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Open Access Publications from the University of California

Scholarly Works (17 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2024)

The hydration of calcium-silicate-hydrate (C-S-H) gel, a predominant hydration product of ordinary Portland cement, plays a pivotal role in determining the performance and service life of widely used cement-based materials. Despite its significance, the complete resolution of the C-S-H gel structure remains elusive, particularly regarding the unclear reaction mechanisms at the micro- and nanoscales, impeding a comprehensive understanding of the hydration process and mechanisms. In this study, a combination of electron microscopy and molecular simulation techniques is employed to decode the atomic-resolution fundamental composition of the C-S-H gel. The research delves deep into the microstructural and compositional evolution of C-S-H gel during hydration and elucidates its service and degradation patterns under various extreme environmental conditions. The findings contribute to a profound exploration of the fundamental principles underlying cement hydration, offering theoretical guidance for regulating the hydration process and enhancing the performance of cementitious materials. The main conclusions are summarized as follows:1. Identification of intrinsic defects in cement particles and their crucial role in early hydration processes and C-S-H gel nucleation and growth. Advanced scanning transmission electron microscopy is utilized to reveal defects at the single-atomic level within tricalcium silicate particles, including vacancies, doping, dislocations, rough surfaces, and grain boundaries. Defects in cement particles are found to play a vital role in promoting initial dissolution and providing nucleation sites for hydration products. A comprehensive understanding of defect formation mechanisms in cement particles at the single-atomic level is provided, suggesting new strategies for defect engineering in cement manufacturing. 2. Clarification of the thermal response and stability of C-S-H gel at the nanoscale. Structural changes in C-S-H gel under thermal induction (20 to 800°C) are investigated using in-situ transmission electron microscopy. The gel exhibits volume contraction characteristics, with an average rate of 0.02 μm²/°C, starting from 400°C. Additionally, high-temperature self-healing of C-S-H gel is observed, with 800 nm pores shrinking and healing due to reconstruction and deformation between C-S-H blocks, accompanied by a decrease in the Ca/Si ratio. Electron diffraction results detect temperature-driven phase transitions and degradation of C-S-H gel: above 800°C, the gel transforms into a metastable calcium silicate mineral. This work provides experimental evidence for the thermal stability of C-S-H gel at high temperatures and contributes to understanding the degradation mechanisms in concrete under thermal stress. 3. Investigation of the dynamic processes of morphology, composition, and structure of hydration products during carbonation, revealing phase transitions and carbonation mechanisms in C-S-H gel. Nanoscale observations highlight the formation and evolution of aragonite calcite crystals during carbonation: spindle-shaped carbonate initially forms on the C-S-H matrix, transforming into layered rhombic particles and eventually into polyhedral particles. An intrinsic relationship between microstructure and mechanical properties is established using atomic force microscopy, directly measuring the elastic constant of post-carbonation aragonite crystals as approximately 68 GPa. This work provides new opportunities for understanding potential carbonation mechanisms at the nanoscale, offering crucial theoretical guidance for shape control methods of aragonite and the design of advanced carbonation techniques. The research not only provides profound theoretical insights into the carbonation mechanism but also offers essential theoretical guidance for shape control methods and future advanced carbonation technologies. Through this study, a solid foundation is laid for understanding and applying carbonate materials, providing a fresh perspective for constructing more durable and efficient building materials in the future. In conclusion, this study, through an in-depth exploration of the micro-nano structure and properties of calcium-silicate-hydrate gel, deciphers the impact of multiscale defects on cement hydration. The dynamic nucleation and growth of C-S-H gel during hydration are thoroughly investigated, shedding light on new mechanisms at the nanoscale. The response and stability of C-S-H gel under various extreme temperature and carbonation environments are elucidated, providing experimental evidence for the understanding and regulation of cement hydration. The research opens up new avenues for controlling the hydration process and enhancing the performance of cement-based materials.

