Characterization and Chemical Reactions of Surfactant Monolayer Films

5 Characterization and Chemical Reactions of

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 5, 2016 | http://pubs.acs.org Publication Date: June 1, 1980 | doi: 10.1021/ba-1980-0184.ch005

Surfactant Monolayer Films

STEVEN J. VALENTY General Electric Company Corporate Research and Development, Schenectady, NY 12301

The study of chemical reactions of suitably functionalized surfactant monolayer films is suggested as a corollary ap proach toward understanding the chemistry of bonding modifiers to electrode and catalytic surfaces. Liquid- and vapor-phase chromatography have been used in conjunc tion with absorption, fluorescence, and IR spectrometry to detect and quantitate the chemistry occurring in such films containing aldehyde or ester molecules. Carboxylic acid surfactant derivatives of ruthenium(II)tris(2,2'-bipyridine) have been used to assess solid surface acidity. The obser vation of methylene blue adsorption to photogalvanic elec trodes is related to the orientation and absorption spectra of its surfactant analogs in monolayer films. The effect of counterion on luminescence properties of derivatives of ruthenium(II)tris(2,2'-bipyridine) are unique to the posi tively charged interface.

The

s t u d y of i n t e r f a c i a l photoprocesses e m p h a s i z i n g energy c o n v e r s i o n

a n d c h e m i c a l synthesis is p r e d i c a t e d u p o n t h e e x p e c t a t i o n t h a t c o n s t r a i n i n g s p e c i a l l y t a i l o r e d r e a c t i o n centers t o a surface w i l l

produce

r e a c t i o n p r o d u c t s o r k i n e t i c s different f r o m w h a t is o b s e r v e d i n either of t h e a d j o i n i n g h o m o g e n e o u s phases

alone.

I n some experimental a p

p r o a c h e s , a surface is m o d i f i e d b y c o v a l e n t l y a t t a c h i n g s p e c i a l i z e d m o l e cules w h o s e v a r i e d f u n c t i o n s i n c l u d e selective e l e c t r o n transfer w i t h a specific r e d o x c o u p l e i n a n a d j o i n i n g e l e c t r o l y t e s o l u t i o n , p r e v e n t i o n o f electrode corrosion, a n d preferential b i n d i n g of reactant molecules. 0-8412-0474-8/80/33-184-069$07.25/0 © 1980 American Chemical Society Wrighton; Interfacial Photoprocesses: Energy Conversion and Synthesis Advances in Chemistry; American Chemical Society: Washington, DC, 1980.

It

70

INTERFACIAL

PHOTOPROCESSES

is c l e a r t h a t t h e c h e m i s t r y i n v o l v e d i n c o u p l i n g t h e m o d i f y i n g m o l e c u l e t o t h e surface a n d t h e n a t u r e of the c o v a l e n t b o n d so f o r m e d are i m p o r t a n t to b o t h t h e m e c h a n i s m of t h e m o d i f i e r s a c t i o n a n d its o p e r a t i o n a l lifetime.

A v a r i e t y of t e c h n i q u e s , i n c l u d i n g e l e c t r o n spectroscopy

c h e m i c a l analysis ( E S C A ) , a t o m i c e m i s s i o n spectroscopy o p t i c a l spectroscopy,

for

( A E S ) , IR,

a n d electroanalytical methods, have been used to

c h a r a c t e r i z e a surface b e f o r e a n d after c h e m i c a l m o d i f i c a t i o n . W h e r e a p p l i c a b l e the s t u d y of c h e m i c a l reactions of s u i t a b l y f u n c Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 5, 2016 | http://pubs.acs.org Publication Date: June 1, 1980 | doi: 10.1021/ba-1980-0184.ch005

tionalized surfactant monolayer

films

at t h e g a s - w a t e r i n t e r f a c e

another approach towards understanding this chemistry.

offers

O p e r a t i n g at

t h e a i r - w a t e r i n t e r f a c e a n d , hence, w i t h i n t h e c o n s t r a i n t of

aqueous-

b a s e d c h e m i s t r y , this t e c h n i q u e a l l o w s the p r e p a r a t i o n of a v a r i e t y of f u n c t i o n a l i z e d surfaces b y f o r m i n g a m o n o l a y e r f r o m selected s y n t h e t i c surfactant monomers.

