Browsing by Author "Rodrigues, Debora F."
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Item Accelerated Alkali-Silica Reaction and Corrosion of Reinforcing Steel in Concrete: Application on Dry Casks(2016-08) Attar, Arezou; Gencturk, Bora E.; Willam, Kaspar J.; Vipulanandan, Cumaraswamy; Meen, James K.; Rodrigues, Debora F.The durability is one of the main reasons making concrete the most abundantly consumed material in the world after water. However, severe exposure conditions and improper or low quality mixture designs can cause physical and chemical changes in concrete which lead to deterioration and premature failure of the structure. This process is called aging. Two of the main aging mechanisms in reinforced concrete structures are corrosion and alkali-silica reaction (ASR). These two processes occur very slowly and to assess them in a short period of time, they need to be accelerated. Furthermore, these mechanisms are dependent on the geometry and boundary conditions of the structure. Therefore, research on these aging mechanisms is structure specific and depends on the scale of observation. This study proposes a method through addition of chemicals to the concrete mixture for accelerating aging that is applicable to both small- and large- specimens. The aging is accelerated through addition of sodium hydroxide to accelerate ASR and calcium chloride to the mixture to accelerate corrosion. The effect of the addition of these chemicals on both physical and mechanical properties of concrete was investigated through a series of destructive and non-destructive testing at the materials and structural levels. The results indicate that the addition of sodium hydroxide to the concrete mix, combined with the use of reactive aggregate and no fly ash, considerably accelerates ASR and crack propagation on the surface of the specimens. Similarly, the addition of calcium chloride effectively accelerates corrosion. To investigate the validity of the proposed approach at the structural level, a vertical concrete dry cask for storage of nuclear waste was chosen as the case study. In this case study, three 1/3-scale dry casks were subjected to accelerated ASR and corrosion with the addition of chemicals to the mixture and their effect was measured over eighteen months. Furthermore, the service life of the scaled down casks was estimated considering the real life conditions. This approach is expected to help researchers to better understand the long term behavior of reinforced concrete dry casks.Item Antibacterial properties and mechanisms of toxicity of sonochemically grown ZnO nanorods(RSC Advances, 2015) Okyay, Tugba O.; Bala, Rukayya K.; Nguyen, Hang N.; Atalay, Ramazan; Bayam, Yavuz; Rodrigues, Debora F.In this study, we present a simple, fast and cost-effective sonochemical growth method for the synthesis of zinc oxide (ZnO) nanorods. ZnO nanorods were grown on glass substrates at room temperature without the addition of surfactants. The successful coating of substrates with ZnO nanorods was demonstrated by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). The antimicrobial properties of ZnO nanorods against the planktonic Bacillus subtilis and Escherichia coli and their respective biofilms were investigated. The cytotoxicity of ZnO nanorods were evaluated using the NIH 3T3 mammalian fibroblast cell line. Moreover, to understand the possible mechanisms of ZnO nanorod toxicity, glutathione oxidation, superoxide production, and release of Zn2+ ions by the ZnO nanorods were determined, and the LIVE/DEAD assay was employed to investigate cell membrane damage. The results showed that sonochemically grown ZnO nanorods exhibited significant antimicrobial effects to both bacteria and prevented biofilm formation. ZnO nanorods did not present any significant toxicity to fibroblast cells. The main anti-microbial mechanisms of ZnO nanorods were determined to be H2O2 production and cell membrane disruption.Item Antimicrobial Applications of Electroactive PVK-SWNT Nanocomposites(Environmental Science and Technology, 11/17/2011) Ahmed, Farid; Santos, Catherine M.; Vergara, Regina Aileen May V.; Tria, Maria Celeste R.; Advincula, Rigoberto C.; Rodrigues, Debora F.The antibacterial properties of a nanocomposite containing an electroactive polymer, polyvinyl-N-carbazole (PVK) (97 wt %), and single-walled carbon nanotubes (SWNT) (3 wt %) was investigated as suspensions in water and as thin film coatings. The toxic effects of four different PVK-SWNT (97:3 wt %) nanocomposite concentrations (1, 0.5, 0.05, and 0.01 mg/mL) containing 0.03, 0.015, 0.0015, and 0.0003 mg/mL of SWNT, respectively, were determined for planktonic cells and biofilms of Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis). The results showed that the nanocomposite PVK-SWNT had antibacterial activity on planktonic cells and biofilms at all concentration levels. Higher bacterial inactivation (94% for E. coli and 90% for B. subtilis) were achieved in planktonic cells at a PVK-SWNT concentration of 1 mg/mL. Atomic