Cloud Point and LiquidâLiquid Equilibrium Behavior of

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Cloud Point and Liquid-Liquid Equilibrium Behavior of ThermoSensitive Polymer L61 and Salt Aqueous Two-Phase System Wenwei Rao, Yun Wang, Juan Han, Lei Wang, Tong Chen, Yan Liu, and Liang Ni J. Phys. Chem. B, Just Accepted Manuscript • DOI: 10.1021/acs.jpcb.5b03201 • Publication Date (Web): 27 May 2015 Downloaded from http://pubs.acs.org on June 2, 2015

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The Journal of Physical Chemistry

Cloud Point and Liquid-Liquid Equilibrium Behavior of Thermo-Sensitive Polymer L61 and Salt Aqueous Two-Phase System

Wenwei Rao†, Yun Wang*, †, Juan Han*, ‡, Lei Wang†, Tong Chen§, Yan Liu†, Liang Ni†

†

School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang,

212013, PR China ‡

School of Food and Biological Engineering, Jiangsu University, Zhenjiang, 212013,

PR China §

Zhenjiang Entry-exit Inspection Quarantine Bureau, State Key Laboratory of Food

Additive and Condiment Testing, Zhenjiang, 212013, PR China

* Corresponding author: Tel: +86-0511-88790683 Fax: +86-0511-88791800 Email address: [email protected]；

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ACS Paragon Plus Environment


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Abstract The cloud point of thermo-sensitive triblock polymer L61, poly (ethylene oxide)-poly (propylene oxide)-poly (ethylene oxide) (PEO-PPO-PEO), was determined in the presence of various electrolytes (K2HPO4, (NH4)3C6H5O7 and K3C6H5O7). The cloud point of L61 was lowered by the addition of electrolytes and the cloud point of L61 decreased linearly with increasing electrolytes concentration. The efficacy of electrolytes on reducing cloud point followed the order: K3C6H5O7 > (NH4)3C6H5O7 > K2HPO4. With the increase of salt concentration, aqueous two-phase systems exhibited a phase inversion. In addition, increasing the temperature reduced the concentration of salt needed that could promote phase inversion. The phase diagrams and liquid-liquid equilibrium data of the L61-K2HPO4/ (NH4)3C6H5O7/ K3C6H5O7 aqueous two-phase systems (before the phase inversion but also after phase inversion) were determined at T = (25, 30 and 35) oC. Phase diagrams of aqueous two-phase systems were fitted to a four parameter empirical non-linear expression. Moreover, the slopes of the tie-lines and the area of two-phase region in the diagram have a tendency to rise with increasing temperature. The capacity of different salts to induce aqueous two-phase system formation was the same order with the ability of salts to reduce the cloud point.

Introduction Aqueous two-phase system (ATPS) was firstly used to separate chlorophyll successfully by Albertsson1 and his colleagues in 1956s, after that it has regarded as a

2


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new biological separation technology which was widely used for separation and purification of biological materials, laundry products and other medical products.2-5 ATPSs have many advantages including high biocompatibility, rapid separation, mild operating condition, low interfacial tension and friendly environment. ATPSs are usually composed of two water soluble polymers, a single polymer and a kosmotropic salt6 or two salts (one chaotropic salt and the other a kosmotropic salt). So far, the most commonly used ATPS is the polymer-salt ATPS, due to possessing the advantages of low cost and viscosity, harmless, rapid phase-separation as well as high extraction capacity. In the previous researches, polymer-salt ATPSs always used polyethylene glycol (PEG) or polypropylene glycol (PPG)5,7-9 as the phase-forming polymer, however, these polymers had high phase-separation temperature (above 100 o

C), which led to some difficulties in separating target biomolecules from the

polymer-rich phase. Furthermore, high temperature would make the biological material lose biological activity or even damage its molecular structure when using these ATPSs. Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer is a kind of thermosensitive polymers. It is a nonionic macromolecule surfactant that has a hydrophobic PPO block in the middle and two hydrophilic PEO blocks at the ends. When the temperature increases to certain degree, the surfactants solution will separate into two phases. Alternatively, the aqueous solutions of these surfactants could separate into two phases by the addition of electrolytes

at

a

certain

temperature.10

These

triblock

3


copolymers

have


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macromolecules with the ability of self-association to form micelles. Moreover, the triblock copolymer PEO-PPO-PEO has good biocompatibility, as well as low viscosity and commercial availability. In recent years, PEO-PPO-PEO has attract increasing interest because of their potential application in biochemistry for purification of biological materials, such as proteins, enzymes, and cell organelles.11-13 The most important characteristic feature of nonionic surfactant solutions is that when the solutions are heated they display a clouding phenomenon losing their solubility at certain temperature, the special temperature being known as the cloud point (CP). 14 The CP depends on the structure and the concentration of surfactants. Meanwhile, CP can also be modified by other additives, such as electrolytes, amino acid, sugar, alcohols and glycerol. 15 So far, there are many researches discussing the effect of electrolytes on CP in nonionic surfactants solution, including Triton X-114, Octylphenol Ethoxylate (30EO), polyoxyethylene (30) lauryl ether (Brij-35) and Triton X-45. 16-18 The research about thermo-sensitive polymer PEO-PPO-PEO has few been reported in the previous literatures. Phase diagram were necessary to optimize the application of ATPS formed, detailed information on the liquid-liquid equilibrium (LLE) data and the physicochemical properties is crucial.19 At the present time, liquid-liquid equilibria (LLE) of PEO-PPO-PEO based (L35-salt, F68-salt, L64-salt) ATPSs have been widely reported. 20-22

