Optical studies of supramolecular tubular structures generated by taper-shaped side groups in the columnar hexagonal phase

(1)

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Optical studies of supramolecular tubular structures generated by taper-shaped side groups in the columnar

hexagonal phase

Jian-Feng Li, James Heck, Virgil Percec, Charles Rosenblatt, Joseph Collura, Michael Fisch

To cite this version:

Jian-Feng Li, James Heck, Virgil Percec, Charles Rosenblatt, Joseph Collura, et al.. Optical studies of supramolecular tubular structures generated by taper-shaped side groups in the columnar hexagonal phase. Journal de Physique II, EDP Sciences, 1994, 4 (10), pp.1813-1822. �10.1051/jp2:1994234�.

�jpa-00248080�

(2)

/ P/>;.I II Fian(.e 4 (1994) 1813-1822 OCTOBER 1994, PAGE f813

C la,, ii icJtion Pfi;ii< _I A/>,ha<1,

61 311E 64.71)M

Optical studies of supramolecular tubular structures generated by taper-shaped side _groups in the columnar hexagonal phase

Jian-Feng

Li

i').

James A. Heck

(2). Virgil

Percec

(2),

Charles Rosenblatt

('

² *),

Jo,eph

S. Collura

i~)

anLl Mich;tel R, Fi,ch I' "i

l'J Department of Phy,ic,, Ca,e We,tern Re;erve Univer~ity, Cleveland, Ohio 44106, U-S-A-

l~) Maeromolecular Science, Ca;e We,tern Re,erve University, Cleveland, Ohio 44106, U.S,A.

l'l Dep~itmcnt of Phi,ic,, John Carioll Umver,itv. Uiivcr,itj, Height,, ^Ohio ^441IX. ^U-S-A-

1R<.< t-i1 <></ ^~ Alai / 994. _i_i-i _{t-i i} ail _iii fiiifil jai _m f> ./iiiii> / 994, _iii ₍epic<I ?.i ,/im<> / 994

Ah,tract. Biieliiigcncc tic,i,urcmcnt, _ii the ct>luiin,ir he,agi>n,il phn,e 1'/>~,j,ii(I tit.bi(lily,

tic<i,uiciicnt, _ii the high temper,itui c i,t>tit>pie ph,i,c II h;i~c been per( oriictl _tin _;i pal viieih,iciy- late (I'AG-4EO-PhlAl h,iviig t<ipcr-,hiipctl ,itlc pinup, ; the _,miic iica,urcmcnt, _~,cic ~il,t>

pcilt>riictl _tin _~i ,all-~i,,ciibliig lit>m>iicric prccui,i>1 l12-AG-4EO-OH). We lountl th~it the t>ptiL~il ict~iitl~itit>n _iicrc~i,c, ,tionglj with tlccic~i,rig iciiiperatuic ii the

</)~, ph~i,e, whcrc~i, the

tit.bitlitj ,ht>~, _nt) ,j,tciii~itic pieti~ii,itit>n<il bch~ivit>i _tin ~ippio~ichiig the </)~,-l ph,i,c ti~ii,rut>n

ieiipci,nut c /

,j rt>iii ibt>~ _c. Atltliiit>nallj _we ^((>anti i large bi,ph;i,iL _cgit)n _ii(>Lint(

/

j lt>i nil,tL,ic, iii the iiit>nt>iiiei ,intl p<>lyniei Thc,e ic,ult, _me tli,cLi,,ctl _in tci iii, iii the tui hitliij, hemp di>ii ii,itetl hi Lt>I _uiiii~ii ~ithei th,ii t>neat,itit>ii;iI, uctu;ilion,.

Introducti<in.

It hit, heen kno~.n for nimij< yew-, that

aniphiphilic

niolecitle, niay ,elf'-it,,enible ii ,olLition

into,uprmiiolecular,tructure,

^al ^~,m.ion,

,hJpe,

which, _ii turn, iu;iy liirni

orgmiile(I lytitropic

liLjuiLl

cry,talline ph~i,e, (1-.1j,

A ,>erj<

gooLl e~muple

^I, ^the

lyotropic,j<,tern

pota,,iiiu ^lair.ate.

w>hich lorni,

cylinLlrical

^niicelle, in ~.ater. A, _;i tiiiction of'concentration an(I teniperature, one

iua» ohtmn t~,o uiiJ~ml _neniatic

ph,i,e,,

it, ~,ell _a, _a hiitxial

ph~i,e (4(.

