表面活性剂胶束实现疏水分子在聚合物微凝胶层层组装膜中的高效负载

基于层层组装技术制备了聚烯丙基胺-葡聚糖微凝胶(记作PAH-D)/透明质酸钠(HA)膜, 将包覆有芘分子的十二烷基硫酸钠(SDS)表面活性剂胶束基于静电作用力负载到PAH-D/HA微凝胶膜中, 实现了疏水分子芘在微凝胶膜中的高效负载. 紫外-可见吸收光谱和荧光光谱证实了SDS胶束包覆的芘分子被稳定地负载在PAH-D微凝胶膜中. 透过光谱表明负载有芘分子的(PAH-D/HA)*10微凝胶膜在可见光区仍保持良好光学透过性. 芘在膜中的负载量可以通过改变PAH-D/HA微凝胶膜的沉积周期数和SDS胶束中包覆芘分子的浓度而实现调控. 具有光致变色性质的螺吡喃分子同样可以借助SDS胶束负载到PAH-D/HA微凝胶膜中, 制备具有光致变色性质的层层组装膜. 本工作为疏水有机分子在层层组装聚合物膜中的高效负载提供了一种简便、易行的方法.     

Enhanced Salt Tolerance of Polyurethane Based Multilayer Films

In our previous study, polyurethane (PU) based multilayer films assembled with weak polyelectrolytes exhibited controllable loading and release properties, but would be decomposed in high salt solution. Herein, a strong polyelectrolyte, poly(styrene sulfonic acid) sodium (PSS), was introduced to fabricate multilayer films. The salt tolerance of the film was investigated by evaluating the loading and release profiles towards model drug in salt solution with different concentrations. Results showed that the release behavior of the film, as well as its loading capacity, can be tuned by varying the salt concentrations. And the film showed a good salt tolerance that can remain integrity even after 6 cycles of drug loading and release in 600 mmol·L^?1 NaCl solution. It showed that the salt tolerance of PU based films can be greatly improved through assembling with strong polyelectrolyte.     

导尿管表面具有抗菌功能的层层组装微凝胶膜

以化学交联的聚烯丙基胺盐酸盐拟葡聚糖微凝胶和透明质酸为构筑基元,在导尿管表面层层组装构筑了厚度小于500 nm可控释放抗菌药物的聚合物微凝胶膜。 广谱抗菌药物头孢曲松钠通过扩散吸附的方法在2 min内快速负载到聚合物微凝胶膜中,并且在生理盐水中可控释放时间达3 h。 抗菌实验表明,组装有层层组装微凝胶膜并负载广谱抗菌药物的导尿管具有令人满意的抗菌效果,避免感染的发生。     

Fabrication of free-standing multilayer films by using pH-responsive microgels as sacrificial layers

A facile way to prepare free-standing polyelectrolyte multilayer films of poly(sodium 4-styrenesulfonate)(PSS)/poly(diallyldimethylammonium)(PDDA) was developed by applying a new pH-dependent sacrificial system based on cross-linked poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) microgels. The tertiary amine groups of PDMAEMA microgels can be protonated in acidic environment, and the protonated microgels were deposited by layer-by-layer (LbL) technique with PSS. PSS/PDDA multilayer films were constructed on the top of the PSS/microgels sacrificial layers. The LbL assembly process was investigated by UV–vis spectroscopy. Further study shows that the free-standing PSS/PDDA multilayer films can be obtained within 3 min by treating the as-prepared films in alkali aqueous solution with a pH of 12.0. The pH-triggered exfoliation of PSS/PDDA multilayer films provides a simple and facile way to prepare LbL assembled free-standing multilayer films.     

Controlled loading and release of methylene blue from LbL polyurethane/poly(acrylic acid) film

The layer‐by‐layer (LbL) assembled multilayer films are widely used in the biomedical field for the controlled drug delivery. Here, multilayer films were assembled by LbL technique through alternating deposition of cationic polyurethane (PU) and poly(acrylic acid) (PAA) on glass slides. Methylene blue (MB) was used as a model drug to investigate the loading and release ability of the prepared multilayer film. The results showed that the loading rate and loading amount of MB were greatly influenced by pH value of the dye solution, and the release rate of MB was controlled both by ionic strength and pH value of immersing solution. The result also indicated that the film had a good reversibility of drug loading and release. It suggested that the PU/PAA multilayer film had potential applications in drug delivery and controlled release. Copyright © 2011 John Wiley & Sons, Ltd.     