    • Article
    • Peer Reviewed
    UC Riverside Previously Published Works (2023)
    With the availability of high dimensional genetic biomarkers, it is of interest to identify heterogeneous effects of these predictors on patients survival, along with proper statistical inference. Censored quantile regression has emerged as a powerful tool for detecting heterogeneous effects of covariates on survival outcomes. To our knowledge, there is little work available to draw inference on the effects of high dimensional predictors for censored quantile regression. This paper proposes a novel procedure to draw inference on all predictors within the framework of global censored quantile regression, which investigates covariate-response associations over an interval of quantile levels, instead of a few discrete values. The proposed estimator combines a sequence of low dimensional model estimates that are based on multi-sample splittings and variable selection. We show that, under some regularity conditions, the estimator is consistent and asymptotically follows a Gaussian process indexed by the quantile level. Simulation studies indicate that our procedure can properly quantify the uncertainty of the estimates in high dimensional settings. We apply our method to analyze the heterogeneous effects of SNPs residing in lung cancer pathways on patients survival, using the Boston Lung Cancer Survivor Cohort, a cancer epidemiology study on the molecular mechanism of lung cancer.
      Cover page: Inference for High-Dimensional Censored Quantile Regression.
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2021)
      Fire poses a substantial threat to concrete structures because calcium silicate hydrate (C-S-H) is not thermally stable at high temperatures. Herein, in situ TEM at temperatures from 20 to 800 °C was conducted to study the thermal-induced structural changes in C-S-H. We captured C-S-H shrinks at an average rate of 0.02 μm2/oC upon heating with three stages observed, including induction, constant, and rapid periods. Our observation revealed that an 800 nm pore could be healed during pore structure evolution owing to the reconstruction and deformation among C-S-H blocks. The Ca/Si ratio was dropped at higher temperatures because of the leakage of calcium ions from the C-S-H structure to form CaO precipitates. The temperature-driven phase transformation and degradation were also detected using electron diffraction that C-S-H was transformed into metastable calcium silicate minerals above 800 °C. This work provides insights into the nanoscale transformation of C-S-H at high temperatures.
        Cover page: In situ TEM observation of calcium silicate hydrate nanostructure at high temperaturesCreative Commons 'BY-NC' version 4.0 license
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2016)
        We perform a joint experimental and computational study of ion transport properties in a systematic set of linear polyethers synthesized via acyclic diene metathesis (ADMET) polymerization. We measure ionic conductivity, σ, and glass transition temperature, Tg, in mixtures of polymer and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. While Tg is known to be an important factor in the ionic conductivity of polymer electrolytes, recent work indicates that the number and proximity of lithium ion solvation sites in the polymer also play an important role, but this effect has yet to be systematically investigated. Here, adding aliphatic linkers to a poly(ethylene oxide) (PEO) backbone lowers Tg and dilutes the polar groups; both factors influence ionic conductivity. To isolate these effects, we introduce a two-step normalization scheme. In the first step, Vogel-Tammann-Fulcher (VTF) fits are used to calculate a temperature-dependent reduced conductivity, σr(T), which is defined as the conductivity of the electrolyte at a fixed value of T - Tg. In the second step, we compute a nondimensional parameter fexp, defined as the ratio of the reduced molar conductivity of the electrolyte of interest to that of a reference polymer (PEO) at a fixed salt concentration. We find that fexp depends only on oxygen mole fraction, x0, and is to a good approximation independent of temperature and salt concentration. Molecular dynamics simulations are performed on neat polymers to quantify the occurrences of motifs that are similar to those obtained in the vicinity of isolated lithium ions. We show that fexp is a linear function of the simulation-derived metric of connectivity between solvation sites. From the relationship between σr and fexp we derive a universal equation that can be used to predict the conductivity of ether-based polymer electrolytes at any salt concentration and temperature.
          Cover page: Universal Relationship between Conductivity and Solvation-Site Connectivity in Ether-Based Polymer Electrolytes
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2023)
          Understanding nanodiamond structures is of great scientific and practical interest. It has been a long-standing challenge to unravel the complexity underlying nanodiamond structures and to resolve the controversies surrounding their polymorphic forms. Here, we use transmission electron microscopy with high-resolution imaging, electron diffraction, multislice simulations, and other supplementary techniques to study the impacts of small sizes and defects on cubic diamond nanostructures. The experimental results show that common cubic diamond nanoparticles display the (200) forbidden reflections in their electron diffraction patterns, which makes them indistinguishable from new diamond (n-diamond). The multislice simulations demonstrate that cubic nanodiamonds smaller than 5 nm can present the d-spacing at 1.78 Å corresponding to the (200) forbidden reflections, and the relative intensity of these reflections increases as the particle size decreases. Our simulation results also reveal that defects, such as surface distortions, internal dislocations, and grain boundaries can also make the (200) forbidden reflections visible. These findings provide valuable insights into the diamond structural complexity at nanoscale, the impact of defects on nanodiamond structures, and the discovery of novel diamond structures.
