In Chapter 1, we briefly review the thermodynamics of polymer solutions, including the ideal solution based on the Flory-Huggins lattice chain model. The entropy change in the mixing of macromolecules with small solvent molecules is much smaller than that in the mixing of two kinds of small molecules. Therefore, the effect of the solution temperature is also smaller. / In Chapter 2, we describe the basic difference between the complicate polymeric and simple Newtonian fluid and list some dimensionless numbers relevant to various physical phenomena, including the Reynolds number (Re) and the capillary number (Ca), respectively related to the inertial effect and the interfacial tension. As a fluid goes down to the micro scale, the inertial effect is usually negligible so that the flow becomes laminar. However, the interfacial tension starts to play a significant role, which leads to the development of some droplet-based (or digital) microfluidic systems. Using small droplets leads to the following advantages: (1) the reagents are limited within a small boundary of each droplet; and (2) no complex microfluidic device is required. / In Chapter 3, we use PNIPAM in water as a model system to detail how to construct a polymer phase diagram by using a microfluidic device, including the choice of the carrier fluid, the principle and experimental procedure of forming concentration-controllable PNIPAM droplets, the determination of PNIPAM concentration in each droplet by using a fluorescein probe, the effect of fluorescein on the phase transition, and the detection of the phase transition by dark field viewing. For comparison, we also did the normal LLS measurement of the phase transition of PNIPAM in water. / In Chapter 4, PS in cyclohexane is used as a model system to illustrate how to handle organic solvents because cyclohexane swells the PDMS channels. The swelling is much eliminated by directly loading the PS solution into the junction via glass capillaries. Since the addition of a fluorescence concentration probe dramatically influences the PS phase transition, we have to use a so-called parallel experimental method to produce concentration-controllable PS droplets. In this method, several PDMS chips from the same batch are used in the formation of small PS droplets. When the numbers of small PS droplets produced in the same procedure are similar to each other, the PS concentrations in different corresponding droplets are comparable. Therefore we are able to index the PS concentration in each droplet by comparing it with the droplets prepared by the same procedure, but with some added fluorescence probes. / In Chapter 5, on the basis of numerous experiments, we find inorganic salts play a significant role on the droplet forming. Thus we propose that droplet formation is a kinetics governed process when two immiscible liquids meet each other in microchannels. / In this thesis we have proposed and established a new method of constructing polymer phase diagrams. By employing the droplets-based microfluidic system, we are able to form an array of droplets of polymer solutions with several nanoliters in size. Each droplet has a controllable composition. The array of polymer droplets can be transferred and stored in a glass capillary; there the turbidity of each droplet due to the difference of scatted light immediately after the phase transition can be monitored under a microscope via dark field viewing, when the solution temperature changes. Therefore, we are able to construct a polymer phase diagram by simply combing each phase transition temperature with its corresponding compositions of polymer solution droplets. / This method has two distinguished advantages; namely, minimal sample consumption and much reduced experimental time required for the phase transition to reach its equilibrium at each given temperature. This is because the greatly increased surface-to-volume ratio allows rapid diffusion and fast heat transfer. To demonstrate the principle, we have chosen PS in cyclohexane with an upper critical solution temperature (UCST) and Poly(N-isopropylacrylamide) (PNIPAM) in water with a lower critical solution temperature (LCST) as two model systems. Primarily established phase diagrams of these two polymer solutions have demonstrated the feasibility of using droplets-based microfluidic system to construct polymer phase diagrams. / Shi, Feng. / Advisers: Chi Wu; Bo Zheng. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3532. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / 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.
| Identifer | oai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_344271 |
| Date | January 2008 |
| Contributors | Shi, Feng., Chinese University of Hong Kong Graduate School. Division of Chemistry. |
| Source Sets | The Chinese University of Hong Kong |
| Language | English, Chinese |
| Detected Language | English |
| Type | Text, theses |
| Format | electronic resource, microform, microfiche, 1 online resource (v, 108 leaves : ill.) |
| Rights | Use of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/) |
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