Tethered Polymer Chains Research Articles

Densely Packed Tethered Polymer Nanoislands: A Simulation Study.

COordinated Responsive Arrays of Surface-Linked polymer islands (CORALS) allow for the creation of molecular surfaces with novel and switchable properties. Critical components of CORALs are the uniformly distributed islands of densely grafted polymer chains (nanoislands) separated by regions of bare surface. The grafting footprint and separation distances of nanoislands are comparable to that of the constituent polymer chains themselves. Herein, we characterize the structural features of the nanoislands and semiflexible polymers within to better understand this critical constituent of CORALs. We observe different characteristics of grafted semiflexible polymers depending on the polymer island’s size and distance from the center of the island. Specifically, the characteristics of the chains at the island periphery are similar to isolated tethered polymer chains (full flexible chains), while chains in the center of the island experience the neighbor effect such as chains in the classic polymer brush. Chains close to the edge of the islands exhibit unique structural features between these two regimes. These results can be used in the rational design of CORALs with specific interfacial characteristics and predictable responses to external stimuli. It is hoped that this the discussion of the different morphologies of the polymers as a function of distance from the edge of the polymer will find applications in a wide variety of systems.

Tailoring adhesion characteristics of poly(L-lactic acid)/graphene nanocomposites by end-grafted polymer chains: An atomic-level study

Tethered polymer chains are known to have a great potential in tailoring interfaces and promoting interfacial adhesion in polymer-based nanocomposites. In this context, this paper is aimed to explore the adhesion characteristics of poly(L-lactic acid)/graphene (GR) samples having a modified interface, where the PLLA chains at different grafting densities are attached on the GR surface. This is achieved through conducting pull-off tests employing all-atom molecular dynamics simulations. Monitoring the evolution of interfacial energy and pull-off force combined with the microstructural studies indicates that there exists an optimum coverage ratio (i.e., 0.002), beyond which the interfacial interactions would be disrupted. This is supported by the trend observed for variations of the adhesion characteristic such as interfacial normal strength and work of adhesion with the grafting density. To deeply analyze this issue, we further proceed to design composite systems of different architectures referred to as mushroom and brush-like conformations. It is demonstrated that the most effective molecular morphology is the one providing the highest degree of polymer chains entanglement. Also, failed attempts to reinforce adhesion by increasing the grafting density suggest that to have a beneficial chain arrangement, one should control several factors such as diffusion conditions, manufacturing methods, and grafting techniques.

Polymer tethered graphene oxide influences miscibility and cooperative relaxation in LCST blends

The miscibility of a classical lower critical solution temperature (LCST) system; PMMA/SAN was probed by different rheological fingerprints such as isochronal temperature ramps, and isothermal frequency sweeps, in presence of graphene oxide (GO) and PMMA tethered GO. The chain length of the grafted polymer was varied to study its effect on miscibility, volume cooperativity, entanglement density and localization in the blends. The PMMA tethered GO alters the chain dynamics both at local and cooperative length scale through entropic and enthalpic interactions. It was perceived that the thermodynamic miscibility, cooperative relaxations and concentration fluctuation in PMMA/SAN blends are controlled by the spatial distribution of GO in the blend. By varying the chain length, we were able to understand that shorter tethered chains lead to early phase separation whereas the tethered chain length similar to that of the host matrix delays phase separation. Interestingly, irrespective of the length of the tethered polymer chain, the grafted GO sheets were not localized in the thermodynamically preferred phase (here PMMA). These findings are of great importance to further help us understand the theories and simulations which pertain to chain dynamics of PMMA/SAN blends containing polymer-tethered nanoparticles with large specific surface area like GO.

Computer simulation study on the self-assembly of tethered nanoparticles with tunable shapes.

