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Polymerization in non-aqueous lyotropic liquid crystals: Influence of the unsaturation site
CoIl0id.s anti SltrJflrcs. 69 (1993) 239-247 Elscvicr Scicno: Publishxs B.V.. Amsterdam
239
Polymerization in non-aqueous lyotropic Influence of the unsaturation site
liquid crystals:
Stig E. Friberg”, Bing YIP’, Ahsan U. Ahmed” and Gregory A. Campbell” a Department of Clxwristry. Cmter forAdrxrrceri Marerids Processi!tg. Clarkmu University. Potsdam. NY 13699-5814, USA b Department of Chnical Ertgineerhg, Potsdam, NY 13699-5814. USA (Received
6 Aprii 1992; accepted
Ce?lter.for. rldvar;cz
15 September
1992)
Two surfactants. bis[3-(dodccyloxycarbonyl)c1l~yl](p-vinylbcnz~yl)mcti~ylammonium ch!oridc (Sk) and bis[2-(IO-rmdcccnoylo.uycurbonyl)cthyl](p-mcthylbcnzoyl)mcthylammonium chkidc (Sli) wcrc synthesized and copoIymcrizeG with polar and non-polar monomers to form regularly laycrcd structures. The results showed a pronounced di!Tcrcncc between thr: two surfactants. SI with the dnuhle bond close to the polar group accepted ;I large number or monomers, in contrast to the behavior of SII. For SI the polymctitation changed the conlormation of the p-vinylbcnzoyl group dcpcnding on the location of the added monomer while copolymcrization of the monomers with SIl gave no significant change. A comparison with carlicr results from bis[Z-( IO-undcccnoyloxycarbonyl)cthyl]( p-vinylbcnzoyl)mcthylammonium chloride provided proof ofcopolymcrization of all the groups. Kc_wortl.s:
Detergents:
lyotropic
liquid crystals:
microcmulsions:
small-rrngie
Introduction
Polymerization in amphiphilic association structures in isotropic solutions has attracted some interest [i __I1UJ I-vt-L~JSC; - T-i’-of ilie ptiieiiiia! iir PLt-pare small uniform latex particles of water-soluble polymers [4,5] or to prepare highly porous Iatex particles [6]. Lyotropic hquici crystais, however, have received limited interest. Very early work [7.8] was followed by a few papers [9-I 1] and by extenstve investigations by Finkelmann and co-workers [ 12- 151. The work of Finkelmann should be noted because he --Corre.sporl,lerrl,e to: SE. Fribcrg, Dept. or Chemistry, Ccntcr for Advanced Materials Proccssmg, Clarkson University. Potsdam. NY 13699-5314. USA. ’ Prcscnt address: Rokm Sr Haas Corp., Spring House, PA 19477. USA. 0166~6622/93/SO6.00
CiJ 1993 -
Elscvicr
Science
Ytiblishcrs
X-ray diffraction;
surf;lctant
polymerization.
demonstrated that polymerization can stabilize the long-range order of the liquid crystal. The recent work by Anderscn and Strom [ 161 is of pronounced interest because the polymerization of a c.ubic liquid crystal was used to prepare a structure with extremely well-defined pores. It appears that this approach may find interesting applications in the future in generating membranes of well-defined pore size. However, the research in this area has not attracted interest beyond a few specialists, and. as a result, the properties of the polymeric materials have never been investigated. A probable reason for the lack of’ interesz is the fact that the liquid crystals have, until recently, been based on water as the polar solvent. With water as an essential part of the structure, a large number of applications would automatically be prohibited. B.V. Ali rights
reserved.
240
However, this disadvantage is removed by the non-aqueous lyotropic liquid crystals which were introduced a few years ago [17-19-J. In these structures, the water is replaced by a polar solvent with a polymerizable monomer as a natural and expected choice [20]. An extension of this would be to use a polymerizable surfactant combined with monomers to create a polymer in which polar and non-polar compounds are organized in a regularly layered structure. Such a material has recently been introduced [20]. In this paper, the polymerized structure is evaluated with respect to the influence of the site of unsaturation on the surfactant. Experimental
+,C% H,C=CH(CH2),;-OCH,CH,/
I.4bH2-o-CH%H2
0
S 0 H,CtCH,&OCH,CH, H,C(CH&C-OCH&H,
\
+ ,
_lN
CH,
Cl -
‘CH,oCH=CH,
II
0
SI
z
H,C=CH(CH$,C-OCH,CH, H,C=CH(CH2),C-OCH,CH,/
\
+ ,
CH,
N hH,--Q-CH;’
-
6
SP
Lauroyl chloride (98%, Aldrich), x-chloro-pxylene (9870, Aldrich), styrene (99.9% Fisher Scicntific), divinylbenzene (technica Aldrich), 1,&heptadiene (9970, Aldrich) and 2,2-azobis(2-methylpropionitriIe) (99% Eastman Kodak) were used without further purification.
