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Columbia Dissertations and Theses > Doctoral Dissertations
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| Author(s): | Mehta, Somil C. |
| Title: | Role of functionalization in the interfacial properties of hybrid silicone polymers and the underlying mechanisms. |
| Physical Description: | 132 p. |
| Issue Date: | 2008 |
| Description: | Source: Dissertation Abstracts International, Volume: 69-03, Section: B, page: 1867. Thesis (Ph.D.)--Columbia University, 2008. |
| Bookmark as: | http://hdl.handle.net/10022/AC:P:18524 |
| Full Text (ProQuest): | /ac/proxit.jsp?url=http://gateway.proquest.com/ope... |
| Abstract: | Hybrid silicones are unique due to their distinct hydrophobic/hydrophilic properties. Currently, the preferred hydrophilic moiety for modifying silicones is based on non-ionic groups are seldom used due to a lack of fundamental understanding. Thus the objective of this research is to understand changes in the property hybrid silicones with systematic variation in their structures. The knowledge gained will enable wider utilization or the hybrid silicones. Non-ionic and ionic (anionic, cationic and amphoteric) silicone polymers were synthesized and their behaviors at air-water and liquid-liquid interfaces were investigated. Interfacial properties were measured using Langmuir isotherm, phase diagram, rheometric and microscopic experiments. The observed properties were correlated to the polymer architectures using concepts in solubility parameter, three dimensional Hydrophilic-Lipophilic Balance (HLB) and scaling theory. In addition, molecular simulations were used coupled with the experimental and theoretical finding to develop physical insights into interfacial conformations and energies of interactions. From the air-water interfacial studies, it is postulated that silicone chains undergo conformational transitions from serpentine to coiled above a critical point. These transitions are controlled by interfacial concentrations and interactions (electrostatic and van-der-Waals) with bulk phases. At the silicone oil-water interface, functional groups interact with the water phase whereas siloxane backbone interacts with the oil. Hybrid silicones are observed to alter interfacial shapes to stabilize water-in-oil/oil-in-water emulsions depending on the nature and the degree or hydrophilic modifications. Film of coiled hybrid silicone polymers is proposed to stabilize the liquid-liquid interface in contrast of the polymer precipitation proposed earlier. A preliminary model based on HLB concepts has been developed to predict the above mentioned properties of hybrid silicones. In conclusion, it is established that hybrid silicones stabilize interfaces by film formation in linear/coiled conformations. At water surface, these conformations undergo transition from linear to coiled form at a progressive increase in difficulty with increase in hydrophilicity. Further it is established that with increase in hydrophilic/hydrophobic ratio, interfacial shape changes from concave to convex towards water, thus controlling the nature of emulsions formed. |
| Collection(s): | Doctoral Dissertations |
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