Preparation and Property of Perfluoropolyether Emulsions

polymers

Article Preparation and Property of Perﬂuoropolyether Emulsions

Dianlong Zhang 1, Yiqiang Zhang 2 , Yanyun Bai 2 , Xiumei Tai 2, Wanxu Wang 2 and Guoyong Wang 1,2,*

1 Department of Chemistry, Shanxi Datong University, Datong 037009, China; [email protected] 2 China Research Institute of Daily Chemical Industry, 34 Wenyuan Street, Taiyuan 030001, China; [email protected] (Y.Z.); [email protected] (Y.B.); [email protected] (X.T.); [email protected] (W.W.) * Correspondence: [email protected]; Fax: +86-351-4040802

Received: 4 April 2019; Accepted: 14 May 2019; Published: 29 May 2019

Abstract: Perﬂuoropolyether (PFPE) glycerol emulsions were prepared. Three diﬀerent green surfactants (AES (sodium laureth sulfate), APG (alkyl polyglycoside), and SDS (sodium dodecyl sulfate)) were chosen to emulsify the PFPE. Their properties and performance in shampoo were also investigated. Centrifuge stability measurements show that three PFPE emulsions have good stability. They are stable for 60 min when the centrifugal speed is 6000 r/min. In addition, a change of droplet size was observed with time. Moreover, its rheological properties and application performance was studied. The AES emulsion was the most stable emulsion and it was found to improve the slip and lubricity performance of the cotton, so it has potential applications in shampoo.

Keywords: PFPE; droplet size; Ostwald ripening; application performance

1. Introduction Silicone oil, polymerized siloxane with organic side chains, is one of the most important polymer materials. Silicone oil has attracted much scientific and commercial interest because of its relatively high thermal stability and lubricating properties [1]. As of now, silicone oil is widely used in detergents as a conditioning agent. This is because silicone oil can smooth out scales and reduce the friction of the hair, so that the hair is smooth and easy to comb [1]. However, according to research [2], amino silicone oil shows obvious ecological acute toxicity. At the same time, amino silicone oil is mainly discharged into the environment through the sludge treatment of sewage. Only a small amount of amino silicone oil is discharged into water in the environment, and sediments, along with the waste water and the amino silicone oil, cannot be effectively biodegraded during the anaerobic biochemical treatment of wastewater. Moreover, since silicone oil is insoluble in water, excessive deposition on the scalp may cause hair follicles to clog, affect the health of the scalp and hair, and may even lead to scalp inflammation and hair loss [1]. Thus, developing a new type of material to replace silicone oil will become increasingly important. Perfluoropolyether (PFPE) is another kind of special liquid material. It is colorless, tasteless, no-poisonous, hypo-allergenic, and has excellent handling properties, excellent chemical stability, lower viscosity, and excellent film-forming ability, so it is suitable for application in the field of cosmetics [2–5]. In a conference of the International Federation of Cosmetic Chemists Societies in Barcelona, 1986, PFPE was first accepted as an added ingredient in cosmetics. Its function is that it can form a thin protective film to prevent corrosion from all kinds of injury [6]. Furthermore, PFPE has excellent chemical stability and corrosion resistance [7,8], so adding PFPE to cosmetics can enhance protection for outdoor workers. Moreover, PFPE has a radiation-proof effect. [9] Under the same dose, the viscosity of PFPE increases