However,

only recently<

iuolecLilm. recognition proce,,e, ^have ^hoer u,eLl to generate well-(lefineLl

progritniiueLl

,uprJni(>leculm.,j,,tori,

(5(, ^Thi, progre,, ha,

pro~iifed

vm.ion, ,trittegie, ^for ^the ^,elf-

~i,,eiuhlj< of',upraiuoleculm.,tructure,

in the iuelt

ph~i,e

^or,oliLl ,tJte with

,uh,eLiuent

liirmJtion of

theriuotropic

liLiuiLl

cry,,t;ilime ph;i,e,

(b(,

Recently tuhulm.,upraiuoleculm.

architecture,

(7(

were

generated

_ii<i the

,elf-a,,eiuhly

^of ,trLictural unit, contmning

tapered

,iLle group, a, e~o-receptor, ^mi(I ^varioLi, crown-ether, mid

E-ii<ii/ <i<fifieii t.,r#ipo _cw,ii ctlu E-mail <i<fill<>it li,chca'jt.v;i,;i _it-u etlu

(3)

1814 _JOURNAL DE PHYSIQUE II N° 10

oligooxyethylenic

_group, a,

enLlo-ieceptor,

(7-f ?(,

T~ipereLl

,iLle group, of,iiuilm.,tructure were Jl,o u,ed to generate ^other iuolecul;tr

(13j,

ni;tcioniolecLilar

j14j.

mi(I

,upramolecular

15, 16 ,tructure,.

One

exmiiple

of _it iiiononieric ,tructurJl unit which ,elf'-a,,eiuhle, _ii<i nioleculitt.

t.ecognition

into _J

tuhulm.,upr;tirolecul;tr

,tructure which

di,play,

_~i

therniotropic

coluirnJt.

he~itgonal (<lJj,) iiie,opha,e

i, ,ho~n in

figuie

la

l~(.

The

carte,pending poljniethacrylJte (Fig,

lh) jury ^Jl,o exhibit _a tubulm. ;trchitecture which

di,play,

_~i

therniotropic

_<fi~,

pha,e.

A ,cheniJtic

repre,ent;ttion

of the tubul;tr,trLicture I,,frown in

figure

~. The

theriiiod»nmiiic ,tability

of [hi,

pha,e

can be

ni;tnipulitted

i-in _v;triou, iuolecul;tr recognition _proce,,e,

l~(.

Kerr _nie;t,ure-

iiient, in the

t,otropic pha,e

ot _;i t.el;tted

tapereLl

unit have heen

t.eporteLl

iii the litet.atut.e

(16(.

whet-e it _wa, found that the Kerr con,tart I,

unu,ually large

in vie~v of the ,niall intrin,ic

optic;tl

ant,otropy ^ot'the ,elf-a,,eiuhled _,tructure. Thi, hehavior _w~i, attrihuted _to the _pre,ence ot it,,ociation, _in

I,otiopic pha,e,

hehJvior con,I,tent with

X-ray

re,Lilt,

(1~

mi(I _;tn

unu,uJllj<

high degree ot'turhidity

fk)und in

optic;tl turhidity experinient,

which _m-e

reported

hereii.

Optical e~perinient,

_in the

<1)~,

pha,e

have been niore

probleniaticJl.

_J, ,w.Lice

Jligiiuent

techniLiue, coiunionly

u,ed with low niolecular

weight liLiuid cry,tal, (17(

h;tve little effect in itll hut the thiiiie,t filiu,.

ALlditionally,

_am- Jtteiupt at

~iligiiuent

ot the </)j,

phit,e hy

e~ternal

niJgnetic

fielLl, ha, not heen ,ucce,,ful,

,ilthoLigh

electric ficlLl,,ho~v

pronii,e. CJlorinietry-

ha,eLl

pha,e dmgrmu,

oi iui~ture, ot'ditteient dianieter

polynier,,

t, well _;t, nii~ture, of

iiiononier, ;tad

polynier,,

indicate the pre,ence of _two colLiinnar

pha,e,

Xl, ^Thi, I,

clearly,

_~i

rich field

of,tudy

_;t,, at thi, titne, there _are nimiy

Liue,tion,

~>hich _reniain Linmi,~ereLl.

