V ol . 1 0 1 ( 2002)
A CT A P HY SIC A P O LO N IC A A
No . 5
P r oceedi ng s o f t h e Sy m p o siu m o n Syn chr otr on Cr y st all ogr ap hy, Kr y n ica, Po l an d 200 1
N an ost r u ctu r e an d T h er m al B eh a v iou r
of L i qu id C r y stallin e Oli go este r
J . Jani c ki
T ech ni cal Aca dem y of Bi elsko- Bi a ¤a, W i l lowa 2, 43-309 Bi el sko-Bi a¤a, Po l and
T h e nanostr ucture an d ther ma l behav iour of li quid cr ystalli ne oli goester
w ere examined by combination of real -time synchrotron small- angl e and
w ide- angle X -ray scattering metho ds w ith di˜erential scanning calorimetry .
T he synthesi zed oligo ester exhibits ability to form a thermotro pic mesophase.
I t was show n that solid crystalli ne state is observed in the temp erature range
25 to 1 2 3 C and liquid crystalli ne state betw een 118 À 1 5 6 C . T he transitio n
temp erature determined from dynamic small- angl e and w ide-angle X -ray
scattering exp eriments agrees very w ell w ith the results obtained from dif ferential scannin g calorimetry .
£
£
PAC S numb ers: 87.64.Bx , 81. 07. N b, 82. 35. Lr
1. I n t r o d u ct io n
D uri n g the l ast decade, l i qui d crysta l l i ne p ol ym ers ( L CP) ha ve b een presented as new com p ounds wi th superi or pro perti es as com pared to conventi onal
p ol ym ers. The search for mel t- pro cessabl e l i qui d crysta l l i ne p ol ym ers, whi ch are
m i scibl e or pa rti al l y m i scibl e wi th conventi onal p ol ym ers, i s sti l l a great chal l enge
i n p olym er science [1, 2]. Therm otro pi c LCP usual l y conta i n ri gi d- ro d chem i cal
structure and theref ore possess uni que pro p erti es such as l ow m elt vi scosity and
hi gh m odul us i n the sol i d form , whi ch is di recti on dep endent. Bl endi ng of therm otro pi c LCP wi th semi crysta l l ine therm opl asti c p ol ym ers to form i n sit u p ol ym er
comp osites i s very attra cti ve b ecause of the adva nta ges i n l oweri ng the vi scosity
duri ng pro cessing and in rei nf orci ng the Ùnal m echani cal pro perti es [3{ 5]. However, the m elti ng tem p erature of l i qui d crysta l l i ne pol ym ers i s usual l y ab o ve 200 C,
whi ch i s to o hi gh for pro cessing semi crysta l l i ne therm opl asti c pol ym ers. In order
to reduce the m elti ng and tra nsiti on tem p erature new LCP , wi th Ûexi bl e uni ts i n
the ma in chai n were synthesi zed, resul ti ng i n a lower m elti ng tem p erature [6{ 8 ].
In thi s search fo r new com p osite materi al s, less attenti on i s pai d to the pro per
chara cteri zati on of the structure of therm otro pi c l i qui d crysta l l ine pol ym ers. It i s
£
( 761)
762
J . Jani cki
shown tha t an una mbig uous chara cteri zati on i s onl y po ssibl e by a com bina ti on of
di ˜erent techni ques such as sm al l- and wi de-ang l e X- ra y scatteri ng ( SAXS, W AXS)
wi th di ˜erenti al scanni ng cal ori metry (D SC).
2 . E x p er i m en t a l
2.1. Mat er i al s
Li qui d crysta l l i ne com p ounds ha vi ng three ri ng s ro d-l i ke m esogen and al i pha ti c end gro ups are synthesi zed. The aro mati c ri ng s i n the mesogen are b onded
to ester gro ups whi l e the al ipha ti c end gro ups, consisti ng of eleven carb o n ato ms
are connected wi th the arom atic ri ng by ester b onds. The m acrom olecul e chain of
ol i goester i s presented i n Fi g. 1.
Fig. 1.
