title: Blends of poly(epsilon-caprolactone) and intermediate molar mass polystyrene as Langmuir films at the air/water interface.
abstract: Poly(epsilon-caprolactone)/polystyrene (PCL/PS) blends, where nonamphiphilic PS is glassy in the bulk state at the experimental temperature of 22.5 degrees C, are immiscible as Langmuir films at the air/water (A/W) interface. Surface pressure-area per monomer isotherm analyses indicate that the surface concentration of amphiphilic PCL is the only factor influencing the surface pressure below the collapse transition. For PS-rich blends, Brewster angle microscopy (BAM) studies at the A/W interface and atomic force microscopy studies on Langmuir-Schaefer films reveal that PS nanoparticle aggregates formed at very low surface pressures can form networks upon further compression. The morphologies seen in PS-rich blends (networklike rings) are consistent with a recent study of a nonamphiphilic polyhedral oligomeric silsesquioxane (POSS), octaisobutyl-POSS, blended with amphiphilic poly(dimethylsiloxane), suggesting that the nonamphiphilic PS aggregates at the A/W interface produce domains with dipole densities that differ from that of pure PCL. In all composition regimes, the amphiphilic PCL phase tends to spread and form a continuous surface layer at the A/W interface, while simultaneously improving the dispersion of nonamphiphilic PS domains. During film expansion, BAM images show a gradual change in the surface morphology from highly continuous networklike structures (PS-rich blends) to broken ringlike structures (intermediate composition) to small discontinuous aggregates (PCL-rich blends). This study provides valuable information on the morphological evolution of semicrystalline PCL-based polymer blends confined in a "two-dimensional" geometry at the A/W interface and fundamental insight into the influence of microstructure (domain size, phase-separated structures, crystalline morphology, etc.) on the interfacial properties of blends as Langmuir films.
authors.affiliation: Department of Chemistry (0212), Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA.
authors.forename: Bingbing
authors.initials: B
authors.lastname: Li
authors.forename: Alan R
authors.initials: AR
authors.lastname: Esker
mesh_terms: D000388:Air; D002627:Chemistry, Physical / Q000379:methods; D003460:Crystallization; D018625:Microscopy, Atomic Force; D015394:Molecular Structure; D053758:Nanoparticles / Q000737:chemistry; D011091:Polyesters / Q000737:chemistry*; D011137:Polystyrenes / Q000737:chemistry*; D011312:Pressure; D013499:Surface Properties; D013696:Temperature; D014867:Water / Q000737:chemistry*
chemical_list: D011091:Polyesters; D011137:Polystyrenes; D014867:Water; C016240:polycaprolactone