Polyelectrolyte blend multilayer films: surface morphology, wettability, and protein adsorption characteristics

We report the influence of polyelectrolyte (PE) multilayer films prepared from poly(styrene sulfonate)-poly(acrylic acid) (PSS-PAA) blends, deposited in alternation with poly(allylamine hydrochloride) (PAH), on film wettability and the adsorption behavior of the protein immunoglobulin G (IgG). Variations in the chemical composition of the PAH/(PSS-PAA) multilayer films, controlled by the PSS/PAA blend ratio in the dipping solutions, were used to systematically control film thickness, surface morphology, surface wettability, and IgG adsorption. Spectroscopic ellipsometry measurements indicate that increasing the PSS content in the blend solutions results in a systematic decrease in film thickness. Increasing the PSS content in the blend solutions also leads to a reduction in film surface roughness (as measured by atomic force microscopy), with a corresponding increase in surface hydrophobicity. Advancing contact angles (theta) range from 7 degrees for PAH/PAA films through to 53 degrees for PAH/PSS films. X-ray photoelectron spectroscopy measurements indicate that the increase in film hydrophobicity is due to an increase in PSS concentration at the film surface. In addition, the influence of added electrolyte in the PE solutions was investigated. Adsorption from PE solutions containing added salt favors PSS adsorption and results in more hydrophobic films. The amount of IgG adsorbed on the multilayer films systematically increased on films assembled from blends with increasing PSS content, suggesting strong interactions between PSS in the multilayer films and IgG. Hence, multilayer films prepared from blended PE solutions can be used to tune film thickness and composition, as well as wetting and protein adsorption characteristics.     

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.     

Influence of solvent quality on the growth of polyelectrolyte multilayers

The effect of solvent conditions on the growth of polyelectrolyte (PE) multilayer films comprising poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate sodium salt) (PSS) on planar substrates was investigated by means of surface plasmon resonance spectroscopy (SPRS), quartz crystal microbalance (QCM), and atomic force microscopy techniques. The solvent quality was varied by the addition of ethanol to the PE solutions used for deposition of the layers, thus tuning the relative strength of electrostatic and secondary intermolecular and intramolecular interactions. Experiments were performed with PE solutions both without added electrolyte and containing 0.5 M NaCl. Decreasing the solvent quality (i.e., increasing the amount of ethanol in the adsorption solution) resulted in a marked increase of both the multilayer film thickness and mass loading, as determined from the SPRS spectra and QCM frequency shifts, respectively. With the solution composition approaching the precipitation point, thick PAH/PSS films were formed due to the screening of the electrostatic intra- and interchain repulsions and enhanced hydrophobic interactions between the polyelectrolyte chains. However, the films formed from water/ethanol mixtures remained stable upon subsequent exposure to water or salt-containing solutions: no significant film desorption occurred after up to 24 h of exposure to water or 0.5 M NaCl solutions. In addition, the effect of postdeposition exposure to water/ethanol mixtures was investigated for PE multilayers assembled from aqueous solutions. In this case, the optical thickness of the films was determined during exposure to water/ethanol mixtures, and instead of swelling, the polyelectrolyte films collapse to the surface as a result of the unfavorable segment-solvent interactions.     