            Cover page: Unveiling the complexity of nanodiamond structuresCreative Commons 'BY' version 4.0 license
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2022)
            Achieving hierarchical nanomaterials from a bottom-up approach remains challenging. Here, we report a closed-cage, onion nanostructure of covalent organic framework (COF) obtained through a low-temperature solvothermal synthesis. Atomic resolution transmission electron microscopy revealed the atomic arrangement in this COF onion, in which rich nitrogen was uniformly embedded in the periodic porous graphitic framework. The COF onion structure displayed graphitic features at a 0.33 nm interlayer spacing with Van der Waals interactions predominated between the layers. The onion layers exhibited significant heterogeneity in layer stacking by adopting a combination of different stacking modes. Defects were also found, such as five- or seven-member rings deviating from the perfect hexagonal lattice. These geometrical defects resulted in curving the 2D layers, which may have promoted the formation of onion nanostructures through a layer-by-layer attachment. We constructed a corresponding model that predicts COF onion properties. This novel onion exhibited a bandgap value of 2.56 eV, resembling other carbon-based nanomaterials, suggesting potential applications in sensors, photocatalysts, and nanoelectronics.
              Cover page: A covalent organic framework onion structure
              • Article
              • Peer Reviewed
              UC Berkeley Previously Published Works (2018)
              We report on the synthesis of poly(diethylene oxide-alt-oxymethylene), P(2EO-MO), via cationic ring-opening polymerization of the cyclic ether monomer, 1,3,6-trioxocane. We use a combined experimental and computational approach to study ion transport in electrolytes comprising mixtures of P(2EO-MO) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt. Mixtures of poly(ethylene oxide) (PEO) and LiTFSI are used as a baseline. The maximum ionic conductivities, σ, of P(2EO-MO) and PEO electrolytes at 90 °C are 1.1 × 10-3 and 1.5 × 10-3 S/cm, respectively. This difference is attributed to the Tg of P(2EO-MO)/LiTFSI (-12 °C), which is significantly higher than that of PEO/LiTFSI (-44 °C) at the same salt concentration. Self-diffusion coefficients measured using pulsed-field gradient NMR (PFG-NMR) show that both Li+ and TFSI- ions diffuse more rapidly in PEO than in P(2EO-MO). However, the NMR-based cation transference number in P(2EO-MO) (0.36) is approximately twice that in PEO (0.19). The transference number measured by the steady-state current technique, t+,ss, in P(2EO-MO) (0.20) is higher than in PEO (0.08) by a similar factor. We find that the product σt+,ss is greater in P(2-EO-MO) electrolytes; thus, P(2EO-MO) is expected to sustain higher steady-state currents under dc polarization, making it a more efficacious electrolyte for battery applications. Molecular-level insight into the factors that govern ion transport in our electrolytes was obtained using MD simulations. These simulations show that the solvation structures around Li+ are similar in both polymers. The same is true for TFSI-. However, the density of Li+ solvation sites in P(2EO-MO) is double that in PEO. We posit that this is responsible for the observed differences in the experimentally determined transport properties of P(2EO-MO) and PEO electrolytes.
                Cover page: Optimizing Ion Transport in Polyether-Based Electrolytes for Lithium Batteries
                • Article
                • Peer Reviewed
                UC Berkeley Previously Published Works (2024)
                Crystallographic defects play a crucial role in cement hydration, with initial dissolution being dominated by the formation of etch pits that rely on the intersection of defects on surfaces. However, the defects present in cement particles have remained a mystery due to the lack of detailed direct observation at the atomic scale. In this study, we used scanning transmission electron microscopy to unravel the defects in alite particles at the single-atom level. Our observations identified different types of defects, including vacancies, doping, dislocations, rough surfaces, and grain boundaries. Atomic ordering in the alite crystal was further examined based on our single-atom recognition method. Our findings indicate that defects in cement particles may serve as reactive sites during the early hydration stage, facilitating the initial dissolution and providing nucleation sites for hydration products. This work provides insights into cement defect formation at the single-atom level and offers new opportunities in tuning the hydration process through defect engineering of cement particles.
