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Pattern Formation in Evaporating Drops

Li, Fang-I (2009) Pattern Formation in Evaporating Drops. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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The redistribution of organic solutes during drop evaporation is a nanoscale self assembly process with relevance to technologies ranging from inkjet printing of organic displays to synthesis of bio-smart interfaces for sensing and screening. Atomic force microscopy studies comparing the behavior of different generation dendrimers with different surface chemistry in two solvent alcohols on mica substrates confirm that the detailed morphologies of condensed dendrimer ring structures resulting from micro-droplet evaporation sensitively depend on the surface chemistry, the solute evaporation rate and the dendrimer generation. For the dilute concentration studied here the presence of periodically ¡¥scalloped¡¦ molecular rings is ubiquitous. The instability wavelength of the scalloped rings is found to be proportional to the width of the ring, similar to observations of the rim instability in dewetting holes. The effect of the surface chemistry of the dendrimer molecules is obvious in the detailed structure of the self assembled rings. Varying the chain length of solvent alcohol leads to modification of ring patterns. The influence of dendrimer generation on ring structure primarily reflects the increase in dendrimer density with generation number. The evolution of G2-50%C12-pentanol rings as a function of dendrimer concentration is also described. High surface mobility and phase transformation phenomena in condensed, micro-scale dendrimer structures are documented, again using atomic force microscopy. Stratified dendrimer rings undergo dramatic temperature, time and dendrimer generation dependent morphological changes associated with large-scale molecular rearrangements and partial melting. These transformations produce ring structures consisting of a highly stable first monolayer of the scalloped structure in equilibrium with spherical cap shaped dendrimer islands that form at the center of each pre-existing scallop (creating a ¡¥pearl necklace¡¦ structure). Analysis of the dendrimer island shapes reveals a dependence of island contact angle on contact line curvature (island size) that varies systematically with dendrimer generation. The morphological transformations in this system indicate the potential for creating complex, dendrimer-based multilevel structures and macroscopic scale arrays using, for example, droplet-on-demand or dip pen nanolithography techniques, coupled with appropriate annealing and stabilizing treatments.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Li, Fang-Ifal12@pitt.eduFAL12
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairBarnard, John Ajbarnard@engr.pitt.eduJBARNARD
Committee MemberNettleship, Iannettles@pitt.eduNETTLES
Committee MemberGray,
Committee MemberWiezorek, Jorg M. Kwiezorek@pitt.eduWIEZOREK
Committee MemberCho, Sung Kwonskc@engr.pitt.eduSKCHO
Date: 28 January 2009
Date Type: Completion
Defense Date: 23 October 2008
Approval Date: 28 January 2009
Submission Date: 6 November 2008
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Materials Science and Engineering
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: dendrimer; micro-droplet; pattern formation; self-assembly
Other ID:, etd-11062008-212517
Date Deposited: 10 Nov 2011 20:04
Last Modified: 15 Nov 2016 13:51


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