PVDF Surface Research Articles

Evaluation of graphene nanosheets influence on the physical properties of PVDF/PMMA blend

In this work, we report the preparation of PVDF/ PMMA/graphene polymer blend nanocomposites via syn- thesis of PMMA/graphene as a masterbatch through in-situ polymerization. The PMMA/graphene masterbatch com- pounded with PVDF by solution mixing in different ratios. The compounding was followed by solution casting to form polymer blend nanocomposites. Solution cast films were subjected to thermal treatments at three different temper- atures. ATR-FTIR results revealed the specific interaction between PVDF and graphene surface and also increasing the percentage of γ-phase on the surface with rising the anneal- ing temperature. SEM photographs of the top surface of casted films showed visible phase fluctuations with increas- ing the annealing temperature especially for 70:30 which is induced by graphene sheets in the mixture of PVDF/ PMMA. Also, presence of fiber pull-out in the fractured surface of 70:30 was related to the increase in cohesive interface due to existence of PMMA. TGA analysis exposed the improvement in thermal stability of PVDF portion of the mixture due to preferentially adsorption of PVDF chains onto the graphene surface during of the heating. Decreasing in Yong's modulus was observed with addition of PMMA but presence of strong GNPs retrieve this negative effect and increases the tensile modulus. The melt-rheological studies illustrated the high interaction between PVDF, PMMA, GNPs and different status of dispersion in three different samples. As well, measuring MFI showed that PMMA caused to decline in melt flow of the polymer blend while the addition of graphene compensate it to some extent revealed lubrication effect of GNPs.

The double effects of silver nanoparticles on the PVDF membrane: Surface hydrophilicity and antifouling performance

In this study, silver nanoparticles were used to endow poly(vinylidene fluoride) (PVDF) membrane with excellent surface hydrophilicity and outstanding antifouling performance. Silver nanoparticles were successfully immobilized onto PVDF membrane surface under the presence of poly(acrylic acid) (PAA). The double effects of silver nanoparticles on PVDF membrane, i.e., surface hydrophilicity and anti-fouling performance, were systematically investigated. Judging from result of water static contact measurement, silver nanoparticles had provided a significant improvement in PVDF membrane surface hydrophilicity. And the possible explanation on the improvement of PVDF membrane surface hydrophilicity with silver nanoparticles was firstly proposed in this study. Membrane permeation and anti-bacterial tests were carried out to characterize the antifouling performance of PVDF membrane. Flux recovery ratio (FRR) increased about 40% after the presence of silver nanoparticles on the PVDF membrane surface, elucidating the anti-organic fouling performance of PVDF membrane was elevated by silver nanoparticles. Simultaneously, anti-bacterial test confirmed that PVDF membrane showed superior anti-biofouling activity because of silver nanoparticles. The above-mentioned results clarified that silver nanoparticles can endow PVDF membrane with both excellent surface hydrophilicity and outstanding antifouling performance in this study.

Modulation of biocompatibility on poly(vinylidene fluoride) and polysulfone by oxygen plasma treatment and dopamine coating

Poly(vinylidene fluoride) (PVDF) and polysulfone (PSf) are two polymers with excellent mechanical properties but insufficient biocompatibility mainly due to their surface hydrophobicity. This study has applied oxygen plasma treatments and dopamine coating on the two polymers and investigated the changes of the surface properties and interactions with mammalian cells. All modification steps were verified by means of Electron Spectroscopy for Chemical Analysis and contact angle measurements. Surface topology of materials and biomolecules was studied by atomic force measurements (AFM) and scanning electron microscopy (SEM). Protein adsorption was quantified by fluorescent imaging and Bradford method. The results showed that O(2) plasma altered the surface hydrophilicity effectively on PSf and more than two folds of oxidation were obtained, when compared with the pristine one. The change of surface wettability was less significant on the O(2) plasma treated PVDF due to less oxidation extent, which was identified by analyzing the chemical compositions. The provided functionalized PVDF and PSf surfaces were tested with bovine serum albumin and L-929 mouse fibroblasts to evaluate the effects of surface modifications on protein adsorption and cell attachments. The biocompatibility was effectively promoted to fourfold and twofold on the hydrophobic PVDF and PSf by applying O(2) plasma treatments within short treatment time. Moreover, the simple immobilization of polymers in dopamine solution resulted in hydrophilic surface coating with stability that caused threefold and twofold increases of biocompatibility on PVDF and PSf correspondingly.

