UV-initiated Graft Polymerization Research Articles

Functionalization of seaweed bloom-derived Ulvan using response surface methodology with application in flocculation of oil-in-water pollution

Utilizing macroalgal waste biomass for pollution management is a highly efficient method for addressing the environmental difficulties associated with its disposal. To accomplish this, we have attempted to synthesize a graft copolymer by combining ulvan, a sulfated polysaccharide isolated from seaweed, with acrylates. A one-pot synthesis method using UV-initiated graft polymerization with V-50 as the photoinitiator resulted in the production of a distinctive, high-performance, and eco-friendly flocculant, Ulvan-g-Poly (acrylamide-co-acrylic acid) referred as P(U_AAm_AAc). The synthesis was optimized using the CCD-RSM approach, employing molecular weight and inherent viscosity as indicators to optimize the parameters. The structural and physio-chemical properties of the synthesized P(U_AAm_AAc) were characterized utilizing XRD, ATR-FTIR, ζ-potential, and H1 NMR spectroscopy. The flocculation performance of P(U_AAm_AAc) was further examined for the removal of oils from samples with high neem oil in urea solution and low crude oil in seawater. By employing a coagulant-flocculant combination of poly-aluminium chloride (PAC) and P(U_AAm_AAc), it was noted that more than 94% of oil was effectively eliminated in both samples. Optimization of the dosage of P(U_AAm_AAc) resulted in enhanced turbidity reduction and improved dewatering efficiency of the filter cake generated following flocculation. An evaluation of performance was conducted using the commercial flocculant APAM, where synthesized P(U_AAm_AAc) demonstrated similar results. In conclusion, the findings of this research highlight the potential of P(U_AAm_AAc) as a sustainable alternative to commercial flocculants with multifaceted solution to coastal waste management, paving the way for a cleaner and healthier marine ecosystem to mitigate oil emulsion pollution.

Effect of hydrophobized PET TeMs membrane pore-size on saline water treatment by direct contact membrane distillation.

This paper describes the desalination process by membrane distillation (MD) using track-etched membranes (TeMs). Hydrophobic track-etched membranes based on poly(ethylene terephthalate) (PET TeMs) with pore diameters from 700 to 1300 nm were prepared by UV-initiated graft polymerization of lauryl methacrylate (LMA) inside the nanochannels. Modified PET TeMs were investigated by Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and contact wetting angle (CA) measurements. Hydrophobic PET TeMs were tested for treating saline solutions of different concentrations by the direct contact membrane distillation (DCMD) method. The influence of membrane pore diameter and salt solution concentration on the water flux and rejection degree were investigated. Membranes with CA 94 ± 4° were tested in the direct contact membrane distillation (DCMD) of 7.5-30 g L-1 saline solution. Hydrophobic membranes with large pore sizes showed water fluxes in the range of 1.88 to 11.70 kg m-2 h-1 with salt rejection values of up to 91.4%.

Performance evaluation and optimization of flocculation process for removing heavy metal

Carboxymethyl chitosan (CMCTS) with active hydroxyl and amino groups is easily modified for chelating and capturing heavy metal, thus showing great potential for application in heavy metal-contaminated wastewater treatment. In this work, a dual-functional MACA copolymer [CMCTS-graft-P(AM-TGA)] with pH resistant was successfully designed and prepared by grafting acrylamide and thioglycolic acid onto CMCTS through UV-initiated graft polymerization. The spectroscopy characterization of functional groups and apparent morphology confirm the successful preparation of MACA. Flocculation conditions for reaching high removal efficiencies and investigating chelation capacity are optimized. A multiobjective evaluation model and a triangular environmental impact, economic benefit, and energy consumption (3E) evaluation model were established and employed to assess the 3E performance of MACA in heavy metal-contaminated wastewater flocculation. Optimal operation modulus is identified using 8 Key performance indicators by 3E triangle model. This work enriches knowledge about flocculation and provides guidance for flocculation parameter control.

