PMID- 15082378
OWN - NLM
STAT- PubMed-not-MEDLINE
DCOM- 20050705
LR  - 20091111
IS  - 0021-9797 (Print)
IS  - 0021-9797 (Linking)
VI  - 273
IP  - 2
DP  - 2004 May 15
TI  - Some anomalous effects of sodium ions on the electrophoretic mobility and 
      heteroaggregation of microgel particles.
PG  - 435-41
AB  - Experiments on the kinetics of heteroaggregation between oppositely charged 
      particles, using both dynamic light scattering and turbidity methods, are 
      reported. The negatively charged particles were cross-linked poly( [Formula: see 
      text] -isopropylacrylamide) [PNIPAM] microgel particles, prepared using a 
      carboxylic-acid-based initiator; these particles are swollen at room temperature. 
      The positive particles were poly(4-vinylpyridine) [P4VP] particles, prepared 
      using an amidinium-based initiator; such particles do not respond to temperature 
      changes but do swell below pH approximately 4, where the pyridine moieties become 
      protonated. As expected, the rate of heteroaggregation was shown to be largely 
      independent of added salt concentration (up to approximately 20 mM), for a 
      variety of alkali metal chlorides (MCl, where M = Li, Na, K, or Rb). However, an 
      unexpected, significant decrease in the aggregation rate was observed at certain 
      specific sodium chloride concentrations (typically at approximately 1 and also 
      approximately 4 mM). Similar effects were not seen with the other alkali metal 
      chloride salts. This strange effect was eventually attributed to the fact that 
      the net charge on the positively charged P4VP particles had been reduced by the 
      adsorption of (anionic) silicate species leached from the glassware container. 
      Sodium silicates are known to be significantly more soluble than those of the 
      other alkali metal ions, particularly at high pH. Moreover, P4VP particles 
      dispersed in water, ostensibly at neutral pH, do buffer the aqueous medium to pH 
      values around 9 or higher. This mechanism was confirmed by determining the 
      electrophoretic mobility of the P4VP particles as a function of pH in the 
      presence of the various alkali metal chloride salts. The mobility remained 
      positive in 1 mM salt solutions over the pH range 3 to 11 for all the salts, 
      except for sodium chloride; in that case the mobility reversed sign at alkaline 
      pH values. A similar effect was observed for a cationic polystyrene latex sample, 
      prepared with the same amidinium-based initiator. These experiments demonstrate 
      the importance of soluble silicates, leached from glass storage vessels, 
      particularly in the presence of sodium ions. Needless to say, the "anomalous" 
      effects disappeared when plastic storage vessels were used in place of the glass 
      ones.
FAU - Routh, Alexander F
AU  - Routh AF
AD  - School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK.
FAU - Vincent, Brian
AU  - Vincent B
LA  - eng
PT  - Journal Article
PL  - United States
TA  - J Colloid Interface Sci
JT  - Journal of colloid and interface science
JID - 0043125
EDAT- 2004/04/15 05:00
MHDA- 2004/04/15 05:01
CRDT- 2004/04/15 05:00
PHST- 2003/06/25 00:00 [received]
PHST- 2004/02/23 00:00 [accepted]
PHST- 2004/04/15 05:00 [pubmed]
PHST- 2004/04/15 05:01 [medline]
PHST- 2004/04/15 05:00 [entrez]
AID - S0021979704002127 [pii]
AID - 10.1016/j.jcis.2004.02.049 [doi]
PST - ppublish
SO  - J Colloid Interface Sci. 2004 May 15;273(2):435-41. doi: 
      10.1016/j.jcis.2004.02.049.