force microscopy (AFM) imaging showed significant reduction of biofilm growth on PVK-SWNT coated surfaces. This study established for the first time that the improved dispersion of SWNTs in aqueous solutions in the presence of PVK enhances the antimicrobial effects of SWNTs at very low concentrations. Furthermore, PVK-SWNT can be used as an effective thin film coating material to resist biofilm formation.Item Antimicrobial PVK:SWNT nanocomposite coated membrane for water purification: Performance and toxicity testing(Water Research, 8/1/2013) Ahmed, Farid; Santos, Catherine M.; Mangadlao, Joey D.; Advincula, Rigoberto C.; Rodrigues, Debora F.This study demonstrated that coated nitrocellulose membranes with a nanocomposite containing 97% (wt%) of polyvinyl-N-carbazole (PVK) and 3% (wt%) of single-walled carbon nanotubes (SWNTs) (97:3 wt% ratio PVK:SWNT) achieve similar or improved removal of bacteria when compared with 100% SWNTs coated membranes. Membranes coated with the nanocomposite exhibited significant antimicrobial activity toward Gram-positive and Gram-negative bacteria (?80–90%); and presented a virus removal efficiency of ?2.5 logs. Bacterial cell membrane damage was considered a possible mechanism of cellular inactivation since higher efflux of intracellular material (Deoxyribonucleic acid, DNA) was quantified in the filtrate of PVK-SWNT and SWNT membranes than in the filtrate of control membranes. To evaluate possible application of these membrane filters for drinking water treatment, toxicity of PVK-SWNT was tested against fibroblast cells. The results demonstrated that PVK-SWNT was non toxic to fibroblast cells as opposed to pure SWNT (100%). These results suggest that it is possible to synthesize antimicrobial nitrocellulose membranes coated with SWNT based nanocomposites for drinking water treatment. Furthermore, membrane filters coated with the nanocomposite PVK-SWNT (97:3 wt% ratio PVK:SWNT) will produce more suitable coated membranes for drinking water than pure SWNTs coated membranes (100%), since the reduced load of SWNT in the nanocomposite will reduce the use of costly and toxic SWNT nanomaterial on the membranes.Item Application of Cupriavidus metallidurans and Ochrobactrum intermedium for Copper and Chromium Biosorption(2013-05) Fan, Jingjing 1988-; Rodrigues, Debora F.; Rixey, William G.; Vipulanandan, CumaraswamyHeavy metals at high concentrations are toxic to the environment and living organisms. The present study aims to investigate the best conditions for the removal of CuSO4.5H2O and KCrO4 by two bacterial species: Ochrobactrum intermedium and Cupriavidus metallidurans. The minimum inhibitory concentrations of C. metallidurans and O. Intermedium were determined to be 750 and 300 ppm for Cu2+, and 100 ppm and 1000 ppm for Cr6+, respectively for each microorganism. Biosorption experiments were also performed with dead and live biomasses of C. metallidurans and O. intermedium. The results show that dead biomass presented better Cu2+ biosorption capacity than live cells. Chromium was removed more efficiently by live cells of O. intermedium than dead biomass; while C. metallidurans dead biomass biosorbed better than live biomass. The biosorption results fitted well with the Langmuir isotherm model. The main mechanism of live biomass adsorption was determined to be through carboxylic, hydroxyl, and amino functional groups.Item Architecture of thermal adaptation in an Exiguobacterium sibiricum strain isolated from 3 million year old permafrost: A genome and transcriptome approach(BMC Genomics, 11/18/2008) Rodrigues, Debora F.; Ivanova, Natalia; He, Zhili; Huebner, Marianne; Zhou, Jizhong; Tiedje, James M.Background: Many microorganisms have a wide temperature growth range and versatility to tolerate large thermal fluctuations in diverse environments, however not many have been fully explored over their entire growth temperature range through a holistic view of its physiology, genome, and transcriptome. We used Exiguobacterium sibiricum strain 255-15, a psychrotrophic bacterium from 3 million year old Siberian permafrost that grows from -5°C to 39°C to study its thermal adaptation. Results: The E. sibiricum genome has one chromosome and two small plasmids with a total of 3,015 protein-encoding genes (CDS), and a GC content of 47.7%. The genome and transcriptome analysis along with the organism's known physiology was used to better understand its thermal adaptation. A total of 27%, 3.2%, and 5.2% of E. sibiricum CDS spotted on the DNA microarray detected differentially expressed genes in cells grown at -2.5°C, 10°C, and 39°C, respectively, when compared to cells grown at 28°C. The hypothetical and unknown genes represented 10.6%, 0.89%, and 2.3% of the CDS differentially expressed when grown at -2.5°C, 10°C, and 39°C versus 28°C, respectively. Conclusion: The results show that E. sibiricum is constitutively adapted to cold temperatures stressful to mesophiles since little differential gene expression was observed between 4°C and 28°C, but at the