Characterization and sludge dewaterability evaluation of a chitosan‐based flocculant CMCTS‐g‐CPAM

AbstractIn this work, a new cationic flocculant, CMCTS‐g‐CPAM was synthesized by acrylamide (AM), methacryloyloxyethyltrimethylammonium chloride (DMC) and carboxymethyl chitosan (CMCTS) through UV initiated graft polymerization techniques. The structure of CMCTS‐g‐CPAM was analysed by infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (1H NMR) and X‐ray diffraction (XRD) techniques which indicates that AM and DMC are grafted successfully onto CMCTS to obtain CMCTS‐g‐CPAM. The potential of CMCTS‐g‐CPAM for the sludge dewatering was investigated. The effects of cationic degree, intrinsic viscosity, dosage and pH on the sludge dewatering performance were studied. The results indicate that the optimal dewatering performance with minimum supernatant turbidity of 5.40 NTU, the moisture content of the filter cake of 79.28% and the specific resistance of the sludge of 1.96 × 1013 m/kg was obtained at 30 mg/L CMCTS‐g‐CPAM at pH 9–10. Finally, from the microscopic and electron micrographs investigation, it was confirmed that the particle size of the CMCTS‐g‐CPAM treated sludge was significantly large to enhance hydrophobicity and improve dewatering performance.

Fabrication of PMPC/PTM/PEGDA micropatterns onto polypropylene films behaving with dual functions of antifouling and antimicrobial activities.

Polymer materials with high biocompatibility and versatile functions are urgently required in the biomedical field. The hydrophobic surface and inert traits of polymer materials usually encounter severe biofouling and bacterial infection which hinder the potential application of polymers as biomedical materials. Although many antifouling or antimicrobial coatings have been developed for modification of biomedical devices/implants, few can simultaneously fulfill the requirements for antimicrobial and antifouling activities. Herein, we constructed bifunctional micropatterns with antifouling and antimicrobial properties onto polypropylene (PP) films using argon plasma activation treatment, photomask technique and UV-initiated graft polymerization method. Different sizes of PMPC/PTM/PEGDA micropatterns were fabricated on PP films to yield patterned PP-PMPC/PTM/PEGDA as evidenced by infrared (IR) spectroscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), where PMPC is poly(2-methacryloyloxyethyl phosphorylcholine) for enhancement of hydrophilicity and biocompatibility, PTM is poly(methacryloyloxyethyltrimethylammonium chloride) for contribution to antimicrobial activity and PEGDA is poly(ethylene glycol diacrylate) as the crosslinker. The surface hydrophilicity of patterned PP-PMPC/PTM/PEGDA was characterized by the static water contact angle test. The results showed that the PP sample with a micropattern with the size of 5 μm exhibited the best hydrophilicity. For biological assays of patterned PP-PMPC/PTM/PEGDA, the micropattern size at 5 μm performed the best for both antiplatelet adhesion and antimicrobial activities. We anticipate that this work could provide a new method for building bifunctional biomedical materials to promote the application of PP in biomedical fields.

Enhanced osteogenic activity of phosphorylated polyetheretherketone via surface-initiated grafting polymerization of vinylphosphonic acid.

Polyetheretherketone (PEEK) is considered to be a prime candidate with the potential to replace biomedical metallic materials as an orthopedic and dental implant on account of its elastic modulus similar to that of human cortical bone. Unfortunately, its biomedical application is impeded by the bioinert surface property and inferior osteogenic activity. In this work, phosphate groups were incorporated onto the PEEK surface through a single-step UV-initiated graft polymerization of vinylphosphonic acid. Diffuse reflectance Fourier transform infrared spectroscopy (DRFTIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) revealed that phosphate groups were successfully introduced onto the PEEK surface without apparently altering its surface topographical feature and roughness. Water contact angle measurements diclosed the increasing hydrophilia after surface phosphonation. In vitro cell adhesion, spreading, proliferation, alkaline phosphatase activity, extracellular matrix mineralization, and real-time PCR analyses showed enhanced adhesion, spreading, proliferation and osteogenic differentiation of MC3T3-E1 osteoblast on the surface-phosphorylated PEEK. An in vivo biological evaluation in the rabbit tibiae proximal defect model by means of a histological analysis confirmed that the surface-phosphorylated PEEK had improved bone-implant contact. The obtained results indicate that enhanced osteogenic activity to surface-phosphorylated PEEK, which gives positive information of its potential applications in orthopedic and dental implants.

