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Influence of contact angle on hysteresis in mercury porosimetry
Influence of Contact Angle on Hysteresis in Mercury Porosimetry S. L O W E L L Quantachrome Corporation, 6 Aerial Way, Syosset, New York 11791 AND
J. E. SHIELDS Department o f Chemistry, C.W. Post College, Greenvale, New York 11548 Received June 9, 1980; accepted S e p t e m b e r 22, 1980 A s t u d y o f the effect of contact angle in m e r c u r y porosimetry has revealed that appropriate a d j u s t m e n t s in the angle result in the elimination o f i n t r u s i o n - e x t r u s i o n hysteresis. W h e n the contact angle is increased for the intrusion curve and d e c r e a s e d for the extrusion curve, the two c u r v e s c a n be brought into coincidence. INTRODUCTION
Hysteresis in mercury porosimetry has been attributed to the pore potential (1) and to °'ink bottle"-shaped pores (2). We have found that changes in contact angles from intrusion to extrusion can also account for porosimetry hysteresis. Our investigations have disclosed that, if adjustments are made to the intrusion and extrusion contact angles, mercury intrusionextrusion curves exhibit no hysteresis. By increasing the contact angle associated with intrusion and decreasing the angle associated with extrusion the two curves can be brought into coincidence. MATERIALS AND METHODS
The mercury intrusion-extrusion curves were obtained on a Quantachrome Scanning Porosimeter (3) from ambient to 60,000 psia. The solids used were porous glass (Fig. 2a), alumina (Figs. 2b and d), and a proprietary catalyst (Figs. la, lb, and 2c). All samples were outgassed at 50/xm and room temperature prior to filling with mercury. The mercury intrusion-extrusion runs
were first made assuming a contact angle of 140° and the pressure-volume data were placed in the memory of the Scanning Porosimeter Micro-Computer. Contact angle changes were made by adjusting the scaling of the pressure axis on an X - Y recorder and then recalling the scan from the Micro-Computer. The intrusion curves were replotted using wetting angles greater than 140° and less than 140° for the extrusion curves. For a given pore radius the curves show the pressure at which intrusion-extrusion will occur for various contact angles. RESULTS AND DISCUSSION
Since some mercury is permanently retained (1) after extrusion from most samples (see Fig. la), the intrusion and extrusion curves cannot be brought into coincidence along their entire path by means of contact angle adjustments. However, those portions of the curves over which intrusion and extrusion occur can be superimposed regardless of the retention of mercury. An example of such superimposition of curves by contact angle changes is given in Fig. lb where, as
192 0021-9797/81/030192-05502.00/0 Copyright © 1981by AcademicPress, Inc. All rights of reproduction in any form reserved.
Journal of Colloidand Interface Science, Vol. 80, No. 1, March 1981
CONTACT
ANGLE/MERCURY
/ a
,5
193
POROSIMETRY
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F I G . 1. (a) 8 = 140 °. (b) ( V , 0 = 160°; V I , 0 = 1 5 0 ° .
) 0 = 140°; (----) I, 0 = 130°; I I , 0 = 120°; I I I , 0 = 108°; I V , 0 = 170°;
Journal of Colloid and Interface Science, Vol. 80, No. 1, March 1981
194
LOWELL
AND
SHIELDS
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FIG. 2. (a) ( ) 0 = 140°; (----) I, 0 = 120°; II, 0 = 110O; III, 0 = 170°; I V , 0 = 150°; V , 0 = 105 °. (b) ( ) 0 = 140°; (----) I, 0 = 130°; II, 0 = 110°; III, 0 = 170°; I V , 0 = 150 ° . (c) ( ) 0 = 140°; (----) I, 0 = 120°; II, 0 = 110°; III, 0 = 170°; I V , 0 = 105 ° . (d) ( ) 0 = 140°; (----) I, 0 = 107°; II, 0 = 170 o.
Journal o f Colloid a n d Interface Science, Vol. 80, No. 1, March 1981
195
CONTACT ANGLE/MERCURY POROSIMETRY
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20
25
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PSIA x 103
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PSIA x 103 FIG. 2.--Continued.
