Pha se Behav ior of the Ternary Solution Involv ing Rodl ike and Random Co il Polym ers 3

Size: px

Start display at page:

Download "Pha se Behav ior of the Ternary Solution Involv ing Rodl ike and Random Co il Polym ers 3"

Henry Ellis
6 years ago
Views:

1 V ol. 16 N o Chem ical R esearch in Ch inese U niversities Pha se Behav ior of the Ternary Solution Involv ing Rodl ike and Random Co il Polym ers 3 L IN J ia2p ing 3 3, WU H e2rong and L I Sh i2jing (D ep artm ent of P olym er S cience and E ng ineering, E ast Ch ina U niversity of S cience and T echnolog y, S hang hai , P. R. Ch ina) (R eceived A p ril 15, 1999) T he p resent paper covers the phase behavior of poly (p 2benzam ide) (PBA ) gn ylon 6gH 2SO 4 and poly (p 2phenylene tereph thalam ide) (PPTA ) gn ylon 6gH 2SO 4 system ṡ T he transition tem 2 peratures detected by the D epolarized L igh t Intensity m easurem ents w ere used to construct the phase diagram in w h ich the influence of temperature w as show n. T he enhanced depolarized ligh t intensity observed in the ternary system suggests that the coil polym er chainsm ay tend to be ex2 tended and contribute to the overall anisotropy of the liquid crystal phase. Keyw o rds Phase diagram, Phase transition, L iquid crystal polym er A rtic le ID (2000) In troduction T ernary system s comp rising a rodlike polym er, a random coil polym er and a solvent have received m uch attention in recent yearṡ T he interest in these types of studies is not only due to the theo retical understanding of lyo trop ic liquid crystal but also due to the m ixed system s including rigid and flexible polym ers having been taken as a w ay to p roduce composite m ateri2 als based on ultrah igh modulus polym er [1, 2 ] A s for the theoretical considerations of the phase behavior for such ternary system s, a lattice model has been p roposed by F lory [3 ]. A ccording to the theory, the flexible polym er is essentially excluded from the anisotrop ic phase, w h ile the isotrop ic phase exh ibits a greater tolerance for the rodlike polym eṙ Som e experim ental results w h ich are in line w ith the theo2 [4 retical guideline have already been reported. For instance, B ianch i et al. ] reported an experi2 m en t on the system PBA gpo lytereph thalam ide of p 2am inobenzhydrazide (X2500 ) gn, N 2 dim ethylacetam ide+ 3% L ic l. In th is system X2500 occurred as a random co il in the so lu2 tion. T he obtained results show that the imm iscibility appeared as the first drop of m esophase w as form ed. T he X2500 component did not occure in detectable quantities in the anisotrop ic phase. Sim ilar results have also been available in the literature [2, 5 ]. 3 Suppo rted by the N ational N atural Science Foundation of Ch ina (Gran t N o ) and the State Educational M inistry for the O versea R eturneeṡ 3 3 To w hom correspondence should be addressed.

2 164 Chem ical R esearch in Ch inese U niversities V ol. 16 M ost experim ents reported so far w ere done at room temperature. N o attemp ts to control the temperature of the samp le accurately w ere m ade. How ever, temperature m ay be an inter2 esting param eter for the comp lete descrip tion of the phase behavior of the ternary solution. T he influence of the variation of temperature can p rovide a further insigh t into the nature of the liquid crystal system. In our p revious work [6 9 ], it w as found that the D epolarized L igh t Intensity (DL I) technique w h ich is used to detect the transitions in the birefringent m aterials by sim ultaneously m easuring samp le temperature and the intensity of the polarized ligh t rotat2 ed by the samp le can be a suitable m ethod for follow ing the comp lex physical changes occur2 ring in the lyotrop ic liquid crystal polym erṡ In the p resent work, by using DL I technique, the phase behavior of poly (p 2benzam ide) (PBA ) gn ylon 6gH 2SO 4 and poly (p 2phenylene tereph thalam ide) (PPTA ) gn ylon 6gH 2SO 4 w as investigated. T he phase diagram s in w h ich the effect of temperature is show n have been m apped according to the DL Im easurem entṡ Exper imen tal T he intrinsic viscosities of PBA and PPTA w ere dl g - 1 and dl g % H 2SO 4 at 25 respectively, corresponding to the molecular w eigh ts(m w ) of and in term s of the [ Γ]2molecular w eigh t relationsh ip s given by Schaefgen et al. in [10 ]. T he intrinsic viscosity of N ylon 6 w as g dl - 1 m easured at 25 in 96% H 2SO 4. A ll the polym ers w ere dried in a vacuum oven at 80 for 48 h before use. T he lyotrop ic solutions w ith various ratios of PBA to N ylon 6 or PPTA to N ylon 6 w ere p repared by dissolving PBA g N ylon 6 or PPTA gn ylon 6 m ixtures in 100% H 2SO 4 under dry N 2 atmosphere at 60 for about one day. A total polym er concentration of 15% (m ass fraction) w as m aintained. T he samp le p reparation w as carried out under a dry atmosphere at about 60. F irst, the samp le w as stirred in order to ensure w ell m ixing. T hen, the anisotrop ic solution w as put betw een tw o cover glass slides, sheared by hand and quenched to room tem perature to allow the so lidi2 fication. T he shearing rate w as of an order of m agnitude 10 2 s - 1. F inally, the samp le w as sealed to avoid moisture contam ination. T he phase transition temperatures w ere determ ined by a D epolarized L igh t Intensity (DL I) instrum ent and a L eitz2o rtholux g Polarized L igh t M icroscope (PLM ). T he detailed descrip tion of the DL I apparatus could be found elsew here [7, 11 ]. A ll DL I m easurem ents w ere perform ed w ith the sam e heating rate of 4 gm in. Results and D iscussion 1 The Phase Trans ition of the Anisotrop ic Te rna ry S olutions For both PBA gn ylon 6gH 2SO 4 and PPTA gn ylon 6gH 2SO 4 solutions, above a critical volum e fraction of the polym er at room temperature, the random ness of the orientation along the long axes of the m acromolecule w as lost and a lyotrop ic liquid crystal could be form ed. How ever, no single homogeneous nem atic phase w as observed for the ternary m ixtures unless an external force w as app lied. A n isotrop ic phase could be form ed if the polym er solution w as

