A STUDY OF THE POL~MORPH[SM OF HsGHER h:ONOACID.rC

T R I G L Y C E R I D E S B~ M E A N S OF A VOLU-~IE . N [ : C R O D I L A T O M E T E R

W I T H A U T O M A T I C R E C O R D I N G

G. B. R a v i c h , B. N. E g o r o v . a n d S. G. K r y l o v

N. S. Kumakov General and knorgamc C2'..c~.~::3 2r.srar.ze, Academ} of Sciences. U ~ R Translated from lzvestDa Akadenm Nauk 553--':-. ~_'~,.J..nle Khinnchesktkh Nau.~. ~:c. 3, pp. 481-487, March, 1963

Original a m c l e subm-tted Ma} 9, 1962

The irtevemlble pol)morplnc changes m hlghe: _:-enoaci2m tngl)cer~dES Is of mt~re~ :a r.he stud) of the spe-

cific phases formed by ahpilanc compounds ~,ith a b.--g chain and aho m the hght of nhe =-_ere general problems m the phys,cs of condensed organic substances. Mono~:cT.c ~ar.~,uons m the sohd state and r wlth the ap~ar-

ante o f intermediate melts ma) alter sigmficantI} r2ne physical _~tab,hty of materials of ~.~an~-.al *mportanec, includ- ing er)stalhne polymers, and ma} also influence the: : ?h)~,eal propert,es to a consLdera~ie exlent. From th~s view-

point, particular interest xs attached to the change m ~ t ju~r-,s in volume at the phase t_ -a~non points on repeated fusion, i.e., in the succusstve changes sohd metas~ble phase - - melt - - sohd stable form. ~ ~e l t . These changes take place on a suffictently raptd increase in the tem2eran::~ of the substance, when the ~--~versible comers~o~a of the metastable phase m the sohd state is unable to ta_'-:e place and t.hts phase does not reek.

There are a large nmnber of hn~ar d l la tomcte~ of ddfErent design for recording the change m the hm, ar di- mensions of substances during extremely rapid p~'.ase cl~=ges. These mstraments naturai!y carmot be used to send} repeated fusion or sohd highly plastic orgamc phase.*. ~ ff.e o ~ e r hand the well-deve!eTel :'n.ethod of volume d~l- atometry generally reqmres the use of a thermostat a=2 s tauc rr..easurements, since this t r . . e~d ~s usually used to study relatavely large specimens and ,t is ,mposslble tc avoid r~hermal merua of the s}s:em be,rig studied.

For the d i la tomcmc atad~, of rap~d phase changr ~e.~fore. ~,e used a volume m t c ~ a ! a t o m e t e r wtth automat- ie record,rig of the results, the dcs,gn of th,s m~trm~a.=t ~ i 1 be described briefly below. A= ~ e same time the data obtained could be compared with the other oblecuve Mr.euc method of differennal thena-,.M azalys~s. We stud~ed ex- t remely pure specimens of the saturated tr,glyeendes- tnIaunn, tnpa lmmn, and tnstean=. The purity charactensncs of the specm~ens were gtven in our prewous papers de';e~ed to the thermal analys~s of these .-7.-atenals [1-6].

Since we stud'.ed the polymorplnsm of the tng l}eendes b} means of a nEW automauc ~-o ,'hz-n.e m,crod~Latometer, we shall deal m more detail w~th the advantages of tLe volume m~croddatometnc method cc..-npared wtth hnear m~- cmdl la tometnc methods and with volume dda ton ;e tnc metkods des:gncd for the stud)' of h r~e specimens. ,45 already noted [7], volume ddatomEtry has a number of adva:=~ges e~er hnear d~latometry. Volm--e mlatometers make ~t possible to study the temperature dependence of the ~2,:c~flc vo ,!ume for htghly plastic a=,1 ~:;md substances, to meas- ure the jumps an volume on fuston, to study the procesz~cs of glass-formatmn and polymEr,.za::oa, and to stud} various chemical reactmns taking place w~,h volume change,, an the conJEnsed phase. Volume d :~ :zmet r~ ~ of pamcular ~mportance in the study of phase changes m highly pLas:.e o:gamc sub:tances close to thei: ~e:amg points. ~[hus ~ ol- ume ddatometers, including m~crodtlatometers, extc::.: ~o.:S.d~rabl) the methods and p o ~ k : e apphcanons of hnear dllatometers to a range of matcrmh and phenomena ~.kich cabinet be stud~ed b~ the latter. ~hcrodtlatometet~, m turn, irrespect,ve of whether they operate on the hnea : or volume prmctple, ha~e a ~tder ~,~=ze of possible apphca- norm in research than ordinary ddatomcters, ~nce the? am u~ed to make measurements at hKh rates of change of temperature and at the same tnne not creating h,gh ten=F~ra:ure gradients m the spccm~e~ bcmg stud~ed and thus not dmtor~mg the true temperature dependence of the dCa:o~re:nc curve. Specimens w~th ~:..all mass and hence ~;th low total heat capac~t~ heat up and acqmre the temFe--am.~ of the surrounding mcdmm m._'~h more rapidly. It much eas~cr to control the temperature, ~.c., to change ~t according to a prcwously deterrmr.~ t~me dependence, for these spec,mcns than for specimens with large ma~s. T'-.~.-efo:-e the use of small spec,.me~ ~ ~ e onl~ way of carry- mg out d , la tometnc study of processes m substancc-~ t m J ~ e m g r2p~d changes at lugh rates e f ~em?craturc change.