As we have seen, the polymer-salt ATPS will separate into two phases where the

top phase is the polymer-rich phase and the bottom phase is the salt-rich phase at a certain temperature by a rise in the salt concentration in previous published articles.23

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In fact, polymer-rich phase is in the bottom at the beginning, as the amount of salt is increased, polymer-rich phase transfers to the top phase from the bottom phase, thus, phase inversion occurs. Therefore, phase equilibrium exists not only before the phase inversion but also after phase inversion.24 However, few researchers pay an attention to this question. In the present study, the CP of non-ionic surfactant (L61) was measured. In addition, the influences of the salts (K2HPO4, (NH4)3C6H5O7 and K3C6H5O7) on the CP were investigated. The influences of temperature on the phase inversion behaviour of the ATPSs composed of (L61-K2HPO4 / (NH4)3C6H5O7 / K3C6H5O7) were evaluated. LLE data of the ATPS was measured and fitted with the most widely used empirical equations. Then the effects of the temperature and salts on LLE data were also studied. Keywords: Aqueous two-phase system; L61; Cloud point; Phase diagram

2 Experimental 2.1 Materials L61, an P(EO)10-P (PO)90-P (EO)10 copolymer, with an average molecular weight (Mn) of 2000 g.mol-1, containing 10% ethylene glycol, was purchased from Aldrich (USA). The analytical grade reagents K2HPO4 (dipotassium phosphate), (NH4)3C6H5O7 (ammonium citrate), K3C6H5O7.H2O (potassium citrate), C25H30N3Cl (Crystal violet) were obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China) Milli-Q Ⅱ water was used to prepare all aqueous solutions.

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2.1 Determination of CP Experiments were carried out with L61 at different concentrations (from 0.1 to 10%, w/w) either in water or in salt solution. The concentrations of the three kinds of salts (K2HPO4, (NH4)3C6H5O7 and K3C6H5O7) ranged from 100 to 500 mM. A certain amount of L61 or L61-salt solution was added to a glass tube, the solution was well mixed after vigorously stirred and then moved to a constant-temperature bath. The CP was determined mainly by visual observation on the temperature at which the clear solutions turned turbid upon heating and the milky solutions losed their turbidity on cooling. The measured CP was reproducible within 0.1 oC. All experiments and measurements were carried out in triplicate. 2.3 Liquid-liquid equilibrium determination 10 g of each ATPSs were prepared by L61, salt (K2HPO4, (NH4)3C6H5O7, or K3C6H5O7) and water in the vessels, within a precision of ± 0.0001 g. After being vigorously stirred and centrifuged under 2000 rpm speed for 20 minutes, the ATPSs were separated into two phases and allowed to settle for 24h at the operation temperature (25 oC, 30 oC and 35 oC) in the thermostat bath (within a precision of ± 0.1 oC). When the volumes of the top and the bottom phases no longer changed with time, and a clear interfacial boundary was formed between the two phases, phase equilibrium was attained. Finally, the two phases were collected respectively for compositional analysis. After reaching the phase equilibrium, salt concentration ( w2 ) was determined by conductivity (DDS-11A Conductivity Meter, Shanghai Dapu instrument Co., Ltd.

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China) in the mass percentage range of (0.1 to 1) % (w/w) and the concentration of L61 ( w1 ) was determined by Abbe refractometer (WZS-I, optical instrument factory Co., Ltd. China) in the mass percentage range of (1 to 6) % (w/w). The following equation (1) is used to represent the relationships between the index of refraction of the mixed solution (n), the mass fractions of L61 ( w1 ), and the mass fractions of salt ( w2 ). n = a0 + a1 w1 + a2 w2

(1)

Where a0 , a1 and a2 are constants, the values of a0 , a1 , a2 were shown in the Table 1. Before starting the measurement w1 and w2 of the two phase systems were diluted to a certain concentration to satisfy equation (1). Table 1. Values of parameters of equation (1) for ATPSs at 25 oC at atmospheric pressure. ATPS

a0

a1

a2

L61 − K 2 HPO4

1.3333

0.1601

0.0052

L61-(NH 4 )3C6 H 5O7

1.3333

0.1480

0.0053

L61-K 3C6 H 5O7 ×H 2 O

1.3333

0.1430

0.0042

2.4 Determination of density Densities of the solutions were measured using density bottle with a volume of about 10 mL calibrated by redistilled water; the density at 25 oC is 0.9971 g·cm−3. To eliminate systematic error, densities of various solutions were measured using the same density bottle. The difference between duplicate measurements is less than 0.00005 g·cm−3. Temperature fluctuation in the thermostatic water bath during the

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measurement was less than 0.1 oC. All the samples were weighted on an electrical balance with a precision of ± 0.0001 g.

