Browsing by Author "Wang, Qiang, advisor"
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Item Open Access Fast off-lattice Monte Carlo simulations of phase transitions in block copolymers and liquid crystals(Colorado State University. Libraries, 2015) Zong, Jing, author; Wang, Qiang, advisor; Bailey, Travis S., committee member; Szamel, Grzegorz, committee member; Watson, A. Ted, committee memberThe basic idea of the so-called fast off-lattice Monte Carlo (FOMC) simulations is to perform particle-based Monte Carlo (MC) simulations in continuum with the excluded-volume interactions modeled by soft repulsive potentials that allow particle complete overlapping, where using soft potentials naturally arises from the application of coarse-grained models. This method is particularly suitable for the study of equilibrium properties of soft matter. One apparent advantage of FOMC is that using soft potentials can greatly improve the sampling efficiency in the simulations. Another advantage is that FOMC simulations can be performed in any statistical ensemble, and all the advanced off-lattice MC techniques proposed to date can be readily applied to further improve the sampling efficiency. Moreover, it provides a powerful methodology to directly compare theoretical results with simulation results without any parameter fitting. Last but not least, using FOMC is the only way to study experimentally accessible fluctuation/correlation effects in many-chain systems. This work makes use of FOMC simulations to study phase transitions in block copolymers and liquid crystals. To compare with the simulations results, various theoretical methods are also applied in the research. Chapter 2 is devoted to study the classic yet unsolved problem of fluctuation/correlation effects on the order-disorder transition (ODT) of symmetric diblock copolymer (DBC). In Chapter 3, we highlight the importance of quantitative and parameter-fitting-free comparisons among different models/methods. In Chapter 4, we investigate the effect of system compressibility on the ODT of DBC melts. In Chapter 5, we extend FOMC simulations to study the isotropic-nematic transition of liquid crystals. Finally, in Chapter 6, we briefly summarize all the studies in this dissertation and give some directions to future work.Item Open Access GPU-accelerated computational study of block copolymer self-assembly with advanced polymer theories(Colorado State University. Libraries, 2024) He, Juntong, author; Wang, Qiang, advisor; Prasad, Ashok, committee member; Bailey, Travis, committee member; Gelfand, Martin, committee memberA high-performance GPU-accelerated software package for self-consistent field (SCF) calculations of block copolymer assembly, PSCF+, has been developed. PSCF+ allows various combinations of chain-connectivity models (including the continuous Gaussian chains, discrete Gaussian chains, and freely jointed chains), non-bonded isotropic pair (including the Dirac δ-function, soft-sphere, dissipative particle dynamics, and Gaussian) potentials and system compressibility (incompressible vs. compressible). The Richardson-extrapolated pseudo-spectral methods, the crystallographic fast Fourier transform, the "slice" algorithm, and the automated calculation-along-a-path are implemented in PSCF+, which not only speed up the SCF calculations and reduce the GPU memory usage significantly, but also make it very efficient in constructing phase diagrams. Given the wide use and great success of SCF calculations in understanding and predicting the self-assembled structures of block copolymer, PSCF+ will be an invaluable computational tool for the polymer community. Using PSCF+, we studied the stability of various Frank-Kasper phases formed by neat diblock copolymer (DBC) A-B melts using the "standard" model and the dissipative particle dynamics chain model and found that in general the SCF phase diagrams of these two models are qualitatively the same but with important differences. We also studied the stability of various Frank-Kasper phases formed by binary DBC blends using the "standard" model and found that the relative stability among the Frank-Kasper phases is dominated by their internal-energy densities. Finally, we performed high-accuracy SCF calculations to study the stability of all known tiling patterns formed by symmetrically interacting ABC miktoarm star triblock terpolymers.Item Open Access Novel applications of advanced integral-equation theories to various polymeric systems(Colorado State University. Libraries, 2021) Wang, Yan, author; Wang, Qiang, advisor; Snow, Christopher, committee member; Bailey, Travis, committee member; Grzegorz, Szamel, committee memberTo view the abstract, please see the full text of the document.