UNIVERSITI PUTRA MALAYSIA

STRUCTURES OF SURFACTANT SYSTEM STUDIED BY POSITRON ANNIHILATION LIFETIME

SPECTROSCOPY

ROSDI BIN HAJI IBRAHIM

FSAS 1996 3

STRUCTURES OF SURFACTANT SYSTEM

STUDIED BY POSITRON ANNIHILATION LIFETIME

SPECTROSCOPY

By

Rosdi B in Haj i I brahim

A Thesis Submitted in Fulfi lment of the Requirements for

the Degree of Master of Science in the

Faculty of Science and Environmental Studies

Un iversiti Pertanian Malaysia

January 1996

ACKNOWLEDGEMENTS

In the name of Al lah , Most Gracious, Most Mercifu l

Be a l l for the Almighty Al lah for g iv ing me the utmost strength and courage to

complete th is project successfu l ly .

It g ives me much pleasure to acknowledge and thank many indiv iduals and

institutions for their s ign ificant contributions dur ing the entire course of this

study.

I would l ike to express my sincerest thanks , gratitude and appreciation to my

chai rman, Prof. Dr . Mohd Yusof Sula iman for h is original idea, helpfu l ,

advice, i nvaluable gu idance, suggestion, encouragement, stimu lating

d iscussions and patience throughout this study.

I am part icu lar ly happy with and appreciate his approachable manner which

made th is exercise a pleasant one.

S im i lar appreciat ion is extended to members of my supervisory commitee,

Assoc. Prof. Dr. Za inal Ab id in Sula iman, Assoc. Prof. Dr. Hamdan Suha imi

and Assoc. Prof. Dr . E l ias Saion for their constructive comments on

surfactant system.

i i

F ie ld and laboratory work were assisted by research staff of the Physics

Department of Universiti Pertanian Malaysia . They are En . Marzuki Ismai l ,

En . Razak Harun, En . Saharuddin , En. Suha im i I brah im and En . Nord in .

Thei r earnestness and hardwork were the decisive factor in making this study

a real ity .

Last but not least , heartfelt appreciation and love are due to my parents, En .

I brah im Sham and Puan Asiah Mat, my brothers, sisters and friends

especial ly to En Shamsul Mohamad (UKM), I wish them every success in this

world and hereafter under the guidance and in the path of Al lah s. w. t

wassalam.

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TABLE OF CONTENTS

Page

ACKNOWLEGEMENTS i i

LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi i

LIST OF F IGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v i i i

LIST OF ABBREVIATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii

ABSTRACT xvi

ABSTRAK xix

CHAPTER

I NTRODUCTION The Positron Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Phase Structures of Surfactant Determined from Positron Lifetime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 1 5

I I SURFACTANT SYSTEM AND MICROEMULSION 7

I I I

I ntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Surfactant and Change of Surface Tension-Critica l Micel le Concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Stabi l ity of Microemulsion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Literature Review of Previous Work on Microemulsion Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

POSITRONIUM FORMATION AND REACTION I N SURFACTANT SYSTEM. . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Diffusion-Recombination Model of Positronium Formation in Surfactant. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 I nfluenc� of M icel les on the Formation Probabi l itty of Positronium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Quantitative Model of Positronium in Micel les Containing Aqueous Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 60 Ortho-Para- Convertion of Positronium in the Micel le-Containing Solutions . . .... ....... . . .... . ... .. .. 71

iv

Page

IV POSITRON L IFETIME METHODOLOGY . . . . . . . . 76 Positron Annih ilation Lifetime (PAL) Spectroscopy . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 Positron Lifetime System and Preparation of Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . '" 78 Instrumentation . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

Plastic Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 Photomultipl ier Tubes . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Fast Timing Discriminators . . . . . . . . . . . . . . . . . . . . 91 Time P ickoff Techniques . . . . . . . . . . . . . . . . . . . . . 92 Constant Fraction D ifferential Discriminator, Ortec Model 583 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 02 Delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 09 Time to Amplitude Convertion . . . . . . . . . . . . . . 1 1 0

Experimental Adjustment for Optimum Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 2

