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Dilatometer for the study of phase transformations of polymers at high hydrostatic pressures
METHODS OF INVESTIGATION DILATOMETER FOR THE STUDY OF PHASE TRANSFORMATIONS OF POLYMERS AT HIGH HYDROSTATIC PRESSURES* N . M. KOTOV a n d V. A . SOKOL'SKII L. Ya. K a r p o v Scientific Research Institute of Physical Chemistry
(Received 11 December 1975) A piston t y p e dilatometer with mercury as intermediate fluid was developed for t h e measurement of volumetric changes in phase transformations; this ensures full hydrostatic pressure a n d excludes the effect of m e d i u m transmitting pressure to the sample. The method developed is also suitable for the s t u d y of kinetics of isothermal crystallization under high pressure. The dilatometer was used to measure volumetric changes in phase transformations of P E at high pressures. \
IT Is known t h a t melting and crystallization of polymers characterized b y several features, compared with metals and low molecular weight compounds: a broad temperature range of conversion, dependence of the temperature of conversion on the rate of temperature variation, the medium in which the sample is situated, the existence of mechanical stress, etc. Therefore, when developing a high pressure dilatometer for polymers a t least two conditions have to be fulfilled: full hydrostatic pressure has to be ensured for polymer samples a n d the effect of medium transmitting pressure onto the sample has to be excluded, t To fulfill these conditions, the design of the dilatomoter is based on the principle of a piezometer with an unsealed piston and intermediate fluid [1]. Mercury was used as interme
* Vysokomol. soyed. A18: No. 11, 2604-2606, "1976. t W e noted t h a t organo-silicon liquids PES-3, PES-4, PES-5 a n d PPMS-2/5L inert in relation to P E under conventional conditions, influence both the structure a n d properties ~and the t y p e of phase transformation of P]~ under high pressure at increased temperatures a n d pressures. Thus, the medium which transmits pressure m a y screen the effects caused b y pressure or produce new effects. 2976
2977
Phase transformations of polymers
placed in the c o m p a r t m e n t of a high pressure apparatus [2], in which temperature conditions were maintained b y a thermo-regulating apparatus. The temperature of the c o m p a r t m e n t m a y v a r y a t a rate of 3 deg/min and less or the compartment m a y be k e p t at constant temperature. The electrodes were introduced into the c o m p a r t m e n t through a multi-channel high pressure electric inlet [3]. Sample temperature and the movement of the piston were recorded using an L K D two-coordinate recording instrument.
b
a 1
TI
LKD X- 7"
l~Io. 1. Dilatometer (45KhMNFA steel) H1RC=50-52 (1, 3, 6) and 35-39 (2-8) (a) and measuring system (b). See t e x t for explanations. The displacement d a t a unit was calibrated under normal conditions (20 °, 1 arm). I n order to m a i n t a i n accuracy of calibration at other pressures and temperatures, constant p o t e n . tim difference U0 was maintained using an RZZ resistance box between stationary petentiometric contacts during calibration and in the course of experiments; in this case for the s a m e position of the piston
U=(p, T) Uo(p, T)
Rx(p, T)I (p, T) Re(p, T)I(p, T)
It= 1.20 °) (1-b%p) (1-}-aTT) Re(1.20 °) (1 +~vp ) (IWa~T)
Rx (1,20°)I(1.20 ° ) Uz (1.20 ° ) ----Ro(1.20o)/(1.20 o) = U0(1.20 o) , where U~ and R x is the potential difference and resistance between mobile potential contacts; Uo a n d R0--between stationary contacts; ~2" and ~v--thermal and baric coefficients of resistance, respectively; I - - c u r r e n t . Pressure p a n d temperature T at which measurement was carried out are shown in brackets. The'(thermocouple was calibrated at conventional a n d high pressures according to melting points of indium, tin and bismuth [4, 5], the correction being less than 1°. Figure 2a shows the relation between volume and temperature, obtained using linear high molecular weight pF, with narrow MWI), the sample weighing ~ 1 g. Temperatures of conversion from the orthorhombic to high baric phase TI and the melting point of the high baric phase Tmelt show satisfactory agreement with these temperatures which had previously been obtained by I)TA [6].The method developed is also suitable for the study of
2978
1~. ]K. KOTOV and V. A. SO~rOL'SKH
kinetics of isothermal crystallization at high pressures (Fig. 2b). According to our estimate the accuracy of measuring temperature using the dilatemetric curve is not less than 4-1 °, volumetric change being -I-2%.