(a)

~~~

_~~~~~~~ ^~

O

CH3~(CH2)ii~ O I-O-(CH~CH~O)4-H

H~-(CH~)ii~

l2-AG~EO-OH

(b)

CH3~(CH~)i

CH~

l2-AG~EO-PMA x

Fig. I. lJ) The ,trLictuic, al [he iiont>tier 1~ AG-4EO-OH ,till (hi the polymer l~-AG-4EO-PMA.

(4)

N° Ill SUPERMOLECULAR COLUMNAR HEXAGONAL PHASE 1815

@FY>

R

Fig. ?. Schciiialic repro,entJtit>n ⁱⁱⁱ the,upr,iiiit>lecul~ii ct>luiiinm _,tiuctuic. For the pt>lynicr, the b~icLbt>ne _i, trite;itie(I tli>wn the _center iii the ct>luiiin.

In [hi, p;tper we report on

optical ellip,oiietry

;tnd

turhi(lity

mea,urement, _a, a tunction ot

temperature t'or hoth the _monomer

2-(2-(~(~-hyLlro~yethoxy) etho~y( ethj<1-3.4.5-tri,in-

dodecan-I-yloxy)

benzoate 11 2-AG-4EO-OH) and the

polymer 2-(2-[2(2~metha-

cryloyloxyethoxy) ethoxy] ethoxyj ethyl-3,4,5-tris(n-dodecan-I-yloxy)

benzoate (12-AG-

4EO-PMA) [12].

We found that in the

iwtropic pha~e

^neither the

polymer

nor the monomer

exhibits _any

systematic

variation of

turbidity

with temperature. ^This ^behavior ^is

usually

indicative of _a

strongly

^first ^order

phase

transition> with _a

large discontinuity

in the nematic

orientational order parameter

S[m (3/2 ^co~~

o

II?)

]. Within the W~

phase,

on the other

hand, both

~pecies

exhibit _a marked increase in the

optical

retardation _a with

decreasing

temperature. Moreover, _we found that the increase in _n _on

cooling through

the Wh~I

phase

transition for the pure

species

is

relatively sharp,

whereas the evolution of

a for the mixture is

considerably

slower.

E,perimental.

12-AG,4EO-OH and 1~-AG-4EO-PMA _were

,ynthe,ized ;tccording

to

proce(lure;

^de,cribed

eI,ewhere

(l~(,

The _tnonomer _~a,

coniplexed

with

LICFjSOI

(lJ.,~ molefinole or niru of

tapered group)

which iacilitate, it,

,eli-it,,enibly

into _J tubul;tr

,upr;tm~lecul;tr,tructure

_tiff ;t

combination

ol'eiido-recognition (generated by

_convergent cavitie, ;tnd

,h;tpe,)

;tnd exo-

recognition

(generated by I;trger

bodie, of,imilar,ile and

,hitpe,,

_or ,urface,) _proce,,e,

(7,

12(.

Endo-recognition,

in which entropy

pl;ty,

;tn

iniportant

role, ha, been ,hown to be nece,,m.y for

,elf-a,,emhly

ot'the

cylindrical ,upr~iiuolecular

architecture

by repl;iceiuent

~li the

oligoethylene

r~ceptor with _~i

nonpolm. iliphatic

_,pacer

(7, I?(. Attempt,

;tt ,urf;tce-

induce(I

alignment

in the coluninar

pha,e

were niitde

hy

_tre~itiig two

gl;t,, niicro,cope

,lide,

with the ,urf;tctant

he~adecyltriiu~thyl;ttuiionium

broniide. The ,lide, _were

,eparitted hy

Mylm.,pitcer,

^of notiitnitl thickne,, 3 _~ni and the cell _wa, l'illed frmii the

e(lge

with the

nionomer ,itlt nii~ture

hi capill;try

;lotion. Texture, characteri,tic ol'a coluninm.

hexagonal

phit,e (1~ itppeared

_on

cooling

at

Jpproxini;ttely

⁴³ ^°C nowhere _ii the cell _wit, _a

,igiiific;tilt

iiionodoni;tit

region

(~ 5 _~ii oh,erved, The _,mue

procedure

_wa, u,ed for the

polyiiier

with

,iiiilm. re,ult,. We _next tried treatiig ^the ^,urt';ice, ^with

nylon

ti16, after which _,ve t.uhbed the

(5)

1816 JOURNAL DE PHYSIQUE II N° lo

,lide,

unidirectionally.

For low iuolecular

weight liLiuid cry,tal,

(hi, preparation

u,ually

re,ult,

in

pl;tn;tr

(«

honiogenou,

»)

aligiiuent

ot'the iuolecule, (17_(.

Again,

for both the _nionoiuer ,alt niixture mid the

polyiiier,

no iionodoniitin

region

_wit, oh,erved _ii the colunin;tr

pha,e,

Al

,et,

of,miiple,

were then

,uh_jecteLl

to _;t niitgnetic ^t'ield

at'itppro~iniately

1.5 T, hut _no

chmigc

~a, oh,er~eLl in (he le~ture,,

Fiiallj,.

~e m;tLle _~i 3

~iu-thicL

capitcitmice ^cell ^front

,eiiitr;tn,p;treat

indiuiu-tin-oxiLle coated ,lide, mid filled it with (he _iiononier -,alt iuixture.

We founLl th;tt

;tpplication

of

t.elatively

,iuall

volt;tge,