Polymers 2019, 11, 932; doi:10.3390/polym11060932 www.mdpi.com/journal/polymers Polymers 2019, 11, 932 2 of 12 very little compared with hydrocarbon and silicon oil after the same radiation. However, because it is oleophobicPolymers 2018 and, 10, hydrophobic, x FOR PEER REVIEW it is very difficult to add PFPE to cosmetics. For PFPE delivery2 of 12 in Polymers 2018, 10, x FOR PEER REVIEW 2 of 12 cosmetics,Polymers emulsions 2018, 10, x FOR have PEER significant REVIEW advantages in terms of cost and safety [10]. 2 of 12 Emulsionradiation. isHowever, a multi-phase becausedispersive it is oleophobic system and to hydrophobic, make oneor it moreis very liquid difficult disperse to add inPFPE another to radiation. However, because it is oleophobic and hydrophobic, it is very difficult to add PFPE to undissolvedcosmetics. liquid For inPFPE the formdelivery of droplets,in cosmetics, where emulsi it isons quite have stable significant [11]. Because advantages PFPE in usuallyterms of appears cost cosmetics. For PFPE delivery in cosmetics, emulsions have significant advantages in terms of cost and safety [10]. as an emulsion,and safety [10]. they are named emulsion or lactescence [12]. The interfacial area of the two liquid phase increasesEmulsion and interfacialis a multi-phase energy dispersive increases system in the newto make system, one or so more the system liquid isdisperse thermodynamically in another Emulsion is a multi-phase dispersive system to make one or more liquid disperse in another undissolved liquid in the form of droplets, where it is quite stable [11]. Because PFPE usually appears unstable.undissolved But the liquid mixing in the of theform emulsifier of droplets, will where decrease it is quite the stable interfacial [11]. Because energy PFPE of the usually system, appears sothe as an emulsion, they are named emulsion or lactescence [12]. The interfacial area of the two liquid systemas will an emulsion, become muchthey are more named stable emulsion [13]. In or the lactes emulsion,cence [12]. the The dispersed interfacial phase area of is the named two disperseliquid phase increases and interfacial energy increases in the new system, so the system is phase increases and interfacial energy increases in the new system, so the system is phasethermodynamically and the unbroken unstable. expanse But is named the mixing dispersant, of the em soulsifier the emulsion will decrease usually the interfacial contains energy three parts:of thermodynamically unstable. But the mixing of the emulsifier will decrease the interfacial energy of dispersant,the system, disperse so the phase, system and will emulsifier become much [14 ].more Emulsions stable [13]. have In the a widespreademulsion, theuse dispersed in personal phase is care the system, so the system will become much more stable [13]. In the emulsion, the dispersed phase is productnamed and cosmeticsdisperse phase to delivery and the nutrients unbroken to theexpanse skin andis named hair [15dispersant,]. The stability so the ofemulsion the emulsion usually [16 ] named disperse phase and the unbroken expanse is named dispersant, so the emulsion usually is an importantcontains three factor parts: affecting dispersant, its application disperse phase, in cosmetics. and emulsifier [14]. Emulsions have a widespread contains three parts: dispersant, disperse phase, and emulsifier [14]. Emulsions have a widespread Inuse the in past personal years, care there product were and researches cosmetics studying to delivery the nutrients PFPE emulsions.to the skin and But hair stability [15]. The is stability too low to use in personal care product and cosmetics to delivery nutrients to the skin and hair [15]. The stability meet theof the requirements emulsion [16] of is practical an important applications. factor affecting Glycerol its application is a commonly-used in cosmetics. additive in cosmetics of the emulsion [16] is an important factor affecting its application in cosmetics. In the past years, there were researches studying the PFPE emulsions. But stability is too low to and glycerinIn the moisturizes past years, the there skin. were We researches chose to emulsifystudying the PFPE PFPE into emulsions. glycerol [But10]. stability We have is too conducted low to a comprehensivemeet the requirements study of the of stability practical of applications. emulsions. Glycerol The emulsion’s is a commonly-used centrifugal additive stability, in cold cosmetics and heat meet the requirements of practical applications. Glycerol is a commonly-used additive in cosmetics and glycerin moisturizes the skin. We chose to emulsify PFPE into glycerol [10]. We have conducted storageand stability, glycerin and moisturizes its particle the skin. size We change chose over to emulsify time were PFPE studied. into glycerol The [10]. rheological We have propertiesconducted of a comprehensive study of the stability of emulsions. The emulsion’s centrifugal stability, cold and the emulsionsa comprehensive were tested. study Comparedof the stability to previousof emulsions. studies, The emulsion’s the emulsions centrifugal we prepared stability, have cold higherand heat storage stability, and its particle size change over time were studied. The rheological properties heat storage stability, and its particle size change over time were studied. The rheological properties stability.of the Finally, emulsions its application were tested. performance Compared to inprevious detergent studies, was the evaluated emulsions [17 we]. prepared have higher of the emulsions were tested. Compared to previous studies, the emulsions we prepared have higher stability. Finally, its application performance in detergent was evaluated [17]. 2. Experimentalstability. Finally, Section its application performance in detergent was evaluated [17]. 2. ExperimentalExperimental SectionSection 2.1. Materials2. Experimental Section Perfluoropolyether2.1. MaterialsMaterials oil (PFPE, kinetic viscosity 40 cSt) was purchased from Shanghai Aiken 2.1. Materials chemical industryPerfluoropolyether Co, Ltd. (Shanghai,oil (PFPE, kinetic China). viscosity Glycerol 40 was cSt) purchasedwas purchased from from Tianjin Shanghai No.2 Chemical Aiken Perfluoropolyether oil (PFPE, kinetic viscosity 40 cSt) was purchased from Shanghai Aiken Reagentchemical Factory industry (Tianjin, Co, China). Ltd. (Shanghai, Sodium China). dodecyl Glycerol sulfate was (SDS) purchased was purchased from Tianjin from No.2 Changzhi Chemical Fatty chemical industry Co, Ltd. (Shanghai, China). Glycerol was purchased from Tianjin No.2 Chemical Acid FactoryReagent (Changzhi,Factory (Tianjin, China). China). Sodium Sodium laureth dodecyl sulfate sulfate（ (AES)SDS） andwas alkyl purchased polyglycoside from Changzhi (APG) Fatty were Reagent Factory (Tianjin, China). Sodium dodecyl sulfate（SDS）was purchased from Changzhi Fatty suppliedAcid by Factory China (Changzhi, Research InstituteChina). Sodium of Daily laureth Chemical sulfate Industry (AES) and (Taiyuan, alkyl polyglycoside China). Structures (APG) were of the Acid Factory (Changzhi, China). Sodium laureth sulfate (AES) and alkyl polyglycoside (APG) were supplied by China Research Institute of Daily Chemical Industry (Taiyuan, China). Structures of the main Materialsupplied by are China listed Research in Table 1Institute. of Daily Chemical Industry (Taiyuan, China). Structures of the main Material are listed in Table 1. main Material are listed in Table 1. Table 1. Structure of the main Material. PFPE: perfluoropolyether; AES: sodium laureth sulfate; APG: Table 1. Structure of the main Material. PFPE: perfluoropolyether; AES: sodium laureth sulfate; APG: alkyl polyglycoside;Table 1. Structure SDS: of the sodium main Material. dodecyl PFPE: sulfate. perfluoropolyether; AES: sodium laureth sulfate; APG: Tablealkyl polyglycoside; 1. Structure of SDS:the main sodium Material. dodecyl PFPE: sulfate. perfluoropolyeth er; AES: sodium laureth sulfate; APG: alkyl polyglycoside; SDS: sodium dodecyl sulfate. Materialalkyl polyglycoside; SDS: sodium dodecyl sulfate. Structure Material Structure Material Structure

PFPEPFPE PFPE

AES AESAES AES

APG APGAPG

SDS SDS SDSSDS

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2.2. Methods and Techniques

2.2.1. Preparation of Emulsions All emulsions were prepared by the high-shear stirring emulsiﬁcation method at room temperature (25 ◦C). Surfactant was used to stabilize the emulsion. In this study, three classic surfactants were used to obtain the emulsion. First, quantitative glycerol was weighed in a beaker. Then the surfactant was added to the beaker and stirred for 5 min. Last, PFPE was added to the beaker at high speed using a high speed homogenizer (model B25, Berthe Mechanical and Electrical Equipment Co., Ltd. Shanghai, China) at 10,000 rpm for 5 min at room temperature. The stability and droplet size were studied. All the emulsions were kept at room temperature for further study [18].

