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Handbook of Size Exclusion Chromatography and Related ...

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3.1 ASimple System: Equilibrium Characterization <strong>of</strong> PVP<br />

This simplest application <strong>of</strong> ACM in the equilibrium context is to ramp the<br />

concentration <strong>of</strong> the polymer in agiven solvent, thus obtaining an automated<br />

Zimmplot,plusintrinsicviscositycharacterization. Thiscanbeusefulincontexts<br />

where one wants to determine [h] <strong>and</strong> the virial coefficients, A2 <strong>and</strong> A3, where it<br />

suffices to have Mw instead <strong>of</strong> the full population distribution, or where<br />

appropriate SEC columns either do not exist or may be damaged by the sample.<br />

Figure 12 shows typical analysis results when RI, TDSLS, <strong>and</strong> viscosity<br />

signals were monitored during an experiment where polymer (PVP) concentration<br />

was ramped continuously from 0 to 0.008g/mL (67). The RI signal allows<br />

conversion <strong>of</strong> the data from the time domain to the concentration domain <strong>of</strong><br />

the component being ramped. The automated Zimm plot yielded Mw (g=mole) ¼<br />

646,300 + 5%, A2(cm3 mole=g2 ) ¼ 3:50 10 4 + 7%, A3(cm6 mole=g2 ) ¼<br />

0:0186 + 8%, kS2l 1=2<br />

z (A˚ ) ¼ 390 + 6%, <strong>and</strong> the viscosity curve gave<br />

[h](cm3 =g) ¼ 154 + 8%, with a coefficient kH ¼ 0:34 + 3% in Eq. (6).<br />

3.2 Effect <strong>of</strong> Salts on Polyelectrolytes<br />

The conformations, interactions, <strong>and</strong> hydrodynamics <strong>of</strong> polyelectrolytes are very<br />

sensitive to the concentration <strong>of</strong> simple electrolyte in the solution; that is, the ionic<br />

strength. When ionic strength decreases polyelectrolytes interact more strongly,<br />

<strong>and</strong> if they are flexible their static <strong>and</strong> hydrodynamic dimensions increase.<br />

Numerous experimental <strong>and</strong> theoretical studies have been carried out on these<br />

issues (68). ACM has recently been used to make detailed studies <strong>of</strong> electrostatically<br />

enhanced second <strong>and</strong> third virial coefficients, static <strong>and</strong> hydrodynamic<br />

dimensions, <strong>and</strong> strong interparticle correlations (69,70). The detail <strong>and</strong> resolution<br />

<strong>of</strong> these latter studies surpasses anything the author is aware <strong>of</strong> in traditional<br />

manual gathering <strong>of</strong> individual data points.<br />

3.3 Interaction <strong>of</strong> Neutral Polymers <strong>and</strong> Surfactants<br />

A more complex multicomponent system is represented by solutions containing<br />

polymer, ionized surfactants, <strong>and</strong> simple electrolytes (salts); that is, there are now<br />

three independent component axes in component space. It is well known that<br />

surfactant micelles can form complexes with neutral polymers (71,72), but it is a<br />

daunting task to choose <strong>and</strong> perform manual experiments at a collection <strong>of</strong><br />

individual points chosen from component space. ACM allows behavior along<br />

arbitrary paths in component space to be followed.<br />

An illustrative system is the interaction <strong>of</strong> PVP <strong>and</strong> sodium dodecyl sulfate<br />

(SDS) (73). SDS forms micelles at its critical micelle concentration (CMC), which<br />

depends on the concentration <strong>of</strong> salt. One ACM strategy for exploring the<br />

© 2004 by Marcel Dekker, Inc.

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