Abstract
The McMillan theory of the smectic-A phase is extended to two dimensions. Its predictions, which strongly differ from those in three dimensions, are found to be in disagreement with the experiment on monolayers of the polymer PLA [poly(l-lactic acid)] at the air–water interface. In contrast to the latter, the theory predicts that the smectic A-phase does not melt into the isotropic phase but first goes through a nematic phase. In addition, the effect of CdSe nanoparticles and Fe2O3 beads on the phase transition from the isotropic liquid-expanded phase to the smectic liquid-condensed phase of PLA monolayers at the air–water interface is investigated experimentally using the Langmuir–Blodgett method. It is found that depending on the size and concentration of the nanoparticles and beads, this transition can be shifted or suppressed altogether.
Highlights
In contrast to three-dimensional colloid–polymer systems, little is known about the phase equilibria of these systems when they are confined to two-dimensions
They are expected to behave in two and three dimensions, exhibiting, in particular, the same types of phase transitions. This expectation has been partly confirmed by theoretical, experimental, and computer simulation studies of depletion interactions.1–7. In all these previous studies, the systems are not truly two-dimensional: only the nanoparticles are confined to a plane, while the polymer is not since its monomers are much smaller than the colloids and can move out of plane
There are few polymers that adopt strictly two-dimensional conformations; mention can be made of the studies by Maier and Rädler, who analyzed the diffusion of DNA on lipid bilayers, by Ni et al, who investigated monolayers of poly(Llactic acid) (PLA) at the water–air interface, and by Nieuwkerk et al, who studied hydrophobically-modified maleic anhydride and maleic acid copolymers on several subphases
Summary
In contrast to three-dimensional colloid–polymer systems, little is known about the phase equilibria of these systems when they are confined to two-dimensions They are expected to behave in two and three dimensions, exhibiting, in particular, the same types of phase transitions. This expectation has been partly confirmed by theoretical, experimental, and computer simulation studies of depletion interactions.. The liquid-condensed phase is expected to exhibit a smectic-A liquid crystalline structure, as was previously observed for monolayers of PLA.10,11 This experimental evidence for our systems, based on Brewster-angle microscopy, has not yet been established and is under investigation. The liquid-condensed phase is expected to exhibit a smectic-A liquid crystalline structure, as was previously observed for monolayers of PLA. This experimental evidence for our systems, based on Brewster-angle microscopy, has not yet been established and is under investigation.
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