Water structure and changes in thermal stability of the system poly(ethylene oxide)–water

Abstract

The phase behaviour of aqueous solutions of poly(ethy1ene oxide), PEO, is analysed by means of a structural model of the system and a simple statistical-mechanical model based thereupon. The intention is to elucidate the structural questions involved in the water-PEO coupling and to gain some insight in possible consequences of this coupling. The experimental partial molar enthalpy and entropy of water can be reproduced, at least in fairly dilute solutions, if a zone with increased structuring of the water is assumed to exist around the PEO chain. The phase separation that takes place at high temperatures is traced back to the increase in total extension of the zones of enhanced water structure that occurs when the water content is increased. The chain-length dependence of the location of the solubility gap is mainly determined by the combinatorial entropy of the chains. The water solubility of PEO, which is unique in this respect among the polyethers, can be explained in terms of a good structural fit between the water and the polymer.

A Review of Recent Studies on Aqueous Binary Mixed Surfactant Systems

“…Different from the present results, azeotropic points (Azp) were very clearly found for SDS/MEGA-n's mixed systems (at X 2 = 0.25 for SDS/MEGA-8 mixed system, at X 2 = 0.33 for SDS/MEGA-9 mixed system and at X 2 = 0.50 for SDS/MEGA-10 mixed system) 38) . In addition, such an azeotropic phenomenon as seen here has been observed even for mixtures of MEGA-8, -9 and -10 with perfluorooctanoate (SPFO) 15,17,42,43) , although a kind of mutual phobicity acts between hydrocarbon and fluorocarbon chains 42,49) , indicating that the interaction between head groups plays a great role for mixed micelle formation 54,55) .…”

“…From the table it can be seen that the mixed systems of MEGA-9 or MEGA-10 with surfactants having a single alkyl chain, such as SDS, a-SMy Me and a-SMy iPr and even SPFO which has a phobicity against hydrocarbon, show a marked synergism. Even the hybrid surfactant FC6-HC4 having a fluorocarbon chain revealed to some appreciable extent a positive synergism; this also suggests that the interaction between head groups or steric fitness of different groups also contributes to the display of synergism 54,55) .…”

“…in the cases of pure C 12 E 10 and Brij56 suggests that NaCl removes water from near the micelle and thereby helps the micelles to approach each other easily. According to Kjellander et al,55) the formation of clouds is entropy-dominated. The ethylene oxide group is highly hydrated, and the nonionic micelles are expected to have water deep inside.…”

Thermodynamics of the self-assembly of non-ionic chromonic molecules using atomistic simulations. The case of TP6EO2M in aqueous solution

“…28 The experimental values range between 0.5 and 6 water molecules per EO group, depending on the on the experimental technique applied, [54][55][56][57][58] with larger numbers associated with both direct and indirect (via water bridges) bound water. 54,56,59,60 …”

Synthesis and Solubility of (Mono-) End-Functionalized Poly(2-hydroxyethyl methacrylate-g-ethylene glycol) Graft Copolymers with Varying Macromolecular Architectures

“…23 For PEG, this interesting behavior has been explained in terms of entropic effects of fitting PEO molecules into the water network, 24 conformationdependent hydrophobicity, 25 and competititive etherwater and water-water H-bonding. 26 …”