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SD

a

ARRAA

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oftac(

0h

Fluid Phase Equilibria 354 (2013) 236–244

Contents lists available at SciVerse ScienceDirect

Fluid Phase Equilibria

journa l h om epage: www.elsev ier .com/ locate / f lu id

altodextrin–SDS interactions: Volumetric, viscometric and surfaceension study

. Chauhan ∗, Vivek Sharma, Kundan Sharmaepartment of Chemistry, Himachal Pradesh University, Shimla-5, India

r t i c l e i n f o

rticle history:eceived 19 March 2013eceived in revised form 20 June 2013ccepted 22 June 2013vailable online 29 June 2013

a b s t r a c t

Carbohydrate–surfactant interactions and micellization behavior of anionic surfactant (sodium dodecylsulfate, SDS) in aqueous solution of (0, 0.5, 1.0 and 1.5% w/v) maltodextrin have been studied using density,sound velocity, viscosity and surface tension in the temperature range of 20–40 ◦C at an interval of 5 ◦C.Density and speed of sound data have been used to derive parameters like isentropic compressibility (�s),apparent molar volume (˚v) and apparent molar isentropic compression (˚k). Surface tension has been

eywords:pparent molar volumealtodextrin

DSurface tension

used to calculate surface excess concentration (�max), minimum area occupied by the surfactant (Amin)and surface film pressure (�cmc) whereas relaxation time (�) is calculated using viscosity data. Volumetricmeasurements indicate that ˚v values are positive and generally increase with rise in temperature aswell as with increase in percentage of maltodextrin (0.5–1.5%). Viscous relaxation time (�) and surfacetension (�) have been found to decrease with rise in temperature.

iscosity

. Introduction

There are different attempts and techniques that have beenade to understand the interactions between carbohydrate and

urfactant system which has a great significance in pharmaceutical,ndustrial and biological systems [1,2]. Some of the relevant studiesn this respect have been cited in literature also [3–5]. The physico-hemical properties of surfactants vary markedly above and belowhe critical micelle concentration (CMC) [6]. Below the CMC val-es, these properties (e.g. conductivity, electromotive force, etc.)f ionic surfactants like sodium dodecyl sulphate (SDS) resembleith those of a strong electrolyte but above the CMC, these proper-

ies change dramatically indicating a highly cooperative associationrocess which is going to take place. This behavior is explained inerms of formation of organized aggregates of large numbers of

olecules called micelles [7] in which the hydrophobic parts ofurfactants associate with each other in interior of the aggregate,eaving the hydrophilic parts to face aqueous medium.

Surfactants are added to a liquid in order to increase its wettingr spreading properties because of their ability to lower the sur-ace tension of a liquid as well as the interfacial tension betweenwo liquids or between a liquid and a solid [8,9]. The surface active

mphiphilic anions are absorbed on water surface where theyreate a characteristic monolayer. The hydrophobic alkyl chainsdodecyl) –CH3 (CH2)11 are oriented outside from the water surface,

∗ Corresponding author. Tel.: +91 177 2830803; fax: +91 177 2830775.E-mail address: chauhansuvarcha@rediffmail.com (S. Chauhan).

378-3812/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.fluid.2013.06.051

© 2013 Elsevier B.V. All rights reserved.

while the hydrophilic OSO3− head group is directed into the aque-

ous environment. The overall process has the tendency to bring thehydrocarbon molecules together, which is known as the hydropho-bic interactions. The critical micelle concentration (CMC) of SDS inpure water at 25 ◦C is 0.0082 mol dm−3 [10] and the aggregationnumber at CMC is usually considered to be about 62 [11].

Maltodextrin is a water-soluble oligosaccharide containinghundreds of sugar molecules and has a variety of applications viz.used as food additives, in pharmaceutical, industrial and in biolog-ical systems [3]. In aqueous solution, it is responsible for differentkinds of interactions occurring among its components [12]. Thestructure of maltodextrin has been shown in Fig. 1.

In view of these facts, in the present work, different parameterslike apparent molar volume (˚v), apparent molar isentropic com-pression (˚k), surface excess concentration (�max), minimum areaoccupied by the surfactant (Amin), surface film pressure (�cmc) andviscous relaxation time (�) in SDS–maltodextrin system has beenstudied by using different techniques for the characterization ofmicellar solution in order to improve the current understanding ofinteractions between carbohydrates and surfactants.

2. Experimental

2.1. Materials

Sodium dodecyl sulphate having purity > 99.5% obtained fromHiMedia Pvt. Ltd. However, a pure sample of SDS was obtained bygiving the following treatment. About 50 g of SDS was dissolved in500 ml of 95% ethanol. Suspension in the solution was removed by

S. Chauhan et al. / Fluid Phase Equilibria 354 (2013) 236–244 237

Ft

fibv2fwas2u

2

AarpdehfljDvT±

SwtMsTo

3

3

ts(Tpu

�

woh

sou

nd

velo

city

, (v)

and

isen

trop

ic

com

pre

ssib

ilit

y,

(�s)

of

aqu

eou

s

SDS

at

dif

fere

nt

tem

per

atu

res

(◦ C).

mol

dm

−3[0

%]

Mal

tod

extr

in

d

(kg

mol

−3)

v

(m

s−1)

�s

(TPa

−1)

20

25

30

35

40

20

25

30

35

40

20

25

30

35

40

998.

