Self‐Organization of Poly(ethylene oxide) on the Surface of Aqueous Salt Solutions

Abstract

It is demonstrated that stable Langmuir films of poly(ethylene oxide) (PEO) can be formed up to surface pressures of 30 mN m(-1) when potassium carbonate K2CO3 is added to the aqueous subphase. Generally, PEO homopolymer cannot stay on the water surface at a surface pressure ≥10 mN m(-1) due to its high water solubility. To prepare stable monolayer films, PEO can be modified with hydrophobic moieties. However, by exploiting the salting out effect by adding certain salts (K2CO3 or MgSO4) into the aqueous subphase, not only very stable films but also unusual self-organization can be achieved by the PEO homopolymer on the surface of the aqueous solution. Thus, a series of OH-terminated PEOs is found to form a stable monolayer at K2CO3 concentrations of 2 M and above in the aqueous subphase, and the stability of the film increases with an increase in K2CO3 concentration. Hysteresis experiments are also carried out. During the phase transition induced by progressive compression, self-organization into well-defined domains with sizes in the micrometer range are observed, and with further compression and holding of the film for 30 min and above the microdomains transform into a crystalline morphology as visualized by Brewster angle microscopy.

Polymer Crystallization on the Surface of Water or Aqueous Salt Solution

“…This agrees with reports on PEO monolayers that showed an increase in surface concentration of PEO when a salt was added to the subphase [51]. Furthermore, a plateau region is observed in the corresponding Langmuir isotherm on a 2 M and a 4 M K 2 CO 3 aqueous subphase [25]. During this transition, the formation of crystalline structures within the monolayer could be followed by BAM as demonstrated in Fig.…”

“…Recently, it has been demonstrated that PEO is able to crystallize on certain aqueous salt solutions [25]. The selection of suitable salts follows the so-called Hofmeister series [26,27].…”

“…When replacing water by aqueous salt solutions it is possible that PEO crystallizes upon compression on the solution-air interface [25]. For this purpose it is necessary to select a kosmotropic salt according to the Hofmeister series [26][27][28].…”

Foam Silica Films Synthesized by Calcium Chloride-Assisted Emulsification

“…Indeed, the PEG-400 is known as an hydrophilic polymer but it can display a "surfactant-like" behavior as it decreases the surface tension of water. [40][41][42][43][44][45][46][47][48] These observations may also explain the differences observed in the obtained porous structures, and how a classical surfactant like F-127 can stabilize for a longer time smaller droplets, delaying the coalescence, while the PEG-400 has a weaker ability to stabilize the droplets. Contact angles measurements (on PTFE substrate) have also been done using water.…”

“…A lot of studies are relative to the salt influence on the behavior of PEG or block copolymers. [45][46][47][48][49][50][51][52][53][54][55] PEG tends to form complex with salts and these complex are considered to have cations trapped within the PEO helices. Salts decrease the cloud point of PEG containing polymers and favorise their phase separation process.…”