effect of temperature towards stability at pit

8/2/2019 Effect of Temperature Towards Stability at PIT

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258Journal of Colloid and Interface Science, Vol. 30, N 2, June 1969, 258-263

The Stability of O/W Type Emulsions as Functions of Temperatureand the HLB of Emulsifiers: The Emulsification by PIT- method

KZ SHINODA and HIROSHI SAITO

Department of Chemistry, Yokohama National University, Ookamachi, Minamiku, Yokohoma, Japan

Received December 2,1968; Revised February 3, 1969

The properties of emulsions containing 3 wt % of polyoxyethylene nonylphenylether per system werestudied as functions of temperature, composition, and the hydrophile-lipophile balance (HLB) of emulsifiers.It has been found that (a) the size of emulsion droplets changes remarkably with temperature and HLB ofemulsifiers, (b) the diameter of droplets is very small but less stable towards coalescence close to the phaseinversion temperature (PIT), (c) relatively stable O/W type emulsions are obtained when the PITs of

respective systems are about 20 - 65C higher than the storage temperature, (d) a stable and fine emulsion isobtained by rapid cooling of an emulsion emulsified at the PIT, which process we shall designate"emulsification by the PIT - method", and (e) the optimum stability of an emulsion is relatively insensitivethe change of the HLB values or PITs of emulsifiers, but the instability of an emulsion is very sensitive to thePIT of the system. It seems difficult to determine the optimum HLB value of an emulsifier accurately fromthe stability vs HLB value relation. On the other hand, since the change in the stability of an emulsion issensitive to the temperature near the PIT, the selection of an emulsifier according to the PIT may be moreaccurate and reliable.

INTRODUCTION

In the preceding paper the phase diagramand the dispersion types of water- cyclohexanesystems containing 3 and 7 wt% of polyoxy-ethylene (9.7) nonylphenylether were studiedas a function of temperature.(1)

The present investigation was undertaken(1) to determine the mean droplet diameter andthe stability of emulsions as functions oftemperature and the hydrophile-lipophilebalance (HLB) of the emulsifier, and (2) todetermine the correlations among the optimum

temperature for stable emulsification, theoptimum hydrophilic chain length, and the PITof emulsifiers. In addition, the emulsificationby the PIT-method, which affords moreuniform and stable emulsions, was created.

EXPERIMENTAL

Materials. The cyclohexane used wasextra pure grade material. Polyoxyethylene

nonylphenylethers used were research samplesfurnished from Kao Soap Co. through the

kindness of Dr. H. Arai. These samples wereused without purification, so that presentresults are directly applicable to the practicaluse of emulsifiers. The comparison betweenthe properties of the purified material and thecommercial material will be publishedelsewhere.

P r o c e d u r e s . About 6 gm of samplecomposed of oil, water, and noionic surfactantwas sealed into an ampoule (inner diameter16.5 mm) and the ampoule was shaken gently

in order to attain approximate dissolutionequilibrium at first. After 1 hour the ampoulewas shaken 20 times in 5 sec with 15 cmamplitude followed by 5 sec settling, and thisprocess was repeated 6 times in 55 sec. Themean volume diameter was determined byobservation through a phase contrastmicroscope. (The mean volume diameter D =

niD

i

3/ n

i

3 ).


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259

0 20 40 60 80 100

PhaseVolume

Mean

DropletDiameter(m)

Temperature (C)

PIT

W/OO/W

0 hr

5 hrs

O/W cream

5 hrs

W/Ocream

O-Phase

W-Phase

(a)

(b)

0 20 40 60 80 100

1

0

6

4

2

0

Fig1. (a) (Upper). The effect of temperature on themean volume diameter of emulsions containing 3 wt%polyoxyethylene (9.7) nonylphenylether, 48.5 wt%cyclohexane and 48.5 wt% water immediately after (0hour) and 5 hours after emulsification. (b) (Lower). Theeffect of temperature on the volume fractions of oil,cream, and water phases in the same system. Afteremulsification with a single emulsifier the system wasmaintained at the temperature indicated for 5 hours.

RESULTS AND DISCUSSION

The effect of emulsification temperature oilon the mean volume diameter of O/W typeemulsions of the ternary system composed of 3wt% of polyoxyethylene (9.7) nonylphenyl-ether, 48.5 wt% of water, and 48.5 wt% ofcyclohexane has been studied and shown inFig. la (upper figure). The volume fractions ofoil cream and water phases of the same system

5 hr after agitation are shown in Fig. 1b (lowerfigure). Cream phase means an O/W typebelow the PIT and a W/O type above the PIT.(The PIT of this system was 72C).