321

997.

152

995.

747

994.

124

992.

299

1482

.99

1497

.13

1509

.37

1520

.08

1529

.15

455.

4633

447.

4243

440.

8182

435.

3380

430.

9802

998.

375

997.

207

995.

800

994.

176

992.

350

1483

.37

1497

.42

1509

.44

1520

.29

1529

.37

455.

2053

447.

2264

440.

7539

435.

1950

430.

8340

998.

419

997.

249

995.

840

994.

212

992.

386

1483

.52

1497

.59

1509

.68

1520

.45

1529

.49

455.

0932

447.

1060

440.

5961

435.

0876

430.

7508

998.

467

997.

297

995.

887

994.

257

992.

430

1483

.80

1497

.81

1509

.85

1520

.63

1529

.65

454.

8996

446.

9532

440.

4761

434.

9649

430.

6416

998.

520

997.

350

995.

935

994.

306

992.

475

1484

.10

1498

.05

1510

.05

1520

.82

1529

.82

454.

6916

446.

7862

440.

3382

434.

8348

430.

5264

998.

582

997.

406

995.

990

994.

359

992.

529

1484

.21

1498

.17

1510

.25

1521

.01

1529

.99

454.

5959

446.

6896

440.

1973

434.

7030

430.

4073

998.

622

997.

456

996.

038

994.

406

992.

574

1484

.39

1498

.42

1510

.46

1521

.12

1530

.09

454.

4675

446.

5182

440.

0537

434.

6196

430.

3315

998.

678

997.

499

996.

082

994.

448

992.

614

1484

.64

1498

.55

1510

.59

1521

.33

1530

.28

454.

2890

446.

4215

439.

9585

434.

4813

430.

2073

998.

725

997.

548

996.

128

994.

493

992.

658

1484

.94

1498

.87

1510

.99

1521

.48

1530

.44

454.

0841

446.

2089

439.

7053

434.

3760

430.

0983

998.

771

997.

592

996.

170

994.

534

992.

699

1484

.87

1498

.78

1510

.90

1521

.38

1530

.32

454.

1060

446.

2428

439.

7391

434.

4151

430.

1480

998.

807

997.

625

996.

204

994.

567

992.

731

1484

.85

1498

.76

1510

.89

1521

.36

1530

.30

454.

1018

446.

2400

439.

7299

434.

4122

430.

1454

998.

856

997.

673

996.

252

994.

615

992.

778

1484

.87

1498

.74

1510

.85

1521

.34

1530

.28

454.

0673

446.

2304

439.

7320

434.

4026

430.

1363

998.

899

997.

712

996.

291

994.

653

992.

814

1484

.87

1498

.72

1510

.82

1521

.31

1530

.23

454.

0478

446.

2249

439.

7323

434.

4031

430.

1488

998.

926

997.

752

996.

326

994.

685

992.

847

1484

.86

1498

.71

1510

.81

1521

.23

1530

.22

454.

0416

446.

2130

439.

7226

434.

4349

430.

1401

nti

es

in

den

sity

mea

sure

men

ts

wer

e

±4

×

10−3

kg

m−3

.

ig. 1. Structure of maltodextrin in which repeating glucose molecules connectedogether by �-(1,4) glycosidic linkage.

ltration and remaining solution was gently warmed on a waterath. As the volume of solution reduced to one fourth of its originalolume, the solution was left to cool at room temperature for about–3 h. The final product was ground gently and dried under vacuumor about two days before use. Maltodextrin having purity > 99%as obtained from Loba Chemie Pvt. Ltd. and used as such without

ny further purification. Water is the main solvent in the presenttudy. Doubly distilled water having conductivity (�) in the range

× 10−6–3 × 10−6 S−1 cm−1 and pH ∼7.0 at 25 ◦C was collected forse.

.2. Equipment and experimental procedure

Density and sound velocity measurement were carried out usingnton Paar 5000 (DSA-5000). The reproducibility of speed of soundnd density data was well within ±0.2 m s−1 and ±2 × 10−6 g cm−3

espectively. The precision in temperature was ±0.001 ◦C. A highrecision water bath fitted with a digital temperature controlledevice used for viscosity measurement supplied by Narang Sci-ntific Works (NSW) Pvt. Ltd. New Delhi. Viscosity measurementsave been carried out by using jacketed Ostwald viscometer havingow time 348 s for distilled water at 25 ◦C. The viscometer was sub-

ected to calibration before use at 25 ◦C using water (� = 0.891 cP),ioxane (� = 1.19 cP) and DMSO (� = 2.01 cP) as solvents. Thesealues agreed reasonably well with the literature values [13,14].he reproducibility of the measurements of viscosity was within0.02 cP.

