Chemical Engineering

In this thesis, I present a developed kinetic model of cyclopentadiene with feed impurities. The model is valid for multiple impurities: isoprene, trans-1,3-pentadiene, 1-pentene, and cyclopentene. The model was developed from experiments over a temperature range of 80 °C to 160 °C. Reaction rate constants across this range were calculated and related activation energies and pre-exponential factors were derived. Overall, the model affirms that CPD self-dimerization is the dominant reaction occurring in the C5 stream, followed by the co-dimerization between cyclopentadiene and isoprene. For impurities, co-dimerization with CPD occurs more readily than self-dimerization.M.S

Current gels used in blood separation tubes create an imperfect barrier between the blood components because of their physical and thixotropic nature. As a result, blood components tend to leak into the gel layer or vice versa during transport and storage. To overcome these problems, we demonstrate the use of a UV-curable thixotropic gel composed of a sorbitol-based gelator in a diacrylate oligomer. Initially, the sample is a physical gel composed of weak, non-covalent bonds, and its thixotropic nature allows it to flow under centrifugation and form a barrier between the density-stratified layers of blood. Immediately afterward, the gel is chemically crosslinked by short exposure to UV light for 10-30 s. This results in a rigid, impenetrable barrier that is freeze-thaw stable. The gel is compatible with blood, allowing blood samples to be stored in the tube and analyzed over long times. We believe the present method is a significant advance in the practice of blood analysis for medical purposes.

The self-assembly of biological surfactants in water is an important topic for study because of its relevance to physiological processes. Two common types of biosurfactants are lecithin (phosphatidylcholine) and bile salts, which are both present in bile and involved in digestion. Previous studies on lecithin-bile salt mixtures have reported the formation of short, rodlike micelles. Here, we show that lecithin-bile salt micelles can be further induced to grow into long, flexible wormlike structures. The formation of long worms and their resultant entanglement into transient networks is reflected in the rheology: the fluids become viscoelastic and exhibit Maxwellian behavior, and their zero-shear viscosity can be up to a 1000-fold higher than that of water. The presence of worms is further confirmed by data from small-angle neutron and X-ray scattering and from cryo-transmission electron microscopy (cryo-TEM). We find that micellar growth peaks at a specific molar ratio (near equimol...

Molecular organogelators convert oils into gels by forming self-assembled fibrous networks. Here, we demonstrate that such gelation can be activated by contacting the oil with an immiscible solvent (water). Our gelator is dibenzylidene sorbitol (DBS), which forms a low-viscosity sol when added to toluene containing a small amount of dimethyl sulfoxide (DMSO). Upon contact with water, DMSO partitions into the water, activating gelation of DBS in the toluene. The gel grows from the oil/water interface and slowly envelops the oil phase. We have exploited this effect for the self-repair of oil leaks from underwater tubes. When a DBS/toluene/DMSO solution flows through the tube, it forms a gel selectively at the leak point, thereby plugging the leak and restoring flow. Our approach is reminiscent of wound-sealing via blood-clotting: there also, inactive gelators in blood are activated at the wound site into a fibrous network, thereby plugging the wound and restoring blood flow.

We have developed microscale polymer capsules that are able to chemically degrade a certain type of polymeric microbead in their immediate vicinity. The inspiration here is from the body's immune system, where killer T cells selectively destroy cancerous cells or cells infected by pathogens while leaving healthy cells alone. The "killer" capsules are made from the cationic biopolymer chitosan by a combination of ionic cross-linking (using multivalent tripolyposphate anions) and subsequent covalent cross-linking (using glutaraldehyde). During capsule formation, the enzyme glucose oxidase (GOx) is encapsulated in these capsules. The target beads are made by ionic cross-linking of the biopolymer alginate using copper (Cu(2+)) cations. The killer capsules harvest glucose from their surroundings, which is then enzymatically converted by GOx into gluconate ions. These ions are known for their ability to chelate Cu(2+) cations. Thus, when a killer capsule is next to a target ...

