Effects of HLB value on oil-in-water emulsions: Droplet size, rheological behavior, zeta-potential, and creaming index

Accepted Manuscript Title: Effects of HLB value on oil-in-water emulsions: droplet size, rheological behavior, zeta-potential, and creaming index Authors: In Kwon Hong, Su In Kim, Seung Bum Lee PII: DOI: Reference:

S1226-086X(18)30313-7 https://doi.org/10.1016/j.jiec.2018.06.022 JIEC 4055

To appear in: Received date: Revised date: Accepted date:

14-3-2018 18-6-2018 24-6-2018

Please cite this article as: In Kwon Hong, Su In Kim, Seung Bum Lee, Effects of HLB value on oil-in-water emulsions: droplet size, rheological behavior, zeta-potential, and creaming index, Journal of Industrial and Engineering Chemistry https://doi.org/10.1016/j.jiec.2018.06.022 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Effects of HLB value on oil-in-water emulsions : droplet size, rheological behavior, zeta-potential, and creaming index

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In Kwon Hong, Su In Kim, Seung Bum Lee✝

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Department of Chemical Engineering, Dankook University, Yongin 16890, Republic of Korea ✝

To whom all correspondences should be addressed.

(E-mail : [email protected], Tel : 82-31-8005-3559, Fax : 82-31-8005-3536)

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Graphical Abstract

The optical microscopy images show that the droplet size in O/W emulsions is dependent on HLB

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value after 70day. The emulsions prepared with MS-01 (HLB=10.8) show smaller droplet size and

MS-01 (HLB=10.8)

MS-01 (HLB=9.1)

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MS-01 (HLB=12.6)

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higher uniformity of droplet size than the other emulsions.

Abstract

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Using mixed nonionic surfactants Span/Tween, we investigated the effects of HLB value

on the O/W emulsion stability and rheological behaviors. In this study, MS-01(Span 60 & Tween 60) and MS-02(Span 80 & Tween 80) was used as mixed nonionic surfactants. We considered required HLB value 10.85 and selected corresponding HLB value range 8 to 13. The droplet size distributions, droplet morphology, rheological properties, zetapotential and creaming index of the emulsion samples were obtained to understand the mechanism and interaction of droplets in O/W emulsion. The results indicated that

optimal HLB number for O/W emulsions was 10.8 and 10.7, while using MS-01 surfactant and MS-02 surfactant respectively. MS-01(HLB=10.8) sample and MS-02(HLB=10.7) sample showed smallest droplet size and highest zeta-potential value. Rheological properties are measured to understand rheological behaviors of emulsion samples. All emulsion samples showed no phase separation until 30days storage time at 25℃.

Keywords : HLB value, emulsifying stability, rheological behavior, SPAN-TWEEN

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surfactants

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1. Introduction

Oil-in-water (O/W) emulsions have various applications in the cosmetic, food and pharmaceutical industries [1-3]. Emulsions are composed of two phases and surfactants

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are an important factor of stable emulsifying process. Addition of appropriate surfactants influences stability of emulsions by decreasing the interfacial tension between oil and

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water phases [4-6]. Moreover, the use of mixture of surfactants for stable emulsions has

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attracted research and commercial attention because of interactions and mechanisms in

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emulsifying systems [7-9]. Non-ionic surfactants consist of a molecule which combines both hydrophilic and lipophilic groups and the balance of these groups is expressed as the hydrophilic-lipophilic balance (HLB) value. Griffin established the method that can

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calculate the HLB value for non-ionic surfactants [10]. The HLB value for optimizing surfactants has been applied to many researches and industries [11-13]. Total HLB value

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of mixed surfactant can be defined by [10]: (1)

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𝐻𝐿𝐵𝑡𝑜𝑡𝑎𝑙 = ∑ 𝐻𝐿𝐵𝑖 ∙ 𝑥𝑖

Stable emulsions are best formulated with surfactants or combinations of surfactants whose HLB value is close to the required HLB value (𝑅 𝐻𝐿𝐵) of the oil phase used [14-15, 20]. Therefore, emulsions are prepared with different ratios of surfactant blends,