(~ l()V at LH/) very

,lowly

eliiuinJted the texture,, ,uch that ,nialler

voltage,

were

reLiuired

near the tr;tn,ition

teniperature _T,j,~ ^;tnd

litrger volt;tge,

_were

t.eLiuired

well below T,j,

~.

Although

the

,;tnipl~

,ippeared

to forni _;i nionodoni;tin. _we _were unahle _to

unequivocally

cont'irni thi, fact. Electric field effect, will he the

,uh_ject

of future

,tuLly.

In orLler to

produce

cell, ,uit;thle tot

optic;tl

ret;trd;ttion nieit,ur~iiient, we u,eLl two

niicro,cope,liLle,, clemieLl,eLiuentially

in _~i

Lletergent,

Lli,tilleLl water, acetone, tnLl eth;tnol. A

,tuall ;tiuount of _niononier -,alt nii,tune _~a,

placeLl

on the ,urface _on _one ,title he;tteLl to

ipproxiiuJtely

61) °C and allowed to nielt, The other,lide _wa, then

placed directly

on the

niaterial and

pre,,ed

down

lightly

_: i ,pacer wa, not u,eLl. The teiuperJture ~.a, then ,lo~

ly

lowereLl

through

_T,j, until texture,

appeared,

it which tiiue further _pre,,ure _w;t,

applied

to the

top,lide.

In thi, _iuanner _we itchieved _a _vet-y thin

,pacing

(/

(liLely

le,, than _one niicron).

although

there _wa, _no way ^to deterniine il. The _vet-y thin

,p;tcing

;tl,o re,ulted _in _a te~ture

con,I,ting

of

I;trger

^dotu;tin, (,11)1) ~iu) a, L)h,erved

through

cro,,etl

polm.iler,.

While

ipplying

LlownwarLl pre,,ure, the top ,liLle _wa, ;tl,o

di,pl;tceLl parallel

to the cell

plitne.

^Thi, ,tddition;tl

;heariig

of the

,;ttuple

re,ulted in very

large

iuonodoiu;tin, with

plitn;tr Jligmuent

of the coluninar _axe,,

fitcilitittiig ellip,oiuetry

nieit,ureiuent,.

The cell _w;t, then trmi,l'erred _to _a ;niall oven (temperature ^controlled to 5() iiiK) which _wa,

iuounte(I _on _;t rotation ,t;tge.

Light

froiu _a 5 niv He-Ne la,er

pa,,ed con,ecutively through

_a

pol;trizer,

the center ot the rotation ,tage, ^the

,ample,

an

;tutoniatically-compen,ating

PocLel, cell. _,m

analyzer,

inLl then into _;t detector. Det;til, of the ;tpp;tratu, itre de,crihed el,ewhere

1~ (. The

light

_wit, focu,ed _to a,pot ^ot

approximately

6() _~iu at the cell in order to

probe only

_~i

,tit;tll unidirection;tl

region

of the

,aniple,

For thi,

experiiiiental cont'iguration

it I, not

nece,,ary for the columnar _ax I, to hi,eat the

angle

^foniied

hi

the

polariler

anti

analyler

axe, in

antler to urea,ure the

optic;tl

retitrd;ttion _a, In,te;td, the orientation of the coluiun~ir a~i, affect,

only

the

,ign;iI-to-noi,e

(SIN ratio, Thu,, to

optimize

the SIN _ratio, the

,;iiiple

wa, rotated

about _;tn a~i,

parallel

to the la,er. Once the

,ignal

_wa, ni;txiniileLl at _J

given

teiuperature, we

found that

only

_very

slight

orientational

adjustments

(one _or two

degrees)

had _to be made _on

cooling,

Thi, inLlicate; that the

in-plane

orient;ttion of the colunin;tr J~i, _wJ, unat'tected

by

teniper;tture, (We note that after

optimization,

the coluiun;tr _;txi, did indeed bi,eat the

;tngle

fonued

by

the

polarizer-;tn;tlyzer

;i~e,, The

optical pha,e

,hill _o I, ,hown in

figure

3 _a, _;t

function of teniper;tture.

Additionally,

we

perfornied

,iiuil;ir niea,urenient, on the

polynier

_a,

i function of teiiipemture, ^which ;tre al,o ,hewn in

figure

3.

Finally,

we niade _a iui~ture

con,I,ting

of 40 %

by weight polyiuer

and 60 ~/

by weight

_nionoiuer -,alt iiii~ture, and the

re,ult, _ire

tgain

,hown in

figure

3. Slice each

,aiiple

ha, _an unknown thicLne,,

(/, _we _;tre liiiiited to

plotting only

the me;t,ured retard;ttion _~i for each of the three

,aiiple,,

rather th;tn the

birefringence

iii (Ail ^all<', where I I, the w;tvector of

light(.

Turbi(lity

tried,urement, were

performed

in _an ;tpp;tratu, ^ba,ed on ;t He-Ne la,er. E;tch of the two ii;tterial, _wa,

placed