3. Results and discussion 3.1. CP behavior of L61 3.1.1. CP data of L61 at different concentration The CP data of L61 solution were shown in Table 2. It was shown that the CP decreased with the increase of L61 concentration. The decrease in CP was due to the increase in micelle concentration, which increased the micelle–micelle interaction. Then the L61 solution was easy to separate into two phase. 17, 18 Table 2. CP of L61 solution with different concentrations. L61 (%,w/w)

CP (oC)

L61 (%,w/w)

CP (oC)

0.1

29.5

4.5

18.5

0.2

28.0

5.0

18.3

0.4

26.5

5.5

18.2

0.6

25.7

6.0

18.0

0.8

24.5

6.5

17.8

1.0

23.5

7.0

17.6

1.5

22.5

7.5

17.5

2.0

21.8

8.0

17.6

2.5

21.0

8.5

17.4

3.0

20.2

9.0

17.3

8


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3.5

19.5

9.5

17.2

4.0

18.8

10.0

17.0

3.1.2 Effect of the addition of salts on CP Electrolytes play a crucial role in surfactant solution, and the ability of changing CP for different electrolytes is different. In this paper, the effect of three salts K2HPO4, (NH4)3C6H5O7 and K3C6H5O7 on the CP of L61 was studied in detail, and the results were shown in Figure 1. It was noted that the addition of these three salts decreased the CP of L61 and the lowering of CP had a linear line trend related to the corresponding salt concentration. Regression equations and regression coefficients (R2) were found from Table 3. As we know, salting-in makes the CP increase and salting-out makes the CP reduce.25 With the addition of the three salting-out salts K2HPO4, (NH4)3C6H5O7 and K3C6H5O7, the L61 tends to form micelles more easily, resulting in a decrease of the CP. In other words, the effect of salting-out make the water molecules be easier to interact with the salt ions, and promote the association of water molecules with the salt by hydrogen bonding instead of their association with the L61, which led to micelle “dehydration”.17, 26, 27 On the other hand, the higher ion concentration of the salt is, the greater the effect on the hydration is, therefore, the copolymer L61 more easily trend to dehydration with increases in the concentration of salt. As shown in Figure 1, we found that the order of the CP was as follows: K3C6H5O7 > (NH4)3C6H5O7 > K2HPO4. The results showed that the capacity of trivalent anion ( C6 H 5O73− ) containing (NH4)3C6H5O7 and K3C6H5O7 to decrease the CP was more 9



effective than divalent anion ( HPO42 − ) containing K2HPO4. In addition, considering that the salts (K2HPO4 and K3C6H5O7) shared a common cation but contained different anions, it was easy to see that the salting-out ability of the anions followed the ordering: HPO42− < C6 H 5O73− . Comparing the salts having the same anion ((NH4)3C6H5O7 and K3C6H5O7), the order of effect was K + > NH 4+ . The higher the lyotropic number of the cation is, the greater the effect on the micellar growth is, in other words, the smaller ions are more hydrated than the larger ones.28 In addition, according to the hydration tendency of ions, this order also follows the Hofmeister series for the strength of the anion.29 18 16

K2HPO4

A

(NH4)3C6H5O7

14

Cloud Point

K3C6H5O7.H2O

12 10 8 20

4 2

K2HPO4

B

18

6

(NH4) 3C6H5O7 K3C 6H5O7 .H2 O

16

Cloud Point

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14 12 10 8 6 4 2

0

100

200

300

400

500

600

Salt concentration (mM)

100

200

300

400

500

Salt concentration (mM)

Figure 1. Effect of different salts on the CP of L61 solution (A: 5% (w/w) L61 solution, B: 1% (w/w) L61 solution).

Table 3. Regression equations and coefficients for all electrolytes.

L61 (%,w/w)

Electrolytes

Regression equations

Regression coefficient(R2)

1

K2HPO4

Y=22.01333-0.02437X

0.9942

10


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1

(NH4)3C6H5O7

Y=21.37333-0.02483X

0.9987

1

K3C6H5O7.

Y=21.60667-0.03111X

0.9987

5

K2HPO4

Y=19.65-0.0299X

0.9978

5

(NH4)3C6H5O7

Y=18.96-0.0308X

0.9994

5

K3C6H5O7

Y=18.11-0.0347X

0.9942

Meanwhile, in order to further confirm the effect of different salts on the CP, the CP behavior of L61 solutions either in water or in the presence of salt was investigated. As showed in Figure 2, with the increase in L61 concentration, the CP decreased, the CP of L61 in salt was lower than in pure water. As we can notice that the effect of K2HPO4, (NH4)3C6H5O7, K3C6H5O7 on the CP was the same as the Figure 1, K3C6H5O7 > (NH4)3C6H5O7 > K2HPO4. 40 none salt K2HPO4

35

(NH4)3C6H5O7

Cloud Point（ oC）

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K3 C 6 H5 O7

30

25

20

15

10 0.05%

0.25%

1%

3%

5%

7%

9%

--

L61 Concentration (w/w) Figure 2. The effect of the concentration of L61 on the CP in the presence of 100mM salts.

