SURFACE ENERGY CHARACTERISTICS -...

CHAPTER-6

SURFACE ENERGY CHARACTERISTICS Surface energy characteristics of the composites were measured using

contact angle measurements of the composites with water and methlene

iodide. The solid surface free energy was calculated from harmonic mean

equations. Various contact angle parameters such as total solid surface

free energy, work of adhesion, interfacial free energy and spreading

coefficient were analyzed. A computer programe was developed for

calculating the different parameters from the harmonic mean equation.

The work of adhesion and interfacial free energy, spreading coefficient,

and Girifalco-Good’s interaction parameter changed with composition.

The results of this chapter have been accepted for publication in International Journal of NanoSystems

166 Chapter VI

6.1 Introduction

The relationship between surface and interfacial energies determines to a

large extent the wetting behaviour of a liquid on a solid surface and the

phase morphology of mixtures of two or more phases. If we consider the

stable configuration of a liquid placed on a solid surface, the equilibrium

shape conforms to the minimum total interfacial energy for all the phase

boundaries present. If the solid–liquid interfacial energy is high, the liquid

tends to form a ball having a small interfacial area. In contrast, if the

solid-vapour interfacial energy is high, the liquid tends to spread out

indefinitely to eliminate the interface.

Contact angle measurements of solids are a widely accepted

characterization technique for the surface energy characteristics such as

wettability and adhesion. Using this technique, one can determine the

surface free energy, interfacial free energy as well as polar and dispersion

components of surface energy. In addition, information regarding

hydrophobic-hydrophilic alterations [1-3], polar group orientations, and

restructuring of the surface in long time contact with a liquid are obtained.

Non wettable solid surface are of great interest in the applications of

microelectronics. Wettable solid surfaces are mostly used in applications

such as biocompatibility, printing, coating and oil recovery, membrane for

reverse osmosis, detergency, ore flotation, and retention of pesticides on

leaves. The surface and interfacial energies of polymers can be varied for

specific applications through their surface modifications. Controlled

wettability of the polymer surface has been accomplished through several

chemical modification techniques. These include oxidation, chemical

etching of the surface, grafting with a reactive substance, ultraviolet

Surface Energy Properties of Polystyrene and Composites 167

irradiation, plasma polymerization and treatment with surface active

compounds

In spite of several chemical modification techniques, reports on contact

angle characterization of physically modified polymers such as polymer

composites are quite large in literature. Composite preparation has been

considered as an important route to fulfill several technological

applications of polymeric materials. In contact angle studies it has been

shown that powder fillers decreases the surface free energy of

thermoplastic polymers [4-6].

In this chapter the results of contact angle characterization of the prepared

composites are reported.

6.1.1 Structure of Surfaces and Interfaces

Many scientifically fascinating and technically important processes

depend on the unique properties of molecules between phases. A surface

is defined as the boundary between two phases; it might be more accurate

to call it an interface, because two phases cannot exist without an

interface. The surface of a phase or the interface between phases is a

region of high energy relative to the bulk [7]

6.1.2 Surface Tension and Surface Energy

It is observed experimentally that a force is required to extend a liquid

surface. The surface tension or interfacial tension ‘γ’ is defined as the

reversible work wr, required to increase the surface of the liquid by a unit

area. It is common to refer ‘γ’ as the surface tension when discussing

fluid surface, and as surface free energy when discussing solid surface [8].

168 Chapter VI

Since surface tension is the force (per unit length) that opposes the

stretching of the liquid film, it is a measure of intermolecular forces.

dwr = γ dA

Fig 6.1 Surface layer between the phases

It is well established from the literature that contact angle measurements

can be used in the calculation of surface energy. In the case of pure

liquids and smooth, homogeneous, rigid and insoluble solid surfaces, the

contact angle is a thermodynamic parameter, which can be used to

calculate the interfacial tension by different techniques. Specification of

the conditions under which this surface work is done allows the surface

tension to be related to other thermodynamic properties of the system. In

two phase multi component system as in fig 6.1, in solid-liquid phase

boundaries, by the first and second law of thermodynamics, the variation

in the internal energy E or the Gibb’s free energy G of the system , is

expressed by the variables, P, V, T and entropy ‘S’ as (equ6.1 and 6.2) [9]

idE TdS PdV dA dnιγ µ= − + + ∑ (6.1)

idG SdT VdP dA dnιγ µ= − + + + ∑ (6.2)

where ‘µi’ is the number of moles and ‘dni’ is the excess moles of ‘i'

within the boundary.These relations apply to systems with a plane

interface separating the bulk phases.

