Entropy of aqueous surfaces. Application to polymeric Langmuir films
Deschênes, Louise ; Lyklema, Hans ; St-Germain, François - \ 2017
Advances in Colloid and Interface Science 247 (2017). - ISSN 0001-8686 - p. 149 - 162.
Jones-Ray effect - Langmuir monolayers - PEO - PPO - Surface entropy - Surface tension
Measuring surface (excess) entropies provides a bounty of valuable structural information that is hard to obtain otherwise. In the paper these quantities are defined and procedures of measurements discussed. Mostly they involve measurements at different temperatures. A review is given for interfaces with aqueous solutions in the absence of polymers. This review illustrates how, sometimes unanticipated, pieces of information are obtained, for example with cloud seeding and a possible explanation of the Jones-Ray effect. As a novel extension the procedure is applied to deposited, or Langmuir, monolayers of poly(ethylene oxide)-poly(propylene oxide) block copolymers. It will be shown how the various phase transitions and associated configurations of these polymers can be recognized and monitored.
Phase transitions in polymer monolayers : Application of the Clapeyron equation to PEO in PPO-PEO Langmuir films
Deschênes, Louise ; Lyklema, J. ; Danis, Claude ; Saint-Germain, François - \ 2015
Advances in Colloid and Interface Science 222 (2015). - ISSN 0001-8686 - p. 199 - 214.
Clapeyron - Monolayers - PEO - Phase transition - PPO
In this paper we investigate the application of the two-dimensional Clapeyron law to polymer monolayers. This is a largely unexplored area of research. The main problems are (1) establishing if equilibrium is reached and (2) if so, identifying and defining phases as functions of the temperature. Once this is validated, the Clapeyron law allows us to obtain the entropy and enthalpy differences between two coexisting phases. In turn, this information can be used to obtain insight into the conformational properties of the films and changes therein. This approach has a wide potential for obtaining additional information on polymer adsorption at interfaces and the structure of their monolayer films. The 2D Clapeyron law was applied emphasizing polyethylene oxide (PEO) in polypropylene oxide (PPO)-PEO block copolymers, based on new well-defined data for their Langmuir films. Values for enthalpy per monomer of 0.12 and 0.23 kT were obtained for the phase transition of two different PEO chains (Neo of 2295 and 409, respectively). This enthalpy was estimated to correspond to 1.2 ± 0.4 kT per EO monomer present in train conformation at the air/water interface.