Interfacial behavior of non-ionic diblock copolymers

PS-based nonionic, but polar, diblock copolymers (polystyrene-b-polymethacrylates, polystyrene-b-polyacrylates, polystyrene-b-poly(dimethyl siloxane)) have been systematically studied using the Langmuir film balance (LFB) technique, transmission electron microscopy (TEM), and atomic force microscopy (AFM). It has been found that these nonionic copolymers can form 2D surface micelles as has been found for ionic diblocks such as polystyrene-b-poly(vinyl pyridinium iodide) diblocks. This suggests that formation of surface micelles is a general phenomenon among AB diblock copolymers. Both structural parameters (aggregation number, aggregate size distribution, corona length and thickness, morphologies, boundaries etc.) and the response to conditions (temperature of the subphase, surface tension of the subphase, hysteresis, compression rates, etc.) have been explored for the monolayers formed from these materials. Many of these diblocks exhibit plateaus or inflections in their isotherms. Experimental data allow for the calculation of the thermodynamic parameters $ rm ( Delta S sb{t}$ and $ rm Delta H sb{t})$ associated with the transitions. Differences between the $ rm Delta S sb{t}$ and $ rm Delta H sb{t}$ values observed with the nonionic diblocks in question and the ionic diblocks studied before suggests that the nonionic diblocks monolayers have unique properties. Different mechanisms of the transitions(s) are proposed for samples which have one transition plateau or inflection and samples which have multiple transitions or inflections. A scaling theory-based calculation of the corona length and $ pi$-A isotherm are reasonably consistent with experimental data and thus provides a useful tool in these studies. Selected properties (i.e. subphase surface tension, waiting time etc.) for several ionic diblocks were also studied. Finally, the minimum chain lengths for circular micelles were calculated using a scaling theory methodology