Nanoheterogeneities in PEO/PMMA blends: A modulated differential scanning calorimetry approach

Disentangling the Calorimetric Glass-Transition Trace in Polymer/Oligomer Mixtures from the Modeling of Dielectric Relaxation and the Input of Small-Angle Neutron Scattering

We have disentangled the contributions to the glass transition as observed by differential scanning calorimetry (DSC) on simplified systems of industrial interest consisting of blends of styrene–butadiene rubber (SBR) and polystyrene (PS) oligomer. To do this, we have started from a model previously proposed to describe the effects of blending on the equilibrium dynamics of the α-relaxation as monitored by broadband dielectric spectroscopy (BDS). This model is based on the combination of self-concentration and thermally driven concentration fluctuations (TCFs). Considering the direct insight of small-angle neutron scattering on TCFs, blending effects on the α-relaxation can be fully accounted for by using only three free parameters: the self-concentration of the components φ_self^SBR and φ_self^PS) and the relevant length scale of segmental relaxation, 2R_c. Their values were determined from the analysis of the BDS results on these samples, being that obtained for 2R_c ≈ 25Å in the range usually reported for this magnitude in glass-forming systems. Using a similar approach, the distinct contributions to the DSC experiments were evaluated by imposing the dynamical information deduced from BDS and connecting the component segmental dynamics in the blend above the glass-transition temperature T_g (at equilibrium) and the way the equilibrium is lost when cooling toward the glassy state. This connection was made through the α-relaxation characteristic time of each component at T_g, τ_g. The agreement of such constructed curves with the experimental DSC results is excellent just assuming that τ_g is not affected by blending.

Polymeric Nanocapsules Containing an Antiseptic Agent Obtained by Controlled Nanoprecipitation onto Water-in-Oil Miniemulsion Droplets

The modified nanoprecipitation of polymers onto stable nanodroplets has been successfully applied to prepare well-defined nanocapsules whose core is composing of an antiseptic agent, i.e., chlorhexidine digluconate aqueous solution. The stable nanodroplets were obtained by inverse miniemulsions with an aqueous antiseptic solution dispersed in an organic medium of solvent/nonsolvent mixture containing an oil-soluble surfactant and the polymer for the shell formation. The change of gradient of the solvent/nonsolvent mixture of dichloromethane/cyclohexane, obtained by heating at 50 degrees C, led to the precipitation of the polymer in the organic continuous phase and deposition onto the large interface of the aqueous miniemulsion droplets. The monodisperse polymer nanocapsules with the size range of 240-80 nm were achieved as a function of the amount of surfactant. Using various polymer contents, molecular weights and types, an encapsulation efficiency of 20-100% was obtained as detected by proton-nuclear magnetic resonance spectroscopy ((1)H NMR) measurements. The nanocapsules could be easily transferred into water as continuous phase resulting in aqueous dispersions with nanocapsules containing an aqueous core with the antiseptic agent. The encapsulated amount of the antiseptic agent was evaluated to indicate the durability of the nanocapsule's wall. In addition, the use of different types of polymers having glass transition temperatures (T(g)) ranging from 10 to 100 degrees C in this process has been also successful.