Ion exchange textiles from the finishing of PET fabrics with cyclodextrins and citric acid for the sorption of metallic cations in water

We describe a chemical method based on the use of cyclodextrins (CDs) and citric acid (CTR) as finishing chemicals for the modification of polyester fibers (PET). It was observed that the reaction between these reactants yielded a cross-linked polymer, by formation of ester functions between the polyol (CD) and the polycarboxylic acid (CTR). This polymer (called polyCTR-CD) permanently coated the PET fibers. The chemical structure of polyCTR-CD consisted of CD moieties and unreacted carboxylate groups. Theses groups resulted from the partial reaction of CTR and yielded ion exchange property to the fibers. The purpose of this paper was to set up the finishing parameters in order to obtain the best possible ion exchange capacity (IEC) of the fabrics. Firstly, we observed that the IEC did not perfectly evolve with the grafting rate (expressed in %-wt) of the fibers; As a matter of fact, we observed that a maximal IEC of 0.4–0.5 mmol/g of fabric was obtained for a compromise between the amount of polyCTR-CD fixed onto the fibers, and its cross-linking rate. In fact, the lesser the cross-linking rate, the more unreacted carboxylic groups remained on the fibers. Second, it was observed that CDs could not be replaced by starch in this process, because the later resulted to inferior IEC values than textiles grafted with CDs and CTR. Finally, the ion exchange finished fabrics were applied in the decontamination of water solutions containing Pb²⁺, Ni²⁺ and Cd²⁺. It was observed that 0.3 mmol of each cation were adsorbed per gram of fabrics.     

Finishing of Polyester Fabrics with Cyclodextrins and Polycarboxylic Acids as Crosslinking Agents

CDs were grafted onto PET fibers by the intermediate of polycarboxylic acids thatplayed the role of crosslinking agents. We evidenced that grafting occurred despitethat no reaction could happen between the polycarboxylic acids and PET. It wasconcluded that the mode of grafting occurred through the formation of a crosslinkedcopolymer between PCA and CDs. This copolymer was not covalently fixed to thefibers, but physically adhered or was entangled into the fibrous network so that grafting was resistant to washings and was permanent. We report that the grafting rate depended on (i) temperature of curing; (ii) time of curing; (iii) the ratio PCA/CD. In the most drastic conditions, the weight increase of the fabrics due to the graft reaction could reach 25–30%-wt. , , -CDs and HP--CD successfully reacted but not RAMEB because of its reduced number of free hydroxyl groups available for the esterification reaction.     

Surface hydrophobization of cotton via laccase-mediated polydopamine deposition and dodecyl gallate grafting

Natural fibers containing components with phenolic hydroxyl groups, such as jute, wool, and silk, can be directly modified by laccase-catalyzed grafting. However, cellulosic fibers like cotton cannot be functionalized in this manner. In this work, we developed a facile two-step method to graft polymers on cotton fabric via laccase catalysis. First, polydopamine (PDA) coating was deposited on the surface of the cotton fabrics via catalysis of laccase/2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) system. Then, the newly formed PDA coating acted as the secondary reaction platform for subsequent laccase-mediated grafting of hydrophobic monomer dodecyl gallate (DG). The oxidation of dopamine (DA) catalyzed with the laccase/TEMPO system was investigated using UV–visible (UV–vis) spectroscopy. The scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) results verified that the PDA was coated on the surface of cotton fibers. Fourier transform infrared (FTIR) spectra indicated that the PDA-coated cotton was successfully grafted with DG (DG-PDA-cotton). According to the weighting method, the grafting percentage was about 1.06%. The hydrophobicity of the DG-PDA-cotton fabrics was greatly improved with a contact angle of 133°. Also, the grafted cotton fabrics show repellency of water-soluble stains like coffee, milk, and tea. This study provides a new strategy for surface modification of cotton by laccase-mediated grafting, which offers the references for the green fabrication of cotton fabrics with improved functionalization.     

