Zhangliang Gui

Fabrication of free-standing polyelectrolyte multilayer films: a method using polysulfobetaine-containing films as sacrificial layers.

A new pH-dependent sacrificial system based on zwitterionic polysulfobetaine was proposed for the fabrication of free-standing polyelectrolyte multilayer films. The zwitterionic polysulfobetaine, poly(4-vinylpyridine propylsulfobetaine) (P4VPPS), was synthesized and its layer-by-layer (LbL) self-assembly behavior with poly(diallyldimethylammonium) (PDDA) as counterpart was investigated by using UV-vis absorption spectroscopy, quartz crystal microbalance (QCM) and atomic force microscopy (AFM). The LbL multilayer films of PDDA/P4VPPS were successfully constructed in acid aqueous solution at pH 2 with 0.5 M NaCl. The resultant PDDA/P4VPPS multilayer films were pH-dependent and could be disintegrated in alkali aqueous solutions, especially with pH > or = 12. This disintegration property rendered such multilayer film as a sacrificial layer for further preparing free-standing polyelectrolyte multilayer films. The PDDA/poly(sodium 4-styrenesulfonate) (PSS) multilayer films deposited on the PDDA/P4VPPS sacrificial layer were confirmed to be successfully released after treated successively by alkali aqueous solution at pH 12 and ethanol. The obtained PDDA/PSS free-standing multilayer films had thicknesses of ca. 847 nm.

Layer-by-layer self-assembly, controllable disintegration of polycarboxybetaine multilayers and preparation of free-standing films at physiological conditions

The self-assembly and disintegration behavior of polyzwitterion, poly(4-vinylpyridiniomethanecarboxylate) (PVPMC), and negatively charged polyelectrolyte, poly(acrylic acid) (PAA), layer-by-layer (LbL) multilayer films were investigated in detail by using UV-vis absorption spectroscopy, quartz crystal microbalance (QCM) and atomic force microscopy (AFM). The results indicated that the PVPMC/PAA multilayer films grew linearly with increasing bilayer number. The disintegration rate of PVPMC/PAA multilayers could be well controlled by varying the concentration of salt in aqueous solution. It was found that PVPMC/PAA multilayer films could be completely disintegrated in 0.9% normal saline solution within 15 min. Such controllable disintegration behavior rendered the PVPMC/PAA multilayer as an excellent sacrificial sublayer for fabricating free-standing LbL multilayer films. Free-standing multilayer films were then successfully fabricated by LbL self-assembly of positively charged polyelectrolyte complex (PEC), made from poly(diallyldimethylammonium) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS), and negatively charged PSS with PVPMC/PAA as a sacrificial sublayer, which was disintegrated in 0.9% normal saline solution. The obtained free-standing films had good mechanical properties with 24.1 MPa tensile strength at break and 0.56 GPa Youngs modulus.

A novel fast response fiber-optic pH sensor based on nanoporous self-assembled multilayer films

Three-component multilayer films were prepared by consecutively depositing a polycation blend of poly(4-vinylpyridiniomethanecarboxylate) (PVPMC) and poly(diallyldimethylammonium) (PDDA) with poly(acrylic acid) (PAA). The self-assembly and disintegration behavior of the multilayer films were investigated in details by UV-vis absorption spectroscopy, quartz crystal microbalance (QCM) and atomic force microscopy (AFM). It was found that nanoporous PDDA/PAA multilayer films can be obtained conveniently by partly disintegrating (PVPMC + PDDA)/PAA multilayer films in a 0.15 M NaCl solution. A novel fast response fiber-optic pH sensor was successfully prepared by constructing nanoporous self-assembly multilayer films on the thin-core fiber interferometer (TCFMI) surface. The response time of a fiber-optic pH sensor deposited with nanoporous PDDA/PAA multilayer film (20 s rise time (tr) and 15 s fall time (tf)) was only one-tenth of that with the nonporous PDDA/PAA multilayer film (240 s and 160 s for tr and tf).