Journal of Colloid and Interface Science, Vol. 80, No. 1, March 1981
196
LOWELL AND SHIELDS
in all Figures, the arrowheads indicate the intrusion or extrusion. In order to eliminate retention of mercury as a factor in this study, wetting angle corrections were made on second-run scans. That is, a complete intrusion-extrusion cycle was first performed in order to permanently trap mercury. During a second cycle the hysteresis loops closed, indicating no additional mercury retention. Figures 2a-2d illustrate that as the contact angle is increased for the intrusion scan and decreased for the extrusion scan, the two curves approach coincidence and can be made to superimpose. Thus, one can choose a contact angle for intrusion and find a corresponding angle for extrusion which will result in superimposition of the curves, e.g., curves II and III in Fig. 2b and curves I and II in Fig. 2d. Conversely, if a value of the contact angle for extrusion is chosen, a corresponding angle for intrusion can be found which will give superimposable curves.
Journal of Colloid and Interface Science, Vol, 80, No. 1, March 1981
However, the true contact angles for intrusion and extrusion remain unknown since an infinite number of choices are possible. The concept of markedly different contact angles for advancing and receding liquids on solid surfaces is a well-documented phenomenon (4). The influence of contact angle on hysteresis is not inconsistent with the pore potential which would act to delay extrusion until a pressure lower than the corresponding intrusion pressure is attained. Indeed it may well be that the changes in contact angle represent the mechanism by which the pore potential exerts its influence. REFERENCES 1. Lowell, S., Powder Technol. 25, 37 (1980). 2. Orr, C., Powder Technol. 3, 117 (1970). 3. Quantachrome Corp., 6 Aerial Way, Syosset, N.Y. 11791. 4. Adamson, A. W., "Physical Chemistry of Surfaces," 2nd ed., p. 359. Wiley-Interscience, New York, 1967.
J. E. SHIELDS Department o f Chemistry, C.W. Post College, Greenvale, New York 11548 Received June 9, 1980; accepted S e p t e m b e r 22, 1980 A s t u d y o f the effect of contact angle in m e r c u r y porosimetry has revealed that appropriate a d j u s t m e n t s in the angle result in the elimination o f i n t r u s i o n - e x t r u s i o n hysteresis. W h e n the contact angle is increased for the intrusion curve and d e c r e a s e d for the extrusion curve, the two c u r v e s c a n be brought into coincidence. INTRODUCTION
Hysteresis in mercury porosimetry has been attributed to the pore potential (1) and to °'ink bottle"-shaped pores (2). We have found that changes in contact angles from intrusion to extrusion can also account for porosimetry hysteresis. Our investigations have disclosed that, if adjustments are made to the intrusion and extrusion contact angles, mercury intrusionextrusion curves exhibit no hysteresis. By increasing the contact angle associated with intrusion and decreasing the angle associated with extrusion the two curves can be brought into coincidence. MATERIALS AND METHODS
The mercury intrusion-extrusion curves were obtained on a Quantachrome Scanning Porosimeter (3) from ambient to 60,000 psia. The solids used were porous glass (Fig. 2a), alumina (Figs. 2b and d), and a proprietary catalyst (Figs. la, lb, and 2c). All samples were outgassed at 50/xm and room temperature prior to filling with mercury. The mercury intrusion-extrusion runs
were first made assuming a contact angle of 140° and the pressure-volume data were placed in the memory of the Scanning Porosimeter Micro-Computer. Contact angle changes were made by adjusting the scaling of the pressure axis on an X - Y recorder and then recalling the scan from the Micro-Computer. The intrusion curves were replotted using wetting angles greater than 140° and less than 140° for the extrusion curves. For a given pore radius the curves show the pressure at which intrusion-extrusion will occur for various contact angles. RESULTS AND DISCUSSION
Since some mercury is permanently retained (1) after extrusion from most samples (see Fig. la), the intrusion and extrusion curves cannot be brought into coincidence along their entire path by means of contact angle adjustments. However, those portions of the curves over which intrusion and extrusion occur can be superimposed regardless of the retention of mercury. An example of such superimposition of curves by contact angle changes is given in Fig. lb where, as
192 0021-9797/81/030192-05502.00/0 Copyright © 1981by AcademicPress, Inc. All rights of reproduction in any form reserved.
