Coil Interpenetration, Segment Aggregation and Adsorption of PEG at Water/Air Interface

Poly(ethylene glycol) (PEG), both as an oligomer and as a high molecular weight polymer, has been used as a surfactant active component in many applications, in its pure and unmodified structure, or as a block segment within more complex structures. Apart from assuming helical or coil conformations it may also undergo aggregation, depending on the solvent. In this work, we characterized the aggregation of PEG in water using surface tensiometry and turbidimetry. Aggregation was characterized by a non-persistent surface tension plateau at higher PEG contents and confirmed by turbidimetry, which was correlated to the derivative of osmotic pressure in relation to concentration. One can divide a surface tension-concentration curve into two regions, delimited by a characteristic concentration: one following a Langmuir adsorption isotherm (starting from a plateau equal to pure water surface tension) ending in a second plateau, and a second one (beginning at this plateau) following a Freundlich isotherm. The calculated surface excess for PEG segment adsorption was consistent with segment aggregation, indicating more two characteristic concentrations correlated to this occurrence. A total of three characteristic mer concentrations were found (6.2 × 10 −7 , 6 × 10 −6 , and 2 × 10 −4 mol L −1 ) and related to PEG segment aggregation states.