4-22

1

t~,hnutes

~

I , L z x g L , ' �9 ~ :

Minutes

~

Fxg. 1. F~g. 2. Fig. 3.

Fig. 1. Tnlaunn, stable B-phase: 1) dl la tometnc curxe. 2) temperature cur~c.

Fig. '2. Tr~launn, metastable r 1) d~Iatometnc curve, 2) temperature cur',,:.

Fxg. 3. Tnpa lmmn, stable 8-phas : : 1) d d a t o m e m c curxe. 2) temperature curxe.

Thus in addmon to the stud) of highly plastic phases and melting points, volume m:c=~&latometr,~ not only ex- tends the posss of studies to the class of compounds obtained m small quantities (rare elements, substances htth hxgh reacnwr) ) but also provides fundamentally neu methods for studying the regular f~atu.-~s cxhzblt~d b) c onder~ed phases and. in pamcular , makes zt possible to estnnate quantitatively the chang,.s, ~,lth tc~=~:atur~; and u,r~e, m the specific volumes of sohd and hqmd substances and thus to make a quantitatxve stud~ of the kmencs o f rapid changes m specific volumes in different ph)s~cochemmal processes.

E X P E R I M E N T A L

ice stud,,ed the polymorphtsm of the triglycerides on the dzlatometnc apparatus dc sc r :~d above. The thermal expansion of the test specJmen ~,as transferred via the working liquid to a s)stem of bello~,s ar.d via tke latter to a capacity recorder whose signal was tra,~ferred to a h,gh-frequency generator block (8 MHz) and from there via an electronic amphf, er scheme to an EPP-09 recorder [8, 9].

Of greatest interest, from the practical vie~,pomt, *s the hzgl~ly sensm~e volume recorAer, "~,hich is designed m such a wa) that it can be used to stud)' the phase changes of specmmns ,~lth dmlen~o.~s of 5 - I00 mm ~ w,th a sens,- t iwty of 0.000~ mm 3 [10]. The recorder consists of a closed s)stem ~,th working volumes .~ la ted from one another. The thermal expansion of the specimen is tra,Merr~d ~ ~a the ~orkmg hqmd m the working volumes to bello~,s. ~,b.,ch are in turn fixed r,g,dly to the plates of a plane parallel measuring condenser. The workiag volumes mutually c o m - pensate s)stemat,e errors arrsmg as a result of the thermal expansmn of the working liquid and the ~esseLs, ,rregular heating of the measuring system, etc.

ICJ ) 100

0 . . . . . . . . . 0 r Ig ~ 2r 3O M a n u r e s

|

O

IC0

L ~

$ /Z 1,9 ) Ok. . .~ ~ , ~ . . _ z _ _ L _ x . - . . . . . l~uute~ ~htmtes

Fig. 4. Fig. 5. Fig. 6.

Fig. 4. Tnpa lmmn, rnetastable c~-phase 1) d,Latometne cur~e, 2) temperature cur~c.

Fig. 5. Tristearm, stable fl-phase 1) d d a t o m ~ m c curve. 2) temperature curve.

Fig. 8. Tnstearin, metastabLe c~-phase 1) d , la tometnc curve, 2) temperatur~ c u ~ .

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t F-tmion o f Fusion I trip'31" " - ] [ o f t r i - !

Minutes

F~g. 7. D~latometr,c c ~ v e (1) and tempera ture cu~ e (2) for t r rpa lnu tm and tr t - stearin p laced ~n different worl~ng spaces o f the vol - ume recorder.

