Grafted Polymer Layers Research Articles

Contamination and Decontamination of Polymer-Coated Surfaces

We study the interaction between a flat surface and a contaminant solution. The surface is protected by a grafted polymer layer. Our primary interest is to better understand and elucidate the effect of simple molecular interactions on the contamination and decontamination of the surface through molecular diffusion. These interactions manifest themselves in the potential of mean force that the contaminant molecule experiences as it diffuses across the grafted polymer layer. For simplicity, we consider that all interactions are of the hard-sphere type. The size of the contaminant molecule is the same as that of the solvent as well as the individual polymer segment. Despite these simplifications, the analysis offers important physical insights and a qualitative description of the contamination and decontamination processes.

Novel highly hydrophilic resins with grafted polymer layers for liquid chromatography

Novel highly hydrophilic resins with grafted polymer layers for liquid chromatography

Surface-Initiated Polymerizations Mediated by Novel Germanium-Based Photoinitiators.

Since surface-initiated photopolymerization techniques have gained increasing interest within the last decades, the coupling of photoinitiators to surfaces and particles has become an important research topic in material and surface sciences. In terms of surface modification and functionalization, covalently coupled photoinitiators and subsequent photopolymerizations are employed to provide a huge variety of surface properties, such as wettability, stimulus responsive features, antifouling behavior, protein binding, friction control, drug delivery, and many more. For this purpose, numerous type I and type II photoinitiators or other photosensitive moieties have been attached to different substrates so far. In our studies, a convenient and straightforward synthetic protocol to prepare a novel germanium-based photoinitiator (bromo-tris(2,4,6-trimethylbenzoyl)germane) in good yields was developed. The immobilization of this photoinitiator at the surface of silicon wafers and quartz plates was evidenced by X-ray photoelectron spectroscopy (XPS). Employing visible-light-triggered surface-initiated polymerization of different functional monomers, including acrylamide, perfluorodecyl acrylate, and fluorescein-o-acrylate, surfaces with various features such as hydrophilic/hydrophobic and fluorescent properties were prepared. This was also achieved in a spatially resolved manner. The polymer layers were characterized by contact angle measurements, UV-vis/fluorescence spectroscopy, spectroscopic ellipsometry, and XPS. The thicknesses of the surface grafted polymer layers ranged between 10 and 126 nm.

Repeated Microphase Separation and Heating-free Distillation-like Behavior of Miscible Binary Liquid Mixtures Using Nanoconfined Grafted Polymer Layers.

Nanoconfinement is known to drive phase separation (often denoted as microphase separation) of two highly miscible liquids by subjecting the two liquids to disparate influences. Here, we propose a paradigm shift to this problem: we introduce the idea of "repeatability" in nanoconfinement-driven microphase separation. A drop consisting of two highly miscible liquids (A and B) is made to pass through a nanochannel grafted with a collapsed layer of polymer that is philic to A but phobic to B. Subsequently, a significant number of molecules of liquid A get imbibed into the polymer layer and the polymer layer partially swells, while the molecules of liquid B mostly remain out of the polymeric layer and are carried away, emerging as a drop on the other side of the polymer bilayer. This passage of drop (of liquids A and B) is continued, and each time liquids A and B get separated with liquid A imbibing into the polymer layer and liquid B being carried away with the drop. This scenario, therefore, points to the repeated occurrence of the microphase separation of miscible binary liquid mixtures, enabling the processing of a much larger volume of liquid, given the fact that the presence of a grafted polymer layer continues to provide a dynamically increasing space where liquid A can get localized after being separated from liquid B. We quantify such repeated microphase separation by noting the extent of separation (of liquid A) and extent of recovery (of liquid B) as functions of nanochannel height and number of passes. Interestingly, we establish that this process also leads to a distillation-like behavior (without any heat addition), where the concentration of liquid B (equivalent to the "less volatile" liquid in a standard distillation process) progressively increases inside the drop after its passage through the nanochannel.