Surface tension measurements were carried out by using Maningh Survismeter supplied by Spectro Lab Equipments Pvt. Ltd.ith number of drops of water equal to 146 at 25 ◦C. The survisme-

er was subjected to calibration before use at 25 ◦C by DMSO andeOH having � values 43.33 and 22.41 m Nm−1 which were rea-

onably in good agreement with those reported in literature [15].he reproducibility for the surface tension measurements comesut to be in the range ±0.10 m Nm−1.

. Results and discussion

.1. Volumetric and acoustic studies

Density (d) and sound velocity (v) of SDS in the concentra-ion range (1–14 mmol dm−3) have been measured in aqueousolution of maltodextrin (0.5–1.5%, w/v) at different temperatures20–40 ◦C) at an interval of 5 ◦C. The data have been summarized inables 1–4 and have been used to calculate the following derivedarameters. The isentropic compressibility (�s) has been calculatedsing the relation [16],

s = 12

(1)

v d

here d (kg m−3) is the density of solution and v (m s−1) is the speedf sound for the solution. The compressibility of micellar solutionsas been proposed to depend mainly on two major contributions Ta

ble

1D

ensi

ty, (

d)

103, [

SDS]

1 2 3 4 5 6 7 8 9 10

11

12

13

14

The

un

cert

ai

238

S. Chauhan

et al.

/ Fluid

Phase Equilibria

354 (2013)

236–244

Table 2Density, (d) sound velocity, (v) and isentropic compressibility, (�s) of SDS in 0.5% (w/v) of aqueous solution of maltodextrin at different temperatures (◦C).

103, [SDS] mol dm−3 [0.5%] Maltodextrin

d (kg mol−3) v (m s−1) �s (TPa−1)

20 25 30 35 40 20 25 30 35 40 20 25 30 35 40

1 1000.182 999.008 997.595 995.963 994.134 1484.24 1498.25 1510.50 1521.14 1530.22 453.8504 445.9257 439.3436 433.9287 429.58322 1000.241 999.067 997.649 996.017 994.187 1484.50 1498.48 1510.69 1521.29 1530.37 453.6647 445.7625 439.2093 433.8197 429.47613 1000.324 999.145 997.727 996.093 994.261 1484.81 1498.75 1510.95 1521.51 1530.51 453.4376 445.5671 439.0238 433.6611 429.36564 1000.344 999.165 997.746 996.112 994.277 1485.02 1498.95 1511.13 1521.68 1530.66 453.3003 445.4393 438.9109 433.556 429.27455 1000.383 999.200 997.780 996.144 994.307 1485.15 1499.10 1511.21 1521.78 1530.72 453.2033 445.3345 438.8495 433.4851 429.22796 1000.441 999.258 997.833 996.194 994.356 1485.47 1499.37 1511.52 1522.03 1530.98 452.9818 445.1483 438.6462 433.3209 429.0617 1000.500 999.314 997.889 996.251 994.411 1485.65 1499.55 1511.69 1522.19 1531.13 452.8453 445.0165 438.5229 433.205 428.95328 1000.551 999.361 997.935 996.293 994.446 1485.87 1499.73 1511.85 1522.33 1531.25 452.6882 444.8888 438.4099 433.1071 428.87099 1000.581 999.392 997.963 996.320 994.481 1485.94 1499.79 1511.87 1522.34 1531.26 452.6319 444.8394 438.386 433.0897 428.8502

10 1000.623 999.423 998.005 996.363 994.521 1486.00 1499.82 1511.90 1522.37 1531.28 452.5764 444.8078 438.3501 433.0539 428.821811 1000.656 999.465 998.033 996.390 994.548 1486.03 1499.75 1511.89 1522.35 1531.26 452.5432 444.8306 438.3436 433.0536 428.821312 1000.707 999.517 998.083 996.438 994.595 1486.03 1499.73 1511.86 1522.32 1531.23 452.5201 444.8193 438.3391 433.0498 428.817913 1000.746 999.551 998.118 996.470 994.626 1486.02 1499.72 1511.85 1522.30 1531.18 452.5086 444.8101 438.3295 433.0472 428.832514 1000.800 999.602 998.180 996.540 994.690 1486.01 1499.71 1511.83 1522.29 1531.17 452.4903 444.7934 438.3139 433.0225 428.8105

The uncertainties in sound velocity measurements were ±0.5 m s−1.

Table 3Density, (d) sound velocity, (v) and isentropic compressibility, (�s) of SDS in 1% w/v aqueous solution of maltodextrin at different temperatures (◦C).

