Highly filled clay-based polymer nano-composites are expected to display discotic nematic orderin... more Highly filled clay-based polymer nano-composites are expected to display discotic nematic ordering. In this study, the Poiseuille capillary flow of discotic nematic liquid crystals is analyzed using the Ericksen-Leslie theory, for three families of static patterns known as escaped and defect core onion textures, defined by the orientation at the capillary’ centerline. The escaped textures have low-elastic energy and high dissipation cores. The defect core texture has a high elastic energy-low dissipation core. The Poiseuille flow of these textures exhibits non-parabolic velocity profiles and their apparent viscosities display shear thickening, with exponents close to 1/5 07 . 0 ± . It is found that core conditions have a strong effect on the Non-Newtonian rheology of discotic nematics displaying the onion texture. We expect that the present work will be of practical utility to the currently intense investigation of the rheology and processing flows of polymer nano-composites. Introd...
Phase behaviour of poly(ethylene oxide) (PEO) and PEO functionalized gold nanoparticles blended w... more Phase behaviour of poly(ethylene oxide) (PEO) and PEO functionalized gold nanoparticles blended with 5CB is characterized and thermodynamically modelled.
The structure and dynamics of early stage kinetics of pressure-induced phase separation of compre... more The structure and dynamics of early stage kinetics of pressure-induced phase separation of compressible polymer solutions via spinodal decomposition is analyzed using a linear Euler-Cahn-Hilliard model and the modified Sanchez Lacombe equation of state. The integrated density wave and Cahn-Hilliard equations combine the kinetic and structural characteristics of spinodal decomposition with density waves arising from pressure-induced couplings. When mass transfer rate is slower that acoustic waves, concentration gradients generate density waves that cycle back into the spinodal decomposition dynamics, resulting in oscillatory demixing. The wave attenuation increases with increasing mass transfer rates eventually leading to nonoscillatory spinodal demixing. The novel aspects of acousto-spinodal decomposition arise from the coexistence of stable oscillatory density dynamics and the unstable monotonic concentration dynamics. Scaling laws for structure and dynamics indicate deviations from incompressible behavior, with a significant slowing down of demixing due to couplings with density waves. Partial structure factors for density and density-concentration reflect the oscillatory nature of acousto-spinodal modes at lower wave vectors, while the single maximum at a constant wave vector reflects the presence of a dominant mode in the linear regime. The computed total structure factor is in qualitative agreement with experimental data for a similar polymer solution.
Page 1. LIQUID CRYSTALS, 1989, VOL. 4, No. 4, 409-422 Analysis of transient periodic textures in ... more Page 1. LIQUID CRYSTALS, 1989, VOL. 4, No. 4, 409-422 Analysis of transient periodic textures in nematic polymers by ALEJANDRO D. REYt and MORTON M. DENN Center for Advanced Materials, Lawrence Berkeley Laboratory ...
ABSTRACTWe present a new theoretical model of nucleation and growth in term of a novel domainspat... more ABSTRACTWe present a new theoretical model of nucleation and growth in term of a novel domainspatial correlation function. This model probes the patterns and spatio-temporal evolution of nucleation and growth process and agrees very well with experimental data. The dynamic domain-spatial correlation function directly and simultaneously explores the transformed volume fraction, the time-dependent domain size distribution function, and the spatial correlation function of domain core centers for the entire process, including the post-nucleation, domain growth and grain formation stages.
We propose a physical model of multiple domain nucleation and growth in order to perform the cros... more We propose a physical model of multiple domain nucleation and growth in order to perform the cross-scale simulation on envelope profiles of the domain and the internal structure. The model utilizes two coupled field: a nonconserved envelope vector field of the local macroscopic growth domains and a vector field of the local mesoscopic lamellae directors. The envelope evolution equation includes an envelope profile function, the domain growth and impingement kinetics, the relaxation of the envelope by a surface tension, a lowest-order nonlinear term, a noise term, and a surface diffusion term. The splay, twist and bend deformation and the interaction between lamellae and noise field are considered in the free energy density equation of the lamellar director field. Results of large-scale computer simulation are reported which are compared with experiments.