As can be seen in Fig. 1a, the mean volumediameter was smallest close to the PIT andmonotonically increased with the temperaturedecrease. In course of time, the dropletdiameter increases rapidly close to the PIT,

because the coalescence proceeds very rapidlynear the PIT, but it increases much moreslowly at lower temperature, because thecoalescence rate is slow and the viscosity of themedium is larger. It is evident from Fig. 1b thatthe mean volume diameter, coalescence rate,

etc., of an emulsion stabilized with a definitenonionic emulsifier vary remarkably withtemperature. As for the O/W type emulsion, thedrainage rate was slow at about 20C below thePIT, but for the W/O type emulsion it was slowat about 10-20C above the PIT. As the PITvaries with the types of oils and the hydrophilicchain lengths of nonionic emulsifiers, it isreadily understood that the optimum PIT, i.e.,the optimum hydrophilic chain length ofemulsifier, is required to get a better emulsion

for respective oils and temperature.The interaction between the hydrophilicmoiety and water increase with the temperaturedecrease, so that the increase of hydrophilicchain length of the emulsifier may have aneffect similar to the temperature decrease of thesystem. In order to confirm this view, the effectof the hydrophilic chain length (the PITs) of aseries of noionic agents on the mean volumediameter and the stability of emulsions of anO/W type has been studied and plotted in Fig.

2a and 2b.The higher the PIT of the emulsifier abovethe experimental temperature, the larger theemulsion droplets. This finding is consistentwith the results obtained in Fig. 1, i,e., thelower the emulsification temperature, the largerthe droplet diameter of a system stabilized witha definite emulsifier. It is concluded from Fig.2 that emulsifiers the PITs of which are about25 - 70C higher than storage temperatureyield the most satble emulsions. Thus, it is

possible to screen a suitable emulsifier forgiven ingredients at a given temperature by theuse of the PIT data.

Emulsification by PIT Method. It is readilyanticipated from the experiments shown in figs.1 and 2 that a better emulsion can be obtainedif a sistem is shaken at first close to the PIT(about 2 - 4C below the PIT is the best) tofine dispersion and then rapidly cooled down


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20 40 60 80 100

PhaseVolume

MeanDro

pletDiameter(m)

Phase Inversion Temperature (C)

0 hr

O/W cream

W-Phase

(a)

(b)1

0

8

6

4

2

020 40 60 80 100

at 25C

at 25C

20 days

Fig. 2. (a) The effect of PIT (hydrophilic chain length)of emulsifier on the mean volume diameter of emulsionscontaining 3 wt% polyoxyethylene (6.3 - 14.6) nonyl-phenylethers, 48.5 wt% cyclohexane and 48.5 wt%water. (b) The effect of PIT of emulsifier on the volumefraction of oil, cream, and water phases 20 days afteremulsification. (Emulsified and stored at 25 using a

series of polyoxyethylene nonylphenylethers the PITs ofwhich vary from 27 to 94C).

to storage temperature, at which the coales-cence rate is slow. We designate this processas "emulsification by the PIT-method". In orderto test this method, the effect of emulsificationtemperature on the mean volume diameter wasstudied in three systems in which the volumeratios of oil vs water were 1, 1/4, an 1/9respectively. The results are plotted in Fig. 3. It

is clear that emulsification at the PIT (slightlybelow) always affords smaller droplets of O/Wtype. On the contrary, emulsification at atemperature higher than the PIT meansemulsification to a W/O type at first and theninversion to an O/W type by cooling. Presentresults tell us that emulsification by theinversion method is not as good asemulsification by the PIT-method.

0 20 40 60 80 100MeanD

ropletDiameter(m)

Emulsification Temperature (C)

storage at 25 C

PIT [ ]

PIT [ ]

PIT [ ]

Fig. 3. The effect of phase volume ratio on the meanvolume diameter of emulsions containing 3 wt% persystem of polyoxyethylene (9.7) nonylphenyletheremulsified at temperature indicated and cooled down to25C for observation. The weight ratios of water to

cyclohexane were 1/1, O; 4/1, ; and 9/1, l.

0 hr

(a)

(b)

at 25C

20 days

0 20 40 60 80 100

PhaseVolume

MeanDropletDiameter(m)

PIT

O/W cream

O-Phase

W-Phase

0 20 40 60 80 1001

0

6

4

2

0

Emulsification Temperature (C)

storage at 25 C

starage

1 day

Fig. 4. (a) The effect of the emulsification temperatureon the mean volume diameter of emulsions containing 3wt% polyoxyethylene (9.7) nonylphenylether, 48.5 wt%cyclohexane, and 48.5 wt% water. (b) The effect of theemulsification temperature on the volume fractions ofoil, cream, and water phases of the same emulsion 20days after agitation. After emulsification with a singleemulsifier the system was stored at 25C.