F u r t h e r , the use of this p a r t i c u l a r

methodology

a l l o w s e x p e r i m e n t a l c o n t r o l , to v a r y i n g degrees, of t h e r e s u l t i n g t w o d i m e n s i o n a l films' c o m p o s i t i o n , o r i e n t a t i o n , a n d e l e c t r i c a l charge.

Be

cause a m o n o m o l e c u l a r l y t h i n l a y e r is b e i n g d e a l t w i t h here, a c h e m i c a l l y m o d i f i e d film c a n b e r e c o v e r e d f r o m the interface a n d separated i n t o its m o l e c u l a r constituents, e a c h of w h i c h c a n t h e n b e q u a n t i t a t e d a n d c h a r a c t e r i z e d . S u c h is n o t the case w h e r e a t t a c h m e n t is m a d e to a b u l k material. Since the monolayer

film

can be transferred from the

gas-water

i n t e r f a c e o n t o a v a r i e t y of s o l i d s u p p o r t s , t h e w e l l - k n o w n surface a n a l y s i s t e c h n i q u e s m e n t i o n e d e a r l i e r c a n b e u s e d for c h a r a c t e r i z i n g these as w e l l .

films

I n some instances, s u c h a p r o c e d u r e w o u l d a l l o w q u a n t i t a t i v e

c a l i b r a t i o n of the surface analysis because t h e exact a m o u n t of m a t e r i a l t r a n s f e r r e d to t h e s o l i d surface is k n o w n . T h e efficiency of procedures

subsequent

to p h y s i c a l l y a d s o r b or c o v a l e n t l y a t t a c h s i m i l a r b u t n o n

s u r f a c t a n t modifiers to this s o l i d surface b y other means c o u l d b e d e t e r m i n e d d i r e c t l y b y reference to the m o n o l a y e r

experiment.

F u r t h e r , t h e response of a s p e c i a l l y t a i l o r e d surfactant, say t o p H as o b s e r v e d b y o p t i c a l spectroscopy, i n a m o n o l a y e r at t h e w e l l - c h a r a c t e r i z e d g a s - w a t e r i n t e r f a c e c o u l d b e u s e d to p r o b e t h e same surface p r o p e r t y of less k n o w n m a t e r i a l s ( i n this case, necessarily t r a n s p a r e n t to t h e o p t i c a l r a d i a t i o n u s e d ) u p o n t r a n s f e r r i n g the m o n o l a y e r t o t h a t surface. I n s u p p o r t of t h e p r e c e e d i n g statements, I s h o u l d l i k e to work done i n characterizing monolayer

films

and chemical

describe reactions

o c c u r r i n g i n t h e m at t h e g a s - w a t e r i n t e r f a c e a n d o n s o l i d surfaces

by

c l a s s i c a l t e c h n i q u e s as w e l l as b y a p p l y i n g n e w e r a n a l y t i c a l m e t h o d s

to

detect a n d q u a n t i t a t e the s m a l l a m o u n t s of m a t e r i a l c o n t a i n e d t h e r e i n . W h i l e no n e w photochemistry mediated b y monolayers w i l l be discussed, a s t r i k i n g e x a m p l e of h o w c o n s t r a i n i n g a m o l e c u l e to a n i n t e r f a c e alters its p h o t o p h y s i c a l b e h a v i o r w i l l b e p r e s e n t e d .

Wrighton; Interfacial Photoprocesses: Energy Conversion and Synthesis Advances in Chemistry; American Chemical Society: Washington, DC, 1980.

5.