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representing various HLB values, and are investigated to determine the 𝑅 𝐻𝐿𝐵 of an oil phase. In order to define total 𝑅 𝐻𝐿𝐵 of an oil phase which is composed of various oils, 𝑅 𝐻𝐿𝐵 was calculated considering the mass fraction of oils (𝑥𝑖 ) as follow: 𝑅 𝐻𝐿𝐵𝑡𝑜𝑡𝑎𝑙 = ∑ 𝑅𝐻𝐿𝐵𝑖 ∙ 𝑥𝑖

(2)

Spans and Tweens are a range of mild nonionic surfactants providing formulating advantages in industries of cosmetic, food and pharmaceutical. They are stable in mild alkalis, acids and electrolytes and have no reaction with ionic ingredients or actives. By using combinations of Spans and Tweens it is possible to prepare a variety of O/W and W/O emulsion systems. Spans (sorbitan esters) are produced by the dehydration of sorbitol. The HLB value of the range decreases with increasing degree of esterification, conferring higher solubility in lipophilic materials. Tweens are hydrophilic in nature and

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are dispersible or soluble in water and dilute solutions of electrolytes. The solubility of

Tweens in water solutions increases with the degree of ethoxylation. The Spans and Tweens offer many benefits including increased stability and formulating flexibility. For

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these advantages, there are many studies using combinations of Span and Tween

surfactants [9,16-17]. In this study, we used Span60 & Tween60 for mixed surfactant (MS-01) and Span80 & Tween80 for mixed surfactant (MS-02). Chemical structure and

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properties of surfactants are presented in Figure1 and Table1.

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We prepared O/W emulsions with different ratios of Span and Tween blends

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representing various HLB values.

The purpose of this study is interpreting the physicochemical and rheological behaviors

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of emulsions. There are many methods that interpret the stability of emulsions. The following parameters were investigated to understand properties and behaviors of the

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O/W emulsions: droplet size distribution, droplet morphology, shear stress, viscosity, modulus (𝐺′, 𝐺′′), zeta-potential and creaming index. The droplet size distribution, droplet morphology,

zeta-potential

and

creaming

index

were

measured

to

study

the

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physicochemical stability of emulsions. To understand the rheological behaviors such as the yield stress and viscoelastic properties, the shear stress, viscosity and modulus were

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investigated.

2. Experimental

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2.1. Materials

The water phase of the emulsions used in this study is consisted of ultrapure water,

glycerin, butylene glycol and methyl paraben. The oil phase is consisted of mineral oil (rHLB=11), octyldodecyl myristate ( 𝑅 𝐻𝐿𝐵 =7.5), Cetyl alcohol ( 𝑅 𝐻𝐿𝐵 =15.5), and propylparaben. Each 𝑅 𝐻𝐿𝐵 value of oil components is found from literature. From the equation(2), calculated ideal 𝑅 𝐻𝐿𝐵 of the oil phase is 10.85. Among the aqueous phase

components, ultrapure water and glycerin are moisturizing agents and butylene glycol is a viscosity reducing agent as well as moisturizing agent. Both mineral oil and ODM are act as a water vapor barrier. Cetyl alcohol is emulsifying stabilizer and thickening agent. Methly paraben and propyl paraben are cosmetic preservatives. The composition and characteristics of each component are shown in Table 2. By considering ideal 𝑅 𝐻𝐿𝐵 value 10.85 of the oil phase, the emulsions were prepared using MS-01 and MS-02 with HLB values ranging between 8 and 13. The surfactant

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concentration of 3.5 wt.% was fixed. Polyoxyethylene sorbitan monostearate (TWEEN 60, HLB = 14.9) and polyoxyethylene sorbitan monooleate (TWEEN 80, HLB = 15.0) were

quantified as a hydrophilic surfactant. Sorbitan monostearate (SPAN 60, HLB = 4.7) and

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sorbitan monooleate (SPAN 80, HLB = 4.3) were used as a lipophilic surfactant. The mixing ratios and HLB values of Span/Tween surfactants are presented in table 3.