Timing Cal ibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 2 Effect of Dynamic Range on Timing Resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . 1 1 4 Measurement of Timing Resolution Using Annealed Copper and 22Na . . . . . . . . . . 1 1 8

Source Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 9 Source Correction '" . . . . . . . . . . . . . . . . . . . . . . . . . '" . . 1 22

V POSITRON LIFETIME ANALYSIS . . . . . . . . . . . . . . . . . . 1 23 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 23 The F itting Programmes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 23 Positronfit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 25 Experience with the Lifetime Analysis . . . . . . . . . . . . . 1 29

VI EXPERIMENTAL PROCEDURE AND RESULTS . . 1 36 D idodecyl D imethylAmmonium Bromide-Water-Octane System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 36 Experimental Section for DidodecylDimethyl AmmoniumBromide ! Water ! Octane System . . . . 1 40 Results for the D idodecylDimethylAmmonium Bromide ! Water ! Octane System . . . . . . . . . . . . . . . . . . . . . . 1 41 (T etradecylTrimethylAmmonium Bromide/Butanol )-2 I Water I Octane System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 53 Results for the (TetradecylTrimethylAmmonium Bromide IButanol)-2 I Water I Octane System . . . . 1 58 (Benzyl D imethylTetradecylAmmonium Chloride! TetradecylTrimethylAmmonium Bromide) I Water I Octane System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 67

v

Page

VI I CONCLUSIONS 175

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 VITA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185

vi

LIST OF TABLES

Table

1 Picosecond Yield of the Positronium Reactions

2 Timing Cal ibation Data Obtained Using Experimental Set-Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . .

3 Data for the Dynamic Range Against Timing Resolution Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4 Positron and SAXS Data for DDAB I Water I Octane

5 Data for Positron Master Plot of DDAB I Water I Octane

6 Data of The Ratio of The Oil Weight Fraction and Gradient of Positron Master Plot, Lattice Parameter, For Different Compositions of DDAB I

Page

66

1 1 4

1 1 8

1 43

1 52

Water I Octane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 56

7 Positron Data for (TTAB/BUTANOL)-2IWaterl Octane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 59

8 Data For Positron Master Plot of (TI AB/Butanol)-2 I Water I Octane System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 65

9 Linear Least F it Data For The (TI AB/Butanol)-2 I Water I Octane System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 66

1 0 Positron Data for (BDTACITTAB)lWater/Octane . . 1 71

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LIST OF FIGU RES

Figure

1 The Vector D iagram of the Momentum Conservation in the Two Gamma

Page

Annih i lation Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Schematic D iagram of Surface Active Agent . . . . . . 8 3 A Schematic Presentation for M ice l le Formation (A),

Adsorption (B) , M ixed M icel le Formation (C) , Sol ib i l ization of Oi l in M icel le (D) , Polymer-Micel le

I nteraction (E ) and Surfactant-Polymer Mixed F i lm at Interfaces (F ) in Surfactant Solutions 1 0

4 A Naive Steric Model Correlating the Shape of Amphiphi le to the Spontaneous Curvature of the Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 8

5 Schematic View of a Cross-Section through a Curved B i layer Formed from a Water I Surfactant M ixture . Integrating the area of a l l para l le l Surfaces from the Interface to the paral le l Surface Traced out by the Head-Groups g ives the Chain Volume (shaded reg ion ) . The hatched Portion of the Interface Marks the I nterfacial Area Occupied by each facing pair of Surfactant Molecu les . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

6 Cross-Section through a Curved Reversed B i layer formed by a Surfactant I Water M ixture . The Shaded Region Indicates the Volume Occupied by Water, Which , together with the Head-Group, defines the Polar Region that ies along the

M inimal Surface (of total thickness 2tp) . . . . . .. . . . . . . 24

v i i i

Figure

7 Cross-Section through a Hypothetical Cubic Phase of a M ixture of Surfactant and Water Consist ing of a Monolayer of Surfactant. The Curved Interface Separates Polar from

Page

Paraffin Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

8 D imensions used to Calculate the Geometry of an O i l -Swol len Curved B i layer, formed by a Ternary M ixture of Surfactant, Water and O i l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