VALENTY

Surfactant

Monolayer

71

Films


Experimental T h e synthesis a n d c h a r a c t e r i z a t i o n of C o m p o u n d s I - X h a v e b e e n described (1,2,3). Stearaldehyde ( S t A l d ) (Supelco, 9 9 + % ) , stearyl a l c o h o l ( S t O H ) ( S i g m a , 9 8 % ) , p o l y - l - l y s i n e ( P L ) (as H B r salt, S i g m a ) , 3-methyl-2-benzothiazolinone hydrazone hydrochloride (reagent, A i d r i c h ) , s o d i u m b o r o h y d r i d e ( A l d r i c h ) , i n o r g a n i c reagents ( a n a l y t i c a l g r a d e ) , a n d o r g a n i c solvents ( B u r d i c k a n d J a c k s o n ) w e r e u s e d w i t h o u t further purification. T r i p l y distilled water from a quartz still was used i n the p r e p a r a t i o n of the m o n o l a y e r s u b p h a s e solutions. M o n o l a y e r s of S t A l d a n d m e t h y l e n e b l u e / r u t h e n i u m b i p y r i d y l s u r f a c t a n t c o m p l e x e s w e r e s p r e a d f r o m d i l u t e n-hexane a n d c h l o r o f o r m solutions, r e s p e c t i v e l y . S u r f a c e p r e s s u r e - a r e a isotherms ( I ) , surface v i s c o s i t y ( 4 ) , o p t i c a l s p e c t r o m e t r y of g l a s s - s u p p o r t e d m o n o l a y e r s ( J ) , e m i s s i o n s p e c t r o m e t r y of m o n o l a y e r s at the a i r - w a t e r i n t e r f a c e ( I ) , h i g h - p e r f o r m a n c e l i q u i d c h r o m a t o g r a p h i c ( H P L C ) analyses ( 5 ) , v a p o r - p h a s e c h r o m a t o g r a p h y ( V P C ) analyses f o r H d i s s o l v e d i n w a t e r ( 6 ) a n d f o r S t A l d / S t O H ( 4 ) were done using apparatus a n d procedures previously described. T h e F o u r i e r t r a n s f o r m I R ( F T I R ) s p e c t r a of m o n o l a y e r s or I o n h y d r o p h i l i c g e r m a n i u m a t t e n u a t e d t o t a l reflectance ( A T R ) plates ( H e r r i c k Scientific, 50 X 20 X 1 m m , 0 = 4 5 ° , single-pass p a r a l l e l - p i p e d , 50 reflections) w e r e r e c o r d e d w i t h a N i c o l e t 7199. T h e A T R - I R s p e c t r a of the S t A l d P L system w e r e o b t a i n e d as d e s c r i b e d e a r l i e r ( 4 ) . T h e field d e s o r p t i o n mass s p e c t r a ( F D M S ) w e r e r e c o r d e d o n a V a r i a n - M a t 731 mass spec t r o m e t e r . T h e c o n s t r u c t i o n d e t a i l s a n d o p e r a t i o n of t h e m u l t i c o m p a r t m e n t t r o u g h have been discussed elsewhere ( 7 ) . 2

Results and

Discussion

Chemical Reactions and the Multicompartment Monolayer T r o u g h . T h e m e c h a n i c s of p e r f o r m i n g a c h e m i c a l r e a c t i o n o n a m o n o l a y e r

film

r e q u i r e s e v e r a l o p e r a t i o n s : ( a ) t h e film m u s t b e s p r e a d at t h e g a s - w a t e r i n t e r f a c e a n d c o m p r e s s e d t o t h e d e s i r e d surface p r e s s u r e ; ( b )

the reac

t i o n m u s t o c c u r u n d e r c o n d i t i o n s w h e r e t h e surface pressure c a n

be

m o n i t o r e d a n d h e l d constant

be

if desired;