3.2 Phase inversion of L61-salt ATPS In our investigated ATPSs, the appearance of the two coexisting phases changed by a rise in concentration of salt. All samples used for photography were dyed by Crystal violet which was mostly concentrated in the L61-rich phase. The relative positions of 11



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the two phases (top phase or bottom phase) were related to the concentrations of L61 and salt in the corresponding ATPS. To find the turning point of phase inversion, the concentration of L61 was held at around 5% (w/w), the L61-rich phase transferred from the bottom phase to the top phase when the salt concentration increased to a certain critical value, which was occurred phase inversion. The results were shown in Figure 3 and Table 4. Phase inversion in this case meant that an increase of the total salts concentration also increased the density of the salt-rich phase compared with L61-rich phase; The densities of the separated phases were shown in Table 5. As shown in Figure 3, the tube 1 and tube 3 represent before the phase inversion (L61-rich phase in the bottom) and after phase inversion (L61-rich phase in the top), respectively. Moreover, the tube 2 shown that the salt concentrations of the ATPS near the phase inversion point, and the densities of the two phases were very close to each other30. The phase inversion points for the three investigated ATPSs were shown in Table 4. The behavior of phase inversion was related to the densities of the two phases (top phase and bottom phase). It was well known that the densities of different salts were various after phase separation occurred, which led to the discrepancy of the ability of phase inversion. This was mainly due to the properties of salt. The lower the amount of salt was used, the stronger the ability of phase inversion was produced by salt.31 It could be concluded that, the effect of different salts concentrations on the phase inversion point was as follows: (NH4)3C6H5O7 > K2HPO4 > K3C6H5O7.

12


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Experimental results also indicated that the capability of the phase inversion would be enhanced with the increase of temperature. In other words, as the temperature increased, the concentration of salt needed to promote phase inversion was decreased. It is because that as the temperature increased, the temperature of the separated phase was close to CP, so the concentration of salt needed to promote phase inversion was lower, and the ability of the salt to boost the phase separation was stronger. Consequently, the behavior of phase inversion was an important property of the thermo-sensitive copolymer, which was provided a suitable experimental condition and necessary theoretical data for aqueous two-phase extraction.

Figure 3. The photographs of extraction of crystal violet in L61-salt ATPS at 25 oC. (A, L61-K2HPO4 ATPS: [1] cK 2 HPO4 =100 mM; [2] cK 2 HPO4 =160 mM; [3] cK 2 HPO4 =200 mM; B, L61-(NH4)3C6H5O7 ATPS: [1] c( NH ) C H O =100 mM; [2] c( NH ) C H O =200 mM; [3] 4 3 6 5 7 4 3 6 5 7

c( NH 4 ) C6 H5O7 =250 mM; C, L61- K3C6H5O7 ATPS: [1] cK2 HPO4 =50 mM; [2] cK2 HPO4 =108 mM; 3

[3] cK 2 HPO4 =150 mM. Table 4. Phase inversion point of L61-K2HPO4 / (NH4)3C6H5O7 / K3C6H5O7 ATPSs. Salt species

Temperature (oC)

Inversion point

(NH4)3C6H5O7

25

200-210 mM

K3C6H5O7

25

108-112 mM

K2HPO4

25

160-165 mM

13



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K2HPO4

30

155-160 mM

K2HPO4

35

145-150 mM

Table 5. Density of two phases at different total salt concentration in L61-salt ATPSs. .

Density (g cm-3)

Total salt ATPSs

o

T ( C)

concentration Salt-rich phase

L61-rich phase

100

1.1170

1.1995

150

1.1215

1.1705

250

1.1315

1.1135

300

1.1595

1.1195

50

1.1105

1.2375

80

1.1200

1.1450

120

1.1280

1.1135

150

1.1510

1.0725

50

1.0435

1.1095

100

1.0870

1.1015

180

1.0955

1.0295

200

1.1335

1.1220

50

1.0020

1.0290

100

1.0340

1.0910

180

1.1365

1.0640

200

1.1380

1.0550

50

1.0610

1.1070

100

1.0850

1.1245

180

1.1260

1.0250

200

1.1605

1.0145

(mM) L61-(NH4)3C6H5O7

25

L61-K3C6H5O7

25

L61-K2HPO4

25

L61-K2HPO4

30

L61-K2HPO4

35

3.3 LLE behavior of ATPS 3.3.1 Experimental data of LLE and correlation 14


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Tables 7 and 8 presented the composition of the top and bottom phases for the L61-K2HPO4 / (NH4)3C6H5O7 / K3C6H5O7 ATPSs at (25oC, 30oC and 35oC). Based on the previous discussion, LLE data were measured before and after the phase inversion at the same time. Four total compositions of ATPS were selected in this part, two of which were the total composition before the phase inversion; others were the total composition after the phase inversion. The results were also shown in Figure 4 - 5. From these figures, the phenomenon of the cross of the tie lines（before the phase inversion）was obviously observed. This was because an increase in salt concentration made the density of the salt phase increase, the L61-rich phase of ATPS transferred gradually to the top phase. Then, the mass fraction of the polymer in the bottom phase decreased when increasing the salt concentration. Tie-line lengths (TLL) and the slope of the tie-line (STL) at different compositions were calculated using as equations (2) and (3), respectively, as followed: 2 2 TLL = ( w1t − w1b ) + ( w2t − w2b )   

(2)

(w − w ) (w − w ) t

STL =

0.5

1

b 1

t 2

b 2

(3)

Where w1t and w2t represent the equilibrium compositions (in mass fraction) of the (L61 and salt) in the top phase, respectively. Similarly, w1b and w2b represent the equilibrium compositions (in mass fraction) of (L61 and salt) in the bottom phases, respectively.

