Cationic Polyacrylamide Conformation on Mica Studied by Single Molecule “Pulling” with Scanning Probe Microscopy

• Published in: Macromolecules Vol. 40; no. 13; pp. 4561 - 4567
• Main Authors: Brotherson, Brett, Bottomley, Lawrence A, Ludovice, Peter, Deng, Yulin
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 26.06.2007
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Structure, morphology and analysis; Scanning probe microscopy; Investigation method; Liquid solid adsorption; Acrylamide copolymer; Adsorbed state; Quaternary ammonium copolymer; Acrylamide derivative copolymer; Experimental study; Mica; Conformation
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma070495d

In recent years, scanning probe microscopy (SPM) has been used to gain information about the conformation of an adsorbed polymer. However, the experimental techniques used make interpretation of the data difficult or impossible without significant assumptions. In this work, an improved “pulling” method, which overcomes many of the limitations of traditional methods, is executed. The sequential adsorption/desorption of cationic polyacrylamide on freshly cleaved mica in deionized water was directly measured using these modified SPM experiments. Our method uses a specially etched tip which ensures only one polymer molecule is adsorbed on the cantilever tip, allowing more accurate interpretation of the results. The results were compared with previous studies showing the applicability of this modified technique to determine the conformation of an adsorbed polymer. The effect of cantilever tip retraction velocity from the surface was shown to be insignificant to the measured loop length distribution. For the first time, SPM was used to show the effects of dwell time on adsorbed polymer conformation.