Polymer-Ligated Nanocrystals with Tunable Dimensions, Compositions, and Architectures

The ability to produce monodisperse nanocrystals with stable and tunable surface chemistry is of key importance to render investigation into their size- and shape-dependent physical properties and thus an array of applications including electronics, photonics, catalysis, sensors, energy storage, information technology, bionanotechnology, etc. In this context, nonlinear block copolymer nanoreactor has emerged as a general and robust route to synthesis of a gallery of nanocrystals with precisely controlled sizes, shapes, compositions, and surface chemistry. In this thesis, I capitalized on a set of rationally designed star-like and bottlebrush-like block copolymer to template the growth of a host of functional 0D and 1D nanocrystals with controlled dimensions, compositions, and architectures, and scrutinize the dependence of physical properties and energy-related applications on their size, shape, and surface chemistry. First, a series of star-like copolymers were synthesized via sequential atom transfer radical polymerization (ATRP) of tert-butyl acrylate (tBA) and styrene from star-like macroinitiators, brominated β-cyclodextrin (β-CD). Due to the living nature of ATRP, the molecular weight of each polymer block can be precisely controlled by simply tuning polymerization time and a low polydispersity index (PDI) can be achieved. The inner hydrophobic poly(tert-butyl acrylate) (PtBA) blocks were then converted into hydrophilic poly(acrylic acid) (PAA), which strongly coordinates with the metal moieties of precursors of targeted nanocrystals, leading to the nucleation and growth of nanocrystals confined within the space occupied by the PAA blocks. As a result, the size and shape of nanocrystals can be readily controlled by the molecular weight of PAA blocks (i.e., diameter of nanoparticles). Moreover, the outer PS blocks, originally covalently linked to the inner PAA blocks, form a layer of permanently anchored ligands on the nanocrystal surface to enable stable surface chemistry. This synthetic strategy were successfully applied for preparing a diversity of functional nanoparticles for the investigation into their physical properties and applications. Specifically, this judiciously designed nanoreactor was utilized to craft monodispersed magnetic spinel CoFe2O4 nanoparticles, which was studied for their magnetic and surface chemistry related electrocatalytic activity. It was the first systematic scrutiny of the influence of spin-pinning effect in spinel nanoparticles realized via surface reconstruction on the oxygen evolution reaction (OER). Second, using the same chemistry, 1D bottlebrush-like PAA-b-PS templates can be realized by employing brominated cellulose (Cell-Br) as macroinitiators. Due to the larger number of side chains on one Cell-Br macroinitiator (ranging from about 40 chains to more than 150 chains), high quality bottlebrush-like block copolymers are more challenging to synthesize than star-like block copolymers, which only have 21 arms. Systematic scrutiny was made to investigate the reaction conditions (e.g., catalyst ratio, ligand ratio, reaction concentration, degassing method, etc.) that affect the uniform growth of the highly dense block copolymer side chains, which has a determining effect on the quality of the bottlebrush-like templates and their application as nanoreactors for the synthesis of 1D nanocrystals. In addition to focusing on the precise synthesis of 0D and 1D nanocrystals via nanoreactor strategy, this thesis also covers the practical application of multi-functional nanocomposites. In this work, a ternary nanocomposite consisting of antibacterial silver (Ag) NPs, photocatalytic titania oxide (TiO2) NPs, and upconverting NPs are prepared, manifesting a greatly enhanced biocidal performance under ambient environment. It was found that the visible light (blue) and ultraviolet (UV) light which were converted from near infrared (NIR) radiation by the NaYF4@Yb:Tm upconverting NPs can be effectively absorbed by Ag and TiO¬2 NPs to generate electrons and electron-hole pairs, respectively. Reactive oxygen species (ROS) could then be produced from the reactions between environment and the electrons and holes to terminate bacteria. The outstanding antibacterial performance of this nanocomposite system renders it the potential to be used in food packaging industry. Moreover, reversible photo responsive Ruddlesden-Popper 2D perovskite nanoplatelets were explored in this thesis. Colloidal two-dimensional RP perovskite nanoplatelets with a general formula L2(ABX3)n-1BX4 are a rapidly emerging type of semiconductor materials with excellent optical and electronic properties. Research on the functional organic spacers (L) has become a popular direction in the past several years. Inspired by our previous research about reversible photo-crosslinkable nanoparticles realized by capitalizing on star-like nanoreactors with photo responsive coumarin containing repeat units in the outer block, the preparation of RP lead halide perovskite nanoplatelets with coumarin containing ammonium as organic spacers was attempted. Molecular modification and mixed organic spacer strategies were adopted to overcome the solubility limitation of coumarin containing molecules in non-polar solvents. Such coumarin containing 2D perovskite nanoplatelets will undergo controllable and reversible layer-by-layer crosslinking and de-crosslinking under radiation of certain wavelength, leading to many intriguing and tunable optical and electronic properties.Ph.D

The Effectiveness of Covert vs. Overt Brand Visibility in Video Advertising

This research is a mixed-methods (qualitative and quantitative) and semi-structured (survey and interview) study on the effectiveness of covert vs. overt commercials towards the influence of the brand attitude and purchase intention of consumers. Covert commercials are video advertisements that present the promoted brand and sponsor unclearly, and make its marketing nature hard to recognize at first sight. Overt commercials are video advertisements that present the promoted brand and sponsor clearly, and disclose its sponsor and marketing nature expressively. The survey and interview are designed to measure participants’ responses to four commercials, either covert or overt, with regards to the AIDA model, advertising skepticism, perceived believability, and brand attitude. This research contributes to the present literature regarding covert and overt video advertising, and gives advertisers and businesses valuable insights into covert commercials and their implications for improving marketing strategies and future study