103, [SDS] mol dm−3 [1.0%] Maltodextrin

d (kg mol−3) v (m s−1) �s (TPa−1)

20 25 30 35 40 20 25 30 35 40 20 25 30 35 40

1 1002.001 1000.837 999.412 997.773 995.937 1485.20 1499.16 1511.45 1522.02 1531.02 452.4410 444.5705 437.9937 432.6409 428.35752 1002.055 1000.877 999.454 997.813 995.976 1485.29 1499.33 1511.53 1522.09 1531.13 452.3618 444.4520 437.9289 432.5837 428.27923 1002.102 1000.915 999.488 997.848 996.011 1485.56 1499.50 1511.78 1522.26 1531.23 452.1762 444.3343 437.7692 432.4719 428.20824 1002.153 1000.964 999.537 997.895 996.055 1485.86 1499.78 1511.94 1522.46 1531.42 451.9706 444.1467 437.6551 432.338 428.08315 1002.204 1001.013 999.585 997.942 996.102 1486.12 1500.01 1512.14 1522.64 1531.58 451.7895 443.9888 437.5183 432.2154 427.97346 1002.262 1001.070 999.640 997.995 996.153 1486.39 1500.25 1512.37 1522.85 1531.77 451.5992 443.8214 437.3612 432.0732 427.84547 1002.349 1001.156 999.723 998.077 996.231 1486.65 1500.40 1512.56 1523.03 1531.94 451.4021 443.6946 437.2150 431.9356 427.71698 1002.399 1001.203 999.770 998.122 996.277 1486.84 1500.57 1512.71 1523.16 1532.06 451.2642 443.5732 437.1078 431.8424 427.63029 1002.406 1001.208 999.774 998.125 996.280 1486.92 1500.71 1512.79 1523.23 1532.12 451.2125 443.4883 437.0598 431.8015 427.5954

10 1002.483 1001.284 999.849 998.198 996.351 1487.03 1500.82 1512.86 1523.31 1532.17 451.1111 443.3896 436.9866 431.7245 427.537111 1002.503 1001.301 999.866 998.214 996.369 1487.08 1500.86 1512.89 1523.32 1532.20 451.0718 443.3584 436.9618 431.7119 427.512612 1002.542 1001.342 999.903 998.252 996.404 1487.12 1500.88 1512.92 1523.34 1532.21 451.0300 443.3285 436.9283 431.6842 427.492113 1002.581 1001.386 999.948 998.297 996.448 1486.87 1500.75 1512.79 1523.21 1532.08 451.1641 443.3858 436.9838 431.7384 427.545614 1002.616 1001.411 999.972 998.319 996.470 1487.17 1500.96 1512.98 1523.40 1532.26 450.9663 443.2507 436.8635 431.6212 427.4358

S. Chauhan

et al.

/ Fluid

Phase Equilibria

354 (2013)

236–244

239

Table 4Density, (d) sound velocity, (v) and isentropic compressibility, (�s) of SDS in 1.5% (w/v) aqueous solution of maltodextrin at different temperatures (◦C).

103, [SDS] mol dm−3 [1.5%] Maltodextrin

d (kg mol−3) v (m s−1) �s (TPa−1)

20 25 30 35 40 20 25 30 35 40 20 25 30 35 40

1 1003.857 1002.660 1001.227 999.580 997.738 1486.36 1500.28 1512.54 1522.99 1531.93 450.8999 442.9818 436.5698 431.3088 427.07652 1003.901 1002.705 1001.273 999.626 997.781 1486.56 1500.46 1512.61 1523.13 1532.08 450.7588 442.9737 436.4516 431.2097 426.97443 1003.940 1002.746 1001.312 999.667 997.821 1486.83 1500.61 1512.80 1523.29 1532.21 450.5776 442.8671 436.3827 431.1014 426.88494 1003.989 1002.792 1001.356 999.706 997.860 1486.99 1500.78 1512.96 1523.43 1532.38 450.4587 442.7464 436.2713 431.0054 426.77355 1004.068 1002.868 1001.431 999.775 997.932 1487.34 1501.01 1513.26 1523.72 1532.61 450.2113 442.5772 436.0656 430.8116 426.61466 1004.138 1002.936 1001.497 999.846 997.997 1487.46 1501.20 1513.35 1523.79 1532.67 450.1072 442.4352 435.9850 430.7414 426.55347 1004.202 1002.996 1001.557 999.903 998.053 1487.58 1501.45 1513.50 1523.93 1532.80 450.0060 442.2614 435.8725 430.6377 426.45728 1004.226 1003.023 1001.580 999.925 998.073 1487.87 1501.57 1513.68 1524.09 1532.94 449.8198 442.1788 435.7588 430.5379 426.37079 1004.259 1003.053 1001.609 999.954 998.103 1488.00 1501.69 1513.77 1524.18 1533.02 449.7264 442.0949 435.6944 430.4745 426.3134

10 1004.295 1003.087 1001.644 999.987 998.134 1488.08 1501.85 1513.85 1524.24 1533.07 449.6620 441.9858 435.6331 430.4264 426.272411 1004.335 1003.130 1001.680 1000.031 998.179 1487.15 1501.89 1513.86 1524.28 1533.07 449.6078 441.9433 435.6002 430.3962 426.258712 1004.380 1003.167 1001.720 1000.061 998.204 1488.28 1501.93 1513.90 1524.28 1533.08 449.5151 441.9034 435.5713 430.3720 426.236913 1004.416 1003.204 1001.758 1000.097 998.241 1488.12 1501.86 1513.85 1524.21 1533.03 449.5232 441.9283 435.5836 430.3960 426.248914 1004.449 1003.234 1001.787 1000.126 998.269 1488.18 1501.89 1513.85 1524.20 1533.01 449.5326 441.8975 435.5710 430.3892 426.2481