2.2.2. Stability of Emulsions This part contains centrifugal stability and storage stability. The emulsions were added to the centrifuge tube respectively; then we centrifuged the samples at 6000 r/min for 60 min. At the same time, three sealed weighing bottles ﬁlled with the three emulsions were placed into a drying beaker at 40 C and three sealed tubes ﬁlled with the samples were placed into a refrigerator at 10– 15 C. Last, ◦ − − ◦ three samples were saved at the room temperature to observe their stability for one month or more [19].

2.2.3. Droplet Size The droplet sizes of all emulsions were obtained by dynamic laser light scattering (Mastersize 2000, malvern, Worcestershire, United Kingdom) [20,21]. The emulsions were added to a beaker ﬁlled with 500 mL of deionized water until they reached the area of the detection (2 mL emulsion, approximately). we made a graph of the percentage over the distribution of particle size. The particle size was detected once per week.

2.2.4. Transmission Electron Microscopy (TEM) The distribution of particle size and micro structure of the emulsions were observed by the JEM-1011 transmission electron microscope (Joel Co., Osaka, Japan). The samples were diluted 250 times with deionized water. A drop of diluted sample was dropped onto a copper grid. Then the sample was left standing still for 10 min. Next we stained the grid, removed the excess liquid, and dried it overnight at the room temperature. Last, the grid was installed in the TEM operating to observe the sample.

2.2.5. Rheological Property The instrument is HAAKE - RheoWin (RS75, Thermo Scientiﬁc, Massachusetts, USA). We initiated the computer, started the main power, and preheated it for at least 30 min. First setting it to zero, we lifted the plate, taking bits of emulsion onto the plate that had been standing overnight to remove any bubbles. After that we made a graph of the oscillation stress sweep which revealed that the sample will not generate deformation. We used this ﬁgure to do an oscillation frequency sweep. The rheological properties can be analyzed from the graph.

2.2.6. Application Performance The prepared emulsions were added to a shampoo formulation [17]. Shampoo formulation is as follows: trisodium citrate (0.5%), dodecyl betaine (10%), APG (4%), AES (7%), glycerol (1%), PFPE emulsions (0.5%), and deionized water (additional to 100%). Among them, four kinds of shampoos were prepared—blank control (no emulsions), AES-PFPE (AES-PFPE emulsion, 0.5%), APG-PFPE (APG-PFPE emulsion, 0.5%), and SDS–PFPE (SDS–PFPE emulsion, 0.5%).Then the performance of the shampoo was tested. (1) The Slip and Lubricity of the Emulsions Polymers 2019, 11, 932 4 of 12 Polymers 2018, 10, x FOR PEER REVIEW 4 of 12

TheThe slip slip and and lubricity lubricity of emulsions of emulsions is evaluated is evaluated by the friction by the experiment. friction experiment. The friction coeTheffi cientfriction of thecoefficient cotton wasof the measured cotton was by measured an Y151 type by an fiber Y151 friction type fiber coeffi frictioncient measuring coefficient instrument measuring to instrument express theto smoothness express the ofsmoothness the cotton. of Thethe cotton. instrument The instrument consists of consists a torsion of balance a torsion and balance an electronic and an electronic speed controlspeed box. control The torquebox. The balance torque can balance measure can the measure friction the between friction the between cotton andthe cotton the roller and mandrel the roller (whichmandrel is connected (which is to connected the electronic to the speed electronic control sp boxeed and control can be box adjusted and can by be the adjusted speed control by the box). speed Firstcontrol we measured box). First the we friction measured coeffi thecient friction of the coeffici wire, thenent immersedof the wire, it inthen the immersed tested solution it in the for tested 4 h, tooksolution it out andfor 4 dried h, took it atit out 40 °C andfor dried 1 h, andit at finally40 ℃ formeasured 1 h, and the finally friction measured coefficient the friction after treatment. coefficient Weafter queried treatment. the coe Wefficient queried of friction the coefficient and converted of friction it to and the coeconvertedfficient ofit to friction. the coefficient of friction. (2) Determination of Detergency 2)Determination of Detergency A whiteness meter and decontamination machine (WSD-3C) was used to test the detergency. Three kindsA whiteness of soiled clothesmeter and with decontamination carbon black, protein, machine and sebum(WSD-3C) were was used used in the to test. test Thethe whitenessdetergency. valueThree of thekinds stained of soiled clothes clothes was measured with carbon before black, cleaning protein, them withand foursebum kinds were of detergentsused in the prepared. test. The Afterwhiteness drying, thevalue whiteness of the stained value was clothes measured was againmeasur anded comparedbefore cleaning with the them previous with valuefour kinds to get of a comparisondetergents prepared. of detergency After performances drying, the whiteness of four detergents. value was measured In this part again the fourand compared detergents with were the dissolvedprevious in value 250 ppm to get hard a comparison water (1 g/L). of detergency performances of four detergents. In this part the four detergents were dissolved in 250 ppm hard water (1 g/L). (3) Foam Performance 3)Foam Performance Foam performance was measured by a foam instrument by the way of a modified Ross–Miles Foam performance was measured by a foam instrument by the way of a modified Ross–Miles method. The four detergents were dissolved in 250 ppm hard water (1 g/L) and stored in 50 ◦C. Then the volume of the foam in 30 s, 3 m, and 5 m was recorded.

3. Results and Discussion The emulsion was prepared by high-shear stirring at 10,000 r/min. Six grams of perfluoropolyether was dissolved in 24 g of glycerol in the presence of 0.6 g SDS (2% of the total mass). Then they were emulsified for 5 min. The other two emulsions with different surfactants were also prepared by the same way.