(c)

the reaction must

q u e n c h e d to o b t a i n a c h e m i c a l l y stable s y s t e m s u c h t h a t later analysis w i l l reflect t h e c o m p o s i t i o n of t h e film w h i l e i t w a s s t i l l at the g a s - w a t e r interface; a n d ( d )

t h e film m u s t b e r e c o v e r e d as q u a n t i t a t i v e l y as p o s

s i b l e f r o m t h e i n t e r f a c e . I n o r d e r to satisfy these r e q u i r e m e n t s , a m u l t i c o m p a r t m e n t t r o u g h has b e e n u s e d t o a l l o w a series of c h e m i c a l reactions to b e p e r f o r m e d u p o n a w e l l - d e f i n e d m o n o l a y e r . T h e m u l t i c o m p a r t m e n t t r o u g h u s e d h e r e is s h o w n i n F i g u r e 1. t r o u g h s u b p h a s e is d i v i d e d i n t o a n u m b e r of i n d i v i d u a l

The

compartments

b y s u b m e r g e d h y d r o p h i l i c glass b a r r i e r s t h a t e x t e n d t h e w i d t h of t h e t r o u g h a n d are c o v e r e d b y c a . 0.5 c m w a t e r . T h e s e v e r a l c o m p a r t m e n t s can

be

filled

and emptied independently.

Surfactant monolayers

are

c o n s t r a i n e d b e t w e e n t h e h y d r o p h o b i c sides of t h e t r o u g h a n d t w o m o t o r -



COMPARTMENT

10 20 SCALE (cm)

DIPPING WELL'

0

- 76 cm i

ABLE SURFACE BARRIERS -

Multicompartment

WASH

monolayer

COMPARTMENT 2 TROUGH SIDE WALLS

SUPPORT TABLE

WASH

• DIPPING WELL

COMPARTMENT 3

61 cm

^BARRIER DRIVE CABLE

trough

VcUBSl -SUBSURFACE COMPARTMENT WALLSHSaHh 61cm Hhl5cmHK

Figure 1.

ACRYLIC TROUGH BASE

WILHELMY PLATE-LVOT ASSEMBLY

tut

BARRIER OISTANCE POTENTIOMETER ASSEMBLY

TROUGH SIDE WALLS


/

BARRIER DRIVE \ - CABLE- MOTOR ASSEMBLY

50.9 cm

w CO

» o o w

x

Q >

to

5.

VALENTY

Surfactant

Monolayer

73

Films

i z e d h y d r o p h o b i c surface barriers w h i c h c a n be d r i v e n independently to c o n t r o l t h e surface pressure (as m e a s u r e d b y a W i l h e l m y b a l a n c e )

or

s i m u l t a n e o u s l y t o l a t e r a l l y t r a n s p o r t t h e film at c o n s t a n t a r e a f r o m t h e surface of one c o m p a r t m e n t t o a n o t h e r o v e r t h e s u b m e r g e d b a r r i e r . Borohydride Reduction of S t A l d . b y aqueous N a B H

4

T h e r e d u c t i o n of S t A l d t o S t O H

i l l u s t r a t e s t h e use of t h i s t r o u g h . A m o n o l a y e r of

S t A l d (3.2 /xmol, 0.86 m g )

was formed on Compartment 1 containing

5.0 X 1 0 " M b o r a t e buffer ( p H 9.0) a n d c o m p r e s s e d t o n — 3

10 d y n / c m .


T h e film w a s m o v e d t o C o m p a r t m e n t 2 ( t r a n s f e r t i m e , 1 m i n ) , w h i c h c o n t a i n e d f r e s h l y p r e p a r e d 1.0 X 1 0 ' M N a B H 2

4

i n a q u e o u s b o r a t e buffer.