Dielectric Properties of Collagen on Plasma Modified Polyvinylidene Fluoride

Problem statement: The attachment of biopolymers such as collagen on inert polymeric template created great challenge due to hydrophobic nature of polymeric material. The modification of PVDF for improved adhesion and introduction of specific functionalities have been widely recognized in various industrial applications. Typical methods for modifying polymer surface such as chemical etching and UV irradiation are not favorable as it requires high temperature and the use of chemical solvents. However plasma modification is suitable as it utilizes low heat and a clean environment, thus preventing contamination on the deposited collagen. Approach: Free standing orientated Poly (Vinylidene Fluoride) (PVDF) films were fabricated by solution casting method and dried in a convention oven. The dried PVDF films were orientated in a tensile machine at temperature 70°C enclosed in a custom made environmental chamber. The pulling rates of 5 mm min-1 were utilized with a draw ratio of 2 (R = Lfinal/Linitial). The PVDF film was plasma treated for 60 sec to enhance the hydrophilic property of PVDF and utilized as template for collagen deposition. The deposited collagen on surface of PVDF was left in desiccators at temperature of 24°C for complete drying. Results: The untreated and plasma-treated PVDF template were observed for water contact angle measurement, the functional group and dielectric properties of collagen were observed and measured by FTIR and SOLARTRON respectively. Conclusion: The orientated PVDF films were produced at pulling speed of 5 mm min-1 and temperature of 70°C. The hydrophobic PVDF surface was transformed to a hydrophilic surface by plasma treatment for collagen deposition. The FTIR result shows the overlapping peaks of C-H and C-F in range 1500-1000 cm-1 which indicates the C-C bonding of collagen and PVDF. The significant increase in dielectric constant is a result from the favorable bonding between collagen and PVDF template.

Surface characteristics and blood compatibility of PVDF/PMMA membranes

Poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) membranes have important applications as biomaterials. In this study, PVDF/PMMA with varying ratios is blown into membranes, the surface property and blood compatibility of which are thoroughly investigated. Membrane surface characteristics including composition and topography exert considerable influence on the blood compatibility. Introduction of PMMA disturbs PVDF crystallization, however, favors the β phase crystal formation. PVDF content, crystallization ability, and surface enrichment have decisive effects on the membrane surface composition. Meanwhile, with increased PMMA fraction, the membrane surface roughness is also increased, and subsequently results in decreased hemocompatibility. While the membranes with PMMA content lower than 30 wt% show good blood compatibility, those with higher PMMA fraction exhibit obvious platelet adhesion to the surface. Thermal annealing promotes the formation of β phase PVDF and generates much smoother surface, thus endowing the membranes with greatly enhanced blood compatibility. These results show the prospect for optimization of processability, surface property, and blood compatibility of PVDF/PMMA membranes through facile modulation of PMMA content and fabrication process.

Green aqueous modification of fluoropolymers for energy storage applications

Fluoropolymers are of prime interest as solution processable materials for electronic applications such as embedded capacitors, multilayer capacitors, and high-energy-density capacitors. Herein, for the first time, we investigated an environmentally friendly green aqueous modification of fluoropolymers, poly(vinylidene fluoride) (PVDF) for energy storage applications. The PVDF polymer was modified in aqueous medium by using bioinspired protein dopamine without any harmful toxic chemicals. Dopamine functionalization onto pre-irradiated PVDF polymer powder was carried out using a simple reflux method to strongly bind dopamine onto the PVDF surface. The resulting dopamine modified PVDF films exhibited excellent dielectric properties, when compared with the pristine PVDF polymer. The dielectric constant can be enhanced up to 32 with fairly low dielectric loss as compared to pristine PVDF. Furthermore, the modified films were found to have good flexibility; they could be curled as easily as pristine PVDF films. Since this method avoids the use of toxic chemicals, it may allow the application of modified PVDF not only for energy storage applications but also for other applications such as in biocompatible materials.

Facile surface glycosylation of PVDF microporous membrane via direct surface-initiated AGET ATRP and improvement of antifouling property and biocompatibility

This paper describes a facile and novel approach for the surface glycosylation of poly(vinylidene difluoride) (PVDF) microporous membrane. A glycopolymer poly(d-gluconamidoethyl methacrylate) (PGAMA) was tethered onto the membrane surface via activators generated by electron transfer atom transfer radical polymerization (AGET ATRP) directly initiated from the PVDF surface. Chemical changes of membrane surface were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). It was revealed that PGAMA was successfully grafted onto the membrane surface and its grafting density can be modulated in a wide range up to 2.4μmol/cm2. The effects of glycosylation on membrane morphology, flux and surface hydrophilicity were investigated. Field emission scanning electron microscopy (FESEM) results indicated shrinkage of the surface pore diameters and the growth of the glycopolymer layer on the membrane surface. The static water contact angle (WCA) of the membrane surface decreased from 110° to 30.4° with the increase of grafting density, indicating that the PGAMA grafts dramatically improved the surface hydrophilicity. The protein adsorption and platelets adhesion experiments indicated that the grafted PGAMA could effectively improve the membrane antifouling property and biocompatibility.

