The sodium poly[2-(3-thienyl)ethyloxy-4-butylsulfonate] polymer (PTH) is a unique water-soluble polymer with pH-dependent optical properties. The polymer solution under basic conditions i.e. at pH > 7 has a pronounced absorption peak at ～ 430 nm. Under acidic conditions of pH 2, it turns dark green with the additional absorption maximum at 780 nm. Layer-by-layer (LbL) deposition of polymers at surfaces is a versatile way to create ultrathin polymer membranes with controlled properties. Layers of a polyanion and a polycation can be stepwise deposited onto a surface through a spin-assisted (SA) assembly, thereby producing robust LbL films. SA-LbL deposition enables a good control over film thickness and thus some properties of the membranes by varying the number of the deposited layers.
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