Bis[2-(dodecyloxycarbonyl)ethyl](p-vin:rlbenzoyl)methylammonium chloride (SI) was synthesized according to Ref. [20] with the IO-undecenoyl chloride replac&l by dodecanoyi chloride (Fig. I). Bis[2-( IO-undccenoyloxycarbonyl)ethyl]p-xylenemethylammonium chloride (SII) was synthesized according to Ref. [20] with the chlorom+hylstyrcne rcpIaced by g-chloro-p-xylene (Fig. I).
The samples invoIving SI were completely po!ymerized after exposure to UV light for 15 h while those with the SII surfactant required heating to 70°C (12 h), with UV light [20] and addition of A!BN inil:ator.
Fig. I. The siruclurc olthc surfnclnnts S (bis[Z-( IO-undoccnoylchlooxycnrbonyl)cthyI J(p-vinyibcnzoyI;mcthylammoniun~ rick). SI and SII.
Small-angle X-ray dimraction measurements were made with a Kiessig low-angle camera (Richard Seifert, Germany). Nickel-filtered copper radiation was used and the reflections were determined by a position-sensitive detector system (Tennelec Model PSD- 100, Memphis, U.S.A.). Results The surfactants were in the form of a lamellar liquid crystal with interlayer spacings according to Table 1. Interiayer spacing prior to polymerization was similar for the two surfactants. After polymerization SI ga;re a strong increase in interlayer spacing (11 A), while the change of the spacing for SII was insignificant (I A). Addition of monomers to the surfactant gave only insignificant changes in the interl;lyer spacing SI, however, showed a for SII (Figs 2A-2C). response that was decisively dependent on the structure of the monomer. Addition of heptadiene
3.L’. Frihcrg c! d./Colloid.~
Surfoccs
2c
0.5
(A)
Volume ratio
0.0 (C) spacing
(B)
0.5
Monomer/Surfactant,
versus the monomer/surfaciant volume ai;d (C) divicylbenzenc. 0, S system;
1.0
0.5
0
1.0
MonomedSurfactant,
Fig. 2. The interlayer
241
69 (1993) 239-247
Monomer/Surfactamt,
Volume ratio
5.0
Volume ratio ratio for the three surfactants X, SI system; A, SII system.
plus (A) heptadiene.
(I3) styrcne
242
S.E. Friherg et al./Colloids Surfaces 69 11993) 239-247
TABLE 1 Interlayer spacings of surf:~ctants Surhtctant
Sl SIt
Interlayer spacing (A) Before polymerization
ANer polymerization
26.7 24.5
37.7 25.5
(Fig. 2A) caused a linear increase of interlayer spacing for additions in excess of i 0%. while the aromatic monomers (Figs. 2B and 2C), caused an initially strong reduction that became less pronounced for higher additions of m o n o m e r for SI. The interlayer spacings for surfaetant, S (bis[2-(I 0-undeeenoyloxycarbonyl) ethyl-I (p- vinylbenzoyl)methylammonium chloride, see Fig. I) [21_-! with unsaturated bonds at both the locations of SI and SII are added for comparison. The variation of interlayer spacing of SI with other monomers is presented in Figs 3 A - 3 D with the corresponding values for S added. The interlayer spacings for SI were greater in all cases, with a retained general shape of the curve with the exception of the combination with acrylonitrile. With this m o n o m e r the reduction of interlayer spacing found for S did not appear. Instead, the interlayer spacing showed a slight in("::ase with added monomer.
Discussion The results demonstrated a decisive importance of unsaturation site for the behavior during polymerization. A comparison of the results from SI, witi~ unsaturatior, close to the polar group, from SII. wRh unsaturatior, at the ends of two long chaii~s : ~ d IYom S [21], with unsaturation at both sites, provides information about the relative ~n~portance of the unsaturation sites in SI and SII. "I'i~e difti~rence between the behavier of surfactant I in this investigation and that of the surfactant with unsar~ration at both sites (S) was a mere modification of the variation in interlayer spacing
rather than a change. The surfactant SIl, however, gave a radically dill?rent response to the introduction of small monomeric species. A discussion about the present results is more usef~d if the interlayer spacings are transformed to penetration values. The definition of penetration is bas,:d on two cases. In the first case, the interlayer spacing remains constant with addition of monomer. In this case, the m o n o m e r is said to penetrate completely; a penetration fraction ~ equal to t. In the second case, the increase in interlayer spacing is proportional to the volume ratio of m o n o m e r added to the original components. The penetration is now said to be zero and the m o n o m e r is located entirely in zone A or C, Fig. 4. Cases between these two are described by linear interpolation and a simple expression is obtained. d=do[I
+(i -~)R]
(!)
