Solution, Interfacial, and Interlayer Studies of Electronically Active Polymers

This thesis describes the solution behavior and interfacial properties of electronically active polymers. The performance of such polymers in devices is often determined by their chain conformation and morphology in solution and in thin films. For example, the intricate balance between polymer domain size and crystalline packing of electron donor and acceptor components, as well as the properties at the polymer-metal interface, are crucial for achieving optimal performance in devices, such as solar cells. Chapter 1 presents the current progress in polymer-based solar cells, their fundamental principles, and key factors to improve their efficiency. Literature precedents on the development of materials for the active layer and electrode modifiers are also described in detail. Chapter 2 centers on the solution-driven assembly of a low band gap polymer (PCDTBT) in a marginal solvent to give semicrystalline nanofibers. In contrast to poly(3-alkylthiophene) nanowires prepared by similar techniques, these truncated nanostructures showed undulated features along the fiber axis. Such morphology suggested the nanofibers were formed from packing of smaller crystalline units, giving valuable insight into the ordering of conjugated polymers in solution-processed thin films. Chapter 3 highlights zwitterionic polymers bearing pendent azulene groups with unique optoelectronic properties. The orthogonal solubility of these polar copolymers is enabling for multilayer device fabrication, and proving useful for improved charge collection efficiency, affording high performance solar cells. Chapter 4 describes sulfobetaine (SB) and phosphorylcholine (PC) functionalized zwitterionic poly(acetylene)s (ZIPAs). SB ZIPA proved amenable to nanofiber formation in solution upon addition of a non-solvent, while PC ZIPA remained well-solvated under similar conditions. Both of these polymers significantly reduced the work function of silver, rendering ZIPAs as promising cathode modifiers. Upon incorporating into polymer-based solar cells, the power conversion efficiency significantly increased from 2.5 % to 9.2%. Lastly, chapter 5 summarizes the thesis and presents a perspective for utilizing interlayer materials to enhance the stability and lifetime of future solar cells. A recent work on employing zwitterionic nanoparticles as interlayer materials is discussed with preliminary results presented in the appendix

Applicability of magnetic force models for multi-stable energy harvesters

Multi-stable piezoelectric energy harvesters have been exploited to enhance performance for extracting ambient vibrational energy from a broadband energy source. Since magnetic force plays a significant role in enhancing the dynamic behavior of harvesters, it is necessary to model and understand the significant influencing of structural parameters on magnetic force. Recently, several theoretical modeling methods, including magnetic dipole, improved dipole, magnetic current, and magnetic charge models, have been developed to calculate the magnetic force in multi-stable energy harvesters. However, the influence of structural parameters and magnet dimensions on the accuracy of magnetic force calculation for these methods has not been analyzed. Therefore, it is necessary to investigate the applicability of these methods under a range of operating conditions. New insights into the accuracy and application constraints of these methods are presented in this paper to calculate the impact of magnetic force on multi-stable energy harvesters. From the theoretical derivation of models and numerical results obtained, a quantitative assessment of errors under different structural parameters and magnet sizes is presented and compared to evaluate the application constraints. Moreover, experimental measurements are performed to verify the applicability of these modeling methods for bi-stable and tri-stable energy harvesters with different structural parameters.</p

The urban politics of housing renewal in transitional Shanghai: Reassessing the Chinese pro-growth coalition perspective.

From the 1990s, market-oriented housing renewal took off at extraordinary pace across Chinese cities, modernising the built environment and displacing millions of residents in the process. One prevailing view is that this has been driven by a "growth coalition" of local government and private businesses with the goal of maximising economic potentials through the intensification of land-use. This thesis examines the evolving policies and practices of urban housing renewal in Shanghai since 1990. It questions whether the above perspective adequately captures the underlying socio-political dynamics at work. Through a comprehensive review of housing policies, interviews and analyses of contrasting case studies, it demonstrates that housing renewal had entailed a more diverse set of policies and mechanisms than commonly depicted. Beyond private-funded redevelopment and displacement, local governments have promoted some socially-oriented schemes, as well as recently supporting the piecemeal gentrification of neighbourhoods. This research shows that it is useful to move beyond a monolithic conception of the Chinese growth coalition. The local government plays an increasingly dualistic role in housing renewal. Beyond its core concern to facilitate economic growth and 'global city' building through comprehensive redevelopment, it has evolved socially- oriented housing policies, enlarged market regulation, and made concessions to disadvantaged groups in the interest of maintaining social harmony. Property developers were not a homogenous profit-seeking group in Shanghai's urban growth-coalition. Various quasi-governmental enterprises played a role in delivering socially-oriented projects under bureaucratic command of the local government. Finally, although grass roots actors are politically excluded, their cumulative actions including neighbourhood rehabilitation and protests can sometimes influence policies and urban planning decisions

Retraction and Generalized Extension of Computing with Words

Fuzzy automata, whose input alphabet is a set of numbers or symbols, are a formal model of computing with values. Motivated by Zadeh's paradigm of computing with words rather than numbers, Ying proposed a kind of fuzzy automata, whose input alphabet consists of all fuzzy subsets of a set of symbols, as a formal model of computing with all words. In this paper, we introduce a somewhat general formal model of computing with (some special) words. The new features of the model are that the input alphabet only comprises some (not necessarily all) fuzzy subsets of a set of symbols and the fuzzy transition function can be specified arbitrarily. By employing the methodology of fuzzy control, we establish a retraction principle from computing with words to computing with values for handling crisp inputs and a generalized extension principle from computing with words to computing with all words for handling fuzzy inputs. These principles show that computing with values and computing with all words can be respectively implemented by computing with words. Some algebraic properties of retractions and generalized extensions are addressed as well.Comment: 13 double column pages; 3 figures; to be published in the IEEE Transactions on Fuzzy System