Journal of Colloid and Interface Science 431 (2014) 200–203
Contents lists available at ScienceDirect
Journal of Colloid and Interface Science www.elsevier.com/locate/jcis
Measuring contact angles inside of capillary tubes with a tensiometer C.W. Extrand ⇑, Sung In Moon Entegris, Inc., 101 Peavey Road, Chaska, MN 55318, United States
a r t i c l e
i n f o
Article history: Received 25 April 2014 Accepted 16 June 2014 Available online 23 June 2014 Keywords: Wetting Contact angles Capillary tubes Hollow fibers
a b s t r a c t We describe a new tensiometry method that allows for determination of wetting inside small diameter tubes or hollow fibers, where the maximum force from the ultimate rise height of liquid is used to estimate advancing contact angles. The technique was first validated with transparent tubes of glass, poly(carbonate) (PC) and poly(tetrafluoroethylene) (PTFE) using four liquids: isopropanol, silicone oil, ethylene glycol and water. Advancing contact angles measured with the tensiometer agreed well with those estimated from final rise height. As this tensiometry technique does not require a view of the liquid, it can be used to measure the wettability inside opaque tubes. We demonstrated this with poly(ether ether ketone) (PEEK) tubes. Ó 2014 Elsevier Inc. All rights reserved.
1. Introduction Contact angle measurements are used widely to assess wettability, cleanliness, surface chemistry and the potential for creating a high strength adhesive bond [1]. The most common method of measuring contact angles involves the use of sessile drops on flat surfaces [2,3]. Alternatively, tensiometers are frequently used to evaluate curved solids, such as rods and fibers. Traditionally in tensiometry, the solid is immersed or withdrawn from a liquid while measuring force [4]. Proper analysis of the interplay between capillary forces and buoyancy allows for indirect estimation of contact angles [5,6]. Tubes and fibers produced for industrial applications may have different inner and outer surfaces. For example, during extrusion of plastic tube, molten polymer usually passes through a liquid cooling tank where its outer surface is rapidly quenched while in contact with various sizing fixtures; in contrast, its inner surface cools slowly in the presence of a gas without further mechanical manipulation. Consequently, the inner and outer surfaces of extruded tubes and hollow fibers may have distinct morphologies. Moreover, the chemistry of the inner surface may be intentionally modified to improve hydrophobicity and/or the outer surface may be rendered more hydrophilic to improve adhesion. In recent work, we developed a new tensiometry technique for evaluating the wetting inside capillary tubes and hollow fibers [7]. Rather than immersing, capillary tubes of diameter D were brought into contact with a liquid of surface tension c and density of q, such
⇑ Corresponding author. E-mail address: [email protected] (C.W. Extrand). http://dx.doi.org/10.1016/j.jcis.2014.06.032 0021-9797/Ó 2014 Elsevier Inc. All rights reserved.
that their bottoms just touched the surface of the liquid, Fig. 1. A meniscus formed around the inner and outer diameter, wetting the inside of the tube with a contact angle of h. If h was 90° inside a tube. Having demonstrated the ability to measure contact angles inside tubes using a tensiometer, we tried opaque PEEK tubes where visual measurement of the liquid height is not an option. Forces and contact angles, measured with three liquids, are included in Table 2. These values are similar to those previously reported for PEEK [12–14]. In the absence of a tensiometer, a tube of known mass could be manually brought into contact with a liquid and then weighed after liquid has risen in it. The force of the liquid mass could be plugged into Eq. (3) to estimate h inside the tube. However, using a tensiometer for capillary rise has a number of advantages over manual measurement. A tensiometer permits for slow, controlled movement of the tube (or liquid) and allows the operator to stop the relative movement of the capillary at the instant it touches the surface of the liquid. If the tube is plunged below the surface and then withdrawn, the measured contact angle may not be an advancing value, but a receding or intermediate value. If the tube is opaque, the operator cannot see the rise of liquid and thus cannot know when the liquid has reached its ultimate height. On the
other hand, with a tensiometer, one can monitor rise via force and thus know definitely when the liquid has reached its ultimate height. Use of a tensiometer also minimizes handling or tilting. While we have focused on wetting and contact angles inside of tubes, this general method can also be used to examine their exteriors (a more traditional use of a tensiometer). Contact angles on the outer surfaces (ho) can be estimated from the maximum value of the force associated with meniscus formation on the outer surface of the tube (fo,max) and its outer diameter (Do),
ho ¼ Arc cos
fo;max : pDo c
ð6Þ
For example, ethylene glycol gave advancing contact angles on the outside of tubes of ho 0–10° for glass, ho = 65° for PC and ho = 63° for PEEK. The values for the outer surface of the PC and PEEK tubes were slightly higher than those measured on the inside of the same tubes. This implies that there may be differences in chemical composition and/or roughness of the inner and outer surfaces of these capillary tubes. 5. Conclusions We successfully employed a simple tensiometry method that allows us to isolate the force associated with liquid rising inside of capillary tubes. That force, along with the tube diameter and surface tension of the liquid, can be used to estimate advancing contact angles inside of tubes. This technique can be used to measure contact angles inside opaque tubes, where the height of the liquid cannot be observed directly. Acknowledgments We thank Entegris management for supporting this work and allowing publication. Also, thanks to T. Edlund, J. McDaniel, L. Monson, J. Pillion, B. Powell and S. Tison for their suggestions on the technical content and text. References [1] S. Wu, Polymer Interface and Adhesion, Marcel Dekker, New York, 1982. [2] A.W. Adamson, Physical Chemistry of Surfaces, fifth ed., Wiley, New York, 1990.