in _a cuvette of

pathlength

(/

= cm. ;tad ,tabilizeLl

approxini;ttely

15 °C above their

re,pective

_T~j, for _;tt le;t,t 31) turn.

Turbidity

tried,ureiiient, were ii;tde _on

decrea,ing

the temperature ^with J ;tabilil;ttion tiiiie of 3()niin

prior

to e;tch

re;tding.

In

figure

4, we,how the

turbidity

_T _I,I, temperature, ^where _Tw ^In

~ ).

^Here ^/ i, the

(

(6)

N° I() SUPERMOLECLILAR COLUMNAR HEXAGONAL PHASE 1817

~ *

A ~ Polymer

A

~ A

~

A ~

6 0.8 A

~ ~

..

~

'

~ ..

~ ~ .

.

*

.Q O-B ^" ^" mm

~ ~

. .

a Mi~ure " m

~ A

E ~

j

_~

~ ~ ~

$

A W

~ ~ A

Monomer- ^*

32 36 40 44 48

Temperature (°C)

Fig ³ Optical rclm.(I;ilit>n _<I _i_I temperature ^[iii the mt)lit>mer (.j, the pt>lyiicr iAj, ,ii(I the mi~turc lmj. Nt>tc ih<it the ,Jmplc lhicLne,,e, _~iie unknown. _,t) that _~ii ~ib,olute coiipari,on

of'a,iiit>ng

three ,et, iii tiara _caiiiot be ii,itle.

e

A A A

5 ^A

S A

k

_.

A

$

~ Polymer

~ ~

# A

n A

I

monomer

~

~aaaAA

A A A A

38

42

(°C)

Fig. 4.

nie;t,ureLl

inten,ity

of the

light p;t,,ing through

the

,aiuple.

;tnd

Iii

_i, the

inten;ity

of the

light

in the itb,ence

of,cJttering

froni the fluid. In the _(fi~,

pha,e,

the

turbidity

ri,e, very

,harply

^with

decre;t,ing

temperature,

re,ulting

in ,aturation of the detector at a few hundred niK below the

on,et of

pha,e

,eparaton. ^In

t'igure,

5 and 6, _we ,how _z _I,I. teniper;tture ⁱⁿ ^the

I,otropic pha;e

of the monomer anti

polyiuer re,pectively, thereby allowing

u, to

expand

the vertical ,cale;. It

I,

iniportant

to note that the ab,olute

turbidity

in the

I,otropic pha,e

_i, much

larger

than

ordinarily

ob,erved in low molecular

weight liLiuid cry,tal,

above _a

nemJtic-I,otropic

IN-I)

pha,e

tr;tn;ition, and niay

play

itn

iiuportant

role in

under,tJnding

the data.

(7)

'

j 2,31

o

_.

~ .

# n

I

~ .29 38

Temperature

Fig. ~. - _urbitlity (

c~p~ii,tori

ol

(8)

N' Ill sUl?ERM()LIICUI-AR COLLIMNAR IIBXACiON,iL PFIASE 1819

con,eLiuence the tritn,ition will he wit,heLl out ovet. a teniperitture _rmige <ii'with

phit,e

coo.,i,tence in (hi, teniperature region. ^The

ellip,onietrj,

_;tpparatu, I,, in that. _,en,itive _to thi,

phenoiiient>n,

miLl

actually

me;t,ut.c,

((y ),

whet-e

(...

Llenote, _J

,pati~l

_average _over the la,er hewn _m.eJ at the

,Jiiiple. Conipm.e(I

to the inLli,>i(lual

,pecie,,

the

hipha,ic region

al'the

nii,lure i,

c()n,i(leiJhly

_it iLler <11

= 5 'C I. In _~i

c~ilorinietrj,,tu(ly

of nil,tuie, of'other

tapeie(I

iiiolecule, Xl, ^it loun(I thitt. _ii ith _iii) iii/t, _~i

,iigle

t/>~,-l

ph~i,e

trmi,itioii ()ccui, ;it 1(>~

t.(>lit.eiiti~iti(>ii t)I iii()ii()iiiei in

p(>I,>iiiei,

l~ut ,it ielati,el,

liigli

iiioiioniei t.(>lit.enti~iti()n, ~i ,et.()ii(I

he~itgonal

coluiunm.

ph;t,e

tritn,ition _ii=, _i t/)~,-(/)j, tran,ition occur,. Thi, hehavior _wa,

i,crihe(I to the

inability

ot the

high

concentration of _niononier, _to interc~il~ite into the

cylinLlricJl

,tructure lornied hv the

polynier. Upon

the ~idLlition at',ufficient _miiount, at LICF;S(); the two '/>j,

phJ,e, niergeLf

into one. The ,aft _w~i,

thought

to enhmice the _co-

a,,enihly

het~een _niononier miLl

polyiiier

a, a re,ult

of'coniple~Jtioii.

(No

pha,e

,epJr;ttion

wa,

reporteLf,

ho~e,>cr). Ha(f there heen _t~o c()luninm.

hexagonal phJ,e,

fi)r the ni~iteiial,

Lfi,cu,,eLf herein, _one woulif have

expecte(I

fi)I the niixture two

relatively ,h;trp

ri,e, ii

(y.

,epm.Jted hy

_iii internietli~te

plateau.

Thi, _w<i,

cleitrlj,

not the _ca,e,

e,pecmlly

_gi,,en the

large

concentrittion

of'LiCF;S();.

Rather, the dittit _in

l'igure

3 _m-e con,I,tent with _;t

,ingle

~l)~,

phJ,c

helo~ _a wiLle

hiphit,ic

_region.

Although

the ,aft facilitate,

c()-;t,,enihly