Fabrication of micropatterns on polypropylene films via plasma pretreatment combined with UV-initiated graft polymerization

In this study, micropatterns on polypropylene films were fabricated via plasma pretreatment and UV-initiated graft polymerization. Firstly, radio-frequency plasma, which does not significantly influence bulk attributes of substrates due to limited penetration depth, was utilized to activate polypropylene films. Then, different sizes of micropatterns of poly(hydroxyethyl methacrylate) (PHEMA) were fabricated on the polypropylene films via UV-initiated graft polymerization of hydroxyethyl methacrylate by using photo-masks. Scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and contact angle (CA) were employed to characterize changes of pristine polypropylene films and modified ones in surface morphology, roughness, hydrophilicity, free energy and the surface chemical composition. All of these confirmed the successful grafting of different sizes of PHEMA micropatterns on the polypropylene surface. Furthermore, the influence of PHEMA micropatterns on cell proliferation and cytotoxicity was evaluated invitro. Analysis of cell behaviour indicated that PHEMA micropatterns of the appropriate size can promote cellular adhesion and proliferation, and the PHEMA-micropatterned polypropylene films had good biocompatibility. The approach presented here provides an alternative to synthesize on the surface of polypropylene films' micropatterns with the aim of using them in a diverse array of applications.

Improved biotribological properties of PEEK by photo-induced graft polymerization of acrylic acid

The keys of biomaterials application in artificial joints are good hydrophilicity and wear resistance. One kind of the potential bio-implant materials is polyetheretherketone (PEEK), which has some excellent properties such as non-toxic and good biocompatibility. However, its bioinert surface and inherent chemical inertness hinder its application. In this study, we reported an efficient method for improving the surface wettability and wear resistance for PEEK, a layer of acrylic acid (AA) polymer brushes on PEEK surface was prepared by UV-initiated graft polymerization. The effects of different grafting parameters (UV-irradiation time/AA monomer solution concentration) on surface characteristics were clearly investigated, and the AA-g-PEEK specimens were examined by ATR-FTIR, static water contact angle measurements and friction tests. Our results reveal that AA can be successfully grafted onto the PEEK surface after UV irradiation, the water wettability and tribological properties of AA-g-PEEK are much better than untreated PEEK because that AA is a hydrophilic monomer, the AA layer on PEEK surface can improve its bearing capacity and reduce abrasion. This detailed understanding of the grafting parameters allows us to accurately control the experimental products, and this method of surface modification broadens the use of PEEK in orthopedic implants.

Membrane distillation by novel hydrogel composite membranes

Novel polyelectrolyte hydrogel composites are developed by UV-initiated graft polymerization of acrylic acid and 2-hydroxyethyl methacrylate (functional monomers) and ethylene glycol dimethacrylate (cross-linker), on polypropylene flat sheet membranes (support). Homogeneous and defect-free hydrophilic hydrogel layer are synthetized on the hydrophobic porous support at different degrees of functionalization, by modulating the molar ratio between the functional monomers.Composites, with good stability against delamination, are effectively used as smart gating devices in membrane distillation (MD) treatment of NaCl solutions. The presence of ionizable groups make polyelectrolyte hydrogel sensitive to salt ions concentration. The retention property and responsive behavior of hydrogel membranes (swelling/shrinking) to salt solutions, and its dependence on the monomers composition in the gel synthesis, provides the unique opportunity to enhance control over mass transport and selectivity in MD processes.The special transport mechanism arises from the synergistic connection between the polyelectrolyte layer and the hydrophobic substrate. Combination of Donnan exclusion effects and the swelling/shrinking behavior of the hydrogel in response to the salt solution, which leads to strong anisotropic deformation of the soft gel layer anchored to the rigid support, affords tuneable water transport and ion rejection compared to conventional uncharged MD membranes. As a result, enhanced permeability and selectivity of composites, compared to pristine polypropylene membranes, are obtained when using saline solutions as feed.

Molecular separation by poly (N-vinyl imidazole) gel-filled membranes

Here we demonstrate the tunable molecular selectivities and corresponding mechanisms of poly(N-vinyl imidazole) (PVI) gel-filled membranes prepared by UV initiated graft polymerization of N-vinyl imidazole from ultraporous polysulfone (PSf) substrate. The separation performance was investigated in detail by extensive filtration tests with various organic molecules in water of varying pH and also in salt or ethanol aqueous solution. The variation of membrane water permeability and solute rejection with the feed pH was attributed to the sensitive pore size and charge characteristics of the membranes upon reversible protonation of the confined PVI gel. The separation results discerned three main mechanisms, i.e. size exclusion (sieving), electrostatic repulsion (Donnan exclusion) and adsorption. The rejection of the neutral molecules and the large dye molecules was mostly ascribed to size exclusion, while that of the small charged solutes was dominated by the electrostatic interactions including repulsion for cationic ones and attraction for anionic ones (causing specific adsorption). Typically, at pH 3 the protonated membranes rejected ~90% of the small cationic Vitamin B1 (VB1) and 100% of the anionic Sunset Yellow (SY) before adsorption saturation, in contrast to less than ~20% rejection of the neutral Vitamin B2 (VB2) having similar molecule size. In the high concentration salt or ethanol solution the membranes still maintained molecular sieving capability. Most notably, the separations of solute mixtures were indeed achieved, depending on the membrane parameters, the solute characteristics as well as the filtration conditions. The PVI gel-filled membranes developed in this work are promising in some specified or environment-sensitive molecular level separations.