where d is the interlayer spacing, do is its value for zero added substance, ~ is the penetration fraction and R is the volume ratio between the added and the original substances. Such a definition is useful when the interlayer spacing is linearly dependent on R, in which case has a single value for all R values. A curved interlayer spacing function versus R requires a different definition. In that case. the penetration fraction is defined for each R value using the tangent to the curve for Eqn (I). The equation for the tangent is obtained from an empirical equation for the d(R) curve. Earlier attempts [:21] have used a Langmuir function with constants a and b. d - do = a R / ( l
+ bR)
(2)
The derivative is 8d/t?R = a/(l + b R ) 2
(3)
and ~ is obtained from Eqn (1) = I -((~d/~R)/d~
(4)
where d~ is the extrapolated value for the tangent, giving - - I - a/[d(I + h R ) 2 - a R ]
(5)
x-x/y X
c-w
o/-o-
/
,! 0.1
0.0
MonomerlSurhctant,
(A)
351
0.2
0.0
Volume ratio
1.0
MonomedSurhctsnt,
(B)
50
0.5
Volume ratio
50
301 0.0
3(
I
0.5
MonomedSurfactant, Fig. 3. lntcrlaycr
1.0
Volume ratio
PI
0.0
0.5
1.0
MonomedSurlhctant,
Volume ratio
spacing versus monomcr/surhchnt volume ratio for 11x two surhctar CI S and SI (Fig. I) plus (A) octadcccnc, (B) glyccryl monomcthacrylatc. (C) acrylonilrilc and (D) acrylic acid. 0. b sys!cm; x . SI system.
where tl is now the interiayer spacing at the point for which Q is calculated. However, the values for SlI obviously cannot be described by Eqn (2). They were, instead, fitted to a simple polynomial ti - tl, = pR + qRZ + r.R3
(6)
and Eqn (5) was ;1ow changed
to
x = 1 - (p + 2qR + 31*R2)/d:, in which’ dh = d - (pR + 2qR’ + 3rR3) and ,n and ~1 are without physical significance.
A B C B A
Fig. 4. The structure of a lamcllar liquid crystill with watcri polar group layers (A). hydrocarbon chains of the amphiphilcs (B) and the region bctwccn the hydrocarbon
chain methyl
groups (C).
With the characterization of the penetration phenomena it is possible to evaluate the structural conscquenccs in the polymer, which are a result of the number and location of the double bonds. The first result is obvious from the interlayer spacings (Figs 2A-2C and Figs 3A-3D). The values for SII were consistently lower than those for the other two surfactants. The reason for this difference is the conformational change of the short chain in S and Si during polymerization. The SII structure did not contain the short chain double bond and consequently the polar group was not involved in the polymerization reaction. The penetration values calculated from the results in Figs 2A-2C illustrate the expected molccular locations in the liquid crystal. The heptadiene molecule is preferentially located in the non-polar part of the lamellar structure prior to polymerization. It will, hence, copolymerize with SII giving a high penetration, supported by the fact that the pmethylbenzoyl group points in the same direction as the long chains, thereby leaving space for the heptadiene molecule towards the end of the two
chains. The surfactant SI, however, offers only the double bond at the p-vinylbenzoyl group for copolymerization, and the moderately high penetration value is a result of some heptadiene molecules being “trapped” penetrating the surfactant structure. The cffcct of heptadicnc penetration is enhanced by the fact that a copolymerization with the p-vinylbenzl)ate group leads to a conformational change of tlic latter to a position pointing towards the long chain direction. The higher penetration value for SI compared to S is a result of this conformational change. No such mechanism is expected for S. This surfactant has two terminal double bonds on the long chains and, hence, ample opportunities for copolymerization with the heptadienc. The