Anisotropic Stimuli-Responsive Polymeric Nanoparticles: Synthesis and Characterization

This dissertation focuses on the design, synthesis and characterization of stimuli-responsive anisotropic nanoparticles with various morphologies. Size- and shape-tunable Janus nanoparticles consisting of poly(methyl methacrylate/n-butyl acrylate) (p(MMA/nBA)), poly(pentafluorostyrene/nBA) (p(PFS/nBA) and poly(2-(N,N′-dimethylamino) ethyl methacrylate/nBA) (p(DMAEMA/nBA)) phases were synthesized via consecutive seeded emulsion polymerization. These Janus nanoparticles are capable of changing size and morphology in response of temperature and/or pH changes, which may have potential applications as solid surfactants. Gibbous and inverse-gibbous nanoparticles were synthesized viacopolymerization of fluorinated monomers in the presence of pMMA or polystyrene (pSt) seed particles. The morphology of the gibbous nanoparticles can be controlled by polymerization conditions. Incorporation and copolymerization of methacrylic acid (pMAA) components results in pH-responsive gibbous nanoparticles with numerous size-tunable bulges. In addition, the gibbous and inverse-gibbous nanoparticles can be controlled to self-assemble in solutions but upon evaporation of solvents form two- and three-dimensional assemblies stabilized by electrostatic interactions and shape-matching topographies. Taking advantage of the heterogeneous nature of emulsion polymerization, surfactant free heterogeneous radical polymerization (SFHRP) was developed to synthesize ultra-high molecular weight amphiphilic block copolymers. This is one-step process of preparing block copolymer morphologies. The amphiphilic block copolymers can form thermochromic inverse micelles in organic solvents, capable of selectively scattering light as a function of temperature. The approach was also utilized to synthesize polymer nanowires via in-situ self-assembly of amphiphilic block copolymers. This kinetically controlled directional growth may lead to many industrial applications, including synthesis of other block copolymers, polymeric nanowire latexes and other morphologies

Stereoselective Synthesis of Spirooxindole Amides and Cyanohydrin Alkyl Ethers

A new family of spirooxindole amides were synthesized by a sequence of hydrozirconation, acylation, and intramolecular cyclization reactions. Three of the four possible diastereomers can be obtained as the major isomers through this process. The spirooxindole structure has many points for diversification, and a 37-membered library was synthesized through this approach by collaborators. A comparison with known compound collections showed that this new spirooxindole library possessed good chemical diversity. Cyanohydrin alkyl ethers, the key intermediate in the above multi-component hydrozironation reaction, were effectively synthesized through a Brønsted acid-mediated hydrocyanation of vinyl ethers. The enantiomerically enriched product can be obtained by asymmetric hydrocyanation of vinyl ethers catalyzed by a chiral Brønsted acid, and the catalyst can be regenerated by PhOH. As far as we know, this research represents the first example of chiral Brønsted acid mediated intermolecular addition of silylated nucleophiles with vinyl ethers. The ion pair interaction between the conjugate base of the chiral Brønsted acid and the oxocarbenium ion was revealed by computational modeling, which explained the origin of the enantioselectivity and the substrate scope of this reaction

Energy Consumption Model of WSN Based on Manifold Learning Algorithm

Energy saving is one of the most important issues in wireless sensor networks. In order to effectively model the energy consumption -in wireless sensor network, a novel model is proposed based on manifold learning algorithm. Firstly, the components of the energy consumption by computational equations are measured, and the objective function is optimized. Secondly, the parameters in computational equations are estimated by manifold learning algorithm. Finally, the simulation experiments on OPNET and MATLAB Simulink are performed to evaluate the key factors influencing the model. The experimental results show that the proposed model had significant advantage in terms of synchronization accuracy and residual energy in comparison with other methods

Screening ethnically diverse human embryonic stem cells identifies a chromosome 20 minimal amplicon conferring growth advantage

