Preparation And Performance Of Poly(Acrylic Acid)/Polyethyleneimine Multilayers Film

Layer-by-layer（Lb L）assembly is a technique to form aggregates or supramolecular structures with complete structure and stable performance base on electrostatic interaction,hydrogen bonding and other weak interactions between molecules.More and more researchers are interested in the Lb L assembly technique,due to its simplicity in assembling process,versatility for different building blocks and substrates,tailorability in film structure and thickness.In recent years,Lb L technique has developed rapidly,the driving forces between two neighboring layers can be electrostatic interactions,hydrogen-bonds,coordination bonds,charge-transfer interactions,biospecific recognition,guest–host interactions,etc.The Lb L assembly technique has expanded its applications to self-healing materials,separation films,biosensing and drug delivery.In this paper,there are two experiments base on Lb L assembly technique:（1）Non-conjugated polymers without typical conjugated fluorophores received tremendous attention owing to their assignable fluorescent properties,outstanding biocompatibility and good biodegradability.Non-conjugated polymers usually possess sub-fluorophore groups,such as heteroatom-containing double bonds（C=O,C=N,N=O）and single bonds（amino-based groups,C—O）.These sub-fluorophores generally show weak fluorescence or even no fluorescence.Either polymerization,chemical crosslinking,or hydrothermal treatment methods for the preparation of non-conjugated fluorescent polymers or nanoparticles are efficient but complicated.Therefore,we hope to use simple method to prepare non-conjugated fluorescent polymers.In this experiment,the quartz substrate was impregnated alternately in PAA and PEI solution by LBL self-assembly technique,and the（PAA/PEI）*n non-conjugated fluorescent polymer films with adjustable deposition layers were prepared.There are no fluorescent chromophores in this polymer film,only some sub-fluorophores,but under the excitation of ultraviolet light will emit bright fluorescence,in the visible region will show multicolor luminescence phenomenon.The fluorescence intensity of polymer film increases with the number of deposited layers.After immersed in Ag⁺or Fe³⁺solution,the polymer film exhibited fluorescence quenching,and the fluorescence quenching degree was positively correlated with the concentration of ion solution in a certain range.（PAA/PEI）*n multilayers films provide a new perspective for the preparation of fluorescent non-conjugated polymer membranes,which avoids complex synthesis routes and has good photostability and biocompatibility.（2）Dopamine（DA）is a kind of mussel biomimetic material,and polydopamine（PDA）is derived from DA oxidation polymerization.PDA has unique wet adhesion capability on a broad spectrum of materials,has been used to prepare various healing materials.Furthermore,PDA is also a good photothermal agent with strong NIR absorption and high photothermal conversion efficiency.As a results,PDA particles were used to introduce into a polymer matrix to trigger self-healing and shape-memory by absorbing NIR light and converting it into thermal energy.The manner of embedding PDA component into a mussel-inspired material always begins with the preparing the PDA micro-/nano-particles.PDA particles can self-polymerize from dopamine monomer that contains both functionalities of catechol and amine groups.After synthesis of PDA particles,the following step is loading PDA particles with other functional monomers or polymers to obtain a PDA-composite material.The whole process is much more complicated.In this experiment,the process of oxidizing polymerization of DA to generate PDA particles was combined with the Lb L assembly step.DA is prone to oxidative self-polymerization to produce PDA under weak alkaline conditions.Taking advantage of this property of dopamine,DA was added to PAA solution（p H=2.5）,and the（PAA&DA）mixed solution was assembled with PEI solution（p H=8.5）to prepare（PAA&DA/PEI）*n polymer film.Polydopamine（PDA）was introduced in the process of polymer film assembly.PDA and PEI were cross-linked by chemical bond,which enriched the types of interlayer forces and accelerated the growth rate of polymer film thickness.（PAA&DA/PEI）*n polymer film has good self-healing and photothermal ability.