9 A Scheme of Fast Positron Track . . . . . . . . . . . . . . . . . . 52

1 0 The Positron Experiment. Positron from a Radioactive I sotope l i ke 22Na Ann ih i late in the Sample Materia l . Positron L ifetime is determined from the Delay between the B i rth Gamma ( 1 . 28MeV) and the Two Ann ih i lat ion Quanta. The Momentum of the Electron -Positron Pair is measured as an Angle deviat ion petween the Two 5 1 1 KeV Quanta or as a Doppler Sh ift i n the Energy of the Ann ih i lation Radiation . . . . 77

1 1 The Output S ignal is Processed in a Ortec 583 Constant Fraction D ifferentia l D iscriminator (CFDD) , which Permit On ly the Passage of Signals which Correspond to a Photon Energy in the 550-1 200 KeV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

1 2 The Output S ignal is Processed in a Ortec 583 Constant Fraction D ifferent ia l D iscriminator (CFDD) , which Permit On ly the Passage of S ignals

which Correspond to a Photon Energy in the 200-5 1 1 KeV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

1 3 The E lectronic Equipment of Positron Ann ih i lation Lifet ime Spectroscopy System . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . 82

ix

Figure

1 4 Schematic D iagram of the Interior of a

Page

Photomult ip l ier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

1 5 Two Dynode Arrangements in Commercial Phototubes (a) Model 6342 RCA, 1 -1 0 are dynode, 1 1 is anode (b) Model 6292 Dumont . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

1 6 J itter and Walk i n Leading-edge Time Derivation and Formation of the Constant Fraction S ignal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

1 7 Functional Representation of a Constant-Fraction D iscriminator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

1 8 System I nterconnection to view Walk Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 00

1 9 Monitor S ignal when Triggered by the Constant­Fraction D iscrim inator Output S ignal for (a) Passive Pu lse Shaping (b) Active Pu lse Shaping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 0 1

20 T iming Resolution as a function of Dynamic Range for Two Constant Fraction D ifferent ia l D iscrim inator in a Fast Timing Coincidence System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 04

2 1 S impl ified B lock D iagram of the Constant Fraction D ifferential D iscrim inator . . . . . . . . . . . . . . . . . 1 06

22 The Measurement Cal ibration System of Positron Annih i lation L ifetime Spectroscopy System . . . . . . . 1 1 3

23 The Measurement Dynamic Range of Positron

24

Ann ih i lation Lifetime Spectroscopy . . . . . . . . . . . . . . . . . . 1 1 6

Timing Spectrum of Annealed Copper 1 1 7

x

Figure

25 The Arrangement of Annealed Copper Materials were Sandwiched between the

Page

Source of 22Na . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 21

26 The Phase Diagram of the System DDAB I Water I Octane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 39

27 P lot of lifet ime of Orthopositronium against Aqueous Weight Fract ion of The Ternary DDAB I Water I Octane System . . . . . . . . . . . . . . . . . . . 1 42

28 P lot of I ntensity against Aqueous Weight Fraction of The Ternary DDAB I Water I Octane System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 45

29 The lifetime, I ntensity and Weight Fraction of System DDAB I Water I Octane . . . . . . . . . . . . . . . . . 1 46

30 P lot of lifet ime of Orthopositronium against Latt ice Parameter for D DAB I Water I Octane System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 47

31 Positron Master P lot for The D-Schwarz Surface of The DDAB I Water I Octane System . . . . . . . . . . 1 50

32 Positron Master P lot for The P-Schwarz Surface of The DDAB I Water I Octane System . . . . . . . . . . 1 51

33 P lot of Data from Table 6 . 3 for The D-Schwarz Surface of The DDAB I Water I Octane System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 54

34 P lot of Data from Table 6 .3 for The P-Schwarz Surface of The D DAB I Water I Octane System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 55

35 Part ia l Phase D iagram For Tetradecyl Trimethyl Ammonium Bromide, Butanol and Octane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 57

xi

Figure

36 Plot of L ifet ime of Orthopositronium against Aqueous Weight Fraction for (TTAB/Butanol )-2

Page

/ Water / Octane System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 60

37 P lot of I ntensity of Orthopositron ium against Aqueous Weight Fraction for (TTAB/Butanol )-2 / Water / Octane System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 61

