How I can increase the micellar aggregation number of nonionic surfactant?
I want increase the hydrophobic microblock length of polymerization.
NaCl dehydrates hydrophilic group nonionic surfactants. Therefore, CMC decreases. The length of the hydrophobic block polymer micelles is not reduced.
For non-ionic surfactants, generally those with a hydrophilic PEO sequence, the water solubility of this sequence is due to H bond interaction of water with the EO units. Therefore it is well-known that the water solubility of PEO decreases with increasing temperature. At a constant hydrophobic sequence of the surfactant the CMC decreases with increasing temperature The aggregation number of the micelles is consequently increasing with temperature..
As above mentioned by Prof. Mirgorod, NaCl decreases the CMC, the cloud point temperature leading to enhanced aggregation. NaCl has somehow a similar effect as a temperature increase.
Even in Google you may find extensive literature on this topic !
See for instance J.A.Molina-Bolivar et al J.Chem. Thermodynamics 2013 57 59-66 and related articles of this research group
There are several factors that influence on the CMC, aggragation number (AN) and cloud point (CP) of nonionic surfactants (NS). Addition of electrolytes usually decrease the CMC, AN and CP of NS. The greater number of oxyettylene (OE) chain the greater should be salt concentration. Activity of salt depends on the position in lyotropic series and is explained by dehydration of OE chains. At constant OE units, the increase in the alkyl chain decreases the CMC and increases the AN. For a fixed alkyl chain the increase of OE units causes an increase of CMC and decrease of AN. So, the greatest AN have NS with 5-7 OE units.
The increase of temperature also dehydrates of OE chains, therefore, leads to rapid decrease in CMC, CP and rapid increase in AN.
just quick adds.
that 's the reason why, on cloud point specification (acc. to EN1890), suppliers could use 1% of NS in water method or 1% of NS in a 5% soln. of NaCl, depending of the EO amount. (till 10%)
higher NaCl% in solution, lower cloud point of the NS (//CMC)
as argued above all additives decreasing cloud point increase aggregation. Therefore also organic additives decreasing cloud point like xylenes and many more can serve this purpose.
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