Aging Properties of Polyvinylidenefluoride-Coated Polyesters Used in Tensioned Membrane Structure: Effect of Loading Protocol and Environment

This paper presents the degradation behaviors of polyvinylidenefluoride- (PVDF-) coated polyesters used in tensioned membrane structure by artificial accelerated tests, in which the effects of environment factors and loading conditions are studied. Results show that the degradation ratio of main mechanical parameters (tensile strength, tear strength, and elastic modulus) is related to the aging depth of substrate and coating. The degradation of weather resistance can be considered as the accumulation of environment and loads. The ultraviolet radiation and the temperature mainly affect the mechanical properties of yarns, while the preloading before aging tests can change the crimp degrees and decrease the coating thickness. The effect of loads should not be ignored in the weather resistance analysis of PVDF-coated polyesters. A simplified method composed of cyclic tests and stress-relaxation tests is suggested to study the long-term weather resistance of PVDF-coated polyesters. It can provide a theoretical reference for the proposal of resistance partial factor in the design of tensioned membrane structure

Understanding the Role of Bounty Awards in Improving Content Contribution: Bounty Amount and Temporal Scarcity

The bounty award system has been implemented on UGC platforms to address specific issues and improve content contributions. This study aims to assess its effectiveness by examining the bounty amount and temporal scarcity. Based on the optimistic bias theory, we posit that the competition for bounty awards among users can have a positive effect, as users may overestimate their chances of winning and persist in their efforts. Additionally, we hypothesize that the amount of bounty award does not have a linear effect on the quantity and quality of user-generated content, but instead follows an inverted U-shaped relationship. Furthermore, drawing on the stuck-in-the-middle (STIM) effect, we hypothesize that temporal scarcity influences contributors\u27 effort allocation in a U-shaped relationship. By exploring these hypotheses, we aim to advance the understanding of the underlying mechanisms of bounty awards and contribute to the development of effective peer incentive strategies

Rapid Invasion of Spartina Alterniflora in the Coastal Zone of Mainland China: Spatiotemporal Patterns and Human Prevention

Given the extensive spread and ecological consequences of exotic Spartina alterniflora (S. alterniflora) over the coast of mainland China, monitoring its spatiotemporal invasion patterns is important for the sake of coastal ecosystem management and ecological security. In this study, Landsat series images from 1990 to 2015 were used to establish multi-temporal datasets for documenting the temporal dynamics of S. alterniflora invasion. Our observations revealed that S. alterniflora had a continuous expansion with the area increasing by 50,204 ha during the considered 25 years. The largest expansion was identified in Jiangsu Province during the period of 1990-2000, and in Zhejiang Province during the periods 2000-2010 and 2010-2015. Three noticeable hotspots for S. alterniflora invasion were Yancheng of Jiangsu, Chongming of Shanghai, and Ningbo of Zhejiang, and each had a net area increase larger than 5000 ha. Moreover, an obvious shrinkage of S. alterniflora was identified in three coastal cities including the city of Cangzhou of Hebei, Dongguan, and Jiangmen of Guangdong. S. alterniflora invaded mostly into mudflats (>93%) and shrank primarily due to aquaculture (55.5%). This study sheds light on the historical spatial patterns in S. alterniflora distribution and thus is helpful for understanding its invasion mechanism and invasive species management

Cache-aided Interference Management Using Hypercube Combinatorial Cache Designs

We consider a cache-aided interference network which consists of a library of $N$ files, $K_T$ transmitters and $K_R$ receivers (users), each equipped with a local cache of size $M_T$ and $M_R$ files respectively, and connected via a discrete-time additive white Gaussian noise channel. Each receiver requests an arbitrary file from the library. The objective is to design a cache placement without knowing the receivers' requests and a communication scheme such that the sum Degrees of Freedom (sum-DoF) of the delivery is maximized. This network model has been investigated by Naderializadeh {\em et al.}, who proposed a prefetching and a delivery schemes that achieves a sum-DoF of $\min\{\frac{{M_TK_T+K_RM_R}}{{N}}, K_R\}$. One of biggest limitations of this scheme is the requirement of high subpacketization level. This paper is the first attempt in the literature (according to our knowledge) to reduce the file subpacketization in such a network. In particular, we propose a new approach for both prefetching and linear delivery schemes based on a combinatorial design called {\em hypercube}. We show that required number of packets per file can be exponentially reduced compared to the state of the art scheme proposed by Naderializadeh {\em et al.}, or the NMA scheme. When $M_TK_T+K_RM_R \geq K_R$, the achievable one-shot sum-DoF using this approach is $\frac{{M_TK_T+K_RM_R}}{{N}}$ , which shows that 1) the one-shot sum-DoF scales linearly with the aggregate cache size in the network and 2) it is within a factor of $2$ to the information-theoretic optimum. Surprisingly, the identical and near optimal sum-DoF performance can be achieved using the hypercube approach with a much less file subpacketization.Comment: 6 pages, 4 figures, accepted by ICC 201