3.1. Stability of the Emulsions with Diﬀerent Surfactants The stability of the emulsion is an important factor in evaluating the emulsion. The following is an experiment to determine the emulsions’ stability. Three surfactants (AES, APG, and SDS) were used to emulsify the PFPE. They had excellent centrifugal properties. In Figure1d, when they were centrifuged at 6000 r /min for 60 min, they were still stable. But when the centrifugal speed was 7000 r/min, the SDS emulsion was stable; the AES and APG emulsions generated a bit of sediment. Compared with the standard [19] (centrifuged at 4000 r/min) their centrifugal property improved a lot.

Figure 1. Cont. Polymers 2018, 10, x FOR PEER REVIEW 5 of 12 Polymers 2019, 11, 932 5 of 12 Polymers 2018, 10, x FOR PEER REVIEW 5 of 12

Figure 1. Stability of the emulsions, a: stored at room temperature; b: stored at 40 °C for 24 h; c: stored at −10–−15 °C; d: centrifugal stability. FigureFigure 1. Stability 1. Stability of the of emulsions,the emulsions,a: stored a: stored at room at room temperature; temperature;b: stored b: stored at 40 at◦C 40 for °C 24 for h; 24c: h; stored c: stored at 10– 15 C; d: centrifugal stability. −at Then−−10–−◦ 15they °C; wered: centrifugal subjected stability. to an aging test. Referring to national standards (GB/T 11543-2008), firstly, three sealed weighing bottles filled with three emulsions were placed into a drying beaker at Then they were subjected to an aging test. Referring to national standards (GB/T 11543-2008), 40 oThenC for they24 h. wereSecondly, subjected three to sealed an aging tubes test. filled Referring with the to samples national were standards placed (GB/Tinto a 11543-2008),refrigerator at firstly, three sealed weighing bottles filled with three emulsions were placed into a drying beaker at firstly,−10–− three15 oC sealedfor 24 weighingh. Last, three bottles samples filled werewith thsavedree emulsions at room temperature were placed for into 2 amonths. drying Thebeaker results at 40 C foro 24 h. Secondly, three sealed tubes filled with the samples were placed into a refrigerator at ◦40are C shownfor 24 h. separately Secondly, in three Figure sealed 1 a–c. tubes Through filled thewith above the samples three experiments, were placed these into samplesa refrigerator were stillat 10– 15 Co for 24 h. Last, three samples were saved at room temperature for 2 months. The results − −10–−stable—ivory−◦15 C for 24 liquid. h. Last, It proved three samples that the wereemulsion saved conformed at room temperature to the standard for of2 months.the storage The stability. results are shown separately in Figure1a–c. Through the above three experiments, these samples were still are shownThe stabilityseparately of inthe Figure emulsion 1 a–c. was Through measured the abovemacroscopically. three experiments, Next we these will observesamples the were stability still stable—ivory liquid. It proved that the emulsion conformed to the standard of the storage stability. stable—ivoryof the emulsion liquid. from It proveda microscopic that the point emulsion of view. conformed to the standard of the storage stability. TheThe stability stability of the of emulsionthe emulsion was measuredwas measured macroscopically. macroscopically. Next weNext will we observe will observe the stability the stability of the emulsionof3.2. the Meanemulsion from Droplet a from microscopic Size a microscopicand Stability point ofpointof view.Emulsion of view. 3.2. Mean DropletFigure 2 Size depicts and Stability different of emulsions’ Emulsion particle size over time. The change of emulsion particle size 3.2. Mean Droplet Size and Stability of Emulsion can reflect the stability of the emulsion. As we can see from Figure 2a–c, the particle size of three Figure2 depicts di fferent emulsions’ particle size over time. The change of emulsion particle emulsionsFigure 2 was depicts 0.03–1 different μm, which emulsions’ indicates particle the emulsion’ssize over time. uniformity The change is good. of emulsion As time particle went on, size the size can reflect the stability of the emulsion. As we can see from Figure2a–c, the particle size of three canpeak reflect width the became stability wider, of the whichemulsion. means As wethe candroplet see fromsize wasFigure getting 2a–c, bigger. the particle However, size ofthe three three emulsions was 0.03–1 µm, which indicates the emulsion’s uniformity is good. As time went on, the emulsionsfigures have was undergone0.03–1 μm, inconspicuouswhich indicates changes, the emulsion’s indicating uniformity that the particleis good. sizeAs timewas wentstable on, and the the peak width became wider, which means the droplet size was getting bigger. However, the three figures peakstability width of became the emulsions wider, waswhich good. means Moreover, the droplet in Fi guresize was2a, the ge ttinglaw ofbigger. change However, is just the the opposite, three have undergone inconspicuous changes, indicating that the particle size was stable and the stability of figuresindicating have thatundergone the droplet inconspicuous size of AES changes,is smalle rindica after tingone month.that the The particle mech sizeanism was still stable needs and further the the emulsions was good. Moreover, in Figure2a, the law of change is just the opposite, indicating that stabilitystudy. of the emulsions was good. Moreover, in Figure 2a, the law of change is just the opposite, the droplet size of AES is smaller after one month. The mechanism still needs further study. indicating that the droplet size of AES is smaller after one month. The mechanism still needs further

study. a 1d b 1d 2w 2w a 1d 4w b 1d 4w 2w 2w

4w 4w

Volume Fraction (%) Fraction Volume Volume Fraction (%) 0.1 1 10 0.1 1 10 Particle Size (μm) Particle Size (μm) Volume Fraction (%) Fraction Volume Volume Fraction (%) 0.1 1 10 0.1 1 10 Particle Size (μm) Figure 2. Cont. μm Particle Size ( )

