Water in Polymers - American Chemical Society

3

T h e S t r u c t u r e of A q u e o u s S y s t e m s a n d the Influence o f Electrolytes WERNER A. P. LUCK

Downloaded by UNIV OF PITTSBURGH on May 4, 2015 | http://pubs.acs.org Publication Date: August 19, 1980 | doi: 10.1021/bk-1980-0127.ch003

Institut Physikalische Chemie, Universität Marburg, D-3550 Marburg, Federal Republic of Germany

One of the most important questions in applied chemistry is the structure of water in solutions and biologic cells or membranes. Progress in modern experimental techniques, such as interpretation of spectra, opens opportunities for useful information and models. 1. Structure of Pure Water. 1a. The Observation Method. Properties of nonpolar liquids can be described surprisingly well by a hole model (1). In the case of water the partition of molecular orientation raises a further complication. The angle dependent Η-bond interaction (2,3) determines about 2/3 of the intermolecular energy of 11.6 kcal/mol in ice. Among a l l others, water molecules stand out be cause of their high OH group content of 110 mole/l at room Τ and an equal content of lone pair electrons, θ. Therefore the dis cussion of the Η-bond content, as a dominant factor, leads to a good approximation of the structure of water (4-12). Because of the dominating role of the fundamental I.R. spectroscopy many overlooked that the overtone spectroscopy is a very useful tool to determine the content of Η-bonds quantitatively(13,14). Solu tions of molecules with OH or NH groups show, contrary to a l l others, an anomalous strong concentration dependence of the OH or NH overtone bands (13,14). The sharp band ν , which appears at F

low concentrations, is replaced at higher concentrations by a broad frequency-shifted band v . The V -band has been established b

F

as vibration of non-H-bonded, so called "free", OH groups c . F

The second band v , with a larger half width Δν b

1/2

but similar

area /edv of the extinction coefficients ε has been associated with Η-bonded species (J_3,jU.). Its frequency shift Δν is pro portional to the Η-bond energy ΔΗ^ (Badger-Bauer rule). Some c r i tics of the overtone method ignored the fact, that Η-bonds change 0-8412-0559-0/ 80 / 47-127-043S07.25 / 0 © 1980 American Chemical Society

In Water in Polymers; Rowland, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

44

WATER IN POLYMERS

- i n c o n t r a s t t o overtones - the area Jedv of fundamentals by a f a c t o r o f 20 or more and t h e r e f o r e the fundamental v i b r a t i o n s make the view "opaque" f o r d e t e r m i n a t i o n o f the " f r e e " OH. The d e t e r m i n a t i o n o f the c o n c e n t r a t i o n CL o f Η-bonds w i t h Ώ

I.R. overtone bands i s c o m p l i c a t e d : i . e . , o v e r l a p p i n g w i t h o t h e r bands and simultaneous one-quantum-absorption by 2 Η-bonded mole cules (15). T h e r e f o r e , the more exact method i s : t o determine C = 0 C ( C : c o n c e n t r a t i o n by weight; 0^: f r a c t i o n o f " f r e e " OH), the content o f " f r e e " OH by the sharp v„ band o f undisturbed moleF

F

Q

q


Γ

cules and t o c a l c u l a t e CL = (1-0.J C . Β F ο With t h i s p r e c i s e technique the s p e c t r a o f OH c o n t a i n i n g so l u t i o n s could be analyzed q u a n t i t a t i v e l y as chemical e q u i l i b r i u m : 0H_ free

+

— ^ free ^

0H_ bond

(1)

E q u i l i b r i u m constants determined by t h i s technique are among the most accurate ones i n p h y s i c a l chemistry (2). With i n c r e a s i n g temperature Τ i n the s p e c t r a o f pure a l c o h o l s appears more and more the same band o f " f r e e " OH (5.). For pure a l c o h o l s the e x t i n c t i o n c o e f f i c i e n t , ε , o f the " f r e e " OH i s max s m a l l e r and the corresponding Δ ν ^ ^ l S than i n s o l u t i o n s , so as t o make the area /εάν the same. The a b b r e v i a t i o n " f r e e " does not mean " g a s - l i k e " but j u s t not Η-bonded; i t i n c l u d e s other i n t e r a c t i o n s l i k e the d i s p e r s i o n t y p e . This appearance o f " f r e e " OH i n a l c o h o l s can be measured q u a n t i t a t i v e l y by the ε of max overtone maxima or byjëdv. I n water too t h i s band o f " f r e e " OH can be observed (with h i g h e s t accuracy w i t h HOD) (Figure 1 and 2) ( U - J 2 ) . The water overtone bands show an i s o s b e s t i c p o i n t below 150°C (6 ,T , 8 ,_16_,JX), f o r example i n the f i r s t overtone o f HOD a r

the r e g i o n 7100 cm -1

—1

3 m, the Li-maximum i s not e a s i l y observable because > 100°C ( 2 6 ) . Because of the many parameters i t i s not easy t o c a l c u l a t e p r o p e r t i e s of aqueous s o l u t i o n s w i t h the simple model of s e c t i o n 1. For i n s t a n c e , the known negative p a r t i a l molar s p e c i f i c heats of ions (k6,Uî) may be r e l a t e d t o a r e d u c t i o n of the i n t e r m o l e c u l l a r p a r t of the s p e c i f i c heat o f water, the p a r t (dO /dT) ΔΗ^ i n T

R

F

equation 2. per degree.