penetration was the lowest for this surfactant. The aromatic monomers initially gave an extremely high penetration, Figs 5B and SC, which changed to a value of 1.G for higher amounts of monomer. They are concentrated towards the polar groups [22] and initial polymerization engages the vinyl group. This polymerization caused a conformation change of the p-vinylbenzoyl group from the extended position in Fig. I to a direction towards the two long chains. The change caused a reduction in interlayer spacing and in addition gave rise to enhanced disorder in the two long chains. Both phenomena caused reduced interlayer spacing, expressed as penetration values. Once the available surfactant vinyl groups had been polymerized the conformational changes ceased and the interlayer spacing remained constant, reflecting the expected location of an aromatic monomer [22]. ‘i he opposite behavior is demonstrated by the remaining polymers in Figs 3B-3D. As an example, the glyoeryl monomethacrylate (Fig. 6Bj shows an initial negative penetration of 0.7, i.e. the addition of the monomer causes an expansion as if all the added monomer plus 0.7 of its volume were restricted to the space between the polar group layers, (zone A, Fig. 4). Glyceryl monomethacrylate is an extremely polar monomer and in its location between the polar groups it will copolymerize with the vinylbenzoyl groups, bringing more of them
S.E. I;riherg
0.0 (A)
et nl./Colloiris
Swfices
69 (1993) 139-247
0.5
MottomedSurfactant,
1.0
Volume rstio
Fig. 5. The
0.5
McrnomerjSurfactant,
(81
Monomer/Surfacktnt,
Vokne
pcnctration fraction (2) for the monomer versus the monomcr/surfaclanl (A) hcpradicnc, (B) styrene and (C) divinylbenzene. 0, S system;
into the ;i::3CS. (mne A, Fig. 4) between tk poiar group layers. ‘i’i\is ;-:,. :hanism ceased at low volume ratios, when all the p-vinylbenzoyl groups were presumably engaged. All the monomers (Figs 6A4D) showed an enhanced penetration for the SI combination com-
1.0
Volume Ratio
1.0
0.5
0.0 (0
0.0
;_a!&
volume raw k:, the three x, SI system; A, S!I sys~~!~~.
wrfactants
pIus
pared to the monomer/S arrangement. This difference is understood from the fact that any monomer copolymerization with the terminal vinyl groups of the long chains brings enhanced order in that part of the molecule, leaving less space for penctration.
246
00
-
<
xv
-1
b U_
_*-
0.0
0.5
MonomerlSurhctant,
(A)
.
1.0
Volume ratio
.1
0.c
0.5
1.0
0.0
0.5
1.0
(B) 1.5
(0
Monomer/Sur6actant,
Volume ratio
(D)
Mollomer/SurTac!3;:~ ~ Voiiime ratio
Fig. 6. The pcnctrotion fraction (2) for the monomer versus the Inonolncrisurfilct;lilt volume ratio for the two surfactants S and SI plus (A) octadcccnc, (B) glyccryl monomc:hacrylatc, (C) acrylonitrilc and (D) ilcrytic acid. 0. S system: x. SI sys~rw.
Summary
4 5
CopoIymerization between two surfactants (bis[2-(dodecyloxycarbonyi)etl~yl](~-vinylbenzoyl) methylammonium chloride, bis[2-( IO-undecenoyIoxycarbonyl)ethyl](p-methylbenzoyl)methylammonium chloride) and different monomers gave results that could be interpreted according to the e>,)ccted location of the monomer in the Iamellar liquid crystalline structure. The changes in interlayer spacmg could be rationally explained from the expected location of the monomer and induced conformational changes of the surfactant structure.
6 7 8 9 IO II 17 13 14
Aclrriuwledgment
15 16
This research was financially supported by the New York State Commission for Science and Technology through its CAMP program at Clarkson University.
17 IY
References C.M. Palcos. Chcm. Sac. Rev.. 14 (1985) 45. J.H. Fcndlcr. Mcmbranc Mimic Chemistry. Wilcy-lntcrscicncc, New York. 1981. M.A. ElNokali (Ed.), Poiymcr Association Structures. ACS Symp. Ser. 384, American Chemical Society, !Gshington. DC. 1989.
