AN INVESTIGATION INTO THE RHEOLOGICAL, DIELECTRIC AND MUCOADHESIVE PROPERTIES OF POLY(ACRYLIC ACID) GEL SYSTEMS

A range of recently introduced poly(acrylic acid) polymers (Carbopols 974P, 934P and EX-214, Noveon AA-1) have been prepared as 2.5% w/w gel s in water using three different neutralising agents; sodium hydroxide , triethanolamine (TEA) and tromethamine (Tris). The structures of the gels were characterised in comparison to unneutralised systems using oscillatory theology and low frequency dielectric spectroscopy. Rheolo gical evaluation indicated that the elastic moduli of the gels decreas ed in the rank order Carbopol 934P, 974P, Noveon AA-1 and Carbopol EX- 214, with the reverse order being observed for the tan delta values. T he effects of changing the neutralising agent: were less marked. The d ielectric responses showed differences between the various polymers an d also between the same polymer with different neutralising agents. In particular, samples neutralised with TEA consistently showed a greate r low frequency conductance than gels neutralised with the other agent s. This effect was associated with charges being more closely bound in to the polymer network in the TEA neutralised gels. It was also noted that the theological and dielectric behaviour of NaOH neutralised Carb opol 974P was markedly different to that of Carbopol EX-214, despite t he supposed equivalence of these two materials. The mucoadhesive prope rties of the various gels were compared using a force of detachment te st. It was shown that Carbopols 934P and 974P showed the greatest muco adhesive strength, with smaller differences being noted between system s containing the various neutralising agents. A correlation between mu coadhesive strength and theological tan delta values was observed.