紫外/臭氧法PDMS表面亲水改性机理研究

紫外/臭氧改性法是一种操作简单、成本低廉的PDMS表面亲水改性方法。采用该方法对PDMS表面进行亲水改性,利用接触角测量仪对改性效果进行评价,并与PDMS无臭氧紫外法进行了比较。测试表明PDMS表面经紫外/臭氧法处理12小时后,表面接触角达到60°左右,在空气中放置两周后仍保持较好的亲水性。其改性机理可以通过多种表征手段进行分析。红外光谱测试可以看出,PDMS在经过紫外/臭氧改性后,其表面官能团变化明显,随改性时间延长,疏水基团—CH₃逐渐减少,亲水基团Si—OH和—OH逐步增加,二氧化硅典型红外光谱峰也同时出现。通过扫描电镜和能谱测试可以看出,PDMS表面经过改性产生了二氧化硅为主的硅的氧化物。综合上述结果,紫外/臭氧处理法能够使PDMS表面亲水基团增多,同时生成类玻璃态SiO_x薄层,既改善了PDMS表面的亲水性,又阻止了PDMS表面疏水性的完全恢复,亲水性可以长时间保持。     

Investigation on the effect of RF air plasma and neem leaf extract treatment on the surface modification and antimicrobial activity of cotton fabric

A thorough investigation on the antimicrobial activity of RF air plasma and azadirachtin (neem leaf extract) treated cotton fabric has been dealt with in this paper. The cotton fabric was given a RF air plasma treatment to improve its hydrophilicity. The process parameters such as electrode gap, time of exposure and RF power have been varied to study their effect in improving the hydrophilicity of the cotton fabric and they were optimized based on the static immersion test results. The neem leaf extract (azadirachtin) was applied on fabric samples to impart antimicrobial activity. The antimicrobial efficacy of the samples have been analysed and compared with the efficacy of the cotton fabric treated with the antimicrobial finish alone. The investigation reveals that the RF air plasma has modified the surface of the fabric, which in turn increased the antimicrobial activity of the fabric when treated with azadirachtin. The surface modification due to RF air plasma treatment has been analysed by comparing the FTIR spectra of the untreated and plasma treated samples. The molecular interaction between the fabric, azadirachtin and citric acid which was used as a cross linking agent to increase the durability of the antimicrobial finish has also been analysed using FTIR spectra.     

Effect of pH on hydrophilicity and charge and their effect on the filtration efficiency of NF membranes at different pH

In this work the effect of pH on membrane structure, its permeability and retention was studied. In addition, we studied whether the possible changes in the membrane properties due to the pH change are reversible. This is important for understanding the performance of nanofiltration membranes at different conditions and for the selection of cleaning processes. Moreover, the results facilitate the choice of membrane for specific applications.

Several commercial NF membranes were studied at different pH values. Their retention and flux were explained by the charge and the hydrophilic characteristics of the membranes. The filtrations were made with uncharged sugar and salt solutions.

The lower the membrane contact angle (i.e., a more hydrophilic membrane) the higher was the change in apparent zeta potential when pH was increased from 4 to 7. As a result, the retention of ions with more hydrophilic membranes changed more than hydrophobic ones when the pH was increased in the feed solution. However, some membranes retained ions well at high pH although their apparent zeta potential or hydrophilicity was relatively low. These membranes had charge inside the pores and it was not detected by streaming potential measurement along the surface or by measuring the contact angle of the surface. Thus, the apparent zeta potential of the exterior membrane surface did not sufficiently describe the ionic transport through the membrane. In addition, some membranes became significantly more open at high pH (i.e., flux increased). This was explained by the chemical nature of the polymer chains in the membrane skin layer, i.e., dissociating groups in the polymer made the surface more hydrophilic and looser when charges of the polymer chains started to repel each other at elevated pH. Generally, the retention of uncharged glucose decreased more at high pH than the salt retention. The changes in permeabilities and retentions were found to be mostly reversible in the pH range studied (very slowly in some cases, however).     