3 N o. 2 L IN J ia2p ing, WU H e2rong and L I Sh i2jing 165 heated to the temperature at w h ich the energy disrup ts the orientational ordering. O n the oth2 er hand, the solidification could occur upon cooling. A s stated in the literature [12, 13 ], the DL I app roach is particularly useful for determ ining the liquid crystal phase transitionṡ By ensuring a constant field of view and samp le th ickness, the m ethod w as extensively emp loyed to inves2 tigate som e liquid crystal transition quantitatively in our p revious work [6 9 ]. A s revealed in the experim ental results, both the solid crystal and the liquid crystalw ere h igh ly anisotrop ic, but the liquid crystal state show ed a h igher intensity of depolarized ligh t than the solid crystal state did, w h ile the isotrop ic state did not rotate the polarized ligh t [11 ]. F ig. 1 a show s the DL I heating curve for PBA gh 2SO 4. W ith temperature increasing, the in2 ten sity of the depo larized ligh t gradually increased, indicating that the PBA gh 2SO 4 gradually transform ed from the solid crystal to the nem atic m esophase. A ccording to the literature [14 ], the orientation of the polym er liquid crystal can be p reserved in the solidification on cooling. T he crystallization invo lved usually does no t change the o rien tational o rder and these align2 m en ts could usually be faithfully rep roduced w ith the increse in tem perature. A s show n by curve a of F ig. 1, upon heating, the depolarized ligh t intensity kep t nearly a constant from 63 to 93, suggesting a stable nem atic state of PBA gh 2SO 4. W ith temperature further in2 creasing, the nem atic2iso trop ic tran sition began, and the liquid crystal passed th rough a biphasic zone in w h ich the nem atic phase w as in equilibrium w ith the isotrop ic phase. A ccord2 ingly, the DL I curve dropped gradually un til the phase tran sition fin ished. T hus the DL I m easurem ent for the PBA gh 2SO 4 reveals two transitionṡ O ne is the solid crystal2anisotrop ic transition at 63, the other is the nem atic2isotrop ic transition at 113. F ig. 1 DL I hea ting curves for the ternary m ixtures of F ig. 2 DL I hea ting curves for the ternary m ixtures of PBA, Nylon 6 and H2SO4. PPTA, Nylon 6 and H2SO4. PBA gn ylon 6= 100g0 (a), 70g30 (b), 50g50 (c). PPTA gn ylon 6= 100g0 (a), 60g40 (b), 40g60 (c). In the case of PBA gn ylon 6gH 2SO 4, upon heating, the crystal2anisotrop ic transition oc2 cured at 19 as show n by curve c of F ig. 1 for the ratio of PBA to N ylon 6 being 50g50. Further increasing tem perature, fo llow ed by a sho rt period of equilibrium state, an in ten sity drop w as observed, indicating that a transition took p lace. It should be noted that th is transi2 tion becam e more obvious w ith the ratio of N ylon 6 to PBA increasing as is seen in F ig. 1. T hen the depo larized ligh t in ten sity kep t a con stan t in a tem perature range. W ith in th is

