The evolution of the three-dimensional (3D) morphology of a Si-based electrode upon cycling (1st discharge, 1st charge and 2nd discharge) is studied by in-situ synchrotron X-ray tomography. The ...Si-based electrode is constituted of silicon/carbon black/carboxymethylcellulose (Si/CB/CMC) embedded in a commercial carbon fiber paper, acting as a flexible 3D current collector. Its initial areal discharge capacity is 4.9 mAh cm−2. A reconstructed volume of 293 × 293 × 137 μm3 is analyzed with a resolution of ∼0.3 μm. Three phases are identified: (i) the solid phase (C fibers + Si + CB + CMC), (ii) the electrolyte phase (pores filled with electrolyte) and (iii) the gas phase (electrolyte-free pores). Their respective volume fraction, size distribution and connectivity, and also the dimensional changes of the electrode along the three axes are quantified during cycling. At the beginning of the 1st discharge (lithiation), the formation of gas channels attributed to the reductive electrolyte decomposition is observed. During the 1st charge, large cracks are formed through the electrode, which reclose during the subsequent discharge. The electrode expansion/contraction due to the Si volume change is partially irreversible, occurs mainly in the transverse direction and is much larger in the bottom part of the electrode.
•Morphological changes of a Si/C paper electrode are investigated by in-situ XRCT.•The reductive electrolyte decomposition induces the formation of gas channels.•The electrode cracking initiates during the 1st charge (delithiation).•The cracks close during the subsequent discharge.•The volume change of the electrode is larger and less reversible in its bottom part.
Nanoscale zero-valent irons (nZVIs) are easy to agglomerate and deactivate, which limited the practical applications in the subsurface for in situ remediation of contaminated groundwater due to poor ...radius of influence. Here, we utilized the dual support effect of coupling surface-modified carbon black with a surfactant (carboxymethyl cellulose (CMC) or sodium dodecyl sulfate (SDS)) to manipulate the charge, electron, and geometric structure of the interface, the obtained Fe/CB/CMC (wt%=1:1:2) and Fe/CB/SDS (wt%=1:2:1) suspensions exhibited superior removal capacity toward As(III) with capacities of 80.7 and 90.7 mg g-1, respectively. In a clay medium, 25.2% and 18.0% of nZVIs in Fe/CB/CMC-1:1:2 and Fe/CB/SDS-1:2:1 can break through the column while approximately 100% are retained in bare nZVIs under the same conditions. In addition, input velocity and ionic strength demonstrate a positive correlation with the retention of nZVIs in the Fe/CB/CMC-112 and a slight impact on the deposition of nZVIs in the Fe/CB/SDS-121 due to the rheology and charge differences between CMC and SDS. This study demonstrates the feasibility of combining anionic surfactants and carbon supports to enhance the reactivity and mobility of nZVIs for in situ remediation.
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•Enhanced mobility of nZVIs is obtained with the assistance of CB and CMC/SDS.•Input velocity and ion strength show a significant effect on nZVIs transport.•Sedimentation is the main mechanism governing the transport of supported nZVIs.
The evolution of the three-dimensional (3D) morphology of a Si-based electrode upon cycling (1 st discharge, 1 st charge and 2 nd discharge) is studied by in-situ synchrotron X-ray tomography. The ...Sibased electrode is constituted of silicon/carbon black/carboxymethylcellulose (Si/CB/CMC) embedded in a commercial carbon fiber paper, acting as a flexible 3D current collector. Its initial areal discharge capacity is 4.9 mAh cm-2. A reconstructed volume of 293293137 µm 3 is analyzed with a resolution of 0.3 µm. Three phases are identified: (i) the solid phase (C fibers + Si + CB + CMC), (ii) the electrolyte phase (pores filled with electrolyte) and (iii) the gas phase (electrolyte-free pores). Their respective volume fraction, size distribution and connectivity, and also the dimensional changes of the electrode along the three axes are quantified during cycling. At the beginning of the 1 st discharge (lithiation), the formation of gas channels attributed to the reductive electrolyte decomposition is observed. During the 1 st charge, large cracks are formed through the electrode, which reclose during the subsequent discharge. The electrode expansion/contraction due to the Si volume change is partially irreversible, occurs mainly in the transverse direction and is much larger in the bottom part of the electrode.
Nanocomposites formed by mixing nanoparticles and polymers offer a limitless creative space for the design of functional advanced materials with a broad range of applications in materials and ...biological sciences. Here we focus on aqueous dispersions of hydrophobic colloidal soot particles, namely carbon black (CB) dispersed with a sodium salt of carboxymethylcellulose (CMC), a food additive known as cellulose gum that bears hydrophobic groups, which are liable to bind physically to CB particles. Varying the relative content of CB nanoparticles and cellulose gum allows us to explore a rich phase diagram that includes a gel phase. We investigate this hydrogel using rheometry and electrochemical impedance spectroscopy. CB-CMC hydrogels display two radically different types of mechanical behaviors that are separated by a critical CMC-to-CB mass ratio \(r_c\). For \(r<r_c\), i.e., for low CMC concentration, the gel is electrically conductive and shows a glassy-like viscoelastic spectrum, pointing to a microstructure composed of a percolated network of CB nanoparticles decorated by CMC. In contrast, gels with CMC concentration larger than \(r_c\) are non-conductive, indicating that the CB nanoparticles are dispersed in the cellulose gum matrix as isolated clusters, and act as physical crosslinkers of the CMC network, hence providing mechanical rigidity to the composite. Moreover, in the concentration range, \(r>r_c\) CB-CMC gels display a power-law viscoelastic spectrum that depends strongly on the CMC concentration. These relaxation spectra can be rescaled onto a master curve that exhibits a power-law scaling in the high-frequency limit, with an exponent that follows Zimm theory, showing that CMC plays a key role in the gel viscoelastic properties for \(r>r_c\). Our results offer a characterization of CB-CMC dispersions that will be useful for designing nanocomposites based on hydrophobic interactions.