The specimen and C~ :urro~.d.ng ~,ozking h : . ~ a . e r e ~ea~e.5 ~y a t~e~.-r.,a!

block and progra~.-cor.trsilc-d assen~bl;,' eopz~st~.ng of a : ~ c - _ r a ~ r e ~ r t t n g de.~ ice,

ER-S-K e lec t romc regulator,and SN-120 vol tage sza~:Lze: . De:zds of the progzar~- control led amembly have been g,ven earl .or [11]. T~e :=~.Tenvm-e ~zs mea,~.rcd ~ t h a copper-constantm thern'ocoup!e, in order to :~c~:ce rS.e error in the ~ e a s u : e - merits due to the increase ,n tcm~,eratere of the ,~ea~'_.-~S ' s)~tem t~-e ~ e r part of the volutne recorder, from the ca?:llaric.s connecting rY_r~ *.orVang v o l z ~ e s to the bel- lows, were l~ept at comtant ter,~perature by meam of a ~a '_er jzcket from an ,~ltra- thermostat . The use of capi l lar ies reduces the effect o f z=m~ra tu re from the heated working l~quid passing through the:at to the bcllo~,~.

Ln the stud)' of t~,e t r igl)cer ides disti l led degas_2 .,~ater v, as ~ e d as ~.orI~.~ag l iquid. The t r ,g l )cer idc specimens ,,ere prepared b) cow~:ess,on at 10000 k~,cm ~ and had a c ) h n d r l c a l shape with diaincter 4 mm anA P.=~ght 3-5 ram.

The d d a t o m e t n c studies were carried out w~tP. tee follo,,~mg g l )cero! esters of higher ahpha t tc acids trtlaurm, t r tpalnutm and tr~s~ear n. All tke su~stanct s ~,cre studied successl~el) under ident ical condlttm~s, ~hic~ r:-.~de it pom~ble to co~par~ rcadtl) the resulting dda tomet r , c cu~'cs. In ~ndl~ldua! e ~ e s . part~culariy ,n the stud) of trlstearm, sonde of the condit, ons, particular1)- ~ e rate of change of ~cmper- ature, were varied over a fairl) ~',dc range ~n order te 2e~crmlne the reasons for the differences in the d i la tonrc tnc cur~es obtained for dzffc_-ent trlg!)cer~des. In the trh-

t i a l stage we recorded the dda tomct r t c curves b)' heating the stable 5-forJns. Subscq~e~.tl) the metastable sohd phases obtained by cooling the mel t were studied .~n more de ta i l under different t empera : :re conditions d~n~,, both heat ing and cool ing.

The d i l a tomet r i c curve recorded for a t rdaurtn specimen in the original state as ".he stable d-modlf~catiop Is shown in Fig. 1. With heat ing at a rate of 6 .4 ' / ram the curve sho~s a lump Ln volume, correspondir.g to [uston of the d- form a t 46-47 ~ Subsequent coohng leads to a volume jump m the opposite dlrcctie.'-~ ~zdicating cr?stalhzat~o~ of the liquid t rdaa rm. Comparison of the magmtudc of these two volume jump~ sho~s tka~ t~e tolunze effect of the crystall~zation of the tr~laurm is much leas than the effect of fusion and alx~ounts to ~T;'-" of the lat ter . This indicates the formation o f a metastable sohd a -phase. S,~bsequcnt heating of the specimen at iV.,: sa:r~e rate of 6.4Vmm (F~g. 2) led to a sharp decrease m the volume of the metastable modification, corresponds.rig to c o n v e ~ o n of tee substance to the stable 3-form, ~hleh on subsequent heating melts a t a temperature of ~47 ~ An ~=terestmg feature ts that the sum of the volume jump accompanying cr )s ta l l tza t ton of the a - f o r m from the reel : (~-e F~gl. 1 and 2) and the vol- ume jump for the monotropic change a - - , B-form equals the volulnc lump for fusion of ~ e 5-phase. this ts to be expected for a given t rdaurm specimen if we assume the following schemes for the pLa~ changes heating of the or iginal specimen leads to f t~on, l .e . , the change d-form -- liquid, subsequent cooling g,~cs the change 1,quid -. c~- form. and reheat ing gives the changes a - f o r m --. g-form -* hqutd.