19 nm‐Thick Grafted‐To Polymer Brushes onto Optimized Poly(Dopamine)‐Coated Surfaces

AbstractGrafting‐to polymer coatings are typically easy to apply, but the thickness of such coatings is typically limited to a few nanometers, which may hamper applications. This paper presents a grafting‐to coating approach that yields polymer brushes up to an unprecedented thickness of 19 nm. To this aim, an easy‐to‐apply poly(dopamine) (PDA) primer layer is optimized. PDA is an easy‐to‐apply, but highly complex and chemically not well understood primer layer. In this study, PDA is deposited on silicon substrates using several deposition protocols (pH 4–7 in presence of NaIO4, and from Tris solution at pH 8.5). The modified surfaces are characterized using X‐ray photoelectron spectroscopy, spectroscopic ellipsometry, static water contact angle measurements, and atomic force microscopy. Subsequently, block copolymers of poly(glycidyl methacrylate)20‐b‐poly(N‐isopropylacrylamide)n are attached onto the PDA films using a grafting‐to approach. The results indicate that the conditions of PDA deposition and the PDA film thickness strongly influence the stability and grafting efficiency of the block copolymers. PDA films deposited at pH 7 with NaIO4 are stable, and yield the most efficient grafting, with grafted polymer layers as thick as 19 nm. Polymer layers of such thickness are rarely achieved using grafting‐to procedures from solution.

Highly dispersed nanocomposites based on polymer/inorganic hybrids and nickel nanoparticles: the role of the matrix structure in the process of in situ formation

A series of polymer/inorganic hybrids based on silica sol and polyacrylamide (SiO2-g-PAAm) with different number and length of PAAm chains was obtained by radical graft polymerization of acrylamide from the surface of SiO2. The main molecular and structural parameters of the hybrids, such as the chemical composition, average radius and charge of SiO2 particles, the number of grafts per one particle and their molecular weight, the average diameter and hydrodynamic volume of hybrid particles, and the thickness of the PAA layer, were determined. For this, elemental analysis, DTGA, static light scattering, viscometry, potentiometric titration, and TEM were used. The functional properties of hybrids as hydrophilic matrices in the in situ synthesis of nickel nanoparticles by borohydride reduction of metal ions from the Ni(NO3)2·6H20 salt in an aqueous medium have been studied. Using the method of UV-Vis spectroscopy and the developed original approach, the kinetics and efficiency of the formation of NiNPs in hybrid solutions were characterized, depending on the structure and concentration of the hybrid matrices and the concentration of the metal salt. An increase in the rate of accumulation and yield of NiNPs in solutions of all hybrids was found with an increase in salt concentration in the range of 0,010-0,078 kg·m-3, as well as a predominant decrease in the reaction rate with an increase in the concentration of hybrid matrices from 0,5 to 2,0 kg·m-3. It was shown that the structure of the hybrid matrices, determined by the number and length of PAAm chains, as well as the permeability of the grafted polymer layer, was one of the key factors affecting the formation rate and yield of NiNPs. It provided greater or lesser accessibility of the active groups of the "corona" and the inorganic "core" for metal ions and reducing agent molecules. Morphological studies of purified reduction products were carried out by TEM. Based on them, the main structural elements of highly dispersed NiNPs/SiO2-g-PAAm nanocomposites were established – swollen hairy particles of hybrids with small amorphous NiNPs (1,7±0,8 nm) included in the polymer "corona".

Photo- and thermo-responsive extracellular matrix mimicking nano-coatings prepared from poly(N-isopropylacrylamide)-spiropyran copolymer for effective cell sheet harvesting

Poly(N-isopropylacrylamide)-spiropyran (PNIPAAm-SP) copolymers were tethered onto the glass substrate using surface-initiated atom transfer radical polymerization (SI-ATRP). The substrate was previously activated by ultra-violet ozone (UVO) irradiation and the pre-synthesized initiator was immobilized on it. A block of PNIPAAm was grafted onto the glass substrates, followed by a second block of mixed NIPAAm and spiropyran acrylate (SPA). The effects of UVO irradiation time and polymerization time of spiropyran containing block on cell sheet formation and detachment characteristics were evaluated. The photo-responsiveness of SPA was evaluated by ultra-violet visible spectroscopy (UV–vis). The presence and thickness of the grafted polymer layers were evidenced by attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FE-SEM). The results of water contact angle (WCA) analysis showed that the modified surfaces became hydrophilic with decreasing temperature from 37 to 20 °C as well as with light irradiation. L929 mouse fibroblast cell culture results indicated a complete cell sheet formation. By applying temperature or light stimuli, the cell sheets were detached in a trypsin-free procedure.

