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제올라이트의 표면 자유 에너지

이재영, 최형기*, 김상욱

서울시립대학교 화학공학과, *국립기술품질원 화학부

Surface Free Energy of Natural Zeolite as an Inorganic

Filler in Epoxy Composite

J. Y. Lee, H. K. Choi* and S. W. Kim

Dept. of Chem. Eng., The Univ. of Seoul, Seoul 130-743

*Div. of Chem., NITQ, Kwacheon 427-010

Introduction

The surface characteristics of solid materials are divided into two category. One is hydrophilic solid whose surface energy is high and the other is hydrophobic solid whose surface energy is low. To facilitate the adhesion of two different materials, the apolar surface should be modified into a high-energy polar surface or the polar surface should be changed to apolar surface by a number of methods. So, knowledge about solid surface free energy is very important for better insight in the processes occurring at the interfaces, both in pure and applied science. In this study, the surface free energy of the clinoptilolite type natural zeolite was studied.

Theory

Fig.1 Contact angles between liquid and solid surface.

The contact angle method has been used to get the surface characteristics of solids. When a liquid drop is put on the solid surface at equilibrium as shown in Fig.1, the interfacial tensions of solid/liquid,□SL, solid/vapor,□SV, and liquid/vapor,□LV can be expressed by the following Young's equation.

□LV ·cos□ = □SL - □SV                          (1)

Where, □ is contact angle. However, the contact angle for a particle can't be measured by the same method in Fig.1. To get the contact angle of a particle, wicking method is applied at constant temperature. In this method, the rate of penetration of probe liquids (usually n-alkane, water and formamide) through the packed solid particle in a closed tube is measured and the data are introduced to the following Washburn's equation.

[eqn: rm h sup 2 ~=~ {t·R·□ sub LV · cos□} OVER 2□]                          (2)

where, h is penetration height(cm), t is time(sec), R is the effective radius parameter(cm) and □ is viscosity of liquid(cP).

□LV ·cos□ in Eq.(1) can be obtained by Eq.(2) and □SL can be calculated by the following Wu's proposal.

[eqn: rm □ sub SL `=` □ sub LV `+` □ sub SV `-` 4 {□ sub LV sup d ·□ sub SV sup d} over{□ sub LV sup d `+` □ sub SV sup d} `-` 4 {□ sub LV sup n ·□ sub SV sup n} over{□ sub LV sup n `+` □ sub SV sup n}]       (3)

where, superscripts d and n are the apolar and polar components for solid and liquid, respectively.

Fig.2 FT-IR spectrum of the natural zeolite.

Experiment

The surface characteristics of clinoptilolite type natural zeolite form Kampo area in Korea to be used as an inorganic filler in epoxy composite were studied.

FT-IR analysis was carried out at a resolution of 2 cm-1 from 4000 cm-1 to 400 cm-1 and surface energy was measured by wicking method.

Results and Discussion

Fig.2 shows the FT-IR spectrum of the natural zeolite. The strongest vibrations in the range of 1294-837 cm-1 are assigned to the internal tetrahedron asymmetric stretch of Si(or Al)-O and the vibrations of 837-668 cm-1 are for the internal tetrahedron symmetric stretch of Si(or Al)-O. The Si(or Al)-O bending is appeared at 474.1 cm-1 and the band of 525.4 cm-1 is related to the presence of the double rings in the framework structures. The broad band of hydrogen-bonded OH is observed at 3453.2 cm-1 and the sharp band of isolated OH is shown at 3645.5 cm-1.

Fig.3 Penetration times of n-hexane, water and formamide

for natural zeolite.

Fig.3 shows the penetration times of the probe liquids, n-hexane for apolar component[eqn: rm □ sub SV sup d] determination, water and formamide for polar component[eqn: rm □ sub SV sup n]determination, i.e. electron acceptor[eqn: rm □ sub SV sup n+] and electron donor[eqn: rm □ sub SV sup n-]. The effective radius parameter, R was calculated by introducing the contact angle of zeolite/n-hexane, □=0 and □LV=18.4 mJ/m2 to Eq.(2) and the slope in Fig.3 was 0.0206, so R was 7.16×10-6cm. The contact angle, viscosity,[eqn: rm □ sub LV],[eqn: rm □ sub LV sup d] and[eqn: rm □ sub LV sup n] of the probe liquids were listed on Table 1 and these values are introduced to Eq.(3) to get the surface energy of the natural zeolite, which were as follows;[eqn: rm □ sub SV = 46.77 ~mJ/m sup 2],[eqn: rm □ sub SV sup d = 18.4 ~mJ/m sup 2] and[eqn: rm □ sub SV sup n = 28.37~ mJ/m sup 2]. These results means that the surface characteristics of the natural zeolite is polar due to the hydroxyl groups in Fig.2.

Table 1. The Contact Angle, Viscosity,[eqn: rm □ sub LV],[eqn: rm □ sub LV sup d] and[eqn: rm □ sub LV sup n]

of the probe liquids

Liquid	□ (degree)	□ (cP)	[eqn: rm □ sub LV] (mJ/m2)	[eqn: rm □ sub LV sup d] (mJ/m2)	[eqn: rm □ sub LV sup n] (mJ/m2)
n-Hexane	0	0.326	18.4	18.4	0
Water	79.7	1.00	72.8	21.8	51.0
Formamide	65.9	4.55	58.0	39.0	19.0

Conclusion

In FT-IR analysis, the broad band of hydrogen-bonded OH is observed at 3453.2 cm-1 and the sharp band of isolated OH is shown at 3645.5 cm-1. The surface energy of the natural zeolite were[eqn: rm □ sub SV = 46.77 ~mJ/m sup 2],[eqn: rm □ sub SV sup d = 18.4 ~mJ/m sup 2] and[eqn: rm □ sub SV sup n = 28.37~ mJ/m sup 2]. These results means that the surface characteristics of the natural zeolite is polar due to the hydroxyl groups.

References

1. A. Ontiveros-Ortega, M. Espinosa-Jimenez, E. Chibowski and F. Gonzalez-Caballero,

J. Colloid Interface Sci., 202, 189(1998).

2. C. J. Van Oss, R. F. Giese, Z. Li, K. Murphy, J. Norris, M. K. Chaudhury

and R. J. Good, "Contact Angle, Wettability and Adhesion", ed. K. L. Mittal,

VSP, p.269 (1993).

3. J. Y. Lee, M. J. Shim and S. W. Kim, Mater. Chem. Phys., 48, 36(1997).