This p a r t gives the energy of the change of H-bonds dO^/dT i s given by the slope of 0 = f (T) (see P

Γ

Γ

F i g u r e 1). With a d d i t i o n s of KF, LdCI or CsCl (.15 water: 1 i o n p a i r ) the slope of 0 i s decreased by 20 % by CsCl and 30 % by L i C I or KF. Bu^NBr, which has a l a r g e p o s i t i v e p a r t i a l molar p

s p e c i f i c h e a t , i n c r e a s e s d0 /dT by 30 %. Q u a n t i t a t i v e c a l c u l a t i o n s r e q u i r e knowledge of i n t e r a c t i o n energies ΔΗ^ i n presence of ions. p

3. M i x t u r e s : Water/Organic L i q u i d s / E l e c t r o l y t e s 3a. S o l u b i l i t y and Acceptor Strength of tne Organic Molecules Weak acceptors f o r H-bonds w i l l i n t e r a c t mainly w i t h the " f r e e " OH i n water. This c o u l d be demonstrated w i t h s o l u t i o n s of NH /H 0 Q


o


3. LUCK

Structure of Aqueous

57

Systems

Figure 6. Top: concentration of total D O, liquid-like D O in 1:1 or 2:1 complexes with ClOf as a function of NaClO concentration at 20°C. Bottom: hydration numbers of ClOf in 1:1 and 2:1 complexes and the mean values of both at 20°C. g

g

k

Δt Λ0-

Q.U3m Κ J (122.6) /^*s^0,763m kCI (71.1) /' *

20·

'\^-0.664ηη Κ Br ( 81.7 ) 0.733m KF(75.0)

0 -201850

1950

2050

2150

2250

nm

Figure 7. Difference spectra for pure water/saturated electrolyte solutions at 23°C. KI, KCI, and KBr reduce the content of free OH (1890 nm) and the content of strongly hydrogen-bonded OH (about 2050 nm) and increase the content of weakly bonded OH (1940 nm). KF has the opposite effect (55).


58

WATER IN POLYMERS


s p e c t r o s c o p i c a l l y (37). Acceptor s t r e n g t h s i m i l a r t o t h a t o f wa t e r o r s t r o n g e r c o u l d d i s t u r b the H-bond system o f pure water. The p o s i t i o n o f h y d r o p h i l i c molecules i n the s e r i e s o f H-bond acceptors can be determined s p e c t r o s c o p i c a l l y by the Badger-Bauer r u l e from Δν o f the water bands (_12 ,*±3.,]i*0. We obtained the s e r i e s : a c e t o n i t r i l e < dioxane H HC0N(CH ) > N ^ C O O C ^ > i - C ^ O H > N H C ^ O H > 2

3

2

C Η OH > t e t r a h y d r o f u r a n e ; a r e d u c t i o n o f T„ was observed f o r glucose < H C=CH-CsN < i-C^HÔH < paraldehyde. 2

The f i r s t group o f o r g a n i c molecules may screen hydrophobic groups, the second one may screen h y d r o p h i l i c groups. J o l i c e u r et a l . (16) have observed a change i n the water s t r u c t u r e by d i f f e r e n t organic s o l u t e s and d e s c r i b e i t by Τ t o o . In'agreestr ment w i t h the PI0P-9 method they found two groups o f o r g a n i c s o l u t e s : 1. Τ . > Τ ( s o l u t i o n ) 2 . Τ . < Τ ( s o l u t i o n ) , str str 3 b . M i c e l l e Formation and E l e c t r o l y t e s . Molecules w i t h more or l e s s separated hydrophobic and h y d r o p h i l i c groups form " c l u s t e r s " o f t h e i r hydrophobic groups i n the shape o f m i c e l l e n u c l e i . Above the c r i t i c a l c o n c e n t r a t i o n (CMC) a l l added mono mers have t o form m i c e l l e s as a r e s u l t o f the e q u i l i b r i u m , η monomers = m i c e l l l e . CMC depends on the HHB-value, the balance between h y d r o p h i l i c i t y and h y d r o p h o b i c i t y . HHB i s s e n s i t i v e t o added s a l t s p a r a l l e l t o the Hofmeister i o n s e r i e s . For i n s t a n c e ,


3.

LUCK


Systems

59

the e q u i l i b r i u m constants Κ . o f m i c e l l e formation o f i - C i L mi ο 17 - ((5) - (0CH CH )^ -0H (PIOP-UO) determined by a U.V. method ( 2 7 , ^ 9 ) are reduced by 0 . 5 m o l / l s a l t s i n the s e r i e s : L i C l < NaCl < B a C l < NaHC0 < (NH^) S0^< Na^SO^) (O.U m) < N a C 0 Q

2

2

Q

3

2

( 0 . 3 m) (at 20°C).

2

0.01.


3

The maximum change o f Κ . i s by a f a c t o r o f m

l

Molecules which are weakly s o l u b l e i n water, can be s o l v a t e d i n the hydrophobic m i c e l l e nucleus. This i s an important t e c h n i c a l process f o r instance f o r detergents. As l e v e l l i n g agent i n t e x t i l e chemistry m i c e l l e s act as b u f f e r s f o r d y e s t u f f s , t h e dyes are s o l u b i l i z e d i n the m i c e l l e nucleus and t h i s e q u i l i b r i u m holds the " f r e e " dye c o n c e n t r a t i o n i n the water phase more o r l e s s con stant d u r i n g the dyeing process (U£,5£) · E l e c t r o l y t e s i n the dyeing bath have two e f f e c t s : 1) s a l t out e f f e c t o f dye t o the f i b r e (5J_), and 2 ) " s a l t - o u t e f f e c t " o f the l e v e l l i n g agent i n c r e a s i n g the m i c e l l e c o n c e n t r a t i o n (27.). The s a l t out e f f e c t on dyes favoures the wash-fastness o f t e x t i l e s : the p a r t i t i o n c o e f f i c i e n t o f the dye between f i b r e and washing bath i s i n c r e a s e d by s t r u c t u r e making s a l t s ( 5 2 ) . 3 c I n t e r f a c e E f f e c t s and E l e c t r o l y t e s . The surface of water i s i n c r e a s e d by ions i n the s e r i e s (26) : S0^