i
"~'--t
I
Z20
a
r~r
III
I~ ~
260
I
300 T, °C
I
I
I0
L
I
20
Time, rain
l~Ig. 2. Dilatometric curves of PE during heating and cooling at a rate of 1 deg/min, p~ffi7000 kg/cm = (a); isothermal curve of crystallization (p=2900 kg/em=; 188°) (b); TI and T~, Air 1 and J lr~ are temperatures and rapid volumetric changes, corresponding to the phase transformation duriug heating and cooling; Tmeltand Ter , AV meltand zi Vet are temperatures and volumetric changes during melting and crystallization, respectively Therauthors are grateful to Yu. A.rZubov for his attention and interest raising the problem:and V. A. Ivanow, Assistant of of the high pressure group of the Institute of Crystallography, U.S.S.R. Academy of Sciences for the consultations in developing the dilatometer. Tranalat, e~ by E. SEVERE
REFERENCES 1. I. N. MAKARENKO, V. A. IVANOV and S. M. STISHOV, Pribory i tekhnika eksperimenta, No. 3, 207, 1974 2. V. A. SOKOL'SKII, N. M. KOTOV, Yu. A. ZUBOV, V. I. SELI-KHOVA, F. Ya. FROLOV and O. S. VESELOV, Vysokomol. soyed. A16: 1420, 1974 (Translated in Polymer SoL U.S.S.R. 16: 6, 1651, 1974) 3. V. A. IVANOV, I. N. MAKARENK0, S. M. STISHOV and V. I. FEDOSIMOV, Pribory i teklmika eksper'~nenta No. 6, 195, 1972. 4. M. L. MeDANIEL, S. E. BABB and Jr. G. J. SCOTT, J. Chem. Phys. 87: 822, 1962 5. V. P. BUTUZOV, M. G. GONTKRERG and S. P. SMIRNOV, Dokl. AI~ SSSR, 89, 651, 1953 6. N. M. KOTOV, N. F. BAKEYEV, G. P. BELOV, A. L. YEFREMOV, Yu. A. ZUBOV, M. B. KONSTANTINOPOL'SKAYA, A. N. OZERIN, V. I. SELIKHOVA, V. A. SOKOL'SKII, V. S. SHIRETS, Vysokomol. soyed. A17: 1141, 1975 (Translated in Polymer Sei. U.S.S.R. 17: 5, 1312, 1975)
(Received 11 December 1975) A piston t y p e dilatometer with mercury as intermediate fluid was developed for t h e measurement of volumetric changes in phase transformations; this ensures full hydrostatic pressure a n d excludes the effect of m e d i u m transmitting pressure to the sample. The method developed is also suitable for the s t u d y of kinetics of isothermal crystallization under high pressure. The dilatometer was used to measure volumetric changes in phase transformations of P E at high pressures. \
IT Is known t h a t melting and crystallization of polymers characterized b y several features, compared with metals and low molecular weight compounds: a broad temperature range of conversion, dependence of the temperature of conversion on the rate of temperature variation, the medium in which the sample is situated, the existence of mechanical stress, etc. Therefore, when developing a high pressure dilatometer for polymers a t least two conditions have to be fulfilled: full hydrostatic pressure has to be ensured for polymer samples a n d the effect of medium transmitting pressure onto the sample has to be excluded, t To fulfill these conditions, the design of the dilatomoter is based on the principle of a piezometer with an unsealed piston and intermediate fluid [1]. Mercury was used as interme
* Vysokomol. soyed. A18: No. 11, 2604-2606, "1976. t W e noted t h a t organo-silicon liquids PES-3, PES-4, PES-5 a n d PPMS-2/5L inert in relation to P E under conventional conditions, influence both the structure a n d properties ~and the t y p e of phase transformation of P]~ under high pressure at increased temperatures a n d pressures. Thus, the medium which transmits pressure m a y screen the effects caused b y pressure or produce new effects. 2976
2977
Phase transformations of polymers
placed in the c o m p a r t m e n t of a high pressure apparatus [2], in which temperature conditions were maintained b y a thermo-regulating apparatus. The temperature of the c o m p a r t m e n t m a y v a r y a t a rate of 3 deg/min and less or the compartment m a y be k e p t at constant temperature. The electrodes were introduced into the c o m p a r t m e n t through a multi-channel high pressure electric inlet [3]. Sample temperature and the movement of the piston were recorded using an L K D two-coordinate recording instrument.
