Zur allgemeinen Theorie der Druckabhängigkeit des Glasübergangs und ihre Anwendung auf den Beginn von Fließerscheinungen in glasartigen Polymeren bei tieferen Temperaturen

Abstract

Carl Schorlemmer" Leuna-Merseburg, Selrtion Physik, DDR -42 Leuna-Merseburg Unter der Voraussetzung, daS fur die Glasubergangskurveii in den Diagrammen log v -T bzw. log v -p WLFGleichungen gelten, sind die Isochronen des Glasubergangs im Druck-Temperatur-Diagramm entweder parallele Geraden oder Hyperbeln mit von der Frequenz unabhangigen Asymptoten p = 17 < 0 und T = 8. Abschatzungen fur polymere Werkstoffe ergeben fur -L7 einige 100MPa und fur 8 -T , etwa 100 bis 200 K. Die Isochronen des Glasuberganges sind Linien, auf denen das Volumen der kooperativen Umlagerungsbereiche naherungsweise konstant ist. Es wird ein Zustandsdiagramm fur glasbildende unterkiihlte Flussigkeiten vorgeschlagen. Mit Hilfe dieser Ergebnisse konnen einige wesentliche Erscheinungen der ersten Etappca der SpannungsriSbildung (craze initiation) erklart werden. 0 6 o6tueii meopuu aaeucwocmu cmemoeanua om aasaefiua u npmenuwocmu ee i~ nauany meqsecmu noaurepos e ~mem006pa3now cocmoanuu npu XUQIEUX mernepamypax nPU YCJIOBEIH, 4TO KpHBbIe IIepeXOna B CTeKJIOO6pa3HOe COCTOHHHe B KOOpAHHaTaX log V -T HJIA log V -p OIIHCbIBa-IOTCR YPaBeHHHHMH BHJIbRMCa-JIaHnenH-~eppH, H3OXPOHbI IIepeXOAa B CTeKJIOO6pa3HOe COCTOHHHe B l'pa@EIKe TaCTOTbI aCHMnTOTaMH p = n < 0 A T = 8. nIyTeM OPHeHTMPOBO4HbIX PaWCTOB AJIR llOJlMMepHk3X MaTepHanOB IIOJIyWUOTcR njIS p -17 HeCKOJIbKO 100 MIIa H 8-T, OKOJIO 100-200"K. H3OXpOHbI IIepeXOAa B CTeKnOO6pa3HOe COCTOHHHe HBJIHIOTCH JIHHHHMH, H a KOTOPMX o 6~e~ KOOIIepaTHBHbIX 0 6 n a c~e t llepeCTpOf8KH OKa3bIBaeTCH IIPEI~JIH-IIepeXOAy B cTeK~l006pa3HOe COCTORHHC?. nOJIyreHHbIe pe3yJIbTaTM IIO3BOJIHH)T 06ZHCHHTb HeKOTOpHbIe OCHOBHbIe JXBJIeHEIH IIepBbIX CTaAEIa PaCTpeCKHBaHHH. EasneHue-TeMnepaTypa O K~~H B~W T C H nm6o napanjIenbHbIMH IIPRM~IMA an60 r~n e p 6 o n a~~i c H~~~B H C R~H M H OT m e m o IIOCTORHHHM. IIpennaraeTcR n n a r p a m a COCTORHEIH AJIH nepeoxnaxgemax mHnKocTet, cnoco6~b1x K On the general theory of the pressure dependence of glass transition and the application to the initiation of flow phenomena in glassy polymers at low temperatures Supposing the glass transition curves can be described by WLF type equations in the diagrams: logarithm frequency against temperature and logarithm frequency against pressure, the isochrones of the glass transition are parallel straight lines or hyperbolas in the diagram pressure against temperature. I n the case of hyperbolas the asymptotes p = L7 < 0 and T = 8 are independent on frequency. Estimations give some 100 MPa for -17 and 100 K to 200 K for 8 -T , in the case of polymers. The volumes of cooperatively rearranging regions are nearly constant along the isochrones. A state diagram for glass forming undercooled liquids is suggested. With the aid of these results some essential phenomena at the first steps of craze initiation can be esplained.

On the pressure evolution of the melting temperature and the glass transition temperature

“…We would like to stress that we have not found a previous suggestion of an asymptotic behavior of T m (P) at negative pressures, although it is clearly pointed out for T g (P) [1,[37][38][39][40][41]. On the other hand, there are no suggestions for T g (P) maximum at very high pressure, although it is well documented for T m (P) [7,8,17,34,35].…”

“…into the negative pressure domain, without any singularity when passing P = 0 [9]. It is noteworthy the existence of negative pressure asymptotes for T g (P) is strongly advised theoretically [1,[37][38][39][40] and supported by the only existing experimental evidence which entered this domain [1,41]. Recalling results of Ref.…”

Discussion of craze formation and growth in amorphous polymers in terms of the multiplicity of glass transition at low temperatures

“…This means, on the other hand, that individual (molecular) time scales are not available or are not suitable for a natural control of the internal processes! iii) A sufficiently large negative pressure (in the order of 100 MPa [13]) is necessary to maintain both the flow processes (in FZ* and EZ). Otherwise, unloading will make the material frozen and brittle.…”

“…It was concluded from phenomenological arguments [3,13] that the isochrones of the glass transition can approximately be represented by hyperbolas in a pressure-temperature (PT) diagram. The picture becomes rather complex if the multiplicity of the glass transition is additionally considered in this diagram.…”