碩士
國立臺灣科技大學
化學工程系
107
The evaporation of solution drop of surfactants (SDS, Triton X-100 and C12E6) on parafilm was studied. The relaxations of wetting diameter, contact angle (CA), drop volume, and ...surface area of the sessile drops of surfactant were monitored using a sessile drop tensiometer during the drop evaporation (relative humidity Hr inside the environmental chamber is ~ 100% at the first 70 s, then Hr ~ 65% at t > 70s). The advancing and receding CA (θa and θr) were then determined from relaxation profile of CA.
For SDS solution droop, the wetting diameter increased slightly right after the sessile drop was formed (at Hr ~ 100%), the CA then remained constant for a specific time period (concentration dependent), at which the θa was determined. For TX-100 and C12E6 solutions, a similar constant CA (set to be the θa) was observed right after the drop being formed. However, the triple line of the sessile drop advanced continuously and then reached a constant wetting diameter. This advance in triple line resulted in a decline in the CA, and another constant CA was observed during as the wetting diameter leveled off. Therefore, two advancing CA (θa1 and θa2) were identified for TX-100 and C12E6 solution drops.
The dynamic, advancing and receding CAs were found to be strongly affected by the concentration (Cb) of the aqueous surfactant solutions. This dependence was attributed to the variations in both the interfacial tension at solid-liquid and liquid-gas interfaces. For diluted solutions, θa and θr were observed to decrease with increasing Cb. The θa of SDS became constant at Cb > cmc; i.e., the relaxation of θa and θr have a clear break at cmc which is similar to that of the equilibrium surface tension of SDS solution. However, the breakpoint of the θa of TX-100, C12E6 were observed at Cb >> cmc. This shift in the breakpoints of θa was attributed to the non-equilibrium adsorption of surfactant molecules at liquid-solid and liquid-gas interfaces that resulted from a relatively slower adsorption rate.
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Esta tese apresenta a preparação e caracterização de derivados de celulose e também de novos materiais multifuncionais baseados na celulose produzida pela bactéria Gluconacetobacter xylinus e nos seus derivados respectivamente. A celulose bacteriana (CB) possui fórmula molecular idêntica a celulose de plantas (CP) e apresenta uma estrutura de nanofios de celulose dispostos numa rede tridimensional. Membranas secas foram utilizadas para a preparação dos derivados celulósicos. Foram obtidos os derivados acetato de celulose (AC), celulose microcristalina (MCC), carboximetilcelulose (CMC) e metilcelulose (MC). O AC apresentou valores de grau de substituição (GS) que foram de 2,3 a 2,8 e solubilidade em acetona ou diclorometano (dependendo do GS). A MCC foi obtida como um pó fino na cor marfim com grau de polimerização em torno de 200 unidades de anidroglucose (AGU), com a vantagem de que nas suas partículas ainda apresenta uma memória da rede tridimensional da CB. Foram obtidos CMCs com GS de 0,1 a 0,8 e com excelente solubilidade em água. Finalmente foram obtidas amostras de MC, com GS de 0,54 para a síntese em iodometano e 2,3 para a síntese em dimetilsulfato (DMS), com boa solubilidade em água. Os derivados, de acordo com suas propriedades e sua solubilidade foram utilizados para a preparação e caracterização de novos materiais na área de aplicações óticas. As membranas de AC,CMC e CB foram utilizados como substratos para a preparação de dispositivos flexíveis de emissão de luz, FOLEDs (Flexible Organic Light Emitting Diodes). Os substratos foram recobertos com um filme fino de ITO. Os FOLEDs foram então obtidos pela deposição de filmes orgânicos por evaporação térmica, na seguinte sequencia: ftalocianina de cobre (CuPC)/ N,N’-difenil-N,N’-bis(1-naftil) (1,1’bifenil)-4,4’diamina (NPB)...
This thesis presents the preparation and characterization of cellulose derivatives and also new multifunctional materials based on cellulose produced by bacteria Gluconacetobacter xylinus and their derivatives respectively. Bacterial cellulose (BC) shows molecular formula identical to plant cellulose (PC) and a three-dimensional cellulose nanowires network. Dried membranes were used for the preparation of cellulose derivatives. The derivatives cellulose acetate, microcrystalline cellulose, carboxymethylcellulose and methylcellulose were obtained. The AC showed values of degree of substitution (DS) of 2.3 to 2.8 and soluble in acetone or dichloromethane. The MCC was obtained as an ivory colored fine powder with degree of polymerization around 200 anhydroglucose units (AGU), with the advantage that particles still present in its memory the three-dimensional network of CB. CMCs were obtained with GS 0.1 to 0.8 and has excellent water solubility. Finally samples of MC were obtained with DS of 0.54 to 2.3 from iodomethane and dimethyl sulfate synthesis respectively, with good water solubility. The derivatives (according to their properties and their solubility) were used for the preparation and characterization of new materials in the field of optical applications. The cellulose acetate and bacterial cellulose membranes were used as substrates for the preparation of flexible devices for light emission, FOLEDs. The substrates were coated with thin films of ITO. FOLEDs were obtained by thermal evaporation, in the following sequence: copper phthalocyanine (CuPc) /(N,N΄-bis(1- naphtyl)- N,N΄-diphenyl-1,1´-biphenyl-4,4´-diamine) (NPB) /tris(8-hydroxyquinoline) aluminum and the aluminum contact. The total maximum luminance values for the FOLED was 530 (cd/m2), which is comparable with a glass OLED prepared with... (Complete abstract click electronic access below)