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2.2. Emulsion preparation

The aqueous phase and oil phase were prepared as shown in Table 2 and then heated

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separately to 75℃. Both phases were homogenized for 3 min at 3500 rpm using high-

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speed homogenizer (Homomixer Mark II, T.K. Primix), respectively. The O/W emulsion was prepared by adding drop by drop the oil phase to the obtained continuous aqueous

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phase. The mass fraction of oils in all emulsions obtained was 31.7 wt.%. The ingredient mixture was then homogenized with the same homogenizer operating for 10min at

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5000rpm. All processes were done at room temperature (24±3℃). The prepared emulsions were stored in an oven at 25℃. 2.3. Measurement of emulsion properties

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The droplet size distributions of the emulsions were measured by using a laser light diffraction instrument (Zen 3600, Malvern) with a dual-wavelength detection system. The

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measurements were done 1day after emulsion preparation. Emulsion samples (0.1ml) were diluted in the glass cell filled with distilled water (100 ml). The microscopic observation of emulsions morphology was done using an optical

microscope (KB-320, Optinity) at a magnification of 400⨯. One drop of emulsion were

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put on a glass slide and covered with a cover slip. The microscopic morphology of emulsions was measured 1day and 70days after the emulsion preparation. The electrical charges on emulsion droplets were examined by using a particle electrophoresis instrument (Zetasizer, Zen 3600, Malvern). The emulsion samples were diluted 1:200 using distilled water in an electrophoresis cell that had electrodes at both ends. The measurements were done 1day after emulsion preparation.

All measurement results were an average from five replicates and were measured at room temperature (24±3℃). 2.4. Rheological measurements Rheological behavior and viscoelastic properties of emulsion samples were measured using a rheometer (Physica MCR500) which operates by the Rheoplus software. The temperature was fixed at 25℃ during the measurements with accuracy of ±0.1℃.

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Samples were placed on the measuring plated and left for 5min because of a structure recovery and temperature equilibrium. Flow experiments were realized for shear stress values varying from 0.1 to 100 Pa. The flow curves of shear rates, shear strains and shear

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viscosities were measured. The yield stress values were expressed from a plot of shear

stress as a function of shear strain by the tangent crossover method. Emulsion viscoelastic parameters such as storage modulus ( 𝐺′ ) and loss modulus ( 𝐺′′ ) were

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determined and frequency was fixed to 1rad/s . All measurements were an average from

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three replicates.

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2.5. Thermal stability measurement

The emulsion sample were stored in a glass vial and sealed with a cap. All samples were

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assessed after 3 freeze-thaw cycles (each cycle: -10℃ for 14 h / 90℃ for 10min). After the cycles, a phase separation of emulsion samples was appeared. The creaming index

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was determined from the percentage of the height of the serum layer at the bottom over the height of the total emulsion sample as below [18]: 𝐻

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Creaming index [%] = (𝐻𝑠 ) × 100 𝑇

(3)

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Where 𝐻𝑠 is the height of a serum layer, 𝐻𝑇 is the total height of an emulsion sample.

3. Results and Discussion

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3.1. Measurement of emulsion droplet size Figure 2 shows the droplet size distribution of emulsion samples stabilized by (a) MS-01

surfactant (b) MS-02 surfactant. As shown in Figure 2, the mean droplet size of emulsions increased as MS-01(HLB=10.8) < MS-01 (HLB=11.7) < MS-01 (HLB=12.6) < MS-01 (HLB=9.9) < MS-01 (HLB=9.1) and MS-02 (HLB=10.7) < MS-02 (HLB=11.6) < MS02 (HLB=12.6) < MS-02 (HLB=9.8) < MS-02 (HLB=8.9). For the emulsions containing MS-

01, a minimum droplet size was observed at HLB=10.8. For the other emulsions containing MS-02, a minimum droplet size was observed at HLB=10.7. Both emulsions HLB value was the closest to the ideal rHLB=10.8. Reducing the size of the droplets increases the emulsion stability to gravitational separation, as described by Stokes’ law.