Surface tension relative to internal energy and Gibb’s free energy as


, , iP T n

GA

δγδ

=

= , , iS V n

EA

δγδ

=

(6.3)

The subscripts refer to the independent variables which have to remain

constant during the increase of surface area by a unit amount [10]

Thus the surface tension of a flat interface is the excess Gibb’s free

energy per unit area. At constant temperature and pressure a small change

in the surface free energy of the system is given by the total differential

with respect to area is taken as zero

S SL LS SL L

dG dG dGdG dA dA dAdA dA dA

= + + (6.4)

but

L S SLdA dA dA= − = where A constitute the solid phase, and

SS

GA

δ γδ

= and so on.

The coefficient L area

GA

δδ

−

gives the free energy change for the

spreading of a film of liquid over the substrate and is called the spreading

coefficient of liquid on solid. Thus

/l s s l sl cS Sγ γ γ= − − = (6.5)

Spreading coefficient is positive if spreading is accompanied by a

decrease in free energy that is spontaneous spreading.

6.1.3 Wetting The relationship between surface and interfacial energies determines to a

large extent the wetting behaviour of a liquid on a solid surface and the

phase morphology of mixtures of two or more phases [11]. Many

170 Chapter VI

important and interesting technical phenomena are related to the

spreading of liquids on solids or wetting. Fig6.2 (a) shows a drop of

liquid on solid surface and three interfacial tensions that govern the shape

of the liquid. (γ sv) is the interfacial tension between solid phase and

vapor phase, (γ sl), is the interfacial tension between solid and liquid

phase and γ lv is the surface tension of the liquid or the interfacial tension

between the liquid and the vapor phase.

The angle between the solid surface and the tangent to the liquid surface

at the contact point, the contact angle, may vary between 0 and 1800. The

angle specifies the conditions for minimum energy according to the

equation (6.6) [12]. The equation is a thermodynamic equilibrium

condition for an ideal solid-liquid system.

(γ lv) cosθ = (γ sv) - (γ sl) (6.6)

where (γ sv) , (γ sl), (γ lv) are the interfacial energies between the phases

actually present in the system at the time of measurement.

For simplicity of the above equations (γ sv), is now onwards taken as (γ s),

and (γ lv) as (γ l)

We may define θ= 900 as the boundary between non wetting (θ>900), and

wetting (θ< 900). Spreading is the condition in which the liquid completely

covers the solid surface (θ= 00) (Fig 6.2[a-g]). Relationship between the

surface energies determine the wetting behavior and spreading coefficient

‘Sc’ as equation 6.5.

For spreading to occur it is necessary that (Sc) be positive. A

corresponding necessary, condition for spreading is that the liquid-vapor

interface energy be less than solid vapor interfacial energy ((γ lv) < (γ sv)).


In general, all the interface energies can be affected by changing

composition.

Fig6. 2 (a)

cos SV SL

LV

γ γθγ

−=

Fig 6.2 (b) θ=1800, drop formation

θ>900, non wetting θ=900

Fig 6.2 (c) Fig 6.2(d)

172 Chapter VI

θ<900, wetting θ~00, nearly complete wetting

Fig 6.2 (e) Fig 6.2 (f)

θ=00 , spreading of liquid on solid

Fig 6.2 (g)

Fig6. 2 (a-g) Forces that control the wetting of a surface.

6.1.4 Wettability Studies Theory and Calculations The contact angle is measured as the tangent angle formed between a liquid

drop and its supporting surface. The techniques for measuring contact angle

have been reviewed in detail by Neumann and Good [13]. The most

commonly used method involves directly measuring the contact angle for a

drop of liquid resting on a horizontal solid surface (a sessile drop). Computer

oriented contact angle goniometers employ a microscope objective to view

the angle directly and capture a digital image of the drop. The contact angle

and other important details are collected from the image.

The classic equation relating the surface energy of a solid in contact with

vapour (γsv ) or (γ s),


liquid in contact with vapor (γlv ), or (γ l), interfacial free energy

between solid and liquid (γsl ) and the contact angle (θ ) due to Young is

given in equation 6.6 [14]. The extensive use of Young’s equation

reflects its general acceptance.