extremities of its Arrhenius growth profile, namely -2.5°C and 39°C, several physiological and metabolic adaptations associated with stress responses were observed.Item Bacterial Adhesion and Motility at Oil-Water Interfaces(2020-12) Dewangan, Narendra Kumar; Conrad, Jacinta C.; Willson, Richard C.; Cirino, Patrick C.; Rodrigues, Debora F.; Louie, Stacey M.Degradation of hydrocarbons by bacteria is one of the most important processes in oil spill cleanup. In attempt to increase the rate of biodegradation, chemical dispersants have been deployed in many oil spill scenarios to increase the surface area per unit volume available to bacteria. Biofilm formation is one of the important pathways in degradation of oil by bacteria. Because adhesion of bacteria to surface is one of the important steps in biofilm formation. It is important to study what factors affect the bacterial adhesion on oil/water interfaces. Adhesion of bacteria on solid surfaces is widely studied but surprisingly, how bacteria adhere on oil/water interface, and the effect of surfactants and bacterial motility on adhesion of bacteria on oil/water interface is not well studied. First, we designed and fabricated a microfluidic device to produce denser monodispersed oil in water emulsion. We developed a method to be able to capture 3D images of bacteria adhering to oil droplets with minimal number of cells attached to imaging chamber and with minimizing the wetting (~ 180° contact angle) of oil droplet to the imaging chamber. We developed tracking algorithms to visualize the cells adhering on the droplet and to calculate the contact angle that each bacterium makes to the droplet surface. In the first part of the project, we studied the effect of surfactant chemistries (anionic [dioctyl sodium sulfosuccinate, dicyclohexyl sodium sulfosuccinate, dibutyl sodium sulfosuccinate], cationic [cetyltrimethylammonium bromide], and nonionic [Tween 20]) and surfactant concentration on adhesion of nonmotile Marinobacter hydrocarbonoclasticus SP17 on dodecane droplets. Secondly, we found that motile bacteria Halomonas titanicae adhering to dodecane droplets were able to move the droplets in aqueous suspension. We explored the physics of droplet rotation driven by bacteria. Droplets rotate in clockwise direction when viewed from the liquid side, due to symmetry-breaking hydrodynamic interactions of bacteria with the surface. We examined the effect of droplet size on angular speed of droplets. We further investigated the effect of surfactant concentration and interfacial affinity of bacteria (by using three different bacteria species Escherichia coli, Shewanella haliotis, and Halomonas titanicae) on droplet rotation. Thirdly, we investigated the effect of bacterial motility on adhesion of bacteria on hexadecane droplets. Here, we show that bacterial motility enhances adhesion to surfactant-decorated oil droplets dispersed in artificial sea water. Motile Halomonas titanicae adhered to hexadecane droplets stabilized with dioctyl sodium sulfosuccinate (DOSS) more rapidly and at greater surface densities compared to nonmotile H. titanicae, whose flagellar motion was arrested through addition of a proton decoupler. Increasing the concentration of DOSS reduced the surface density of both motile and nonmotile bacteria as a result of the reduced interfacial tension. Finally, we investigated the effect of concentration of anionic surfactant dioctyl sodium sulfosuccinate (DOSS) and calcium chloride on aggregation of nonmotile Marinobacter hydrocarbonoclasticus and Halomonas titanicae in synthetic seawater. Bacteria aggregation may occur due to environmental stresses as a protective mechanism or it can occur as a first step towards biofilm formation and subsequent biodegradation. There are two physical mechanisms known in aggregation of bacteria: (1) aggregation by depletion attraction, and (2) aggregation by bridging attraction due to EPS or polymers. In our study, we found that aggregation (size and number density) increases with increase in DOSS concentration and calcium chloride concentration. Motile Halomonas titanicae showed higher aggregation compared to nonmotile bacteria. Together, we studied bacteria motility and adhesion interactions on cell-solid surface, on cell-liquid interfaces, and on cell/cell interfaces. Broadly, this research contributes to the fields of bioremediation and antifouling.Item Biodegradation of graphene oxide-polymer nanocomposite films in wastewater(Environmental Science: Nano, 7/20/2017) Fan, Jingjing; Grande, Carlos David; Rodrigues, Debora F.The synthesis of polymer nanocomposites has been extensively investigated by many researchers, however, the end of life fate of polymer nanocomposites is still largely unknown. It is expected that at the end of their service life, these polymer nanocomposites will most likely end up in soil and water systems where microorganisms will interact and, perhaps, even biodegrade them. In this study, we investigate the ability of wastewater microorganisms to biodegrade