ot the

niononiei mitt

polymer,

the

cylinLler,

tornie(I f'ioni the two ,pecie, iii-e vet-j>

likely

to have

(lifferent Llimueter,.

Co-a,,eiuhlj

w(>ulLl thu, he ,onie~hat

iiupeLle(I, re,ultiig

_in a wiLler

Lli,trihution

at'cylinLlrical

,ile, thmi _in either the pure nionoiuer or the _nionoiiier ,aft

nil;tuie. In con,eLiuence ^the

hipha,ic

_region _i,

e,jiecteLl

to he

c<)tie,ponLlingly

~ider, _i, oh,erveLl.

The ,ec()nLl f'eature ot note i, the hehai>ioi of

<y a, a l'unction

ol'teniperature

_in the

<fij,

phJ,e,

iiLl _in

coil_junction

with the

turhiLlity

in the

I,otropic pha,e.

Withii

e~periiuental

,catter,

likely

Llue to the ,niall rotittion of the

,muple

in antler to

optiniile

the SIN _rittio, the

optical

retm.Llation flit all thiee niateriJl, _ri,e,

appio~iiiJtely

^~(l'/ over a Ii °C teniperitture region helow

f,j,

~.

Although

^thi, ^rel~iti~e ^increa,e ^I, ^,ni;tller ^h,> a tJctor of'two _or three thmi that oh,erveLl ;tt _a

neni;ttic-i,otropic ph;t,e

trmi,ition in cla,,real low niolecular

~eight

_liLiuiLl

cry,tal,,

it would neverthele,, _,eeni _to indicate that the ~l)~,-l

pha,e

tran,ition _i, ,till

relitti~ely weakly

t'ir,t order, with _a

di,continuity,

ii the neiuJtic orLler

p;trmueter,I

,oiuewhat le,, thmi

unity,.

Our

caloriiuetry

Llata for the

poljnier,

for

e~miiple.

,how _~i I;ttent heat L at1).4

J/g.

Thi,

figure

^is not

atypical

for _most N-I

pha~e

transitions

[20].

(Care must neverthele~s be exercised>

,nice tactor, at two or three _in L can have _a very

lm.ge

ettect on the

Lli,continuity

in the neni;ttic

order). Thu,, _on

cooling

into the coluninar

pha,e,

we tit,t l'ind _a

i,lightly,

broitdened)

Lli,continuity

_in the

optical

ret;irtlation, fiillowed

hy a,ignificmit

increa,e in _<y and ihu, _in the neniatic order pm.aiueter on

tleciea,ing

the teiiiper;ttuie. ^Thi,

,uperficiitlly

indic;tte, that the neniittic order _i, not

neitrly

,;tturated (.I

= ju,t ^helow T,j,

~.

The

turbidity

ditto, _on the other hmitl. would ,eeni to indicate _;t different ,art of hehavior.

Near _a liLiuiLl-liLiuiLl ^criticitl

point turhiLlity

rued,urenient, ;tre ,en,itive _to

den,ity

tluctu-

ition,

(~l(. Although

liLiuiLl

cry,tat, unLleigo Llen,ity change,

;tt

pha,e

tran,ition,, the,e

ch;tnge,

tenLl to he ,ni;tll, Ritther,

turhiLlity

iuea,ureiuent, of liLiuiLl

cry,tal,

in the

i,otropic pha,e

tenLl to reflect correlation, ot the orientational orLler

pm.mueter.I,

_a, orientJtional artier I,

,trongly coupled

to the

optical

dielectric _ten,or. Both

polariled

and

depol;iriled light

_,catteriig

;t, J l'unction ot'iuonientum tran,ten q nie;t,ure the

,u,ceptibility

_x and the correlation

length

( ot orientation;tl tiuctuation, of the director (~~(.

TurbiLlity

niea,ure, the

integral

ot'the

,cattering iiten,ity over all

appropriate

w~ivevector,, A,

long

_a,

[q[

f « I, the

turhiLlity

z

cot.t.e,pond,

to the

long witvelength

orientationitl

,u,ceptibility.

Ne;tr _a

neniatic-I;otropic pha,e

trmi,ition, _X woulLl

orLlinarily come,ponLl

to neiii;ttic-like fluctu;ttion; in the

I,otropic pha,e (~~(.

Thu,, the ab,ence of ;tny

,y,tetii;ttic pretran,itional

(9)

beh;tvior in

figure;

5 ;tnd 6

might

_argue th;tt the virtual ;econd order

neurotic-I,otropic pha,e

tr;tn,ition temperature T~_j ^lie, well-below

T,j,~, ~, the fir,t order tran,ition temperature ^from ^the

I,otropic

to the _<fij~

pha,e. (T~

i, ,ometinie, rel'erred _to _a, the

«,upercooling

limit

» of the

I,otropic pha,e).

In con,eLiuence, our dat;t wt~uld

;tpp;trently

^indic;tte th;tt the tran,ition _to _an

orient;ttionally

ordered

ph;i,e,

whether it be _it nem;ttic _or _it columnar

hex;tgon;tl pha,e,

^I,

,tronglj

fir,t order _: the

re,ulting di,continuity