0 2

4 6

2.0

5

2.1

0

2.1

5

2.2

0

2.2

5

2.3

0

2.3

5

2.4

0

2.4

5

2.5

0

104,

v(m

3mol

-1)

20

OC

25

OC

30

OC

35

OC

40

OC

10

3, [SD

S] (

(a)

0 2

4 6

-0.1

8

-0.1

6

- 0.1

4

-0.1

2

-0.1

0

- 0.0

8

- 0.0

6

-0.0

4

-0.0

2

0.0

0

0.0

2

0.0

4

10

3, [SD

S]

(m

k(m

3·mol

-1·TPa

-1)

(b)

Fig. 2.

(a) A

pp

arent

molar

volum

e, ˚

v(m

3m

olcom

pression

, ˚

k(m

3m

ol −1

TPa −1)

of aqu

eous

[17]: (i)

the

comp

ressibility of

the

hyd

rocarbon core

and

(ii) th

ein

teractions

between

the

head

group

s. H

owever,

isentrop

ic com

-p

ressibility is

likely to

be d

epen

den

t on

the

variation of

the

coun

terion

bind

ing

and

the

hyd

roph

ilicity of

the

head

group

[18].Th

e com

pressibility

data

for p

ure

SDS

and

for d

ifferent

percen

t-ages

of m

altodextrin

has

been su

mm

arized in

Tables 1–4

and

show

that

the

comp

ressibility d

ecreases w

ith in

crease in

temp

erature

asw

ell as

with

concen

tration of

SDS

[19], w

hich

makes

the

solution

rather

incom

pressible.

The

value

of �

salso

decreased

with

increase

in th

e p

ercentage

of m

altodextrin

. Th

e low

ering

in com

pressibility

imp

lies th

at th

ere is

enh

ancin

g m

olecular

association in

this

sys-tem

on in

crease in

solute

conten

t, as

the

new

entities

(formed

du

eto

molecu

lar association

) becom

e com

pact

and

less com

pressible.

So th

ere is

increasin

g solu

te–solvent

interaction

s w

ith in

crease in

temp

erature

and

with

concen

tration [17].

The

app

arent

molar

volum

e (˚

v ) h

as been

calculated

usin

g th

erelation

[19],

˚v =

do −

d

md

do

+Md

(2)

wh

ere m

(mol

kg −1)

is th

e m

olality of

the

solution

, M

(kg m

ol −1)

is th

e m

olecular

weigh

t of

surfactan

t, d

(kg m

−3)

is th

e d

ensity

ofth

e solu

tion,

and

do

(kg m

−3)

is th

e d

ensity

of solven

t i.e.

aqueou

ssolu

tion of

maltod

extrin.

8 10

12

14

16

mo

l.dm

-3)

8 1

0 1

2 14

16

ol·d

m-3)

20

OC

25

OC

30

OC

35

OC

40

OC

−1)

and

(b) ap

paren

t m

olar ad

iabaticSD

S at

differen

t tem

peratu

res.

240 S. Chauhan et al. / Fluid Phase Equilibria 354 (2013) 236–244

0 2 4 6 8 10 12 14 16

1.4

1.6

1.8

2.0

2.2

2.4

10

4,

v(m

3m

ol-1

)

103, [SDS] (mol.dm

-3)

20OC

25OC

30OC

35OC

40OC

(a)

0 2 4 6 8 10 12 14 16

-0.1 2

-0.1 0

-0.0 8

-0.0 6

-0.0 4

-0.0 2

0.0 0

0.0 2

0.0 4

k(m

3·m

ol-1

·TP

a-1)

103, [SDS] (mol ·dm

-3)

20OC

25OC

30OC

35OC

40OC

(b)

Fig. 3. (a) Apparent molar volume, ˚v (m3 mol−1) and (b) apparent molar adia-bs

t(b

(

(

dppcsa

(b)

(a)

ΦΦ

atic compression, ˚k (m3 mol−1 TPa−1) as a function of [SDS] in 0.5% (w/v) aqueousolution of maltodextrin at different temperatures.

In the presently studied maltodextrin–surfactant systems, theypes of interactions which are possible among maltodextrinoligosaccharide) and sodium dodecyl sulphate (SDS) solute wille:

(i) Ionic–hydrophilic interactions between the ion (SO2−4 ) of

solute and hydrophilic sites ( OH, C O and O ) of the mal-todextrin.

(ii) Hydrophobic–hydrophilic interactions between hydrophobicpart of SDS and hydrophilic part of maltodextrin.

iii) Hydrophobic–hydrophobic interactions between the alkylchain of the saccharide molecules and hydrophobic part of thesolute (SDS) and

iv) Hydrogen-bonding between maltodextrin and water(H2O).