A f t e r 30 m i n , t h e film w a s m o v e d b a c k t o C o m p a r t m e n t 1, c o m p r e s s e d u n t i l i t c o l l a p s e d i n t o t h r e a d s , s c r a p e d off t h e surface a n d d i s s o l v e d i n c h l o r o f o r m . V P C a n a l y s i s i n d i c a t e d S t O H c o r r e s p o n d i n g t o 84 m o l % the initially spread S t A l d w i t h 1 m o l % e x p e r i m e n t s h a v e s h o w n 85 ±

unreduced aldehyde.

of

Control

2 m o l % r e c o v e r y of e i t h e r t h e o r i g i n a l

S t A l d s p r e a d a n d m a n i p u l a t e d i n t h e a b s e n c e of N a B H

4

or the S t O H

s p r e a d a n d m a n i p u l a t e d i n t h e presence of N a B H . 4

Sequential Chemical Reactions.

A m o r e c o m p l e x series of r e a c t i o n s

is s h o w n b y t h e c o v a l e n t a t t a c h m e n t of a d y e t o a p r e f o r m e d m o n o l a y e r film.

I n t h e presence of a n a l d e h y d e a n d f e r r i c c h l o r i d e , 3 - m e t h y l - 2 - b e n -

z o t h i a z o l i n o n e h y d r a z o n e ( M B T H ) forms a d e e p - b l u e - c o l o r e d c a t i o n v i a o x i d a t i v e c o u p l i n g of t h e i n i t i a l l y f o r m e d a l d i m i n e w i t h a s e c o n d of M B T H

(8,9).

CH

+

3

QCs>= N

MBTH

N H

^

+


mole

74

INTERFACIAL

PHOTOPROCESSES

A m o n o l a y e r of S t A l d (3.0 / r n i o l ) w a s f o r m e d o n 5 X buffer ( p H 9 ) i n C o m p a r t m e n t 1 a n d c o m p r e s s e d The

film

MBTH

=

(n

1 0 " M borate 3

10

dyn/cm).

w a s s h i f t e d o n t o t h e surface of C o m p a r t m e n t 2 c o n t a i n i n g (1.1 X

1 0 M i n p H 9 borate buffer)

a n d a l l o w e d to s t a n d f o r

- 2

30 m i n . T h e film w a s r e t u r n e d to C o m p a r t m e n t 1, c o m p r e s s e d to c o l l a p s e t h e film i n t o w h i t e t h r e a d s , a n d s c r a p e d off t h e surface t o g i v e a h o m o geneous s o l u t i o n i n C C 1 . V P C analysis s h o w e d less t h a n 0.5 m o l

%

4

u n r e a c t e d S t A l d a n d t w o m a j o r c o m p o n e n t s e l u t i n g at m u c h l o n g e r r e


tention times.

VPC-MS

(mass spectrometry)

c o m p o n e n t s h a v e the same m o l e c u l a r i o n (m/e

s h o w e d t h a t these

two

= 420) a n d f r a g m e n t a t i o n

patterns s i m i l a r to the f o r m a t i o n of i s o m e r i c i m i n e s . I n a s e c o n d r e a c t i o n u s i n g i d e n t i c a l c o n d i t i o n s , the film is s h i f t e d f r o m t h e M B T H c o n t a i n i n g subphase directly (no intervening w a s h compartment) freshly prepared w i t h F e C l

3

onto a subphase

d i s s o l v e d i n d i s t i l l e d w a t e r (1.8 X

10" M). 3

A f t e r s t a n d i n g 30 m i n , t h e film is c o l l a p s e d ( a b l u e c o l o r a t i o n is a p p a r e n t ) a n d s c r a p e d off t h e surface to g i v e a d e e p - b l u e h o m o g e n e o u s s o l u tion i n C H C 1 . V P C analysis i n d i c a t e d 3 m o l % S t A l d unreacted a n d the 3

v i s i b l e a b s o r p t i o n s p e c t r u m s h o w e d a m a x i m u m at 673 n m w i t h a s h o u l d e r at 630 n m (1.00:0.83 o.d. r a t i o ) as r e p o r t e d for s i m i l a r c o m p o u n d s (8,9). Using

c

6 7 3

=

5.2 X

1 0 f r o m the l i t e r a t u r e ( 8 ) , t h e y i e l d of t h e 4

r e a c t i o n is 9 m o l % b a s e d o n S t A l d . T h e b l u e c o l o r c a n b e b l e a c h e d b y dithionite a n d recovered b y F e