in ,I would, therefore, be

expected

to be

Liuite large.

A con,eLiuence of (hi, ,cenario I, th;tt the orient;ttion;iI order p;tr;tnieter ⁱⁿ ^the

<fij,

pha,e

would be clo;e to unity. ;tnd _mie would riot e~pect the ,trong temperature

dependence

of _(y in the W~,

ph;i,e

oh,erved in

figure

3,

Discu+I<in.

We thu, hitve two

prohe, turhidity

niea,urement, in the

I,otropic ph;t,e

;tnd

hirefringence

mea,ureiuent, in the ordered

j~h;t,e,

hoth of which _iii-e ,en,itive to different a,peat, ^ot

niicro,copic

order which _gi;e

itpp;trently

dit'ferent re,ult,. The

turhidity

re,ult, _,eeiu to

;trgue in f;tvor of _a very

;trongly

t'ir,t order trmi,ition with

nearly

,~iturated orientational order

below T,j,_~, ^where;t, ^the

bireti.ingence

d;tta m.gue, for _a niuch le,,

,trongly

fir,t order

tr;in,ition.

Although

one

might

_iniagiie other _,cenm.io,. _we ott'er _one

j~o,,ihle

iuechmii,ni

which iuay ^re,olve the aj~p;trent ^conflict. ^Fir,t, we note that ,trong ^coluiunm. correlation,

ippaiently

e~i,t ii the

I,otroj~ic pha,e,

a I[tot horne out

hy

X-ritv

,c~ittering (7-14(

mid Kerr

rue;t,ureiuent,

(15(,

The correlated volume,

(f,j,

I' J,,ociated with columnar fluctu~ition,

would, of'coui,e, entail _,onie

(legree

ol orientational orLler,

ilthough

it I, not nece,,arj< thitt the

local antler pJrJiueter ~j,

iveraged

o,>er (f,~, l'. he ,,erj clo,e to unit». ^Since ^the

ti)~,-l trmi,turn I,,

hit

,»niiuetiy, ^f'ir,t ^or(lei, ^the

ni;ignituLle

al the

,cattering

anti the ;ih,ence ol

in <>h,er,>ahle

pietrmi,itional ,igniiture

lot- _r niaj<

,inipl

_j< iel'lect the I]ict that the i,otr<>pie

to <iihiiiiiiai

/iera,qi>ha/

tritn,ition I,

,tronglj<

^l'ir,t antler, in(1 2) thitt coluninar fluctuation,,

itlthough

not

Lliverging

near the t'ir,t orLler T,j,

j. ire ne,erthele,, _ver,> ,trong ^;inLl therelk>re

Lloiuinate the

,c~ittering

_proce,,e, _in the i,otiopic

pha,e,

Ahove T,j, ^the correlation

length

(,j,~ grow, very

,lowly

,~ith

dearer,ing

teiupcr~iture. ^and ^the

tut.hidity

niirror, the

(rem.ly

teniperJture-independent) optically<-uni~ixi~il

«inn>w<ii

/hi<iii<nil)ii, through

their local orientational order parameter

Sj.

However, since the

turbidity

in the

isotropic phase

i~ _so

large,

the

ordinary pretransitional

behavior associated with nematic-like fluctuations is masked

by

coluiunar aggregate,. ^In ^tbct, iii thi, ,cenm.io the teiuperature diti'erence

7,j,

_{~-T,_~} _niaj, not he

i,

large

_a,

originally thought

(ha,ed _upon the l'latne,, ot

Fig,.

5 mid 6). In con,eLiuence, on

cooling

into the (fij,

j~ha,e,

_one would t'iid _a

long

_range orientationitl order pitrmueter

I, _ii()t _tint (>I.,ail/; _I(>it. h>ie _t() _iiiiit;, which could ,till incre~i,e

,uh,tmitiJll»

on

cooling,

We

note th;tt thi, ,cenm.io

;tj~j~lie,

to hoth the _iuononier anti

polyiuer.

[nil thu, _it teniperature-

dependent

aggregation ^nuniher ^of ^the niononier-hJ,e(I ,elf'-a,,enibletl unit, _i, not

reLiuii.ed.

An a(lditionJl contribution _niay _coiue train conforniittional

change,

_~ ith tenij~erature ^of ^the ,elf-it,,enibled ,tructure,.

X-r;ty

,tudie, indic;tte that the ,tructure of'the

,uj~t.muoleculitr polynier cylinder

doe,, indeed, _vary with teniperature (7-14(. At

higher

teniper~iture, ^the

cylinder

diameter decreit,e,

,lightly, j~erhaj~,

due to _itn increJ,e in the fi;tction

of',qaii<.hc

contoriu~ition, _ii the ,i(le group,, or

po,,ihlj

_;t, _it re,ult of _an increa,ed tilt

;tngle

of the ,ide group, with re,peat to the

plitne

not.trial _to the coluiiin;tr ;txi,.

X-ray itnitly,I,

of _;t rel;tted

polyiuer

l~-ABG-4EO-PMAI (7, 1(). ~3j indicitte, _an

approxiniJtely

5'/ decre;t,e in the

cylinder

dimueter _on

he;tting

th;tt tu;tteri;tl fioni ~5 °C _to 74 °C, which would