> CI > Br > N 0 Li

+

3

+

> I

> Na > K

tension

> SCN

+

This e f f e c t i s caused by two f a c t o r s : 1.) t h e change o f the water s t r u c t u r e by change o f the H-bond system as a r e a l e f f e c t on s u r face energy (j_) and 2 . ) t h e change o f the number o f water molecules per cm o f surface (j_,j+,53.) by i o n s . Consequently a change o f the surface area-pressure diagrams o f monolayers o f C^gH^-(0CH CH ) 0H 2

2

3

(C18-03) by i o n a d d i t i o n s t o the water subphase has

been observed (5}0. The change o f the water s t r u c t u r e by ions i n the s e r i e s o f Hofmeister a l t e r the i n t e r a c t i o n energy between the water subphase and the ethylenoxide groups o f (C18-03) and the r e q u i r e d f o r c e t o get t h e same monolayer area v a r i e s s i m i l a r l y t o a T-change (3}±). 3d. Ion S o l u b i l i t y i n M i x t u r e s : Water Organic S o l v e n t s . S o l u b i l i t y o f s a l t s i n h y d r o p h i l i c s o l v e n t s i s s m a l l e r than i n water; only some p e r c h l o r a t e s o r L i s a l t s have comparable s o l u b i l i t i e s (Figure 9 gives the r e c i p r o c a l i o n s o l u b i l i t y expressed i n mole s o l v e n t ( a l c o h o l o r acetone) per mole s a l t on a l o g s c a l e (55) · Data c o l l e c t e d by B a r t h e l (56_) demonstrate t h a t at 25 C t h e p a r t i a l molar volume o f ions i n methanol a t i n f i n i t e d i l u t i o n i s


60

WATER IN POLYMERS

ι

Τ [Χ]βΟ κ

60


50 n - 2g/l

40

n-10g/l 30 n-50g/l

20 10 -

n-100g/l 1

2 m

3 K3—•

4

5

Figure 8. Rivalry of ion and ether hydrates of PIOP-9 at high ion contents. Above 2m KI, the tubidity point, T , depends on the PIOP concentration (ng/L), and above 4m, the structure-breaking effect of Κ disappears. K

Figure 9. Reciprocal solubility of chlor ides in water and alcohols on a logarithmic scale, demonstrating the important role of the network water structure on ion solu bilities (55)


3.

LUCK


Systems

61

about 25 +U(cm ) s m a l l e r than i n HÔ and about h + 3 (cm ) bigger i n formamide without i n d i c a t i n g systematic v a r i a t i o n s from the given average v a l u e s . I n t e r n a r y m i x t u r e s : water/acetone o r e t h a n o l / s a l t s , the r e c i p r o c a l s a l t s o l u b i l i t y expressed i n HÔ


present per i o n p a i r (Figure 10 ) i s n e a r l y constant u n t i l solvent c o n c e n t r a t i o n reaches about 250 ΗΓ 0 per solvent molecule (the s i z e o f the water " c l u s t e r s " ) (55/ » Above t h i s solvent concen t r a t i o n the s o l u b i l i t y o f s a l t decreases s h a r p l y . I n mixtures o f water/acetone/K^CrO^ two phases appear above 0.03 mole acetone per mol water; the second phase has 0.2*+ acetone per water and the s a l t content i s reduced by a f a c t o r o f 5 . 5 · These types o f experiments i n d i c a t e s t h a t ions need a group o f water molecules t o be d i s s o l v e d . With higher concentrations o f s o l v e n t molecules the content o f such groups o f HÔ decreases and, t h e r e f o r e , t h e s a l t s o l u b i l i t y decreases. The r e l a t i o n s h i p drawn i n F i g u r e 10 has some s i m i l a r i t i e s t o p r o p e r t i e s o f aqueous s a l t s o l u t i o n s : 1) the behaviour changes above c o n c e n t r a t i o n s higher than 1 s o l u t e per about 300 HÔ, 2) the s o l u b i l i t y o f i o n s r e q u i r e s a group o f HÔ molecules, and 3) there i s a r i v a l r y between i o n and s o l v e n t h y d r a t i o n (see 2 pha ses acetone/HÔ). 3e. Organic Hydration. The f o r e g o i n g r e l a t i o n s h i p and others suggest the e x i s t e n c e o f hydrates o f organic molecules. For i n stance above the t u r b i d i t y p o i n t T^ o f PI0P-9 o r s i m i l a r compounds the organic phase has a f a i r l y h i g h water content (26 ), depending on the d i f f e r e n c e (T-T^), s t a r t i n g w i t h about 20 H 0 per ether o

group and decreasing t i l l 2 HÔ.

A d d i t i o n s o f ions t o the water

phase decreases t h i s water content t o a l i m i t i n g value o f 2 HÔ per ether oxygen, a l s o .

This mixture o f PI0P-9 w i t h 2 HÔ per

ether group has a sharp v i s c o s i t y maximum, a maximum o f the v e l o c i t y o f sound, and a s p e c i a l x-ray s t r u c t u r e (10). This s t r u c t u r e has been d e s c r i b e d as meander s t r u c t u r e o f the ethylenoxide groups o r as a h e l i x . Models o f t h i s hydrate show t h a t t h e r e are water p o s i t i o n s p o s s i b l e w i t h a l l H-bond angles β = o. H-bonds bridges o f 2 HÔ from one ether oxygen t o the next t o nearest neighbors may be a m p l i f i e d by cooperative mechanism o f the 2 HÔ. In t h i s case the d i h y d r a t e may be o f s p e c i a l s t a b i l i t y . Warner (57) has d i s c u s s e d p o s s i b l e r e l a t i o n s between h y d r a t i o n o f b i o polymers and i c e - l i k e d i s t a n c e s o f the H-bond acceptor groups o f these polymers (5j[).



