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The adsorbability of bovine serum albumin (BSA) onto styrene/acrylic acid copolymer (PS/PAA) latex prepared without emulsifier was investigated as a function of pH and ionic strength. Polystyrene (PS) latex was used as a reference sample. The adsorption isotherms of BSA onto PS/PAA latices showed a stepwise nature. The thickness of the adsorbed BSA monolayer suggested that BSA molecules adsorbed onto PS/PAA2 latex (here, the subscript, i. e., 2, represents the tool % of acrylic acid used in copolymerization) in a "side-on" mode near the isodectric point (IEP) of this protein. However, in the case of PS/PAAs latex, a portion of the BSA molecules probably adsorbed in a "loop" or an "end-on" mode. The amount of BSA adsorbed onto PS/PAA latices greatly depended on pH and ionic strength; its value showed a maximum in the neighborhood of the IEP of BSA as in PS latex. The amount adsorbed onto PS/PAA latices except in the alkaline pH region was greater than that onto PS latex. Moreover, the amount adsorbed onto PS/PAA 5 latex was greater than that onto PS/PAA2 latex. Both these results are probably attributed to hydrogen bonding between BSA molecule and PS/PAA latex. It was found that the adsorbability of BSA especially at a high ionic strength greatly depended on the surface properties of polymer latices.

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SynopsisSurface characteristics of styrene/acrylamide/acrylic acid copolymer and styrene/2-hydroxyethyl methacrylate/acrylic acid copolymer latexes prepared without emulsifier using potassium persulfate as initiator and their colloidal stabilities were investigated. The negative S-potentials decreased with increasing the amount of acrylamide and 2-hydroxyethyl methacrylate copolymerized. In spite of the increase in surface charge density, the negative {-potentials decreased through the maximum with increasing pH. The colloidal stabilities for NaCl concentration were remarkably enhanced with increasing both pH and the amount of acrylamide and 2-hydroxyethylmethacrylate. These results suggest that the contraction and expansion of water-soluble polymer layer surrounding the particles play an important role in the surface properties.

The surface characteristics of carboxylated polymer latices acid copolymer (PS/PAA) and styrene/methacrylic acid copolymer were investigated. Polystyrene (PS) latex was used as a reference sample. These latices were prepared in a soap-free system, using potassium persulfate as the initiator. Conductometric titration curves of PS and carboxylated latices showed both strong and weak acid groups to exist on the surface of latex particles. The surface charge density (o') for PS/PAA latex was proportional to the amount of acrylic acid (AA) used in the copolymerization (thus, CJ-for PS/PAA5 latex was larger than that for PS/PAA2 latex; the subscripts 5 and 2 represent the of AA monomers used in the copolymerization). However, CJ for PS/PMAA5 latex was smaller than that for PS/PAA5 latex, although the of acid monomers used in the copolymerization was the same for both latices. CJ for carboxylated latices increased with increasing pH, but the pH dependence of CJ for PS latex was not very pronounced. The (-pH curves for these latices were considerably different from the CJ-pH curves. This is probably because the Stern potential and the position of the shear plane in the electrical double layer differ between the two latices. Methylene Blue adsorption onto PS and PS/ PAA latices was measured as a function of pH. The overall tendency of the dye adsorption was more similar to the CJ-pH curves than the (-pH curves. KEY WORDS Surface Characterization I Soap-Free/ Carboxylated Latex I Conductometric and Potentiometric Titrations I (-Potential I Methylene Blue Adsorption I

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