Model Polymer Surface Research Articles

Sulfobetaine Methacrylate Polymers of Unconventional Polyzwitterion Architecture and Their Antifouling Properties

Combining high hydrophilicity with charge neutrality, polyzwitterions are intensely explored for their high biocompatibility and low-fouling properties. Recent reports indicated that in addition to charge neutrality, the zwitterion's segmental dipole orientation is an important factor for interacting with the environment. Accordingly, a series of polysulfobetaines with a novel architecture was designed, in which the cationic and anionic groups of the zwitterionic moiety are placed at equal distances from the backbone. They were investigated by in vitro biofouling assays, covering proteins of different charges and model marine organisms. All polyzwitterion coatings reduced the fouling effectively compared to model polymer surfaces of poly(butyl methacrylate), with a nearly equally good performance as the reference polybetaine poly(3-(N-(2-(methacryloyloxy)ethyl)-N,N-dimethylammonio)propanesulfonate). The specific fouling resistance depended on the detailed chemical structure of the polyzwitterions. Still, while clearly affecting the performance, the precise dipole orientation of the sulfobetaine group in the polyzwitterions seems overall to be only of secondary importance for their antifouling behavior.

Mineralization of plasma treated polymer surfaces from super-saturated simulated body fluids

This study aims to obtain mechanistic understanding of the formation and development of biomedical CaP coating on a model polymer surface of plasma treated polycaprolactone (PCL). Oxygen plasma treatment changed the surface morphology at nanometre scale and introduced negatively charged groups to PCL surface. Nucleation of CaP on the treated PCL surface occurred via two modes of growth, Volmer–Weber and Stranski–Krastanov. EDX and FTIR analysis suggested that the coating progressed from compositions with low Ca/P ratios and solubility to the phases of higher ratios and stability. The results also indicated that CaP clusters formed through Volmer–Weber mode were rich in the CaP phases of the higher Ca/P ratios. This study thus provided mechanistic insights into the coating process of CaP from solution onto functionalized surfaces which could be useful in designing coatings to suit different requirements.

Predicting drug loading in PLA-PEG nanoparticles

Polymer nanoparticles present advantageous physical and biopharmaceutical properties as drug delivery systems compared to conventional liquid formulations. Active pharmaceutical ingredients (APIs) are often hydrophobic, thus not soluble in conventional liquid delivery. Encapsulating the drugs in polymer nanoparticles can improve their pharmacological and bio-distribution properties, preventing rapid clearance from the bloodstream. Such nanoparticles are commonly made of non-toxic amphiphilic self-assembling block copolymers where the core (poly-[d,l-lactic acid] or PLA) serves as a reservoir for the API and the external part (Poly-(Ethylene-Glycol) or PEG) serves as a stealth corona to avoid capture by macrophage. The present study aims to predict the drug affinity for PLA-PEG nanoparticles and their effective drug loading using in silico tools in order to virtually screen potential drugs for non-covalent encapsulation applications. To that end, different simulation methods such as molecular dynamics and Monte-Carlo have been used to estimate the binding of actives on model polymer surfaces. Initially, the methods and models are validated against a series of pigments molecules for which experimental data exist. The drug affinity for the core of the nanoparticles is estimated using a Monte-Carlo “docking” method. Drug miscibility in the polymer matrix, using the Hildebrand solubility parameter (δ), and the solvation free energy of the drug in the PLA polymer model is then estimated. Finally, existing published ALogP quantitative structure-property relationships (QSPR) are compared to this method.Our results demonstrate that adsorption energies modelled by docking atomistic simulations on PLA surfaces correlate well with experimental drug loadings, whereas simpler approaches based on Hildebrand solubility parameters and Flory-Huggins interaction parameters do not. More complex molecular dynamics techniques which use estimation of the solvation free energies both in PLA and in water led to satisfactory predictive models. In addition, experimental drug loadings and Log P are found to correlate well.This work can be used to improve the understanding of drug-polymer interactions, a key component to designing better delivery systems.

