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Understanding the structure of water, ice, and aqueous solutions next to solid surfaces

Anim-Danso, Emmanuel

Abstract Details

2015, Doctor of Philosophy, University of Akron, Polymer Science.
The phase change of water into ice on solid surfaces has significant impact on infrastructure and human activity. In this thesis, we have set out to understand the structure of water as it is systematically cooled to form ice next to solid surfaces. We have coupled a novel heating and cooling device with surface sensitive sum frequency generation spectroscopy (SFG) to observe molecularly how water interacts with solid surfaces as temperature is decreased. This we believe can lead to a better understanding of how to delay ice formation or reduce ice adhesion to surfaces. SFG (used mainly in the total internal reflection geometry) is a nonlinear optical technique which detects the orientation and molecular arrangement at surfaces and interfaces. We used sapphire and mica as model surfaces for our experiments. In the first part of this research, we have performed experiments on a neutral sapphire surface. We have observed that the SFG signal intensity increased considerably when ice was formed. This shows that the water molecules in ice interact strongly with each other and with the solid surface. When temperature was further decreased, the ice peak intensity increased, indicating the increased coherence length of the water molecules in ice. SFG spectra of ice during heating show gradual signal attenuation. Contrary to ice surfaces, no interface premelting of ice was observed during the heating cycle. In the second part, we studied freezing of water next to charged surfaces. The effect of charge or electric field on water has been shown in the literature. Recently, it was indicated that negative and positive charges have opposing effects on the freezing of water; negative charges delayed freezing, while positive charges enhanced it. In this part, we sought to understand the molecular origin of this finding. Our results showed no considerable difference in the freezing temperature of water on both surfaces. However, the structure of water was different. Just like the neutral surface, intense SFG ice signal was observed for positively charged sapphire whereas signal intensity drastically decreased for ice next to negatively charged sapphire and mica surfaces. The signal attenuation observed for negatively charged surface is attributed to the disordering of water molecules at the interface. This could indicate that ice adhesion to negatively charged surfaces should be less than neutral and positively charged surfaces. The third part of this thesis deals with the freezing of a sodium chloride solution next to a sapphire surface. Of interest is how the solution phase separates. Our results show that the brine stays close to the sapphire surface, while the ice segregates away from the sapphire. Despite the presence of a surface, the solution freezes above the equilibrium freezing temperature of sodium chloride solution possibly due to supercooling. The freezing of the salt solution into a hydrate is acknowledged by an intense peak, about three orders of magnitude higher than water signal. No premelting of the hydrate is observed during the heating cycle. The intensity of the hydrate peak, however, decreased significantly until the eventual melting at -22oC. Finally, we have also performed experiments at polymer/water interface. The polymer/water interface is commonly encountered and a molecular understanding of surface restructuring in water will be useful to biomedical science. We studied how poly(n-butyl a-hydroxymethyl acrylate) (PHNB), an amphiphilic polymer, restructures in the vicinity of water using SFG and contact angle measurements. We have observed that at room temperature, the surface resists putting the more hydrophilic groups at the interface with water. Even though such a conformation is thermodynamically favorable, the polymer surface appears to be frozen due to the high polymer Tg. However, when the polymer is heated in water above its Tg (80oC), the surface restructures due to the increased segmental motions in the polymer. Our study into the molecular interactions of water and ice with solid surfaces provides insights into the increased adhesion of ice to surfaces and could lead to the design of materials that could reduce ice adhesion strength on surfaces.
Ali Dhinojwala, Professor (Advisor)
Mesfin Tsige, Professor (Committee Chair)
Tianbo Liu, Professor (Committee Member)
Toshikazu Miyoshi, Professor (Committee Member)
Adam W. Smith, Professor (Committee Member)
142 p.

Recommended Citations

Citations

  • Anim-Danso, E. (2015). Understanding the structure of water, ice, and aqueous solutions next to solid surfaces [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1441318237

    APA Style (7th edition)

  • Anim-Danso, Emmanuel. Understanding the structure of water, ice, and aqueous solutions next to solid surfaces. 2015. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1441318237.

    MLA Style (8th edition)

  • Anim-Danso, Emmanuel. "Understanding the structure of water, ice, and aqueous solutions next to solid surfaces." Doctoral dissertation, University of Akron, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1441318237

    Chicago Manual of Style (17th edition)