Size effects on self-assembly and melting of silver-alkanethiolate on inert surfaces

Hu, Liang

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https://hdl.handle.net/2142/17047 Copy

Description

Title

Size effects on self-assembly and melting of silver-alkanethiolate on inert surfaces

Author(s)

Hu, Liang

Issue Date

2010-08-31T20:30:28Z

Director of Research (if dissertation) or Advisor (if thesis)

Allen, Leslie H.

Doctoral Committee Chair(s)

Allen, Leslie H.

Committee Member(s)

• Geil, Phillip H.
• Zuo, Jian-Min
• Hsieh, Kuang-Chien

Department of Study

Materials Science & Engineerng

Discipline

Materials Science & Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Silver-alkanethiolate
• Self-assembled monolayer
• Size effect
• Melting point depression

Abstract

Self-assembled materials produced in the reaction between alkanethiol and Ag are characterized and compared. It is revealed that the size of the Ag substrate has a significant role in the self-assembly process and determines the reaction products. Alkanethiol adsorbs on the surface of Ag continuous planar thin films and only forms self-assembled monolayers (SAMs), while the reaction between alkanethiol and Ag clusters on inert surfaces is more aggressive and generates a significantly larger amount of alkanethiolate. Two dissimilar products are yielded depending on the size of the clusters. Small Ag clusters are more likely to be converted into multilayer silver-alkanethiolate (AgSR, R = CnH2n+1) crystals, while larger Ag clusters form monolayer-protected clusters (MPCs). The AgSR crystals are initially small and can ripen into large lamellae during thermal annealing. The crystals have facets and flat terraces with extended area, and have a strong preferred orientation in parallel with the substrate surface. The MPCs move laterally upon annealing and reorganize into a single-layer network with their separation distance approximately equal to the length of an extended alkyl chain. AgSR lamellar crystals grown on inert surfaces provide an excellent platform to study the melting characteristics of crystalline lamellae of polymeric materials with the thickness in the nanometer scale. This system is also unique in that each crystal has integer number of layers – magic-number size (thickness). The size of the crystals is controlled by adjusting the amount of Ag and the annealing temperature. X-ray diffraction (XRD) and atomic force microscopy (AFM) are combined to accurately determine the size (number of layers) of the lamellar crystals. The melting characteristics are measured with nanocalorimetry and show discrete melting transitions which are attributed to the magic-number sizes of the lamellar crystals. The discrete melting temperatures are intrinsic properties of the crystals with particular sizes. Smaller lamellar crystals with less number of layers melt at lower temperatures. The melting point depression is inversely proportional to the total thickness of the lamellae – the product of the number of layers and the layer thickness.

Graduation Semester

2010-08

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http://hdl.handle.net/2142/17047

Copyright and License Information

Copyright 2010 Liang Hu

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