Antibacterial resistance is an issue of increasing severity as current antibiotics are losing their effectiveness and fewer antibiotics are being developed. New methods for combating bacterial virulence are required. Modulating molecular communication among bacteria can alter phenotype, including attachment to epithelia, biofilm formation and even toxin production. Intercepting and modulating communication networks provide a means to attenuate virulence without directly interacting with the bacteria of interest. In this work, we target communication mediated by the quorum sensing (QS) bacterial autoinducer-2, AI-2. We have assembled a capsule of biological polymers alginate and chitosan, attached an AI-2 processing kinase, LsrK, and provided substrate, ATP, for enzymatic alteration of AI-2 in culture fluids. Correspondingly, AI-2 mediated QS activity is diminished. All components of this system are "biofabricated" - they are biologically derived and their assembly is accom...

Recently there has been much interest in using light to activate self-assembly of molecules in a fluid, leading to gelation. The advantage of light over other stimuli lies in its spatial selectivity, i.e., its ability to be directed at a precise location, which could be particularly useful in microfluidic applications. However, existing light-responsive fluids are not suitable for these purposes since they do not convert into sufficiently strong gels that can withstand shear. Here, we address this deficiency by developing a new light-responsive system based on the well-known polysaccharide, alginate. The fluid is composed entirely of commercially available components: alginate, a photoacid generator (PAG), and a chelated complex of divalent strontium (Sr 2+) cations. Upon exposure to ultraviolet (UV) light, the PAG dissociates to release H + ions, which in turn induce the release of free Sr 2+ from the chelate. The Sr 2+ ions self-assemble with the alginate chains to give a stiff gel with an elastic modulus ∼2000 Pa and a yield stress ∼400 Pa (this gel is strong enough to be picked up and held by one's fingers). The above fluid is sent through a network of microchannels and a short segment of a specific channel is exposed to UV light. At that point, the fluid is locally transformed into a strong gel in a few minutes, and the resulting gel blocks the flow through that channel while other channels remain open. When the UV light is removed, the gel is gradually diluted by the flow and the channel reopens. We have thus demonstrated a remote-controlled fluidic valve that can be closed by shining light and reopened when the light is removed. In addition, we also show that light-induced gelation of our alginate fluid can be used to deposit biocompatible payloads at specific addresses within a microchannel.

Biopolymers bearing hydrophobic side-chains, such as hydrophobically modified chitosan (hmC), can connect liposomes into a gel network via hydrophobic interactions. In this paper, we show that such liposome gels possess an attractive combination of properties for certain drug delivery applications. Their shear-thinning property allows these gels to be injected at a particular site, while their gel-like nature at rest ensures that the material will remain localized at that site. Moreover, drugs can be encapsulated in the interior of the liposomes and delivered at the local site for an extended period of time. The presence of two transport resistances − from the liposomal bilayer and the gel network − is shown to be responsible for the sustained release; in turn, disruption of the liposomes both weakens the gel and causes a faster release. We have monitored release kinetics from liposome gels of a cationic anticancer drug doxorubicin (Dox) encapsulated in liposomes. Sustained release of Dox from these gels and the concomitant cytotoxic effect could be observed for over a week.

Vesicles are self-assembled nanocontainers that are used for the controlled release of cosmetics, drugs, and proteins. Researchers have been seeking to create photoresponsive vesicles that could enable the triggered release of encapsulated molecules with accurate spatial resolution. While several photoresponsive vesicle formulations have been reported, these systems are rather complex as they rely on special light-sensitive amphiphiles that require synthesis. In this study, we report a new class of photoresponsive vesicles based on two inexpensive and commercially available amphiphiles. Specifically, we employ p-octyloxydiphenyliodonium hexafluoroantimonate (ODPI), a cationic amphiphile that finds use as a photoinitiator, and a common anionic surfactant, sodium dodecylbenzenesulfonate (SDBS). Mixtures of ODPI and SDBS form "catanionic" vesicles at certain molar ratios due to ionic interactions between the cationic and anionic headgroups. When irradiated with ultraviolet (UV) light, ODPI loses its charge and, in turn, the vesicles are converted into micelles due to the loss of ionic interactions. In addition, a mixture of these photoresponsive vesicles and a hydrophobically modified biopolymer gives a photoresponsive vesicle-gel. The vesicle-gel is formed because hydrophobes on the polymer insert into vesicle bilayers and thus induce a three-dimensional network of vesicles connected by polymer chains. Upon UV irradiation, the network is disrupted because of the conversion of vesicles to micelles, with the polymer hydrophobes getting sequestered within the micelles. As a result, the gel is converted to a sol, which manifests as a 40 000-fold light-induced drop in sample viscosity.