WATER IN POLYMERS

0.1

10 100 500 mol H 0 / mol (aceton or C H 0 H ) 2

2

5

Figure 10. Reciprocal salt solubilities in the ternary systems: water/acetone or ethanol/salts at 23° C as a function of the solvent mixture ratio: (Ç), φ) NaCl, (\3> M) KCI, (Δ, A) K CrOj,; open symbols represent acetone systems, closed symbols represent ethanol systems. 2

100 mgX/ml

H 0 2

200, (initial

cone )

Figure 11. Ratio of gelatin and chondrotine sulfate (CS) in the coacervates depends on additives (Χ): Ο NaCl; (X) NaHPO,,; (O) sodium cyclopentanecarboxylate. The coacervate was prepared by mixing 5 mL gelatin (1%) and 3 mL CS (1%) at 40°C and cooling to 20°C (55).


3. LUCK


Systems

63

3f. Coacervates. I n a two phase system, water/organic s o l v e n t , t h e phase e n r i c h e d w i t h the s o l v e n t i s c a l l e d coacervate (Bungenberg de Jong, 58.). The organic phase above the t u r b i d i t y p o i n t o f PIOP-9 behaves l i k e a coacervate. I t s composition can be changed s t r o n g l y by i o n a d d i t i v e s (26,10,55,59). The f o l l o w i n g t a b l e demonstrates i n the second l i n e t h e i n f l u e n c e o f d i f f e r e n t i o n s on the water content o f the organic phase (mole HÔ/ether group) and i n the t h i r d l i n e t h e i n f l u e n c e on the PIOP-9 content o f the water phase (g PIOP-9/l) a t 80°C.


salt

NaSCN

NaClO^

Nal

HÔ content

18

1^.3

11.5

PIOP-9

27

"

salt

k

PIOP-9

0.5

"

ZnCl k

0.39

salt

KCI

MgCl

HÔ content

3.2

3

PIOP-9

"

salt

NaHC0

HÔ content PIOP-9

11

2.2 0.38

3

CuSO 2

h

k. k

CaCl

2

L i CI

NaOH 3.3

3.9

3. 3

3.7

0.26

OJ 49

0.67

NH^Cl

2

3

0.8h

NaBr

2

NaN0

salt

h.Q

2.2

NaCl

HÔ content

Without

A1C1

3

0.82

Na LF

N a co 2.2

2

3

2.8

2.6

0.U6

0.U9

0.3^

MgSO^

ZnSO^

Na S

1.8

1.7

1.6

3

2

0.13

A second experiment o f t h i s type (59) e s t a b l i s h e s t h e s t r o n g i n f l u e n c e o f s a l t s on coacervates and demonstrates t h e importance of t h i s o b s e r v a t i o n f o r b i o l o g i c a l systems. F i g u r e 11 shows t h e composition o f a coacervate i n the system water/gelatine/chondrο ι i n e s u l f a t e /X. D i f f e r e n t a d d i t i o n s o f X change t h e r a t i o g e l a t i n e / c h o n d r o t i n e s u l f a t e depending on the c o n c e n t r a t i o n and type o f a d d i t i v e (59). The two main components are important components of c a r t i l a g e . C a r t i l a g e and c o l l a g e n behave s i m i l a r l y t o coacer vates ( 5 9 ) , which can depend on the type and c o n c e n t r a t i o n o f i o n s i n the aqueous phase. These could encourage r e s e a r c h e r s o f en vironmental p r o t e c t i o n i n s t i t u t i o n s t o prove i n f l u e n c e s o f i o n s on the human body. Compare the d i f f e r e n c e by a f a c t o r 10^ of i o n s on g e l a t i o n o f s o l s ( 6 θ ) , o r the s h i f t o f the m e l t i n g p o i n t o f g e l a t i n e (Δ Τ t i l l 35°) by d i f f e r e n t i o n s (6_1_), and f u r t h e r examp l e s (10). Already Ostwald ( 6 2 ) d i s t i n g u i s h e d primary h y d r a t i o n spheres around organic s o l u t e s and a second d i f f u s e hydrate sphere. Bungenberg de Jong assumed coacervate formation as combination of


WATER IN POLYMERS

64


the primary h y d r a t i o n spheres and s e p a r a t i o n from the d i f f u s e one. This process i s s i m i l a r t o i o n p a i r hydrate formation ( 6 3 , 6 ί , 6 5 ) , where the primary h y d r a t i o n sphere i s connected (Figure 1 2 ) . From our model experiments w i t h PIOP-9 we would assume as p r e l i m i n a r y step o f c o a c e r v a t i o n the connection o f the second h y d r a t i o n s h e l l s (Figure 1 2 ) . The coacervate formation o f PIOP-9 at higher Τ (at low Τ o n l y one phase e x i s t s ) b e l o n g s t o a group o f p r o c e s s e s , which i s favoured at h i g h Τ ( p o l y m e r i s a t i o n of tabacco mosaic p r o t e i n or hemoglobin of anaemia s i c k l e c e l l s , d i v i s i o n o f f e r t i l i z e d eggs, p r e c i p i t a t i o n of p o l y - L - p r o l i n e above 25°C e t c . ) ( K),66 ). L a u f f e r (66) c a l l s these e f f e c t s "entropy d r i v e n p r o c e s s e s " and assumes t h a t the en t r o p y i n c r e a s e o f water is_ i t s cause. The i n c r e a s e i n hydrophobic interaction a l s o favours these changes. k.

Aqueous Systems.