I9 20 ‘I 22
F. Candau. F. Zckhuini and J.P. Curand. J. Colloid Intcrracc Sci.. 114 (1986) 386. F. Candau. Y. Lcong and R. Fitch, J. Polym. Sci.. Chcm. Ed.. 23 ( 1985) 193. E. Hague and S. Qutubuddin. J. Polym. Sci., Polym. Lctt. Ed., 26 (1858) 429. C. Sndron. Pure Appl. Chem., 4 (1962) 347. P. Recamp and V. Luzzatti, J. Hen.. F. Reis-Husson, J. Polym. Sci., Chem. Ed.. 4 (1963) 1175. S.E. Fribcrg. R. Thundathii ad J.O. Sto~eer. Scicncc, 205 (1979) 607. R. Thundsthil. S.E. Fribrrg and J.O. Stoffcr. J. Polym. Sci.. Chcm. Ed.. IX (1980) ‘629. F.D. Blum. Pcrsclsill communication. 1991. H. Finkclmann, J. Kolci&of and H. Ringsdorff, .Angcw. Chcm., 90 (1978) 992. H. Finkclmann, B. Liiman and G. Rehagc, Cc!loid Poiym. sci., x0 [ 1982) 56. E. Johns and H. Finkelmaan, Colloid Polym. Sci.. 765 (1987) 304. B. Liiman and H. Finkclmann, Colloid Polym. Sci., 265 (1987) 506. D.M. tindcrson and P. Striim. ir. M.A. ElNokali (Ed.), Polymer Association Structuw: Microcmulsions and Liquid Crystals, Ar7S Symp. %I, 3%. An,zrican Chcmioti: Socicly. Washington. DC. 1989. Chapter 13. N. Moucharafieh and S.E. Fribcrg, Mol. Cryst. Liq. Cryst., 49 (1979) 231. M.A. EINokali, L.D. Ford. S.E. Fribcrg and D.W. Lnrscr?. J. Colloid lnterfxx Sci., 84 (198!) 1%. D.F. Evans, E.W. Kalcr and W.J. Bcnton. J. Phys. Chcnr., 87 (1%;; 533. S.E. Fribcrg. ChS. Wohn ;md F.E. Lockwood. Macromolecules, 20 i 1% ,:) 2057. S.E. Fribcrg, B. Yu and G.A. Campbcl!, J. Disp. Sri. Techno).. in press. H. Christenson. D.W. Larsen and SE. Fribcrg, J. Phys. Chcm.. 84 (1980) 3633.
239
Polymerization in non-aqueous lyotropic Influence of the unsaturation site
liquid crystals:
Stig E. Friberg”, Bing YIP’, Ahsan U. Ahmed” and Gregory A. Campbell” a Department of Clxwristry. Cmter forAdrxrrceri Marerids Processi!tg. Clarkmu University. Potsdam. NY 13699-5814, USA b Department of Chnical Ertgineerhg, Potsdam, NY 13699-5814. USA (Received
6 Aprii 1992; accepted
Ce?lter.for. rldvar;cz
15 September
1992)
Two surfactants. bis[3-(dodccyloxycarbonyl)c1l~yl](p-vinylbcnz~yl)mcti~ylammonium ch!oridc (Sk) and bis[2-(IO-rmdcccnoylo.uycurbonyl)cthyl](p-mcthylbcnzoyl)mcthylammonium chkidc (Sli) wcrc synthesized and copoIymcrizeG with polar and non-polar monomers to form regularly laycrcd structures. The results showed a pronounced di!Tcrcncc between thr: two surfactants. SI with the dnuhle bond close to the polar group accepted ;I large number or monomers, in contrast to the behavior of SII. For SI the polymctitation changed the conlormation of the p-vinylbcnzoyl group dcpcnding on the location of the added monomer while copolymcrization of the monomers with SIl gave no significant change. A comparison with carlicr results from bis[Z-( IO-undcccnoyloxycarbonyl)cthyl]( p-vinylbcnzoyl)mcthylammonium chloride provided proof ofcopolymcrization of all the groups. Kc_wortl.s:
Detergents:
lyotropic
liquid crystals:
microcmulsions:
small-rrngie
Introduction
Polymerization in amphiphilic association structures in isotropic solutions has attracted some interest [i __I1UJ I-vt-L~JSC; - T-i’-of ilie ptiieiiiia! iir PLt-pare small uniform latex particles of water-soluble polymers [4,5] or to prepare highly porous Iatex particles [6]. Lyotropic hquici crystais, however, have received limited interest. Very early work [7.8] was followed by a few papers [9-I 1] and by extenstve investigations by Finkelmann and co-workers [ 12- 151. The work of Finkelmann should be noted because he --Corre.sporl,lerrl,e to: SE. Fribcrg, Dept. or Chemistry, Ccntcr for Advanced Materials Proccssmg, Clarkson University. Potsdam. NY 13699-5314. USA. ’ Prcscnt address: Rokm Sr Haas Corp., Spring House, PA 19477. USA. 0166~6622/93/SO6.00
CiJ 1993 -
Elscvicr
Science
Ytiblishcrs
X-ray diffraction;
surf;lctant
polymerization.
demonstrated that polymerization can stabilize the long-range order of the liquid crystal. The recent work by Anderscn and Strom [ 161 is of pronounced interest because the polymerization of a c.ubic liquid crystal was used to prepare a structure with extremely well-defined pores. It appears that this approach may find interesting applications in the future in generating membranes of well-defined pore size. However, the research in this area has not attracted interest beyond a few specialists, and. as a result, the properties of the polymeric materials have never been investigated. A probable reason for the lack of’ interesz is the fact that the liquid crystals have, until recently, been based on water as the polar solvent. With water as an essential part of the structure, a large number of applications would automatically be prohibited. B.V. Ali rights
reserved.