Photoactivated surface grafting from PVDF surfaces

Economic and easy methods to tune surface properties of polymers as Poly(vinylidene fluoride) (PVDF) without altering bulk properties are of major interest for different applications as biotechnological devices, medical implant device… UV irradiation appears as one of the simplest, easy and safe method to modify surface properties. In the case of self-initiated grafting, it is generally assumed that the pre-treatment of the PVDF surface with UV irradiation can yield alkyl and per-oxy radicals originating from breaking bonds and capable of initiating the subsequent surface grafting polymerizations. Surprisingly, the present work shows that it is possible to obtain polymer grafting using low energetic UV-A irradiation (3.1–3.9 eV) without breaking PVDF bonds. An EPR study has been performed in order to investigate the nature of involved species. The ability of the activated PVDF surface to graft different kinds of hydrophilic monomers using the initiated surface polymerization method has been tested and discussed on the basis of ATR FT-IR, XPS and NMR HRMAS results.

Patterned Immobilization of Biomolecules on a Polymer Surface Functionalized by Radiation Grafting

Patterned graft polymerization of a functional monomer on a hydrophobic polymer surface was proposed for biomolecule patterning. A poly(vinylidene fluoride) (PVDF) film surface was selectively activated by ion implantation through a pattern mask and acrylic acid (AA) was then graft polymerized onto the activated regions of the PVDF surfaces. The peroxide concentration on the implanted surface depended on the fluence, which had a considerable effect on the grafting degree of AA. Afterwards, amine-functionalized biotin and probe DNA were immobilized on the poly(acrylic acid)-grafted regions of the PVDF surfaces. Specific binding of biotin with streptavidin and hybridization of probe DNA with complimentary DNA proved successful protein and DNA patterning and well-defined 50 microm dot-type patterns of the streptavidin and DNA were obtained. These results confirmed the potential of this strategy for patterning of various biomolecules.

Thermoresponsive surface prepared by atom transfer radical polymerization directly from poly(vinylidene fluoride) for control of cell adhesion and detachment

AbstractThermoresponsive surface was prepared from commercial poly(vinylidene fluoride) (PVDF) films via surface‐initiated atom transfer radical polymerization. The direct initiation of the secondary fluorinated site of PVDF facilitated grafting of the N‐isopropylacrylamide (NIPAAm) monomer. The PVDF surfaces grafted with poly(N‐isopropylacrylamide) [P(NIPAAm)] were characterized by X‐ray photoelectron spectroscopy. Kinetics study revealed that the P(NIPAAm) chain growth from the PVDF surface was consistent with a “controlled” process. The temperature‐dependent swelling behavior of the surfaces in aqueous solution was studied by atomic force microscope. At 37°C [above the lower critical solution temperature (LCST, about 32°C) of NIPAAm], the seeded cells adhered and spread on the NIPAAm grafted PVDF surface. Below the LCST, the cells detached from the P(NIPAAm)‐grafted PVDF surface spontaneously. The thermoresponsive surfaces are potentially useful as stimuli‐responsive adhesion modifiers in the biomedical fields.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Hydrophilic monomers suppress the adsorption of plasma protein onto a poly(vinylidene fluoride) membrane

Dialysis is the single most important therapy for chronic kidney disease. However, protein adsorption onto hemodialysis membranes promotes clot formation. The aim of the present study was to develop a surface-modified membrane which suppresses protein adsorption. Using plasma polymerization, hydrophilic N-vinyl pyrrolidone (VP) and acryloyl morpholine (ACMO) were polymerized on hydrophobic poly(vinylidene fluoride) (PVDF) surfaces. PVDF is employed as a biomaterial owing to its extraordinary durability. These membranes were then characterized using static contact angle measurement, ATR-FTIR spectra and polyacrylamide gel electrophoresis. The surface-modified PVDF membranes showed a transition of the surface from relatively hydrophobic to hydrophilic. Less proteins were adsorbed on the VP and ACMO grafted PVDF surfaces than on the unmodified membrane and the commercially available hemodialysis membrane. In conclusion, VP and ACMO grafted PVDF membranes have a high potential for the inhibition of protein adsorption in high-performance hemopurification devices.