A nanoscale study of the adhesive contact

Abstract Analysis of adhesive and mechanical properties of model polymer surfaces can be achieved with an Atomic-Force Microscope (AFM), in contact mode. The purpose of this study is to dissociate the different contributions (chemical and mechanical) included in an AFM force-distance curve in order to establish relationships between interfacial tip-polymer interactions and surface viscoelastic properties of the polymer. Surface force measurements are, in a first step, done on chemically modified silicon substrates (grafted with hydroxyl, amine, methyl and ester functional groups). In order to investigate the effects of mechanical or viscoelastic contributions, force measurements on model polydimethylsiloxane (PDMS) networks, whose surfaces are chemically modified with the same functional groups as for silicon substrates, were achieved. New relationships are proposed between the local adhesion force and both the dissipation energy in the tip-polymer contact and the surface properties of the materials (thermodynamic work of adhesion). Moreover the dissipation function is related to Mc, the mass between crosslinks of the polymer network. To cite this article: M. Brogly et al., C. R. Chimie 9 (2006).

The delamination of polymeric coatings from steel. Part 1: Calibration of the Kelvinprobe and basic delamination mechanism

In the first part of this study are presented the theory and the experimental techniques which are necessary to investigate the delamination of model coatings on steel. It is shown that the electrochemical reactions taking place at the substrate/electrolyte and substrate/polymer interfaces are responsible for delamination. Due to the fact that the electrochemical reactions are accompanied by changes in the corrosion potential, it is possible to identify and follow the delamination by measuring the corrosion potential as a function of time and local position. Furthermore, it is demonstrated that the Volta-potential difference between a reference metal and the model polymer surface is determined by the corrosion potential, whereas the influence of the Donnan-potential is small and constant. By combining several experimental techniques, like the Scanning Kelvinprobe, Auger electron spectroscopy and mechanical de-adhesion tests, the delamination process is studied in detail and a model is presented, which is based on the existence of a galvanic element at the substrate/polymer interface. The uncoated iron is the local anode, where the iron dissolution predominates, whereas the delaminated part represents the local cathode and, within this area, only the oxygen reduction takes place. The second and third part of this paper deal with an experimental verification of this model.

Analytic theory of surface segregation in compressible polymer blends

We present an analytical theory for the competing influences of polymer–surface and polymer–polymer interactions, density and composition variations, and blend asymmetries on the surface profiles of a multicomponent polymer blend near an interacting, impenetrable interface. The theory is explicitly applied in the limit of small continuum model polymer–surface interaction parameters, a limit which still enables treating all qualitative behaviors of polymers that individually tend either to aggregate toward or to segregate from the surface. The formulation is based on an analytic combined self-consistent field-density functional theory for inhomogeneous polymer systems. The theory describes the compressible polymer system with a generic Gaussian chain–random mixing type model, which in the bulk phase reproduces a Sanchez–Lacomb-type description of the bulk thermodynamics. The analytic expressions for the density profiles, surface excesses, surface densities, and surface correlation lengths are all presented explicitly for binary compressible systems, but we note how to make the trivial extension to more components. The surface excess and surface correlation length are shown to diverge along the bulk phase spinodal, in rough accord with the increases found in recent experiments by Genzer and Composto. The relation between the continuum model interaction parameters and microscopic (e.g., lattice-model-type) interaction parameters is used to understand recent observations of a surface free energy that displays a higher than quadratic dependence on the surface composition and of the strong surface segregation exhibited by isotopic polymer blends.

Deposition and properties of hydrophilic films prepared by plasma polymerization of Ar/ n-hexane/H 2O

Plasma polymer films were prepared using a direct current (dc) discharge operated in a working gas mixture Ar/ n-hexane/H 2O. Langmuir probe measurements were used to characterize the discharge conditions. The plasma polymer films were deposited on a plasma polymer of Ar/ n-hexane that served as a model polymer surface to be modified for wettability. This was found to increase (as observed by contact angle measurement using an air bubble method) with the increase of water vapour concentration in the Ar/ n-hexane/H 2O working gas mixture. Deposition rate was determined using a quartz crystal microbalance. The rate became negative, i.e. etching (ablation) of model polymer surface took place at low n-hexane concentrations. Plasma polymer film structure and composition were studied by FTIR and ESCA and showed an increase of polar groups in a film when water vapour increased in a working gas mixture during deposition. SEM micrographs appear to confirm that films are predominantly structureless.

