Thermodynamic and morphological transitions in crystalline and soft material interfaces

Interfaces are defects present in all materials. Interface transitions are characterized by abrupt changes in interface structure, chemistry and/or morphology under suitable conditions. They exist in many material systems and often produce profound changes in material properties. Several interface transitions in crystalline and soft materials that have not been previously well understood were studied in this thesis. In the first part of this thesis, a diffuse-interface thermodynamic framework was developed for grain boundary structural and chemical transitions. A graphical construction method was developed to predict conditions for grain boundary transitions. A grain boundary premelting transition is predicted for systems of fixed stoichiometry. When extended to binary systems, the diffuse-interface model predicts the existence of a coupled grain boundary premelting/prewetting transition, which produces cooperative grain boundary disordering and segregation at sub-eutectic and sub-solidus temperatures. The analysis rationalizes the thermodynamic origin of intergranular glassy films (IGFs) widely observed in multi-component ceramics and alloys, for which thermodynamic stability has not been well explained in previous research. Predictions on the conditions for IGF's formation are consistent with experiments. As part of this work, a prototype of "grain boundary complexion diagrams" was constructed which delineates the stability domains of different grain boundary "complexions" on bulk phase diagrams. Morphological transitions of interfaces in soft materials such as surfactant self-assembled structures were investigated in the second part of this thesis. A phase-field model was developed for simulating morphological evolution of surfactant aggregates in solutions.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Materials Science and Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2008

Author dc:creator

• Tang, Ming, Ph. D. Massachusetts Institute of Technology

Advisor dc:contributor.advisor

• W. Craig Carter and Yet-Ming Chiang.

• Materials Science and Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/44316

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/44316