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261

0 20 40 60 80 100

PhaseVolume

Mean

DropletDiameter(m)

Stored Temperature (C)

PIT

W/OO/W

0 hr

5 hrs

O/W cream

5 hrs

(a)

(b)

0 20 40 60 80 100

1

0

6

4

2

0

0 hr

5 hrs

PIT

W

Fig. 5. (a) The mean volume diameter of O/W typeemulsions (3 wt% polyoxyethylene (9.7) nonyl-phenylether, 48.5 wt% cyclohexane, and 48.5 wt%water) emulsified at the PIT and then cooled to and heldat the temperature indicated. Holding times were 0 hourand 5. Dotted curve illustrates the mean droplet diameterof the same system emulsified and stored at onetemperature. (b) The effect of storage temperature on thevolume fractions of the oil, cream, and water phases of

the system prepared as in 5(a) and stored 5 hours.

In the usual emulsification by the inversionmethod an emulsifier is dissolved in the oilphase. The emulsion may then be formed byadding water directly to the mixture. In thiscase, a W/O emulsion is formedat first andthen inverted to an O/W type by the addition offurther water. On the other hand in"emulsification by PIT-method", emulsifier, oil

and water are mixed at the same time atslightly below the PIT. An O/W type emulsionmay be formed at this temperature, and thenthe emulsion is cooled down to the storagetemperature. In this respect also, the PIT is animportant characteristic property of emulsion.

20 40 60 80 100

PhaseVolume

MeanDr

opletDiameter(m)

Phase Inversion Temperature (C)

0 hr

O/W cream

W-Phase

(a)

(b)1

0

6

4

2

0

stored at 25C

20 days

20 40 60 80 100

stored at 25C

Fig. 6. (a) The effect of the PIT, i.e., the hydrophilicchain length, of the emulsifier on the mean volumediameter of emulsions containing 3 wt% of poly-oxyethylene nonylphenylethers, 48.5 wt% cyclohexane,and 48.5 wt% water. (b) The volume fractions of the oil,cream, and water phases of the above systems 20 days

after agitation (emulsified at the PIT and stored at25C).

As the effect of phase volume is notsignificant, the stability of an emulsion as afunction of emulsification temperature hasbeen observed for a system which containsequal amounts of oil and water and is plotted inFig. 4. Although the effect of emulsificationtemperature on the stability of the emulsion

judged from the phase volumes of oil, cream,an water phases is not very distinct,emulsification at a higher temperature(especially near the PIT) and cooling to storagetemperature are effective in obtaining fine anduniform dispersions.


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7 (a)

7 (b)

Fig. 7. (a) Emulsion prepared by the PIT-Method, emulsified at 49C and cooled down to25C. The PIT of this system was 52C. (b) Emulsion prepared by simple shaking at 25C.

Comparison of Emulsions Prepared by

Simple Shaking and Those by the PIT-Method. The mean volume diameters ofemulsions emulsified at the PIT and cooleddown to various storage temperature, as wellas the phase volumes of oil, cream, andwater phases of the same system, are shownin Fig. 5. The mean volume diameter ofemulsions made at several temperatureswithout cooling is also shown for

comparison by the dotted line. It is evident

from Fig. 5 that (1) the smaller droplets areobtained by emulsification at the PITregardless of the storage temperature andthus (2), emulsions stored at lowertemperatures, at which the coalescence rateis slow, are more stable.

Using a series of polyoxyethylenenonylphenylethers the PITs of which changeover a wide temperature range, we applied


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263the emulsification by the PIT-method for thecyclohexane - water system. The meanvolume diameter and phase volumes of therespective phases as a function of the PITsof emulsifiers are plotted in Fig. 6. Theinitial droplet was equally small regardlessof the PITs, whereas the emulsions shaken

and stored at 25C show gradual increase ofdroplet size with the PIT rise, as shown inFig. 2. It is concluded from Fig. 6 thatemulsifiers the PITs of which are about 20 -65C higher than the storage temperatureafford more stable emulsions.

The PIT change from 27 - 94C in thisexperiment corresponds to the change ofHLB - value from 11.1 to 14.7. It is clearfrom Fig. 6 that the optimum HLB value orPIT can not be accurately determined from

the stability vs HLB value relation, becausethe maximum stability is insensitive to the

change in HLB value change. On the otherhand, the instability of the emulsion is verysensitive to the PIT, so that the selection of asuitable emulsifier by the PIT data is muchmore accurate and reliable, provided thetemperature difference between the storagetemperature and the optimum PIT is known.

The comparison between the hase-contrastmicroscopic photographs of emulsionsprepared by the PIT-method and by a simpleshaking is shown in Fig. 7. The systemcontains 3 wt% polyoxyethylene (8.6)nonylphenylether, 77.6 wt%water, and 19.4wt% cyclohexane.

REFERENCES

[1] SHINODA, K., AND SAITO, H., J.Colloid and Interface Sci. 26, 70 (1968).

effect of temperature towards stability at pit

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