Predicting oligomer/polymer compatibility and the impact on nanoscale segregation in thin films

Abstract

Compatibility between oligomers and polymers was systematically assessed using differential scanning calorimetry (DSC) and was correlated with similarity in saturation and solubility parameter. These measurements enabled validation of detailed volume of mixing calculations using Statistical Association Fluid Theory (SAFT-γ Mie) and molecular dynamics (MD) simulations, which can be used to predict behaviour beyond the experimentally accessible conditions. These simulations confirmed that squalane is somewhat more compatible with poly(isoprene), "PI" than poly(butadiene), "PB", and further enabled prediction of the temperature dependence of compatibility. Surface and interfacial segregation of a series of deuterated oligomers was quantified in rubbery polymer films: PI, PB and hydrogenated poly(isoprene) "hPI". A striking correlation was established between surface wetting transition and mixtures of low compatibility, such as oligo-dIB in PB or PI. Segregation was quantified normal to the surface by ion beam analysis and neutron reflectometry and in some cases lateral segregation was observable by AFM. While surface segregation is driven by disparity in molecular weight in highly compatible systems this trend reverses as critical point is approached, and surface segregation increases with increasing oligomer molecular weight.

Wetting dynamics of polydimethylsiloxane mixtures on a poly(ethylene terephthalate) fiber

“…When it is too high, the surface segregation can be inhibited [39] or within the time scale required for our spreading experiments will be partially realized. This surface migration has been confirmed experimentally using X-ray photoemission spectroscopy [40] and neutron reflectivity [41]. Since the molecular size of PDMS5 is much smaller than the one of PDMS500, we do expect such segregation at the liquid/air interface.…”

“…Two plausible mechanisms are proposed to account for them. When a homogenous polymer mixture having different mobile components is exposed to air, it has been confirmed that the smaller molecule component migrates to the free surface [38][39][40][41], if the concentration of big molecules is not too high. When it is too high, the surface segregation can be inhibited [39] or within the time scale required for our spreading experiments will be partially realized.…”

Assessing the transferability of common top-down and bottom-up coarse-grained molecular models for molecular mixtures

“…Unfortunately, for many systems the combining rules do not work as well. 107 However, simple improvements to the fitting of thermodynamic data within SAFT-γ Mie can be made by allowing the k i j parameter to vary from zero. 108 A further interesting comparison between the bottom-up and top-down approaches is the shape of the potentials they produce.…”

Influence of PVAc/PVA Hydrolysis on Additive Surface Activity

“…Experimental data for complex, yet well-defined systems are needed to define the influence of molecular structure on those models. For example, molecular weight (Mw) is included in basic models for compatibility such as Flory Huggins theory, but modern theories need to consider the dependence of chain flexibility, free volume, and specific interactions on mixing in order to have a useful predictive capacity [15].…”

“…Following the method described by Sabattié et al [15], samples for DSC analysis were produced by adding drops from the mixed solutions to standard DSC aluminum pans, drying each drop in an oven set to 40 • C and repeating the process until 4-6 mg of solid material had been deposited into the aluminum pan. DSC analysis of the resulting samples was run on a Perkin Elmer DSC8500 instrument using nitrogen as the purge gas at a flow rate of 20.0 mL min −1 .…”