3 +

oxidation. Since the i m i n e appears to be

p r o d u c e d i n h i g h y i e l d i n the initial reaction a n d remains i n the b l u e c o l o r e d f i l m b y V P C a n a l y s i s , its c o n v e r s i o n to the r e l a t i v e l y l a r g e r s t r u c t u r e of the d y e c a t i o n is l i m i t i n g o v e r a l l r e a c t i o n y i e l d . I n c r e a s i n g t h e surface a r e a a v a i l a b l e p e r m o l e c u l e b y u s i n g o n e - t h i r d the a m o u n t S t A l d i n c r e a s e d t h e y i e l d of d y e c a t i o n to c a . 1 5 % . T h e taining monolayer

film

can be

transferred w i t h the

of

dye-cation-con two-dimensional

s t r u c t u r e i n t a c t to a glass s l i d e a n d its a b s o r p t i o n s p e c t r u m c a n b e r e corded.

T h e v i s i b l e s p e c t r u m of t h e d y e c a t i o n i n t h e m o n o l a y e r

is

c o m p a r e d w i t h t h a t i n h o m o g e n e o u s s o l u t i o n i n F i g u r e 2. Polycondensation Chemistry.

I n an experimental approach seeking

t o synthesize p l a n a r , u l t r a t h i n p o l y m e r films possessing r u b b e r e l a s t i c i t y a n d f u n c t i o n a l sites t h a t m i g h t p r o v e u s e f u l i n m o d e l l i n g b i o l o g i c a l m e m b r a n e s t r u c t u r e a n d selective t r a n s p o r t c a p a b i l i t y , p o l y c o n d e n s a t i o n r e a c tions i n m o n o l a y e r

films

obtain such a

grafts s u r f a c t a n t m o n o m e r s of

monolayer

film

were studied (4).

T h e s y n t h e t i c strategy

to

StAld formed i n a

array onto linear, b u t r a n d o m l y coiled, water-soluble

PL

c h a i n s . A sufficient n u m b e r of u n r e a c t e d l y s y l a m i n o g r o u p s are left t o f o r m the interchain crosslinkage u p o n further condensation w i t h a d i a l d e h y d e s u c h as g l u t a r a l d e h y d e . T h u s , t h e t w o d i m e n s i o n a l surface a c t i v e n e t w o r k is a c h i e v e d . T h e m e a s u r e m e n t of i n t r i n s i c v i s c o s i t y p r o v i d e s a c o n v e n i e n t i n d i c a t i o n of b u l k - p h a s e p o l y m e r i z a t i o n s . M o s t of t h e l i t e r a t u r e c l a i m i n g t o



2

710

2

s

674

3

s

4

652

Figure 2. Absorption spectra of StAld-MBTH reaction product as a monohyer coating both sides of a hydrophilic glass slide ( , transferred from 1.8 X 10~ M FeCl at Π = 30 dyn/cm, A = 5.6 X JO" , A = 4.5 X 10' ); and in CHCl solution ( , ε = 5.2 X J O , intensity arbitrarily scaled).


1

150

200 60 100 AREA, A / MOLECULE

^

X

PHOTOPROCESSES

I ^.

U

150

200

2

Figure

11.

II-A curves for I and IX on aqueous subphases 0.01 M in NaX, 22-24°C

strongly condensing

counterions

(e.g.

C 1 0 " ) , s o m e surface 4

pressure

d e c a y is o b s e r v e d after r a p i d c o m p r e s s i o n to h i g h n a n d t h e r e is a s m a l l a m o u n t of c o m p r e s s i o n - e x p a n s i o n hysteresis i n c y c l i n g . T h i s hysteresis is l a r g e l y r e v e r s i b l e , since a s e c o n d c o m p r e s s i o n c u r v e close a p p r o x i mates t h e i n i t i a l c o m p r e s s i o n .