We give three d i f f e r e n t examples f o r water p r o p e r t i e s i n complica t e d systems o f the s o l i d t y p e . Ua. Polyamide F i b r e s . The water content o f polyamide f i b r e s i s important f o r dye d i f f u s i o n processes ( 6 j , 6 8 , 6 9 ). A c i d dyes have a v e r y low d i f f u s i o n i n polyamides at ambient humidity and room temperature; the d i f f u s i o n can be a c c e l e r a t e d by i n c r e a s i n g the r e l a t i v e h u m i d i t y . For i n s t a n c e the d i f f u s i o n r a t e o f a P e r l i ton dye at 60°C contacted w i t h l i q u i d water i s s i m i l a r t o t h a t i n a i r at 150°C at low humidity ( 6 8 ) . The water d i f f u s i o n c o e f f i c i e n t D i n polyamide i t s e l f i n c r e a ses w i t h water c o n c e n t r a t i o n . D o f HÔ (80°C) i n 6-polyamide i s reduced at 25 % r e l a t i v e h u m i d i t y t o 18 % o f i t s v a l u e at 100 % r e l a t i v e humidity ( 6 8 ) . This may be important f o r i n s e c t s i n a r i d areas. D r y i n g at the surface may reduce the water d i f f u s i o n from inside. S a l t s change the water contents o f polymers and t h e r e w i t h the d i f f u s i o n p r o c e s s e s . In 6-polyamide at T0°C we found an i n c r e a s e of water uptake t o 132 % w i t h 1 m NaClO^ i n the water phase and a decrease t o 82 % w i t h 1 m Na S0^ 2

(10).

An important and o f t e n n e g l e c t e d f a c t o r i s the pretreatment of polymers. For i n s t a n c e , the p a r t i t i o n c o e f f i c i e n t o f s t r o n g a c i d s between 6-polyamide/water i s about 200 at = U-5. To r e n duce the a c i d content o f a 6-polyamide f i b r e e q u i l i b r a t e d w i t h HC1 o f ρ = k t o 50 % i t i s necessary t o t r e a t i t about 200 times η i n e q u i l i b r i u m w i t h pure water at volume r a t i o s 1:1 (52). 9



3.

LUCK


Systems

65

kb. Water i n B i o l o g i c Systems. I n recent years there have been d i s c u s s i o n s on the important r o l e o f d i f f e r e n t types o f wa t e r molecules i n b i o l o g i c a l c e l l s , d i f f e r e n t i a t e d as "bonded" and "unbonded" ( 1 0 , 7 0 - 7 6 ) . To prove t h i s assumption we a p p l i e d our I.R. overtone method t o water i n c a r t i l a g e o r c o l l a g e n (55.»77)· In these probes t h e r e i s a frequency s h i f t o f the water bands at low h u m i d i t i e s (Figure 1 3 ) . I n the r e g i o n t o about 50 % r e l a t i v e humidity the f i r s t h y d r a t i o n s h e l l o f the biopolymers i s formed. I n t h i s r e g i o n o f the formation o f the f i r s t h y d r a t i o n s h e l l the polymer I.R. band changes w i t h water a d d i t i o n s , i n d i c a t i n g s m a l l change o f the polymer p r o p e r t i e s . A f t e r f i l l i n g the f i r s t h y d r a t i o n s h e l l the water uptake i n c r e a s e s r a p i d l y ; the wa t e r frequency changes i n the d i r e c t i o n o f weaker H-bonds, but t h e polymer band i s now constant (Figure 1 3 ) . Such experiments con ducted w i t h g l u c o s e , amylose, amylopectin, glycogen and d e x t r i n e , e s t a b l i s h two d i f f e r e n t types o f water: 1) f i r s t h y d r a t i o n s h e l l ( r e l a t i v e h u m i d i t i e s < 50 %) water i s a l i t t l e stronger bonded than i n the l i q u i d s t a t e , 2 ) secondary h y d r a t i o n ( 5 0 % < r e l a t i v e humi d i t i e s < 98 %) w i t h l i t t l e d i s t u r b e d l i q u i d - l i k e water s t r u c t u r e and 3) at h i g h water c o n t e n t s , l i q u i d - l i k e water. These three types were confirmed w i t h d i f f e r e n c e s p e c t r a i n the t h r e e humidity regions (55.). The d i f f e r e n c e s are very s i m i l a r i n each s t a t e but q u i t e d i f f e r e n t from t o another humidity r e g i o n . The water amount o f the t h i r d type can be i n f l u e n c e d by i o n s . The water uptake o f f r e s h l y prepared bovine n a s a l c a r t i l a g e i s d i f f e r e n t i f contacted w i t h l i q u i d water o r s o l u t i o n s (115 % pure water, 106 % a t 0 . 0 8 NaCl). The e x i s t e n c e o f d i f f e r e n t types o f water, c a l l e d bonded and non bonded, has been e s t a b l i s h e d by the s p e c t r o s c o p i c method. The f i r s t h y d r a t i o n water was found t o be a l i t t l e more s t r o n g l y bonded than i n the l i q u i d s t a t e . Instead o f "bonded water" we c a l l i t hydrate water. The excess water i s l i q u i d - l i k e w i t h s m a l l d i s t u r bance . On the b a s i s o f the s p e c t r a i t would be b e t t e r t o c a l l the s e cond type l i q u i d - l i k e water r a t h e r than unbonded, because i t i s c h a r a c t e r i z e d by normal Η-bonding and the bond-differences t o l i quid water are only s m a l l . The b i o l o g i c a l consequences o f the two types o f water are unexpectedly l a r g e compared w i t h the s m a l l spec t r a l d i f f e r e n c e s . Seed does not grow a t low humidity: food s t a b i l i t y can be r e a l i z e d by s m a l l r e d u c t i o n o f the water a c t i v i t y w i t h sugar, s a l t e t c . ; microorganism do not grow on food as a r e s u l t o f s m a l l r e d u c t i o n s o f the r e l a t i v e humidity. These changes seems t o depend upon l i q u i d - l i k e water. The d i f f e r e n c e s between the two o r three d i f f e r e n t water s t a t e s could be i n t e r p r e t e d too w i t h t h e s t r u c t u r e temperature. I n the middle p a r t o f F i g u r e 13 i s given on the r i g h t s c a l e the wavelength o f the water maxima i n tendon o r g e l a t i n e a t d i f f e r e n t r e l a t i v e h u m i d i t i e s and on the l e f t s c a l e t h e s t r u c t u r e temperature Τ ^ » which pure water should have i n d i c a t i n g the same wavelength maxima.