Apparent molar values, ˚v for SDS in aqueous maltodextrin atifferent temperatures have been reported in Tables S1–S4 (sup-

lementary data). Figs. 2(a)–5(a) show that the values of ˚v areositive, increases with rise in temperature as well as with per-entage of maltodextrin. A similar conclusion is drawn in case ofurfactant system as reported in the literature [18,20]. The value ofpparent molar adiabatic compression, ˚v has been calculated by

Fig. 4. (a) Apparent molar volume, ˚v (m3 mol−1) and (b) apparent molar adia-batic compression, ˚k (m3 mol−1 TPa−1) as a function of [SDS] in 1% (w/v) aqueoussolution of maltodextrin at different temperatures.

using the relation [19],

˚k = �s − �o

mdo+ ˚v�s (3)

where �o is the isentropic compressibility for the solvent, �s is theisentropic compressibility for the solution, ˚v is the apparent molarvolume and do is the density of solvent respectively.

The ˚k values, thus obtained have been reported in Tables S1–S4(supplementary data). A perusal of data along with Figs. 2(b)–5(b)depicts the behavior of ˚k at different concentrations of maltodex-trin as well as at different temperatures. At lower concentrationof maltodextrin, (i.e. at 0.5%, w/v) ˚k are initially negative whichgradually increase with rise in [SDS] at all temperatures. The non-linear behavior in ˚k values becomes more prominent at highermaltodextrin concentration.

Both ˚v and ˚k values show strong temperature dependenceas well. It is apparent from these graphs that added sugar seems tointeract with charged head groups of surfactant electro-statically[18].

S. Chauhan et al. / Fluid Phase Equilibria 354 (2013) 236–244 241

Table 5Viscosity, (�) of SDS in 0% and 0.5% (w/v) aqueous solution of maltodextrin at different temperatures (◦C).

103, [SDS] mol dm−3 � (cp)

0% 0.5%

20 25 30 35 40 20 25 30 35 40

1 1.0023 0.8889 0.8026 0.7202 0.6528 1.0050 0.8990 0.8005 0.7112 0.65512 1.0043 0.8904 0.8038 0.7216 0.6536 1.0052 0.8996 0.8013 0.7118 0.65573 1.0052 0.8918 0.8058 0.7223 0.6543 1.0057 0.9000 0.8018 0.7123 0.65634 1.0076 0.8925 0.8064 0.7226 0.6549 1.0062 0.9003 0.8026 0.7127 0.65665 1.0100 0.8931 0.8073 0.7231 0.6553 1.0065 0.9007 0.80320 0.7130 0.65696 1.0115 0.8966 0.8106 0.7266 0.6569 1.0070 0.9013 0.8035 0.7134 0.65747 1.0151 0.8983 0.8119 0.7284 0.6596 1.0080 0.9020 0.8043 0.7142 0.65858 1.0154 0.8988 0.8124 0.7286 0.6601 1.0088 0.9034 0.8047 0.7149 0.65899 1.0156 0.8990 0.8134 0.7290 0.6609 1.0111 0.9050 0.8074 0.7171 0.6601

10 1.0161 0.8992 0.8153 0.7297 0.6612 1.0114 0.9055 0.8078 0.7173 0.660411 1.0164 0.8993 0.8155 0.7306 0.6639 1.0118 0.9059 0.8082 0.7174 0.6606

000

3

t

Fco

12 1.0166 0.8994 0.8157 0.7312

13 1.0169 0.8998 0.8158 0.7318

14 1.0170 0.9000 0.8163 0.7325

.2. Viscometric studies

Viscosity of SDS in water and in different percentage of mal-odextrin (w/v) has also been carried out by using Ostwald

0 2 4 6 8 10 12 14 16

2.30

2.32

2.34

2.36

2.38

2.40

2.42

2.44

2.46

2.48

10

4,

v(m

3m

ol-1

)

103, [SDS] (mol.d m

-3)

20OC

25OC

30OC

35OC

40OC

(a)

0 2 4 6 8 10 12 14 16

-0.08

-0.07

-0.06

-0.05

-0.04

-0.03

-0.02

-0.01

0.00

0.01

0.02

0.03

0.04

k(m

3·m

ol-1

·TP

a-1)

103, [SDS] (m ol·dm

-3)

20OC

25OC

30OC

35OC

40OC

(b)

ig. 5. (a) Apparent molar volume, ˚v (m3 mol−1) and (b) apparent molar adiabaticompression, ˚k (m3 mol−1 TPa−1) as a function of [SDS] in 1.5% aqueous solutionf maltodextrin at different temperatures.