nanocomposite films containing different graphene oxide (GO) loads (0% to 0.6%, (w/w%)) embedded in a model biopolymer (i.e. chitosan). The ability of wastewater microorganisms to grow and form biofilms on the surface of the nanocomposite films was determined by live and dead staining assisted with confocal laser scanning microscopy. The capability of wastewater biofilms to biodegrade nanocomposites was assessed through nanocomposite film weight losses, Fourier transformed infrared (FTIR) and scanning electron microscopy (SEM) analyses. Results showed that microorganisms present in the activated sludge can grow on the surface of the nanocomposites and biodegrade the polymer surrounding the graphene oxide nanoplatelets. As the biopolymer gets degraded, there is increasing exposure of GO on the surface, which yields microbial inactivation and biofilm growth inhibition. To determine the evolution of the toxicity of the nanocomposite during biodegradation. We determined the emergence of the sharp edges of GO on the surface of the nanocomposite through atomic force microscopy (AFM), as well as the production of reactive oxygen species (ROS) with the Ellman's assay before and after biodegradation of the nanocomposites. The results show that as GO surfaces the nanocomposite film during biodegradation, there is increasing production of ROS, which explains the increasing inactivation of the microorganisms.Item Biological Degradation and Biostability of Nanocomposites Based on Polysulfone with Different Concentrations of Reduced Graphene Oxide(Macromolecular Materials and Engineering, 2/14/2018) Peña?Bahamonde, Janire; San?Miguel, V.; Cabanelas, Juan C.; Rodrigues, Debora F.Increasing incorporation of rGO in the polysulfone polymer generates materials with improved chemical and mechanical stability and less prone to biodegradation at the end of the nanocomposite life cycle. The results of attenuated total reflection infrared (ATR?IR) and mechanical strength, after exposure to wastewater influent, show that the increasing concentrations of rGO into the polymer matrix reduce changes in the nanocomposite properties. The increasing incorporation of rGO also increases growth inhibition of the wastewater microbial population on the surface of nanocomposites. Highest biofilm inhibition and material stability are observed with nanocomposites containing 3 wt% rGO. These results suggest that reduction in the material biodegradation is linked to the inhibition of biofilm growth on the nanocomposite surface due to the antimicrobial properties of rGO. This study demonstrates, for the first time, that the amount of rGO incorporated in the nanocomposite impact the biodegradability and end of life of polysulfone nanocomposites.Item Carbon Dioxide Sequestration through Microbially-Induced Calcium Carbonate Precipitation Using Ureolytic Environmental Microorganisms(2015-05) Onal Okyay, Tugba; Rodrigues, Debora F.; Hu, Yandi; Rixey, William G.; Cooper, Timothy F.; Willson, Richard C.The development of affordable and eco-friendly strategies for carbon dioxide sequestration has become a matter of paramount importance to reduce or mitigate the effects of global climate changes. Today, the most used solution to sequester CO2 is its immobilization in geological reservoirs, commonly referred to as carbon capture and storage; however this technique is not completely reliable because of leakage risks, when storing vast quantities of CO2 in geological strata. Alternatively, precipitation of CO2 as solid carbonates may constitute an alternative strategy for carbon immobilization. The reaction to form calcium carbonates is generally not chemically favorable in the environment, unless at pH values higher than 9. On the other hand, microorganisms, through metabolic activities, have been shown to induce calcium carbonate precipitation, provided that certain environmental conditions are met. In this dissertation, I investigate the diversity and physiology of diverse ureolytic consortia and isolates able to induce calcium carbonate precipitation to better understand their roles in carbon sequestration. These microorganisms were obtained from karstic environments that are rich in calcium and present natural input of urea, which are considered to be key factors in calcium carbonate precipitation. These urease-positive microorganisms were classified phylogenetically and their physiology was investigated. The relationship amongst urease activity, microbially-induced calcium carbonate precipitation (MICP), and carbon sequestration by the different consortia and isolates were shown to be dependent on the species and directly influenced by their growth conditions.Item Chemiluminescent Detection of 1,5-Anhydroglucitol in Saliva for Diabetes Mellitus Screening(2018-05) Hlavinka, Victoria M.; Willson, Richard C.; Orman, Mehmet A.; Rodrigues, Debora F.Diabetes mellitus is a severe, chronic disease that affects over 420 million people worldwide. The onset of complications due to diabetes can be delayed or even prevented when the