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c 1d c 1d 2w 2w 4w 4w

Volume Fraction (%) Fraction Volume 0.1 1 10 Volume Fraction (%) Fraction Volume 0.1 1μm 10 Particle Sizeμm ( ) Particle Size ( ) FigureFigure 2.2. TheThe distributiondistribution ofof didifferentfferent emulsion’s emulsion’s particle particle size size over over time: time:a a:: AES,AES, bb:: APG,APG, cc:: SDS.SDS. Figure 2. The distribution of different emulsion’s particle size over time: a: AES, b: APG, c: SDS. InIn Figure Figure3, the 3, the mean mean droplet droplet size size of APGof APG and and SDS SDS emulsions emulsions continued continued to grow.to grow. It proved It proved that that In Figure 3, the mean droplet size of APG and SDS emulsions continued to grow. It proved that thethe droplet droplet size size tends tends to getting to getting bigger. bigger. The oil The/water oil/ interfacewater interface provisionally provisionally created bycreated the high by energythe high the droplet size tends to getting bigger. The oil/water interface provisionally created by the high inputenergy may input not be may fully not covered be fully with covered surfactant with molecules, surfactant so molecules, small droplets so small tend droplets to dissolve tend into to largerdissolve energy input may not be fully covered with surfactant molecules, so small droplets tend to dissolve onesinto to larger reduce ones the oilto /reducewater interface the oil/water area overinterface time. area However, over time. once However, the systems once reach the equilibriumsystems reach into larger ones to reduce the oil/water interface area over time. However, once the systems reach andequilibrium oil droplets and are oil tightly droplets encircled are tightly by surfactantencircled by molecules, surfactant the molecules, increase the in droplet increase size in droplet tends to size equilibrium and oil droplets are tightly encircled by surfactant molecules, the increase in droplet size slow.tends This to processslow. This could process also becould explained also be by explained the classical by the disperse classical system disperse instability system theory: instability Ostwald theory: tends to slow. This process could also be explained by the classical disperse system instability theory: ripening.Ostwald According ripening. toAccording this theory, to this smaller theory, drops smaller have drops higher have chemical higher potential, chemical and potential, larger dropletsand larger Ostwald ripening. According to this theory, smaller drops have higher chemical potential, and larger willdroplets grow at will the grow cost ofat thethe smallercost of the ones smaller to reduce ones the to reduce potential the energy potential ofthe energy whole of systemthe whole [22 system–26]. droplets will grow at the cost of the smaller ones to reduce the potential energy of the whole system Asma[22–27]. Chebil Asma et al. Chebil have reportedet al. have similar reported results similar [26]. results The droplet [27]. growthThe droplet rate (growthω) can berate calculated (ω) can be [22–27]. Asma Chebil et al. have reported similar results [27]. The droplet growth rate (ω) can be usingcalculated the following using the equation following [25, 26equation]: [25–27]: calculated using the following equation [25–27]: 32 32dr38 DC∞ V γ 2 ω ==cmdrc 8DCγ Vmγ drcm= 8 DC=∞ V ∞ (1) ω ==ω dt9 RT (1) (1) dtdt 9 RT 9RT where ω is the ripening rate, C∞ is the solubility of the dispersed phase at the planar interface, rc is where ωω isis thethe ripeningripening rate, rate, C C∞is is the the solubility solubility of of the the dispersed dispersed phase phase at theat the planar planar interface, interface,rc is r thec is the number average radius ∞of the particles at a given time, Vm is the molar volume of the dispersed thenumber number average average radius radius of the ofparticles the particles at a givenat a given time, time,Vm is V them is molar the molar volume volume of the of dispersed the dispersed phase phase material, D is the translational diffusion coefficient of the dissolved dispersed phase in the phasematerial, material,D is the D translational is the translational diffusion diffusion coefficient co ofefficient the dissolved of the dissolved dispersed phasedispersed in the phase continuous in the continuous phase, γ is the interfacial tension between the dispersed and the continuous phases, ρ is continuousphase, γ is the phase, interfacial γ is the tension interfacial between tension the dispersedbetween the and dispersed the continuous and the phases, continuousρ is the phases, density ρ ofis the density of the oil (kg/m3), R is the universal gas constant, and T is the absolute temperature. the density oil (kg/m of3 ),the R isoil the (kg/m universal3), R is gasthe constant,universal andgas Tconstant, is the absolute and T is temperature. the absolute temperature.

0.7 0.7 AES 24 AES a AES 24 b AES a APG b APG 0.6 APG SDS 20 APG SDS 20 ) 0.6) SDS SDS 3 ) ) 3 16 nm μm

0.5 16 7

nm μm

0.5 7 12 12 (*10

0.4 3 (*10 r D[0.5]( 0.4 3 8 r D[0.5]( 8 0.3 0.3 1h 1w 2w 3w 4w 0 6 12 18 24 1h 1w 2w 3w 4w 0 6 125 18 24 time time(*105 s) time time(*10 s) Figure 3. (a) the comparison of the mean droplet size of three emulsions over time; (b) the fitting curve Figure 3. (a) the comparison of the mean droplet size of three emulsions over time; (b) the fitting curve Figureof the mean 3. (a) the droplet comparison size over of time. the mean droplet size of three emulsions over time; (b) the fitting curve of the mean droplet size over time. of the mean droplet size over time. Mean droplet size is the most representative point. Figure2 shows the mean droplet size and its Mean droplet size is the most representative point. Figure 2 shows the mean droplet size and its fittingMean curve. droplet Some size specific is the data most of representative the fitting curve point. is listed Figure in Table2 shows2. the mean droplet size and its fitting curve. Some specific data of the fitting curve is listed in Table 2. fitting curve. Some specific data of the fitting curve is listed in Table 2.

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Table 2. Ostwald Ripening Rate (ω) of the Emulsions.

AES APG SDS Polymers 2019ω(*10, 11,2nm 932 3/s) -6.51032 7.19765 9.76552 7 of 12 R 0.72454 0.67792 0.81203

Table 2. Ostwald Ripening Rate (ω) of the Emulsions. Figure 3b indicated that, there were good correlations between r3 and time, proving that Ostwald ripening is the main reason that causesAES the instability. The APG Ostwald ripening SDS rate (ω) was obtained from the slope of every fitting curve in Table 2 [26]. From the ω, the APG emulsion is better than the ω (*102nm3/s) 6.51032 7.19765 9.76552 − SDS emulsion. SmallerR ω represents more 0.72454 stable emulsions. 0.67792 The change of 0.81203the AES still need further study.