Wetting of crystalline polymer surfaces: A molecular dynamics simulation

Molecular dynamics has been used to study the wetting of model polymer surfaces, the crystal surfaces of polyethylene (PE), poly(tetrafluoroethylene) (PTFE), and poly(ethylene terephthalate) (PET) by water and methylene iodide. In the simulation a liquid droplet is placed on a model surface and constant temperature, rigid body molecular dynamics is carried out while the model surface is kept fixed. A generally defined microscopic contact angle between a liquid droplet and a solid surface is quantitatively calculated from the volume of the droplet and the interfacial area between the droplet and the surface. The simulation results agree with the trend in experimental data for both water and methylene iodide. The shape of the droplets on the surface is analyzed and no obvious anisotropy of the droplets is seen in the surface plane, even though the crystal surfaces are highly oriented. The surface free energies of the model polymer surfaces are estimated from their contact angles with the two different liquid droplets.

Study of the interactions of model polymer surface with cold plasmas. II. Degradation rate versus pressure and gas flow rate

AbstractThis work deals with the influence of pressure, gas flow rate, and gas mixture on the etching rates of polymer model molecules such as hexatriacontane (C36H74) and octadecyl octadecanoate (OOD) treated in an oxygen or argon plasma. Mass spectrometry and optical emission spectroscopy have been used to monitor the formation and evolution of the fragments coming from chain breaking in terms of their concentration and emission intensity, respectively. It was demonstrated that pressure and gas flow rate are two important parameters in the interaction of cold plasmas and of polymer surfaces. The results obtained can be explained by combined effects such as electron energy and its density, residence time, “quenching effect,” as well as chemical reactions. © 1992 John Wiley & Sons, Inc.

A computer simulation method for studying the ablation of polymer surfaces by ultraviolet laser radiation

A computer algorithm designed to simulate the ablation of polymer surfaces by ultraviolet laser radiation is presented. The method is based on a synthesis of the dressed state picture of radiation-matter interactions and a semiclassical ‘‘surface hopping’’ technique. A primary feature of the algorithm is that the intrinsically quantum mechanical process of ultraviolet photon absorption can be simulated while classical molecular dynamics techniques are simultaneously employed to integrate the equations of motion for the nuclear positions and momenta of the polymers. Illustrative results obtained from the algorithm are presented for the ablation of a model polymer surface. Quite different energy redistribution behavior is observed for electronic excitations to a repulsive electronic potential energy surface versus excitations to surfaces that have the possibility of bound vibrational motion. These results suggest that the postulated ‘‘direct’’ photochemical (bond-breaking) ablation mechanism for 193 nm lasers may be dynamically distinct from thermal ablation processes that result from intense local heating of the material by longer wavelength lasers.

Calculation of solvation interaction energies for protein adsorption on polymer surfaces