Surface-grafting of phosphates onto a polymer for potential biomimetic functionalization of biomaterials

In the human body, phosphate groups play important roles in signaling and the biological functions of proteins and peptides. Despite the importance of phosphate groups, polymer surfaces have not been directly grafted with phosphate groups by chemical reactions because the usual organic solvents used to graft phosphate groups can dissolve or swell polymers. We focused this study on grafting phosphate groups onto a poly(ethylene-co-acrylic acid) (PEAA) surface in an aqueous solution. O-phospho L-serine and O-phosphoethanolamine were grafted on PEAA surfaces to introduce phosphate groups by activating carboxylic acid groups of PEAA using N-hydroxysuccinimide (NHS) and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) in an aqueous environment. X-ray photoelectron spectroscopy (XPS) was used to elucidate the process by which surface grafting occurs and the process that the phosphate group is cleaved into a phosphate ion and a hydrolyzed molecule at high pH. It was found that under appropriate reaction conditions the phosphate groups could be successfully grafted on the polymer surfaces. The phosphate-grafted polymer surfaces showed lower water contact angles than the initial polymer surfaces likely due to their highly mobile and hydrophilic phosphate side groups. This work demonstrates a technique to successfully graft phosphate groups onto organic polymer surfaces in a biocompatible aqueous environment, which may open new avenues to functionalizing synthetic polymeric and natural macromolecule derived biomaterials.     

Plasma-mediated grafting of poly(ethylene glycol) on polyamide and polyester surfaces and evaluation of antifouling ability of modified substrates

A simple cold plasma technique was developed to functionalize the surfaces of polyamide (PA) and polyester (PET) for the grafting of polyethylene glycol (PEG) with the aim of reducing biofilm formation. The surfaces of PA and PET were treated with silicon tetrachloride (SiCl4) plasma, and PEG was grafted onto plasma-functionalized substrates (PA-PEG, PET-PEG). Different molecular weights of PEG and grafting times were tested to obtain optimal surface coverage by PEG as monitored by electron spectroscopy for chemical analysis (ESCA). The presence of a predominant C-O peak on the PEG-modified substrates indicated that the grafting was successful. Data from hydroxyl group derivatization and water contact angle measurement also indicated the presence of PEG after grafting. The PEG-grafted PA and PET under optimal conditions had similar chemical composition and hydrophilicity; however, different morphology changes were observed after grafting. Both PA-PEG and PET-PEG surfaces developed under optimal plasma conditions showed about 96% reduction in biofilm formation by Listeria monocytogenes compared with that of the corresponding unmodified substrates. This plasma functionalization method provided an efficient way to graft PEG onto PA and PET surfaces. Because of the high reactivity of Si-Cl species, this method could potentially be applied to other polymeric materials.     

In vitro study of a HPγ-cyclodextrin grafted PET vascular prosthesis for application as anti-infectious drug delivery system

Hydroxypropyl-γ-cyclodextrin (HPγ-CD) was grafted onto woven polyester (PET) vascular prosthesis by using citric acid (CTR) as crosslinking agent. A polyCTR-HPγ CD polymer was physically fixed onto the PET fibers. An optimal compromise between fixation temperature and fixation time was found and a grafting rate of 6.7% was obtained. The study of the inclusion of ciprofloxacin (CFX) and HPγ-CD was evidenced by using spectrophotometry. Sorption tests also showed that modified prosthesis could adsorb 5 times more CFX than the control. Biological tests revealed proliferation rates of human pulmonary micro-vascular endothelial cells (HPMEC) of 73 and 48% on virgin and modified prostheses respectively. We demonstrated that this was rather due to the increase of surface roughness of the fibers after their modification than to a toxic effect the polyCTR-HPγCD polymer coating. Prostheses samples modified with HPγCD and impregnated with CFX stayed up to 24 h in blood plasma. At various moments some aliquots were withdrawn from the medium and a positive antibacterial activity against Staphylococcus epidermidis was observed within the 24 h period for the grafted sample, whilst that of the virgin one had disappeared within 4 h. So, cyclodextrin coating of vascular prostheses may be suitable for the controlled release of CFX, and thus should help to the prevention of post surgery complications.     