The optical microscopy images displayed in Figure 3 and Figure 4 show that the droplet

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size in O/W emulsions is dependent on HLB value. From the optical images, some large coalesced oil drops and larger droplets were observed after 70day than 1day. This aggregation and flocculation of droplets allows the creation of protective layer for the

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big droplets [19]. The emulsions prepared with MS-01(HLB=9.1) and MS-02 (HLB=8.9) show bigger droplet size and lower uniformity of droplet size than the other emulsions

(Figure 3 & Figure 4). Similarly, the peaks of MS-01(HLB=9.1) and MS-02 (HLB=8.9) are

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separated to two peaks which means the lack of uniformity of droplet size (Figure 2). These results showing that used HLB value of two emulsions is now required in the O/W

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emulsions. The uniformity of droplets prevents creaming as a result of Oswald ripening.

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Moreover, the emulsions prepared with MS-01 showed larger droplet size and more flocculated droplets than the emulsions using MS-02. Despite Both mixed surfactants

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have similar HLB value; the emulsions with MS-02 (Tween80 & Span80) were more stable because of their lipophilic parts containing a double bond, more hydrophilic than a linear

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carbon chain. This result is in accordance with M. Royer et al [20]. 3.2. Rheological characterization understand

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The rheological behavior of O/W emulsions with different HLB was investigated to the

macroscopic

mechanism

of

emulsifying

stability.

Rheological

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measurements of the emulsions were carried out at 25℃. Figure 5 illustrates the influence of HLB value and shear rate on the shear stress of

emulsions using (a)MS-01 and (b)MS-02. The steady shear viscosity as a function of shear rate for the emulsions using (a)MS-01 and (b)MS-02 are illustrated in Figure 6. The shear

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stress increased linearly leading to an increase of the shear rate in Figure 5. In addition, the increase of shear stress was changed little bit steeply according to an increase of the shear rate. In figure 6, the viscosity of emulsions decreased linearly with increasing shear rate showing their shear-thinning behavior. All samples behaved as a non-Newtonian fluid. Shear-thinning behavior is a characteristic for various fluids emulsions, gels and polymer solutions. It is generally considered to be the result of microscale structural

rearrangements within the fluid [21-22]. Figure 6 show the shear viscosity at the given shear which are increased as MS01(HLB=10.8) < MS-01 (HLB=11.7) < MS-01 (HLB=12.6) < MS-01 (HLB=9.9) < MS-01 (HLB=9.1) and MS-02 (HLB=10.7) < MS-02 (HLB=11.6) < MS-02 (HLB=12.6) < MS-02 (HLB=9.8) < MS-02 (HLB=8.9). The viscosity of emulsion increases with the decreasing droplet size in this study. The smaller droplet size the greater the surface area of dispersion for continuous phase. This increases the fluidity of the fluid, thereby increasing

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the viscosity of the fluid. Previous study showed that droplet sizes seem to become important and have influences on the effective viscosity of emulsions [23].

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Figure 7 illustrates the steady shear viscosity as a function of shear stress for emulsions

using (a) MS-01 (b) MS-02. The relationship between shear viscosity and shear stress shows the existence of yield stress. In Figure 7, all emulsions showed considerable

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increase of the viscosity at low shear stress. From this result, the existence of yield stress was proved and also shear-thinning behavior was appeared [24]. The yield stress has

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important roles of structured fluids because it helps stabilizing the material. A higher

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yield stress prevents the phase separation, sedimentation or aggregation of emulsions [25]. From Figure 5~7, MS-01(HLB=10.8) and MS-02 (HLB=10.7) have the highest yield

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stress, which means the greatest stability of emulsions.

The viscoelastic characteristics were investigated to characterize the strength of network structure of the emulsions. Storage modulus (𝐺′) shows the magnitude of energy stored

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in fluid, whereas loss modulus (𝐺′′) defines the energy loss because of viscous dissipation. Therefore, viscous properties of fluid dominated at 𝐺′<𝐺′′ and elastic properties of fluid

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dominated at 𝐺′>𝐺′′.