The International Stem Cell Initiative analyzed 125 human embryonic stem (ES) cell lines and 11 induced pluripotent stem (iPS) cell lines, from 38 laboratories worldwide, for genetic changes occurring during culture. Most lines were analyzed at an early and late passage. Single-nucleotide polymorphism (SNP) analysis revealed that they included representatives of most major ethnic groups. Most lines remained karyotypically normal, but there was a progressive tendency to acquire changes on prolonged culture, commonly affecting chromosomes 1, 12, 17 and 20. DNA methylation patterns changed haphazardly with no link to time in culture. Structural variants, determined from the SNP arrays, also appeared sporadically. No common variants related to culture were observed on chromosomes 1, 12 and 17, but a minimal amplicon in chromosome 20q11.21, including three genes expressed in human ES cells, ID1, BCL2L1 and HM13, occurred in >20% of the lines. Of these genes, BCL2L1 is a strong candidate for driving culture adaptation of ES cells

Rationally Designed Gibbous Stimuli-Responsive Colloidal Nanoparticles

Multiphase colloidal copolymer nanoparticles, if properly designed, offer a number of unique properties and well-documented technological opportunities for drug delivery, nanolithography, high surface area colloidal crystals, or hollow nanoparticles, to name just a few. Using a simple free radical polymerization process, we synthesized copolymer nanoparticles with controlled stimuli-responsive phase-separated gibbosities. The topography of the gibbous phase can be controlled by the copolymer composition and polymerization conditions. When pH-sensitive monomers were copolymerized onto surface bulges, pH changes resulted in localized gibbous phase dimensional changes. Facilitated by monomer diffusion into interfacial particle seed solution regions, localized polymerization near the surface is responsible for the formation of phase-separated gibbous topographies. This general approach may offer a number of possibilities for controllable design of ordered heterogeneous copolymer morphologies for a variety of applications

Damage Characteristics and Energy Evolution of Bituminous Sandstones under Different Cyclic Amplitudes

In many underground engineering projects, rocks are often subjected to cyclic loading and unloading, such as repeated excavation of roadway surrounding rock, which will lead to damage to underground rocks, and the energy of rocks also changes. Therefore, to study the energy evolution and damage characteristics of rocks under cyclic loading and unloading, different cyclic loading and unloading tests of bituminous sandstones under constant amplitude were conducted. Under cyclic loading and unloading, the lower limit stress was 40% of the rock peak intensity, the cyclic amplitude was 20–40% of the peak intensity, and the number of loading–unloading cycles was 10–30. The quantitative characterization of the damage degrees of bituminous sandstone was realized by the ultrasonic wave velocity and elasticity modulus methods. The energy evolution and damage characteristics of bituminous sandstone under different amplitudes and number of loading–unloading cycles were investigated through the energy dissipation method. Results showed that under cyclic loading and unloading, the ultrasonic wave velocity and elasticity modulus of bituminous sandstone decreased gradually; The damage variable shows a trend of rapid and then stable growth and has a power function relationship with the number of cycles; The input energy density and dissipation energy density curves were in L-shaped distribution, whereas the elastic energy density remained stable. The results of this study can provide some theoretical references to underground engineering construction

Regioselective Bromination of Thieno[2′,3′:4,5]pyrrolo[1,2‑d][1,2,4]triazin-8(7H)‑one and Sequential Suzuki Couplings

Regioselective bromination of thieno[2',3':4,5]pyrrolo[1,2-d][1,2,4]triazin-8(7H)-one at 2 or 9-position was achieved by modulating the basicity of the reaction conditions. An anion directed site-specific bromination mechanism was proposed. In addition, a one-pot bromination-Suzuki coupling protocol was developed for quick access of analogs at 9-position

Effects of Yak Dung Biomass Black Carbon on the Soil Physicochemical Properties of the Northeastern Qinghai-Tibet Plateau