Journal of Colloidand Interface Science, Vol. 80, No. 1, March 1981
CONTACT
ANGLE/MERCURY
/ a
,5
193
POROSIMETRY
f
I0
I5
20
25
30
35
40
45
50
55
60
50
55
60
PSIA x I0 ~
-J
/ j-
b
5
I0
j
15
/" .J,.*
20
i¢~"
]~
25
J~/
30
.- -
.
35
40
45
PSIA x I0 ~
F I G . 1. (a) 8 = 140 °. (b) ( V , 0 = 160°; V I , 0 = 1 5 0 ° .
) 0 = 140°; (----) I, 0 = 130°; I I , 0 = 120°; I I I , 0 = 108°; I V , 0 = 170°;
Journal of Colloid and Interface Science, Vol. 80, No. 1, March 1981
194
LOWELL
AND
SHIELDS
Ld
lIi =/
J 0 >
/ r r
i
i
5
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FIG. 2. (a) ( ) 0 = 140°; (----) I, 0 = 120°; II, 0 = 110O; III, 0 = 170°; I V , 0 = 150°; V , 0 = 105 °. (b) ( ) 0 = 140°; (----) I, 0 = 130°; II, 0 = 110°; III, 0 = 170°; I V , 0 = 150 ° . (c) ( ) 0 = 140°; (----) I, 0 = 120°; II, 0 = 110°; III, 0 = 170°; I V , 0 = 105 ° . (d) ( ) 0 = 140°; (----) I, 0 = 107°; II, 0 = 170 o.
Journal o f Colloid a n d Interface Science, Vol. 80, No. 1, March 1981
195
CONTACT ANGLE/MERCURY POROSIMETRY
5
I0
15
20
25
.'50
35
40
45
50
40
45
50
55
60
PSIA x 103
0
5
I0
15
20
25
30
35
55
60
PSIA x 103 FIG. 2.--Continued.
Journal of Colloid and Interface Science, Vol. 80, No. 1, March 1981
196
LOWELL AND SHIELDS
in all Figures, the arrowheads indicate the intrusion or extrusion. In order to eliminate retention of mercury as a factor in this study, wetting angle corrections were made on second-run scans. That is, a complete intrusion-extrusion cycle was first performed in order to permanently trap mercury. During a second cycle the hysteresis loops closed, indicating no additional mercury retention. Figures 2a-2d illustrate that as the contact angle is increased for the intrusion scan and decreased for the extrusion scan, the two curves approach coincidence and can be made to superimpose. Thus, one can choose a contact angle for intrusion and find a corresponding angle for extrusion which will result in superimposition of the curves, e.g., curves II and III in Fig. 2b and curves I and II in Fig. 2d. Conversely, if a value of the contact angle for extrusion is chosen, a corresponding angle for intrusion can be found which will give superimposable curves.
Journal of Colloid and Interface Science, Vol, 80, No. 1, March 1981
However, the true contact angles for intrusion and extrusion remain unknown since an infinite number of choices are possible. The concept of markedly different contact angles for advancing and receding liquids on solid surfaces is a well-documented phenomenon (4). The influence of contact angle on hysteresis is not inconsistent with the pore potential which would act to delay extrusion until a pressure lower than the corresponding intrusion pressure is attained. Indeed it may well be that the changes in contact angle represent the mechanism by which the pore potential exerts its influence. REFERENCES 1. Lowell, S., Powder Technol. 25, 37 (1980). 2. Orr, C., Powder Technol. 3, 117 (1970). 3. Quantachrome Corp., 6 Aerial Way, Syosset, N.Y. 11791. 4. Adamson, A. W., "Physical Chemistry of Surfaces," 2nd ed., p. 359. Wiley-Interscience, New York, 1967.