Controlled Grafting of Poly(methyl methacrylate) Brushes on Poly(vinylidene fluoride) Powders by Surface‐initiated Atom Transfer Radical Polymerization

AbstractControlled grafting of well‐defined polymer brushes of methyl methacrylate (MMA) on the poly(vinylidene fluoride) (PVDF) powders was carried out by the surface‐initiated atom transfer radical polymerization (ATRP). The ATRP initiator was anchored on the PVDF surface by alkaline treatment, followed by UV‐induced bromination; then methyl methacrylate (MMA) was grafted onto the brominated PVDF by the ATRP technique. The chemical composition changes of PVDF were characterized by Fourier transform‐infrared spectroscopy (FT‐IR) and X‐ray photoelectron spectroscopy (XPS). FT‐IR and XPS results clearly indicated the successful graft of poly(methyl methacrylate) onto the PVDF surface.

Effect of Complex Ion Beam/Plasma Treatment of the Surface Functionalization and Crystal Phase Transition of Piezoelectric Poly(vinylidene fluoride)

We scrutinized the effect of complex ion beam and plasma treatment on the surface functionalization and crystal phase change of poly(vinylidene fluoride) films. The stretched and poled PVDF films were used for this investigation. Ion-beam and plasma treatment were employed for the surface modification of PVDF. The surface treatments induced some changes of chemical composition as well as changed the morphology of PVDF surface. It had a large influence on the interfacial adhesion with thermally deposited metal electrodes on the PVDF. Surface modifications such as ion beam irradiation and plasma treatment played a pivotal role in the determination of interfacial strength between PVDF and electrodes as well as the change of crystal structure in electromechanical PVDF film. While the amount of β-phase crystal in PVDF decreased with treatment time, the interfacial adhesion increased with the modification time. In this research, we were able to find optimum treatment conditions for enhancing the adhesion and retaining piezoelectric structure.

XPS analysis of laser transmission micro-joint between poly (vinylidene fluoride) and titanium

Micro-joints between poly (vinylidene fluoride) (PVDF) film and titanium (Ti) foil with a joint width of 250 μm were fabricated by a transmission laser joining technique. The Ti and PVDF surfaces exposed by debonding the joint were studied by X-ray photoelectron spectroscopy (XPS). The XPS results suggest that laser joining leads to the formation of Ti–F and Ti–C chemical bonds at the interface.

Kinetics of radiation-induced carbonization of poly(vinylidene fluoride) film surface

The kinetics of radiation-induced carbonization of PVDF surfaces aiming at carbyne (one-dimensional carbon allotrope) synthesis have been studied. A sample of poly(vinylidene fluoride) film was exposed to Mg Kα radiation ( ħω = 1253.6 eV) in an ESCALAB Mk II spectrometer for 14 h with the aim of surface carbonization. Some 221 spectra of C 1s electrons were measured and expanded using 7 Gaussian curves to reveal and identify species being created on the film surface during its carbonization. A decrease in the content of CF 2 groups, the emergence of CF species in two different states, and growth of a number of fluorine-free carbon atoms have been detected. Simultaneous variations of CH/CH 2, CF and CF 2 peaks suggest elimination of H and F atoms as HF. A proposed model shows three probabilistic factors affecting the rate of degradation, one of which remains uncertain.

A FACILE APPROACH FOR THE SURFACE MODIFICATION OF POLY(VINYLIDENE FLUORIDE) MEMBRANE VIA SURFACE-INITIATED ATOM TRANSFER RADICAL POLYMERIZATION

A novel approach for the surface modification of poly(vinylidene fluoride) (PVDF) membrane was successfully realized through alkaline treatment, UV-induced bromine addition, and followed by surface-initiated atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). Chemical changes on the PVDF membrane before and after modification were analyzed with attenuated total reflectance Fourier transform infrared spectroscopy (ATR/FT-IR) and X-ray photoelectron spectroscopy (XPS). Primary kinetic study revealed that the chain growth of poly(methyl methacrylate) (PMMA) from the PVDF surface is consistent with a "controlled" process.