Solution properties of spherical gold nanoparticles with grafted DNA chains from simulation and theory.

There has been a rapidly growing interest in the use of functionalized Au nanoparticles (NPs) as platforms in multiple applications in medicine and manufacturing. The sensing and targeting characteristics of these NPs, and the realization of precisely organized structures in manufacturing applications using such NPs, depend on the control of their surface functionalization. NP functionalization typically takes the form of polymer grafted layers, and a detailed knowledge of the chemical and structural properties of these layers is required to molecularly engineer the particle characteristics for specific applications. However, the prediction and experimental determination of these properties to enable the rational engineering of these particles is a persistent problem in the development of this class of materials. To address this situation, molecular dynamic simulations were performed based on a previously established coarse-grained single-stranded DNA (ssDNA) model to determine basic solution properties of model ssDNA-grafted NP-layers under a wide range of conditions. In particular, we emphasize the calculation of the hydrodynamic radius for ssDNA-grafted Au NPs as a function of structural parameters such as ssDNA length, NP core size, and surface coverage. We also numerically estimate the radius of gyration and the intrinsic viscosity of these NPs, which in combination with hydrodynamic radius estimates, provide valuable information about the fluctuating structure of the grafted polymer layers. We may then understand the origin of the commonly reported variation in effective NP “size” by different measurement methods, and then exploit this information in connection to material design and characterization in connection with the ever-growing number of applications utilizing polymer-grafted NPs.

UV-Assisted Li+-Catalyzed Radical Grafting Polymerization of Vinyl Ethers: A New Strategy for Creating Hydrolysis-Resistant and Long-Lived Polymer Brushes as a "Smart" Surface Coating.

A facile synthetic route was developed to prepare a surface-grafted brush layer of poly(vinyl ethers) (PVEs) directly by a radical mechanism, with the "naked" Li+ acting as a catalyst. Density functional theory calculations suggested that complexation of naked Li+ to VEs significantly reduced the highest unoccupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap from 5.08 to 0.68 eV, providing a better prospect for electron transfer. The structure, morphology, and surface properties of grafted polymer layers were characterized using attenuated total reflection Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and dynamic water contact angle (DCA). Moreover, ellipsometry data indicated that the thickness of the polymer brushes was in the range of 20-60 nm, which corresponds to the grafting densities of 0.65-1.15 chain/nm2, and DCA decreased from 84.4 to 45.3°. Most importantly, no hydrolysis was observed for the modified surface after 30 days of exposure to phosphate-buffered saline solution, 0.1 mol/L NaOH(eq) and 0.1 mol/L HCl(eq), demonstrating excellent hydrolysis resistance with long service life. In addition, as a proof of concept, the side hydroxyl groups of grafted PVEs provide active sites for efficient fixation of bioactive molecules, e.g., glycosaminoglycan and serum protein.

Flow-Through Macroporous Polymer Monoliths Containing Artificial Catalytic Centers Mimicking Chymotrypsin Active Site

Synthetic catalysts that could compete with enzymes in term of the catalytic efficiency but surpass them in stability have a great potential for the practical application. In this work, we have developed a novel kind of organic catalysts based on flow-through macroporous polymer monoliths containing catalytic centers that mimic the catalytic site of natural enzyme chymotrypsin. It is known that chymotrypsin catalytic center consists of L-serine, L-histidine, and L-aspartic acid and has specificity to C-terminal residues of hydrophobic amino acids (L-phenylalanine, L-tyrosine, and L-tryptophan). In this paper, we have prepared the macroporous polymer monoliths bearing grafted polymer layer on their surface. The last one was synthesized via copolymerization of N-methacryloyl-L-serine, N-methacryloyl-L-histidine, and N-methacryloyl-L-aspartic acid. The spatial orientation of amino acids in the polymer layer, generated on the surface of monolithic framework, was achieved by coordinating amino acid-polymerizable derivatives with cobalt (II) ions without substrate-mimicking template and with its use. The conditions for the preparation of mimic materials were optimized to achieve a mechanically stable system. Catalytic properties of the developed systems were evaluated towards the hydrolysis of ester bond in a low molecular substrate and compared to the results of using chymotrypsin immobilized on the surface of a similar monolithic framework. The effect of flow rate increase and temperature elevation on the hydrolysis efficiency were evaluated for both mimic monolith and column with immobilized enzyme.