Τ

may give a more reasonable


scale

66

WATER IN POLYMERS

A : Primary Hydration

B . S e c o n d a r y Hydration

A

Ion-Solution


Ion-Solvent

Solution

Ion Pair H y d r a t e Interaction

Coacervate

M o d i f i e d C o a c e r v a t e Model

Figure 12.

Similarity between the model of ion-pair hydration and hydrates in a coacervate

Figure 13. Hydration of tendon or gela tin. Top: change of a polymer IR band during formation of the first hydration shell. Middle: during the formation of the first hydration shell, the water IR over tone band indicates slightly stronger hy drogen bonds, similar to liquid-like water CTstr: —45° to —50°C). Bottom: desorption isotherm (55). Symbols: (Φ, O) ten don, (^, 0, 0) gelatin.


3.

LUCK


67

Systems


t o understand t h a t s m a l l changes o f the p o s i t i o n o f the water I.R. maxima are accompanied w i t h b i g b i o l o g i c e f f e c t s . There are a l o t o f s a l t e f f e c t s on b i o l o g i c a l samples, which can be ordered by the Hofmeister i o n s e r i e s (J_0). A l l these e f f e c t s i n d i c a t e changes o f the water s t r u c t u r e and i t s importance f o r living cells. he. Mechanism o f D e s a l i n a t i o n Membranes. The decrease o f the water content o f PIOP-9 coacervates w i t h Τ seems t o o f f e r a method f o r d e s a l i n a t i o n as f o l l o w s : 1) add PIOP-9 t o sea-water, 2) warm up t o the t u r b i d i t y p o i n t , 3) separate the aqueous phase, k) heat the organic phase, and 5) separate the water phase t h a t has appeared. T h i s experiment was c a r r i e d out but i n the new water phase the i o n c o n c e n t r a t i o n was s i m i l a r t o the o r i g i n a l . I n t h i s coacervate these may be two d i f f e r e n t types o f HÔ: the primary hy d r a t i o n phase and a more d i f f u s e secondary water phase, which i s l i q u i d - l i k e and s o l v a t e s i o n s . This l e a d s t o the p o s t u l a t e t h a t d e s a l t i n g m a t e r i a l s should have h y d r a t i o n water but no l i q u i d - l i k e water phase. Uptake o f water t h a t i s l i q u i d - l i k e could d i s solve ions should be suppressed by s t e r i c hindrance ( 7 8 , 7 9 ) . Such experiments done w i t h copolymers o f ethylene/propyleneoxide d e r i v a t i v e s (reduced HÔ a f f i n i t y ) gave an i o n r e d u c t i o n i n step 5 (78,79,80).

Spectra o f water i n d e s a l i n a t i o n membranes ( c e l l u l o s e a c e t a t e , p o l y i m i d e , porous g l a s s ) show i n c o n t r a s t t o b i o l o g i c a l Studies a s m a l l e r Δν and i n d i c a t e a weaker Η-bonded system i n these mem branes compared w i t h l i q u i d water ( 7 8 , 7 9 ) . The s p e c t r o s c o p i c overtone r e s u l t s i n d i c a t e a water s t r u c t u r e i n membranes d i f f e r e n t from l i q u i d water. The observed weaker Hbond system would favour a q u i c k e r -flux. The water uptake i n mem branes gives an estimate o f the s i z e o f "pores" between the p o l y mer o r g l a s s c h a i n s , c a l c u l a t e d i n u n i t s o f HÔ s i z e : 1) c e l l u l o s e a c e t a t e , about h 2) examined g l a s s membranes 8 , and 3) t e c h n i c a l g l a s s f i b r e s about 5 . This could mean t h a t i n these l a y e r s t h e r e are not s u f f i c i e n t water f o r the i o n s o l u b i l i t y mechanism. E x p e r i ments by Pusch (8j_) e s t a b l i s h e d t h i s concept; i o n r e j e c t i o n de creases i n the s e r i e s : Na_S0, > CaCl^ > NaF > NaCl. Na S0» needs 2 4 2 2 k more water molecules t o be d i s s o l v e d i n the membrane pores than NaCl. Disturbance o f the water s t r u c t u r e by the formation o f hy drates w i t h membrane m a t e r i a l f u r t h e r reduce the e f f i c i e n c y o f the membrane water t o s o l v a t e i o n s . On the b a s i s o f the membrane r e s e a r c h we p r e f e r the f o l l o w i n g nomenclature o f water types i n aqueous systems : 1) f i r s t s h e l l o f water h y d r a t e , 2) second s h e l l o f d i s t u r b e d l i q u i d - l i k e water and, 3) l i q u i d - l i k e water. The s a l t t r a n s p o r t i n membranes, the d i f f u s i o n o f dyes i n f i b r e s o r the b i o c h e m i s t r y i n l i v i n g c e l l s need the e x i s t e n c e o f water o f types 2 o r 3 . Other methods t o study d i f f e r e n t water types see r e f e r e n c e s ( 1 0 , 7 3 , 7 * 0 . 9

o


68

WATER IN POLYMERS

L i s t o f Symbols θ CL

lone p a i r e l e c t r o n s c o n c e n t r a t i o n o f non Η-bonded OH groups f r a c t i o n o f non Η-bonded OH groups

dO /dT F

slope o f 0

F

i nFig. 1


c o n c e n t r a t i o n by weight "Β

c o n c e n t r a t i o n o f Η-bonded OH groups

0IÎ

non-bonded or " f r e e " OH

F

Η-bonded OH ΔΗ

Η

H-bond energy frequency o f the band maximum o f non Η-bonded OH groups frequency o f t h e band maximum o f Η-bonded OH groups

v

b Δν Δν

frequency 1/2

ε π

s h i f t between: " f r e e OH" and "Η-bonded OH"

h a l f width o f bands e x t i n c t i o n c o e f f i c i e n t at band maximum Temperature

