Structure and Function of Switchable Surfaces.

Self-assembled Monolayers;Low-density;Impedance;Stability;Mobility;Intercalation;Chemical Engineering;Engineering;Chemical Engineering

Peng, DavidMayer, Michael ;

University of Michigan

关键词: Self-assembled Monolayers;    Low-density;    Impedance;    Stability;    Mobility;    Intercalation;    Chemical Engineering;    Engineering;    Chemical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/57699/dkpeng_1.pdf?sequence=2&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The loosely-packed structure of low-density self-assembled monolayers (SAMs) enables the constituent molecules of these surfaces to undergo reversible conformational transitions in response to electrical stimulation, leading to controllable changes in macroscopic surface properties such as wettability. This dissertation reports key new findings on the structure and function of these dynamically switchable surfaces.Low-density SAMs can switch their electrochemical impedance properties in response to applied electrical potential. This function is tunable, such that the magnitude of the impedance response can be selected by the user, and reversible, such that the material can be returned to its initial state after switching. These switchable impedance characteristics are exhibited by low-density SAMs of both 16-carbon and 11-carbon chain length, assembled on both gold and silver.Low-density SAMs show robust stability in long-term storage conditions including air, argon at room temperature, argon at 4 °C, and ethanol. Analyses by infrared spectroscopy, electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy reveal the insensitivity of low-density SAMs to degradative phase-segregation, adventitious contamination, and oxidation.Thiolates within a SAM can migrate laterally from high-density regions into low-density regions. This phenomenon is a function of temperature, with higher temperatures promoting greater lateral mobility, and a function of SAM chain length, with shorter SAMs exhibiting mobility at lower thermal thresholds as a result of their weaker inter-chain interactions.Low-density SAMs also have interstitial spaces between their thiolates which can accept the intercalation of linear hydrophobic and amphiphilic analyte molecules. Electrochemical impedance spectroscopy, infrared spectroscopy, and surface plasmon resonance analysis reveal the intercalation of stearic acid, palmitic acid, and octadecyl rhodamine into low-density SAMs, with more polar solvents encouraging greater levels of intercalation.This dissertation thus expands our understanding of the unique characteristics of switchable low-density SAMs, providing a foundation for further study, optimization, and innovation. Such developments may ultimately lead to next-generation technologies such as diagnostic sensors for non-invasive detection of disease markers and dynamic substrates for cell growth and tissue development.