.6630 1.0122 0.9066 0.8090 0.7179 0.6607

.6638 1.0128 0.9069 0.8092 0.7181 0.6618

.6640 1.0136 0.9078 0.8094 0.7185 0.6613

viscometer at different temperatures. Viscosity of solution is cal-culated by using the relation [19],

�s = �otsds

twdw(4)

where �o is the viscosity of solvent, tw the time of flow of solvent,ts the time of flow of solution, dw the density of solvent, and ds thedensity of solution. The viscosity data for aqueous SDS and for dif-ferent concentration of maltodextrin (0.5, 1, 1.5%, w/v) at differenttemperatures have been reported in Tables 5 and 6. The viscosityvalues have been further used to calculate viscous relaxation time(�) which is calculated by using the relation [20]

� = 4�s

3v2d(5)

The dependence of � on SDS concentration in aqueous solutionof maltodextrin has been reported in Tables S5–S6 (supplementarydata). Viscous relaxation time increases gradually with increase inconcentration of surfactant, SDS and same decrease with rise intemperature. This is mainly due to the structural relaxation pro-cesses occurring due to the re-arrangement of the molecules [21].These observations, therefore lead to conclusion that there existssignificant amount of interactions between SDS and maltodextrin.

3.3. Surface tension studies

Surface tension of SDS in water and in different percentage ofmaltodextrin (w/v) at 25 and 35 ◦C has been carried out by usingMan Singh Survismeter. The surface tension (�s) is calculated byusing the relation [19],

�s = �0nwds

nsdw(6)

where �s is the surface tension of the solution, �o the surfacetension of the solvent, nw the number of drops of solvent, ns thenumber of drops of solution, dw the density of solvent, and ds

the density of solution. Surface tension measurements used toprovide information about the binding of SDS to maltodextrin. If themaltodextrin–SDS complex is surface active, then it would reducethe surface tension of solvent molecule [3].

The surface tension data have been presented at different per-centages of maltodextrin in Fig. 6(a)–(d) which shows a decreasesin the surface tension with rise in temperature [22] as well as

with percentage of maltodextrin. Below cmc, (i.e. 0.0082 mol dm−3)surface tension of SDS in maltodextrin decreases sharply tominimum, which is indicating the adsorption of SDS to theair–water interface. Initially, at lower surfactant concentration,

242 S. Chauhan et al. / Fluid Phase Equilibria 354 (2013) 236–244

Table 6Viscosity, (�) of SDS in 1.0% and 1.5% (w/v) aqueous solution of maltodextrin at different temperatures (◦C).

103, [SDS] mol dm−3 � (cp)

1.0% 1.5%

20 25 30 35 40 20 25 30 35 40

1 1.0050 0.8990 0.8005 0.7112 0.6550 0.9993 0.9112 0.8126 0.7198 0.64992 1.0053 0.8995 0.8013 0.7118 0.6557 0.9998 0.9116 0.8131 0.7203 0.65023 1.0057 0.9000 0.8018 0.7123 0.6563 0.9999 0.9120 0.8134 0.7205 0.65064 1.0062 0.9003 0.8026 0.7127 0.6566 1.0004 0.9126 0.8139 0.7207 0.65095 1.0065 0.9007 0.8032 0.7130 0.6569 1.0009 0.9134 0.8141 0.7210 0.65146 1.0070 0.9012 0.8035 0.7134 0.6574 1.0013 0.9143 0.8146 0.7214 0.65167 1.0079 0.9020 0.8043 0.7142 0.6585 1.0029 0.9155 0.8185 0.7237 0.65328 1.0088 0.9034 0.8048 0.7149 0.6589 1.0062 0.9182 0.8210 0.7249 0.65469 1.0111 0.9050 0.8074 0.7171 0.6601 1.0069 0.9194 0.8218 0.7252 0.6550

10 1.0114 0.9055 0.8079 0.7173 0.6604 1.0073 0.9197 0.8220 0.7253 0.655311 1.0117 0.9059 0.8082 0.7174 0.6606 1.0077 0.92014 0.8224 0.7256 0.655412 1.0121 0.9066 0.8090 0.7179 0.6608 1.0080 0.92014 0.8228 0.7258 0.6555

00

thmt(f

13 1.0128 0.9069 0.8092 0.7182

14 1.0136 0.9073 0.8094 0.7185

he binding of maltodextrin with SDS is electrostatic, whereas atigher concentration of surfactant, hydrophobic interactions make

icellization becomes more favorable. The surface tension values

hen used to calculate different parameters such as surface excess� max), minimum area occupied by the surfactant (Amin) and sur-ace film pressure (�cmc). The adsorption behavior of SDS at the

-3.0 -2.8 -2.6 -2.4 -2.2 -2.0 -1.8

35

40

45

50

55

60

65

(mN

m-1)

Log[SDS]

25OC

35OC

(c)

-3.0 -2.8 -2.6 -2.4 -2.2 -2.0 -1.8

35

40

45

50

55

60

65

70

mN

m-1)

Log [SDS]

25OC

35OC

(a)

Fig. 6. Surface tension (m Nm−1) as a function of log[SDS] in (a) 0.0, (b) 0.5, (c) 1.0 a

.6610 1.0083 0.9204 0.8232 0.7260 0.6556

.6613 1.0085 0.9206 0.8236 0.7262 0.6557

interface is calculated by using Gibbs adsorption isotherm equation[19]

�max = −(

12.303nRT

)(∂�

∂ log[C]

)T,P

(7)

-3.0 -2.8 -2.6 -2.4 -2.2 -2.0 -1.8

35

40

45

50

55

60

65

(mN

m-1

)

log[SDS]

25OC

35OC

(b)

-3.0 -2.8 -2.6 -2.4 -2.2 -2.0 -1.8

35

40

45

50

55

60

(mN

m-1)

Log[SDS]

25OC

35OC

(d)

nd (d) 1.5% (w/v) aqueous solution of maltodextrin at different temperatures.