Radiation‐assisted controlled grafting and reaction parameter optimization of an industrially important polyolefin elastomer (POE)

Controlled (low degree) grafting of a polar group to a non‐polar polymer or reverse is an important means to change the polarity of the base polymer, maintaining the properties of the polymer. In the present study, a polar monomer, methacrylic acid (MAA), was grafted onto three different types of “Engages” (a special type of polyolefin elastomer) in aqueous medium by gamma radiation. Grafting parameters (total dose, MAA concentration, and Mohr's salt concentration) were optimized for the desired amount of low‐degree grafting (less than 15 wt%). The grafting yields were measured gravimetrically. Pure and grafted Engages were characterized by Fourier transformed infrared spectroscopy, contact angle measurement, and scanning electron microscope. Fourier transformed infrared spectroscopy spectra confirmed the successful grafting of MAA onto the Engages. For all three, the best yields were found at 3‐kGy gamma radiation dose, 25‐vol% MAA, and 20‐mM Mohr's salt concentration. The grafting efficiencies follow a descending trend like Engage 8150 > Engage 7447 > Engage 8003. From contact angle measurement, it was seen that the hydrophilicities of all Engage surfaces were increased after grafting. Scanning electron microscope illustrated the best distribution of grafted MAA molecules to be on Engage 8150 surface followed by Engage 7447 and Engage 8003, respectively. The tensile testing results suggested that the mechanical properties of the base polymers remained almost unchanged after grafting. Thus, without detrimenting any basic properties, polyolefin elastomers can be grafted to achieve desired yield by an environmental‐friendly method, gamma radiation grafting, in aqueous media. Copyright © 2016 John Wiley & Sons, Ltd.     

Guided tissue regeneration membranes with controlled delivery properties of chlorhexidine by their functionalization with cyclodextrins

In parodontology, guided tissue regeneration (GTR) is a new technique to cure periodontal lesions. Where the association of the GTR with an antimicrobial agent does not yield optimal results, we used the properties of cyclodextrins (CDs) to improve the membrane used in RTG to control the release and to increase the quantity of antimicrobial agent stocked on the membrane. We successed in fixing 14%-wt of cyclodextrin polymer on polyvinylidene difluoride (PVDF) membranes thank to citric acid (CTR) as crosslinking agent. We studied the complexation of chlorhexidine diacetate (CHX), the antiseptic agent used in this study, with CDs in UV-spectrophotometry and ROESY NMR. We observed complexation of CHX by β, γ, hydroxypropylated (HP) βCD. We studied the biological properties of the cyclodextrin polymer onto (PVDF) membranes and observed that the CDs-polymer is not harmful for the cells. Moreover it stimulates their growth with native CD. A kinetic of release of the CHX was performed. Raw membranes released all CHX stocked in few hours, whereas grafted membranes released more than tenfold this quantity during 60–80 days.     

Photografting of polymers onto nanosized silica surface initiated by eosin moieties immobilized onto the surface

The photograft polymerization of various vinyl monomers onto nanosized silica surfaces was investigated. It was initiated by eosin moieties introduced onto the silica surface. The preparation of the silica with eosin moieties was achieved by the reaction of eosin with benzyl chloride groups on the silica surface.These were introduced by the reaction of surface silanol groups with 4‐(chloromethyl)phenyltrimethoxysilane in the presence of t‐butyl ammonium bromide as a phase‐transfer catalyst. The photopolymerization of various vinyl monomers, such as styrene, acrylamide, acrylic acid, and acrylonitrile was successfully initiated by eosin moieties on the silica surface in the presence of ascorbic acid as a reducing agent and by oxygen. The corresponding polymers were grafted from the silica surface. The grafting efficiency (percentage of grafted polymer to total polymer formed) in the photoinitiation system was much larger than that in the radical polymerization initiated by surface radicals; these radicals were formed by the thermal decomposition of azo groups introduced onto the silica surface. It was found that the polymer‐grafted silica gave stable dispersions in good solvents of grafted polymer and the wettability of the surfaces can be easily controlled by grafting of polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 600–606, 2005     