The storage modulus (𝐺′) and loss modulus (𝐺′′) of the emulsions containing MS-01 and

MS-02 are shown in Figure 8(a) and Figure 8(b), respectively. G’ was presented using filled symbols with color and 𝐺′′ was presented with lines using same color. At low strain

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values, the emulsions showed a typical linear viscoelastic behavior. At medium to high strain values, the non-linear behavior was followed by a yield point and a crossover point was defined. The viscoelastic behavior obtained show that 𝐺′ is greater than 𝐺′′ (viscous liquid-like behavior) in the low strain range and 𝐺′′ is greater than 𝐺′ (solid-like behavior) after the crossover point. The constant value of crossover strain indicates a transition from viscous to elastic behavior.

A significant decrease of 𝐺′ and 𝐺′′ suggests that the network structure of fluid starts rearranging. Beyond a critical value of strain, the transition indicates the destruction of network [19,26]. The crossover strain of the emulsions using MS-01 was shown from 1 to 10rad/s, whereas the emulsions using MS-02 showed the crossover strain above 5 rad/s. The highest shear strain at crossover point was observed in the emulsion using MS-01 with HLB 10.8 and MS-02 with HLB 10.7, respectively. These rheological results indicate than the others. 3.3. Dependence of zeta-potential on HLB value and emulsifier.

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that the stable emulsion need higher shear strain to break down the network structure

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Figure 9 shows the zeta-potential values of the emulsions prepared with MS-01 and MS-02 according to the HLB values. Zeta-potential is the surface electrical property of colloidal particles suspended in a liquid, and indicates the criteria of electrical attraction

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and repulsion at the surface between suspended solids through potential values. The zeta-potential value is large when the particles are stable without agglomeration. When

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the coagulation between particles occurs due to Brownian motion, the stability is lowered

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and the repulsive force between the particles is decreased and the zeta-potential value is decreased [27].

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The highest zeta-potential value was found at an MS-01 (HLB=10.8) and MS-02 (HLB=10.7) in Figure 9. This indicates that the emulsions are stable without

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agglomeration and flocculation. The emulsions with an HLB value above 11 indicated higher zeta-potential values than the emulsions with an HLB value under 10. This result is probably associated with the presence of the polyoxyethylene group. The zeta potential

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value can be increased due to the hydrogen bonds with the OH − groups, hydrogen bonds at the ether-oxygen of the polyoxyethylene chain, with the succeeding oxonium

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formation. Therefore, increasing of the polyoxyethylene group per chain makes the zeta potential value higher. However, as the surface concentration of the chain increases, the ether-oxygen becomes closer to the surface of the emulsion, resulting in shielding and the zeta-potential value decreases due to the crowding effect. In conclusion, if the HLB

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value increases beyond the critical point, the zeta-potential value becomes smaller [28]. 3.4. Stability of emulsions after freeze thawing test The result of creaming index after freeze thawing test of emulsions with MS-01 (Figure10.a) and with MS-02 (Figure10.b) are shown. Several researchers understand the destabilization mechanism of emulsions after the freeze-thawing test [29-30]. The

emulsions were kept at freezing temperature of -10℃ for 14h and thawed at 90℃ for 10min. After cycles, destabilized oil layer was not observed but creamed layer was appeared. Creaming index was measured considering the height of total layer and serum layer as mentioned before. The emulsion with HLB 10.8 showed the lowest creaming index and the other emulsion with HLB 9.1 showed the highest creaming index in Figure 10(a). The graph of Figure 10(b) show that the lowest creaming index at HLB 10.7 and the highest creaming index at HLB 8.9. The creaming index can show the stability of

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emulsion formulation. The droplet size is associated with creaming index. As Stokes’ law, small size of droplets increases the emulsion stability and decreases the creaming index

to gravitational separation [31-33]. As a result, the creaming index measurements are

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consistent with the results obtained from the droplet size measurements.

