

Adsorbent : The material used to adsorb the gas

Adsorbate : The substance being adsorbed
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실

Physical adsorption
 Van der Waals forces
 Reversible
 Temperature, pressure
 desorption (the removal of the adsorbate from
the adsorbent)

Chemisorption
 Chemical bond
 Irreversible
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실

The relationship between the amount of gas
physically adsorbed on a solid and the equilibrium
pressure or concentration at constant temperature
Fig. 15-18
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
x
1n
y
 kp
m
 y : the mass of gas x adsorbed per unit mass m of
adsorbent
 k, n : constants
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
ymbp
y
1  bp

p
1
p


y
bym
ym
 y : the mass of gas adsorbed per gram of adsorbent
at pressure p and at constant temperature
 ym : the mass of gas that 1 gram of the adsorbent can
adsorb when the monolayer is complete
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
Fig. 15-20
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
p
1 b 1 p


y  p0  p  y m y m b p0



P : the pressure of the adsorbate in mmHg at which
the mass y of vapor per gram of adsorbent is
adsorbed
p0 : the vapor pressure when the adsorbent is
saturated with adsorbate vapor
ym : the quantity of vapor adsorbed per unit mass of
adsorbent when the surface is covered with a
monomolecular layer
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
Langmuir equation
c
1
c


y
by m
ym
 c : the equilibrium conc. In milligrams of
alkaloidal base per 100mL solution
 y : the amount of alkaloidal base x in milligrams
adsorbed per gram m of clay
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실

Wetting agent
: A surfactant that, when dissolved in water, lowers
the advancing contact angle
Fig. 15-24
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
s = SL + L cos 
S = L ( cos  -1 )
Wa = WSL = L ( 1- cos  )
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실

Surface tension
at cos  = 1
(c)
Fig. 15-25
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실







Emulsifying agents
Detergents
Wetting agents
Solubilizing agents
Antibacterial agents
Protective agents
Aids to absorption of drug
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
Fig. 15-28
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
Nernst potential (E)
: aa’
Zeta potential ()
: bb’
Fig. 15-29
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실

Concentration of electrolyte 
 Screening effect of the counterion 
 Potential falls off more rapidly with
distance
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실