S. Chauhan et al. / Fluid Phase Equilibria 354 (2013) 236–244 243

-0.20.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

90

92

94

96

98

100

102

104

106

108

110

112

114

Am

in (

nm

2)

% w/v

25OC

OC 35

(b)

-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

30.0

30.5

31.0

31.5

32.0

32.5

33.0

33.5

34.0

34.5

cm

c

% w/v

25OC

35OC

(c)

-0.20.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

1.45

1.50

1.55

1.60

1.65

1.70

1.75

1.80

1.85

ma

x (

mo

l cm

-2)

10

10

% w/v

25OC

35OC(a)

F tion ot

wbcoi

A

wcwi

TA

ig. 7. (a) The variation of � max (mol cm−2), (b) variation of Amin (nm2) and (c) variaemperatures.

here (∂�/∂ log[C]), the slope calculated from the graph plotetween � vs log[C], n = 2 in all the cases, R is the universal gasonstant and T is the absolute temperature. The minimum areaccupied by the surfactant molecule at the saturated air/solutionnterface (Amin) calculated from the equation [23]

min = 1018

�maxNo(8)

here No is Avogadro’s number and the factor 1018 arises as aonversion factor of area from m2 to nm2. Amin at cmc increasesith increase in percentage of maltodextrin and also increases with

ncrease in temperature. The lowering of the surface tension of a

able 7 study of interfacial parameters (� max), Amin and ˘cmc (m Nm−1) of SDS in different perc

% age of maltodextrin (w/v) 1010, � max (mol cm−2)

298.15 308.15

0.0 1.83 1.74

0.5 1.80 1.67

1.0 1.74 1.64

1.5 1.62 1.46

f �cmc (m Nm−1) of SDS at CMC in different percentages of maltodextrin at different

solvent by the surface film at cmc can be expressed in terms of thesurface film pressure [23]∏

cmc= �o − �cmc (9)

where �o is the surface tension of solvent and �cmc the surfacetension at cmc. These parameters are reported in Table 7. � max

is a useful measure of the amount of surfactant adsorbed at air-water interface and decrease in � max of SDS in the presence ofmaltodextrin as compare to water however, indicates increasedhydrophilic character of the SDS–maltodextrin complex, also there-

fore a decrease in � max value of SDS is observed with the increasein temperature in aqueous solution of maltodextrin as shown inFig. 7(a). Accordingly, Amin increases with rise in temperature whichis also in agreement with literature [24]. Such binding thus explains

entages of maltodextrin (0.0–1.5%) at different temperatures (◦C).

102, Amin (nm2) ˘cmc(m Nm−1)

298.15 308.15 298.15 308.15

90.64 95.61 32.14 30.0692.13 99.20 33.26 31.7295.25 101.20 34.33 32.38

102.41 113.41 33.04 31.31

2 se Equ

tTtaF

4

ptItcrssS

A

mmrt

A

t

[

[[

[

[[[[

[

[

[

[

44 S. Chauhan et al. / Fluid Pha

he stability of SDS–maltodextrin complex at air–water interface.he surface pressure, ˘cmc however, decreases with increase inemperature and is found to be consistent with the effect outlinedbove. The schematic plots for Amin and ˘cmc have been shown inig. 6(b)–(c) respectively.

. Conclusion

In summary, we have concluded that the volumetric studiesoint the delayed micellization for SDS in presence of maltodex-rin which is further supported well by the surface tension studies.n case of maltodextrin with SDS, at lower surfactant concentra-ion, there are appreciable electrostatic interactions but at higheroncentration of surfactant, hydrophobic interactions play majorole. Surface excess (� max) and minimum area occupied by theurfactant (Amin) complimenting each other, thus, reveals the con-iderable amount of an association or interactions taking place inDS–maltodextrin system.

cknowledgments

S. Chauhan and Kundan Sharma thank University Grant Com-ission, New Delhi for their financial assistance under theajor research project (F. No. 32-237/2006(SR)) and awarding

esearch fellowship (No. F.4-1/2006 (BSR)/7-75/2007(BSR)) respec-ively.

ppendix A. Supplementary data

Supplementary data associated with this article can be found, inhe online version, at http://dx.doi.org/10.1016/j.fluid.2013.06.051.

[[

[

ilibria 354 (2013) 236–244

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