In equation (6.6), γ s and (γ sl) are not amendable to direct measurement.

A plot of (θ) against surface tension for a homologous series of liquids,

(γl) can be extrapolated to give a critical surface tension γc, at which

cosθ=1. γc, has taken as an approximate measure of surface free energy γs,

of the surface. However, a limitation of this consideration is that the

precise value of γc, depend on the particular series of liquids used to

determine it.

6.1.5 Semi empirical model.

A model that has proved to be very stimulating to research on contact

angle phenomena begins with the proposal by Girifalco and Good [15]. If

it is assumed that the two phases are mutually entirely immiscible and γs1

is related to γs and γ1 through geometric mean law relationship i.e.

γs1 is equivalent to (γ1 γs) ½ through the interaction parameter φ

Interfacial free energy should obey the equation

γs1 = γs + γ1 -2φ (γ1 γs) ½ (6.7)

The parameter φ is the interaction parameter.

In order to include other interactions such as dipolar or hydrogen bonding,

many semi empirical approaches have been tried, including adding terms

to the above equation or modifying the definition of ‘φ’. Perhaps the most

174 Chapter VI

well known of these approaches is come from Fowkes [16-18] suggesting

that the interaction across a water –hydrocarbon interface are dominated

by dispersion forces such that

γs1 = γs + γ1 -2φ (γ1d

γsd) ½ (6.8)

Where (γ1d

γsd) denote the surface tension due to the dispersion or Van

Der Waals component of the interfacial tension [19,20].

Later, Owens Wendt [21] and Kaelble [22] modified Fowkes approach

further by assuming the polar attraction component of forces which also

included in the surface forces. Wu [23, 24] has found a still better

agreement to obtain γs when he uses harmonic mean equations which

combines both the dispersion and polar interactions. Many researchers

have tested this model on several materials to find the surface tension

components [25, 26]

In order to verify Wu’s approach, by including the two component of

surface tension, two liquids of dissimilar polar types are to be selected

[27]. One polar liquid (water) and other non polar liquid (methylene

iodide) are selected for study

Wu’s harmonic mean equations are

(1 cos( )) wrωθ+ = 4d d p p

w s w sd d p p

w s w s

r r r rr r r r

+ + +

(6.9)

and

(1 cos( ))m mrθ+ = 4d d p p

m s m sd d p p

m s m s

r r r rr r r r

+ + +

(6.10)


where the superscripts d and p stand for contributions due to dispersion

and polar forces, respectively. Data for water and methylene iodide were

taken from the literature (Water γw = 72.8 mJ/m2, γdw = 21.8 mJ/ m2,,

γpw = 51.0 mJ/ m2,, methylene iodide; γm = 50.8 mJ/m2, γd

m = 49.5mJ/m2,

γpm = 1.3 mJ/m2

. Dispersive and polar component of surface energy of the

composites γds and γp

s for different compositions of PS were determined

by solving equations (6.9) and (6.10) with the help of computer program

in C language (Appendix). According to Owens-Wendt theory, the total

solid surface free energy is represented as

γs = γds + γp

s (6.11)

The work of adhesion, WA, was calculated using the equation

WA = (1 + cos θ) γ1 (6.12)

Where γ1 is the surface tension of the liquid used for the contact angle

measurement.

The interfacial free energy, γs1 was calculated from Dupres equation [28]

γs1 = γs + γ1 - WA (6.13)

Girifalco – Goods interaction parameter,φ, between the polymer and the

liquid was determined using the equation given below [29]

1/ 2

(1 cos2( )

l

l s

rr r

θφ + )= (6.14)

The total surface energy γs and its dispersive and polar components are

shown in Table 6.1 & 6.2.

176 Chapter VI

6.2 Results and Discussion

The wetting behaviour of the composites with respect to water and

methylene iodide is analyzed which focuses on the effect of volume

percentage of the filler on wetting characteristics such as work of

adhesion, total surface free energy, interfacial free energy and spreading

coefficient. The hydrophobic nature of the composites is found to increase

with the addition of fillers.

6.2.1 Contact angle variations

The composites posses higher contact angle with water and methylene

iodide compared to neat PS (fig 6.3[a-d] &6.4[a-b]).

(a) (b )

(c) (d)

Fig 6.3 Representative figures of contact angle measurements of (a) BNN40 with methylene Iodide (b) PS with metylene Iodide (c) BNN40 with water (d) PS with water.