Grafting from ramie fiber with poly(MMA) or poly(MA) via reversible addition-fragmentation chain transfer polymerization

Reversible addition-fragmentation chain transfer (RAFT) polymerization was utilized to control the grafting of methyl methacrylate (MMA) and methyl acrylate (MA) from natural ramie fibers substrate. The hydroxyl groups of ramie fibers were first converted to 2-dithiobenzoyl isobutyrate as a RAFT chain transfer agent (CTA), which was further grafted with MMA or MA mediated by the RAFT polymerization in a presence of 2-(ethoxycarbonyl)prop-2-yl dithiobenzoate as a free chain transfer agent. Hydrophobic poly(MMA) or poly(MA) modified ramie fibers with contact angles greater than 130° were obtained. The modified ramie fibers were analyzed by gravimetry, Fourier transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry, thermogravimetry and contact angle measurements. The results indicate that the polymer chains had indeed been grafted from the surface of the ramie fibers with an average 33% of the hydroxyl groups in the raw ramie fiber substituted by 2-bromoisobutyryl bromide and an average grafting ratio of 25% poly(MMA) or poly(MA) related to ramie fiber. The homopolymers formed in the copolymerization were also analyzed to estimate molecular weights and polydispersity indices of grafting chains from the surface of ramie fibers by size exclusion chromatography, which showed narrow polydispersity with the PDIs to be <1.32. This study provides a novel and feasible approach to the preparation of functional composite materials for utilizing the abundant natural ramie fiber cellulose resource.     

PM-IRRAS spectroscopy for the characterization of polymer nanofilms: chains conformation,anisotropy and crystallinity

This paper is focused on the use of the Polarization-Modulation Infrared Reflection-Absorption Spectroscopy (PM-IRRAS) for studying thin polymer films at interfaces. When forming a polymer film on a metallic substrate, for instance by spin-coating, the characterization of the polymeric layer becomes very difficult given the small amount of matter deposited and also because of the contact with the metal. Among the techniques well adapted to surface and interface analyses, the PM-IRRAS spectroscopy represents an excellent tool to probe ultra-thin films. Different systems have been selected in this study such as polyamides (PA) and ethylene-co-vinyl acetate (EVA) nanofilms spin-coated onto chemically controlled surfaces (i.e. thiol self-assembled monloayers grafted onto gold coated glass slides). PM-IRRAS spectroscopy allowed us to characterize the polymer anisotropy (chains orientation and conformation), to suggest a model for chain organization at the polymer/substrate interface, and to calculate the orientation angles. Moreover, we were able to determine, by using PM-IRRAS, the degree of crystallinity of PA and EVA films of nanometric dimensions without any calibration procedure needed by other techniques.     

Integrated surface modification of fully polymeric microfluidic devices using living radical photopolymerization chemistry

Surface modification using living radical polymerization (LRP) chemistry is a powerful technique for surface modification of polymeric substrates. This research demonstrates the ability to use LRP as a polymer substrate surface‐modification platform for covalently grafting polymer chains in a spatially and temporally controlled fashion. Specifically, dithiocarbamate functionalities are introduced onto polymer surfaces using tetraethylthiuram disulfide. This technique enables integration of LRP‐based grafting for the development of an integrated, covalent surface‐modification method for microfluidic device construction. The unique photolithographic method enables construction of devices that are not substrate‐limited. To demonstrate the utility of this approach, both controlled fluid flow and cell patterning applications were demonstrated upon modification with various chemical functionalities. Specifically, poly(ethylene glycol) (375) monoacrylate and trifluoroethyl acrylate were grafted to control fluidic flow on a microfluidic device. Before patterning, surface‐functionalized samples were characterized with both goniometric and infrared spectroscopy to ensure that photografting was occurring through pendant dithiocarbamate functionalities. Near‐infrared results demonstrated conversion of grafted monomers when dithiocarbamate‐functionalized surfaces were used, as compared to dormant control surfaces. Furthermore, attenuated total reflectance/infrared spectroscopy results verified the presence of dithiocarbamate functionalities on the substrate surfaces, which were useful in grafting chains of various functionalities whose contact angles ranged from 7 to 86°. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1404–1413, 2006     

