Defect mediated melting in colloidal monolayers
Polystyrene microspheres placed carefully on the surface of water form ordered structures ranging from weakly interacting gasses to defect-sparse two dimensional solids. These systems are microscopically observable and are ideal for observing defect evolution as the systems melt. Using microscopy in combination with image processing techniques the equation of state, defect structures, and the translational and orientational correlation functions are found as the systems melt (solidify) when isothermally expanded (compressed). The data are analyzed with the specific intent of examining the validity of the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) theory of two dimensional defect mediated melting. In this theory melting occurs in a two step continuous process governed by the separation of bound topological defects. The solid first loses its translational order by the unbinding of bound dislocation pairs. This results in an orientationally ordered intermediate phase called the Hexatic that evolves to a true liquid by disclination unbinding. Two particle sizes, 2.88 ..mu..m dia. and 1.01 ..mu..m dia., were examined in this work. The 2.88 ..mu..m system showed evidence of defect mediated melting and of an intermediate hexatic phase, in partial accord with the KTHNY theory. However, the loss of orientational order was mediated by the formation of grain boundaries and the predicted disclination unbinding transition was not observed. Melting in the 1.01 ..mu..m system appeared to proceed by a weak first order transition. It is suggested that the difference between the two systems is attributable to the core energy required to create bound dislocation pairs. From observations on the number and frequency of occurrence of virtual dislocation pairs in these systems, an additional mechanism for dislocation unbinding is postulated. 72 refs., 61 figs., 2 tabs.
- Research Organization:
- Colorado Univ., Boulder (USA). Dept. of Physics
- DOE Contract Number:
- FG02-86ER45236
- OSTI ID:
- 6529085
- Report Number(s):
- DOE/ER/45236-T2; ON: DE89005908
- Country of Publication:
- United States
- Language:
- English
Similar Records
Studies of melting, crystallization, and commensurate-incommensurate transitions in two dimensions: Third year progress report
Evidence of hexatic phase formation in two-dimensional Lennard-Jones binary arrays
Related Subjects
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
COLLOIDS
CORRELATION FUNCTIONS
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DISPERSIONS
EQUATIONS
EQUATIONS OF STATE
FUNCTIONS
GRAIN BOUNDARIES
HYDROGEN COMPOUNDS
IMAGE PROCESSING
MATERIALS
MATHEMATICS
MELTING
MICROSPHERES
MICROSTRUCTURE
ORGANIC COMPOUNDS
ORGANIC POLYMERS
OXYGEN COMPOUNDS
PETROCHEMICALS
PETROLEUM PRODUCTS
PHASE TRANSFORMATIONS
PLASTICS
POLYMERS
POLYOLEFINS
POLYSTYRENE
POLYVINYLS
PROCESSING
SYNTHETIC MATERIALS
TOPOLOGY
WATER