F o r t h e ions e x h i b i t i n g i n t e r m e d i a t e b e

h a v i o r ( S C N " , I " ) , there is also some hysteresis, b u t t h e shape of compression

c u r v e persists w i t h e x p a n s i o n a n d r e c o m p r e s s i o n

the

cycles.

A l t h o u g h t h e i r m o l e c u l a r areas are a p p r o x i m a t e l y t w i c e as l a r g e , t h e r u t h e n i u m surfactants h a v e n - A curves s i m i l a r i n shape to a n d s h o w i n g t h e same c o u n t e r i o n specificity as those of s u c h s i n g l y c h a r g e d c a t i o n i c surfactants as d o c o s y l t r i m e t h y l a m m o n i u m b r o m i d e

(18).

W h e n films of I are s p r e a d o n m i x e d c h l o r i d e - p e r c h l o r a t e solutions, a h i g h s e l e c t i v i t y is o b s e r v e d .

T h u s , the curve on 10" M C I " + 2

C I C V is i d e n t i c a l to t h a t o n C 1 C V a l o n e ; f o r 1 0 " M C I " + 2

10~ M 3

10" M C10 " a 4

4

s m a l l e x p a n s i o n at n < 5 d y n / c m occurs, b u t at h i g h e r n t h e c u r v e a g a i n

I X m a t c h e s t h a t o n C 1 0 " ; o n 1 0 " M C I " + 1 0 " M CIO4", t h e c o m p r e s s i o n c u r v e agrees w i t h t h a t o b t a i n e d o n C I " a l o n e , b u t a hysteresis l o o p is o b s e r v e d o n e x p a n s i o n i n t h e r a n g e 30 > n > 17 d y n / c m . 4

2

5


5.

VALENTY

Surfactant

Monolayer

Films

89

T h e s p e c i f i c i t y o f these d o u b l y c h a r g e d c o m p l e x e s f o r CIO4" o v e r C I " c a n also b e d e m o n s t r a t e d b y F T I R analysis o f m o n o l a y e r films o f I t r a n s f e r r e d off m i x e d a n i o n subphases

onto h y d r o p h i l i c g e r m a n i u m A T R

plates. A s s h o w n i n F i g u r e 12, e v e n a t C 1 0 " : C 1 " — 1:1000, t h e a b s o r p 4

t i o n a t 1100 c m "

1

attributable t o C 1 0 " is observed. 4

L i t t l e difference i n

r e l a t i v e intensities o f t h e C 1 C V is n o t e d f o r C 1 0 " : C 1 " > 1:100. 4

T h e more tightly b o u n d nature of

CIO4"

r e l a t i v e t o C I " is e m p h a s i z e d

i n t h e field d e s o r p t i o n mass s p e c t r a ( F D M S ) o f s o l i d I X as b o t h t h e Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 5, 2016 | http://pubs.acs.org Publication Date: June 1, 1980 | doi: 10.1021/ba-1980-0184.ch005

p e r c h l o r a t e a n d c h l o r i d e salt (see F i g u r e 1 3 ) . T h e m o l e c u l a r i o n o f t h e c h l o r i d e salt s h o w s t h e loss o f b o t h a n i o n s ; t h e m o l e c u l a r i o n o f t h e p e r c h l o r a t e c o m p o u n d shows o n l y a loss o f one a n i o n . MONOLAYER L

LIGHT

Ge

CRYSTAL MONOLAYER

~7~

;c*o

DETECTOR

CIO4"