Effect of bidispersity in grafted chain length on grafted chain conformations and potential of mean force between polymer grafted nanoparticles in a homopolymer matrix

In efforts to produce polymeric materials with tailored physical properties, significant interest has grown around the ability to control the spatial organization of nanoparticles in polymer nanocomposites. One way to achieve controlled particle arrangement is by grafting the nanoparticle surface with polymers that are compatible with the matrix, thus manipulating the interfacial interactions between the nanoparticles and the polymer matrix. Previous work has shown that the molecular weight of the grafted polymer, both at high grafting density and low grafting density, plays a key role in dictating the effective inter-particle interactions in a polymer matrix. At high grafting density nanoparticles disperse (aggregate) if the graft molecular weight is higher (lower) than the matrix molecular weight. At low grafting density the longer grafts can better shield the nanoparticle surface from direct particle-particle contacts than the shorter grafts and lead to the dispersion of the grafted particles in the matrix. Despite the importance of graft molecular weight, and evidence of non-trivial effects of polydispersity of chains grafted on flat surfaces, most theoretical work on polymer grafted nanoparticles has only focused on monodisperse grafted chains. In this paper, we focus on how bidispersity in grafted chain lengths affects the grafted chain conformations and inter-particle interactions in an implicit solvent and in a dense homopolymer polymer matrix. We first present the effects of bidispersity on grafted chain conformations in a single polymer grafted particle using purely Monte Carlo (MC) simulations. This is followed by calculations of the potential of mean force (PMF) between two grafted particles in a polymer matrix using a self-consistent Polymer Reference Interaction Site Model theory-Monte Carlo simulation approach. Monte Carlo simulations of a single polymer grafted particle in an implicit solvent show that in the bidisperse polymer grafted particles with an equal number of short and long grafts at low to medium grafting density, the short grafts are in a more coiled up conformation (lower radius of gyration) than their monodisperse counterparts to provide a larger free volume to the longer grafts so they can gain conformational entropy. The longer grafts do not show much difference in conformation from their monodisperse counterparts at low grafting density, but at medium grafting density the longer grafts exhibit less stretched conformations (lower radius of gyration) as compared to their monodisperse counterparts. In the presence of an explicit homopolymer matrix, the longer grafts are more compressed by the matrix homopolymer chains than the short grafts. We observe that the potential of mean force between bidisperse grafted particles has features of the PMF of monodisperse grafted particles with short grafts and monodisperse grafted particles with long grafts. The value of the PMF at contact is governed by the short grafts and values at large inter-particle distances are governed by the longer grafts. Further comparison of the PMF for bidisperse and monodisperse polymer grafted particles in a homopolymer matrix at varying parameters shows that the effects of matrix chain length, matrix packing fraction, grafting density, and particle curvature on the PMF between bidisperse polymer grafted particles are similar to those seen between monodisperse polymer grafted particles.     