carte,pond

to _~i

three _or tkiur

degree

increa,e in the downwm.d tilt of the ,ide chain,, It cont'oriuational

chitnge,

in _our m;tterial, _were ,iiuilar, the

re,ulting chmige,

_ii _a ~vould be,e~.eral percent.

Although

(10)

N° lo SUPERMOLECULAR COLUMNAR HEXAGONAL PHASE 1821

this eiiect is

unlikely

to

fully

account ior the temperature

dependence

oi

n in the

@~~

phase,

it i~

likely

to make a measureable contribution,

Another ob;ervation which needs _to be addre;sed is the

similarity

in the

general shape

of

n ii-I temperature ^for ^the monomer and

polymer.

Thi, would

apparently

indicate that the

major

diiierence between the two, I-e,, the

polymer

repre;ents a

thermally

robust structure whereas

the _monomer unit i~ ,tatistical in nature,

play;

little role in

n. GPC measurements ior 1~-ABG-

4EO-PMA indicate _a

degree

oi

polymerization

oi

approximately

19

[?3

_]. Thi;

corresponds

to

approximately

two to three columnar

layers compri;ing

the

cylinder

^formed

by

one

polymer

molecule, and thu, the

cylinder

i;

clearly

oblate _in character,

Supramolecular

tubule; iormed

irom the monomer are statistical units there should be _a thermal di~tribution of aggregation

number; driven

by entropic

^and

energetic

con;ideration,, At lower temperature; entropy

become; les~

important,

It I, well-known in ;uriactant-water ;ystem; ^that

aggregation

number

increa;e, with

decrea~ing

temperature

(1-3j,

Such _a

phenomenon

_may be

occurring

here _as

well, i>I=., the a,pect ^ratio ^R

(length

diameter) oi the

cylinder;

I;

likely increasing

with

decrea;ing

temperature. ^For

large

aspect ^ratio ;tructure; (R » ;uch _a; tobacco mo;aic _viru,

or

pho;pholipid

tubule;

(24.

?5 ),

change,

in R tend to have little effect _on orientational order

within _an ordered

pha;e,

^However, ^if ^the a,pect ^ratio ^I,

relatively

,mall, _e-g,, of order

unity

(similar to the

polymer

I?-ABG-4EO-PMA), it

might

be

expected

that

change,

of

R with temperature ^would ^tend to have _a much _more

;ignificant impact

on the orientational order within ,uch _a

pha;e.

Therefore, ;ince the

profile,

of _a _i>,I. temperature ^t'or ^the two

specie~

are ,imilar, _one would conclude that either the

aggregation

number of the _monomer I; _tint

changing rapidly

with temperature, or that the nematic order of the

,upramolecular

;tructure in

the ~fi~~

pha;e

ⁱⁿ not

very,en;itive

to R.

Conclusions.

Thi, work repre;ent, an initial ;tep ⁱⁿ

understanding

_a

polymer-ba,ed

and monomer-bJ,ed

columnar

hexagonal phase.

We have ob;erved similaritie, and, to a le,;er extent, difference;

in their behavior; (;uch _a, the temperature

dependence

^of ^the orientational order) around the

~P~~-I

pha,e

tran,ition.

Additionally,

we ha~e ob;erved behaviur from retardation and

turbidity

measurements which

;uperficially

^I, incon;I,tent with ,trong nematic-like fluctuation; _in the

high

temperature

I,otropic pha;e.

We have oiiered _one

po;;ible

,olution, _ii=., that ;trong

columnar iluctuation, i~ay be

ma;king

the nematic-like

pretran,itional

behavior and thereiore

lie at the heart oi our ob;ervation, above

T,j,~, j. Below

T,j,~, the

primary

contributor to the

thermally-driven change,

in _n I; _an enhancement of nematic order.

Clearly

^additional work,

including probe;

,uch a, neutron

,cattering,

need, to be

periormed

to confirm _our

conjecture,.

Acknowledgements.

We _are indebted _to John Blackwell for many u;eiul di,cu,,ion;. Thi; work

wa;,upported bj,

the National Science Foundation under grant, DMR-~l~2~27, DMR-9?06781, DMR-

900744~, and NATO.

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(11)

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