Document Detail

Interfacial friction of surfaces grafted with one- and two-component self-assembled monolayers.
MedLine Citation:
PMID:  15924469     Owner:  NLM     Status:  MEDLINE    
We present a quantitative study of the nanoscale frictional properties of one-component (pure) and two-component (mixed) alkylsilane self-assembled monolayers (SAMs). The load and velocity dependence of the friction force was measured in air and ethanol using lateral force microscopy (LFM). It was observed that for SAMs with well-ordered structure (pure SAMs and mixed SAMs composed of two long chain molecules) friction depends nonlinearly on load, at low loads, both in air and in ethanol. These observations are consistent with the low-load contact area predictions of the Johnson-Kendall-Roberts (JKR) theory, indicating that for well-ordered SAMs friction force is proportional to contact area and that the true contact area is determined by elastic deformation of the SAM by the LFM probe. In ambient air, the magnitude of the friction force measured using mixed SAMs is found to be similar to that obtained using pure SAMs at the same external load. Changing the medium to ethanol, however, leads to dramatically lower friction in the mixed SAMs. An analysis of the friction data using a thermally activated Eyring model that takes into account the monolayer viscoelasticity suggests that the better friction properties of the mixed SAMs are a consequence of greater disorder and higher molecular mobility in the outer layer/canopy. These findings indicate that multi-tiered SAM coatings comprising a highly ordered underlayer and a disordered, mobile canopy can provide the basis for low-friction coatings for small mechanical systems.
Qing Zhang; Lynden A Archer
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  Langmuir : the ACS journal of surfaces and colloids     Volume:  21     ISSN:  0743-7463     ISO Abbreviation:  Langmuir     Publication Date:  2005 Jun 
Date Detail:
Created Date:  2005-05-31     Completed Date:  2006-07-28     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  9882736     Medline TA:  Langmuir     Country:  United States    
Other Details:
Languages:  eng     Pagination:  5405-13     Citation Subset:  IM    
School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, USA.
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MeSH Terms
Membranes, Artificial*
Microscopy, Atomic Force
Models, Chemical
Silanes / chemistry*
Surface Properties
Reg. No./Substance:
0/Membranes, Artificial; 0/Silanes; 10025-78-2/trichlorosilane

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