C.W. Extrand, S.I. Moon / Journal of Colloid and Interface Science 431 (2014) 200–203 [3] P.C. Hiemenz, R. Rajagopalan, Principles of Colloid and Surface Science, third ed., CRC Press, New York, 1997. [4] L. Wilhelmy, Ann. Phys. 195 (6) (1863) 177–217. [5] J. Chappuis, J.-M. Georges, J. Chim. Phys. 71 (4) (1974) 567–575. [6] D.A. Martin, E.A. Vogler, Langmuir 7 (2) (1991) 422–429. [7] C.W. Extrand, S.I. Moon, J. Colloid Interface Sci. 407 (1) (2013) 488–492. [8] P.S. Laplace, Mécanique Celeste. Courier: Paris, 1805; vol. t. 4, Supplément au Xe Livre.
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[9] R.C. Weast, Handbook of Chemistry and Physics, 73rd ed., CRC, Boca Raton, FL, 1992. [10] J.R. Dann, J. Colloid Interface Sci. 32 (2) (1970) 302–320. [11] C.W. Extrand, S.I. Moon, Langmuir 26 (14) (2010) 11815–11822. [12] N.L. Franchina, T.J. McCarthy, Macromolecules 2411 (1991) 3045–3049. [13] I. Mathieson, R.H. Bradley, Int. J. Adhes. Adhes. 16 (1) (1996) 29–31. [14] N. Inagaki, S. Tasaka, T. Horiuchi, R. Suyama, J. Appl. Polym. Sci. 68 (2) (1998) 271–279.
Contents lists available at ScienceDirect
Journal of Colloid and Interface Science www.elsevier.com/locate/jcis
Measuring contact angles inside of capillary tubes with a tensiometer C.W. Extrand ⇑, Sung In Moon Entegris, Inc., 101 Peavey Road, Chaska, MN 55318, United States
a r t i c l e
i n f o
Article history: Received 25 April 2014 Accepted 16 June 2014 Available online 23 June 2014 Keywords: Wetting Contact angles Capillary tubes Hollow fibers
a b s t r a c t We describe a new tensiometry method that allows for determination of wetting inside small diameter tubes or hollow fibers, where the maximum force from the ultimate rise height of liquid is used to estimate advancing contact angles. The technique was first validated with transparent tubes of glass, poly(carbonate) (PC) and poly(tetrafluoroethylene) (PTFE) using four liquids: isopropanol, silicone oil, ethylene glycol and water. Advancing contact angles measured with the tensiometer agreed well with those estimated from final rise height. As this tensiometry technique does not require a view of the liquid, it can be used to measure the wettability inside opaque tubes. We demonstrated this with poly(ether ether ketone) (PEEK) tubes. Ó 2014 Elsevier Inc. All rights reserved.
1. Introduction Contact angle measurements are used widely to assess wettability, cleanliness, surface chemistry and the potential for creating a high strength adhesive bond [1]. The most common method of measuring contact angles involves the use of sessile drops on flat surfaces [2,3]. Alternatively, tensiometers are frequently used to evaluate curved solids, such as rods and fibers. Traditionally in tensiometry, the solid is immersed or withdrawn from a liquid while measuring force [4]. Proper analysis of the interplay between capillary forces and buoyancy allows for indirect estimation of contact angles [5,6]. Tubes and fibers produced for industrial applications may have different inner and outer surfaces. For example, during extrusion of plastic tube, molten polymer usually passes through a liquid cooling tank where its outer surface is rapidly quenched while in contact with various sizing fixtures; in contrast, its inner surface cools slowly in the presence of a gas without further mechanical manipulation. Consequently, the inner and outer surfaces of extruded tubes and hollow fibers may have distinct morphologies. Moreover, the chemistry of the inner surface may be intentionally modified to improve hydrophobicity and/or the outer surface may be rendered more hydrophilic to improve adhesion. In recent work, we developed a new tensiometry technique for evaluating the wetting inside capillary tubes and hollow fibers [7]. Rather than immersing, capillary tubes of diameter D were brought into contact with a liquid of surface tension c and density of q, such
⇑ Corresponding author. E-mail address: [email protected] (C.W. Extrand). http://dx.doi.org/10.1016/j.jcis.2014.06.032 0021-9797/Ó 2014 Elsevier Inc. All rights reserved.