Reversible disulfide cross-linking in layer-by-layer films: preassembly enhanced loading and pH/reductant dually controllable release

This paper describes the fabrication of polyelectrolyte multilayer film which combines preassembly of poly(allylamine hydrochloride) (PAH) and 5,10,15,20-tetraphenyl-21H,23H-porphine-p,p',p' ',p' '-tetrasulfonic acid tetrasodium hydrate (TPPS) in aqueous solution with the layer-by-layer (LbL) assembly of the PAH-TPPS complex and cross-linkable polyelectrolyte, PAASH60, which is a poly(acrylic acid) with 60% of its carboxylic acid grafted of thiol groups. During preassembly, TPPS was incorporated into PAH chains. After oxidative cross-linking to form disulfide bonds in between the layers, the multilayer with preassembly of the PAH-TPPS complex allowed for release and loading of TPPS in a reproducible way. The release of TPPS from the loaded film was a pH-controlled process. To compare with the conventional multilayer, the reloading capacity was greatly enhanced, which was related to the charge binding sites that formed by release of TPPS from the multilayer. Moreover, the release of TPPS could also be achieved by breaking off the cross-linking through reduction of disulfide bonds, and the release rates could be controlled by the reductive efficiency of the reductants in the media. In this way, the release of TPPS is pH/reductant dually controllable, thereby facilitating a new route to multistimuli controllable materials.     

Combining hydrogen-bonding complexation in solution and hydrogen-bonding-directed layer-by-layer assembly for the controlled loading of a small organic molecule into multilayer films

We have combined hydrogen-bonding complexation in solution and layer-by-layer assembly for the controlled loading of a water-insoluble small organic molecule, bis-triazine (DTA), an azobenzene derivative containing multiple hydrogen bond donors and acceptors, into layer-by-layer multilayer films of poly(acrylic acid) and diazo-resin. UV-visible spectroscopy indicates that DTA has been loaded into multilayer films, with the loading amount increasing linearly with the number of layers. The loading amount can be well tuned either by changing the concentration of DTA or the solvent composition at the complexation step. Fourier transform infrared spectroscopy has revealed that both the complexation and layer-by-layer assembly are driven by hydrogen bonding. After photo-cross-linking and immersion in dimethyl sulfoxide to release DTA, the film can serve as an absorbent for DTA. This study provides a new unconventional layer-by-layer assembly that combines hydrogen-bonding complexation in solution and hydrogen-bond-driven layer-by-layer assembly at the interface. This method provides a new route to load a variety of water-insoluble functional organic molecules into layer-by-layer films.     

Electrical properties of multilayers from low- and high-molecular-weight polyelectrolytes

The formation of stable multilayer films by using as constituents sodium poly(4-styrene sulfonate) (PSS) and poly(4-vinyl pyridine) (PVP) was studied by electrooptics. A strong increase in basicity of the pyridine rings in the electrical field of the oppositely charged PSS chains was suggested to be the driving force for multilayer film formation. A linear increase in the film thickness was registered after deposition of the first three layers, with no dependence on the polyelectrolyte molecular weight. The electrooptical effect was found to increase with increasing area of each next layer, but depended on the molecular weights of both polymers. Polarization of "condensed" counterions along the chains of the last-adsorbed layer was suggested to explain this dependence. Following the counterion dynamics, we come to the conclusion that the electrical properties of the top layer govern the electrooptical behavior of the PSS/PVP film.     

交联结构对肝素/壳聚糖层层组装多层膜内皮细胞相容性的影响

采用1-乙基-(3-二甲基氨基丙基)碳酰二亚胺交联技术对具有抗凝血抗菌作用的肝素/壳聚糖多层膜进行交联, 研究了交联结构对多层膜稳定性和血管内皮细胞亲和性的影响. QCM-D结果显示, 交联可有效地提高多层膜的稳定性, 在模拟人体血液流速(3.0 cm/s)下保持良好的稳定. 体外内皮细胞的研究结果显示, 多层膜的交联可有效地调节肝素/壳聚糖多层膜表面粘弹性, 并显著增加内皮细胞的粘附与生长. 交联的肝素/壳聚糖多层膜有望成为理想的心血管功能界面涂层材料.     