SUBPHASE ciof/cr c r ONLY

M000

M00

:|0

CIO4" ONLY Ru(C00C|8)(CI)2 2

ir=30 DYN/CM 3000 2900 2800 1800 1700 1600 1200 1100 1000 WAYENUMBERS

2 1 #

c

Figure 12. Partial FTIR of I transferred from 10~ M NaCI, I 0 M NaCI/ 10~ M NaClO , I0~ M NaCl/10~ M NaClO 10 M NaCl/l&M NaClO and 10~ M NaClO aqueous subphases at IT = 30 dyn/cm, 2VC as a single monolayer on both sides of a hydrophilic Ge ATR plate. 3

6

3

h

3

5

k9

3

3

k


h


90

INTERFACIAL

i

r

i

1090

92

94

•

i

96

1

1

r

1

1

98

1100

02

04

06

PHOTOPROCESSES

r—

5

08 1110

MASS

Ru (C,.) (CI0 ) -1 CI0 2

'

i

1190

4

l

2

4

*

l

92

94

I

l

96

98

\

1200

1

1

02

04

"

MASS Figure 13.

FDMS

T

06

of the perchlorate and chloride salts of solid IX


"

^

5.

VALENTY

Surfactant

LUMINESCENCE.

Monolayer

91

Films

T h e m o s t s t r i k i n g effect of c o u n t e r i o n s is t h e i r m a j o r

i n f l u e n c e o n m o n o l a y e r l u m i n e s c e n c e at t h e a i r - w a t e r i n t e r f a c e (see ure

14).

Fig

S u c h differences are u n i q u e t o t h e i n t e r f a c e a n d are n o t f o u n d

e i t h e r i n h o m o g e n e o u s a q u e o u s o r g a n i c solutions of I ( o r I X ) w i t h a d d e d salts or i n w h o l l y aqueous solutions of I I a n d I I I at levels of 4M K C 1 a n d N a C 1 0 . B e c a u s e of t h e i n a b i l i t y to estimate t h e q u a n t u m y i e l d of l u m i 4

nescence i n t h e m o n o l a y e r fluorimeter, i t is not p o s s i b l e t o d e c i d e w h e t h e r t h e difference i n l u m i n e s c e n c e i n t e n s i t y results f r o m a r e d u c t i o n i n y i e l d b y ions s u c h as C I " , or a n e n h a n c e m e n t b y C 1 0 " , as c o m p a r e d w i t h y i e l d s Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 5, 2016 | http://pubs.acs.org Publication Date: June 1, 1980 | doi: 10.1021/ba-1980-0184.ch005

4

i n o t h e r e n v i r o n m e n t s . T h e l a r g e solvent effects o n l u m i n e s c e n c e y i e l d of Ru(bpy)

3

2 +

d e r i v a t i v e s (19,20,21)

suggest t h a t t h e e n v i r o n m e n t c h a n g e

i n d u c e d b y i n t e r a c t i o n w i t h t h e s t r o n g l y c o n d e n s i n g C 1 0 * ions m i g h t 4

e n h a n c e l u m i n e s c e n c e . A n o t h e r case of a n i o n a l t e r a t i o n ( i n c r e a s e d l i f e t i m e , r e d u c e d n o n r a d i a t i v e d e c a y r a t e ) of l u m i n e s c e n c e p r o p e r t i e s for a t r a n s i t i o n m e t a l b i p y r i d y l c o m p l e x has b e e n

reported recently

(22),

a l t h o u g h since i n t h a t s i t u a t i o n a different t y p e of e x c i t e d state is affected and

t h e effect is o b s e r v e d i n aqueous s o l u t i o n , t h e observations m a y b e

unrelated. Forster theory calculations based on the small overlap between ab s o r p t i o n a n d e m i s s i o n s p e c t r a of I i n C H C 1 c e n c e q u a n t u m y i e l d , — L

R

0

=

solution (using a lumines

3

0.18) leads to a n e n e r g y transfer d i s t a n c e ,

15 A ( I f this v a l u e is c o r r e c t e d f o r t h e m o n o l a y e r e n v i r o n m e n t b y

i n t r o d u c i n g

Characterization and Chemical Reactions of Surfactant Monolayer Films

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