38 P lot of Lifetime of Orthopositron ium against D ifferent Rat io of Water/Octane for (TTAB/Butanol ) -2 / Water / Octane System . . . . . . . . .. . . . . . . . . . . . . . . . . . . . 1 62

39 P lot of I ntensity of Orthoposi tronium against D ifferent Ratio of Water/Octane for (TTAB/Butanol ) -2 / Water / Octane System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 63

40 Positron Master P lot of The (TTAB/Butanol )-2 / Water / Octane System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 64

4 1 Positron Master P lot of The (TTAB/Butanol )-2 / Water / Octane System for Aqueous Weight Fraction 0 .2 , 0 .3 , 0 .4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 68

42 Positron Master P lot of The (TTAB/Butanol )-2 / Water / Octane System for Aqueous Weight Fraction 0 .5 , 0.6, 0 .7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 69

43 P lot of Lifet ime of Orthopositron ium Against Aqueous Weight Fract ion for (BDTAC/TTAB) / Water / Octane System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 72

44 P lot of I ntensity of Orthopositronium Aga inst Aqueous Weight Fraction for (BDTACITTAB) / Water / Octane System. . .. . . . . . . . . . . . . . . . ... . . . . . . . . . . . . 1 73

45 P lot of Intensity of Orthopositron ium Against Ratio of Water/Octane for (BDTAC/TTAB) / Water / Octane System. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . 1 74

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ABS

ACAR

ADC

AOT

ARC

bcc

BDTAC

C1

C2

CFA

CF ckt

CFDD

CMC

CTAB

o

DAC

DAP

DBS

DDAB

DHBS

DVM

eV

FWHM

LIST OF ABBREVIATIONS

Alkyl Benzene Sulphonate

Angular Correlation of Ann ih i lat ion Rad iation

Analog to D ig ital Converter

D ioctyl Su lfosuccinate

Ampl itude and Rise Time Compensated

Body-Centred Cubic

Benzyl D imethylT etradecylAmmonium Chloride

Cubic Phase

Cubic Phase

Zero-Crossing P ickoff

Constant Fraction C i rcuitry

Constant Fraction D ifferentia l D iscrim inator

Crit ical Mice l le Concentration

CetylTrimethylAmmonium Bromide

D iamond

D igital Analogue Converter

DodecylAmmonium Prepionate

Doppler Broadening Spectroscopy

D idodecy lD imethylAmmonium Bromide

Podihexylbenzene Sodium Sulphonate

D ig ital Voltmeter

E lectron Volts

Fu l l Width at Half Maximum

xi i i

H Hexagonal Phase

H2O Water

12 I ntensi ty

I -WP Monolayer Structure

keV Ki loelectron Volts

LEAD Leading Edge Arming D iscriminator

MCA Multichannel Analyzer

22Na Sodium-22 Radioactive

NaCI Sodium Choride

NALS Sod ium Lauryl Sulfate

N IM Nuclear Instrumentat ion Modules

NMR Nuclear Magnetic Resonance

O/W O i l/Water

PAL Positron Ann ih i lation Lifet ime

PAS Positron Ann ih i lat ion Spectroscopy

PATFIT Positronium F it

Ps Positron ium

PMT Photomult ip l ier Tube

OPC Ortho-Para Converter

o-Ps Orthopositronium

p-Ps Parapositron ium

SANS Smal l Ang le Neutron Scattering

SAXS Smal l Ang le X-ray Scattering

s .c. S ingle Cubic

SCA S ingle Channel Analyzer

SDS Sod ium Dodecyl Su lfate

xiv

Surfactant

TAC

TTAB

W/O

12

Surface Active Agent

Time to Ampl itude Converter

Tetradecyl Trimethyl Ammonium Bromide

Water/Oi l

L ifet ime

xv

Abstract of the thesis .submitted to the Senate of Universiti Pertanian Malaysia in fulfi lment of the requ i rements for the Degree of Master of Science.