We built a tethered nanoparticle (TNP) model that is composed of a nanoparticle with a hydrophobic tethered polymer chain. The shape of the nanoparticle can be tuned from a pure rigid cube to a soft sphere, mimicking the increase of grafting density on the nanocube surfaces. With this model, we study the self-assembly of TNPs in dilute solution using a dissipative particle dynamics simulation technique, and especially focus on the influence of particle shape, tethered chain length, and grafting density on the self-assembly structures. Some intriguing aggregates such as spherical micelles, pearl-necklace-like structures, cubic columnar structures, handshake structures, core–shell–corona micelles, and four-patch micelles have been observed when varying the interactions between cubes and solvents and the lengths of tethered chain. Modifying the nanocube surface with some hydrophilic grafted chains helps the TNPs form small micelles. Increased steric repulsion due to chain overlapping at larger grafting densities results in shape transformation of the nanoparticle from a rigid cube to a soft sphere. In these cases, the self-assembled structures are characterized by the packing of nanoparticles on the micelle surface, and the typical packing mode turns from rectangular (typical for cubes) to hexagonal (typical for spheres).

Controlling the Surface Properties of Binary Polymer Brush-Coated Colloids via Targeted Nanoparticles.

This paper explores a novel mechanism for controlling the surface properties of polymer-coated colloids using targeted ("sticky") nanoparticles which attract monomers of certain polymer species. In our study, colloids are coated by two types of tethered polymer chains having different chemical properties. Attraction of nanoparticles to the monomers of one polymer type causes these polymer chains to contract toward the grafting surface, rendering the other type more exposed to the environment. Thus, the effective surface properties of the colloid are dominated by the intended polymer type. We use coarse-grained molecular dynamics (CGMD) simulation to demonstrate that introducing nanoparticles which interact preferentially with certain types of polymers makes it possible to switch between different surface properties of the colloid. This mechanism can in principle be exploited in drug delivery systems and self-assembly applications.

Cellulose Nanocrystals with Tethered Polymer Chains: Chemically Patchy versus Uniform Decoration

The site-specific surface modification of colloidal substrates, yielding "patchy" nanoparticles, is a rapidly expanding area of research as a result of the new complex structural hierarchies that are becoming accessible to chemists and materials scientists through colloidal self-assembly. The inherent directionality of cellulose chains, which feature a nonreducing and a reducing end, within individual cellulose nanocrystals (CNCs) renders them an interesting experimental platform for the synthesis of asymmetric nanorods with end-tethered polymer chains. Here, we present water-tolerant reaction pathways toward patchy and uniformly modified CNC hybrids based on atom transfer radical polymerization (ATRP) and initiators that were linked to the CNCs with carbodiimide-mediated coupling and Fischer esterification, respectively. Various monomers, including N-isopropylacrylamide (NIPAM), [2-(methacryloyloxy)ethyl]trimethylammonium chloride (METAC), and sodium 4-vinylbenzenesulfonate (4-SS), were polymerized from both types of initiator-modified CNCs, yielding chemically patchy and uniform CNC hybrids, via surface-initiated ATRP (SI-ATRP). Interestingly, the stereochemistry of tethered PNIPAM was affected by the precise location of ATRP initiating sites, as evidenced by 1H NMR and circular dichroism (CD) spectroscopy. This effect may be related to the inherent right-handed chirality of CNCs. CNC/PMETAC hybrids were labeled with gold nanoparticles (AuNPs) in order to visualize the precise location of polymer tethers via cryo-electron microscopy. In some instances, the AuNPs were indeed concentrated at the end groups of the patchy CNC hybrids.