disease is diagnosed early. However, it is estimated that nearly a quarter of all diabetes cases are undiagnosed. Screening in communities without adequate access to healthcare can drastically reduce the number of undiagnosed cases of diabetes in these areas. We have developed a chemiluminescence assay to quantify 1,5-anhydroglucitol (AHG), a glucose analog that falls in concentration during periods of hyperglycemia, in saliva for diabetes screening. We have demonstrated the ability of the assay to distinguish between healthy and diabetic individuals by testing 250 human samples (p < 0.0001). The accuracy of the assay determined by a receiver operating characteristic curve is 81%. The resultant study suggests that our assay can be used as a noninvasive tool to screen for diabetes.Item Chronic toxicity of graphene and graphene oxide in sequencing batch bioreactors: A comparative investigation(Journal of Hazardous Materials, 2/5/2018) Nguyen, Hang N.; Rodrigues, Debora F.The present study investigates the chronic toxicity of graphene (G) and graphene oxide (GO) in activated sludge. Sequencing batch bioreactors were fed with influents containing 0, 1 and 5 mg L?1 of GO or G (12 h cycles) for ten days. Reduction in performance of the bioreactors in relation to chemical oxygen demand, ammonia and phosphate removals was observed after three days in the bioreactors fed with 5 mg L?1 of nanomaterials. After about eight days, these reactors reached a steady state nutrient removal, which corresponded to recovery of certain groups of ammonia oxidizing bacteria and phosphate accumulating bacteria despite the increasing accumulation of nanomaterials in the sludge. These results suggested that biological treatment can be affected transiently by initial exposure to the nanomaterials, but certain groups of microorganisms, less sensitive to these nanomaterials, can potentially strive in the presence of these nanomaterials. Results of 16S rRNA gene deep sequencing showed that G and GO affected differently the microbial communities in the activated sludge. Between the two nanomaterials investigated, GO presented the highest impact in nutrient removal, gene abundance and changes in microbial population structures.Item Complete Genome Sequence of the Thermophilic Exiguobacterium sp. AT1b.(Journal of Bacteriology, 4/1/2011) Vishnivetskaya, Tatiana A.; Lucas, Susan; Copeland, Alex; Lapidus, Alla; del Rio, Tijana Glavina; Dalin, E.; Tice, Hope; Bruce, David C.; Goodwin, Lynne A.; Pitluck, Sam; Saunders, E.; Brettin, Tom; Detter, Chris; Han, Cliff; Larimer, Frank; Land, Miriam L.; Hauser, Loren J.; Kyrpides, Nikos C.; Ovchinnikova, Galina; Kathariou, Sophia; Ramaley, Robert F.; Rodrigues, Debora F.; Hendrix, Christie; Richardson, Paul; Tiedje, James M.Here we present the genome of strain Exiguobacterium sp. AT1b, a thermophilic member of the genus Exiguobacterium whose representatives were isolated from various environments along a thermal and physico-chemical gradient. This genome was sequenced to be a comparative resource for study of thermal adaptation with a psychroactive representative of the genus, Exiguobacterium sibiricum strain 255-15, that was previously sequenced by the U.S. Department of Energy's (DOE) Joint Genome Institute (JGI) (http://genome.ornl.gov/microbial/exig/).Item Computational Modeling of Structural Energy Storage(2020-05) Aderyani, Sarah; Ardebili, Haleh; Sharma, Pradeep; Kulkarni, Yashashree; Ryou, Jae-Hyun; Rodrigues, Debora F.Flexible structural energy storage is a rapidly emerging area with tantalizing applications such as integrated devices in textiles and smart suits, portable electronic devices and electric vehicles (EV). Due to several outstanding properties, graphene oxide (rGO)/ aramid nanofiber (ANF) composite material has emerged as a compelling choice as a structural electrode for supercapacitors and batteries. A key question of significant technological relevance pertains to what kind of nanoscale architecture motifs may lead to enhanced ionic diffusivity — the key characteristic dictating the overall performance of the electrode. In this work, we attempt to address this precise question, through multiphysics computational modeling in the context of several experimentally realizable nanoarchitectures, namely, “layered” and “house of cards” nanostructures. We investigate different arrangements (staggered, aligned and square) with various degrees of waviness of the rGO nanosheets inside the ANF polymer matrix. Nanoarchitecture modeling results indicate that decreasing waviness of the rGO sheets can enhance the ion diffusivity in the staggered and aligned arrangements of the electrode material, while this effect is stronger in staggered arrangement than aligned arrangement. The results obtained from nanoarchitecture computational modeling are compared to the porous media approach. It is shown that the widely used porous electrode theory such as Bruggeman or Millington-Quirk relations, overestimates the effective diffusion coefficient. Also, the results from