Flexible Sers-Active Substrates Based on Silver Nanoparticles Grown in Poly(Acrylic Acid) Grafted to a Polypropylene Film

Flexible SERS substrates were obtained by the photo-activated synthesis of silver nanoparticles in a thin (10–170 nm) layer of poly(acrylic acid) chemically grafted to the surface of a polypropylene fi lm. The plasmonic absorption and the SERS activity of the substrates were studied as a function of the thickness of the grafted layer for a fixed time of nanoparticle synthesis. The results indicate dense three-dimensional packing of plasmonic nanoparticles in the grafted polymer layer. The substrates have a storage-stable and surface-uniform SERS activity.

Towards the description of water adsorption in slit-like nanochannels with grafted molecular brushes. Density functional theory

We have explored a model for adsorption of water into slit-like nanochannels with two walls chemically modified by grafted polymer layers forming brushes. A version of density functional method is used as theoretical tools. The water-like fluid model adopted from the work of Clark et al. [Mol. Phys., 2006, 104, 3561] adequately reproduces the bulk vapour-liquid coexistence envelope. The polymer layer consists of chain molecules in the framework of pearl-necklace model. Each chain molecule is chemically bonded to the pore walls by a single terminating segment. Our principal focus is in the study of the dependence of polymer layer height on grafting density and in the microscopic structure of the interface between adsorbed fluid and brushes. Thermal response of these properties upon adsorption is investigated in detail. The results are of importance to understand shrinking and swelling of the molecular brushes in the nanochannels.

Author Correction: Photoinduced self-initiated graft polymerization of methacrylate monomers on poly(ether ether ketone) substrates and surface parameters for controlling cell adhesion

One of the super engineering plastics, poly(ether ether ketone) (PEEK), was functionalized by photoinduced self-initiated graft polymerization of various methacrylate monomers. Anionic, cationic, zwitterionic, nonionic hydrophilic, and nonionic hydrophobic polymer layers were formed onto PEEK substrates. Physical and chemical surface characterizations of the resultant polymer-grafted PEEK substrates were performed through measurements of their surface free energies and ζ potentials. The values of these parameters varied in the ranges of 39–71 mJ/m2 and −69 to 46 mV, respectively. These parameters reflected the chemical structures of the grafted polymers. To understand the effects of these surface parameters on cell adhesion behavior at the substrate surface, the amount of fibronectin adsorbed on the plasma-contacting surface and the density of fibroblast cells adhered to the surface were determined. The adherent cell density showed a good linear correlation with the amount of fibronectin adsorbed on the plasma-contacting surface. The polymer surface with zero ζ potential showed a lower adsorbed fibronectin density. Both anionic and cationic polymer layers had increased cell adhesion compared with that on the original PEEK substrate, whereas the zwitterionic polymer layers significantly prevented cell adhesion. In conclusion, grafting zwitterionic polymers onto a PEEK substrate is anticipated to be useful in the development of a biomedical PEEK substrate. To obtain functionalization of super-engineering plastic, poly(ether ether ketone) (PEEK) substrate, photoinduced self-initiated graft polymerization of several kinds of functional methacrylate was carried out. Graft polymerization proceeded well, and 50–250 nm in thickness graft polymer layers were generated on the PEEK substrate. Surface characteristics such as surface free energy and surface ζ potential on the polymer-grafted PEEK substrate were corresponded to the chemical structure of the graft polymers. Cell attachment on the polymer-grafted PEEK substrate was examined. The surface ζ potentials of the polymer-grafted PEEK substrates governed the cell adhesion density.

