The Policy Process Research of Family Doctor System in China: from the Perspective of the Multiple-Streams Theory

Under context of aging population and chronic disease with high occurrence as well as difficulty and expensive costs in medical treatment, the establishment about system of family doctors has been brought about in China, but there lacks domestic research for process of policy evolution endowed with such significance. This paper tries to analyze process of institutional establishment of family doctors in view of multiple-streams theory; the evolution process about institutional construction of family doctors should have systematic classification with analysis of problem stream, policy stream and political stream respectively as well as facts based on fundamental challenges of grassroots public health; explanation should be made for features and inspiration about institutional construction of family doctors to further verify feasibility of multiple streams theory in China. The fact has found that social background and actor will influence agenda about institutional construction of family doctors, some agenda of basic public health service policy will not be promoted by accidental focus events; active public participation and attention will exert influence for formation of political stream. Keywords: family doctor, multiple-streams theory, policy process, agenda setting

Doctor of Philosophy

dissertationIonic transport is ubiquitous in the world. Energy-storage systems, such as lithiumion batteries (LIBs), alkaline fuel cells (AFCs), and electric double layer capacitors (EDLCs), rely upon an efficient built-in ion transport within the devices. In this dissertation, three typical systems related to energy storage/conversion applications are systematically investigated via molecular dynamics (MD) simulation: alkaline fuel cell membranes, solvate ionic liquids, and solid polymer electrolytes for next-generation of LIBs. Using combined reactive and nonreactive MD simulation approach the chemical structure of polymer and the morphology of hydrated AFCs membranes are correlated with the ion transport mechanisms. Specifically, it is demonstrated that the Grotthuss mechanism plays a vital role in facilitating the transport of OH- through the bottlenecks in water channels inside the membrane. The Grotthuss mechanism also contributes significantly to the overall diffusion in the water-rich domain. The degradation mechanisms of ammonium-based functional groups are investigated as a function of size and/or structure of alkyl groups attached to the cationic groups of polymer chains. The long alkyl chains can significantly stabilize the functional groups, reducing the reaction rates, but lead to increased heterogeneity in water domain size distribution. The asymmetrically modified cationic groups, i.e., those modified with long and short alkyl chains, can promote the formation of larger water channels with uniform size. Therefore, the asymmetrical modification patterns are expected to yield AFC membranes with high performance. iv In battery systems, solvate ionic liquids (SILs) and solid polymer electrolytes (SPE) are considered as next-generation electrolytes. However, with the transport mechanism of Li+ and the origin of low Li+ transference number in SILs, the molecular mechanisms needed to tune the ionic conductivity in SPE remain poorly understood. Based on the joint MD simulation and electrochemical experiment study, the molecular origin of those limits for application of SILs and SPEs are explored. The anticorrelated motion of cations and anions in SILs leads to a low transference number of Li+ due to the necessity of satisfying the conservation of momentum. Adding excessive free solvents or/and using solvents with weaker binding energy between Li+ and solvent are needed to increase the transference number of Li+. MD simulations conducted on supramolecular polyrotaxanes selfassembled from poly(ethylene oxide) (PEO), cyclodextrin (CD), and lithium bistriflimide salts showed that methylation of the hydroxy groups on CD generated higher ionic conductivity. Analysis of structural properties indicated that 70%-80% of Li+ are located outside of the channels formed by the CD rings threaded on PEO chains, providing a new insight into mechanisms of Li+ transport in these structurally complex environments. The spatial distribution of Li+ inspired further modification of CD by grafting polycaprolactone. Both experimental measurements and simulations demonstrated a remarkable increase in ionic conductivity

Transport mechanism of lithium ions in non-coordinating P(VdF-HFP) copolymer matrix

Polymer films based on poly(vinylidene difluoride-co-hexafluoropropylene) (P(VdF-HFP)) with different amounts of bis(trifluoromethane)sulfonimide lithium salt (LiTfSI) were prepared from acetone solution in a doctor blade casting machine under controlled and reproducible drying conditions.The modification of the copolymer-based layers show a significant enhancement of conductivity over several orders of magnitude for increasing LiTfSI content and a constantly low electronic conductivity. The addition of salt results in a structural change of the crystalline areas in the semi-crystalline copolymer matrix from α- to γ-phase of P(VdF), which has been studied using Raman spectroscopy and X-Ray diffraction. Lithium ions are coordinated by oxygen atoms of TfSI− as verified by Raman spectroscopy and molecular dynamics simulations. Based on the experimental data and simulation results, we propose a transport mechanism for the lithium ions through salt channels in the amorphous regions of the non-coordinating copolymer matrix via hopping between stabilized positions