PREPARATION OF POLYMER BRUSHES FROM POLY(VINYLIDENE FLUORIDE) SURFACES BY UV IRRADIATION PRETREATMENT

Grafting of polymer brushes from the poly(vinylidene fluoride) (PVDF) surfaces was carried out. The active species, such as peroxide and hydroperoxide, on the surface were generated via ultraviolet (UV) irradiation pretreatment in nitrogen, followed by air exposure. Homopolymer brushes of methyl methacrylate (MMA) were prepared by the surface-initiated free radical polymerization from the peroxide initiators on the PVDF surface. The peroxides formed on UV-treated and air-exposed PVDF surfaces were determined quantitatively by the reaction with 2,2-diphenyl-1-picrylhydrazyl (DPPH) in toluene. The chemical composition and topography of the graft-functionalized PVDF surfaces were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance (ATR) FT-IR spectroscopy, and atomic force microscopy (AFM). ATR FT-IR revealed an increase in the graft concentration of poly(methyl methacrylate) (PMMA) on PVDF surfaces with an increase of the UV irradiation pretreatment time. Water contact angles on PVDF surfaces were reduced by surface grafting of PMMA.

Controlled grafting of polymer brushes on poly(vinylidene fluoride) films by surface‐initiated atom transfer radical polymerization

AbstractControlled grafting of well‐defined polymer brushes on the poly(vinylidene fluoride) (PVDF) films was carried out by the surface‐initiated atom transfer radical polymerization (ATRP). Surface‐initiators were immobilized on the PVDF films by surface hydroxylation and esterification of the hydroxyl groups covalently linked to the surface with 2‐bromoisobutyrate bromide. Homopolymer brushes of methyl methacrylate (MMA) and poly(ethylene glycol) monomethacrylate (PEGMA) were prepared by ATRP from the α‐bromoester‐functionalized PVDF surface. The chemical composition of the graft‐functionalized PVDF surfaces was characterized by X‐ray photoelectron spectroscopy (XPS) and attenuated total reflectance (ATR)–FTIR spectroscopy. Kinetics study revealed a linear increase in the graft concentration of PMMA and PEGMA with the reaction time, indicating that the chain growth from the surface was consistent with a “controlled” or “living” process. The “living” chain ends were used as the macroinitiator for the synthesis of diblock copolymer brushes. Water contact angles on PVDF films were reduced by surface grafting of PEGMA and MMA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3704–3712, 2006

Preparing polymer brushes on poly(vinylidene fluoride) films by free radical polymerization

AbstractGrafting of polymer brushes on the poly(vinylidene fluoride) (PVDF) films was carried out by the surface‐initiated free radical polymerization. Surface‐initiators were immobilized on the PVDF films by surface hydroxylation and esterification of the surface‐tethered hydroxyl groups with 4,4′‐azobis(4‐cyanopentanoic acid) (ACP). Homopolymer brushes of methyl methacrylate (MMA) were prepared by free radical polymerization from the azofunctionalized PVDF surface. The chemical composition and topography of the graft‐functionalized PVDF surfaces were characterized by X‐ray photoelectron spectroscopy (XPS), attenuated total reflectance (ATR) FTIR spectroscopy, and atomic force microscopy (AFM). Kinetics study revealed an exponential increase in the graft concentration of polymer brushes with the reaction time, indicating that the chain growth from the surface was consistence with a chain polymerization. Water contact angles on PVDF films were reduced by surface grafting of MMA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 857–862, 2006

Atom transfer radical polymerization directly from poly(vinylidene fluoride): Surface and antifouling properties

AbstractThe direct preparation of grafting polymer brushes from commercial poly (vinylidene fluoride) (PVDF) films with surface‐initiated atom transfer radical polymerization (ATRP) is demonstrated. The direct initiation of the secondary fluorinated site of PVDF facilitated grafting of the hydrophilic monomers from the PVDF surface. Homopolymer brushes of 2‐(N,N‐dimethylamino)ethyl methacrylate (DMAEMA) and poly (ethylene glycol) monomethacrylate (PEGMA) were prepared by ATRP from the PVDF surface. The chemical composition and surface topography of the graft‐functionalized PVDF surfaces were characterized by X‐ray photoelectron spectroscopy, attenuated total reflectance/Fourier transform infrared spectroscopy, and atomic force microscopy. A kinetic study revealed a linear increase in the graft concentration of poly[2‐(N,N‐dimethylamino)ethyl methacrylate] (PDMAEMA) and poly[poly(ethylene glycol) monomethacrylate] (PPEGMA) with the reaction time, indicating that the chain growth from the surface was consistent with a controlled or living process. The living chain ends were used as macroinitiators for the synthesis of diblock copolymer brushes. The water contact angles on PVDF films were reduced by the surface grafting of DMAEMA and PEGMA. Protein adsorption experiments revealed a substantial antifouling property of PPEGMA‐grafted PVDF films and PDMAEMA‐grafted PVDF films in comparison with the pristine PVDF surface. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3434–3443, 2006