Bioactive heparin immobilized onto microfluidic channels in poly(dimethylsiloxane) results in hydrophilic surface properties

A new composition of heparin coating for microfluidic systems made out of poly(dimethylsiloxane) (PDMS) was developed and evaluated. The coating that consists of a conditioning polyamine layer followed by two heparin/glutaraldehyde layers, resulted in channel surfaces with sufficient wettability to obtain flow of human normal plasma by capillary force alone. Hydrophilic channel walls are a desirable characteristic in microfluidic devices, since alternative pumping mechanisms must otherwise be included into the system. The immobilized heparin showed high antithrombin-binding capacity and a low degree of blood–material interaction. Plasma in contact with heparin-coated PDMS formed no detectable fibrin in a spectrophotometric assay by which plasma in contact with non-treated PDMS showed complete coagulation. The quartz crystal microbalance technique with energy dissipation monitoring (QCM-D) was utilized to obtain detailed information regarding adsorption kinetics and structural properties of the different layers composing the heparin coating.     

Crystallization behavior and hydrophilicity of poly (vinylidene fluoride) (PVDF)/poly (styrene-<Emphasis Type="Italic">co</Emphasis>-acrylonitrile) (SAN) blends

Poly (styrene-co-acrylonitrile) (SAN) is a hydrophilic non-crystalline copolymer, which is initially used in this paper to improve the hydrophilicity of poly (vinylidene fluoride) (PVDF). Investigation of the crystallization behavior of PVDF/SAN blends showed that the samples presented only α phase regardless of SAN content as cooling from the melt. A double-melting phenomenon was related to the perfection or crystal size of PVDF crystals. As the SAN content is increasing, crystallization of PVDF was limited, leading to a decreased crystallinity and lamellar growth. Besides, the hydrophilicity of PVDF was improved by blending with SAN. The sample containing 70 wt.% SAN performed a similar surface property of the neat SAN owing to the besieging of the PVDF phase by SAN. Observed from the cross section of the blends, PVDF/SAN blends were partially miscible with less than 50 wt.% SAN addition. As the SAN content was more than 50 wt.%, the crystalline PVDF particles clearly dispersed in the amorphous matrix.     

Preparation and characterization of polyaniline/polysulfone nanocomposite ultrafiltration membrane

Novel nanocomposite membrane was prepared through the filtration of polyaniline (PANI) nanofiber aqueous dispersion with polysulfone (PS) ultrafiltration (UF) membrane. Scanning electron microscope (SEM) images showed that PANI nanofiber layer was formed on the PS membrane surface. Atomic force microscopy (AFM) analysis indicated that the nanocomposite membrane had rougher surface than the PS substrate membrane. Compared with the PS substrate membrane, the nanocomposite membrane had much better permeability for the good hydrophilicity of PANI nanofiber layer, and had almost the same rejection performance. In addition, the nanocomposite membrane had positive surface potential under acidic condition because PANI could be protonated easily by acid. During the filtration of BSA solution, the nanocomposite membrane showed much better antifouling performance than the substrate membrane for the hydrophilicity and steric hindrance effect of its nanofiber layer. Moreover, under acidic solution condition, strong electrostatic repulsion between PANI nanofibers and BSA existed and improved membrane antifouling performance further.     

聚乙二醇-b-聚乳酸的合成及其电纺形成超细纤维研究

为了提高聚乳酸的亲水性,以辛酸亚锡为催化剂、聚乙二醇单甲醚(mPEG)为大分子引发剂进行丙交酯(LLA)开环聚合,合成聚乙二醇-b-聚乳酸两嵌段共聚物(PELA).以红外光谱1、H核磁共振谱、接触角测试、差热扫描量热分析等方法对PELA的结构及性能进行表征.结果表明,通过调控mPEG与LLA的投料比可以控制PELA的相对分子质量,而随着mPEG组分含量或链长增加,共聚物亲水性增强,但其Tg、Tcc、Tm有所降低.由普通电纺制备PELA超细纤维,并分别由乳液电纺和同轴电纺得到以水溶性聚氧化乙烯(PEO)为芯、PELA为壳的芯/壳结构复合超细纤维(E-PEO/PELA和C-PEO/PELA).扫描电镜和透射电镜结果表明,PELA、E-PEO/PELA和C-PEO/PELA超细纤维形貌良好.随着PELA中mPEG含量的增加,电纺PELA纤维膜的吸水率增强,而由乳液电纺和同轴电纺制备的PEO/PELA芯/壳结构超细纤维膜,亲水性均好于PELA超细纤维膜.     