240
However, this disadvantage is removed by the non-aqueous lyotropic liquid crystals which were introduced a few years ago [17-19-J. In these structures, the water is replaced by a polar solvent with a polymerizable monomer as a natural and expected choice [20]. An extension of this would be to use a polymerizable surfactant combined with monomers to create a polymer in which polar and non-polar compounds are organized in a regularly layered structure. Such a material has recently been introduced [20]. In this paper, the polymerized structure is evaluated with respect to the influence of the site of unsaturation on the surfactant. Experimental
+,C% H,C=CH(CH2),;-OCH,CH,/
I.4bH2-o-CH%H2
0
S 0 H,CtCH,&OCH,CH, H,C(CH&C-OCH&H,
\
+ ,
_lN
CH,
Cl -
‘CH,oCH=CH,
II
0
SI
z
H,C=CH(CH$,C-OCH,CH, H,C=CH(CH2),C-OCH,CH,/
\
+ ,
CH,
N hH,--Q-CH;’
-
6
SP
Lauroyl chloride (98%, Aldrich), x-chloro-pxylene (9870, Aldrich), styrene (99.9% Fisher Scicntific), divinylbenzene (technica Aldrich), 1,&heptadiene (9970, Aldrich) and 2,2-azobis(2-methylpropionitriIe) (99% Eastman Kodak) were used without further purification.
Bis[2-(dodecyloxycarbonyl)ethyl](p-vin:rlbenzoyl)methylammonium chloride (SI) was synthesized according to Ref. [20] with the IO-undecenoyl chloride replac&l by dodecanoyi chloride (Fig. I). Bis[2-( IO-undccenoyloxycarbonyl)ethyl]p-xylenemethylammonium chloride (SII) was synthesized according to Ref. [20] with the chlorom+hylstyrcne rcpIaced by g-chloro-p-xylene (Fig. I).
The samples invoIving SI were completely po!ymerized after exposure to UV light for 15 h while those with the SII surfactant required heating to 70°C (12 h), with UV light [20] and addition of A!BN inil:ator.
Fig. I. The siruclurc olthc surfnclnnts S (bis[Z-( IO-undoccnoylchlooxycnrbonyl)cthyI J(p-vinyibcnzoyI;mcthylammoniun~ rick). SI and SII.
Small-angle X-ray dimraction measurements were made with a Kiessig low-angle camera (Richard Seifert, Germany). Nickel-filtered copper radiation was used and the reflections were determined by a position-sensitive detector system (Tennelec Model PSD- 100, Memphis, U.S.A.). Results The surfactants were in the form of a lamellar liquid crystal with interlayer spacings according to Table 1. Interiayer spacing prior to polymerization was similar for the two surfactants. After polymerization SI ga;re a strong increase in interlayer spacing (11 A), while the change of the spacing for SII was insignificant (I A). Addition of monomers to the surfactant gave only insignificant changes in the interl;lyer spacing SI, however, showed a for SII (Figs 2A-2C). response that was decisively dependent on the structure of the monomer. Addition of heptadiene
3.L’. Frihcrg c! d./Colloid.~
Surfoccs
2c
0.5
(A)
Volume ratio
0.0 (C) spacing
(B)
0.5
Monomer/Surfactant,
versus the monomer/surfaciant volume ai;d (C) divicylbenzenc. 0, S system;
1.0
0.5
0
1.0
MonomedSurfactant,
Fig. 2. The interlayer
241
69 (1993) 239-247
Monomer/Surfactamt,
Volume ratio
5.0
Volume ratio ratio for the three surfactants X, SI system; A, SII system.
plus (A) heptadiene.
(I3) styrcne
242
S.E. Friherg et al./Colloids Surfaces 69 11993) 239-247
TABLE 1 Interlayer spacings of surf:~ctants Surhtctant
Sl SIt
Interlayer spacing (A) Before polymerization
ANer polymerization
26.7 24.5
37.7 25.5
(Fig. 2A) caused a linear increase of interlayer spacing for additions in excess of i 0%. while the aromatic monomers (Figs. 2B and 2C), caused an initially strong reduction that became less pronounced for higher additions of m o n o m e r for SI. The interlayer spacings for surfaetant, S (bis[2-(I 0-undeeenoyloxycarbonyl) ethyl-I (p- vinylbenzoyl)methylammonium chloride, see Fig. I) [21_-! with unsaturated bonds at both the locations of SI and SII are added for comparison. The variation of interlayer spacing of SI with other monomers is presented in Figs 3 A - 3 D with the corresponding values for S added. The interlayer spacings for SI were greater in all cases, with a retained general shape of the curve with the exception of the combination with acrylonitrile. With this m o n o m e r the reduction of interlayer spacing found for S did not appear. Instead, the interlayer spacing showed a slight in("::ase with added monomer.
