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Conformational dynamics of poly(acrylic acid). A study using surface plasmon resonance spectroscopy
Diptabhas Sarkar1, P Somasundaran
1NSFIIUCR Center for Studies in Novel Surfactants, Langmuir Center for Colloids and Interfaces, Columbia University, 911 Mudd Building, 500 West 120th Street, New York, New York 10027, USA.
Langmuir : the ACS Journal of Surfaces and Colloids
|June 23, 2005
Summary
Poly(acrylic acid) conformational changes were observed in real-time using surface plasmon resonance (SPR) spectroscopy. The polymer stretches slower than it collapses, with dynamics influenced by molecular weight and Ca2+ ions.
Area of Science:
- Polymer Science
- Surface Chemistry
- Spectroscopy
Background:
- Poly(acrylic acid) (PAA) is a polyelectrolyte sensitive to environmental changes.
- Understanding polymer dynamics is crucial for developing advanced materials.
Purpose of the Study:
- To investigate the conformational dynamics of PAA upon pH change.
- To analyze the kinetics of PAA stretching and coiling.
- To explore the influence of molecular weight and divalent cations on PAA conformation.
Main Methods:
- Immobilization of PAA on a gold surface.
- Real-time monitoring of conformational changes using surface plasmon resonance (SPR) spectroscopy.
- Kinetic analysis of SPR angle changes.
Main Results:
- A unique SPR response profile was observed, predominantly governed by thickness or refractive index changes.
- PAA takes longer to stretch than to collapse, with rate constants varying by an order of magnitude.
- SPR angle changes and kinetic constants showed a linear dependence on molecular weight.
- Ca2+ ions locked PAA into a specific conformation due to cation binding.
Conclusions:
- The study reveals novel insights into PAA conformational dynamics and SPR response.
- Kinetic parameters are predictable based on molecular weight.
- Multivalent cations can effectively control PAA conformation.