0 10 20 30 4034

36

38

40

42

44

46

48

Methylene iodide Water

Volume of YBCO, %

Con

tact

ang

le (θ

) met

hyle

ne io

dide

84

86 Contact angle (θ) w

ater

(a)

0 10 20 30 40

34

36

38

40

42

44

46

48

50

52

54

methylene Iodide Water

Volume of BNN, %

Con

tact

ang

le(θ

) met

hyle

ne io

dide

84.0

84.2

84.4

84.6

84.8

Contact angle(θ) w

ater

(b)

Fig 6.4 (a) & (b) Variation of contact angle with water and M.I of the composites with (a) filler YBCO (b) filler BNN

178 Chapter VI

The increase in contact angle with water shows an increment in the

hydrophobic nature of the composites. Even though the water absorption

percentage of PS is 0.05, and the addition of fillers increases the

hydrophobic nature to a higher value. The increase in contact angle value

can also be compared with the increase in surface roughness of the polymer

surface [30].The roughness of the sample surfaces increases by the addition

of BNN and YBCO. The roughness increases highly in YBCO40 and a

rapid rise in its contact angle with water and methylene iodide. The

roughness of the composite surface was observed with SEM also.

6.2.2 Surface Free energy

Surface energy is the energy associated with the interface between two

phases. The solid surface is rich in hydrocarbon molecule. The forces that

hold between hydrocarbons together are much weaker than the force that

acts between water molecules and consequently water on a hydrocarbon

surface remain in non wetting foam. Surface free energy based on contact

angle values of water and methylene iodide is reported in table 6.1&6.2.

It can be seen that the surface free energy decreases with filler and the

least value was observed in the case of BNN40. Hydrophobicity is

indicated by higher contact angle and smaller surface energy. Addition of

ceramic powders results a reduction in surface free energy [31]. Thus the

surface energy of the composites drops below 46.2564, which is the

surface energy of the neat PS at room temperature [32]. This depression

which occurs over the whole range of the concentration must result from a

decrease in free energy due to the mixing of two components at the

interface. Surface energy can be divided into polar and non polar

components. The dispersive (non polar) component of surface energy is


found to decreases and polar component increases with filler content

whereas, no significant variation in total surface energy. YBCO composites

and BNN composites have almost equal surface free energy values. This

suggests that the natures of forces acting at the surface of these two

composites are approximately the same. The polar surface free energy of

the composites goes on increasing with the nature of filler. BNN, being a

ferroelectric material shows maximum value for polar component and that

is for its higher loading. Due to the polar nature of YBCO and BNN

functional groups formed on the surface of the polymer increases polar

surface energy. In the case of YBCO40, polar surface energy is less than

YBCO30 because of percolation of the filler. Improved contact angle has

been related to the decrease of surface free energy [33].

Table 6.1 Components of surface energy of BNN-PS

Name Contact Angle

(water0)

Contact angle

(meth.Iod0)

(Dispersion component) of surface energy

γsd (mj/m2)

(Polar component) of surface energy γs

p

(mj/m2)

( Surface free energy) (mj/m2)

γs=γsd + γs

p

PS 84 35 39.6814 6.575 46.2564

BNN10 84.6 50 32.89 7.585 40.475

BNN20 84.7 51 32.33 7.665 39.995

BNN30 84.72 52 31.8814 7.75 39.6314

BNN40 84.8 53 31.4652 7.805 39.2702

180 Chapter VI

Table 6.2 Components of surface energy of YBCO-PS

Name Contact Angle

(water 0)

Contact angle

(meth.Iod 0)

(Dispersion component) of

surface energy γsd

(mj/m2)

(Polar component) of surface energy γs

p

(mj/m2)

( Surface free energy)

(mj/m2) γs=γs

d + γsp

PS 84 35 39.6814 6.575 46.2564

YBCO10 84.1 45 35.2204 7.3556 42.576

YBCO20 84.15 46 34.759 7.3845 42.1435

YBCO30 84.18 46.5 34.5255 7.4165 41.942

YBCO40 86 47 34.6486 6.725 41.3736

6.2.3 Work of adhesion The work of adhesion, (WA) which is the work required to separate the

composite surface and the liquid drop, decreases with filler concentration.