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4. Conclusion

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This study explored the effect of HLB value on O/W emulsion using mixed nonionic surfactants (Span60/Tween60 & Span80/Tween80). The emulsions are prepared with

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different ratios of surfactant blends, representing various HLB values. We considered

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ideal required HLB value 10.85 and determined corresponding HLB value range from 8 to13. To understand the mechanism and interaction of droplets, the droplet size

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distributions, droplet morphology, rheological properties, zeta-potential and creaming index of the emulsion samples were obtained in O/W emulsion. The minimum droplet size and high uniformity of droplet size were observed in emulsions with MS-01

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(HLB=10.8) and MS-02 (HLB=10.7). All emulsions prepared with MS-01 and MS-02 behaved as a non-Newtonian fluid. The emulsions with MS-01 showed lower shear stress

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than the emulsions with MS-02 at their crossover point. The emulsions with MS-01 (HLB=10.8) and MS-02 (HLB=10.7) showed the highest shear strain at crossover point beyond a critical value of strain. The highest zeta-potential value and the lowest creaming index were observed in the emulsions with MS-01 (HLB=10.8) and MS-02

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(HLB=10.7). In conclusion, the ideal required HLB value of the oil phase is about 10.85 and consequently surfactants with HLB of approximately 10.8 and 10.7 created the most stable formulations in this study. Both mixed surfactants have similar HLB value but emulsions

using MS-02 was more stable. From these results, we found that the HLB value affects the stability of emulsions but also chemical structure of the surfactants can be influential.

Acknowledgement

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The present research was conducted by the research fund of Dankook University in 2016.

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(a) Polyoxyethylene sorbitan monostearate (or Polyoxyethylene sorbitan monooleate)

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(b) Sorbitan monostearate (or Sorbitan monooleate)

Figure 1. Chemical structures of (a) Polyethoxylated sorbitan esters (TWEEN type)

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(b) Sorbitan esters (SPAN type).

(a) MS-01

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HLB = 12.6 HLB = 11.7 HLB = 10.8 HLB = 9.9 HLB = 9.1

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20

0 10

10000

1000

100

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Droplet Size [nm]

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(b) MS-02

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30

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Volume Distribution [%]

40 HLB = 12.6 HLB = 11.6 HLB = 10.7 HLB = 9.8 HLB = 8.9

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Volume Distribution [%]

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0 10

100

1000

10000

Droplet Size [nm]

Figure 2. Droplet size distributions in volume of emulsions at 25℃.

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(a) HLB = 12.6 (after 1day & 70days)

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(b) HLB = 10.8 (after 1day & 70days)

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(c) HLB = 9.1 (after 1day & 70days)

Figure 3. Optical microscope images of emulsion droplets stabilized by MS-01. (Scale bar : 50000nm.)

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(a) HLB = 12.6 (after 1day & 70days)

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(b) HLB = 10.7 (after 1day & 70days)

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PT

ED

(c) HLB = 8.9 (after 1day & 70days)

Figure 4. Optical microscope images of emulsion droplets stabilized by MS-02. (Scale bar : 50000nm)

(a) MS-01

1000

IP T

Shear Stress [Pa]

100

HLB = 12.6 HLB = 11.7 HLB = 10.8 HLB = 9.9 HLB = 9.1

SC R

10

0.1 0.1

1

10

100

-1

Shear Rate [s ]

A

N

(b) MS-02

ED

PT

CC E

Shear Stress [Pa]

100

HLB = 12.6 HLB = 11.6 HLB = 10.7 HLB = 9.8 HLB = 8.9

M

10000

1000

U

1

10

A

1 0.1

1

10

100

-1

Shear Rate [s ]

Figure 5. Shear stress as a function of shear rate for emulsions using (a) MS-01 (b) MS-02 at 25℃.

(a) MS-01

10000

HLB = 12.6 HLB = 11.7 HLB = 10.8 HLB = 9.9 HLB = 9.1

Viscosity [Poise]

1000

IP T

100

10

SC R

1

0.01 0.1

1

10

100

-1

N

Shear Rate [s ]

A

(b) MS-02

10

ED

100

PT

1000

CC E

Viscosity [Poise]

HLB = 12.6 HLB = 11.6 HLB = 10.7 HLB = 9.8 HLB = 8.9

M

100000

10000

U

0.1

1

A

0.1 0.1

1

10

100

-1

Shear Rate [s ]

Figure 6. Steady shear viscosity as a function of shear rate for emulsions using (a) MS-01 (b) MS-02 at 25℃.