Τ Τ

c r i t i c a l temperature s t r u c t u r e temperature o f a s o l u t i o n , Τ o f pure water w i t h str' s i m i l a r content o f non Η-bonded OH lowest temperature o f two phase formation

Γ =Τ : t r a n s i t i o n -T o f r i b o n u c l e a s e trans Μ s p e c i f i c heat i n l i q u i d s t a t e a t s a t u r a t i o n l i n e ν,id R

s p e c i f i c heat a t constant volume o f i d e a l gas s t a t e Gasconstant p a r t i a l molar volume o f water i n e l e c t r o l y t e s o l u t i o n s H-bond a n g l e , β=0 i f angle between a x i s OH and lone p a i r e l e c t r o n s i s zero

Κ HN OH A y PIOP-9

cs d.w. I.R.

cation h y d r a t i o n number hydrated anion w i t h ΗΝ = χ hydrated c a t i o n w i t h HN = y p - i s o - o c t y l p h e n o l w i t h 9 ethylenoxide chondroitinesulfat dry weight I n f r a Red

groups


3. LUCK

Structure of Aqueous Systems

69


Literature Cited 1. Luck, W.A.P. Angew.Chem., 1979, 91, 408; Angew.Chem.Int.Ed., 1979, 18,350. 2. Luck, W.A.P. Naturwissenschaften, 1965, 52, 25, 49; 1967, 54, 601. 3. Luck, W.A.P., in Schuster-Zundel-Sandorfy (Ed.), "The Hydrogen Bond", Verlag North Holland Publ.: 1976, p.527. 4. Luck, W.A.P. Angew.Chem., 1979, in press. 5. Luck, W.A.P.; Ditter, W. Ber.Bunsenges.Phys.Chem., 1968, 72,365. 6. Luck, W.A.P. Ber.Bunsenges.Phys.Chem., 1963, 67, 186; 1965, 69, 626. 7. Luck, W.A.P.; Ditter, W. Ζ.f.Naturforschung, 1969, 24b, 482. 8. Luck, W.A.P., "Structure of Water and Aqueous Solutions"; Verlag Chemie/Physik Verlag; Weinheim, 1974, p. 222, 248. 9. Luck, W.A.P., in Schuster-Zundel-Sandorfy (Ed.), "The Hydrogen Bond"; Verlag North Holland Publ.: 1976, p. 1369. 10. Luck, W.A.P. Topics in Current Chemistry, 1976, 64, 113. 11. Luck, W.A.P.; Schiöberg, D. Advan.Mol.Relaxation Processes, 1979, 14, 277. 12. Luck, W.A.P. Progr.Colloid & Polymer S c i . , 1978, 65, 6. 13. Mecke, R. Wissenschaftliche Veröffentlichungen 1937-1960, Festschrift zum 65. Geburtstag, Freiburg 1960. 14. Luck, W.A.P., in Felix Franks (Ed.), "The Hydrogen Bond in Water:" "A comprehensive Treatise", Plenum Publishing Corp.: New York, 1973, p. 225. 15. Schiöberg, D.; Buanam-Om, C; Luck, W.A.P.; Spectroscopy Letters, 1979, 12, 83. 16. Paquette, J.; Joliceur, C. J.Sol.Chem., 1977, 6, 403. 17. Worley, J.D.; Klotz, I.M. J.chem.Physics, 1966, 45, 2868. 18. Stillinger, F.H.; Rahman, A. J.Chem.Phys., 1972, 67, 1281. 19. Geiger, Α.; Rahman, Α.; Stillinger, F.H. J.Chem.Phys., 1979, 70, 263. 20. Geiger, Α., Karlsruhe 1979, Film. 21. Rahman, Α.; Stillinger, F.H. J.Chem.Phys., 1971, 55, 3336. 22. Stillinger, F.H.; Rahman, A. J.Chem.Phys., 1974, 60, 1545. 23. Luck, W.A.P. Discuss.Faraday Soc., 1967, 43, 115. 24. Luck, W.A.P. Ber.Bunsenges.Phys.Chem., 1965, 69, 69. 25. Luck, W.A.P. Proc. of the 4th Internat. Symposium on Fresh Wa ter from the Sea, Heidelberg, 1973, p. 531. 26. Luck, W.A.P. Fortschr.chem.Forschung, 1964, 4, 653. 27. Luck, W.A.P. III.Internat.Kongr.f.Grenzflächenaktive Stoffe, 1960, 264, Köln. 28. Bernal, J.D.; Fowler, R.H. J.Chem.Phys., 1933, 1, 515. 29. Von Hippel, P.H.; Wong, K.Y. J.Biol.Chem., 1965, 240, 3909. 30. Luck, W.A.P. "Ullmanns Enzyklopädie der techn.Chemie", Verlag Chemie; Weinheim, 3.ed., Vol. 18, 1967, p. 401. 31. Philip, P.R.; Joliceur, C. J.Phys.Chem., 1973, 77, 3076. 32. Luck, W.A.P. Naturwissenschaften, 1976, 63, 39. 33. Hermans, J . Biochim.Biophys.Acta, 1959, 36, 534.



