Malaria parasite infects more than 200 million people and about 435 000 succumb to the illness annually (WHO, 2019). Victims are mostly young children and pregnant women. It is transmitted by the bite of the infected female Anopheles mosquitoes. Indoor protection is provided by bed nets and residual spraying of insecticides. Mosquitoes typically bite ankles and feet most of the time (93%) whilst in outdoor settings. Long lasting insect-repellent anklets/bracelets/footlets may provide a strategy for reducing mosquito bites outdoors in the lower limb regions. This study considered long-lasting repellent anklets that may be used for outdoor protection against mosquito bites. Experiments were performed to investigate the incorporating of mosquito repellents into the thermoplastic polymers, poly(ethylene-co-vinyl acetate) (EVA) and linear low-density polyethylene (LLDPE). Two different mosquito repellents, namely DEET and Icaridin, were employed. The target was to develop cost-effective bracelets with long-lasting efficacy, i.e., slow release of the active ingredient over extended periods. In this way, it is expected to protect people from acquiring mosquito-borne diseases during the time they spend outdoors. The proposed concept utilises microporous polymer strands manufactured via conventional plastic extrusion processes. The internal open-cell polymer foam structure serves both as a reservoir and a protective environment for the active ingredient trapped inside. An outer dense skin layer covering the strands may provide the necessary diffusion barrier that controls the release of repellent at effective levels over a considerable period. The objective was achieved by phase separation via spinodal decomposition (SD), triggered by extruding the molten strands directly into ice-cold water. Thermogravimetric analysis (TGA) and solvent extraction confirmed that all of the repellents were embedded in the polymer matrices. Scanning Electronic Microscopy (SEM) confirmed the porous co-continuous repellent-polymer microstructure. The stability of the polymer matrix was studied by estimating the swelling and shrinkage of the polymer matrix. The release of the active ingredient in the polymer/repellent system was followed as a function of oven-ageing temperature and time. The kinetics of the release rate of the repellent from microporous polymer matrix strands was mathematically modelled using semi-empirical models. The performance of the repellent-based strands was evaluated using foot-in-cage repellence testing. Finally, an attempt was made to predict the phase diagrams of the LLDPE/repellent system on the basis of alkane/repellent systems data. The results confirmed that EVA and LLDPE are suitable scaffold matrices, acting as reservoirs, for liquid repellents that were released at a constant rate. As expected, the repellent swelled EVA more than LLDPE. As a result, it also shrank significantly more when the repellent was released, i.e. EVA showed poor dimensional stability compared to LLDPE. The semi-empirical repellent release models were found valuable as they provided insights into the way that the repellent was being released. They allowed differentiating between diffusion and relaxation mechanisms. It was found that repellence efficacy can be maintained for more than 90 days. Future developments of sandals and anklets based on this approach may assists in preventing outdoor mosquito bites, thereby decreasing malaria infection rates. / Thesis (PhD)--University of Pretoria, 2019. / Deutsche Forschungsgemeinschaft (DFG) Grant AN 212/22-1 / Chemical Engineering / PhD / Unrestricted

Ngai To. / "May 2003." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Polymer solutions in which there are strong specific interactions between the polymer and the solvent are of interest in a number of biological applications. Of particular interest are polymer solutions in which supercritical carbon dioxide (CO2) is the solvent, because polymer processing with CO2 is an important application of green chemistry. Unfortunately, experimental data on the phase behavior of polymer - CO2 systems are relatively scarce, as are models that describe the phase behavior of such systems. The focus of this research is therefore on developing a thermodynamic model based on lattice theory for calculating phase behavior of high pressure polymer solutions with specific intermolecular interactions. A new model, termed the LELAC (Lattice-based Extended Liquid Activity Coefficient) model is proposed based on the gART-L model of Sukhadia and Variankaval. The new model incorporates the compressibility effect at high pressures. The parameters of the model are (1) the equilibrium constant for association between a polymer segment and a solvent, (2) the specific interaction energy between a polymer segment and a solvent, and (3) the dispersion interaction energy. The dispersion interaction energy is calculated using Regular Solution Theory and therefore depends on the pure component properties. One or both of the remaining parameters is obtained from independent measurements such as FT- IR spectra. Alternatively, the two parameters can be obtained by fitting data. Cloud point curves of polymer - CO2 systems have been successfully correlated (1.3 % error) with the new model. Also, using fitted parameters from cloud point data, the sorption behavior of CO2 in polymers has been predicted. The polymer investigated include PBMA, PVAc and Polyacrylates. Comparison of cloud points with those obtained using the SAFT model revealed that the new model performs better than the SAFT model (3.6% error) with two adjustable parameters. The use of FT-IR to investigate interactions between CO2 and a number of polymers has been studied. The results confirm that complexes are formed between CO2 and PMMA, PEMA, PBMA, PVMK, and PVAc. A complex of PVC and CO2 is reported and a new mechanism involving a carbon oxygen triple bond is postulated for this system.