b
a 1
TI
LKD X- 7"
l~Io. 1. Dilatometer (45KhMNFA steel) H1RC=50-52 (1, 3, 6) and 35-39 (2-8) (a) and measuring system (b). See t e x t for explanations. The displacement d a t a unit was calibrated under normal conditions (20 °, 1 arm). I n order to m a i n t a i n accuracy of calibration at other pressures and temperatures, constant p o t e n . tim difference U0 was maintained using an RZZ resistance box between stationary petentiometric contacts during calibration and in the course of experiments; in this case for the s a m e position of the piston
U=(p, T) Uo(p, T)
Rx(p, T)I (p, T) Re(p, T)I(p, T)
It= 1.20 °) (1-b%p) (1-}-aTT) Re(1.20 °) (1 +~vp ) (IWa~T)
Rx (1,20°)I(1.20 ° ) Uz (1.20 ° ) ----Ro(1.20o)/(1.20 o) = U0(1.20 o) , where U~ and R x is the potential difference and resistance between mobile potential contacts; Uo a n d R0--between stationary contacts; ~2" and ~v--thermal and baric coefficients of resistance, respectively; I - - c u r r e n t . Pressure p a n d temperature T at which measurement was carried out are shown in brackets. The'(thermocouple was calibrated at conventional a n d high pressures according to melting points of indium, tin and bismuth [4, 5], the correction being less than 1°. Figure 2a shows the relation between volume and temperature, obtained using linear high molecular weight pF, with narrow MWI), the sample weighing ~ 1 g. Temperatures of conversion from the orthorhombic to high baric phase TI and the melting point of the high baric phase Tmelt show satisfactory agreement with these temperatures which had previously been obtained by I)TA [6].The method developed is also suitable for the study of
2978
1~. ]K. KOTOV and V. A. SO~rOL'SKH
kinetics of isothermal crystallization at high pressures (Fig. 2b). According to our estimate the accuracy of measuring temperature using the dilatemetric curve is not less than 4-1 °, volumetric change being -I-2%.
i
"~'--t
I
Z20
a
r~r
III
I~ ~
260
I
300 T, °C
I
I
I0
L
I
20
Time, rain
l~Ig. 2. Dilatometric curves of PE during heating and cooling at a rate of 1 deg/min, p~ffi7000 kg/cm = (a); isothermal curve of crystallization (p=2900 kg/em=; 188°) (b); TI and T~, Air 1 and J lr~ are temperatures and rapid volumetric changes, corresponding to the phase transformation duriug heating and cooling; Tmeltand Ter , AV meltand zi Vet are temperatures and volumetric changes during melting and crystallization, respectively Therauthors are grateful to Yu. A.rZubov for his attention and interest raising the problem:and V. A. Ivanow, Assistant of of the high pressure group of the Institute of Crystallography, U.S.S.R. Academy of Sciences for the consultations in developing the dilatometer. Tranalat, e~ by E. SEVERE
REFERENCES 1. I. N. MAKARENKO, V. A. IVANOV and S. M. STISHOV, Pribory i tekhnika eksperimenta, No. 3, 207, 1974 2. V. A. SOKOL'SKII, N. M. KOTOV, Yu. A. ZUBOV, V. I. SELI-KHOVA, F. Ya. FROLOV and O. S. VESELOV, Vysokomol. soyed. A16: 1420, 1974 (Translated in Polymer SoL U.S.S.R. 16: 6, 1651, 1974) 3. V. A. IVANOV, I. N. MAKARENK0, S. M. STISHOV and V. I. FEDOSIMOV, Pribory i teklmika eksper'~nenta No. 6, 195, 1972. 4. M. L. MeDANIEL, S. E. BABB and Jr. G. J. SCOTT, J. Chem. Phys. 87: 822, 1962 5. V. P. BUTUZOV, M. G. GONTKRERG and S. P. SMIRNOV, Dokl. AI~ SSSR, 89, 651, 1953 6. N. M. KOTOV, N. F. BAKEYEV, G. P. BELOV, A. L. YEFREMOV, Yu. A. ZUBOV, M. B. KONSTANTINOPOL'SKAYA, A. N. OZERIN, V. I. SELIKHOVA, V. A. SOKOL'SKII, V. S. SHIRETS, Vysokomol. soyed. A17: 1141, 1975 (Translated in Polymer Sei. U.S.S.R. 17: 5, 1312, 1975)