Alkali-Soluble Resin을 포함한 PBMA 라텍스 필름의 표면 성질에 미치는 Annealing 효과

신진섭, 이덕연, 김중현

연세대학교 화학공학과 고분자소재연구실

Effect of Annealing on Surface Energetics of PBMA Latex Films Containing Alkali-Soluble Resin

Jin-Sup Shin, Doug-Youn Lee and Jung-Hyun Kim

Department of Chemical Engineering, Yonsei University,

134 Shinchon-dong, Sudaemoon-ku, Seoul 120-749, Korea

INTRODUCTION

Although monodispersity and the particle-size diameter are essential factors determining film properties, it is also important to establish interactions between individual latex components. For example, since the properties of latex films may be influenced by the surface activity of surfactants, determination of the distribution of surfactant throughout the latex film is essential and plays a significant role in the film properties such as adhesion and other physical properties. Especially, the latex composition at the film-air interfaces is of particular interest.

The interfacial characteristics of a material in real applications, many of which involve aqueous environments, are usually quite different from those determined in air or vacuum. This situation can be best understood by considering the top surface region of a material as the surface state, which is significantly different from the state of bulk material.[1]

Recently, Zhao et al. demonstrated the kinetics of surfactant exudation in latex films containing anionic surfactants by attenuated total reflectance Fourier transform infrared (ATR FTIR). Surfactant enrichment at both the film-air and film-substrate interface was observed.[2] Other studies emphasized the fact that surfactant was likely to undergo phase segregation with the latex polymer, forming surfactant domains in the bulk of the film or migrating to the surface.[3]

A modern analytical tool such as X-ray photoelectron spectroscopy (XPS) has very limited use in dealing with the quick surface-configuration change which occurs in water at ambient temperature. While the simple method of contact angle measurement could provide information change due to the change of surrounding medium, the interpretation of data depends entirely on the basic concept of the interfacial phenomenon.[4]

The aim of the present study is to investigate the effects of postadded alkali-soluble resin, poly(styrene/alpha-methylstyrene/acrylic acid) [SAA], to emulsifier-free monodispersed poly(n-butyl methacrylate) [PBMA] latexes on surface properties with various annealing temperature, its duration and concentration of SAA .[5]

The dynamic (receding) contact angles of 50/50 wt% mixture of ethylene glycol and D.D.I. water on polymeric surfaces were investigated by contact angle goniometer. The exudation of SAA molecules to film-air interface was investigated by ATR FT-IR.

EXPERIMENTAL

A known weight of a SAA solution at 10.0 wt% was added slowly to 100g of emulsifier-free monodispersed PBMA latex (solid content: 10%). A series of mixed PBMA latex dispersion containing various weight of SAA solution  was prepared. All films were air-dried for 24h at 25℃. The films prepared on the glass were studied by ATR and by contact angle.

A contact angle goniometer was operated, using the injected a drop of 50/50 wt% mixture of ethylene glycol and D.D.I. water at 25℃. The data was obtained at more than 10 points on each specimen, and the data collected for each material at each period were averaged.

RESULTS and DISCUSSION

The surface properties of PBMA latex films containing SAA were investigated with annealing time, temperature, and various SAA concentration. As annealing at 90℃ and 150℃, the increase of SAA  concentration in the film surface was observed by ATR FT-IR. Especially, the exudation of SAA to film surface was clearly observed at 150℃ above glass transition temperature of SAA. This resulted in the change of film surface properties. Figure 1 and Figure 2 illustrate the exudation of SAA to film surface during annealing at 90℃ and 150℃, respectively.

The values of contact angles of pure SAA films prepared from water and THF as solvents respectively were quite different each other. These results had their origin in difference of chain conformation between pure SAA film prepared from water and from THF as solvents. Before annealing, the values of contact angles of all PBMA films containing SAA were similar to that of pure SAA film prepared from water as a solvent. These results explained that the chain conformation of SAA in the PBMA films were similar to that of pure SAA prepared from water as a solvent. The value of contact angle of PBMA film containing 5wt% SAA is slightly different from that of the other PBMA films containing SAA. This result was explained by the fact that the SAA in the  PBMA film containing 5wt% SAA did not sufficiently cover the most sites of film-air interface. The results of contact angles of all film samples shown in Table 1 and Figure 3.

The exudation of SAA in the film to film surface could make SAA cover sufficiently the most sites of film-air interface after annealing at 150℃.  After annealing at 90℃ and 150℃ respectively, the values of contact angles of all PBMA films containing SAA, including the PBMA latex film containing 5wt% SAA, were similar to that of pure SAA film prepared from THF as a solvent. These results explained that the chain conformation of SAA in the  PBMA films were transformed into that of pure SAA film prepared from THF during annealing process. The exudation and conformation change of SAA molecules were shown in Figure 4.

We could observe that annealing at elevated temperature led to exudation of SAA to film surface and conformational change of SAA.

REFERENCES AND NOTES

1. Yasuda H., Charlson E. J., Charlson E.M., Yasuda T., Miyama M., and Okuno T., Langmuir, 7, 2394 (1991).

2. Zhao C. L., Holl Y., Pith T., and Lambla M., Coll. Polym. Sci., 265, 823 (1987).

3. Roulstone B. J., Wilkinson M. J., and Hearn J., Polym. Intern., 27, 43 (1992).

4. Holmes-Farley S. R. and Whitesides G. M., Langmuir, 3, 62 (1987).

5. Park Y. J., Lee D. Y., Ho C. C., and Kim J. H., Langmuir, in press.

Table 1. Contact angles of pure PBMA, pure SAA, and a series of mixture of PBMA and SAA

a 90℃ and 150℃ are annealing temperature.

b contact angle measured at 1 minutes later after dropping a 50/50 wt% mixture of ethylene glycol and D.D.I. water at 25℃.

c contanct angle measured at 40 minutes later after dropping a 50/50 wt% mixture of ethylene glycol and D.D.I. water at 25℃.

d wt% based on PBMA

Film Samples	before annealing		90 ℃a		150 ℃a
	□ib	□fc	□i	□f	□i	□f
PBMA+5wt%d SAA	67.50	60.90	72.00	63.60	78.23	70.68
PBMA+10wt% SAA	65.20	57.10	75.98	67.50	78.61	70.30
PBMA+20wt% SAA	62.50	57.10	76.49	68.10	78.13	70.45
PBMA+40wt% SAA	62.69	56.40	76.48	68.60	78.89	70.44
SAA(prepared from water)	62.32	56.83	-	-	-	-
SAA (prepared from THF)	81.68	71.73	-	-	-	-
pure PBMA	76.28	68.40	-	-	-	-

Figure . ATR FTIR spectra in the 720 to 680□-1 after annealing PBMA film containing 40wt% SAA  at 90℃ ; (A) before annealing ; (B) 1 hour ; (C) 2 hour ; (C) 3 hour.

Figure . ATR FTIR spectra in the 720 to 680□-1 after annealing PBMA film containing 40wt% SAA  at 150℃ ; (A) before annealing ; (B) 1 hour ; (C) 2 hour ; (C) 3 hour.

Figure . Decay characteristics of contact angle of EG(50%) + water (50%) on PBMA series samples with concentration of SAA at 25℃ before annealing.

Figure . Decay characteristics of contact angle of EG(50%) + water (50%) on PBMA series samples with concentration of SAA at 25℃ after annealing at 150℃.