STUDY ON SIDE REACTION IN THE SYNTHESIS OF HYPERCROSSLINKED POLYMERS

The systematical study about side reactions have revealed the formation mechanism of oxygen-containing groups of hypercrosslinked polymers. Surface chemistry and functionality of the polymers are characterized by Fourier-transform infrared spectroscopy （FT-IR）, solid state nuclear magnetic resonance （NMR） and contact angle. The results showed that the ether groups were from chloromethylated reaction, and the alcohol groups arose from partial hydrolysis of chloromethyl groups during the post-crosslinking reaction, and the carbonyl functionality was formed by further oxidation of the alcohol groups. Catalyst and solvent used in the postcrosslinking reaction would greatly influence the surface chemistry of the polymer.     

Amino acids functionalized graphene oxide for enhanced hydrophilicity and antifouling property of poly(vinylidene fluoride) membranes

Herein, functionalized graphene oxide (GO) was prepared by the covalent functionalization with amino acids (lysine, glycine, glutamic acid and tyrosine) in this study. Zeta potential results demonstrated that covalent functionalization of GO with amino acids was favourable for their homogeneous dispersion in water and organic solvents. Based on the higher absolute value of zeta potential and the better dipersion stability of GO-lysine, the PVDF/GO-lysine hybrid membranes were then prepared via the phase inversion induced by immersion precipitation technique. SEM images showed a better pore diameter and porosity distribution on the PVDF/GO-lysine membrane surface. The zeta potential absolute value of the PVDF/GO-lysine membrane surface was higher than that of the virgin PVDF membrane. Furthermore, the PVDF/GO-lysine membranes surface exhibited good hydrophilicity. The water flux of PVDF/GO-lysine membranes can reach to two times of that of the virgin PVDF membrane. And the BSA adsorbed amount on PVDF/GO-lysine surface was decreased to 0.82 mg/cm² for PVDF/GO-lysine-8% membrane. Filtration experiment results indicated that the fouling resistance was significantly improved for the PVDF/GO-lysine membranes. As a result, lysine functionalized GO will provide a promising method to fabricate graphene oxide based hybrid membranes with effective antifouling property and hydrophilicity.     

Surface modification of polypropylene membranes by γ-ray induced graft copolymerization and their solute permeation characteristics

Porous hydrophobic polypropylene (PP) membranes were subjected to the surface modification by the γ-ray induced graft copolymerization with hydrophilic 2-hydroxyethyl methacrylate (HEMA). The structural changes and surface morphologies of the modified PP membranes were characterized by a Fourier transform infrared spectroscopy (FT-IR), elemental analysis (EA) and field emission scanning electron microscopy (FE-SEM). Peroxides produced from γ-ray irradiation were determined by a 1,1-diphenyl-2-picryl hydrazyl (DPPH) method and the surface hydrophilicities of membranes were measured by a static contact angle measurement. The contact angle of the modified membranes reduced with the degree of grafting (DG) of HEMA onto the membrane surface, and it decreased up to about half of that before modification. The permeation behaviors of all membranes were investigated by a bovine serum albumin (BSA) filtration experiment. As a result, the DG of the modified membrane increased with the reaction time. However, in the case of irradiation dosage it showed the maximum value at 20 kGy. Also, the modified membrane showed a higher solution flux, lower BSA adsorption, and the better flux recovery after cleaning than that of the unmodified membrane. Particularly, 40.6% grafted membrane showed a two-fold increase in a BSA solution flux, 62% reduction in total fouling and three-fold increase in flux recovery after chemical cleaning.