Interfacial self-assembly of cellulose-based polyelectrolyte complexes: pattern formation of fractal “trees”

A two-step procedure was adopted to prepare cellulose-based polyelectrolyte complexes (PECs) nanoparticles dispersed in water. First, an aqueous solution of a weak anionic polyelectrolyte of sodium carboxymethyl cellulose (CMCNa) was mixed with four types of cationic polyelectrolytes (poly 2-methacryloyloxy ethyl trimethylammonium chloride (PDMC), cationic cellulose, poly diallyldimethylammonium chloride (PDDA), chitosan (CS)) in HCl aqueous solutions. Four types of CMCNa-based PEC solids (CMCNa-PDMC, CMCNa-cationic cellulose, CMCNa-PDDA and CMCNa-CS), were obtained, purified and dried. Second, these PECs were re-dispersed in NaOH aqueous solutions. PEC solids and their aqueous dispersions were characterized by FT-IR, wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and dynamic light scattering (DLS), respectively. It was found that well grown fractal patterns (referred to as fractal “trees”) with diameters ranging from 5–300 μm for the four PECs were obtained after their aqueous dispersions were dried on silicon wafers or glass slides at 30 °C. This PECs interfacial self-assembly phenomenon is interesting but not shown in literature, even though various other PECs dispersions have also been dried in the similar way. Fractal dimensions of these fractal “trees” were calculated and their structures were characterized by polarized light microscopy (PLM), filed emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The formation mechanism of these fractal “trees” was tentatively examined by time-dependent FESEM. Moreover, effects of drying temperature, PEC concentration and solvent composition on fractal “trees” formation were studied. Potential applications of the fractal pattern formation in fields such as fast bottom-up nanofabrication, surface patterning and membrane separation were discussed.

Construction and deconstruction of multilayer films containing polycarboxybetaine: Effect of pH and ionic strength

The influences of pH and NaCl concentration of dipping solutions and the pH and NaCl concentration of disintegration solutions on the disintegration behaviors of poly(4-vinylpyridiniomethanecarboxylate) (PVPMC)/poly(sodium 4-styrenesulfonate) (PSS) (PVPMC/PSS) multilayer films were investigated by ultraviolet-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FT-IR), quartz crystal microbalance (QCM) and atomic force microscopy (AFM). It was found that the disintegration rates and degrees of PVPMC/PSS multilayer films in neutral water could be well controlled by changing pH of dipping solutions and immersion time during the disintegration process. Furthermore, PVPMC/PSS multilayer films could be disintegrated completely and rapidly in pH 8 alkali solution or physiological condition (i.e., 0.15 M NaCl solution). The controllable disintegration of PVPMC/PSS multilayer films was then utilized to fabricate PEC/PSS free-standing multilayer films, in which PEC was a positively charged polyelectrolyte complex made from excessive poly(diallyldimethylammonium) (PDDA) and PSS. The experimental results indicated that the disintegration rates of PVPMC/PSS sacrificial sublayer strongly affected the integrity of the resultant PEC/PSS free-standing multilayer films. Only free-floating PEC/PSS was released from neutral water by disintegrating PVPMC/PSS multilayer sublayers. However, large size flat and tube-like PEC/PSS free-standing multilayer films with good mechanical properties were obtained facilely from pH 8 alkali solution and 0.15 M NaCl solution, respectively. The preparation of such free-standing films at physiological condition may be useful in the biological or medical application.

Tunable disintegration of layer-by-layer assembly multilayer films based on hydrolytical-polybetaine at wide-range time.

A cationic hydrolytical-polycarboxybetaine (HPCB), poly(N-ethyl acetate-4-vinylpyridinium bromide) was synthesized by incorporating ester group into the side chain of polycarboxybetaine (PCB). The hydrolytic behaviors of HPCB samples in pH 7.4 phosphate buffer saline (PBS) were investigated by FT-IR and (1)H NMR. The layer-by-layer (LbL) assembly of HPCB/poly (sodium 4-styrenesulfonate) PSS and the disintegration of HPCB/PSS multilayer films were monitored by UV-vis absorption spectroscopy, quartz crystal microbalance (QCM) and atomic force microscopy (AFM). The disintegrated behavior of multilayer films was studied in detail by changing the cationic degree of HPCB and the pH of the immersion solution (PBS) in the disintegration process. The disintegration time of HPCB/PSS multilayer films could be controlled widely from 2 min to 30 days in PBS.