For t r ipa lmi tm, which ts a gl~ccride with a higher molecular weight, we obtained d~!atometrtc cur~.s ( f igs . 3 and 4) of shght ly different form. The heating cur~c for the stable B-modification, obta laed at a rate of heating of 6.4~ is ~dentical ~l th the corresponding dda tome t r i c cur~e for t rdaurm the curve ~.o~s one volume change ef- fect a t 56", ev ident ly corresponding to fusion. The coohng curve however d~ffcrs saga~f~cantl) t t sho',s two phase changes a t 52 ~ and 43 ~ whLch apparcnt!y correspond rcspcctl~ely to cr}stalhzat~on of a 5"-form and convers~oi~ of tI~c b ' to the a - f o r m , which on subsequent hearing (see F~g. 4) melts (w~th an increase an vo' .zme) co gtv,: a hquld which c r ) s t a lhzes to give the stable tS-forln (with a decrease m volume) followed by fusion of type ~-form (wxth an ,~crea~c m volume) , T r i p a h m t m thus sho~,s the double fusion effect . Wc ha~c thus, apparentl 2" for the first t , ~ e . recorded the change in volume for the fusion of a metastablc phase in the short tinge interval co , .~$~nd ing to tke ex,s~el~ce of this Liquid phase before crys ta l l iza t ion of the hqu~d to the stable form. These changes ,a t r l pa lm , tm ~:m take place according to the following schemes, t lea tmg of the original specimen t~-form --* hqu~d~ coo!~ng of tke mcl~ 1,quid

B'-form -0, a - f o r m , reheating or-form --* hqutd --* ~- form -- hqmd.

The * ~ n e t , e ~ dda tome t r i c ewdence for the non-cqu, l, brium processes (unu~.r c~.,-.A,t~or~ of rap,d heating) ,s even more d~stmct in the case of tnstcarm, l.c~ the h,gher ahpha t ic acid g l ) ' ccndc ~,tt'. ~.e highest molecular ~.c%ht. The d d a t o m e t r i c cu:x'es fcr tr istearm (Figs. 5 and 6) for a rate of change of temperat,'~-e c f 6 4"/m.,n rescmb!e thins, ~ f~r t n p a l m i t m and tr , laurln. The curve for the heat ing of the stable d-form and its sa~.~que~.t cool ing(Fag. 5) is

434

, den t ica l to the analogous cun 'e for t n l au rm (Fig . 11. ~ a = s ~ a n d , n g to formation of the c~-modlf icahon. Su~,aqucnt hea t ing o f the substance at the same rate g,~es the doable ~as~on effect. ~,I~dch Ls ~ho~n m Fig. 6 and resembie.~ ~ke double fusion effect for t r i pahmtm {F~g. 4) and takes p lace according to an tdem~,caI ~chcme a-fo~-m ~ hqu, d ~ B-

form --- hquid . 1"he sudden volume change, from 52 to 5S" c ~haracterizes fusion of the nmtastabIe a - p h a s e . Thu phase is able to r ec r ) s t a lhze to form the ~-phase. a~ ind,cated b) the equa! l ) ~harp change ,n voNn-e m the t,am- perature range 61-66". followed immed ia t e l ) b} a ne~, j~q~p ( increase) m volume due to fiumn of the stabte ~-pha~e. This cttrve sho~vs exce l l en t agreement w,th the therr::os for tns tcarm recorded tulder the same heating conditmr~s. As in the case of t r ipa lmi tm, the double fusmn effect fo: ms tea r in ~s shown at h~gh rates of heating of the a - p h a s e .

To confirm the quant t tan~e eanmates of the ~:-agmtude of the volume effects of the ptnse changes b~ tt~e : e l - a t ive metlmd on the au tomanc mmrodda tomete r ~e can-ied out further experm~ents b~ s~multaneou~l~ ~tud~mg d;e changes in vo!mne w~th temperature for t~o sp~cn~era of different substances placed m d,fferent ~,orkmg ~paces m the dda tomete r . In th~s case the instrument recordg ~ e ovc~oall volume changes for the t~,o spemmens, the spec. '- mere act on the volume recorder m d~ffer~.nt d,rcct~o.'-a, so that the ~olume jumps for fiasmn of the su~tances am re- corded m opposite phases (one is d~rected m a positive darectmn and the other m a ncgat~ c d~rectton). We recorded a d d a t o m e t n c cur~e of th~s t )pe for specm~ens of tr, s,%a.in and t n p a h n , t m v, tth d~fferent original ~oluqqes, t h s c m ' e is shown m Fig. 7. According to the hterature data ~1,.. 13]. the coeffm~ents of thermal expan~mn of th~.~ sohd ~-phases of tns t ea rm and t n p a l m m n arc equal . The,r volLm~.e jamps on fusion are a!~o ~qual (~11-~). Since the mel t ing points of the two substances d,ffer shght l ) (~2 ~ and ~.5"), we obtained a s ) m m e t n c a l d , l a tome tnc cun 'e , ,h,ch ts the a lgebra ,e sum of the t~,o d d a t o m e t n c cur~ ~ obta ,ncd ~eparau:ly for each ~.ubstance. The horizontal sec tmn of the curve m the temperature range below the mel t ing [,oint of t n p a h m t m and above the melt ing point of trtst,aanu. md~cates that the coeffm~ents of thermal expansmn of tE~a t , ,o substances m the sohd and hqu~d state~ arc p r a t t , c a l l ) equal . The fact that after the fusion of tns tearm the d d a t o m e m c cur~e returns to the original point rod:cares that the volume jumps accompanying fusmn of the t~o sub~ances are equal . Th~s confmns the above htera ture data on the volume characteris t ics of the tngl)cer~des and sho'~s f l a t , t t s possible to use this mmrodt la tometer for the quan- t i t a m e est~matmn of the volume changes of ne~, substances, wh,ch have not ) a t been stud~ed, b) means of th,s re la - t ive method of measurement. The automat ic ~ olume m,c. , 'odilatometer can be mad successfall) to record cur~-es giving the volume change of metastable phases under condmons adequate for the carr) ,ng out of d , f fe renual ther',p, al