We demonstrate that the morphological diversity in liquid-crystal hybrid systems is much richer t... more We demonstrate that the morphological diversity in liquid-crystal hybrid systems is much richer than previously anticipated. More importantly, we reveal the existence of a dual mechanism for self-assembly of nanoparticles via morphological instabilities at phase boundaries. Using numerical simulations, we study the growth of isolated nematic droplets in an isotropic liquid crystal (LC) doped with nanoparticles (NPs) and provide insight into the nature of microstructure evolution in LC hybrids. Our work expands the numerically accessible time and length scales in these systems, capturing morphologies which develop under the competition of nonequilibrium elastic interactions, diffusive instabilities mediated by NP transport, and the anisotropy of the nematic field. By mapping nematic morphologies, we also propose a methodology for estimating various important LC material parameters that are difficult to obtain experimentally.
ABSTRACT This paper reports a novel Ab initio density functional theory (DFT) simulation approach... more ABSTRACT This paper reports a novel Ab initio density functional theory (DFT) simulation approach to the study of surface defects in self-assembled monolayers (SAMs) on gold (0 0 1) surfaces. Surfaces defects can cause changes in gold atom spacing and the ligand footprint. DFT calculations of 6-mercapto-hexane on Au(0 0 1) surfaces have been performed as a function of ligand footprints of 18, 20, 22, 24 and 26 Å2, using a slab geometry and periodic boundary conditions with varying gold atom spacing. The simulation results indicate that as the ligand packing density increases, the position of ideal binding sites changes from fcc to bridge sites. The packing density of 24 Å2 corresponds to the highest binding energy and to a 28.85° cant angle. These results are in good agreement with the experiments from ligand-capped gold nanoparticles. The simulation results also prove that the SAM structure of short-chain alkanethiols on gold is dominated by surface interactions rather than ligand interactions. The electron density mapping study confirms this observation, where only the top two layers of gold atoms contributed charge transfer to sulphur atom and no charge transfer was observed from the alkane chain.
Highly filled clay-based polymer nano-composites are expected to display discotic nematic orderin... more Highly filled clay-based polymer nano-composites are expected to display discotic nematic ordering. In this study, the Poiseuille capillary flow of discotic nematic liquid crystals is analyzed using the Ericksen-Leslie theory, for three families of static patterns known as escaped and defect core onion textures, defined by the orientation at the capillary’ centerline. The escaped textures have low-elastic energy and high dissipation cores. The defect core texture has a high elastic energy-low dissipation core. The Poiseuille flow of these textures exhibits non-parabolic velocity profiles and their apparent viscosities display shear thickening, with exponents close to 1/5 07 . 0 ± . It is found that core conditions have a strong effect on the Non-Newtonian rheology of discotic nematics displaying the onion texture. We expect that the present work will be of practical utility to the currently intense investigation of the rheology and processing flows of polymer nano-composites. Introd...
Phase behaviour of poly(ethylene oxide) (PEO) and PEO functionalized gold nanoparticles blended w... more Phase behaviour of poly(ethylene oxide) (PEO) and PEO functionalized gold nanoparticles blended with 5CB is characterized and thermodynamically modelled.
The structure and dynamics of early stage kinetics of pressure-induced phase separation of compre... more The structure and dynamics of early stage kinetics of pressure-induced phase separation of compressible polymer solutions via spinodal decomposition is analyzed using a linear Euler-Cahn-Hilliard model and the modified Sanchez Lacombe equation of state. The integrated density wave and Cahn-Hilliard equations combine the kinetic and structural characteristics of spinodal decomposition with density waves arising from pressure-induced couplings. When mass transfer rate is slower that acoustic waves, concentration gradients generate density waves that cycle back into the spinodal decomposition dynamics, resulting in oscillatory demixing. The wave attenuation increases with increasing mass transfer rates eventually leading to nonoscillatory spinodal demixing. The novel aspects of acousto-spinodal decomposition arise from the coexistence of stable oscillatory density dynamics and the unstable monotonic concentration dynamics. Scaling laws for structure and dynamics indicate deviations from incompressible behavior, with a significant slowing down of demixing due to couplings with density waves. Partial structure factors for density and density-concentration reflect the oscillatory nature of acousto-spinodal modes at lower wave vectors, while the single maximum at a constant wave vector reflects the presence of a dominant mode in the linear regime. The computed total structure factor is in qualitative agreement with experimental data for a similar polymer solution.