This fact is clear from fig 6.5, which represents the variation of (WA) with

respect to the change in filler content .The values of work of adhesion

related to water and methylene Iodide are presented in the third column of

table 6.3, 6.4, 6.5 & 6.6. Work of adhesion decreased as the interfacial

bonding is decreased [34]. The possibility of polar non-polar interactions

across interface is a measure of adhesion between the test liquid and

polymer surface. For maximum adhesion the ratio of polar to non polar

component across the interface should be same. In the studied composites

the ratio between water composite systems should be same as that

between composite water system for perfect adhesion of water and

composite. This ratio is greater than one for water-composite systems and

less than one for composite water system. This ratio is less than one for


M I –composite system and greater than one for composite-M.I system

.The trend is same but in opposite manner because of the inherent

property of water as polar liquid and M I as non polar liquid. The

magnitude of difference between work of adhesion of neat polymer and

that of composites are much higher for M.I than that of water. Generally

work of adhesion can be correlated to the filler matrix interaction. Thus

the effective dispersion of fillers into the matrix that have caused decrease

in work of adhesion, and that is due to the increment in the hydrophobic

nature of the composite.

0 10 20 30 40

78

80

82

84

86

88

90

92

94

Wor

k of

adh

esio

n (m

j/m2 )

Volume of filler %

YBCO-PS with water BNN-PS with water YBCO-PS with MI BNN-PS with MI

Fig 6.5 Variation of work of adhesion with different volume % of the

filler with two liquids

182 Chapter VI

Table 6.3 Properties of BNN-PS composites related to water

Name Contact Angle

(water0 )

Work of adhesion

(WA)=(1+cosθ)γ1

Interfacial energy γs1

= γs + γ1 - WA(mj/m2)

Spreading coefficient Sc = γs - γs1

-γ1(mj/m2)

Interaction parameter Φw

γ1 1/ 2l

(1+cos )2(r )sr

θ

PS 84 80.4648 38.5916 -65.1352 .6933

BNN10 84.6 79.650 33.624 -65.949 .7366

BNN20 84.7 79.5245 33.2705 -66.0755 .7368

BNN30 84.72 79.4992 32.9322 -66.1008 .7400

BNN 40 84.8 79.3980 32.6722 -66.202 .7424

Table 6.4 Properties of YBCO-PS composites related to water

Name Contact Angle (water)

Work of adhesion

(WA)=(1+cosθ)γ1


= γs + γ1 - WA(mj/m2)

Spreading coefficient

Sc = γs - γs1 -

γ1(mj/m2)

Interaction parameter

Φw =γ1

1/ 2l

1(1+cos )2(r )sr

θ

PS 84 80.4096 38.5916 -65.1352 .6933

YBCO10 84.1 80.2832 35.093 -65.3168 .7210

YBCO20 84.2 80.2201 34.723 -65.3799 .7241

YBCO30 84.6 80.821 34.5599 -65.4179 .7255

YBCO40 86 77.8782 36.2954 -67.7218 .7095


Table 6.5 Properties of BNN-PS composites related to methylene Iodide

Name Contact angle

(meth.Iod)

Work of adhesion

(WA)=(1+cosθ)γ1


= γs + γ1 - WA(mj/m2)


Sc = γs - γs1 -

γ1(mj/m2)


Φm =γ1

1/ 2l

1(1+cos )2(r )sr

θ

PS 35 92.4129 4.6435 -9.1871 0.9532

BNN10 50 83.4536 7.8214 -18.1464 0.9202

BNN20 51 82.7694 8.0256 -18.8306 0.9181

BNN30 52 82.0756 8.3558 -19.5244 0.9146

BNN40 53 81.3722 8.698 -20.2278 0.9109

Table 6.6 Properties of YBCO-PS composites related to methylene Iodide

Name Contact angle

(meth.Iod)

Work of adhesion

(WA)=(1+cosθ)γ1


= γs + γ1 - WA(mj/m2)


Sc = γs - γs1 -

γ1(mj/m2)


