In-Situ AFM Studies of the Phase-Transition Behavior of Single Thermoresponsive Hydrogel Particles

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• 作者：Justyna Wiedemair ; Michael J. Serpe ; Jongseong Kim ; Jean-Francois Masson ; L. Andrew Lyon ; Boris Mizaikoff ; Christine Kranz
• 刊名：Langmuir
• 出版年：2007
• 出版时间：January 2, 2007
• 年：2007
• 卷：23
• 期：1
• 页码：130 - 137
• 全文大小：364K
• 年卷期：v.23,no.1(January 2, 2007)
• ISSN：1520-5827

文摘

The volume phase transition (VPT) behavior of individual thermally responsive poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAm-co-AAc) hydrogel microparticles was studied by in-situ dynamic mode atomic force microscopy(AFM) and force spectroscopy during heating and cooling cycles. Hydrogel samples were prepared by electrostaticimmobilization of microparticles to amine-modified gold surfaces. The AFM studies of particle deswelling wereperformed by varying the force applied on the particles during imaging as a function of the geometry and materialof the AFM probe. Aluminum-coated silicon cantilevers were found to influence substantially the behavior of theparticles during the VPT, leading to a significant shape change. Low force impact magnetic excitation of the AFMprobe (MAC mode) during dynamic mode measurements resulted in an undisturbed deswelling behavior enablingobservation of the expected volume changes of the particles without significant tip-sample interaction. Hence, MAC-mode AFM was determined to be the most suitable technique for in-situ AFM studies on volume and shape changesat single hydrogel particles during VPT. Elasticity measurements performed at single particles at temperatures belowand above the VPT revealed a 15-fold increase in the Young's modulus after passing the VPT, indicating the transitionfrom a soft, swollen network to a stiffer, deswollen state.