                  Cover page: Atomic-scale identification of defects in alite
                  • Article
                  • Peer Reviewed
                  UC San Francisco Previously Published Works (2019)
                  Photosensitizer (PS) serves as the central element of photodynamic therapy (PDT). The use of common nanoparticles (NPs) for PDT has typically been rendered less effective by the undesirable aggregation-caused quenching (ACQ) effect, resulting in quenched fluorescence and reduced reactive oxygen species (ROS) generation that diminish the imaging quality and PDT efficacy. To overcome the ACQ effect and to enhance the overall efficacy of PDT, herein, integrin ανβ3-targeted organic nanodots for image-guided PDT were designed and synthesized based on a red emissive aggregation-induced emission (AIE) PS. Methods: The TPETS nanodots were prepared by nano-precipitation method and further conjugated with thiolated cRGD (cRGD-SH) through a click reaction to yield the targeted TPETS nanodots (T-TPETS nanodots). Nanodots were characterized for encapsulation efficiency, conjugation rate, particle size, absorption and emission spectra and ROS production. The targeted fluorescence imaging and antitumor efficacy of T-TPETS nanodot were evaluated both in vitro and in vivo. The mechanism of cell apoptosis induced by T-TPETS nanodot mediated-PDT was explored. The biocompatibility and toxicity of the nanodots was examined using cytotoxicity test, hemolysis assay, blood biochemistry test and histological staining. Results: The obtained nanodots show bright red fluorescence and highly effective 1O2 generation in aggregate state. Both in vitro and in vivo experiments demonstrate that the nanodots exhibit excellent tumor-targeted imaging performance, which facilitates image-guided PDT for tumor ablation in a hepatocellular carcinoma model. Detailed analysis reveals that the nanodot-mediated PDT is able to induce time- and concentration-dependent cell death. The use of PDT at a high PDT intensity leads to direct cell necrosis, while cell apoptosis via the mitochondria-mediated pathway is achieved under low PDT intensity. Conclusion: Our results suggest that well-designed AIE nanodots are promising for image-guided PDT applications.
                    Cover page: Theranostic Nanodots with Aggregation-Induced Emission Characteristic for Targeted and Image-Guided Photodynamic Therapy of Hepatocellular CarcinomaCreative Commons 'BY-NC' version 4.0 license
                    • Article
                    • Peer Reviewed
                    UCLA Previously Published Works (2024)
                    Electrified solid-liquid interfaces (ESLIs) play a key role in various electrochemical processes relevant to energy1-5, biology6 and geochemistry7. The electron and mass transport at the electrified interfaces may result in structural modifications that markedly influence the reaction pathways. For example, electrocatalyst surface restructuring during reactions can substantially affect the catalysis mechanisms and reaction products1-3. Despite its importance, direct probing the atomic dynamics of solid-liquid interfaces under electric biasing is challenging owing to the nature of being buried in liquid electrolytes and the limited spatial resolution of current techniques for in situ imaging through liquids. Here, with our development of advanced polymer electrochemical liquid cells for transmission electron microscopy (TEM), we are able to directly monitor the atomic dynamics of ESLIs during copper (Cu)-catalysed CO2 electroreduction reactions (CO2ERs). Our observation reveals a fluctuating liquid-like amorphous interphase. It undergoes reversible crystalline-amorphous structural transformations and flows along the electrified Cu surface, thus mediating the crystalline Cu surface restructuring and mass loss through the interphase layer. The combination of real-time observation and theoretical calculations unveils an amorphization-mediated restructuring mechanism resulting from charge-activated surface reactions with the electrolyte. Our results open many opportunities to explore the atomic dynamics and its impact in broad systems involving ESLIs by taking advantage of the in situ imaging capability.
                      Cover page: Atomic dynamics of electrified solid–liquid interfaces in liquid-cell TEMCreative Commons 'BY' version 4.0 license
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