Many small molecules can self-assemble by non-covalent interactions into fibrous networks and thereby induce gelation of organic liquids. However, no capability currently exists to predict whether a molecule in a given solvent will form a gel, a low-viscosity solution (sol), or an insoluble precipitate. Gelation has been recognized as a phenomenon that reflects a balance between solubility and insolubility; however, the distinction between these regimes has not been quantified in a systematic fashion. In this work, we focus on a well-known gelator, 1,3:2,4-dibenzylidene sorbitol (DBS), and study its self-assembly in various solvents. From these data, we build a framework for DBS gelation based on Hansen solubility parameters (HSPs). While the HSPs for DBS are not known a priori, the HSPs are available for each solvent and they quantify the solvent's ability to interact via dispersion, dipole-dipole, and hydrogen bonding interactions. Using the three HSPs, we construct three-dimensional plots showing regions of solubility (S), slow gelation (SG), instant gelation (IG), and insolubility (I) for DBS in the different solvents at a given temperature and concentration. Our principal finding is that the above regions radiate out as concentric shells: i.e., a central solubility (S) sphere, followed in order by spheres corresponding to SG, IG, and I regions. The distance (R 0) from the origin of the central sphere quantifies the incompatibility between DBS and a solvent-the larger this distance, the more incompatible the pair. The elastic modulus of the final gel increases with R 0 , while the time required for a super-saturated sol to form a gel decreases with R 0. Importantly, if R 0 is too small, the gels are weak, but if R 0 is too large, insolubility occurs-thus, strong gels fall within an optimal window of incompatibility between the gelator and the solvent. Our approach can be used to design organogels of desired strength and gelation time by judicious choice of a particular solvent or a blend of solvents. The above framework can be readily extended to many other gelators, including those with molecular structures very different from that of DBS. We have developed a MATLAB program that will be freely available (upon request) to the scientific community to replicate and extend this approach to other gelators of interest.

Recently, there has been much interest in photorheological (PR) fluids, i.e., fluids whose rheological properties can be tuned by light. In particular, there is a need for simple, low-cost PR fluids that can be easily created using inexpensive, commercially available ingredients and that show substantial, reversible changes in rheology upon exposure to different wavelengths of light. Towards this end, we report a class of photoreversible PR fluids prepared by combining the azobenzene derivative 4-azobenzene carboxylic acid (ACA) (in its salt form) with the cationic surfactant erucyl bis(2-hydroxyethyl)methyl ammonium chloride (EHAC). We show that certain aqueous mixtures of EHAC and ACA, which are lowviscosity solutions at the outset, undergo nearly a million-fold increase in viscosity when irradiated with UV light. The same solutions revert to their initial viscosity when subsequently exposed to visible light. Using an array of techniques including UV-vis and NMR spectroscopies, small-angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM), we have comprehensively characterized these PR fluids at the molecular, nanostructural, and macroscopic scales. Initially, EHAC-ACA are selfassembled into unilamellar vesicles, which are discrete container structures and give the sample a low viscosity. Upon exposure to UV light, ACA undergoes a trans to cis photoisomerization, which alters the geometry of the EHAC-ACA complex. In turn, the molecules self-assemble into a different structure, viz. wormlike micelles, which are long, entangled chains and impart a high viscosity to the sample. The above changes in viscosity are repeatable, and the sample can be reversibly cycled back and forth between low and high viscosity states. Our photoreversible PR fluids can be easily replicated in any industrial or academic lab, and it is hoped that these "smart" fluids will eventually find a host of applications.