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An empirical equation was used to correlate the phase diagram of the investigated ATPSs. Equation (4) was used in the correlation of phase diagram for the L61-salt ATPS.

(

w1 = exp a + bw20.5 + cw2 + dw22

)

（4）

Where w1 and w2 represent the equilibrium compositions (in mass fraction) of the (L61 and salt), respectively. The coefficients a, b, c and d are the fitting parameters. The fitting parameters, corresponding correlation coefficient (R2) of equation (4) for the investigated systems were given in Table 6. It can be concluded that equation (4) shows a satisfactory accuracy in fitting the phase diagram of the investigated ATPSs. Table 6. Parameter values of equation (4) for L61-salt ATPSs.

ATPSs

a

b

c

d

R2

T=25oC, L61-(NH4)3C6H5O7

5.3850

-161.5672

742.1193

-4243.1306

0.9935

T= 25oC, L61-K3C6H5O7

6.8049

-195.4360

886.3290

-4335.7620

0.9856

T= 25oC, L61-K2HPO4

4.2085

-127.8451

625.3065

-4803.2791

0.9546

T= 30oC, L61-K2HPO4

3.3598

-128.5067

694.8967

-6363.2122

0.9687

T= 35oC, L61-K2HPO4

1.9363

-82.2447

341.0892

-1868.6400

0.9794

16


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0.8

A

0.7

L61% (w/w)

0.6 0.5 0.4 0.3 0.2 0.1 0.0

0.00

0.01

0.02

0.03

0.04

K2HPO4 (%(w/w)) 1.0

B

0.8

C

0.8

L61% (w/w)

L61% (w/w)

0.6

0.4

0.2

0.6

0.4

0.2 0.0

0.0 0.00

0.01

0.02

0.03

0.04

0.00

0.01

K2HPO4(% (w/w) )

0.02

0.03

0.04

K2HPO4 (% (w/w))

Figure 4. Phase diagram of the L61-K2HPO4 ATPS (A: 25 oC; B: 30 oC; C: 35 oC). 0.8

0.7

A

0.6

B

0.7 0.6

L61% (w/w)

0.5

L61% (w/w)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.4 0.3 0.2

0.5 0.4 0.3 0.2

0.1

0.1

0.0

0.0 0.00

0.01

0.02

0.03

0.04

0.05

0.00

0.06

0.01

0.02

0.03

0.04

0.05

0.06

0.07

K3C6H5O7.H2O% (w/w)

(NH4)3C6H5O7 % (w/w)

Figure 5. Phase diagram of the ATPSs at T=25 oC (A: L61 - (NH4)3C6H5O7 ATPS; B: L61K3C6H5O7 ATPS).

Table 7. LLE data of the L61-K2HPO4 ATPS (T=25 oC, 30 oC and 35 oC).

system

overall

Polymer phase

Salt phase

17


TLL

STL


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

wL 61

ws

wL 61

ws

wL 61

Page 18 of 28

ws

T=25oC, L61-K2HPO4 ATPS 1

0.0500

0.0209

0.6191

0.0021

0.0312

0.0217

0.5882

-30.51

2

0.0500

0.0243

0.5185

0.0251

0.0360

0.0251

0.4830

-21.05

3

0.0500

0.0348

0.7143

0.0367

0.0106

0.0367

0.7046

-20.35

4

0.0500

0.0383

0.7471

0.0406

0.0093

0.0406

0.7389

-19.10

o

T=30 C, L61-K2HPO4 ATPS 1

0.0500

0.0209

0.6655

0.0014

0.0262

0.0217

0.6396

-31.50

2

0.0500

0.0244

0.5655

0.0013

0.0323

0.0253

0.5337

-22.19

3

0.0500

0.0348

0.7832

0.0011

0.0364

0.0359

0.7476

-21.49

4

0.0500

0.0383

0.8244

0.0012

0.0262

0.0396

0.7991

-20.80

o

T= 35 C, L61-K2HPO4 ATPS 1

0.0500

0.0209

0.6495

0.0012

0.0256

0.0209

0.6443

-31.67

2

0.0500

0.0244

0.5871

0.0011

0.0215

0.0254

0.5662

-23.22

3

0.0500

0.0348

0.8097

0.0010

0.0142

0.0366

0.7963

-22.56

4

0.0500

0.0383

0.8384

0.0009

0.0104

0.0402

0.8289

-21.06

Table 8. LLE data for the L61-K2HPO4 ATPS, L61-(NH4)3C6H5O7 ATPS, L61-K3C6H5O7 o

ATPS at T=25 C.

