Surfactants And Interfacial Phenomena

Glycerol droplets at a nematic-liquid-crystal-air interface form two different lattices--hexagonal and dense quasihexagonal--which are separated by the energy barrier and can coexist. Director distortions around each droplet form an elastic dipole. The first order transition between the two lattices is driven by a reduction of the dipole-dipole repulsion through reorientation of these dipoles. The elastic-capillary attraction is essential for the both lattices. The effect has a many-body origin.

http://absimage.aps.org/image/MAR07/MWS_MAR07-2006-003923.pdf

Coexistence of two colloidal crystals at the nematic liquid crystal-air interface

Self-discharge and leakage current mitigation of neutral aqueous-based supercapacitor by means of liquid crystal additive

We investigate the crystallization-induced ordering of C18 grafted 14 nm diameter spherical silica nanoparticles (NPs) in a short chain (Mw = 4 kDa, ĐM ≈ 2.3) polyethylene and a commercial high-den...

Nanoparticle Organization by Growing Polyethylene Crystal Fronts

Fluids with competing short range attraction and long range repulsive interactions between the particles can exhibit a variety of microphase separated structures. We develop a lattice-gas (generalised Ising) model and analyse the phase diagram using Monte Carlo computer simulations and also with density functional theory (DFT). The DFT predictions for the structures formed are in good agreement with the results from the simulations, which occur in the portion of the phase diagram where the theory predicts the uniform fluid to be linearly unstable. However, the mean-field DFT does not correctly describe the transitions between the different morphologies, which the simulations show to be analogous to micelle formation. We determine how the heat capacity varies as the model parameters are changed. There are peaks in the heat capacity at state points where the morphology changes occur. We also map the lattice model onto a continuum DFT that facilitates a simplification of the stability analysis of the uniform fluid.

/pdf/two-dimensional-colloidal-fluids-exhibiting-pattern-qpf2us3ffv.pdf

Two-dimensional colloidal fluids exhibiting pattern formation

The fundamental understanding of nematic liquid crystal (NLC) alignment on solid surfaces is significant for the operation of liquid crystal displays and devices. We investigate the effect of structure and concentration of surfactants on the anchoring of NLC 4-cyano-4′-pentylbiphenyl (5CB) at 5CB–solid interface. 5CB molecules undergo an ordering transition from parallel to normal anchoring near the surfactant critical micelle concentration depending on the chemical structure of the surfactant tails. In contrast to the previous studies which point to the solubilization of 5CB in surfactant micelles, our experiments indicate that NLC anchoring transition occurs due to the ability of 5CB molecules to penetrate into the surface surfactant layer. The surfactant-driven 5CB anchoring is further related to the surface tension of 5CB (γ5CB), surfactant adsorbed substrate surface energy (γsa), anisotropic 5CB–surface interfacial energy (Δγsl), and spreading coefficient (S). Our experimental results agree w...

Experimental study of surfactant driven nematic liquid crystal (NLC) anchoring transitions at solid surfaces: role of solid surface energy and anisotropic NLC – solid interfacial energy

A fundamental understanding of the heterogeneous olefin polymerization process is critical for imparting desired properties to the final polymer product. In this work, we have developed a comprehensive model integrating the meso-scale level intraparticle resistances to mass and heat transfer as well as the micro-scale level kinetics. The model formulation is based on the combination of the polymer flow model with the intrinsic kinetic model derived using the method of moments approach. The model is employed to study the effect of varying the mass transfer and kinetic parameters on the monomer concentration and temperature profiles inside the growing polymer macro-particle and the subsequent implications on the catalyst activity, polymer molecular weights and the polydispersity index (PDI). The simulation results showed that the steeper monomer concentration gradients in the polymer macro-particle arose on decrease of the bulk diffusivity (Db) and increase of the number of active sites. The model also predicted the interdependence between the radial monomer concentration and temperature profiles. Further, with appropriate choice of $$D_{\text{b}}$$
 , the number of active catalyst sites, initial catalyst active site concentration and kinetic rate constants, the model predicted the catalyst activity exceeding 100 kg/g cat.hr and PDI values higher than 2. We showed that the model is capable of predicting the experimental reported polymer product properties for Ziegler–Natta, hybrid Ziegler–Natta/metallocene and supported metallocene catalyst systems.

A comprehensive model for the micro and meso-scale level olefin polymerization: framework and predictions

We investigate the rheological implications of partitioning and self-assembly of colloidal particles at the grain boundaries (GBs) of hexagonal (H1) liquid crystal (LC) phase as a function of particle loading, shape and phase transition kinetics. The rheology of spherical silica particles (SiO2, diameter = 140 nm)/H1 and irregular hematite particles (Fe2O3, size = 110 nm)/H1 composites is measured as the samples are cooled from an isotropic to H1 phase at 2 and 0.2 °C/min. At 2 °C/min, SiO2/H1 composites show a consistent increase in G′ as the particle loading increases from 0.5 to 7.5 wt. % while Fe2O3/H1 composites exhibit a small drop in G′ above 2.5 wt. % particle loading. On the other hand, SiO2/H1 and Fe2O3/H1 composites show a monotonic increase in G′ with particle loading at a cooling rate of 0.2 °C/min. Microscopy observations reveal that at 0.2 °C/min, both SiO2 and Fe2O3 particles aggregate at the H1 GBs. The different rheological responses of SiO2/H1 and Fe2O3/H1 composites at 2 °C/min are due...

Partitioning and self assembly of silica and hematite particles at grain boundaries of hexagonal liquid crystals: Implications on rheology

The rheology of self-assembled elongated iron oxyhydroxide (FeOOH) and spherical silica (SiO2) particles in hexagonal (H1) liquid crystal (LC) phase of water and non-ionic surfactant C12E9 is investigated by varying particle concentration and cooling rate. The rheology data shows that both SiO2/H1 and FeOOH/ H1 LC composites exhibit a higher G′ when compared to the particle-free H1 phase, with increasing particle loading and cooling rate. FeOOH particles improve G′ of the H1 phase more significantly than SiO2 particles due to the formation of an interconnected network at H1 domain boundaries at cooling rates of 1 and 2 ∘C/min. We hypothesize that self-assembly of particles at domain boundaries leads to a decreased mobility of defects causing an increase in elasticity of particle-laden H1 phase. Dynamic strain sweep and creep experiments show a non-linear stress–strain relationship attributed to the alignment of micellar cylindrical rods under shear.

Siddharth Kulkarni

Papers

Experimental study of surfactant driven nematic liquid crystal (NLC) anchoring transitions at solid surfaces: role of solid surface energy and anisotropic NLC – solid interfacial energy

A comprehensive model for the micro and meso-scale level olefin polymerization: framework and predictions

Partitioning and self assembly of silica and hematite particles at grain boundaries of hexagonal liquid crystals: Implications on rheology

Rheology of colloidal particles in lyotropic hexagonal liquid crystals: the role of particle loading, shape, and phase transition kinetics

Colloidal and fumed particles in nematic liquid crystals: Self-assembly, confinement and implications on rheology