Chai rman

Faculty

STRUCTURE OF SU RFACTANT SYSTEM STU DIED BY POSITRON ANNIHILATION

LIFETIM E SPECTROSCOPY

by

Rosd i B in Hj . I brah im

January 1 996

: Prof. Mohd. Yusof Sula iman, PhD

: Science and Environmental Studies

Surfactant system has many app l ications in i ndustry. Many

investigations have been carried out on surfactants using various methods

such as smal l-angle neutron scattering (SANS) , smal l-ang le x-ray scatter ing

(SAXS) , conductivity freeze-fracture electron m icroscopy and nuclear

magnetic resonance (NMR) . In the positron annih i lat ion l ifet ime spectroscopy

techn ique, the l ifet ime ('t2)of positron that intracts with surfactant med ium is

measured using fast co incidence system. The intensity of formation of

orthopositron ium(12) , when positron interact with aggregate of surfactant

system are sensitive to phase changes. In amph iph i l ic system with

xvi

bicont inous character geometry of periodic phase can be exp la ined using

m inimal surfaces. Factors influencing the topology includes the length of

surfactant and cosurfactant tai l s and the aqueous volume fraction. Positron

are readi ly attracted to these centres. Changes in the geometry of the

interfacia l layer thus wi l l i nfluence the l ifet ime and intensity of the

orthopositroni um atom formed. These parameters are obtai nable using the

POSITRONFIT programme.

In th is study, three surfactant systems were investigated . F irst ly , the

intensity (12) and l ifet ime ("(2) of the D idodecy lD imethylAmmonium Bromide

(ODAB) - Water - Octane system were measured at various amount of water

content in the surfactant system in the d iamond and body centred cubic

phases. A symmetry transit ions from d iamond phase to body-centred cubic

phase was observed in th is system.

Secondly , the equivalent data were measured against rat io of (BDTAC/TTAB)

of cubic phase area of Benzy lD imethylTetradecylAmmonium Chloride

(BDTAC) I TetradecylTrimethylAmmonium Bromide (TTAB) - Water - Octane

system. Th i rdly, for the TetradecylTrimethylAmmonium Bromide (TTAB) I

Butanol - 2 - Water - Octane system, the

xvi i

intensity (12) and l ifetime ('t2) were measured against d ifferent composit ion

rat io of Octane/Water.

I n a l l the three systems, an attempt was made to expla in the behaviour

of the positron ium atom in the b icontinous phase of the surfactant.

xvi i i

Abstrak tesis yang d ikemukakan kepada Senat Universiti Pertanian Malaysia bagi memenuhi syarat untuk memperolehi Ijazah Master Sains.

Pengerusi

Fakult i

KAJIAN KE ATAS SISTEM SU RFAKTAN DENGAN M ENGGUNAKAN KAEDAH MASAHAYAT

M USNAHABISAN POSITRON

oleh

ROSOl I BRAH I M

Januari 1 996

: Prof. Mohd. Yusof Sula iman, PhD

: Sains dan Pengaj ian Alam Sekitar

S istem surfaktan mempunyai pelbagai kegunaan dalam industr i .

Banyak kaj ian mengenai surfaktan telah d ijalan dengan menggunakan

pelbagai kaedah seperti kaedah serakan sudut keci l neutron (SANS) ,

kaedah serakan sudut kec i l x-ray (SAXS) , spektroskopi penga l i ran e lektron

"freeze-fracture" dan nuklear magnetik resonan (NMR). Oalam tekn ik

spektroskopi masa hayat musnah-habisan positron (PALS), masa hayat

positron yang berinteraksi dengan medium surfaktan d iukur dengan

menggunakan s istem kesekenaan. Perubahan Pembentukan Keamatan o-Ps

(12) bila positron berinteraksi dengan s istem aggregat surfaktan adalah

xix

sensit if terhadap perubahan fasa. Dalam sistem amfifi l i k dengan geometri

bersifat "b icontinuous" , fasa berkala dapat d i terang dengan menggunakan

perkalaan permukaaan terkeci l . Faktor yang mempengaruhi topologi adalah

panjang surfaktan dan ekor kosurfaktan dan fraksi is ipadu akuas. Pos itron

adalah tersedia tertarik kepusat in i . Perubahan geometri lapisan antara muka

akan mempengaruhi masahayat dan keamatan pembentukan atom

orthopositronium. Parameter-parameter diperolehi dengan menggunakan

program POSITRONFIT.