nanoarchitecture modeling are validated with experimental measurements obtained from impedance spectroscopy (EIS) and cyclic voltammetry (CV). The effective diffusion coefficients obtained from nanoarchitectural modeling show better agreement with experimental measurements. The effective properties obtained from nanoarchitecture modeling is used to simulate cyclic voltammetry (CV) of rGO/ANF structural supercapacitors. Various electrochemical kinetics evaluated to characterize structural supercapacitors. The insights obtained from this study can lead to a more effective design of electrode architectures. Finally, the effect of temperature on solid polymer Li-ion batteries is investigated through a 1D model that predicts the discharge behavior of flexible pouch cells at different temperatures. The simulations results show a good agreement with experimental measurements and yields fundamental insight which is essential for future developments in flexible solid polymer Li-ion batteries.Item Controlling Pathological Mineralization Using Molecular Modifiers(2021-08) Kim, Do Young; Rimer, Jeffrey D.; Vekilov, Peter G.; Palmer, Jeremy C.; Rodrigues, Debora F.; Lee, T. RandallThe development of new methods to prevent mineral scale formation can have significant impact on natural, biological, and industrial process. A ubiquitous approach to regulating crystal formation is through the use of modifiers, which are (macro)molecules that interact with crystals to inhibit nucleation and/or growth. Understanding the fundamental mechanisms of crystallization inhibitors is relevant to a broad range of fields, including their frequent use in crystal engineering and biomineralization. This dissertation focuses on two types of pathological crystals: calcium oxalate monohydrate (COM), the primary component of kidney stones, and magnesium ammonium phosphate hexahydrate (struvite). Struvite is a key constituent of infection stones (e.g., kidney stones); and it is also a common scale in water purification and transport. Despite considerable interest in this material, the fundamental understanding of struvite growth is still at its infancy due to the lack of appropriate platforms to assess growth over multiple length scales. The use of flow systems to study infection stone formation is promising, as they can simulate the flow conditions where struvite naturally forms (e.g., urinary tract systems, catheter, pipelines, etc.). This dissertation has established a new method of evaluating struvite crystal growth under flow using a combination of microfluidics and in situ atomic force microscopy (AFM). Through these synergistic approaches, we quantified anisotropic kinetics of crystallization over a broad range of conditions and resolved the molecular mechanism of growth and its inhibition whereby layers on crystal surfaces advance from either screw dislocations or 2-dimensional generation and spreading of islands – both of which are classical pathways. Growth modifiers range from small ions and molecules to large macromolecules. Here, we examined the impact of bio-inspired small molecules on both struvite and COM crystallization. Several phosphate-based molecules exhibit an unparalleled dual mode of action capable of suppressing both nucleation and growth of crystals. Time-resolved AFM images of struvite surface at varying inhibitor concentration revealed a unique mode of crystal growth inhibition, wherein surfaces become laden with an amorphous layer that leads to roughened interfaces and growth succession through dynamic sequences that are not commonly witnessed for other minerals. In studies of COM, we observed that modifiers irreversibly stunt crystal growth in timescales that are relevant to pathological COM kidney stone formation. Comparisons between phosphate-based modifiers and two reference compounds previously identified as highly effective COM inhibitors, carboxylate-based hydroxycitrate and the urinary protein osteopontin, revealed that phosphate-based inhibitors suppress COM crystallization at substantially lower concentrations than both conventional modifiers, thus highlighting the unique efficacy of these newly evaluated bio-inspired molecules. In addition, the results presented in this dissertation address knowledge gaps that are beneficial to the development of effective inhibitors with the potential to replace existing therapeutics for these widespread maladies. Collectively, this dissertation presents research efforts aimed at inhibiting the formation of pathological crystals, focusing on an understanding of crystal growth under dynamic conditions and pathways to arrest growth via modifiers (i.e., inhibitors) that may serve as model compounds for preventative drugs.Item Controlling the Molecular Weight Distribution of Polymer Brushes to Tune Stimulus-Response and Bacterial Adhesion(2017-08) Yadav, Vivek; Conrad, Jacinta C.; Robertson, Megan L.; Krishnamoorti, Ramanan; Willson, Richard C.; Louie, Stacey M.; Rodrigues, Debora F.Bacterial biofilms ubiquitously foul surfaces in technological