Preparation and characterization of poly (N-vinyl imidazole) gel-filled nanofiltration membranes

Poly (N-vinyl imidazole) (PVI) gel-filled nanofiltration (NF) membranes were synthesized by UV-initiated graft polymerization of N-vinyl imidazole (VI) monomer, with and without crosslinker N,Nʹ-methylenbisacrylamide (MBAA) on/in a polysulfone (PSf) ultrafiltration (UF) substrate. A comprehensive characterization of the resulting composite membranes was conducted in terms of surface chemical composition (ATR-FTIR, XPS), surface morphology (SEM), surface charge (zeta potential), surface wettability (water contact angle) and barrier properties (water permeance, neutral solute/ions rejection and membrane stability). From rejection data of neutral solutes, including Vitamin B12 and PEGs, the average pore sizes and pore size distributions of membranes were further determined. These results confirmed the prepared membranes as stable, defect-free, smooth, hydrophilic NF membranes with effective pore size between ~1.5 and 2nm and water permeance between ~0.5 and 10Lm−2h−1bar−1. Moreover, owing to the weak polybase characteristic of the incorporated PVI gel, the membranes would carry slight positive charge in neutral or slightly acidic solution. The small pore size membranes displayed high salt rejections in the order of MgCl2>NaCl≈MgSO4>NaSO4 at near-neutral condition (pH 5.9±0.3).This testified their NF separation capability based on size exclusion, facilitated by Donnan repulsion. At last, by comparison with another reported type of gel-filled NF membranes with microporous substrate, and by applying a gel model, we delivered a qualitative description of the underlying fundamental parameters controlling the performance of such gel-filled membranes. Overall, these novel weak polybase gel-filled NF membranes with desirable nanometers-size pores and potentially tunable charge characteristics could offer great versatility for molecular-level separations.

High flux positively charged nanofiltration membranes prepared by UV-initiated graft polymerization of methacrylatoethyl trimethyl ammonium chloride (DMC) onto polysulfone membranes

To achieve high water flux, the majority of positively charged NF membranes consist of a thin active skin deposited on a thick, permeable support, while the connection force between the active layer and the support is a physical force which may cause the membrane unstable in the long running. In general, chemical bond connection may show superior stability. Based on this consideration, a series of positively charged nanofiltration (NF) membranes were prepared by UV-initiated graft polymerization of methacrylatoethyl trimethyl ammonium chloride (DMC) onto polysulfone ultrafiltration membranes in this work. The salts rejection order of these membranes is MgCl 2 > NaCl > MgSO 4 ≥ Na 2SO 4. Fourier transform infrared spectroscopy in attenuated total reflection mode (FTIR-ATR), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and water contact angle were employed to characterize the resulting membranes. The results indicated that the grafting degree (DG) increased with increasing the monomer concentration, prolonging the irradiation time and reducing the irradiation distance. However, the filtration performance was not well correlated with the increasing DG. The NF membrane prepared by photografting in a 1.5 M DMC solution for 5 min demonstrated high MgCl 2 rejection (94.8%) accompanied with high flux (20.3 L/m 2 h) at 0.2 MPa. When operation pressure increased to 0.8 MPa, the solution flux increased to 60 L/m 2 h, while MgCl 2 rejection nearly maintained stable about 92.4%. An interesting phenomenon was also observed in this experiment that the flux of pure water was less than that of salt solution for some NF membranes.