4 166 Chem ical R esearch in Ch inese U niversities V ol. 16 range, the PLM show ed a biphasic nem atic phase. F inally, the depo larized ligh t in ten sity started to decrease at 105, suggesting a biphasic nem atic2isotrop ic transition. T h is transi2 tion finished at 123. the sim ilar phase behavior w as also observed for PPTA gh 2SO 4 and PPTA gn ylon 6gH 2SO 4. T he DL I heating curves are show n in F ig. 2 accordingly. 2 The Extended Cha in Conform a tion of the Random Coil Polym e r A s show n in F ig. 1 and F ig. 2, the DL I m easurem ents for both PBA gn ylon 6gH 2SO 4 and PPTA gn ylon 6gH 2SO 4 exh ibited an additional transition w h ich turned more obvious as the content of the N ylon 6 component increased. T he intensity of the depolarized ligh t before the transition is h igher than that of the depolarized ligh t after transition. A s reported in our p revious studies [6, 7 ] and the literature [15 ], the intensity of the depolarized ligh t is p roportional to the fraction of the liquid crystal at phase transition. T herefore it can be speculated that in PBA gn ylon 6gH 2SO 4 or PPTA gn ylon 6gH 2SO 4 system, by app lying an external force in the samp le p reparation, i. e., shearing in th iswork, the rodlike molecules could bind the N ylon 6 and cause the chain conform ation of the N ylon 6 to be extended, resulting in an induced liquid crystal. T hus an accommodation of the N ylon 6 in the anisotrop ic phase w as expected and correspondingly a som ew hat homogeneous texture w as view ed under PLM. T hese molecular alignm ents can be p reserved in the solidification and rep roduced upon heating. A s temperature rising further, after going th rough a equilibrium range in w h ich the extended N ylon 6 chain w as held by the nem atic field, the induced liquid crystalline N ylon 6 chain could relax to nor2 m al, and w as separated from the nem atic phase due to the incompatibility of the rodlike poly2 m er and the random coil polym er p redicted by the theory [3 ]. tensity in DL I curve upon PBA gn ylon 6 or PPTA gn ylon 6 separation. T h is causes a decrease of the in2 T urning to the morphological changes upon the phase separation, before the separation, a rather grainy texture of very sm all anisotrop ic dom ains tum bling over each other w as view ed as show n in F ig. 3 (A ) for PBA gn ylon 6 gh 2SO 4. T he apparent size of the dom ains in2 creased, w h ile the am oun t of the liquid crystal decreased, w ith increase of tem perature. nally the separation of PBA gn ylon 6 occurred and resulted in a stable and clear texture spot2 ted w ith PBA liquid crystalline dom ains w h ich can be seen in F ig. 3 (B). F i2 F ig. 3 Polar ized l ight m icroscopy for PBAgNylon 6gH2SO 4 before the pha se separa tion (A) and af ter the pha se separa tion (B). PBA gn ylon 6= 40g60 ( 320)

5 N o. 2 L IN J ia2p ing, WU H e2rong and L I Sh i2jing 167 T he induced liquid crystal w ith a h igh chain rigidity can also be considered in term s of the thermodynam ic components for a m ixing of rodlike and coil polym ers in the anisotrop ic so2 lution, G= H - T S. A ccording to the literature [2 ], neither entropy nor enthalpy acts in the direction of com patibility. T herefo re, in the usual case, the co il po lym er is excluded from the m esophase. How ever, in the p resence of the external fields, a negative extra term m ust be added to the free energy change of the m ixing [16 ]. T hus, the G can be expected to be fa2 vorable to the compatibility. To accommodate the coils in the ordered m esophase of the rods, the coils m ust take som ew hat extended conform ation as p redicted by the theory [2, ]. T he free energy required for increasing the rigidity of the coil polym er is supp lied by the external force. T he induced liquid crystalw ith extended chain conform ation causes the intensity of the depolarized ligh t before phase separation to be h igher than that of the depolarized ligh t after separation. 3 Phase D iag ram s of PBAgNylon 6gH2SO 4 and PPTA gnylon 6gH2SO 4 T he phase diagram s for the ternary m ixtures of PBA gn ylon 6gH 2SO 4 and PPTA gn ylon 6gH 2SO 4 w ere also constructed according to the DL I m easurem ents and PLM observationṡ T he transition temperatures as indicated in F ig. 1 and F ig. 2 w ere used to m ap the phase dia2 gram ṡ A s show n in F ig. 4, the phase diagram for PBA gn ylon 6gH 2SO 4 is divided into four F ig. 4 The Pha se diargram s of the ternary m ixtures of PBA, Nylon 6 and H2SO 4 a t a g iven polym er ( PBA + Nylon 6) concentra tion of 15% (ma s fraction). Y : the m ass fraction of N ylon 6 to the total poly2 m er w eigh t; T n2i ( biphasic2isotrop ic ); T s (PBA gn ylon 6 phase separation), g T c2n ( solid crystal2nem atic ); A : isotrop ic; B: nem atic + iso trop ic; C: hom ogeneous nem atic; D: so lid crystal. F ig. 5 Pha se diargram s of the ternary m ixtures of PPTA, Nylon 6 and H2SO 4 a t a given polym er (PPTA + Nylon 6) concen tra tion of 15% (ma s fraction). Y: the m ass fraction of the amount of N ylon 6 to the total polym er w eigh t; T n2i (biphasic2isotrop2 ic ); T s ( PBA gn ylon 6 phase separation ), g T c2n ( solid crystal2nem atic); A : isotrop ic; B: nem atic + isotrop ic; C: hom ogeneous nem atic; D: solid crystal.