Layer-by-layer-assembled multilayer films of polyelectrolyte-stabilized surfactant micelles for the incorporation of noncharged organic dyes

Noncharged pyrene molecules were incorporated into multilayer films by first loading pyrene into poly(acrylic acid) (PAA)-stabilized cetyltrimethylammonium bromide (CTAB) micelles (noted as PAA&(Py@CTAB)) and then layer-by-layer (LbL) assembled with poly(diallyldimethylammonium chloride) (PDDA). The stable incorporation of pyrene into multilayer films was confirmed by quartz crystal microbalance (QCM) measurements and UV-vis absorption spectroscopy. The resultant PAA&(Py@CTAB)/PDDA multilayer films show an exponential growth behavior because of the increased surface roughness with increasing number of film deposition cycles. The present study will open a general and cost-effective avenue for the incorporation of noncharged species, such as organic molecules, nanoparticles, and so forth, into LbL-assembled multilayer films by using polyelectrolyte-stabilized surfactant micelles as carriers.     

Fabrication of polyelectrolyte multilayer films comprising nanoblended layers

Polyelectrolyte multilayer thin films were prepared via the alternate deposition of poly(allylamine hydrochloride) (PAH) and a blend of poly(acrylic acid) (PAA) and poly(styrenesulfonate) (PSS). When the pH of the blend solution was 3.5, the presence of PAA in this solution significantly increased the total film thickness. With only 10 wt % PAA in the blend adsorption solution, a large increase in film thickness was observed (92 nm cf. 18 nm). It was also demonstrated that the total amount of PSS adsorbed was enhanced by the presence of PAA in the blend solution, showing that the blend solution composition influenced that of the multilayer films. Thin films prepared with nanoblended layers also showed improved pH stability, because they exhibited reduced film rearrangement upon exposure to acidic conditions (pH = 2.5).     

Assembly of poly(N-isopropylacrylamide)-co-acrylic acid microgel thin films on polyelectrolyte multilayers: Effects of polyelectrolyte layer thickness, surface charge, and microgel solution pH

Temperature- and pH-sensitive poly(N-isopropylacrylamide)?Cco-acrylic acid (pNIPAm-co-AAc) microgels were deposited on glass substrates coated with polyelectrolyte multilayers composed of the polycation poly(allylamine hydrochloride) (PAH) and the polyanion poly(sodium 4-styrenesulfonate) (PSS). The microgel density and structure of the resultant films were investigated as a function of: (1) the number of PAH/PSS layers (layer thickness); (2) the charge on the outer layer of the polyelectrolyte multilayer film; and (3) the pH of microgel deposition solution. The resultant films were studied by differential interference contrast optical microscopy, atomic force microscopy, and scanning electron microscopy. It was found that the coverage of the microgels on the surface was a complex function of the pH of the deposition solution, the charge on the outer layer of the polyelectrolyte thin film and the PAH/PSS layer thickness; although it appears that microgel charge plays the biggest role in determining the resultant surface coverage.     

Formation and dielectric properties of polyelectrolyte multilayers studied by a silicon-on-insulator based thin film resistor

The formation of polyelectrolyte multilayers (PEMs) is investigated using a silicon-on-insulator based thin film resistor which is sensitive to variations of the surface potential. The buildup of the PEMs at the silicon oxide surface of the device can be observed in real time as defined potential shifts. The influence of polymer charge density is studied using the strong polyanion poly(styrene sulfonate), PSS, combined with the statistical copolymer poly(diallyl-dimethyl-ammoniumchloride-stat-N-methyl-N-vinylacetamide), P(DADMAC-stat-NMVA), at various degrees of charge (DC). The multilayer formation stops after a few deposition steps for a DC below 75%. We show that the threshold of surface charge compensation corresponds to the threshold of multilayer formation. However, no reversion of the preceding surface charge was observed. Screening of polyelectrolyte charges by mobile ions within the polymer film leads to a decrease of the potential shifts with the number of layers deposited. This decrease is much slower for PEMs consisting of P(DADMAC-stat-NMVA) and PSS as compared to PEMs consisting of poly(allylamine-hydrochloride), PAH, and PSS. From this, significant differences in the dielectric constants of the polyelectrolyte films and in the concentration of mobile ions within the films can be derived.     

Polarity of layer-by-layer deposited polyelectrolyte films as determined by pyrene fluorescence.