Wettability Patterning by UV-Initiated Graft Polymerization of Poly(acrylic acid) in Closed Microfluidic Systems of Complex Geometry

Many microfluidic applications require modified surface wettability of the microchannels. Patterning of wettability within enclosed microfluidic structures at high spatial resolution has been challenging in the past. In this paper, we report an improved method for altering the surface wettability in poly(dimethylsiloxane) (PDMS) microchannels by UV-induced graft polymerization of poly(acrylic acid). Our method presents significant improvements in terms of wettability contrast and spatial resolution of the patterned structures as compared to recent literature and is in particular applicable to complex microfluidic structures with a broad range of channel sizes and aspect ratios. A key part of our work is the clear description of the surface treatment process with the identification of key parameters, some of which have been overlooked, neglected, or misinterpreted in previous works. We have studied these key parameters in detail and provide recommended values for each parameter supported by experimental results. This detailed understanding of the treatment process and the effects of the critical parameters on it allowed us to significantly improve quality and reliability of the treatment process.

Covalently Attached, Silver-Doped Poly(vinyl alcohol) Hydrogel Films on Poly(l-lactic acid)

Covalently attached, soft poly(vinyl alcohol) (PVA) hydrogel films containing silver particles were prepared on solid biodegradable poly(l-lactic acid) (PLLA) samples by a multistep procedure involving oxygen plasma treatment, UV-initiated graft polymerization, and chemical grafting methods. The modification steps were followed and verified using attenuated total reflection infrared spectroscopy and X-ray photoelectron spectroscopy. 2-Hydroxyethyl methacrylate (HEMA) was graft polymerized from the surface of oxygen plasma-treated PLLA film samples and the alcohol functionality in the grafted polyHEMA chains was oxidized using pyridinium dichromate to obtain an aldehyde-rich surface. PVA was then grafted onto this surface using acid catalysis (acetal formation). The "freeze/thaw method" was used to form a PVA hydrogel layer that incorporated the covalently grafted PVA chains in the physically cross-linked gel. This composite film (PLLA-PVA(gel)) was doped with silver ions, which were reduced to silver using NaBH(4). Scanning electron microscopy of cross sections of PLLA-PVA(gel) indicates robust attachment of the PVA hydrogel layer to the PLLA film. PLLA-PVA(gel/Ag(0)) film samples exhibit both antibacterial and reduced cell adhesion properties due to the antibacterial properties of silver nanoparticles and high water content, respectively. This method provides a route to mechanically sound biodegradable materials with tunable soft material surface properties. Potential applications in tissue engineering and biomedical devices are envisioned.

Reduction of nanofiltration membrane fouling by UV-initiated graft polymerization technique

Nanofiltration polyethersulfone membrane has been modified by means of UV-initiated graft polymerization technique using the weakly acidic monomer acrylic acid and the immersion method. Different UV-irradiation times and acrylic acid concentrations in water were studied. Both the unmodified and the modified polyethersulfone nanofiltration membranes were characterized by attenuated total reflection-Fourier transform infrared spectra (FTIR-ATR) and atomic force microscopy (AFM). Irreversible membrane fouling has been studied by using humic acid model solutions at two different pH values (7 and 3). It was observed that some modified membranes exhibited higher permeance than the unmodified polyethersulfone nanofiltration membrane. The humic acid rejection factor was higher for all modified membranes compared to the unmodified membrane and the irreversible fouling by humic acid molecules was reduced after UV-initiated graft polymerization by acrylic acid.

Response surface modeling and optimization of composite nanofiltration modified membranes

The experimental design and response surface methodology (RSM) have been used to develop predictive models for simulation and optimization of nanofiltration modified membranes by UV-initiated graft polymerization technique. The objective is to prepare optimum membrane with high nanofiltration performance and low fouling. The factors considered for experimental design were the UV-irradiation time, UV-intensity and the concentration of the monomer N-vinyl-2-pyrrolidone (NVP) in aqueous grafting solution. The dip method has been followed for membrane grafting employing 365 nm wavelength UV-lamp. The significant factors were optimized using a central composite design of orthogonal type. The nanofiltration membrane performance has been studied using humic acid model solution 15 mg/L at a pH value 7. Pure water permeation flux, permeate flux when using humic acid feed solution, rejection factor and irreversible membrane fouling parameters have been determined. The nanofiltration performance index and the recoverable flux ratio have been considered as responses. The quadratic models between each response and the independent parameters were developed and the response surface models were tested with analysis of variance (ANOVA). By applying the desirability function approach maximal output responses have been predicted and confirmed experimentally. The obtained optimal point was located in the valid region and the experimental confirmation tests were conducted showing a good accordance between the predicted optimal points and the experimental ones. The optimum operating conditions determined were a monomer concentration of 5.13 g/L, UV-intensity of 16.57 × 10 4 mW/m 2 and UV-irradiation time of 37.9 s. Under these optimal conditions maximum nanofiltration performance index, 84.88 L/m 2 h and recoverable flux ratio 88.14% have been achieved. These values are the highest compared to all experimental data carried out within the overall region of experimentation. The optimum NVP UV-grafted membrane exhibits low humic acid fouling tendency than the unmodified membrane.