Structural and Dynamical Properties of Tetraalkylammonium Bromide Aqueous Solutions: A Molecular Dynamics Simulation Study Using a Polarizable Force Field

Understanding the behavior of aqueous solutions containing tetraalkyl­ammonium (TAA) cations is of great significance in a number of applications, including polymer membranes for fuel cells. In this work, a polarizable force field has been used to perform atomistic molecular dynamics (MD) simulations of aqueous solutions containing tetramethyl­ammonium (TMA) or tetrabutyl­ammonium (TBA) cations and Br counterions. Extensive MD simulations of TMA-Br/water and TBA-Br/water systems were conducted as a function of solution composition (ion pair:water molar ratios of 1:10, 1:20, 1:30, 1:63, and 1:500) at atmospheric pressure and 298 K. Our simulations demonstrate excellent agreement with available experimental data for solution densities and diffusion coefficients of different species as a function of solution composition, providing us confidence in analyzed structural and dynamic correlations. Various ion–ion and ion–water spatial distributions and the extent of cation aggregation are discussed in light of changes in the structure of cations hydration shells. The delicate balance between cation ionic core interactions with water and the hydrophobic interactions of alkyl tails leads to nontrivial self-assembly of TAA cations and the formation of an interpenetrating cationic network at higher concentrations. The ions and water dynamics are strongly coupled with the observed structural correlations and are analyzed in terms of various residence time, diffusion coefficients, and ionic conductivity

Supramolecular Self-Assembly of Methylated Rotaxanes for Solid Polymer Electrolyte Application

Li+-conducting solid polymer electrolytes (SPEs) obtained from supramolecular self-assembly of trimethylated cyclodextrin (TMCD), poly(ethylene oxide) (PEO), and lithium salt are investigated for application in lithium-metal batteries (LMBs) and lithium-ion batteries (LIBs). The considered electrolytes comprise nanochannels for fast lithium-ion transport formed by CD threaded on PEO chains. It is demonstrated that tailored modification of CD beneficially influences the structure and transport properties of solid polymer electrolytes, thereby enabling their application in LMBs. Molecular dynamics (MD) simulation and experimental data reveal that modification of CDs shifts the steady state between lithium ions inside and outside the channels, in this way improving the achievable ionic conductivity. Notably, the designed SPEs facilitated galvanostatic cycling in LMBs at fast charging and discharging rates for more than 200 cycles and high Coulombic efficiency

Small Groups, Big Impact: Eliminating Li+ Traps in Single-Ion Conducting Polymer Electrolytes

Single-ion conducting polymer electrolytes exhibit great potential for next-generation high-energy-density Li metal batteries, although the lack of sufficient molecular-scale insights into lithium transport mechanisms and reliable understanding of key correlations often limit the scope of modification and design of new materials. Moreover, the sensitivity to small variations of polymer chemical structures (e.g., selection of specific linkages or chemical groups) is often overlooked as potential design parameter. In this study, combined molecular dynamics simulations and experimental investigations reveal molecular-scale correlations among variations in polymer structures and Li+ transport capabilities. Based on polyamide-based single-ion conducting quasi-solid polymer electrolytes, it is demonstrated that small modifications of the polymer backbone significantly enhance the Li+ transport while governing the resulting membrane morphology. Based on the obtained insights, tailored materials with significantly improved ionic conductivity and excellent electrochemical performance are achieved and their applicability in LFP||Li and NMC||Li cells is successfully demonstrated

A Fluorine Rich Borate Ionic Additive Enabling High-Voltage Li Metal Batteries

Lithium-metal batteries (LMBs) are promising alternatives to state-of-the-art Lithium-ion batteries (LIBs) to achieve higher energy densities. However, the poor cyclability of LMBs resulting from Li metal anode (Li0) irreversibility and concomitant electrolyte decompositions limits their practical applications. In this study, we reported a per-fluorinated salt, lithium tetrakis(perfluoro-tertbutyloxy)borate (abbreviated as Li-TFOB) as an electrolyte additive for Li metal batteries, which contains 36 F atoms per molecule. This newly designed ionic additive tuned the chemical composition of the solid-electrolyte interphase (SEI) on Li0 by increasing the amount of LiF and Li-B-O inorganic species. DFT calculations and Molecular dynamics (MD) simulations indicated the preferential reduction of the TFOB anions at Li0, which occurs with a lower free energy change than PF6- anions. The designed ionic additive enables the 4.6 V Li||LiNi0.6Mn0.2Co0.2O2 (NMC622) cell to achieve an average CE of 99.1% and a high-capacity retention of > 50% after 500 cycles. This experiment-simulation joint study illustrated an attractive approach to accelerating the design of electrolytes and interphases for LMBs