Grafting acrylic polymers from flat nickel and copper surfaces by surface-initiated atom transfer radical polymerization

Acrylic polymers, including poly(methyl methacrylate), poly(2,2,2-trifluoroethyl methacrylate), poly( N,N'-dimethyaminoethyl methacrylate), and poly(2-hydroxyethyl methacrylate) were grafted from flat nickel and copper surfaces through surface-initiated atom transfer radical polymerization (ATRP). For the nickel system, there was a linear relationship between polymer layer thickness and monomer conversion or molecular weight of "free" polymers. The thickness of the polymer brush films was greater than 80 nm after 6 h of reaction time. The grafting density was estimated to be 0.40 chains/nm2. The "living" chain ends of grafted polymers were still active and initiated the growth of a second block of polymer. Block copolymer brushes with different block sequences were successfully prepared. The experimental surface chemical compositions as measured by X-ray photoelectron spectroscopy agreed very well with their theoretical values. Water contact angle measurements further confirmed the successful grafting of polymers from nickel and copper surfaces. The surface morphologies of all samples were studied by atomic force microscopy. This study provided a novel approach to prepare stable functional polymer coatings on reactive metal surfaces.     

Preparation and Characterization of Carbon Fibers from Lyocell Precursors Grafted with Polyacrylamide via Electron-Beam Irradiation

Carbon fibers, which act as reinforcements in many applications, are often obtained from polyacrylonitrile (PAN). However, their production is expensive and results in waste problems. Therefore, we focused on producing carbon fibers from lyocell, a cellulose-based material, and analyzed the effects of the process parameters on their mechanical properties and carbon yields. Lyocell was initially grafted with polyacrylamide (PAM) via electron-beam irradiation (EBI) and was subsequently stabilized and carbonized. Thermal analysis showed that PAM grafting increased the carbon yields to 20% at 1000 °C when compared to that of raw lyocell, which degraded completely at about 600 °C. Stabilization further increased this yield to 55%. The morphology of the produced carbon fibers was highly dependent on PAM concentration, with fibers obtained at concentrations ≤0.5 wt.% exhibiting clear, rigid, and round cross-sections with smooth surfaces, whereas fibers obtained from 2 and 4 wt.% showed peeling surfaces and attachment between individual fibers due to high viscosity of PAM. These features affected the mechanical properties of the fibers. In this study, carbon fibers of the highest tensile strength (1.39 GPa) were produced with 0.5 wt.% PAM, thereby establishing the feasibility of using EBI-induced PAM grafting on lyocell fabrics to produce high-performance carbon fibers with good yields.     

Controlled grafting of MMA onto cellulose and cellulose acetate

Homogeneous graft copolymerization of methyl methacrylate onto cellulose and cellulose acetate was carried out in various solvents and solvent systems taking ceric ammonium nitrate, tin (II) 2-ethyl hexanoate [Sn(Oct)₂] and benzoyl peroxide as initiators. The effect of solvents, initiators, initiator and monomer concentration, on graft yield, grafting efficiency and total conversion of monomer to polymer were studied. Formation of Ce³⁺ ion during grafting in presence of CAN enhances the grafting efficiency. Methylene blue was used as a homopolymer inhibitor and controlled the molecular weight of the grafted polymer and its effect on grafting was also studied. In presence of MB, amount of PMMA homopolymer formation reduced and consequently grafting efficiency increased. The number average molecular weights and polydispersity indices of the grafted PMMA were found out by gel permeation chromatography. The products were characterized by FTIR and ¹H-NMR analyses and possible reaction mechanisms were deduced. Finally, thermal degradation of the grafted products was also studied by thermo-gravimetric and differential thermo-gravimetric analyses.     

Patterned immobilization of biomolecules by using ion irradiation‐induced graft polymerization

A new method for biomolecular patterning based on ion irradiation‐induced graft polymerization was demonstrated in this study. Ion irradiation on a polymer surface resulted in the formation of active species, which was further used for surface‐initiated graft polymerization of acrylic acid. The results of the grafting study revealed that the surface graft polymerization using 20 vol % of acrylic acid on the poly(tetrafluoroethylene) (PTFE) film irradiated at the fluence of 1 × 10¹⁵ ions/cm² for 12 h was the optimum graft polymerization condition to achieve the maximum grafting degree. The results of the fluorescence microscopy also revealed that the optimum fluence to achieve the maximum fluorescence intensity was 1 × 10¹⁵ ions/cm². The grafting of acrylic acid on the PTFE surfaces was confirmed by a fluorescence labeling method. The grafted PTFE films were used for the immobilization of amine‐functionalized p‐DNA, followed by hybridization with fluorescently tagged c‐DNA. Biotin‐amine was also immobilized on the acrylic acid grafted PTFE surfaces. Successful biotin‐specific binding of streptavidin further confirmed the potential of this strategy for patterning of various biomolecules. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6124–6134, 2009     

