Concentration-dependent dye aggregation in the LbL-assembly of fluorescein isothicyanate labeled poly(allylamine hydrochloride) and poly(acrylic acid) on cotton fabrics

Abstract

In this work, we prepared layer-by-layer (LbL) assembled films of fluorescein isothicyanate labeled poly(allylamine hydrochloride) (PAH-FITC) and poly(acrylic acid) (PAA) on cotton fabrics, and researched the influence of the PAH-FITC concentration on the FTIC aggregation. With the LbL assembly, the ratio of FITC dimers to monomers in films approached a constant that was decided by the deposition situation of PAH-FITC on cotton. The concentration increase of the PAH-FITC solution induced more FTIC dyes to deposit on fabrics, thus generating a higher degree of H-aggregation. Interestingly, as the PAH-FITC concentration decreased, a high content of FITC dimers was obtained in LbL-assembled films as well. The possible reason is the excessive PAA in LbL films made the counter PAH-FITC chains coil overlap, increasing the aggregation degree. Additionally, the H-aggregates with weak fluorescence were effectively inhibited in PAH-FITC films, which were prepared by a multi-immersion in the PAH-FITC solution. This work shows the concentration-dependent dye aggregation in LbL-assembly, providing a new strategy for the applications of dye molecules on fabrics.