The polarity of polyelectrolyte (PE) multilayer films is investigated with pyrene as a polarity-sensitive probe. Multilayer films of poly(styrene sulfonate) (PSS) and various polycations were prepared by the layer-by-layer self-assembly technique. Pyrene (PY) molecules were inserted into the films by exposing the multilayers to pyrene solutions. By this method a homogeneous distribution of pyrene molecules at low concentration within the film was obtained. The ratio of the fluorescence intensities of the first (I) to the third (III) vibronic band (Py-value) of the pyrene emission spectrum is employed here to determine the polarity of the PE films. PSS and poly(allylamine hydrochloride) (PAH) multilayer films yielded a pyrene value close to the solvent polarity of acetone, while multilayers of PSS and poly(diallyldimethylammonium chloride) (PDADMAC) displayed a value higher than the one corresponding to water. The pyrene values of the polyelectrolyte films were independent from the solvent employed for probe dissolving. Although no direct relationship between solvent polarity and dielectric constant (epsilon) is available, an estimate of the static dielectric constant of the films can be provided by comparing the Py-values of the films with those of various solvents. Changes in the humidity conditions of the film environment in a closed cell did not affect the film polarity. However, a drastic and irreversible reduction of polarity could be induced by actively drying the samples by a nitrogen flow.     

聚合物层状组装膜

介绍了近几年来我们研究组在层状组装膜的构筑以及功能化研究方面取得的一些最新进展.包括结合表面溶胶-凝胶技术与静电层状组装技术,实现了二阶非线性基团在层状组装多层膜中的非对称排列,制备了具有二阶非线性效应的膜材料;采用室温压印技术,发展了一种简便、经济和具有普适性的层状组装聚合物膜图案化方法;以轻度交联的聚合物微凝胶为构筑基元,制备了具有高负载量的聚合物层状组装膜;发展了一种基于离子剥离技术的层状组装自支持膜制备方法;基于层状组装技术,制备了具有超疏水和抗反射功能的涂层.     

The pH stimulated reversible loading and release of a cationic dye in a layer-by-layer assembled DNA/PAH film

Through the layer-by-layer (LbL) deposition method, DNA was assembled into an ultrathin film with a cationic poly(allylamine hydrochloride) (PAH). The loading and release of a typical cationic dye, 5, 10, 15, 20-tetrakis(4-N-methylpyridyl)porphine-tetra-(p-toluenesulfonate) (TMPyP), in the DNA/PAH films were investigated. It has been found that the LbL-assembled DNA/PAH film was very stable in both acidic and alkaline solutions. Stimulated by the pH change of the dye solution, the dye can be easily loaded into or released from the DNA/PAH film. In an alkaline solution, the dye could be rapidly loaded into the DNA/PAH film at room temperature, while in an acidic solution, the dye could be rapidly released. The mechanism of such pH-stimulated loading and release in the DNA/PAH film was discussed. It was further observed that the loading and release of the dye in the DNA/PAH film was reversible upon pH change and the process could be repeated many times.     

Polymer multilayer film formation studied by in situ ellipsometry and electrochemistry

Polyelectrolyte multilayer films adsorbed on gold surfaces were studied by combined ellipsometric and electrochemical methods. Multilayers were composed of “synthetic” (poly(4-styrenesulfonic acid) ammonium salt (PSS) and poly(allylamine hydrochloride) (PAH) (PSS/PAH)) and “semi-natural” (carboxymethyl cellulose (CMC) and chitosan (CHI) (CMC/CHI)) polyelectrolytes. It was found that only PSS/PAH Layer-by-Layer (LbL) assembled structures result in dense surface confined films that limit permeability of small molecules, such as ferri-/ferrocyanide. The PSS/PAH assemblies can be envisaged as films with pinholes, through which small molecules diffuse. During the LbL deposition process of these films a number of pinholes quickly decay. A representative pinhole diameter was found to be approximately 20 μm, which determines the diffusion of small molecules through LbL films, and yet remains constant when the film consists of a few LbL assembled polyelectrolyte bilayers. CMC/CHI LbL assemblies at gold electrode surfaces give very low density films, which do not limit the diffusion of ferri-/ferrocyanide between the surface of the electrode and the solution.