analysts.

Thus we are no~, able, by developing " k m e u c dxlarometr~", to examine not only the thermal effects, a,.; can be done by thermal measurements, but also the jumps m v d a , ne accompanDng the fus,on of metastab!e forms, b) meas- uring th~s ~ffect in the short n ,ne mter~ al corresponding ~o the: eMstence of a hv!md phase before recrystalhzat~on to a more stable form w~ttl a h,gher mel t ing point. !n pa :nca l a r , th~s opens up the poss~bthty of ca lcula t ing the fte!ds

o f metas table phases from the Clausms-Clape) ron equauon.

S U M M A R Y

1. The phase changes (fusmn, crys ta lhzat lon, anJ monotrop,c changes) of tn laurm, tr~palmltln, and tn:~t~:arm

have been stud~ed on a new au tomatm volun]e ll11cro~A!atoIYictcr.

2. The phenomenon of double fusLon m tnpah~.~,_m and tns tcarm has been dt.tected and studmd.

3. The relat ive s tabdl ty of the metastabl,, c~-foa:-a increases with recreate m the molecular ~,eight of tl.e t n -

g lycendes O.e., from tn laurm to ms tearm) .

2. 3. 4. 8. 6. 7.

9.

L I T E R A T U R E C I T E D

G. B. Ra~,Ich and G. G. Isurmo~,, The Phase S t .~ tu~c of Tngl )ccr ,dc~ [m Russian], Xzd. AN SSSR, Moscow, t1952).

G. B. Ra~ich, DoM. AN SSSR, 36, 9, 294 (1942). G. B. Ravsch and G. G. Tsurmov, DoM. AN SSS% 38, 9, 331 (194:3). G. B. Rawch0 G. G. Tsnnno~, V. A. Vol 'nova, ap~ N. P. P~.tro',, [zv. AN SSSR. Otd. khlm. n. (1945s 5 t l . G. B. Rawch and G. G. Tsurmov, Izv. AN SSSR, C ~ . ~him. n. (1946), 609. G. B. Pavlch. V. A. Vol 'nova, and G. G. T_cunr~v. Dokl. AN SSSR, 51, 5, 365 (1946). G. B. P.avlch and 13. N. s Co[Icct ion: "F~_'.~e~.s of Science, Chem. Science, Ph)s lcochcmlca l Anal)sis" tin Rt~,aii}. lzd. AN SSSR, Moscow (1959J, Vol. 4. p. 2 I. N. KLdm and A. V. Panov, Zavodsk. u~bo:a tcq :a . I, 48 (1957). G. B. Ravich and B. N. Egorov, Zh. n~organ, tJ~a:n~,, 5. 11, 2603 (1960).

435

10. I.M. Otck -c.~a~..n}:o, V..~& Nclmark, N. K. Ermllov, a~d .p,R. N. Egorov, Zavodsk. laboratorl)a (in ~c p~c~), 11. B.N. Egorov, N. K. Errc.s and I. M. Otchcnashenl<o, Zh. fiz. klumi=, I, 170 (1962). 12. A.E. Bailey. ~lting ~j Solidification of fats, N. Y. (1950), 13. B.M. Craig. J..Amcr. O~L C~.ern. Soc., 29, 128 (1952).

All abbrev~t~oms of perzodtCals in the abo~e blbhography =,re letter-by-letter translzter-

mtiorts of the abbrewat=ons as gl~en m the original Russian journal. Some or all of thls per)-

o c l i c a l h f e r a t u r e ~.ay- ~ l l b e a v a i l a b l e in E n ~ h s h t r a n s l a t z o n . A corr, p l e t e l i s t of the c o v e r - t o -

Cover ~n~.lash tramslations appears at the back o f th=s issue.

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