Discussion The results demonstrated a decisive importance of unsaturation site for the behavior during polymerization. A comparison of the results from SI, witi~ unsaturatior, close to the polar group, from SII. wRh unsaturatior, at the ends of two long chaii~s : ~ d IYom S [21], with unsaturation at both sites, provides information about the relative ~n~portance of the unsaturation sites in SI and SII. "I'i~e difti~rence between the behavier of surfactant I in this investigation and that of the surfactant with unsar~ration at both sites (S) was a mere modification of the variation in interlayer spacing
rather than a change. The surfactant SIl, however, gave a radically dill?rent response to the introduction of small monomeric species. A discussion about the present results is more usef~d if the interlayer spacings are transformed to penetration values. The definition of penetration is bas,:d on two cases. In the first case, the interlayer spacing remains constant with addition of monomer. In this case, the m o n o m e r is said to penetrate completely; a penetration fraction ~ equal to t. In the second case, the increase in interlayer spacing is proportional to the volume ratio of m o n o m e r added to the original components. The penetration is now said to be zero and the m o n o m e r is located entirely in zone A or C, Fig. 4. Cases between these two are described by linear interpolation and a simple expression is obtained. d=do[I
+(i -~)R]
(!)
where d is the interlayer spacing, do is its value for zero added substance, ~ is the penetration fraction and R is the volume ratio between the added and the original substances. Such a definition is useful when the interlayer spacing is linearly dependent on R, in which case has a single value for all R values. A curved interlayer spacing function versus R requires a different definition. In that case. the penetration fraction is defined for each R value using the tangent to the curve for Eqn (I). The equation for the tangent is obtained from an empirical equation for the d(R) curve. Earlier attempts [:21] have used a Langmuir function with constants a and b. d - do = a R / ( l
+ bR)
(2)
The derivative is 8d/t?R = a/(l + b R ) 2
(3)
and ~ is obtained from Eqn (1) = I -((~d/~R)/d~
(4)
where d~ is the extrapolated value for the tangent, giving - - I - a/[d(I + h R ) 2 - a R ]
(5)
x-x/y X
c-w
o/-o-
/
,! 0.1
0.0
MonomerlSurhctant,
(A)
351
0.2
0.0
Volume ratio
1.0
MonomedSurhctsnt,
(B)
50
0.5
Volume ratio
50
301 0.0
3(
I
0.5
MonomedSurfactant, Fig. 3. lntcrlaycr
1.0
Volume ratio
PI
0.0
0.5
1.0
MonomedSurlhctant,
Volume ratio
spacing versus monomcr/surhchnt volume ratio for 11x two surhctar CI S and SI (Fig. I) plus (A) octadcccnc, (B) glyccryl monomcthacrylatc. (C) acrylonilrilc and (D) acrylic acid. 0. b sys!cm; x . SI system.
where tl is now the interiayer spacing at the point for which Q is calculated. However, the values for SlI obviously cannot be described by Eqn (2). They were, instead, fitted to a simple polynomial ti - tl, = pR + qRZ + r.R3
(6)
and Eqn (5) was ;1ow changed
to
x = 1 - (p + 2qR + 31*R2)/d:, in which’ dh = d - (pR + 2qR’ + 3rR3) and ,n and ~1 are without physical significance.
A B C B A
Fig. 4. The structure of a lamcllar liquid crystill with watcri polar group layers (A). hydrocarbon chains of the amphiphilcs (B) and the region bctwccn the hydrocarbon
chain methyl
groups (C).
