Assembling And Compression Of Polyelectrolyte Multilayers And Their Property Manipulation

Over the past decades, the polyelectrolyte multilayers assembled with thelayer-by-Layer (LbL) technique have been well developed because of theircontrollable compositions, structures and properties. The polyelectrolyte multilayershave achieved great success in both of fundamental researches and practicalapplications. CIBA-Vision has announced the first commercially available productthat is equipped with a multilayer coating in 2002. The functional polyelectrolytemultilayers can also be fabricated by changing their structures or introducingfunctional materials such as nanoparticles or luminescent quantum dots. Recently, ourgroup has reported the irreversible compression of polyelectrolyte multilayers bypressing a poly(dimethylsiloxane) (PDMS) stamp against the films. It furtheraugments the technique for fabricating physical patterns of the polyelectrolytemultilayers. It also brings new properties after the multilayers are compressed.In this work, the focus is on the polyelectrolyte poly(4-styrenesulfonicacid-co-maleic acid) sodium salt (PSSMA) containing both strongly charged andweakly charged blocks. The assembling behaviour, properties and compression ratiosof the PSSMA/poly(diallyldimethylammonium chloride) (PDADMAC) multilayerscan be easily controlled by adjusting salt concentrations and salt type or theassembling pH value. Combining compression with in situ synthesis nanoparticles,the multilayers are endowed with new functions as well.Firstly, influence of salt on assembly and compression of PSSMA/PDADMACmultilayers was studied. Results reveal that the compression ratio increased alongwith the increase of NaCl concentration, whereas kept constant when NaBr was used.It shows that the properties and compression ratios of the multilayers were reversiblymediated by the salts.Secondly, controlling the properties and compression of the multilayers by pHand effect of compression on in situ synthesis of Ag nanoparticles in the multilayerswere carried out. Influence of pH on the thickness, morphology and compression of the multilayers was detailedly studied. The multilayers assembled at pH 4 showed thelargest exponential growth, and it was thickest. With the increase of pH, the degree ofexponential growth of the multilayers decreased. The multilayers assembled at pH 2and pH 10 showed the linear growth. Ag nanoparticles were obtained by in situsynthesis in the multilayers. When the multilayers were assembled at pH 2, 4, and 5,the numbers of Ag nanoparticles in the compressed multilayers were much fewer thanin the uncompressed multilayers, while the multilayers were assembled at pH 6, thenumbers of Ag nanoparticles in the compressed multilayers and in the uncompressedmultilayers were both very few. Results reveal that the process of in situ synthesisnanoparticles plays a key role in readjustment of the polyelectrolyte chains.Then, the properties and compression of the multilayers were tuned by copperions. The copper ions concentrations affected the multialers growth. When themultilaylers contained the copper ions, their compression ratios were small; however,when the copper ions were removed from the multilayers, the compression ratioscould be largely improved.Finally, we found that the pattern formation of the multilayers was dependent onthe drying time of the multilayers prior to compression. Along with the prolongationof drying of the multilayers, compression of the multilayers by a stamp with linearpatterns obtained double strips, high ridges and linear patterns on the multilayers,respectively. Based on these observations, a theoretical model was suggested. Thestability kinetics of the pattern for the compressed multilayers and the stabilitycontrolling of the pattern were studied. Based on the mechanism of the lateral flow ofthe multilayers, the compression process was simplified, and we successfully arrayedthe nanoparticles on the multilayers.