overall

system

wL 61

ws

Polymer

wL 61

Salt phase

ws

wL 61

TLL

STL

ws

L61 - (NH4)3C6H5O7 ATPS 1

0.0500

0.0438

0.4697

0.0020

0.0168

0.0260

0.4535

-19.50

2

0.0500

0.0486

0.4076

0.0025

0.0159

0.0324

0.3928

-13.10

3

0.0500

0.0584

0.5884

0.0021

0.0156

0.0422

0.5742

-14.24

4

0.0500

0.0632

0.6748

0.0026

0.0151

0.0486

0.6614

-14.11

L61 - K3C6H5O7 ATPS 1

0.0500

0.0260

0.5986

0.0023

0.0319

0.0456

0.5683

13.11

2

0.0500

0.0324

0.5716

0.0022

0.0309

0.0506

0.5429

11.16

3

0.0500

0.0422

0.6903

0.0021

0.0261

0.0618

0.6669

11.14

4

0.0500

0.0487

0.7484

0.0021

0.0257

0.0657

0.7255

11.36

3.3.2 Effect of temperature on the phase equilibrium 18


Page 19 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The effect of temperature on each phase diagram of the ATPSs was shown in Figure 6. The results for the systems indicated that the biphasic area significantly increased as the temperature increased. This behavior confirmed that the phase-separation process was endothermic. With the increase in temperature, the concentration of salt to form ATPSs could decrease. It was because that the hydrophobic PO segments of the copolymer tried to achieve aggregates with tightly packed chains at higher temperatures. Thus, increase the hydrophobicity of the copolymer would benefit phase separation of the ATPS. In addition, the effect of temperature on the phase equilibrium compositions could be also investigated through STL values that were given in Table 7 and Table 8. We choose the two points after the phase inversion to compare the influence of temperature on the phase equilibrium. As we can see from Figure 6 B, STL tended to increase with increasing temperature. A possible explanation for this change was the spontaneous diffusion of water molecules from the top phase to the bottom phase, resulting in an increase in the L61 concentration in the top phase and a reduction in the copolymer concentration in the bottom phase. In general, the higher the temperature was, the higher the capacity of phase separation promoted by the salt was. These findings was consistent with the reported results for other ATPSs containing triblock copolymer L35 and L68.16, 20

19



1.0

1.0

A

25oC 30oC 35oC

0.8

L61% (w/w)

0.8

0.6

L61% (w/w)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 28

B

0.6

0.4

0.2

0.0 0.00

0.4

0.01

0.02

0.03

0.04

K2HPO4%(w/w)

25oC 30oC 35oC

0.2

0.0

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

K2HPO4% (w/w)

Figure 6. Effect of temperature on each phase diagram of L61-salt ATPS. A: Effect of temperature on each phase diagram; B: Effect of temperature on the slopes of the tie-lines.

3.3.3 Effect of salt on the phase equilibrium The salt effect on the phase composition was shown in Figure 7. The results provided evidence that the capacity of the salts to induce ATPS formation followed the Hofmeister series, that is, K3C6H5O7 > (NH4)3C6H5O7 > K2HPO4, which was the same as the order for salts to reduce the CP. Both of the orders were attributed to the effect of salting-out. Citrate has shown a better capability to cause phase separation when compared to phosphate, and the capability of K+ was stronger than NH4+. This was because the citrate ion was preferentially hydrated, causing the removal of water molecules from the copolymer hydrophilic layer. As a result, copolymer solubility decreased and phase separation was liable to occur.23, 32 In the present work,

34

it was

found that the phase-separate ability of salt was related to the Gibbs free energy 20


Page 21 of 28

(∆Ghyd) of hydration of the ions. It was well known that the bigger the absolute value of negative ∆Ghyd of the ion (anion or cation) of salts was, the stronger the phase separation ability of the salts was.33 As observed in some literatures,34-36 the ∆Ghyd of hydration of these salts as follows: △( C6 H 5O73− ) = -2793kJ/mol > ∆Ghyd ( HPO42 − ) = -1789 kJ/mol, ∆Ghyd ( K + ) = -295 kJ/mol ∆Ghyd ( NH 4+ ) = -285 kJ/mol. In summary, the value of ∆Ghyd is always consistent with the results of the experiment and the phase-separate ability of salt evaluated by ∆Ghyd was appropriate for ATPSs of this article.

0.8

K2HPO4 K3C6H5O7.H2O

0.7

(NH4)3C6H5O7

0.6

L61% (w/w)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.5 0.4 0.3 0.2 0.1 0.0 0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

salt % (w/w) Figure 7. Effect of the salts on the phase diagram of the L61-salt ATPSs at 25 oC.

Conclusions In this study, the effects of various electrolytes on the cloud point of thermo-sensitive copolymer L61 solutions were investigated. The results pointed out that the cloud point of L61 was lowered by the addition of electrolytes. In most cases, a linear relationship between cloud point and additive concentration was found. The efficacy 21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

of the salts on reducing cloud point followed the order: K3C6H5O7 > (NH4)3C6H5O7 > K2HPO4. Added salts not only decreased the cloud point, but also changed the concentrations and densities of the two phases of the aqueous two-phase system that led to the phenomenon of phase inversion. The results showed the lower the added salt was, the stronger the phase-inversion ability of salt was. The experimental phase diagram and liquid-liquid equilibrium data for the aqueous two-phase systems were investigated, showing that an increase in the slopes of the tie-lines and two-phase region with the increasing temperature, and the aqueous two-phase system formation process was endothermic. The capacity of the salts to induce phase segregation followed the Hofmeister series, that is K3C6H5O7 > (NH4)3C6H5O7 > K2HPO4. Meanwhile, taking Gibbs free energy as criteria for the evaluation of phase-separated of salt was appropriate in this article.