3 3.3. TEMFigure of3 theb indicated Emulsions that, there were good correlations between r and time, proving that Ostwald ripening is the main reason that causes the instability. The Ostwald ripening rate (ω) was obtained fromFigure the slope 4 is of TEM every of ﬁttingthree curveemulsions. in Table From2[ 26the]. TEM From image, the ω, thewe APGcan more emulsion intuitively is better feel than the themicrostructure SDS emulsion. and Smallerchange ofω particrepresentsle size more of the stable emulsion emulsions. droplets. The change of the AES still need furtherAs study.time passed, the microstructure of APG and SDS emulsions changed. As we can see in the Figure 4, small droplets began to gather because of the effect of Ostwald ripening. In the SDS 3.3.emulsion TEM of(Figure the Emulsions 4f), the particle size is bigger than it in the APG emulsion (Figure 4d). But in Figure 4a,b,Figure the particle4 is TEM size ofchanged three emulsions.a little. In the From figure, the there TEM are image, still many we can emul moresion intuitivelyparticles with feel small the microstructureparticle size, and and there change is no of large-scale particle size particle of the polymerization emulsion droplets. phenomenon. It proved that the order of the stability is AES ＞ APG ＞ SDS.

Figure 4. Cont.

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Polymers 2019, 11, 932 8 of 12 Polymers 2018, 10, x FOR PEER REVIEW 8 of 12

Figure 4. a, c, and e are the AES, APG, and SDS emulsions’ TEM images after one hour. b, d, and f are the AES, APG, and SDS emulsions’ TEM images after 3 weeks.

3.4. Rheological Properties The rheological properties of the emulsion will affect its performance in applications. Figure 5 shows the viscoelasticity and viscosity as a function of shear rate of three emulsions. In AES, as viscosity decreased with increasing shear frequency, it proved that the AES emulsion Figure 4. a, c, and e are the AES, APG, and SDS emulsions’ TEM images after one hour. b, d, and f are is pseudoplasticFigure 4. a, c, and colloids. e are the The AES, visc APG,osity and of SDS the emulsi pseudoplasticons’ TEM imagescolloids after decreases one hour. with b, d , theand increasef are of the AES, APG, and SDS emulsions’ TEM images after 3 weeks. the theshear AES, rate APG, because and SDS of emulsionthe presences’ TEM of images floccul afteration 3 weeks.and demagnetization in the dispersion. Under theAs action time of passed, shear, thethe microstructureflocculation is damaged, of APG and ma SDSking emulsions the system changed. into a mobile As we state. can see Therefore, in the Figure3.4.increasing Rheological4, small the droplets Propertiesshear rate began and to destroying gather because the ofcolloidal the e ff ectstructure of Ostwald can result ripening. in a Indecrease the SDS in emulsion viscosity. (FigureIn APGThe4f), rheologicaland the SDS particle emulsions, properties size is bigger the of viscosity the than emulsion it had in the no will APG significant affect emulsion its changes performance (Figure over4d). frequency,in But applications. in Figure proving4a,b, Figure that the 5its particleshowsviscosity the size viscoelasticityremained changed astable. little. and In In viscosity addition, the figure, as thea there fu viscositynction are stillof ofshear many AES rate emulsion of three particlesis emulsions. larger withthan smallthe viscosity particle of size,the andInothers. AES, there Accordingas is viscosity no large-scale to decreased the Stokes particle with formula, polymerization increasing the higher shear phenomenon. the frequency, viscosity, it the Itproved proved slower that that the the phase the AES order separation.emulsion of the stabilityisThe pseudoplastic viscosity is AES of> colloids. APGemulsion> SDS. The is related viscosity to its of stability.the pseudoplastic So the AES colloids emulsion decreases is more stablewith the than increase the others. of the shearIn Figurerate because 5a–c, G’of theand presence G’’ had ofan floccul intersection.ation and In demagnetization0.01–5 Hz, the G’’ in of the the dispersion. emulsions Under are all 3.4. Rheological Properties thegreater action than of shear, G’, showing the flocculation that the liquid-like is damaged, viscosity making is dominant. the system In into5–12 a Hz, mobile the G’ state. of the Therefore, emulsions increasingareThe all greater rheological the shear than propertiesrateG’’, andshowing destroying of theelasticity emulsion the predomicolloidal will anating. ffstructureect its It performance shows can result that inthe in a applications. emulsiondecrease inwe viscosity. Figure prepared5 showsInwas APG a the viscoelasticand viscoelasticity SDS emulsions, system and based the viscosity viscosity on stic askiness ahad function no and significant emulsion of shear changes rate fluidity of three over was emulsions. frequency,good. proving that its viscosity remained stable. In addition, the viscosity of AES emulsion is larger than the viscosity of the others. Accordinga to the Stokes formula, the higher the viscosity, the slower the phase separation. The viscosity of emulsion is related to its stability. So the AES emulsionb is more stable than the others. 100 In Figure 5a–c, G’ G'and G’’ had an intersection. In 0.01–5100 Hz, the G’’ ofG' the emulsions are all greater than G’, showing G'' that the liquid-like viscosity is dominant. In 5–12 Hz, G'' the G’ of the emulsions

are all greater than G’’, showing elasticity predominating. It shows that the emulsion we prepared 10 was a viscoelastic system based on stickiness and emulsion10 fluidity was good.