T he macromolecula r chain of liqui d crystalli ne oligo ester.
2.2. Met hods
The SAXS and WAXS i nv esti gati ons were carri ed out using synchro tro n
b eam l i ne on the X3 3 doubl e focusi ng cam era of the EMBL i n Hasyl a b, on the
sto ra ge ri ng D O RIS I I I of the D ESY i n Ha m burg at a wavel ength of 0.15 nm .
The SAXS pi nho l e patterns of l i qui d crysta l ol i goester (LCO) were recorded using
sam pl e{ detecto r di sta nce of 2.8 m to cover the ra ng e of magni tude of the scatteri ng vecto r 0 : 0 1 2 ç s ç 0 : 8 9 4 nm 1 ( s = 2 sin ˚ = Ñ , where 2 ˚ is the scatteri ng ang le
and Ñ i s the wa vel ength). Duri ng the real -ti me measurem ents, SAXS and WAXS
pa tterns were sim ulta neously recorded every 6 seconds gi vi ng a tem p erature resol uti on of 1 C p er one pa ttern, using a sta nda rd acqui siti on system wi th two del ay
l i ne detecto rs connected i n series [9, 10]. The ra nge of scatteri ng vecto rs was cali bra ted usi ng the Ùrst ni ne i nterf erence orders of dry col la gen wi th a spacing of
64 nm . The WAXS da ta were col l ected o ver the ang ul ar ra ng e 1 1 : 7 ç 2 ˚ ç 4 6
cal ibra ted wi th a sili con sta nda rd. The SAXS and W AXS i ntensi ti es were no rm al i zed to the intensi ty of the pri m ary b eam a nd correcte d for the detecto r response.
Fi nal l y, an a veraged m elt pattern wa s subtra cted fro m each curve to eli m ina te
ba ckg round scatteri ng .
The di ˜erenti al scanni ng cal ori m etry m easurem ents were carri ed out on a
Perki n El m er{ Pyri s instrum ent. The tem p erature was cal i bra ted wi th the m elti ng poi nts of i ndi um (1 5 6 :6 C) and b enzopheno ne ( 4 8 C) and the entha l py was
cal ibra ted wi th i ndi um (2 8.45 J g 1 ). The contri buti on of an empty pa n wa s subtra cted fro m each measurem ent. The bl ock surro undi ng the m easurem ent uni ts was
therm o stated at À 1 0 C wi th li qui d ni tro gen and the m easuri ng cell wa s Ûushed
wi th ni tro gen g as. The heati ng and cool i ng rate of sam pl es was 1 0 C / mi n.
À
£
£
£
£
À
£
£
N anost r uct ure and T her mal Beha vi our
763
. ..
3 . R esu l t s an d d i scu ssio n
Inf orm ati on concerni ng the therm al b ehavi our of l i qui d crysta l l i ne ol i goester
wa s obta i ned by di ˜erenti al scanni ng cal ori metry . D SC heati ng and cool ing curves
of ol i goester col l ected at the ra te 1 0 C/ m i n are shown in Fi g. 2. The heati ng
curves exhi bi t three endotherm i c p eaks. The Ùrst wi de p eak i s connected wi th the
gl ass tra nsiti on tem perature whi ch was eval ua ted as 5 6 C, a nd so- cal l ed col d crysta l l i zati on whi ch i s observed duri ng heati ng ab o ve the gl ass tra nsiti on [11]. The
m ai n endotherm i c p eak i ndi cates the melti ng tem pera ture ( 1 1 8 : 7 C) and the thi rd
one the i sotro pi zati on tem p erature ( 1 5 6 : 6 C). W hen a cool i ng run is p erform ed
after i ni ti al heati ng , three exotherm i c p eaks are observed. The tra nsiti on tem peratures and the corresp ondi ng entha l pi es duri ng heati ng and cool i ng are presented
i n T abl e.
£
£
£
£
Fig. 2.
DSC heating and cooling curves for LC O;
Tg, Tm
,
T c, Ti
are glass transition,
melting, crystalliza tion , and isotropizati on temp erature, respectively .