Page 1. LIQUID CRYSTALS, 1989, VOL. 4, No. 4, 409-422 Analysis of transient periodic textures in ... more Page 1. LIQUID CRYSTALS, 1989, VOL. 4, No. 4, 409-422 Analysis of transient periodic textures in nematic polymers by ALEJANDRO D. REYt and MORTON M. DENN Center for Advanced Materials, Lawrence Berkeley Laboratory ...
ABSTRACTWe present a new theoretical model of nucleation and growth in term of a novel domainspat... more ABSTRACTWe present a new theoretical model of nucleation and growth in term of a novel domainspatial correlation function. This model probes the patterns and spatio-temporal evolution of nucleation and growth process and agrees very well with experimental data. The dynamic domain-spatial correlation function directly and simultaneously explores the transformed volume fraction, the time-dependent domain size distribution function, and the spatial correlation function of domain core centers for the entire process, including the post-nucleation, domain growth and grain formation stages.
We propose a physical model of multiple domain nucleation and growth in order to perform the cros... more We propose a physical model of multiple domain nucleation and growth in order to perform the cross-scale simulation on envelope profiles of the domain and the internal structure. The model utilizes two coupled field: a nonconserved envelope vector field of the local macroscopic growth domains and a vector field of the local mesoscopic lamellae directors. The envelope evolution equation includes an envelope profile function, the domain growth and impingement kinetics, the relaxation of the envelope by a surface tension, a lowest-order nonlinear term, a noise term, and a surface diffusion term. The splay, twist and bend deformation and the interaction between lamellae and noise field are considered in the free energy density equation of the lamellar director field. Results of large-scale computer simulation are reported which are compared with experiments.
We demonstrate that the morphological diversity in liquid-crystal hybrid systems is much richer t... more We demonstrate that the morphological diversity in liquid-crystal hybrid systems is much richer than previously anticipated. More importantly, we reveal the existence of a dual mechanism for self-assembly of nanoparticles via morphological instabilities at phase boundaries. Using numerical simulations, we study the growth of isolated nematic droplets in an isotropic liquid crystal (LC) doped with nanoparticles (NPs) and provide insight into the nature of microstructure evolution in LC hybrids. Our work expands the numerically accessible time and length scales in these systems, capturing morphologies which develop under the competition of nonequilibrium elastic interactions, diffusive instabilities mediated by NP transport, and the anisotropy of the nematic field. By mapping nematic morphologies, we also propose a methodology for estimating various important LC material parameters that are difficult to obtain experimentally.
ABSTRACT This paper reports a novel Ab initio density functional theory (DFT) simulation approach... more ABSTRACT This paper reports a novel Ab initio density functional theory (DFT) simulation approach to the study of surface defects in self-assembled monolayers (SAMs) on gold (0 0 1) surfaces. Surfaces defects can cause changes in gold atom spacing and the ligand footprint. DFT calculations of 6-mercapto-hexane on Au(0 0 1) surfaces have been performed as a function of ligand footprints of 18, 20, 22, 24 and 26 Å2, using a slab geometry and periodic boundary conditions with varying gold atom spacing. The simulation results indicate that as the ligand packing density increases, the position of ideal binding sites changes from fcc to bridge sites. The packing density of 24 Å2 corresponds to the highest binding energy and to a 28.85° cant angle. These results are in good agreement with the experiments from ligand-capped gold nanoparticles. The simulation results also prove that the SAM structure of short-chain alkanethiols on gold is dominated by surface interactions rather than ligand interactions. The electron density mapping study confirms this observation, where only the top two layers of gold atoms contributed charge transfer to sulphur atom and no charge transfer was observed from the alkane chain.
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Papers by Alejandro Rey