Φm =γ1

1/ 2l

1(1+cos )2(r )sr

θ

PS 35 92.4129 4.6435 -9.1871 0.9532

YBCO10 45 86.7210 6.649 -14.879 0.9291

YBCO20 46 86.0886 6.8549 -15.5114 0.9371

YBCO30 46.5 85.7684 7.9736 -16.8316 0.9290

YBCO40 47 85.4455 6.7281 -16.1545 0.9318

184 Chapter VI

6.2.4 Interfacial energy

The interfacial energy between the composites and the liquids are

reported in the fourth column of the tables 6.3, 6.4, 6.5&6.6. The

interface between phases is a region of high energy relative to the bulk. In

order to maintain the lowest total energy for the system, the configuration

of the surface adapts itself to minimize its excess energy. The dipoles

orient themselves in such a way as to give minimum surface energy. Ions

can fit on the surface with relatively low energy only if they are highly

polarizable ions, such that the electron shells can be distorted to minimize

the energy increase produced by the surface configuration. Consequently

highly polarizable ions tend to form the major fraction of the surface

layer. The interfacial energy is defined as the energy necessary to form a

unit area of the new interface in the system. This is always less than the

sum of the separate surface energies of the two phases, since there is

always some energy of attraction between the phases. It may be any value

less than this sum, depending on the mutual attraction of the two phases.

In general, interfacial energy between immiscible phases is low compared

with the sum of their surface energies [35]. The interfacial free energy γs1

between the composite surface and the test liquids, water and methylene

iodide behaves in opposite manner. With water the interfacial free energy

decreases markedly and with methylene iodide it increases compared to

neat PS. The polar sites present in the surface gave path for the increment

in interfacial energy with methylene iodide. The different kinds of

intermolecular forces such as dispersion, hydrogen bonding and polar

may not equally contribute to solid-solid, liquid-liquid and solid-liquid

interactions. For water composite system, the potential function of water


contains important hydrogen bonding contributions that are absent in MI

composite system. The effects of polar-polar and polar non polar

interactions are not contributing in an additive manner with the two

composite systems (M.I-composite system, Water-composite systems).

There has been considerable theoretical development in the treatment of

interfacial tension and work of adhesion. As illustrated in fig 6.6(a),

schematic model for interfacial tension, ‘γsl’ may be regarded as the sum

of work to bring solid and liquid molecules to their respective solid-

vapour and liquid-vapour interface less the free energy of interaction

across the interface. This is determined through equ 6.13. Calculation of

this can be carried out if potential energy function for solid-liquid

interaction is known. Equation 6.14 is based on the geometric mean law

relation ship and the calculations were done according to the above

Relations.

(a)

Solid

Liquid

186 Chapter VI

0 10 20 30 40

5

10

15

20

25

30

35

40

Inte

rfaci

al e

nerg

y (m

j \ m

2 )

Volume of filler, %

BNN-PS with water YBCO-PS with water BNN-PS with M.I YBCO-PS with M.I

(b)

Fig 6.6 (a) Schematic model of interfacial energy (b) Variation of interfacial energy with different volume % of the filler with different liquids

6.2.5 Spreading Coefficient

The spreading coefficient (Sc) implies that a liquid will spontaneously

wet and spread on the solid surface if the value is positive whereas, a

negative value of (Sc) implies the lack of spontaneous wetting. This

means the existence of a finite contact angle. (i.e. θ >0). The spreading

coefficients of composites for water and methylene iodide are given in the

fifth column of tables6.3, 6.4, 6.5&6.6. By the fig.6.7, it can be noted that

the wetting due to methylene iodide and water decreases upon filler

addition. Comparing water and methylene iodide, the less negative value

is given by methylene Iodide which means that it is a better wetting agent

for the current composites. Thus wetting has decreased for water with the

addition of fillers indicating more hydrophobic nature of the composites


and which in turn reduces the water absorption capacity of

Polystyrene[36,37]. The polar –polar interactions across the interface is a

measure of wetting. The ratio of polar to polar interactions in water-

composite system is much greater than polar to polar interactions between

composite water system. The ratio of polar to polar interactions in MI-

composite system is much less than polar to polar interactions between

composite MI system. The trend is same for both composite system but in

opposite manner. A less negative value for spreading coefficient is

experienced in between M.I-composite system.