70

WATER IN POLYMERS

34. Lewin, S. Biochem.J., 1966, 99, 1P; Arch.Biochem. Biochem. Biophys., 1966, 115, 62. 35. Hübner, G.; Jung, K.; Winkler, E. "Die Rolle des Wassers in biologischen Systemen", Berlin: Akademie Verlag und Braunschweig: Vieweg 1970. 36. Gmelins "Handbuch der anorganischen Chemie" Nr. 15, Silicium Β. Verlag Chemie, Weinheim, S. 414, 439, 447, 453, 503. 37. Luck, W.A.P. J.Chem.Phys., 1970, 74, 3687. 38. Luck, W.A.P.; Zukovskij, A.P. Ed. A.J.Sidorovo "Molecular Physics and Biophysics of Water Systems", Leningrad University, 1974, p. 131. 39. Choppin, G.R.; Buijs, K. J.Chem.Phys., 1963, 39, 2042. 40. Falk, Μ., Knop, O. Ed. F. Franks "Water, A Comprehensive Treatise" Plenum Press, New York-London, 1973, p. 55. 41. Buanam-Om, C.; Luck, W.A.P.; Schiöberg, D. Z.Phys.Chem., 1979, in press. 42. Zundel, G. "Hydration and Intermolecular Interaction", Academic Press, New York, 1969. 43. Schiöberg, D.; Luck, W.A.P. Spectroscopy Letters, 1977, 10(8), 613. 44. Schiöberg, D.; Luck, W.A.P. J.Chem.Soc.Faraday Trans. 1979, 75, 762. 45. Palinkas, G.; Riede, W.O.; Heinzinger, K. Ztschr.Naturforsch., 1977, 82a, 1137. 46. Wicke, E. Angew.Chem.Int.Ed. 1966, 5, 106. 47. Rüterjans, H. et al. J.Phys.Chem., 1969, 73, 986. 48. Franks, F . ; Reid, D.S. "Water A Comprehensive Treatise", Plenum Press, New York-London, 1973, p. 336. 49. Luck, W.A.P. Angew.Chem., 1960, 72, 57. 50. Luck, W.A.P. J.Soc.Dyers and Coulourists, 1958, 74, 221. 51. Luck, W.A.P. Melliand, 1960, 41, 315. 52. Luck, W.A.P. Chimia, 1966, 20, 270. 53. Luck, W.A.P. "Physikalische Chemie und Anwendungstechnik der grenzflächenaktiven Stoffe, Kongreßband VI. Internationaler Kongreß für grenzflächenaktive Stoffe in Zürich 1972", Carl Hanser Verlag, München, 1973, p. 83. 54. Luck, W.A.P.; Shah, S.S. Progr.Colloid & Polymer Sci., 1978, 65, 53. 55. Kleeberg, H. Thesis, Marburg, in preparation. 56. Barthel, J . "Ionen in nichtwäßrigen Lösungen", Dr.Dietrich Steinkopff Verlag, Darmstadt, 1976. 57. Warner, D.J.Ann.New York Acad.Sci., 1965, 125, 605; Nature, 1962, 196, 1055. 58. Bungenberg de Jong, H.G.; Kruyt, H.R. Koll.-Z., 1930, 50, 39. 59. Kleeberg, H.; Luck, W.A.P. Poster "Is cartillage a coacervate?" 6th Colloquium of the Federation of European Connective Tissue Clubs, August, 28.-30. 1978. 60. Kruyt, H.R. "Colloid Science", Vol.I, p.335, Elsevier, Amsterdam 1952.


3.

61. 62. 63. 64. 65. 66.


67. 68. 69. 70. 71. 72. 73. 74. 75. 76. 77. 78. 79. 80. 81.

LUCK

Structure of Aqueous Systems

71

Riese, H.C.A.; Vienograd, S.R. J.phys.chem., 1956, 60, 1299. Ostwald, Wo.; Hertel, R.H. Koll.-Z., 1929, 47, 258, 357. Franks, H.S.; Wen, W.V. Disc.Farad.Soc., 1957, 24, 133. Lilley, T.H. in F.Franks (Ed.) "Water a comprehensive Treatise", Plenum Press, New York, 1973, Vol.3, p. 266. Gurney, R.W. "Ionic Processes in Solution" McGraw H i l l , New York, 1953. Lauffer, M.A. Entropy-Driven-Processes in Biology, Berlin-Heidelberg-New York, Springer 1975. Luck, W.A.P. 100 Jahre BASF, 1965, 259. Luck, W.A.P. in H.Freund (Ed.) "Handbuch der Mikroskopie in der Technik", Umschau-Verlag, Frankfurt, Bd.VI, Teil I, S. 345, 1972. Luck, W.A.P. Ber.Bunsenges.Phys.Chem., 1965, 69, 255. Hauser, H. Lipids, in F.Franks (Ed.) "Water a comprehensive Treatise", Plenum Press, New York, 1975, p. 209. F.Franks (Ed.) "Water a comprehensive Treatise", Plenum Press, New York, 1972-1975, Volumes 4. and 5. International Meeting organized by CNRS Roscoff June 1975, Paris, Editions Centre National Recherche Scientifique, Nr. 246, 1975. Hazlewood, C.F. Annals New York Acad.Sci., Vol.204, 1973. Hazlewood, C.F. in W.Drost-Hansen a.Clegg, J . (Ed.) "CellAssociated Water", Academic Press New York, 1979, p. 165. Garlid, K.D. in W.Drost-Hansen a. Clegg, J . (Ed.) "Cell-Associated Water", Academic Press, New York, 1979, p. 293. Berendsen, H.J.C. in F.Franks (Ed.) "Water a Comprehensive Treatise" Vol. 5, p. 293, 1975. Kleeberg, H . ; Luck, W.A.P. Naturwissenschaften, 1977, 64, 223. Luck, W.A.P.; Schiöberg, D.; Siemann, U. Ber.Bunsenges.Phys. Chem., 1979, 83, in press. Luck, W.A.P.; Schiöberg, D.; Siemann, U. Trans.Far.Soc., in press. Luck, W.A.P. DBP Offenlegungsschrift, Nr.2151/207. Pusch, W. in Luck, W.A.P. (Ed.) Structure of Water and Aqueous Solutions, Chemie Verlag, Weinheim, 1974, p. 551.

RECEIVED January 4, 1980.


Water in Polymers - American Chemical Society

Recommend Documents