settings – damaging oil pipelines,1-3 medical implants,4-6 and marine engineering equipment.7-8 Stimuli-responsive polymer brushes provide one route to control adhesion of bacteria to surfaces by tuning bacterial-surface interactions, and prevent long-term bacterial attachment and fouling through brush conformational changes triggered by external stimuli (pH, temperature). Both thickness and molecular-weight distribution in brushes can change the conformation of a stimulus-responsive polymer brush,9-10 suggesting that these parameters may play distinct roles in detachment of bacteria. Surprisingly, how molecular weight distribution (quantified as dispersity) in stimuli-responsive brushes affects the response and fouling-release properties is largely unexplored. First, we developed a method to systematically increase the dispersity of polymers synthesized through a widely-applicable polymerization method, atom transfer radical polymerization (ATRP), by identifying a reagent (phenylhydrazine) capable of reacting with propagating polymer chains. Polymerizations conducted with phenylhydrazine exhibited chain termination and increased dispersity, controlled through the phenylhydrazine concentration. Reaction kinetics in the presence of phenylhydrazine deviated from that observed in typical ATRP syntheses, and a theoretical model was developed that showed excellent agreement with experimental data. Second, we investigated the effects of brush dispersity on the pH-response of poly(acrylic acid) (PAA) brushes. Increase in brush dispersity lead to greater pH-response at low pH, and additionally, variation in contact angle measurements at intermediate pH (hysteretic memory behavior) was observed when the pH was decreased from 10 to 3 and increased to 10 thereafter. We posited that dispersity-driven conformational changes at low pH lead to observed hysteretic behavior. Finally, we studied the effect of PAA brush thickness and dispersity on bacterial attachment at pH 4 and detachment at pH 9. Increasing either thickness or dispersity led to greater bacterial detachment. Bacterial attachment depended non-monotonically on brush thickness, with brushes of thickness between 13 – 18 nm showing lowest attachment, and attachment was independent of brush dispersity. Together, these results identify brush dispersity as a design parameter to tune pH-response with applications in sensors, controlled drug-release, and separation processes. Separate control over bacterial attachment and detachment via the molecular-weight distribution, demonstrated here, opens new options for smart antifouling surfaces.Item Degradation of PET Microplastics by Controlled Microbial & Photocatalytic, MoO3, Exposure(2020-09-29) Harris, Kristen E.; Holt, ZacharyPolyethylene Terephthalate (PET) plastic is a material widely used to manufacture common household items like clothing and water bottles. Unfortunately, millions of tons of microplastic PET waste matriculate into our environment annually, resulting from dumped wastewater and litter. Microplastic PET fibers are extremely difficult to hydrolyze and can release chemicals, creating a potential for toxicity in seafood that has unknown consequences on human health. This research is a comparative study of the chemical and biological degradation of PET microplastics by photocatalytic and microbial means. The chemical degradation process was performed with the use of the photocatalyst, MoO3, under visible light irradiation for sixty hours with PET in water. The biodegradation process was initiated by an incubation period of soil media with microplastic discs analyzed for degradation every eight weeks. The photocatalytic degradation of PET was analyzed with atomic force microscopy (AFM) and by measuring the changes in the contact angle of a water droplet on its surface to evaluate its hydrophilic nature. The biodegradation process is ongoing but has not yet shown progress in breaking the fundamental groups of the PET polymer. Our results from the photocatalytic degradation show an increase in the hydrophilic nature of the PET surface and average surface roughness, suggesting that chemical degradation is an effective method for PET microplastic waste removal. Furthermore, there are limitations to photocatalytic degradation of PET in wastewater treatment and more research needs to be done to establish parameters for exposure time when using MoO3 as a photocatalyst in water.Item Dendron Stabilized Hybrid nanoparticles: Synthesis: Characterization, and Energy Transfer Studies(2012-08) Puno, Katherine 1974-; Lee, T. Randall; Advincula, Rigoberto C.; Thummel, Randolph P.; Czernuszewicz, Roman S.; Rodrigues, Debora F.Hybrid organic-inorganic nanoparticles are developed as a new class of material with a wide range of application based on their spectroscopic and electrochemical properties. Designing these materials to fine tune their properties as an energy or charge transfer pair calls for an ease of synthesis to produce stable and tunable nanoparticles. Chapter 2 describes