0 10 20 30 40-70

-60

-50

-40

-30

-20

-10

BNN-PS with waterYBCO-PS with water BNN-PS withM.I YBCO-PS with M.I

spre

adin

g co

effic

ient

(mj/m

2 )

Vol ume of filler,%

Fig 6.7 Variation of spreading coefficient of the composites with

volume % of the filler

6.2.6 Interaction Parameter

Girifalco-Good’s interaction parameter (Φ) calculated using the equation 6.17

provides a good understanding of the degree of interaction between the test

liquid and the polymer surface as shown in fig 6.8. Empirically the value of (Φ)

188 Chapter VI

ranges from 0.5 to 1.15. In this type of calculation Skapski [38] type of approach

is used, all interactions except nearest neighbour interactions are neglected. The

different kinds of nearest neighbour intermolecular forces (dispersion, polar,

hydrogen bonding etc) may not be equally contributed to solid-solid, liquid-

liquid, and solid-liquid interactions. For water composite system, the potential

function for water contains important hydrogen bonding contribution that are

absent in M.I-composite interactions. Work of adhesion and spreading

coefficient are less in water-composite system and that is a measure of

interaction parameter. The values are given in the last column of table 6.3, 6.4,

6.5 & 6.6. A higher value indicates greater interaction. Φw and Φm are the

Girifalco Good’s interaction parameter due to water and methylene iodide

respectively. Thus based on Girifalco-Good’s interaction parameter, Φw and Φm

it can be suggested that the interaction parameter, Φw is less than Φm. [39-40].

0 10 20 30 40

0.68

0.70

0.72

0.74

0.76

0.78

0.80

0.82

0.84

0.86

0.88

0.90

0.92

0.94

0.96

Inte

ract

ion

para

met

er

Volume of filler,%

Water(YBCO-PS)Water(BNN-PS)M.I(YBCO-PS)M.I(BNN-PS)

Fig 6.8 Variation of Interaction parameter of the composites with

different volume % of the fillers and with different liquids


6.2.7 Theoretical Modeling of Contact angle

Li and Neumann sought an equation of state of interfacial tensions of the

form ( , )sl l sfγ γ γ= .Based on a series of measurements of contact angles

on polymeric surfaces; they revised an older empirical law to produce a

numerically robust expression. The equation holds good for some solid

liquid systems. But some controversy has surrounded the equation [41-44]

1/ 2 22( ) exp 0.0001247( )sl l s l s l sγ γ γ γ γ γ γ= + − − − (6.15)

or when combined with the Young equation

1/ 2

2cos 1 2 exp 0.0001247( )sl s

l

γθ γ γγ

= − + − −

(6.16)

Table 6.7 Modeling (Contact angle) (Water)

Sample name Equ (6.16) (θ) Experimental(θ)

Poly 62.60 84

YBCO10 68.60 84.1

YBCO20 69.30 84.2

YBCO30 69.57 84.6

YBCO40 70.54 86

BNN10 71.99 84.6

BNN20 72.76 84.7

BNN30 73.35 84.72

BNN40 73.93 84.8

190 Chapter VI

Table 6.8 Modeling (Contact angle) ( Methylene Iodide)

Sample name Experimental By equation 6.16

Value of θ Value of θ

Poly 35 25.37

YBCO10 45 35.35

YBCO20 46 36.41

YBCO30 46.5 36.90

YBCO40 47 38.27

BNN10 50 40.39

BNN20 51 41.5

BNN30 52 42.33

BNN40 53 43.16

The experimental and theoretical values of contact angles are given in

Table 6.7&6.8. It can be seen that theoretical predictions do not match

with the experimental results. Some controversy has still surrounded the

equation of state for modeling. In theoretical and experimental

calculations the value of (θ), the contact angle is found to be increased

with filler concentrations

6.3 Conclusions

The contact angle with water and methylene Iodide got increased by the

addition of ceramic filler to polystyrene matrices. The nature of surface

forces appears to be the same in YBCO and BNN composites. The

hydrophobic nature of PS increases with composite formation. The

decrease in solid surface free energy of the composite is the result of


accumulation of excess polar sites at the surfaces. γsd is decreased due to

the restricted chain mobility by the addition of fillers. The solid surface

free energy of the composites decreased and thereby decreased work of

adhesion by the addition of filler to PS. Methylene Iodide showed less

negative value for the spreading coefficient than water and it is a good

wetting agent than water. Finally the nature of the particle and particle

dispersion in the matrix affected the various parameters analyzed as each

one of them changed according to the filler loading.

Theoretical predictions of contact angle and the experimental results

showed the similar trend with progression in contact angle with filler

addition.

References

1 Hameed N, Thomas S. P, Abraham R, Thomas S; Exps Polyr Lett

1, (2007) 345.

2 Laibinis P E, Bain CD, Nuzzo R.G, Whitesides G M; J. Phys

Chem 99(1995) 7663.

3 Thomas S P, Thomas S, Abraham R, Bandhyopadhya S; Expr

Polym Lett 2, (2008) 528.