Of the interactions that govern protein adsorption on polymer surfaces, solvation interactions (repulsive hydration and attractive hydrophobic interactions) are thought to be among the most important. The solvation interactions in protein adsorption, however, have not been dealt with in theoretical calculation of the adsorption energy owing to the difficulties in modelling such interactions. We have evaluated the solvation interaction energies using the fragment constant method of calculating the partition coefficients of amino acids. The fundamental assumption of this approach is that the partition coefficients of amino acids between water and organic solvent phases are related to the free energies of transfer from bulk water to the polymer surface. The X-ray crystallographic protein structures of lysozyme, trypsin, immunoglobulin Fab, and hemoglobin from the Brookhaven Protein Data Bank were used. The model polymer surfaces were polystyrene, polypropylene, polyethylene, poly(hydroxyethyl methacrylate) [poly(HEMA)], and poly(vinyl alcohol). All possible adsorption orientations of the proteins were simulated to study the effect of protein orientation on the solvation interactions. Protein adsorption on either hydrophobic or hydrophilic polymer surfaces was examined by considering the sum of solvation and other interaction energies. The results showed that the contribution of the solvation interaction to the total protein adsorption energy was significant. The average solvation interaction energy ranged from -259.1 to -74.1 kJ/mol for the four proteins on the hydrophobic polymer surfaces, such as polystyrene, polypropylene, and polyethylene. On the other hand, the average solvation interaction energies on hydrophilic surfaces such as poly(HEMA) and poly(vinyl alcohol) were larger than zero. This indicates that repulsive hydration interactions are in effect for protein adsorption on hydrophilic polymer surfaces. The total interaction energies of the proteins with hydrophobic surfaces were always lower than those with more hydrophilic surfaces. This trend is in agreement with the experimental observations in the literature. This study suggests that consideration of the solvation interaction energies is necessary for accurate calculation of the protein adsorption energies.

Some model surfaces made by RF plasma aimed for the study of biocompatibility

Some model polymer surfaces were created by plasma polymerization on silicon substrate surfaces for biocompatibility research. Six model surfaces which were different in respect to functional groups, hydrophobicity or surface mobility were investigated. Surfaces were characterized by ellipsometry, electron spectroscopy for chemical analysis (ESCA) and contact angle measurements. It was demonstrated that the ratio of the pressures after ignition and before ignition was almost linearly related to the increase of refractive index of the polymer films, irrespective of the monomer used. Adsorption of plasma proteins on different surfaces were different.

Infrared laser-induced chaos and conformational disorder in a model polymer crystal: Melting vs ablation

Molecular dynamics-based computer simulations are presented for the interaction of one and two infrared (IR) laser beams with a model polymer surface. When a single laser beam system is studied over a wide range of intensities, only melting of the polymer, or melting followed by bond dissociation, is observed for up to 100 picoseconds. In contrast, the two-laser simulation results exhibit a marked difference in the energy absorption behavior of the irradiated polymer which, in turn, results in multiple bond dissociations. The results for the one- and two-laser cases studied can be divided into four different classes of physical behavior: (a) the polymer remains in the solid state; (b) the polymer crystal melts; (c) the polymer ablates, but with significant melting (charring); or (d) the polymer ablates with minimal melting. Damage to the model polymer crystal from absorption of energy from either one or two lasers occurs through a mechanism that involves the competition between the absorption of energy and internal energy redistribution. The rate of energy loss from the absorption site(s) relative to the rate of absorption of energy from the radiation field determines rather the polymer melts or ablates (low absorption rates lead to melting or no change and high rates lead to ablation). A sufficiently large rate of energy absorption is only obtainable through the use of two lasers. Two lasers also significantly decrease the total laser intensity required to cause polymer crystal melting. The differences between the one- and two-laser cases are studied by adapting novel signal/subspace techniques to analyze the dynamical changes in the mode spectrum of the polymer as it melts.

Interaction of metals with model polymer surfaces: Core level photoemission studies

Core level photoemission studies have been performed on the in situ interactions of Cr and Cu on two model systems which are related to the pyromellitic dianhydride (PMDA) and oxydianiline (ODA) parts of PMDA–ODA polymide. The model compound which is related to the PMDA constituent is N,N′-diphenylpyromellitimide and the model polymer which is related to the ODA constituent is poly(2,6-dimethylphenylene oxide) (PMPO). Cr evaporation on the PMDA model compound changes the PMDA-related features of the C 1s spectrum, whereas Cu evaporation has comparatively little effect on the PMDA-related features. The results are consistent with Cr bonding with the PMDA part of the related model compound, or fracturing of the carbonyl bonds and/or other bonds contained in the PMDA structure. Cr evaporation on PMPO results in a new peak at lower binding energy without appreciable changes in the shape of the original bands. Cu predominantly affects the peak in the C 1s spectrum of PMPO which originates from carbons in ether linkages.