G' G''(Pa) G' G''(Pa) 1a Polymers 2018, 10, x FOR PEER REVIEW 1 b 9 of 12 0.1 1 10 0.1 1 10 100 G' f (Hz) 100 G' f (Hz) G'' G'' 1000 c 2.4 AES 10 d 10 APG SDS G' G''(Pa) 100 G' G' G''(Pa) 2.1 ) G'' a 1

1 1.8 0.1 1 10 0.1 1 10 10 f (Hz) f (Hz) η(Pas) G'G''(P 1.5

1 0.1 1 10 0.1 1 10 f (Hz) f (Hz) FigureFigure 5. The 5. The viscoelasticity viscoelasticity and viscosityand viscosity as a function as a func oftion shear ofrate shear of threerate of emulsions three emulsionsa: AES, b a:: APG,AES, b: c: SDS,APG,d :c the: SDS, viscosity d: the viscosity of three emulsions. of three emulsions.

3.5. Application in Shampoo of the Emulsions

In practical application, many factors of a product will affect consumers’ purchasing choices, for example, safety parameters, sensorial parameters, foam quality parameters, and cleaning parameters. The basic function of shampoo is cleaning. Due to the limitation of experimental conditions, this paper studied the application performance of the product from the following three aspects.

3.5.1. The Slip and Lubricity of the Emulsions The slip and lubricity of emulsions was evaluated by the friction experiment. The improvement of fabric softness by emulsion was measured by the friction coefficient. The cotton’s friction coefficient was measured before and after treatment to get a conclusion that whether the emulsions affect the slip and lubricity of the cotton. Friction coefficients of cotton after processing by emulsions were listed in Table 3.

Table 3. Friction coefficient of cotton after processing by emulsions.

Friction Coefficient

1 2 3 4 5 Average Before treatment 0.6886 0.9233 0.5835 0.7208 1.0672 AES - After processing 0.5046 0.7331 0.3833 0.5205 0.5835 PFPE Rate of decline (%) 26.72 20.6 34.31 25.94 45.32 30.58 Before treatment 0.6751 0.5373 0.5737 0.555 0.5288 APG - After processing 0.604 0.5046 0.4894 0.5288 0.6621 PFPE Rate of decline (%) 10.53 6.09 14.69 4.72 -25.21 9.01 Before treatment 0.626 0.5288 0.5205 0.6148 0.626 SDS - After processing 0.5205 0.5288 0.3388 0.4351 0.4969 PFPE Rate of decline (%) 16.9 0 34.91 29.23 20.62 25.42

In this Table 3, the AES-PFPE emulsion’s effect on the smoothness of the cotton is the most obvious. The difference between before and after is as high as 45%, meaning that the cotton’s friction coefficient was improved a lot after treatment by AES-PFPE emulsion. In Table 4, the cotton’s friction coefficient was measured after treatment by water and a diluted AES–PFPE emulsion. It proved that the water has no effect on the change of the friction coefficient. The diluted emulsion can reduce the cotton’s friction coefficient and improve the slip and lubricity of the cotton.

Table 4. Friction coefficient of cotton after processing by diluted AES-PFPE emulsion.

Polymers 2019, 11, 932 9 of 12

In AES, as viscosity decreased with increasing shear frequency, it proved that the AES emulsion is pseudoplastic colloids. The viscosity of the pseudoplastic colloids decreases with the increase of the shear rate because of the presence of flocculation and demagnetization in the dispersion. Under the action of shear, the flocculation is damaged, making the system into a mobile state. Therefore, increasing the shear rate and destroying the colloidal structure can result in a decrease in viscosity. In APG and SDS emulsions, the viscosity had no significant changes over frequency, proving that its viscosity remained stable. In addition, the viscosity of AES emulsion is larger than the viscosity of the others. According to the Stokes formula, the higher the viscosity, the slower the phase separation. The viscosity of emulsion is related to its stability. So the AES emulsion is more stable than the others. In Figure5a–c, G’ and G” had an intersection. In 0.01–5 Hz, the G” of the emulsions are all greater than G’, showing that the liquid-like viscosity is dominant. In 5–12 Hz, the G’ of the emulsions are all greater than G”, showing elasticity predominating. It shows that the emulsion we prepared was a viscoelastic system based on stickiness and emulsion fluidity was good.

3.5. Application in Shampoo of the Emulsions In practical application, many factors of a product will aﬀect consumers’ purchasing choices, for example, safety parameters, sensorial parameters, foam quality parameters, and cleaning parameters. The basic function of shampoo is cleaning. Due to the limitation of experimental conditions, this paper studied the application performance of the product from the following three aspects.

3.5.1. The Slip and Lubricity of the Emulsions The slip and lubricity of emulsions was evaluated by the friction experiment. The improvement of fabric softness by emulsion was measured by the friction coefficient. The cotton’s friction coefficient was measured before and after treatment to get a conclusion that whether the emulsions affect the slip and lubricity of the cotton. Friction coefficients of cotton after processing by emulsions were listed in Table3.

Table 3. Friction coeﬃcient of cotton after processing by emulsions.

Friction Coeﬃcient 1 2 3 4 5 Average Before treatment 0.6886 0.9233 0.5835 0.7208 1.0672 AES-PFPE After processing 0.5046 0.7331 0.3833 0.5205 0.5835 Rate of decline (%) 26.72 20.6 34.31 25.94 45.32 30.58 Before treatment 0.6751 0.5373 0.5737 0.555 0.5288 APG-PFPE After processing 0.604 0.5046 0.4894 0.5288 0.6621 Rate of decline (%) 10.53 6.09 14.69 4.72 25.21 9.01 − Before treatment 0.626 0.5288 0.5205 0.6148 0.626 SDS-PFPE After processing 0.5205 0.5288 0.3388 0.4351 0.4969 Rate of decline (%) 16.9 0 34.91 29.23 20.62 25.42

In this Table3, the AES-PFPE emulsion’s e ffect on the smoothness of the cotton is the most obvious. The difference between before and after is as high as 45%, meaning that the cotton’s friction coefficient was improved a lot after treatment by AES-PFPE emulsion. In Table4, the cotton’s friction coe fficient was measured after treatment by water and a diluted AES–PFPE emulsion. It proved that the water has no effect on the change of the friction coefficient. The diluted emulsion can reduce the cotton’s friction coefficient and improve the slip and lubricity of the cotton. Polymers 2019, 11, 932 10 of 12

Table 4. Friction coeﬃcient of cotton after processing by diluted AES-PFPE emulsion.