1. Methodology and materials. Materials: acrylic acid (AA, Sigma), N,N'-methylene-bis(acrylamide) (MBAA, Sigma), ferric chloride hexahydride (FeCl 3 .6H 2 O, Baker), ammonium persulfate (APS, Sigma), sodium citrate(Sigma),Hydrogen dioxide (Fisher Scientific), Rhodamine B, Tetramethylethylenediamine (TEMED)were used as received. A stock solution of APS was prepared by dissolving APS in distilled water to a concentration of 0.5g/mL. Hydrogel synthesis. A typical hydrogel was prepared by free radical polymerization of an aqueous solution containing 1.39 mol/L of AA, 1.25% FeCl 3 (mol/mol AA) and 0.1% MBA (mol/mol AA). The solution was degassed by purging with argon gas. A 5% (wt% compared with AA) of APS stock solution was then added to initiate the reaction. The solutions were sealed and left undisturbed for 16 hours at 25°C. Hydrogels with different physical cross-linking densities were produced by varying the concentrations of FeCl 3 between 0%, 0.5%, 1.25% and 2.5% (mol/mol, compared with AA). Hydrogels with different chemical cross-linker content were synthesized by using MBAA with a concentration of 0%, 0.1%, 0.5% and 1% (mol/mol AA). The details of the hydrogel recipe were listed in table 1. In order to precisely study the self-healing behavior, all experimental hydrogel samples were fabricated in cylindrical shapes with a diameter of 1 cm. The polymerization reactions for the experimental hydrogels were carried out as described above. 2. Stretching property test of hydrogel. We studied the self-healing behavior of the hydrogel by mechanically stretching the hydrogel. We define the Maximum strain (ε) as ε = L/L 0 ×100%, where L is the stretched length at the breaking point and L 0 is the original length (un-stretched length). The healing efficiency of a hydrogel (ƒ) is defined as ƒ= ε´/ε, where ε´ is the modulus of the healed hydrogel and ε is the strength of the original hydrogel (uncut hydrogel). The value of ƒ was used to assess the self-healing property of this hydrogel.

The ability to modulate the physical properties of a supramolecular hydrogel may be beneficial for biomaterial and biomedical applications. We find that guanosine (G 1), when combined with 0.5 equiv of potassium borate, forms a strong, self-supporting hydrogel with elastic moduli >10 kPa. The countercation in the borate salt (MB(OH) 4) significantly alters the physical properties of the hydrogel. The gelator combination of G 1 and KB(OH) 4 formed the strongest hydrogel, while the weakest system was obtained with LiB(OH) 4 , as judged by 1 H NMR and rheology. Data from powder XRD, 1 H double-quantum solid-state magic-angle spinning (MAS) NMR and small-angle neutron scattering (SANS) were consistent with a structural model that involves formation of borate dimers and G4•K + quartets by G 1 and KB(OH) 4. Stacking of these G4•M + quartets into G4-nanowires gives a hydrogel. We found that the M + cation helps stabilize the anionic guanosine-borate (GB) diesters, as well as the G4-quartets. Supplementing the standard gelator mixture of G 1 and 0.5 equiv of KB(OH) 4 with additional KCl or KNO 3 increased the strength of the hydrogel. We found that thioflavin T fluoresces in the presence of G4•M + precursor structures. This fluorescence response for thioflavin T was the greatest for the K + GB system, presumably due to the enhanced interaction of the dye with the more stable G4•K + quartets. The fluorescence of thioflavin T increased as a function of gelator concentration with an increase that correlated with the system's gel point, as measured by solution viscosity

We describe the creation of polymeric microcapsules that can exhibit autonomous motion along defined trajectories. The capsules are made by cross-linking aqueous microdroplets of the biopolymer chitosan using glutaraldehyde. A coflow microfluidic tubing device is used to generate chitosan droplets containing nanoparticles (NPs) with an iron (Fe) core and a platinum (Pt) shell. The droplets are then incubated in a Petri dish with the cross-linking solution, and an external magnet is placed below the Petri dish to pull the NPs together as a collective "patch" on one end of each droplet. This results in cross-linked capsules (∼150 μm in diameter) with an anisotropic (patchy) structure. When these capsules are placed in a solution of H2O2, the Pt shell of the NPs catalyzes the decomposition of H2O2 into O2 gas, which is ejected from the patchy end in the form of bubbles. As a result, the capsules (which are termed micromotors) move in a direction opposite to the bubbles. Furth...

Iron loaded spherical mesoporous silica particles were synthesized to prevent agglomeration of iron particles. By carrying out sol-gel process in presence of dissolved ferric salt and subsequent reduction of the obtained particles yielded zero valent iron loaded spherical mesoporous silica particles. The results indicated that mean diameter of the particles reduced from 627 nm to 229 nm on increasing the iron content from 0.00 mmol to 1.25 mmol, depicting an inverse relationship between the particle size and molar ratio of the iron salt. The surface area analysis at lower iron loading revealed surface area of the particles significantly high (417 m 2 /g). In batch experiments, the synthesized particles successfully removed 95% of trichloroethylene in short duration (60 min). The results of this study illustrate the potential use of iron loaded spherical mesoporous silica particles for dechlorination of chlorinated organic compounds in underground waters and contaminated soil.