Spontaneous Degrafting of Weak and Strong Polycationic Brushes in Aqueous Buffer Solutions

Polymers grafted to substrates have traditionally been considered stable because of the covalent bonds that hold the polymers attached to the substrate. However, several recent reports have indicated that grafted polymers may detach from substrates under specific conditions. In this work, we report on a systematic study of polymer degrafting involving polycationic brushes with different degrees of quaternization (DQ, mol %), which have been incubated in three different buffer solutions (pH 4, 7.4, and 9) with the same ionic strength of 0.05 M. We have varied the molecular weight (MW) and grafting density (σ) of the polymer brushes using a combinatorial setup to examine the effect of MW, σ, and DQ on polymer degrafting. Furthermore, we explored the effect of the bonding environment at the base of the initiator (mono- vs. tri-functional) of the grafted polymer layer at the substrate on the overall stability of polymer brushes on the substrate. The two major findings in this paper are (1) degrafting of polyc...

Spatially Controlled Surface Modification of Porous Silicon for Sustained Drug Delivery Applications

A new and facile approach to selectively functionalize the internal and external surfaces of porous silicon (pSi) for drug delivery applications is reported. To provide a surface that is suitable for sustained drug release of the hydrophobic cancer chemotherapy drug camptothecin (CPT), the internal surfaces of pSi films were first modified with 1-dodecene. To further modify the external surface of the pSi samples, an interlayer was applied by silanization with (3-aminopropyl)triethoxysilane (APTES) following air plasma treatment. In addition, copolymers of N-(2-hydroxypropyl) acrylamide (HPAm) and N-benzophenone acrylamide (BPAm) were grafted onto the external pSi surfaces by spin-coating and UV crosslinking. Each modification step was verified using attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, water contact angle (WCA) measurements, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). In order to confirm that the air plasma treatment and silanization step only occurred on the top surface of pSi samples, confocal microscopy was employed after fluorescein isothiocyanate (FITC) conjugation. Drug release studies carried out over 17 h in PBS demonstrated that the modified pSi reservoirs released CPT continuously, while showing excellent stability. Furthermore, protein adsorption and cell attachment studies demonstrated the ability of the graft polymer layer to reduce both significantly. In combination with the biocompatible pSi substrate material, the facile modification strategy described in this study provides access to new multifunctional drug delivery systems (DDS) for applications in cancer therapy.

Covalent hyperbranched porous carbon nanospheres as a polymeric stationary phase for ion chromatography.

This work presents a method for covalent quaternization of porous carbon nanospheres (PCNSs) and their application as anion exchanging stationary phase for ion chromatography. The PCNSs were covalently quaternized via the dehydration condensation between surface carboxyl groups and polyethyleneimine. This was followed by a repeated epoxy-amine addition reaction with ethylene glycol diglycidyl ether. As a result, surface methylamino groups are formed. The electrostatic interaction between quaternized PCNSs and sulfonated poly(polystyrene-co-divinylbenzene) resulted in the formation of an agglomerated stationary phase. The capacities (41.5-90.2 μequiv) and pressures (540-1150psi) of column packed with novel phases (100 × 4.0mm i.d.) were further increased with grafted polymer layer counts (2-5). Common inorganic anions, small organic acids and saccharides were rapidly separated on the new phases. The column efficiencies for seven inorganic anions ranged from 38,400 to 13,200 plates m-1. Through 8days of flushing test, the RSD values for retention time and efficiencies varied from 0.56% to 1.32%, and from 0.34% to 0.74%, respectively. Graphical abstract Schematic presentation of the covalent modification of porous carbon nanospheres (PCNSs) with hyperbranched quaternized polymers via the amidation and epoxy-amine addition reaction was depicted. Functionalized PCNSs were further applied as agglomerated materials of polymeric stationary phase for ion chromatography (IC).

Tethered hydrophilic polymers layers on a polyamide surface

ABSTRACTModification of the hydrophilicity of a polyamide surface with tethered poly(acrylic acid), poly(vinylsulfonic acid), or poly(2‐hydroxyethyl methacrylate) was accomplished by atmospheric pressure plasma surface activation, followed by free radical graft polymerization with vinyl monomers. Surface activation was more effective with He relative to H2 plasma leading to thicker grafted polymer layers of higher surface density. The thickness and surface roughness of the tethered layers were up to ~9.7 nm and ~3.6 nm, respectively. Upon surface modification, the free energy of hydration decreased (25–51%) and the polar component of the surface energy increased (by a factor of 3.0–6.5); the above indicating increased hydrophilicity of the modified surface which also correlated with the tethered polymer layer thickness and surface roughness. The present study suggests that surface hydrophilicity tuning is feasible through the combination of surface chemistry, plasma surface treatment, and graft polymerization conditions. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46843.

