Processability Of Polyelectrolyte Complexes And The Construction Of Their Functional Materials

Polyelectrolyte complexes (PEC) is an important type of multicomponent polymeric material. Dilute PEC dispersions have found applications in various fields such as gene/DNA delivery, drug release, microencapsulation, flocculation, paper strengthing and so on. However, PEC solids are generally insoluble, infusible and not processable, and this blocks the realization of their multi-functionalities. In this work, a novel strategy of "acid protection-deprotection" was proposed to prepare solution processable PEC. On the basis of this strategy, high performance PEC pervaporation (PV) membranes, PEC nanocomposite membranes, functional PEC multilayer films and PEC fractal pattern formation were explored and studied in details.Poly (diallyldimethylammonium chloride) (PDDA), poly (2-methacryloyloxy ethyl trimethylammonium chloride) (PDMC) and chitosan (CS) were utilized as cationic polyelectrolytes, and sodium carboxymethyl cellulose (CMCNa) was utilized as anionic polyelectrolyte for preparing PEC. Solution processable PEC (PDDA-CMCNa, PDMC-CMCNa and CS-CMCNa) with tunable ionic complexation degree (ICD) and compositions were prepared in the "acid protection-deprotection" method. FT-IR, element analysis, DSC, TGA and WAXD were utilized to characterize PEC solids, which were found to be non-crystalline and having no glass transition. Viscosity, zeta potential, DLS, FESEM, TEM and AFM were utilized to characterize PEC dispersions. It was found that PEC dispersions were composed of ionic crosslinked, negtively charged and needle/rod shaped PEC aggregate (PECA) nanoparticles. Furthermore, the self assembly behavior of PEC dispersion was studied, showing that tree-shaped fractal pattern ("fractal trees") formed during the evaporation of PEC dispersions. These PEC "fractal trees" are formed via the self assembly of PECA nanoparticles, and have a thickneess of 400-600nm and a fractal dimension of 1.75～1.81. The self assembly of PECA particles follows the diffusion limited aggregation model, and the shielding effect between PECA branches is a key issue for the pattern formation of "fractal trees". As a result, increasing of PEC concentration, solvent evaporation temperature, decreasing of PEC dispersion's pH, adding organics into PEC dispersion, and modifying the chemical structures of PEC all block the fractal self assembly process and the formation of "fractal trees".Three PEC membranes (HPECM) including PDDA-CMCNa, CS-CMCNa and PDMC-CMCNa were made by casting their dispersions (2 wt%) on polysulfone supporting membranes. These three HPECM were utilized in pervaproation dehydration of aqueous isopropanol, and they all show very high selectivity (water in permeate> 99.1 wt%) and ultra-high permeation flux. For example, the flux of PDMC-CMCNa HPECM0.46 (ICD=0.46) is as high as 4.2 kg/m2h in dehydrating 10 wt%water-isopropanol at 70℃. This flux is 4 and 5 times higher than that of CMCNa and commerical polyvinyl alochol (PVA) membranes, respectively. "Water channel" structures were proposed to explain HPECM's ultra high PV performance. Moreover, PDDA-CMCNa PEC0.27/PVA blend membrane were preparaed, and it (PEC:PVA=1:1) shows a flux of 1.35 kg/m2h in dehydrating 10 wt%water-isopropanol at 70℃, which is about one time higher than that of commerical PVA membranes.Two PEC nanocomposites, PDDA-CMCNa PEC/SiO2 and PDDA-CMCNa PEC/MWCNT, were prepared in in-situ ionic complexation method. FESEM, TEM and AFM show that SiO2 and MWCNT were finely dispersed in PEC matrix under a limit content of 5 wt%and 7 wt%, respectively. The mechanical strength, modulus, and elongation at break for PDDA-CMCNa PEC/MWCNT containing 7 wt%MWCNTs are 65 Mpa,2.8 Gpa,3.4%, which are 2.7,2.3 and 1.8 times of the pristine PEC respectively. The permeation fluxes of PDDA-CMCNa PEC/SiO2 and PDDA-CMCNa PEC/MWCNT membranes are 2.1 kg/m2h and 2.3 kg/m2h in dehydrating 10 wt%water-isopropanol at 70℃.PECA nanoparticles were utilized as novel building blocks for LbL self-assembly on different substrates such as quartz slids, polyacrylonitrile supporting membranes, and optical fibers. It was found that the film thickness growth speed of PEC multilayers is fast. For example, thickness growth of (PDDA-CMCNa PECA-/ PDDA-PSS PECA+)10 multilayer films is 200 nm/bilayer. The thickness growth rate of PEC multilayer films increases with increasing ionic complexation degree of PEC, increasing of salt concentration in dipping solution, and decreasing of dipping soloution's pH. The LbL assembly of PECA nanoparticles has found applications in fast prepration of free-standing LbL films (sacrifice layer free), pervaporation, and sensitive pH sensors (0.5 nm/pH).