TABLE
Enthalpies and temp eratures of face transitio ns.
H eating
C]
56
C ooling
[ C]
[J /g]
[ C]
[J /g]
[ C]
[J /g]
[ C]
[J /g]
118.7
17. 5
156. 6
2.3
114. 8
{11. 0
155
{2. 6
,
,
,
are glass transitio n, melting, crystallizati on
and isotropizati on temp erature, respectively ,
,
,
are enthalpy of melting, crystalli zati on, and isotropi zatio n,
respectively .
T ra nsiti on tem pera tures of ol i goester, determ i ned f rom DSC duri ng heati ng ,
are schemati cal ly shown b elow:
sol i d crysta l li ne state
li qui d crysta l l ine state
isotro pi c m elt :
764
J . Jani cki
Ba sed on D SC results i t seems to b e clear tha t the synthesi zed ol i goester
exhi bi ts the abi l i ty to form the therm otro pi c m esopha se i n the tem p erature ra nge
118À 1 5 6 C. The l iqui d crysta l l i ne state is deta ched both duri ng heati ng and cooli ng , whi ch i s typi cal of an enanti otro pi c l iqui d crysta l comp ound.
£
Fig. 3.
WA X S patterns
of LC O as a function of temp erature during heating.
Fig. 4.
SA X S curves after background subtraction for LC O as a function of temp erature
during heating.
In order to determ i ne the na nostructure of ol i goester, the WAXS and SAXS
rea l- ti m e synchro tro n experi m ents were p erform ed duri ng heati ng and cool i ng at
the ra te of 1 0 C/ mi n. The WAXS pa tterns of l i qui d crysta l li ne o li go ester as a
functi on of tem p erature duri ng heati ng are presented i n Fi g. 3. Ba sed on a qua l i ta ti ve a nal ysi s one can say tha t stro ng crysta l li ne p eaks on the WAXS curves
observed fro m 25 to 1 2 3 C and very l ow am orpho us hal o i ndi cate the well -ordered
structure. Crysta l l i ne peaks di sapp ear at 1 2 3 C and the scatteri ng curve at hi gher
tem p erature i ndi cates the l i qui d crysta l l ine sta te. Mo re structura l para m eters can
b e obta i ned fro m the SAXS i nvesti gatio ns. SAXS curves f or ol i goester duri ng heati ng are shown i n Fi g. 4. The SAXS curves exhi bi t two di sti nct di ˜ra cti on m axi ma,
correspondi ng to sol i d crysta l l i ne sta te and l i qui d crysta l l i ne sta te, respecti vely.
The angul ar po siti on of the peaks is connected wi th the superm ol ecular structure
wi th di ˜erent el ectro n densiti es o f pha ses, whi ch are separa ted by a rep eated di sta nce. The val ues of the rep eated di sta nce ( d - space) were eval ua ted using Bra gg' s
l aw and are presented i n Fi g. 5. The val ues of the d -space cal culated ba sed on
the ang ul ar p ositi on of the Ùrst SAXS p eak are consta nt and equal to 4.33 nm
and they are chara cteri sti c of the sol i d sta te. Ba sed on com puter m odel li ng , the
l ength of m acrom ol ecular chai n was esti mated as 4.2 nm , whi ch is i n goo d agreem ent wi th the result deri ved fro m the SAXS m easurem ents. D uri ng the m elti ng
pro cess, m acromol ecular chai ns b ecome m ore Ûexibl e and values of the d - space
steadi l y decrease, whi ch i s shown i n Fi g . 5 b. The equi l i bri um sta te app ears at
1 2 3 C since the d -space i s consta nt a nd equal to 3.57 nm . The structure of LCO
£
£
£
£
N anost r uct ure and T her mal Behavi our
765
. ..
exam ined under p ol ari zing opti cal m i croscop e (no t rep orted i n thi s pap er) was
i denti Ùed as a sm ecti c pha se. Two very sharp p eaks on the SAXS curves and
correspondi ng chang es of d - space are chara cteri sti c o f the sm ecti c l iqui d crysta l
structure and conÙrm the result obta i ned f rom opti cal mi croscop e observ ati ons.