The physicochemical properties of soils might be affected by the addition of biomass black carbon, a special black carbon produced by incomplete combustion of biomass. Therefore, this study performed experiments to explore the effects of yak dung biomass black carbon (YBC) on physicochemical properties of soils in the northeastern Qinghai-Tibet Plateau. Three YBCs (pyrolyzed at 300, 500, and 700 degrees C) were separately added into four typical soils with three addition amounts (1%, 5%, and 10%). Changes of soil texture, pH, electrical conductivity (EC), cation exchange capacity (CEC), CHN contents, morphologies, functional groups, and mineral constituents of soils were comparatively studied. The results showed that addition of YBCs affected physicochemical properties of soils. Soil pH, EC, CEC, and carbon/nitrogen content were positively related with addition amount of YBCs. YBC particles were unevenly distributed among soil particles and positively related with addition amount. Addition of YBCs did not change texture, functional groups, and mineral constituents of soils. These results indicated that addition of YBC would be beneficial to stability of the soil ecosystem and sustainability of the northeastern Qinghai-Tibet Plateau

Instantaneous Directional Growth of Block Copolymer Nanowires During Heterogeneous Radical Polymerization (HRP)

Polymeric nanowires that consist of ultrahigh molecular weight block copolymers were instantaneously prepared via one-step surfactant-free heterogeneous radical polymerization (HRP). Under heterogeneous reaction and initiator-starvation conditions, the sequential copolymerization of hydrophilic and hydrophobic monomers facilitates the formation of amphiphilic ultrahigh molecular weight block copolymers, which instantaneously assemble to polymeric nanowires. As polymerization progresses, initially formed nanoparticles exhibit the directional growth due to localized repulsive forces of hydrophilic blocks and confinement of the hydrophobic blocks that adopt favorable high aspect ratio nanowire morphologies. Using one-step synthetic approach that requires only four ingredients (water as a solvent, two polymerizable monomers (one hydrophilic and one hydrophobic), and water-soluble initiator), block copolymer nanowires ∼70 nm in diameter and hundreds of microns in length are instantaneously grown. For example, when 2-(<i>N</i>,<i>N</i>-dimethylamino)­ethyl methacrylate (DMAEMA) and styrene (St) were copolymerized, high aspect ratio nanowires consist of ultrahigh (>10⁶ g/mol) molecular weight pDMAEMA-<i>b</i>-St block copolymers and the presence of temperature responsive pDMAEMA blocks facilitates nanowire diameter changes as a function of temperature. These morphologies may serve as structural components of the higher order biological constructs at micro and larger length scales, ranging from single strand nanowires to engineered biomolecular networks capable of responding to diverse and transient environmental signals, and capable of dimensional changes triggered by external stimuli

Tri-Phasic Size- and Janus Balance-Tunable Colloidal Nanoparticles (JNPs)

These studies show synthesis of triphasic size- and Janus balance (JB)-tunable nanoparticles (JNPs) utilizing a two-step emulsion polymerization of pentafluorostyrene (PFS) and 2-(dimethylamino)­ethyl methacrylate (DMAEMA) and <i>n</i>-butyl acrylate (nBA) in the presence of poly­(methyl methacrylate (MMA)/nBA) nanoparticle seeds. Each JNP consists of three phase-separated copolymers: p­(MMA/nBA) core, temperature, and pH-responsive (p­(DMAEMA/nBA)) phase capable of reversible size and shape changes, and shape-adoptable (p­(PFS/nBA)) phase. Due to built-in second-order lower critical solution temperature (II-LCST) transition of p­(DMAEMA/nBA) copolymer, macromolecular segments collapse when temperature increases from 30 to 45 °C, resulting in size and shape changes. The p­(DMAEMA/nBA) and p­(MMA/nBA) phases within each JNP assume concave, flat, or convex shapes, forcing p­(PFS/nBA) phase to adopt convex, planar, or concave interfacial curvatures, respectively. As a result, the JB can be tuned from 3.78 to 0.72. The presence of pH-responsive DMAEMA component also facilitates the size and JB changes due to protonation of the tertiary amine groups of p­(DMAEMA/nBA) backbone. Synthesized in this manner, JNPs are capable of stabilizing oil droplets in water at high pH to form Pickering emulsions, which at lower pH values release oil phase. This process is reversible and can be repeated many times