Much theoretical and experimental work has focused on chain dynamics in semidilute polymer solutions for over three decades. The fast relaxation mode (namely, the cooperative diffusion of chain segments between two neighboring entanglement points, i.e., the "blobs") has been well understood. But for the slow mode that observed from time to time, its earlier attribution to the "reptation" is clearly wrong. There are a school of people in the world who thought that it was due to some experimental artifacts. However, there are also many experimentalists who believe that it is real and try to explain it in different ways. Up to now, the questions about whether this observed slow mode is real and its nature are still remained as a challenging problem. In this study, dynamics of liner polystyrene semidilute solution in both toluene and cyclohexane was comparatively studied by laser light scattering. In toluene, a thermodynamically good solvent, four different narrowly distributed polystyrene standards over a wide molar mass range (1.15 x 105 - 6.85 x 106 g/mol) were studied. The highest concentration (C) studied was ∼21 times of the overlap concentration (C*) at which polymer chains start to "touch" each other. As expected, only one fast diffusive relaxation was observed, attributing to the blob diffusion The static and dynamic correlation lengths (xiD and xiS) are also expectedly scaled to the concentration as xiS or xiD ∼ C -0.72 +/- 0.02. In cyclohexane, a poor or marginal solvent, depending on the solution temperature, an additional slow relaxation mode repeatly appeared. In the range 32-50°C, the polystyrene chains extend as the temperature increases because cyclohexane becomes a better solvent. In this way, C* decreases. Therefore, we can use the solution temperature to switch such a polystyrene solution from dilute to semidilute for a given polymer concentration. By comparing the intensity contribution and characteristic decay time of the slow mode, we found that the temperature has a much stronger effects on the slow mode. Our results indicate that the fast and slow modes are coupled and the slow mode is due to relaxation of segments around the entanglement point, that is, the knots. These interacted segments fluctuation corresponds to some density with a correlation length longer than that of individual blobs. / On the way, we also studied the random copolymer poly(N-isopropylacrylamide - co- x 2'-methacryloylaminoethylene-3alpha,7alpha,12alpha-trihydroxy-5beta-cholanoamide) poly(NIPAM-co-xMACA) in dilute solutions. MACA is a methacrylamide derivative of bioactive cholic acid. The copolymers were made by free-radical polymerization and "x" represents the composition of MACA (1.0, 2.9 and 4.8 mol%). Poly(N-isopropylacrylamide) (PNIPAM) is a thermally sensitive polymer, namely, it is soluble in water with a lower critical solution temperature (LCST ∼32°C). Due to incorporation of different amounts of hydrophobic MACA, the LCST of the copolymer is shifted to different lower values. At temperatures higher than the LCST, the copolymer chains undergo intrachain contraction or/and interchain association, depending on the polymer concentration and chain structure. Our laser lightscattering study of such chain contraction and association reveal an unexpected result; namely, the formation of stable aggregates of these hydrophobically modified copolymer chains is stronger easier than PNIPAM homopolymer chains under the same conditions. Our finding that that insertion of more hydrophobic comonomers into a hydrophilic chain backbone surprisingly led to the formation of smaller aggregates in water is apparently contradict to our conventional wisdom. A higher content of hydrophobic MACA or a quick heating of the solution can make the intrachain contraction so dominant that each resultant aggregate on average only contains a few collapsed chains with a lower chain density. We successfully attributed the stabilization to the viscoelastic effect, namely, hydrophobic association inside each aggregate increases the chain relaxation time (taue). When taue becomes much longer than the interaction time (tau c) of two colliding aggregates, each aggregate behaves like a tiny non-adhesive "glassy" ball. This stabilization mechanism is completely different from our conventional thermodynamic consideration in which we normally try to make the particle surface hydrophilic to reduce tauc. We also observed that in the cooling process, the collapsed chains inside the aggregates swell first before they can detachment and dissolve in the solution. The hydrophobic association induced in the collapsed solute at higher temperatures cannot be completely removed even at a temperature as low as 10°C. The dilution of the copolymer solution can completely suppress interchain association so that individual chains can undergo an intrachain coil-to-globule transition. The association of a limited number of heteropolymer chains in dilute solutions to form a stable/metastable mesoglobular phase between single-chain globules and macroscopic precipitates resembles the association of some protein chains. / We further comparatively studied the chain dynamics of a pair of diblock poly(styrene-b-butadiene) (PS210-b-PB 960) and triblock poly(styrene-b-butadiene- b-styrene) (PS200-b-PB1815- b-PS200) copolymers in both dilute and semidilute toluene solutions. As expected, the mutual diffusion of individual chain in dilute solutions became a fast cooperative diffusion of the "blobs" for both the copolymers in semidilute solutions. Further increase of the polymer concentration also lead to an additional slow relaxation mode. For the triblock chains, there existed an extra middle relaxation mode between the fast and the slow modes. The concentration dependence of the average characteristic decay time of the fast mode (⟨tauf⟩) follows a scaling of 1/⟨tau f⟩ ∼ C-alpha with 0.33 < alpha < 0.44, much smaller than 0.75 (predicted) or 0.72 (observed) for linear homopolymer chains in a thermodynamically good solvent. Note that toluene is a less good solvent for PB block. Such a difference in solubility leads us to speculate that the PB and PS blocks are transiently segregated in semidilute solutions. The relaxation of these transient PB and PS richer domains might lead to the observed slow mode. Our speculation is supported by the appearance and disappearance of the slow relaxation mode in a polyisoprene-b-polystyrene- b-polyisoprene semidilute solution in cyclohexane, a selective solvent for PS block at lower temperatures because the solubility of PS decreases as the solution temperature. / Li Wei. / "September 2006." / Adviser: Chi Wu. / Source: Dissertation Abstracts International, Volume: 68-03, Section: B, page: 1664. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

Thesis (Ph. D.)--University of Missouri--Rolla, 1993. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed January 25, 2010) Includes bibliographical references (p. 150-155).

No description available.

No description available.

Thesis (Ph. D.)--School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 2005. Directed by Amyn S. Teja. / Dr. Thomas H. Sanders, Committee Member ; Dr. Peter J. Ludovice, Committee Member ; Dr. J. Carson Meredith, Committee Member ; Dr. William J. Koros, Committee Member ; Dr. Amyn S. Teja, Committee Chair. Includes bibliographical references.

No description available.

by Niu Aizhen. / "Mar., 2001." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.