Investigation of poly(vinylidene chloride) distribution in perfluorinated cation-exchange membranes MF-4SK upon UV- and γ-initiated graft polymerization

A new process for grafting poly(vinylidene chloride) (PVDC) to the membrane material MF-4SK by UV-initiated graft polymerization of the monomer from the gas phase has been developed. Modified membranes containing up to 20 wt % of UV-grafted PVDC have been obtained. Microphotographs of thin sections of the modified membranes have been investigated. It has been shown that the pretreatment of the membranes and variation of UV- or γ-grafting conditions make it possible to achieve an uniform distribution of grafted PVDC both along the thickness of the membrane and in a thin surface layer. The values of the parameters determining the character of the distribution have been estimated. Numerical simulation of the UV- and γ-initiated graft polymerization of VDC gave solutions for the grafted-PVDC distribution fitting with the experimental data.

Photolithographically Patterned Surface Modification of Poly(dimethylsiloxane) via UV-Initiated Graft Polymerization of Acrylates

Patterned surface modification of poly(dimethylsiloxane) (PDMS) is achieved by combining ultraviolet-initiated graft polymerization (UV-GP) and photolithography. Poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) patterns were grafted onto PDMS with micrometer-scale feature edge resolution. The morphology and chemical composition of the grafted layers were assessed by optical and atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and XPS imaging. AFM section analyses demonstrated the deposition of 33 +/- 1 and 62 +/- 8 nm thick patterned films of PAA and PMAA, respectively. Spatially resolved C 1s XPS provided images of carboxylic acid functionalities, verifying the patterned deposition of acrylate films on PDMS. These observations demonstrate the general usefulness of UV-GP and photolithography for micropatterning.

Nanoscale Single Polymer Chains on a Chip Poly(Glycidylmethacrylate) Grafted on Silicon (100) Surfaces

In previous studies reported in the literature it was shown that polymer chains could be sparsely grown on a mica surface and then imaged, after appropriate solvent treatment, as nanoscale droplets, each droplet consisting of a single polymer chain. With a view to eventual molecule-size devices on a chip, we wished to obtain such structures on silicon wafers. The method employed was UV-initiated graft polymerization. Previous studies had shown that silicon wafers that were plasma-treated and then exposed to air formed peroxide-like compounds on the surface. These could then be UV-irradiated in the presence of monomers to obtain surface-grafted polymer. It was expected that under sparse conditions of grafting, molecular droplets could be obtained in this way on silicon wafers. The monomer selected in the present work was glycidylmethacrylate (GMA), of special interest because poly(GMA) is a potential biomolecule surface linker. Single chain molecular droplets were indeed obtained when the polymerization time was sufficiently short, and an appropriate postpolymerization solvent treatment was used.

NANOSCALE SINGLE POLYMER CHAINS ON A CHIP: POLY(GLYCIDYLMETHACRYLATE) GRAFTED ON SILICON (100) SURFACES

In previous studies reported in the literature it was shown that polymer chains could be sparsely grown on a mica surface and then imaged, after appropriate solvent treatment, as nanoscale "molecular droplets," each droplet consisting of a single polymer chain. With a view to eventual molecule-size devices on a chip, we wished to obtain such structures on silicon wafers. The method employed was UV-initiated graft polymerization. Previous studies had shown that silicon wafers that were plasma-treated and then exposed to air formed peroxide-like compounds on the surface. These could then be UV-irradiated in the presence of monomers to obtain surface-grafted polymer. It was expected that under sparse conditions of grafting, molecular droplets could be obtained in this way on silicon wafers. The monomer selected in the present work was glycidylmethacrylate (GMA), of special interest because poly(GMA) is a potential biomolecule surface linker. Single chain molecular droplets were indeed obtained when the polymerization time was sufficiently short, and an appropriate postpolymerization solvent treatment was used.