The relaxation time spectrum in blends of architecturally different polymers with strongly disperse time scales has been investigated by their time-dependent small angle neutron scattering signal after a fast uniaxial step strain. Modelhyperbranched dendrimeric polymers of second generation, dilutely dispersed within linear homopolymer matrices, acted like sensitive probes for structurally, though not firmly, established features of the tube model for bidisperse melts. We showed that the equilibration time of the linear matrix determines the size of the fluctuations that the outer and inner arms experience. Within a random phase approximation (RPA) treatment, which accounts for the different degrees of freedom inherent to the broad time scales, the observed loss of anisotropy with time was described in terms of two parameters only, namely the tube diameter and the fraction of relaxed arms of the minority component. The scattering data reveal details of mechanisms, which cannot be extracted from but determine the macroscopic flow properties. At intermediate times, a tube relaxation process was detected. At long times, the dynamic dilution model is confirmed. ■ INTRODUCTIONIn the last few decades, the flow behavior of branched polymers has attracted an increasing attention and the description of their linear rheology by means of the tube model has achieved remarkable progress. 1−16 Of particular interest is that the dynamics of branched polymers is, on one hand, much more complex and demanding as compared to that of simple linear chains but, on the other hand, allows to distinguish different processes according to the hierarchy of times in branched polymers. Therefore, the coupling and competition of diffusive reptation and contour length fluctuations, which have dominate until today the understanding of the dynamics of linear chains in detail, does not occur in the same way. 17−20 Also, interesting new properties due to this hierarchical approach emerge in the nonlinear rheological response. This bears consequences especially on processing. Blends of short and long linear chains 21,22 as well as those consisting of linear and long-chainbranched polymers have well-known additional advantages. Here, we investigated branched polymers immersed in a linear matrix as the major constituent. This allows controlling the time constants of the matrix in relation to the characteristic times of different sections of the branched chains. 9,11,19,23,24 Vice versa, the branched polymer may be regarded as a probe for mechanisms of topological constraints and constraint release processes in linear systems, comparable to probe rheology, which was recently reintroduced by Bailly et al. 25 Although probe rheology is a very sensitive and interesting technique for systems with sufficiently different time scales, it is based on the subtraction of large modulus contributions to isolate the response function of the probe without its environment. A rigorous underlying theory like the Random phase Approximation (RPA) for scattering is, unfor...

Engineering flow processes to direct the microscopic structure of soft materials represents a growing area of materials research. In situ small-angle neutron scattering under flow (flow-SANS) is an attractive probe of fluid microstructure under simulated processing conditions, but current capabilities require many different sample environments to fully interrogate the deformations a fluid experiences in a realistic processing flow. Inspired by recent advances in microfluidics, we present a fluidic four-roll mill (FFoRM) capable of producing tunable 2D flow fields for in situ SANS measurements, that is intended to allow characterization of complex fluid nanostructure under arbitrary complex flows within a single sample environment. Computational fluid dynamics simulations are used to design a FFoRM that produces spatially homogeneous and sufficiently strong deformation fields. Particle tracking velocimetry experiments are then used to characterize the flows produced in the FFoRM for several classes of non-Newtonian fluids. Finally, a putative FFoRM-SANS workflow is demonstrated and validated through the characterization of flow-induced orientation in a semi-dilute cellulose nanocrystal dispersion under a range of 2D deformations. These novel experiments confirm that, for steady state straining flows at moderate strain rates, the nanocrystals orient along the principal strain-rate axis, in agreement with theories for rigid, rod-like Brownian particles in a homogeneous flow.

Complex nanoemulsions, comprising multiphase nanoscale droplets, hold considerable potential advantages as vehicles for encapsulation and delivery as well as templates for nanoparticle synthesis. Although methods exist to controllably produce complex emulsions on the microscale, very few methods exist to produce them on the nanoscale. Here, we examine a recently developed method involving a combination of high-energy emulsification with conventional cosurfactants to produce oil-water-oil (O/W/O) complex nanoemulsions. Specifically, we study in detail how the composition of conventional ethoxylated cosurfactants Span80 and Tween20 influences the morphology and structure of the resulting complex nanoemulsions in the water-cyclohexane system. Using a combination of small-angle neutron scattering and cryo-electron microscopy, we find that the cosurfactant composition controls the generation of complex droplet morphologies including core-shell and multicore-shell O/W/O nanodroplets, resulting in an effective state diagram for the selection of nanoemulsion morphology. Additionally, the cosurfactant composition can be used to control the thickness of the water shell contained within the complex nanodroplets. We hypothesize that this degree of control, despite the highly nonequilibrium nature of the nanoemulsions, is ultimately determined by a competition between the opposing spontaneous curvature of the two cosurfactants, which strongly influences the interfacial curvature of the nanodroplets as a result of their ultralow interfacial tension. This is supported by a correlation between cosurfactant compositions that produces complex nanoemulsions and those that produce homogeneous mixed micelles in equilibrium surfactant-cyclohexane solutions. Ultimately, we show that the formation of complex O/W/O nanoemulsions is weakly perturbed upon the addition of hydrophilic polymer precursors, facilitating their use as templates for the formation of polymer nanocapsules.

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