With the characterization of the penetration phenomena it is possible to evaluate the structural conscquenccs in the polymer, which are a result of the number and location of the double bonds. The first result is obvious from the interlayer spacings (Figs 2A-2C and Figs 3A-3D). The values for SII were consistently lower than those for the other two surfactants. The reason for this difference is the conformational change of the short chain in S and Si during polymerization. The SII structure did not contain the short chain double bond and consequently the polar group was not involved in the polymerization reaction. The penetration values calculated from the results in Figs 2A-2C illustrate the expected molccular locations in the liquid crystal. The heptadiene molecule is preferentially located in the non-polar part of the lamellar structure prior to polymerization. It will, hence, copolymerize with SII giving a high penetration, supported by the fact that the pmethylbenzoyl group points in the same direction as the long chains, thereby leaving space for the heptadiene molecule towards the end of the two
chains. The surfactant SI, however, offers only the double bond at the p-vinylbenzoyl group for copolymerization, and the moderately high penetration value is a result of some heptadiene molecules being “trapped” penetrating the surfactant structure. The cffcct of heptadicnc penetration is enhanced by the fact that a copolymerization with the p-vinylbenzl)ate group leads to a conformational change of tlic latter to a position pointing towards the long chain direction. The higher penetration value for SI compared to S is a result of this conformational change. No such mechanism is expected for S. This surfactant has two terminal double bonds on the long chains and, hence, ample opportunities for copolymerization with the heptadienc. The penetration was the lowest for this surfactant. The aromatic monomers initially gave an extremely high penetration, Figs 5B and SC, which changed to a value of 1.G for higher amounts of monomer. They are concentrated towards the polar groups [22] and initial polymerization engages the vinyl group. This polymerization caused a conformation change of the p-vinylbenzoyl group from the extended position in Fig. I to a direction towards the two long chains. The change caused a reduction in interlayer spacing and in addition gave rise to enhanced disorder in the two long chains. Both phenomena caused reduced interlayer spacing, expressed as penetration values. Once the available surfactant vinyl groups had been polymerized the conformational changes ceased and the interlayer spacing remained constant, reflecting the expected location of an aromatic monomer [22]. ‘i he opposite behavior is demonstrated by the remaining polymers in Figs 3B-3D. As an example, the glyoeryl monomethacrylate (Fig. 6Bj shows an initial negative penetration of 0.7, i.e. the addition of the monomer causes an expansion as if all the added monomer plus 0.7 of its volume were restricted to the space between the polar group layers, (zone A, Fig. 4). Glyceryl monomethacrylate is an extremely polar monomer and in its location between the polar groups it will copolymerize with the vinylbenzoyl groups, bringing more of them
S.E. I;riherg
0.0 (A)
et nl./Colloiris
Swfices
69 (1993) 139-247
0.5
MottomedSurfactant,
1.0
Volume rstio
Fig. 5. The
0.5
McrnomerjSurfactant,
(81
Monomer/Surfacktnt,
Vokne
pcnctration fraction (2) for the monomer versus the monomcr/surfaclanl (A) hcpradicnc, (B) styrene and (C) divinylbenzene. 0, S system;
into the ;i::3CS. (mne A, Fig. 4) between tk poiar group layers. ‘i’i\is ;-:,. :hanism ceased at low volume ratios, when all the p-vinylbenzoyl groups were presumably engaged. All the monomers (Figs 6A4D) showed an enhanced penetration for the SI combination com-
1.0
Volume Ratio
1.0
0.5
0.0 (0
0.0
;_a!&
volume raw k:, the three x, SI system; A, S!I sys~~!~~.
wrfactants
pIus
pared to the monomer/S arrangement. This difference is understood from the fact that any monomer copolymerization with the terminal vinyl groups of the long chains brings enhanced order in that part of the molecule, leaving less space for penctration.
246
00
-
<
xv
-1
b U_
_*-
0.0
0.5
MonomerlSurhctant,
(A)
.
1.0
Volume ratio
.1
0.c
0.5
1.0
0.0
0.5
1.0
(B) 1.5
(0
Monomer/Sur6actant,
Volume ratio
(D)
Mollomer/SurTac!3;:~ ~ Voiiime ratio
Fig. 6. The pcnctrotion fraction (2) for the monomer versus the Inonolncrisurfilct;lilt volume ratio for the two surfactants S and SI plus (A) octadcccnc, (B) glyccryl monomc:hacrylatc, (C) acrylonitrilc and (D) ilcrytic acid. 0. S system: x. SI sys~rw.
Summary
4 5
CopoIymerization between two surfactants (bis[2-(dodecyloxycarbonyi)etl~yl](~-vinylbenzoyl) methylammonium chloride, bis[2-( IO-undecenoyIoxycarbonyl)ethyl](p-methylbenzoyl)methylammonium chloride) and different monomers gave results that could be interpreted according to the e>,)ccted location of the monomer in the Iamellar liquid crystalline structure. The changes in interlayer spacmg could be rationally explained from the expected location of the monomer and induced conformational changes of the surfactant structure.
6 7 8 9 IO II 17 13 14
Aclrriuwledgment
15 16
This research was financially supported by the New York State Commission for Science and Technology through its CAMP program at Clarkson University.
17 IY
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I9 20 ‘I 22
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