(a) MS-01

40

HLB = 12.6 HLB = 11.7 HLB = 10.8 HLB = 9.9 HLB = 9.1

IP T

20

10

0 10

20

30

40

50

N

Shear Stress [Pa]

60

U

0

SC R

Viscosity [Poise]

30

M

A

(b) MS-02

250

ED PT

150

100

CC E

Viscosity [Poise]

200

HLB = 12.6 HLB = 11.6 HLB = 10.7 HLB = 9.8 HLB = 8.9

50

A

0

0

100

200

300

400

500

Shear Stress [Pa]

Figure 7. Steady shear viscosity as a function of shear stress for emulsions using (a) MS-01 (b) MS-02 at 25℃.

(a) MS-01

1000

HLB = 12.6 HLB = 11.7 HLB = 10.8 HLB = 9.9 HLB = 9.1

IP T

10

1

1

10

100

U

0.1 0.1

Strain [%]

A

N

(b) MS-02

M

100000

HLB = 12.6 HLB = 11.6 HLB = 10.7 HLB = 9.8 HLB = 8.9

PT

1000

ED

10000

100

CC E

Modulus [Pa]

SC R

Modulus [Pa]

100

10

A

1 0.1

1

10

100

Strain [%]

Figure 8. Strain amplitude dependence of the storage modulus 𝐺′ (symbols) and loss modulus 𝐺′′ (lines) of emulsions using (a) MS-01 (b) MS-02 at 25℃.

MS-01 MS-02

-45

SC R

-40

-35

U

-30

N

Zeta Potential [mV]

IP T

-50

-20 9

10

11

ED

HLB Value

12

13

M

8

A

-25

14

A

CC E

PT

Figure 9. Dependence of zeta-potential on HLB value in emulsions using MS-01 & MS-02.

(a) MS-01

100

IP T

60

40

20

0 10

11

12

13

U

9

N

HLB Value

A

(b) MS-02

M

100

ED PT

60

CC E

Creaming Index [%]

80

40

SC R

Creaming Index [%]

80

A

20

0

9

10

11

12

13

HLB Value

Figure 10. Creaming index after temperature cycling test of emulsions using (a) MS-01 (b)MS-02 with different HLB values.

Table 1. Physical Properties of Various Nonionic Emulsifiers in this Study

Emulsifier

HLB

Formula

MW [g/mol]

polyoxyethylene sorbitan monostearate (TWEEN 60)

14.9

C64H128O26

1,314

sorbitan monostearate (SPAN 60)

4.7

C24H46O6

430.62

polyoxyethylene sorbitan monooleate (TWEEN 80)

15.0

C64H124O26

1,310

sorbitan monooleate (SPAN 80)

4.3

C24H44O6

428.60

A

CC E

PT

ED

M

A

N

U

SC R

MS-02

IP T

MS-01

Table 2. Specifications of Cosmetic Emulsion in this Study Ingredient Ultrapure water

58

Glycerin

7.0

Butylene glycol

3.0

Humectant, Reduce the viscosity

Methyl paraben

0.3

Antiseptic, Antibacterial effect

Surfactant

3.5

Mixed surfactant

Mineral Oil

20.0

Evaporation blocker

5.0

Evaporation blocker

Cetyl alcohol

3.0

Emulsifying stabilizer, Increase the viscosity

Propyl paraben

0.2

Antiseptic, Antibacterial effect

100.0

ED

IP T

M

Total

Humectant

SC R

myristate

Simple polyol compound, Viscous liquid,

U

Octyldodecyl

Main substance of water phase, Humectant

N

Oil phase

Characteristics

[wt.%]

A

Aqueous phase

Composition

Table 3. Composition and HLB Ratio of Mixed Surfactants in this Study 2.4

2.1

1.8

1.5

SPAN 60 [wt.%]

0.8

1.1

1.4

1.7

2.0

Total HLB

12.6

11.7

10.8

9.9

9.1

TWEEN 80 [wt.%]

2.7

2.4

2.1

1.8

1.5

SPAN 80 [wt.%]

0.8

1.1

1.4

1.7

2.0

Total HLB

12.6

11.6

10.7

9.8

8.9

PT

2.7

CC E

MS-01

TWEEN 60 [wt.%]

A

MS-02