that their bottoms just touched the surface of the liquid, Fig. 1. A meniscus formed around the inner and outer diameter, wetting the inside of the tube with a contact angle of h. If h was 90° inside a tube. Having demonstrated the ability to measure contact angles inside tubes using a tensiometer, we tried opaque PEEK tubes where visual measurement of the liquid height is not an option. Forces and contact angles, measured with three liquids, are included in Table 2. These values are similar to those previously reported for PEEK [12–14]. In the absence of a tensiometer, a tube of known mass could be manually brought into contact with a liquid and then weighed after liquid has risen in it. The force of the liquid mass could be plugged into Eq. (3) to estimate h inside the tube. However, using a tensiometer for capillary rise has a number of advantages over manual measurement. A tensiometer permits for slow, controlled movement of the tube (or liquid) and allows the operator to stop the relative movement of the capillary at the instant it touches the surface of the liquid. If the tube is plunged below the surface and then withdrawn, the measured contact angle may not be an advancing value, but a receding or intermediate value. If the tube is opaque, the operator cannot see the rise of liquid and thus cannot know when the liquid has reached its ultimate height. On the
other hand, with a tensiometer, one can monitor rise via force and thus know definitely when the liquid has reached its ultimate height. Use of a tensiometer also minimizes handling or tilting. While we have focused on wetting and contact angles inside of tubes, this general method can also be used to examine their exteriors (a more traditional use of a tensiometer). Contact angles on the outer surfaces (ho) can be estimated from the maximum value of the force associated with meniscus formation on the outer surface of the tube (fo,max) and its outer diameter (Do),
ho ¼ Arc cos
fo;max : pDo c
ð6Þ
For example, ethylene glycol gave advancing contact angles on the outside of tubes of ho 0–10° for glass, ho = 65° for PC and ho = 63° for PEEK. The values for the outer surface of the PC and PEEK tubes were slightly higher than those measured on the inside of the same tubes. This implies that there may be differences in chemical composition and/or roughness of the inner and outer surfaces of these capillary tubes. 5. Conclusions We successfully employed a simple tensiometry method that allows us to isolate the force associated with liquid rising inside of capillary tubes. That force, along with the tube diameter and surface tension of the liquid, can be used to estimate advancing contact angles inside of tubes. This technique can be used to measure contact angles inside opaque tubes, where the height of the liquid cannot be observed directly. Acknowledgments We thank Entegris management for supporting this work and allowing publication. Also, thanks to T. Edlund, J. McDaniel, L. Monson, J. Pillion, B. Powell and S. Tison for their suggestions on the technical content and text. References [1] S. Wu, Polymer Interface and Adhesion, Marcel Dekker, New York, 1982. [2] A.W. Adamson, Physical Chemistry of Surfaces, fifth ed., Wiley, New York, 1990.
C.W. Extrand, S.I. Moon / Journal of Colloid and Interface Science 431 (2014) 200–203 [3] P.C. Hiemenz, R. Rajagopalan, Principles of Colloid and Surface Science, third ed., CRC Press, New York, 1997. [4] L. Wilhelmy, Ann. Phys. 195 (6) (1863) 177–217. [5] J. Chappuis, J.-M. Georges, J. Chim. Phys. 71 (4) (1974) 567–575. [6] D.A. Martin, E.A. Vogler, Langmuir 7 (2) (1991) 422–429. [7] C.W. Extrand, S.I. Moon, J. Colloid Interface Sci. 407 (1) (2013) 488–492. [8] P.S. Laplace, Mécanique Celeste. Courier: Paris, 1805; vol. t. 4, Supplément au Xe Livre.
203
[9] R.C. Weast, Handbook of Chemistry and Physics, 73rd ed., CRC, Boca Raton, FL, 1992. [10] J.R. Dann, J. Colloid Interface Sci. 32 (2) (1970) 302–320. [11] C.W. Extrand, S.I. Moon, Langmuir 26 (14) (2010) 11815–11822. [12] N.L. Franchina, T.J. McCarthy, Macromolecules 2411 (1991) 3045–3049. [13] I. Mathieson, R.H. Bradley, Int. J. Adhes. Adhes. 16 (1) (1996) 29–31. [14] N. Inagaki, S. Tasaka, T. Horiuchi, R. Suyama, J. Appl. Polym. Sci. 68 (2) (1998) 271–279.
