An investigation into the rheological, dielectric and mucoadhesive properties of poly(acrylic acid) gel systems

Abstract

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 gels 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 rheology and low frequency dielectric spectroscopy. Rheological evaluation indicated that the elastic moduli of the gels decreased in the rank order Carbopol 934P, 974P, Noveon AA-1 and Carbopol EX-214, with the reverse order being observed for the tan δ values. The effects of changing the neutralising agent were less marked. The dielectric responses showed differences between the various polymers and also between the same polymer with different neutralising agents. In particular, samples neutralised with TEA consistently showed a greater low frequency conductance than gels neutralised with the other agents. This effect was associated with charges being more closely bound into the polymer network in the TEA neutralised gels. It was also noted that the rheological and dielectric behaviour of NaOH neutralised Carbopol 974P was markedly different to that of Carbopol EX-214, despite the supposed equivalence of these two materials. The mucoadhesive properties of the various gels were compared using a force of detachment test. It was shown that Carbopols 934P and 974P showed the greatest mucoadhesive strength, with smaller differences being noted between systems containing the various neutralising agents. A correlation between mucoadhesive strength and rheological tan δ values was observed.