Fig. 5.
T he
d -spacing
values for LC O:
a
|
solid crystallin e phase,
b
|
liquid crystallin e
phase.
Fig. 6.
T he inv ariants of LC O:
a
|
solid crystalli ne phase,
b
|
liquid crystalli ne phase.
An im p orta nt para m eter tha t can b e obta i ned fro m SAXS i s i nvari ant. The
i nv ari an t Q ( T ) i s the to ta l scatteri ng power of the system , whi ch i s indep endent
of the size and the shap e of the scatteri ng enti ti es a nd i s a functi on o f the mean
square o f el ectro n density di ˜erences of pha ses. The i nva ri ant can be cal cul ated
by i ntegra ti on of the scatteri ng i ntensi ty . The val ues of cal cul ated i nv ari an ts for
ol i goester (Fi g. 6) as a functi on of tem p erature i ndi cate two sta tes existi ng i n di fferent tem p erature ra nges. Starti ng f rom ro om tem p erature the sol i d crysta l l i ne
pha se i s descri b ed by the curve a i n Fi g. 6. The second pa rt of i nvari ant functi on
corresponds to the l i qui d crysta ll i ne sta te. In Fi g. 7 the SAXS and WAXS curves
are presented to gether for better vi sual i zati on of the pha se tra nsiti on duri ng heati ng . The tra nsi ti on tem p eratures, determ i ned fro m SAXS and W AXS experi m ents,
agree very wel l wi th obta i ned by D SC and supp ort previ ous concl usions.
Fig. 7.
T he SA X S/W A X S patterns of LC O during heating.
Ba sed on the results obta i ned, the fol l owing conclusio ns can b e dra wn:
766
J . Jani cki
|
The synthesi zed ol i goester exhi bi ts abi l i ty to form therm o tro pi c mesopha se.
|
Sol i d crysta l l i ne state i s observed in the tem p erature rang e fro m 25 to
|
Li qui d crysta l l i ne state i s observed i n the tem pera ture ra nge 118À
|
The real - ti m e synchro tro n SAXS and WAXS m easurem ents al l owed to observe the pha se tra nsiti o n and to study the nano structure of l i qui d crysta l
p ol ym ers.
|
The smecti c typ e of m esopha se i s observed fo r the ol i goester i nvesti gated.
|
Li qui d crysta l l i ne ol i goester can b e used as a pro per comp ound for pro cessing
wi th semi crysta l l i ne therm o pl asti c p ol ym ers due to l ow mel ti ng tem p erature
and wi de tem p erature ra nge of m esopha se.
123£
156
£
C.
C.
Ac kn owl ed gm en t s
The autho r tha nks Pro fessor H. Reyna ers and D r. B. G oderi s fro m Catho l ic
Uni versi ty of Leuven fo r hel p duri ng synchro tro n m easurem ents and frui tf ul di scussion.
R ef er en ces
[1] G. C osta, D. Meli, Y. Song, A . T urturro,
Poly mer 4 2, 8035 (2001).
B. Valenti, M. C astellano, L. F alqui,
[2] J.C . H o, K -H . W ei, J . Po l ym. Sci ., Po ly m. Phy s. Ed. 38, 2124 (2001).
[3] J.C . H o, K .H . W ei, M acr omo lecules 33, 5181 (2000).
[4 ] H . H akeni, Po ly mer 4 1, 6145 (2000).
[5] B. Liang, L. Pan, X . H e, J. A ppl. Po ly m. Sci .
[6] M. Pracella, D. Daniel li , E. C hielini ,
[7] W. Brostow ,
217 (1 997).
2387 (1986).
979 (1990).
[8 ] T . Mitev a, L. Minko v a, P. L. Magagnini ,
(1998).
[9] M. H .J . K och, J . Bordas,
1519
461 (1985).
[10] C.J . Boulin , R. K empf , A . Gabriel , M. H .J. K och,
178 (1995).
[11] J. Greb ow icz, B. W underlich,
141 (1983).
© Copyright 2024 Paperzz
