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Possible evidence for the existence of a hairy layer at the surface of polymer latex particles †
Author(s) -
Said Ziad F. M.
Publication year - 1998
Publication title -
polymer international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.592
H-Index - 105
eISSN - 1097-0126
pISSN - 0959-8103
DOI - 10.1002/(sici)1097-0126(199812)47:4<459::aid-pi84>3.0.co;2-t
Subject(s) - electrolyte , emulsion polymerization , ionic strength , styrene , polymer , materials science , polymer chemistry , polymerization , monomer , chemical engineering , ionic bonding , chemistry , ion , composite material , organic chemistry , aqueous solution , copolymer , electrode , engineering
In this work, an attempt is made to verify the existence of a hairylayer at the surface of polymer latex particles, and determine itsthickness under different conditions. Two systems have been studied.In one system, sodium dodecyl sulphate (SDS) and sodiumdodecanoate (laurate‐SL) were used, separately, asemulsifiers in ab initio (unseeded) emulsionpolymerization of styrene carried out at different ionic strengths. Atlow levels of electrolyte (NaCl in the range 0·00–0·10M), the hydrodynamic radius( d H ) was found to decrease gradually,reaching a minimum value at 0·10M, about 7–9nm smallerthan the original value in the absence of electrolyte. At electrolytelevels higher than 0·10M, d H increasedmonotonically. In the first observation, the results are interpretedin terms of a hairy layer model, which suggests that the thickness ofthis layer is reduced by the presence of an electrolyte because ofcharge shielding, while the increased d H at highionic strength is interpreted in terms of coalescence between latexparticles. The extent of the effect depends mainly on theconcentration of emulsifier. In the second system, the effect on a seeded emulsionpolymerization of styrene was investigated. In this system, a seedlatex containing about 10% solids was prepared with SDS asemulsifier. The monomer was then further polymerized at differentionic strengths with no more added emulsifier. The effect on d H was very similar to that of the first system.However, in a previous investigation on this system( Polym . Int ., 40 (1996) 307) therate of seeded polymerization was not affected in the electrolyterange 0·0–0·1M, while it was found to increasewith increasing electrolyte level in the range0·10–0·20M. Post‐addition of electrolyte(0·0–0·1M) to the seed latex results ina 4–6nm size contraction due to an increase in thehydrophobicity of the surface, leading to a backward extension awayfrom the aqueous phase. © 1998 Society of ChemicalIndustry