Acknowledgment This work was supported by the National Natural Science Foundation of China (Nos. 31470434, 21406090, 21206059 and 21407058), the Natural Science Foundation of Jiangsu Province (Nos. BK20141289 and BK20131258), Ph.D. Programs Foundation of Ministry of Education of China (No. 20133227120006), the Science Foundation of Jiangsu Entry-exit Inspection Quarantine Bureau (Nos. 2015KJ27 and 2015KJ28), and Zhenjiang Social Development Project (No. SH2014021).

22


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References (1) Albertsson, P. A. Chromatography and Partition of Cells and Cell Fragments. Nature. 1956, 177, 771-774.

(2) Abbasiliasi, S.; Tan, J. S.; Ibrahim, T. A. T. Primary Recovery of A Bacteriocin-Like Inhibitory Substance Derived from Pediococcus Acidilactici Kp10 by An Aqueous Two-Phase System. Food. Chem. 2014, 151, 93-100. (3) Han, J.; Wang, Y.; Yu, C. Separation, Concentration and Determination of Chloramphenicol in Environment and Food Using An Ionic Liquid/Salt Aqueous Two-Phase

Flotation

System

Coupled

with

High-Performance

Liquid

Chromatography. Anal. Chim. Acta. 2011, 685, 138-145. (4) Banik, R. M.; Prakash, M. Purification and Characterization of Laundry Detergent Compatible Alkaline Protease from Bacillus Cereus. J. Biotechnol. 2006, 5, 380-384. (5) Pereira, J. F. B.; Santos, V. C.; Johansson, H. O. A Stable Liquid-Liquid Extraction System for Clavulanic Acid Using Polymer-Based Aqueous Two-Phase Systems. Sep. Purif. Technol. 2012, 98, 441-450.

(6) Zafarani-Moattar, M. T.; Hamzehzadeh, S. Salting-out Effect, Preferential Exclusion, and Phase Separation in Aqueous Solutions of Chaotropic Water-Miscible Ionic Liquids and Kosmotropic Salts: Effects of Temperature, Anions, and Cations. J. Chem. Eng. Data. 2010, 55, 1598-1610.

(7) Chen, J. P.; Lee, M. S. Enhanced Production of Serratia Marcescens Chitinase in PEG/Dextran Aqueous Two-Phase Systems. Enzyme. Microb. Technol. 1995, 17, 1021-1027.

23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 28

(8) Wu, C.; Wang, J.; Pei, Y. Salting-out Effect of Ionic Liquids on Poly (propylene glycol) (PPG). J. Chem. Eng. Data. 2010, 55, 5004-5008. (9) Nandini, K. E.; Rastogi, N. K.; Liquid-Liquid Extraction of Lipase Using Aqueous Two-Phase System. Food. Bioprocess. Tech. 2011, 4, 295-303. (10) Mortensen, K. Structural Studies of Aqueous Solutions of PEO-PPO-PEO Triblock Copolymers, Their Micellar Aggregates and Mesophases; A Small-Angle Neutron Scattering Study. J. Phys. Condens. Matter. 1996, 8, A103-A124. (11) Dembczyński, R.; Białas, W.; Jankowski, T. Partitioning of Lysozyme in Aqueous

Two-Phase Systems

Containing Ethylene

Oxide-Propylene

Oxide

Copolymer and Potassium Phosphates. Food. Bioprod. Process. 2013, 91, 292-302. (12) Amid, M.; Shuhaimi, M.; Sarker, M. Z. I. Purification of Serine Protease from Mango (Mangifera Indica Cv. Chokanan) Peel Using An Alcohol/Salt Aqueous Two Phase System. Food. Chem. 2012, 132, 1382-1386. (13) Azevedo, A. M.; Gomes, A. G.; Rosa, P. A. J.; Ferreira, I. F.; Pisco, A. M. M. O.; Aires-Barros,

M.

R.

Partitioning

of

Human

Antibodies

in

Polyethylene

Glycol-Sodium Citrate Aqueous Two-Phase Systems. Sep. Purif. Technol. 2009, 65, 14–21. (14) Mukherjee, P.; Padhan, S. K.; Dash, S. Clouding Behaviour in Surfactant Systems. Adv. Colloid Interface Sci. 2011, 162, 59-79. (15) Santos-Ebinuma, V. C.; Lopes, A. M.; Converti, A. Behavior of Triton X-114 Cloud Point in the Presence of Inorganic Electrolytes. Fluid. Phase. Equilib. 2013, 360, 435-438.

24


Page 25 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(16) Wang, Z.; Xu, J. H.; Zhang. W. Cloud Point of Nonionic Surfactant Triton X-45 in Aqueous Solution. Colloids. Surf. B. 2008, 61, 118-122. (17) Rocha, S. A. N.; Costa, C. R.; Celino, J. J. Effect of Additives on the Cloud Point of the Octylphenol Ethoxylate (30EO) Nonionic Surfactant. J. Surfact. Deterg. 2013, 16, 299-303.

(18) Batıgöç, Ç.; Akbaş, H. Spectrophotometric Determination of Cloud Point of Brij 35 Nonionic Surfactant. Fluid. Phase. Equilib. 2011, 303, 91-95. (19) Lladosa, E.; Silvério, S. C.; Rodríguez, O. (Liquid + Liquid) Equilibria of Polymer-Salt Aqueous Two-Phase Systems for Laccase Partitioning: UCON 50-HB-5100 with Potassium Citrate and (Sodium or Potassium) Formate at 23 oC. J. Chem. Thermodyn. 2012, 55, 166-171.