Dalam kaj ian in i , t iga sistem surfaktan akan d igunakan. Pertama,

keamatan ( I) dan masahayat (-t2) d iukur untuk s istem Didodecy lD imethyl

Ammonium Bromide (DDAB) - Air - Oktana, bagi kandungan air yang

berbeza-beza dalam s istem surfaktan yang berada pada fasa intan seh ingga

terja l i n transis i fasa intan kepada kubus berpusat jasad.

Keduanya, keamatan ( I) dan masahayat (t2) d iukur terhadap n isbah

(BDTACITTAB) dalam kawasan fasa kubus d idalam sistem Benzy lD imethyl

TetradecylAmmonium Chloride (BDTAC) I TetradecylTrimethylAmmonium

Bromide (TTAB) - Air - Oktana, dan akh i r seka l i , s istem yang

xx

ketiga adalah TetradecylTrimethylAmmonium Bromide I Butanol .... 0 . 2 - Air -

Oktana. Keamatan ( I) dan masahayat (12) d iukur terhadap perubahan

komposisi Oktana/Air.

Bagi ketiga-tiga s istem surfaktan diatas, usaha telah d ibuat untuk

menjelaskan pemerhatian secara teori.

xxi

CHAPTER I

INTRODUCTION

The lepton , positron, is the antiparticle of the electron. I ts existence was

predicted by Dirac ( 1 930). I n condensed matter, in it ial ly fast positron annihi lates

after having reached equi l ibrium with the surroundings. The characteristics of

the quantum electrodynamic annihi lation process depend almost ent irely on the

state of the positron-electron system of the medium. D iscoveries of new features

in the positron interaction with matter have maintained continuous interest and

increasing activity in the field . A striking feature is thus the great d iversity of the

fields in which positron annih i lation method is now applied. In addition to solid­

state and material physics, there are intensive activities in atomic physics and

radiation chemistry, the latter extending even into biochemistry and biology.

The Positron Method

The positron method can be established by discussing the annihi lation

process of free positrons. The positron - electron annih i lation is a relativistic

2

process where the particle masses are converted into electromagnetic energy -

the annihilation photons. From the invariance properties of quantum

electrodynamics, several selection rules can be derived. Firstly, one-gamma

annihilation is possible only in the presence of a third body absorbing the recoil

momentum and its relative probability is negligible. The main process is the two­

gamma annihilation, since the spin-averaged cross section for the three-gamma

annihilation is 0.27% of that for the two gamma annihilation. The three-gamma

annihilation is important only in a spin-correlated state like orthopositronium,

where the selection rules forbid the two-quantum process.

From the non relativistic limit of the two gamma annihilation cross-section

derived by Dirac (1930), one obtains the annihilation probability per unit time or

the annihilation rate

(1 . 1 ]

which is independent of the positron velocity. Here, ro Is the classical electron

radius, c the velocity of light and ne is the electron density at the site of the

positron. By measuring the annihilation rate A, the inverse of which is the mean

lifetime t, one directly obtains the electron denSity n. encountered by the

positron.

3

The kinetic energy of the annihi lating pair is typical ly a few electron volts.

In the centre-of-mass frame the photon energy is exactly moc2 = 511 keV and the

photons are moving into opposite directions. Because of the non zero

momentum of the pair, the photons deviate from col l inearity i n the laboratory

frame. As i l lustrated in F igure 1, the momentum conservation yields a result,

[1.21

where 1800 - 9 is the angle between the two photons in the laboratory frame and

PT is the momentum component of the electron-positron pair transverse to the

photon emission d i rection.

P1 = moc + 1/2pl E1 = moc2 + 1/2PlC

P2 = moc - 1/2pl E2 = moc2

- 1/2plC

Figure 1 : The Vector D iagram of the Momentum Conservation in the Two Gamma Annih i lation Process.

Usually 9 is very small (9< 10) and equation 1.2 is val id . Because the

momentum of the thermalised positron is almost zero, the measured angular