Hydration of Spherical PEO-Grafted Gold Nanoparticles: Curvature and Grafting Density Effect

Nanoparticle modification by water-soluble polymers, such as poly(ethylene oxide) (PEO), relies on polymer hydration to ensure nanoparticle solubility, dispersion, and protection from undesirable interactions. The state of polymer hydration in grafted polymer layers is not easily assessible experimentally but can be ascertained from computer simulations. Using atomistic molecular dynamics simulations, we studied the equilibrium and dynamic properties of spherical PEO brushes grafted to gold nanoparticles of different radii (1, 2, and 3 nm). We obtained the volume fraction of PEO (Φ(r)) as a function of radial distance r (counted from micelle core center) which is found to follow the Daoud–Cotton model, Φ(r) ∼ r–4/3, except for low grafting density when PEO adsorption onto the gold surface is observed, in agreement with experimental observations. With an increase of grafting density σ (up to 4.17 nm–2), the PEO chains become more stretched and oriented along the radial direction leading to an increase of t...

Polymer-Grafted Nanoparticle Membranes with Controllable Free Volume

Polymer-based membranes play a key role in several industrially important gas separation technologies, e.g., removing CO2 from natural gas, with enormous economic and environmental impact. Here, we develop a novel hybrid membrane construct comprised entirely of nanoparticles grafted with polymers. These membranes are shown to have broadly tunable separation performance through variations in graft density and chain length. Computer simulations show that the optimal NP packing forces the grafted polymer layer to distort, yielding regions of measurably lower polymer density. Multiple experimental probes confirm that these materials have the predicted increase in “polymer free volume”, which explains their improved separation performance. These polymer-grafted NP materials thus represent a new template for rationally designing membranes with desirable separation abilities coupled with improved aging characteristics in the glassy state and enhanced mechanical behavior.

Preparation of molecule imprinted membrane of single enantiomer of amino acid with an innovative strategy and study on its chiral recognition and resolution properties

BACKGROUND The molecularly imprinted membranes (MIMs) with high performance are very valuable in the chiral resolution of amino acids. In this work, a novel molecularly imprinted membrane of the single enantiomer of amino acids with graft type was successfully prepared by using an advanced surface imprinting technique. The aminated microfiltration membrane of polysulfone, AMPSF membrane, was first prepared, and so a surface-initiating system of -NH2/S2O8- was constituted. In an aqueous solution, the molecules of dimethylaminoethyl methacrylate (DMAEMA) as functional monomer were combined around L-glutamic acid (L-Glu) as template by right of electrostatic interaction and hydrogen bonding. By initiating of -NH2/S2O8- system, DMAEMA and the crosslinking agent N,N′-Methylenebisacrylamide (MBA) produced graft/crosslinking-polymerization on the surface of AMPSF membrane, whereas L-Glue molecules were wrapped within the grafted polymer layer, obtaining grafting type L-Glue molecule-imprinted membrane (L-Glue-MIM). The ability of the chiral recognition and enantioseparation of L-Glue-MIM were examined. RESULTS The experimental results show that L-Glue-MIM possesses specific chiral recognition selectivity and excellent enantioseparation ability. In the permeation experiment, L-Glue molecules in the raceme solution can smoothly pass across L-Glue-MIM, but D-Glue molecules are seriously blocked. As a result, Glu raceme solution is well separated, and the optical purity (ee value) of the penetrating fluid gets up to 82%. CONCLUSION Grafting type molecularly imprinted membrane of the single enantiomer of amino acids was successfully prepared by using an innovative and advanced surface-imprinting technique of “synchronously graft-polymerizing and molecule imprinting”, and it supplies a newer route to prepare imprinted membrane with high performance for chiral resolution of amino acids and other chiral drugs. Such study is reported for the first time. © 2017 Society of Chemical Industry