Charged microcapsules for controlled release of hydrophobic actives. Part III: the effect of polyelectrolyte brush- and multilayers on sustained release

Abstract

Poly(methyl methacrylate) microspheres have been prepared by the internal phase separation method using either of the three conventional dispersants poly(vinyl alcohol) (PVA), poly(methacrylic acid) (PMAA), or the amphiphilic block copolymer poly(methyl methacrylate)-block-poly(sodium methacrylate). The block copolymer based microsphere, which has a polyelectrolyte brush on the surface, was surface modified with up to two poly(diallyldimethylammonium chloride)-poly(sodium methacrylate) bilayers. The microspheres were loaded with the hydrophobic dye 2-(4-(2-chloro-4-nitrophenylazo)-N-ethylphenylamino)ethanol (Disperse Red 13) and its release from aqueous dispersions of microspheres with the different surface compositions was measured by spectrophotometry. The burst fraction, burst rate and the diffusion constant were determined from a model combining burst and diffusive release. Out of the three dispersants, the block copolymer gave the slowest release of the dye, with respect to both burst release and diffusive release. A very pronounced further reduction of the diffusion constant was obtained by applying polyelectrolyte multilayers on top of the microspheres. However, the diffusion constant was very weakly dependent on further polyelectrolyte adsorption and one polyelectrolyte bilayer appeared to suffice.

Encapsulation of actives for sustained release

“…2A, the addition of a polyelectrolyte brush layer and, in particular, a thin PEM resulted in a substantial reduction of the permeability of the hydrophobic dye Disperse Red 13 (expressed as an effective diffusion coefficient for the entire microcapsule). 18 The permeability decrease follows a hyperbolic function of the PEM thickness (derived from eqn (6) and (7)) and it can be seen in Fig. 2 that the PEM becomes the rate-determining barrier (eqn (7)) at very low layer numbers, which is theoretically illustrated in Fig.…”

Bacterial protease triggered release of biocides from microspheres with an oily core

“…Such microspheres can have a wide variety of applications and they are of particular interest for controlled release of actives, e.g. biocides in paints [11], additives in food, pharmaceuticals, etc. [12].…”

A facile strategy to improve the encapsulation efficiency of polymer microcapsules containing water‐soluble salt cores

“…Hydrophobic materials were chosen as shells of the microcapsules to retain the cores' water solubility . However, the difference of surface energy between the water‐soluble cores and hydrophobic shells was distinct . Accordingly, the cores were difficult to be encapsulated into hydrophobic materials efficiently; the encapsulation efficiency of the resulting microcapsules was low.…”