a facile synthesi of a nanoparticle-cored dendrimer with electroactive carbazole dendron conjugated onto the amine surface of a generation three cystamine-core PAMAM dendrimer. The disulfide on the cystamine core of this dendrimer is reduced to produce dendrons that stabilize the AuNPs. Such manner of synthesis avoids the tedious stepwise process of attaching the dendrons to the AuNOs by convergent approach. Spectroscopic and electrochemical properties of this system are reported. Chapter 3 discusses the energy transfer involved between CdSe quantum dots and Au nanoparticles placed proximal to each other. The CdSe quantum dots are stabilized by generational carbazole dendrons which provide a control in the distance of these nanoparticles thereby controlling the donor-acceptor interaction. Quite uniquely, the reduction of the Au3+ ions did not necessitae any external reducing agent. The formation of this hybrid nanoparticle is a one-pot synthesis wherein the reduction of the Au3+ to Au(0) provides a simultaneous cross-linking of the carbazole units which overall affords a formation of a three-component hybrid nanoparticles. Generally, there is a potential in exploring the optimization of this facile synthetic protocol to produce the customized hybrid nanoparticles needed for specific optoelectronic applications.Item Designing polymeric adhesives for antimicrobial materials: poly(ethylene imine) polymer, graphene, graphene oxide and molybdenum trioxide – a biomimetic approach(Journal of Materials Chemistry B, 5/10/2017) Nguyen, Hang N.; Nadres, Enrico T.; Alamani, Bryan G.; Rodrigues, Debora F.The synthesis of biocompatible polymers for coating applications has gained significant attention in recent years due to the increasing spread of infectious diseases via contaminated surfaces. One strategy to combat this problem is to apply antimicrobial coatings to surfaces prone to microbial contamination. This study presents a series of biomimetic polymers that can be used as adhesives to immobilize known antimicrobial agents on the surfaces as coatings. Several polymers containing dopamine methacrylate as co-polymers were synthesized and investigated as adhesives for the deposition of an antimicrobial polymer (polyethyleneimine) and antimicrobial nanoparticles (graphene, graphene oxide and molybdenum trioxide) onto glass surfaces. The results showed that different antimicrobials required different types of adhesives for effective coating. Overall, the coatings fabricated from these composites were shown to inactivate E. coli and B. subtilis within 1 h. These coatings were also effective to prevent biofilm growth and demonstrated to be non-toxic to the human corneal epithelial cell line (htCEpi). Leaching tests of the coatings proved that the coatings were stable under biological conditions.Item Developing Chitosan-Morphed Graphene Composite Based Functional Materials by Compression Molding and Laser Lithography(2020-12) Raghatate, Amruta; Robles Hernandez, Francisco C.; Balan, Venkatesh; Rodrigues, Debora F.; Karim, AlamgirChitosan could be chemically and enzymatically processed from Chitin that is widely present in crustaceans, mollusks, insects, and fungus. It has outstanding biodegradability, biocompatibility, nontoxicity, chemical reactivity, and finds applications in tissue engineering, artificial kidney, wound healing, burn treatment, biosensors, and electronics. The main goal of this study is to develop a fabrication process for producing Chitosan Morphed Graphene Composite (CMGC) using traditional sintering (compression molding) and study their properties. First, we produced CMGC using established methods that combine mechanical milling and sintering at temperatures ranging from 120°C to 180°C. Second, the integrity of the chitosan matrix was studied by material characterization including scanning electron microscopy, Raman spectroscopy, Transmission Electron Microscopy, and Fourier-Transform Infrared spectroscopy. Spectroscopy studies confirm that the processing conditions used in this study produced CMGC without degrading the chitosan molecule; although crystallinity is modified. Third, we studied different mechanical properties of CMGC, that are then compared with conventional polymers. The compression modulus is comparable to that of polyethylene, the compression strength is similar to Nylon-6, while toughness and bulk density is superior to commercial polymers. Fourth, the CMGC is biodegradable and compostable when exposed to water or is mixed in moist soil. Also, it is non-toxic and can easily be used as compost to sustain plants without visible inhibitions. Fifth, CMGC can be processed by means of laser lithography to manufacture final products for a long-range of applications which opens up an endless opportunity for fabricating biodegradable CMGC for different applications. Ideally, in future work, we plan to use the CMGC for applications such as computers, electronics, batteries, and defense weaponry such as tasers that will help to accomplish net zero emissions.