(20) Virtuoso, L. S.; Vello, K. A. S. F.; de Oliveira, A. A.; Measurement and Modeling of Phase Equilibrium in Aqueous Two-Phase Systems: L35+ Sodium Citrate+ Water, L35 Sodium Tartrate+ Water, and L35+ Sodium Hydrogen Sulfite+ Water at Different Temperatures. J. Chem. Eng. Data. 2012, 57, 462-468. (21) Rodrigues, G. D.; Teixeira, L. S.; Ferreira, G. M. D. Phase Diagrams of Aqueous Two-Phase Systems with Organic Salts and F68 Triblock Copolymer at Different Temperatures. J. Chem. Eng. Data. 2009, 55, 1158-1165. (22) Rodrigues, G. D.; da Silva, M. C. H.; da Silva, L. H. M. Liquid-Liquid Phase Equilibrium of Triblock Copolymer L64, Poly (ethylene oxide-b-propylene oxide-b-ethylene oxide), with Sulfate Salts from (278.15 to 298.15) K. J. Chem. Eng. Data. 2009, 54, 1894-1898.

25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(23) Han, J.; Pan, R.; Xie, X. Liquid-Liquid Equilibria of Ionic Liquid 1-Butyl-3-Methylimidazolium Tetrafluoroborate + Sodium and Ammonium Citrate Aqueous Two-Phase Systems at (298.15, 308.15, and 323.15) K. J. Chem. Eng. Data. 2010, 55, 3749-3754. (24) Alvarenga, B. G.;Virtuoso, L. S.; Lemes, N. H. T. Phase Behaviour at Different Temperatures of An Aqueous Two-Phase Ionic Liquid Containing ([Bmim] BF< sub> 4+ Manganese Sulfate+ Water). J. Chem. Thermodyn. 2013, 61, 45-50. (25) Hao, L.; Nan, Y.; Liu, H. Salt Effects on Aqueous Cationic/Anionic Surfactant Two-Phase Regions. J. Dispersion. Sci. Technol. 2006, 27, 271-276. (26) Alam, M. S.; Nareshkumar. V.; Vijayakumar. N. Effect of Additives on the Cloud Point of Mixed Surfactant (Non-ionic Triton X-114+ Cationic Gemini 16-6-16) solutions. J. Dispersion. Sci. Technol. 2014, 194, 206-211. (27) Shaheen, A.; Kaur, N.; Mahajan, R. K.; Influence of Various Series of Additives on the Clouding Behavior of Aqueous Solutions of Triblock Copolymers. Colloid. Polym. Sci. 2008, 286, 319-325.

(28) Maiti, K.; Mitra, D.; Guha, S. Salt Effect on Self-Aggregation of Sodium Dodecyl Sulfate (SDS) and Tetradecyl Trimethyl Ammonium Bromide (TTAB): Physicochemical Correlation and Assessment in the Light of Hofmeister (Lyotropic) Effect. J. Mol. Liq. 2009, 146, 44-51. (29) Nascimento, K. S.; Yelo, S.; Cavada, B. S. Liquid-Liquid Equilibrium Data for Aqueous Two-Phase Systems Composed of Ethylene Oxide Propylene Oxide Copolymers. J. Chem. Eng. Data. 2011, 56, 190-194.

26


Page 26 of 28

Page 27 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(30) Nan, Y. Q.; Hao, L. S. Salt-Induced Phase Inversion in Aqueous Cationic/Anionic Surfactant Two-Phase Systems. J. Phys. Chem. B. 2008, 112, 12326-12337. (31) Shang, Y.; Liu, H.; Hu, Y. Effect of Salts on the Aqueous Two-Phase System in Mixed Solutions of Gemini (12-3-12, 2Br−) and Sodium Dodecyl Sulfate. Colloids. Surf. A. 2007, 302, 58-66.

(32) Zhao, X.; Xie, X.; Yan, Y. Liquid-Liquid Equilibrium of Aqueous Two-Phase Systems Containing Poly (propylene glycol) and Salt ((NH4)2SO4, MgSO4, KCl, and KAc): Experiment and Correlation. Thermochim. Acta. 2011, 516, 46-51 (33) Rogers, R. D.; Bond, A. H.; Bauer, C. B.; Zhang, J.; Griffin, S. T. Metal Ion Separations in Polyethylene Glycol-Based Aqueous Biphasic Systems: Correlation of Partitioning Behavior with Available Thermodynamic Hydration Data. J. Chromatogr. B. 1996, 680, 221-229

(34) Marcus, Y. Thermodynamics of Solvation of Ions. Part 5. - Gibbs Free Energy of Hydration at 298.15 K. J. Chem. Soc. Faraday Trans. 1991, 87, 2995-2999. (35) Blankschtein, D.; Thurston, G. M.; Benedek, G. B.; Phenomenological Theory of Equilibrium Thermodynamic Properties and Phase Separation of Micellar Solutions. J. Chem. Phys. 1986, 85, 7268-7288.

(36) Rao, J. R.; Nair, B. U.; Novel Approach Towards Recovery of Glycosaminoglycans from Tannery Wastewater. Bioresour. Technol. 2011, 102, 872-878..

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Table of Contents Graphic

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