Molecular Level Study of Intra- and Inter-Particle Intractions in Polyelectrolyte Nanogel Systems

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This research project aims to elucidate at the molecular level the nature of volume-phase transitions in polyelectrolyte gels. Our experimental strategy is to measure the dimensional changes in polyelectrolyte nanoparticles with and without cross-links and to compare these with the volume change of polyelectrolyte bulk gels with the same chemical compositions. We have synthesized and used both cross-linked and linear polymers based on N-isopropylacrylamide, to which anions and cations as well as both (ampholytes) were bound via copolymerizations or terpolymerizations. Static light scattering, dynamic light scattering and electrophoretic light scattering were employed to study the following subjects : (i)Effects of pH, temperature and ionic strength on the hydrodynamic radius and radius gyration of cross-linked polyelectrolyte nanoparticles (nanogels) and on their electrophoretic mobilities as an indication of net charges of polyelectrolytes. (ii)Comparison of the results obtained in (i … More )with those of linear polyelectrolytes as an analog of the nanogels. (iii)Complex formation of polyelectrolyte nanogels with linear polyions whose charges are opposite each other (polymer-particle interactions in charged colloidal systems). (iv)Complex formation between oppositely charged nanogel particles (particle-particle interactions in charged colloidal systems). In addition, we studied the complex formation of neutral polymers with proteins with the intention of synthesis of a novel ionic nanogel in which globular multipartial charges (i.e., proteins) are in a "cage" of neutral polymer network (i.e., ionic nanogels with entrapped protein charges). It has become apparent that all of the results obtained from the present study can be well accounted for in terms of our balance model [(a)Ilmain, F. ; Tanaka, T. ; Kokufuta, E. Nature 1991,349,400 ; (b)Kokufuta, E. In : Physical Chemistry of Polyelectrolytes ; Radeva, T., Ed. ; Marcel Dekker, Inc., New York, Basel,2000;Chapter 17] ; that is, the volume phase transition in gels can be determined by hypothesizing a balance between the repulsion and attraction among functional groups attached to the network-When a repulsive force, usually electrostatic in nature, overcomes an attractive force, the gel undergoes a swelling change ; hydrogen bonding and hydrophobic interaction, other than the usual electrostatic attraction, are considered as the attractive force. As result, the present research strongly supports the balance model, then we have started a new project in which the balance model is allowing the design of ionic nanogels whose responsive performance is the same as observed in the corresponding graft or block copolymers. Less