3 Decker E L, Garoff; Langmuir 12 (1996) 2100.

4 Siao W Y, Yao T C,Chia H C, King H W; Macromol Rap

Commun. 25(2004) 1679.

5 Defay R, Prigogine I; Surface Tension and Adsorption, Wiley,

New York (1966).

192 Chapter VI

6 Neumann A W, Spelt J K; Applied Surface thermodynamics,

Marcel Dekker Inc. New York (1996).

7 Mahanty J, Ninham B W; Dispersion Forces, Academic, New

York (1976).

8 Johnson R E Dettre, R H; Surface and Colloid Science, Vol2,

Wiley Interscience, New York (1966).

9 Vemulapalli G K; Physical chemistry Prentice-Hall of India, New

Delhi (2002).

10 Arthur W Adamson; Physical Chemistry of Surfaces Wiley

Interscience Publ New York,(1997).

11 Rowlinson J.S, Wisdom B; Molecular theory of capillarity

Clarendon Press Oxford (1982).

12 Harkins W D; The Physical Chemistry of Surfaces Reinhold, New

York (1952).

13 Neumann A W, Good R J; Techniques of measuring contact

angles Vol 2, Plenum New York (1979).

14 Fruzsina Kadar, Lazloszazdi; Langmuir 22 (2000 )7848.

15 Girifalco L A, Good R J; J. Phys Che 61,(1957) 904.

16 Fowkes F M; J. Phys. Chem 67 (1963) 2358.

17 Fowkes F M; Adv. Chem. Ser; 43, (1964) 99.

18 Fowkes F M; Chemistry and Physics of interfaces, S Ross ed.

American Chemical Society, (1971).


19 Zheng P, Zhen H G, Linlin Z; Macrol mater. Engg 289 (2004)

743.

20 Korosi G, E. Kovats ; Colloids and Surfaces 2, (1981) 2604.

21 Ownes D K, Wendt R C; J. Appl. Polym. Sci. 13, (1969)1741.

22 Kaelble D H; J. Adhesion 2, (1970) 66.

23 Wu S; J. Poly Sci. Part C 34,(1971) 19.

24 Wu S.; J Adhes 5, (1973) 39.

25 Norris J, Giess R F; J Clays & Clay Miner. 40(1992) 327, C J Van

Oss, R J Good ; Langmuir, 6 (1990) 1711.

26 Israelachvili J N; Intermolecular and Surface Fores, Academia,

San Diego, (1992).

27 F London, Trans. Farady Soc. 33(1937) 8, W B Russel, D.A.

Saville, Colloid dispersions, Cambridge University Press (1989).

28 Dupre A ; Theore Mechanique de la Chaleur, Gauthier Villars

Paris (1869).

29 Girifalco L A, Good R J; J Phys. Che. 61 (1957) 904.

30 Lin J W P, Dudek L P, Majumdar D ; J Appl Polyr Sci, 33, (1987)

657.

31 Arthur W; Adamson Physical chemistry of surfaces 6 thed, John

Wiley& Sons New York (1997).

32 Varughese K T, De PP, Sanyal S K; J Adhe Sci Techno 3, (1989)

541.

194 Chapter VI

33 Neumann A.W, Wood R J, Hope CJ, Sejpal M; J. Colloid

interface Sci. 49(1974) 291.

34 Adamson A W; Physical Chemistry of Surfaces, J. Wiley & Sons,

New York 5th edition (1990).

35 Li D, Neumann A W; J. Colloid Interface Sci. 148(1992)190.

36 Johnson R E, Dettre R H; Langmuir 5 (1989) 293.

37 Morrison I D; Langmuir 5(1989) 540.

38 Skapski A S; J Chem. Phys 16 (1948) 386.

39 Li D, Moy E, Neumann A W; Langmuir6, (1990) 885.

40 Hull D; Introduction to dislocations, Pergamon (1965).

41 Li D, Neumann A W, Langmuir, 9(1993) 3728.

42 Grundke K, Bogumil T, Gietzelt T, Jacobasch H J, Kwok D Y

Neumann A W; Progren Collo and Polyr Scie 101 (1996)58.

43 Cooke D J, Dong CC, Lee JR, Thomas RK; J. Phys. Chem. B. 102

(1998) 4912.

44 Wade G A, Cantwell W J; Materl Scien lett 19 (2000) 1829.

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