6 168 Chem ical R esearch in Ch inese U niversities V ol. 16 region s, A - D. A bove the tran sition tem peratures from the biphasic to the iso trop ic, an isotrop ic phase of PBA and N ylon 6 (region A ) w as observed. O n low ering the temperature, a biphasic phase w as observed (region B). It should be noted that in the case of PBA gh 2SO 4, upon heating, a pure nem atic phase could be observed. In region C, the PLM observation gave a grainy texture of very sm all anisotrop ic dom ains and the accommodation of the induced N ylon 6 liquid crystalw ith an extended chain w as expected. In region D, the PBA gn ylon 6g H 2SO 4 is in the solid crystal form. For PPTA gn ylon 6gH 2SO 4, a phase diagram sim ilar to that of PBA gn ylon 6gH 2SO 4 can also be constructed w ith the data determ ined from DL I test2 ing (see F ig. 5). Refe rences [ 1 ] C iferri, A., K rigbaum, W. R. and M eyer, R. B., Polym er L iquid C rystals, A cadem ic P ress, N ew York, 1982 [ 2 ] C iferri, A., L iquid crystallinity in Polym er, V CH Publisher, Inc., N ew York, 1991 [ 3 ] F lory, P. J., M acromolecules, 11, 1138 (1978) [ 4 ] B ianch i, E., C iferri, A. and Tealdi, A., M acromolecules, 15, 1268 (1982) [ 5 ] B ianch i, E., C iferri, A., M arsano, E. and Tealdi, A., M acromolecules, 17, 1526 (1984) [ 6 ] L in, J., W u, H. and L i, S., Polym er International, 32, 339 (1993) [ 7 ] L in, J., W u, H. and L i, S., Polym er International, 34, 141 (1994) [ 8 ] L in, J., W u, H. and L i, S., European Polym er Journal, 30, 231 (1994) [ 9 ] L in, J., X i, S., W u, H. and L i, S., European Polym er Journal, 33, 1601 (1997) [ 10 ] Schaefgen, J. R., Soldi, V. S., Logullo, F. M., Gold, V. H., Culrich, L. M. and K illian, K. L., Polym. P rep ṙ, Am. Chem. Soc., D iv. Polym. Chem., 17, 69 (1967) [11 ] Barrall, E. M. and Gallegos, E. J., J. Polym. Sci. Part A 225, 113 (1967) [12 ] O ber, C. K., J in, J. and L enz, R. W., A dvances in Polym er Science, 59, 101 (1984) [13 ] Galli, G., Ch iellini, E., O ber, C. and L enz, R. W., M ak romol. Chem., 183, 2693 (1982) [14 ] Donald, A. M. and W indless, A. H., L iquid C rystalline Polym ers, Cam bridge P ress, 1992 [15 ] L iu X., H u S., Sh i L. et al., Polym er, 30, 273 (1989) [16 ] Khokh lov, A. R. and Sem enov, A. N., M acromolecules, 15, 1272 (1982) [17 ] N yrkova, İ A. and Khokh lov, A. R., V ysokomol. Soyed, 29B, 375 (1989) [18 ] L in, J., Polym er, 38, 4837 (1997) [19 ] L in, J., Polym er, 39, 5495 (1998)

V o l. 21, N o. 2 M ar., 2002 PRO GR ESS IN GEO GRA PH Y ,, 2030, (KZ9522J 12220) E2m ail: w igsnrr1ac1cn

21 2 2002 3 PRO GR ESS IN GEO GRA PH Y V o l. 21, N o. 2 M ar., 2002 : 100726301 (2002) 022121209 30, (, 100101) : 30,, 2030 16, 3,, 2030,,, 2030, 13110 6 hm 2 2010 2030 420 kg 460 kg, 5 79610 8 kg7 36010