Friction Coeﬃcient 1 2 3 4 5 Average Before treatment 0.1818 0.1574 0.2021 0.1627 0.2144 water After processing 0.1875 0.1627 0.2113 0.1627 0.2113 Rate of decline (%) 0 0 0 0 0 0 Before treatment 0.1904 0.1734 0.1707 0.1904 0.2021 10% After processing 0.1734 0.1574 0.1548 0.1762 0.1680 Rate of decline (%) 8.93 9.23 9.31 7.46 16.87 10.36 Before treatment 0.2021 0.1707 0.1992 0.1653 0.2144 30% After processing 0.1627 0.1653 0.1818 0.1734 0.1600 Rate of decline (%) 19.5 3.16 8.73 0 25.37 14.19 Before treatment 0.1790 0.1846 0.1707 0.1962 0.1600 60% After processing 0.1790 0.1653 0.1992 0.1790 0.1421 Rate of decline (%) 0 10.46 0 8.77 11.19 10.14

3.5.2. Effect of the Emulsions on the Detergency of Different Shampoo Perfluoropolyether (PFPE) is another kind of special liquid material. It is colorless, tasteless, no-poisonous, hypo-allergenic, and has excellent handling properties, excellent chemical stability, lower viscosity, and excellent film-forming ability, so it is suitable for application in the field of cosmetics. Because of the emulsions’ good dispersion in water, emulsions were added to the shampoo to test its application performance. The shampoo formulation was as follows: trisodium citrate (0.5%), dodecyl betaine (10%), APG (4%), AES (7%), glycerol (1%), and deionized water (additional to 100%). Among them, four kinds of detergent were prepared—blank control (no emulsions), AES-PFEP (AES-PFPE emulsion, 0.5%), APG-PFPE (APG-PFPE emulsion, 0.5%), and SDS-PFPE (SDS-PFPE emulsion, 0.5%). Decontamination ability is an important symbol to evaluate the quality of shampoo. The most basic function of shampoo is cleaning. It can remove excess grease and dirt from the scalp.

whiteness of sample Decontamination Index = (2) whiteness of standard In Table5, the decontamination index was close to 1.00, indicating the addition of the emulsions did not affect the detergency of the shampoo. Among them, the addition of the AES-PFPE emulsion had a promoting effect in removing protein. In general, the addition of three emulsions did not affect the detergency performance of the shampoo itself. In addition, three emulsions had no obvious difference in detergency performance.

Table 5. Decontamination index of various emulsions.

Average C1 P1 S1 C2 P2 S2 CPS AES-PFPE 0.966 0.963 1.110 0.992 1.090 0.891 0.979 1.0265 1.0005 APG-PFPE 0.995 1.019 0.956 1.006 0.973 0.931 1.0005 0.996 0.9435 SDS-PFPE 0.971 0.977 1.016 1.037 1.027 0.920 1.0004 1.002 0.968 (C:carbon, P:protein, S:sebum).

3.5.3. Effect of the Emulsions on the Foam Performance of Different Shampoo The foam ability of shampoo is the most sensitive choice indicator for consumers, so we explored whether the addition of the emulsion will affect the foaming performance of shampoo. In Table6, the foam volume of the three samples was comparable to the blank sample, indicating that the addition of Polymers 2019, 11, 932 11 of 12 three emulsions did not affect the foam performance of the shampoo. Moreover, the foam performance and stability was better when we added the SDS-PFPE emulsion to the shampoo.

Table 6. Foam property test of emulsions with various surfactants.

Volume Blank Control AES-PFPE APG-PFPE SDS-PFPE (mL) 1# 2# 1# 2# 1# 2# 1# 2# 30s 340 330 320 320 330 310 330 340 3m 325 310 320 308 316 310 320 330 5m 315 310 310 298 315 305 320 330

4. Conclusions In this paper, perfluoropolyether oil was successfully emulsified and added into a shampoo formulation, and its performance was tested. The emulsions prepared with the three surfactants we chose have respective advantages. In the centrifugal property, the SDS emulsion is the best, and the storage stability of the three emulsions has reached the national standard. We drew a conclusion that the main mechanism for instability was Ostwald ripening by analyzing the mean droplet size over time. The Ostwald ripening rates of the three emulsions were different. AES is the slowest, followed by APG, and finally SDS. Through analysis of their rheological properties, three kinds of emulsions can be said to be shear thinning fluids as they meet the requirements for application. Compared to previous work, these emulsions are more stable. The diluted AES-PFPE emulsion can improve the slip and lubricity performance of cotton. In the actual formulation system, the addition of three emulsions will not affect the shampoo’s detergency and foam performance. In certain aspects, the improved detergent has a better performance. For example, SDS-PFPE emulsion has better centrifugal stability and the detergent with added SDS-emulsion has better foaming performance and foam stability. The AES emulsion is the most stable emulsion and its detergency is the best among them. In general, AES emulsions have the best performance in three emulsions.

Author Contributions: Conceptualization, G.W.; Formal analysis, Y.Z. and Y.B.; Investigation, Y.Z. and D.Z.; Methodology, D.Z. and G.W.; Resources, D.Z., X.T., W.W. and G.W.; Software, Y.Z. and Y.B.; Writing—original draft, Y.Z.; Writing—review and editing, G.W. Acknowledgments: This work was supported by (the National Key R & D plan) under (Grant No. 2017YFB0308704) and (National Natural Science Found of China) under (Grant No 21872088). Conﬂicts of Interest: The authors declare that they have no competing interests.

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