Evolution of microscopic heterogeneity and dynamics in choline chloride-based deep eutectic solvents

Deep eutectic solvents (DESs) are an emerging class of non-aqueous solvents that are potentially scalable, easy to prepare and functionalize for many applications ranging from biomass processing to energy storage technologies. Predictive understanding of the fundamental correlations between local structure and macroscopic properties is needed to exploit the large design space and tunability of DESs for specific applications. Here, we employ a range of computational and experimental techniques that span length-scales from molecular to macroscopic and timescales from picoseconds to seconds to study the evolution of structure and dynamics in model DESs, namely Glyceline and Ethaline, starting from the parent compounds. We show that systematic addition of choline chloride leads to microscopic heterogeneities that alter the primary structural relaxation in glycerol and ethyleneglycol and result in new dynamic modes that are strongly correlated to the macroscopic properties of the DES formed

Importance of thermodynamic interactions on the dynamics of multicomponent polymer systems revealed by examination of the dynamics of copolymer/homopolymer blends.

The effect of copolymer composition oil their dynamics in a homopolymer matrix has been studied using specular neutron reflectivity (NR). We have monitored the segregation process of random copolymers, containing styrene (S) and methyl niethacrylate (MMA), to the d-PS/d-PMMA interface from a polymer matrix. Four random copolymers containing 50, 54, 67, and 80% MMA were studied at 10 wt % loading in d-PMMA, where the interfacial excess, Z*, growth scaled as t(1/2) as predicted by theory. These results are correlated to the diffusion-limited growth of a copolymer wetting layer at the d-PS/d-PMMA interface. The mutual and tracer diffusion coefficients and the effective friction coefficients for these copolymers were then determined. The results demonstrate that the copolymer composition has a significant impact on its dynamics. Copolymer dynamics are significantly faster than those for a diblock copolymer at the same composition, which indicates that the impact of the change in composition is more than that due to an increase in the MMA content in the copolymer. Analysis of the friction factor using the Lodge-McLeish model indicates that the local composition around a copolymer is richer in styrene than the model predicts. We attribute this to the fact that the model uses only chain connectivity to calculate the self-concentration and does not include contributions due to thermodynamic interactions between the two blend components. The observation that the local environment around a copolymer is richer in styrene is in agreement with our simulation results and indicates that the styrene monomers in the copolymer aggregate together to minimize contact with the PMMA matrix. These results exemplify the importance of thermodynamic interactions on the dynamics of multicomponent polymer systems, particularly miscible homopolymer/copolymer blends. © 2008, American Chemical Societ

Suspensions of titania nanoparticle networks in nematic liquid crystals: rheology and microstructure

We study the influence of confinement on the rheology and structure of nematic liquid crystals (NLCs). NLCs get confined in networks of titania (TiO2, primary particle size = 21 nm) nanoparticles in suspensions of TiO2 and NLC, N-(4-methoxybenzylidene)-4-butylaniline (MBBA). Suspensions with TiO2 nanoparticle volume fraction (ϕ) of 0.006–0.017, form viscoelastic solids with low elastic modulus (G′) of 101 Pa–102 Pa and short relaxation times. Increase in TiO2 nanoparticle ϕ leads to a rise in G′ with TiO2 nanoparticles forming a percolating network at a critical volume fraction (ϕ c) = 0.023, and G′ of ~103 Pa. TiO2/MBBA NLC suspensions at and above ϕ c = 0.023 show G′ ~ ω x−1 scaling, where ω is the angular frequency and the minimum in loss modulus (G′′) with ω. The effective noise temperature, x decreases and approaches 1 with the increase in the TiO2 nanoparticle ϕ from 0.023–0.035, is indicative of an increase in the glassy dynamics. Through the polarized light microscopy and differential scanning calorimetry experiments, we propose that the progressive addition of TiO2 nanoparticles introduces a quenched random disorder (QRD) in the NLC medium which disturbs the nematic order. This results in metastable TiO2/MBBA NLC suspensions in which NLC domains get confined in the network of flocs of TiO2 nanoparticles. We also show that the salient rheological signatures of soft glassy rheology develop only in the presence of NLC MBBA and are absent in the isotropic phase of MBBA.by Siddharth Kulkarni and Prachi Tharej