紫外光引发LDPE膜接枝含氟丙烯酸酯的研究

通过紫外光引发表面接枝聚合反应的方法 ,把含氟丙烯酸酯单体R 5 6 1 0引到LDPE薄膜上 .对经丁酮抽提后的接枝膜进行FTIR、ESCA、SEM和DSC等表征 ,证实含氟聚合物以化学键的方式接枝在LDPE基体膜上 .在一定范围内 ,增加紫外光强、引发剂和单体浓度以及反应温度等均有利于提高接枝率 .经计算R 5 6 1 0的紫外光引发接枝聚合反应总活化能为 5 4 2kJ mol.接枝膜的接触角随着接枝率的提高逐步增大 ,直至趋于恒定 .作者提出接枝膜存在一个在接触角测定时影响基体膜与探测水滴相互作用过程的边界层 .当接枝率较低、接枝层厚度小于边界层临界厚度时 ,基体LDPE影响接触角的大小 ,但随着接枝率提高 ,接枝层逐渐变厚 ,氟聚合物层对接触角的贡献逐渐占优势 ,导致接触角随之增大 .当接枝率超过一定值以后 ,接枝层厚度超过边界层临界厚度 ,接枝层对接枝膜的接触角起全部贡献 ,接触角测定值随之稳定     

Surface‐initiated atom transfer radical polymerization grafting of poly(2,2,2‐trifluoroethyl methacrylate) from flat silicon wafer surfaces

Poly(2,2,2‐trifluoroethyl methacrylate) (PTFEMA), a partially fluorinated polymer, was directly grafted from silicon wafer surfaces by a surface‐initiated atom‐transfer radical polymerization (ATRP). The polymer layer thickness increased linearly with monomer conversion and molecular weight of free polymers in solution. The thickness was mainly determined by the experimental conditions such as activator/deactivator ratio, monomer/catalyst ratio, and monomer concentration. PTFEMA layers of more than 100‐nm thick were obtained. The grafted PTFEMA chains were “living” and allowed the extension of a second block of PMMA. X‐ray photoelectron spectroscopy study showed that the chemical compositions at the surfaces agreed well with their theoretical values. A novel surface‐attachable difunctional initiator was also synthesized and applied to the grafting of PTFEMA. The grafting density was doubled using this difunctional initiator, from 0.48 to 0.86 chains/nm². © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1252–1262, 2006     

Nanomechanical properties of polymer brushes by colloidal AFM probes

Nanomechanical properties of end grafted polymer layers were studied by AFM based, colloidal probe compression measurements. Zwitterionic poly(sulfobetaine methacrylate) (PSBMA) brush was grafted from planar Si surface and poly(methyl methacrylate) (PMAA) brush was grown on colloidal probe by surface initiated atom transfer radical polymerization. PMAA brush was further modified with adhesion promoting arginyl-glycyl-aspartic acid (RGD) peptide sequences. Force–distance curves were obtained for systems where the polymer brushes were probed on unmodified surfaces or face to each other. For each systems the grafting density of the polymer brush was determined applying a ‘box’ like polymer brush model based on the theory by de Gennes. ‘Average’ grafting density was calculated in cases when two polymer brushes face each other: RGD functionalized PMAA or PMAA against PSBMA. For our systems the values for the grafting density was between 0.04 and 0.11 nm^?2. Furthermore the measured approach force–distance curves were fitted according to the Hertz model and the apparent Young’s modulus was determined for all measurements being in a range of around 250 kPa at physiological conditions.