Molecular Origins of Temperature-Induced Jamming in Self-Suspended Hairy Nanoparticles

Suspensions of solvent-less, polymer-grafted nanoparticles have previously been reported to exhibit enhanced elasticity, glassy dynamics, and jamming as temperature is increased. This so-called thermal jamming behavior is not predicted by current models for soft glassy materials and is opposite to what is normally observed for polymer melts. Here we report results from a detailed study of structural, dynamic, and rheological transitions in solvent-less silica–poly(ethylene glycol) methyl ether (SiO2–PEGME) hybrid particles aimed at understanding the molecular origins of the phenomenon. We find that interdigitated PEGME corona chains enforce coupling between SiO2 cores analogous to cross-links in associating polymer networks leading to elastic behavior at low strains and small deformation rates. Pullout and slippage of interdigitated corona chains is thought to produce yielding of the materials in nonlinear shear flow and stretched exponential relaxation following small amplitude step shear. We show with the help of small-angle X-ray scattering, density functional theoretical calculations, and a constitutive model previously reported for deformation and flow of physically associating polymer networks, that thermal jamming of solvent-less polymer-grafted nanoparticles originates from enhanced cross-linking of the cores produced by increased stretching and interpenetration of particle-tethered polymer molecules to satisfy the space-filling constraint on tethered polymer chains.

Nanoscopic Structural Investigation of Physically Cross-Linked Nanogels Formed from Self-Associating Polymers.

The detailed structure of a nanogel formed by self-association of cholesterol-bearing pullulans (CHPs) was determined by contrast variation small-angle neutron scattering. The decomposition of scattering intensities into partial scattering functions of each CHP nanogel component, i.e., pullulan, cholesterol, and the cross-term between the pullulan and the cholesterol, allows us to investigate the internal structure of the nanogel. The effective spherical radius of the skeleton formed by pullulan chains was found to be 8.1 ± 0.3 nm. In the CHP nanogel, there are about 19 cross-linking points where a cross-linking point is formed by aggregation of trimer cholesterol molecules, and the spatially inhomogeneous distribution of the cross-linking points in the nanogel can be represented by the mass fractal dimension of 2.6. The average radius of gyration of the partial chains can also be determined to be 1.7 ± 0.1 nm by analyzing the extracted cross-correlation between the cross-linker and the tethered polymer chain quantitatively, and the size agrees with the value assuming random distribution of the cross-linkers on the chains. As the result, the complex structure of the nanogels is coherently revealed at the nanoscopic level.

Preparation of ZnO hybrid nanoparticles by ATRP

Zinc oxide (ZnO) is a wide bandgap semiconductor material that has attracted widespread interest as particle filler in polymer nanocomposite materials. However, its applications have been hindered by the limited dispersibility and surface-modification techniques. Herein, three distinct approaches for the synthesis of polymer-tethered ZnO hybrid materials are compared in terms of uniformity and yield of the particle-brush product: “grafting-from”, “grafting-onto”, and “grafted-copolymer template” methods. In the “grafting-from” method, pristine ZnO nanoparticles (NP) were first functionalized with atom transfer radical polymerization (ATRP) initiators followed by grafting-from process to form poly(methyl methacrylate) (PMMA) or poly(styrene-co-acrylonitrile) (PSAN) tethered polymer chains. In the “grafting-onto” method, PMMA-b-PAA (poly[acrylic acid]) and PSAN-b-PAA diblock copolymers were prepared and attached onto the surface of ZnO NPs using sonication bath. For the “grafted-copolymer template” method, PSAN-b-PtBA-Br (poly[tert-butyl acrylate]-Br) macroinitiators were crosslinked with divinylbenzene (DVB) to form PSAN-b-PtBA-PDVB core-shell star polymers. After hydrolysis to form PSAN-b-PAA-PDVB star polymers, the functional stars were used as polymer templates for the synthesis of ZnO NPs within the PAA-core of the stars. Core-shell molecular bottlebrushes with PAA-b-PS block-copolymer side chains were also used as anisotropic analogues of star template to prepared worm-like ZnO particles. Several ZnO precursors, zinc nitrite, zinc 2-ethylhexanoate, and zinc acetate were evaluated as precursors of ZnO. Conditions were identified that enable the synthesis of polymer-tethered ZnO with excellent size uniformity and dispersion characteristics using the star-template method.

Interactions, Structure, and Dynamics of Polymer-Tethered Nanoparticle Blends.

We report on the structure, jamming, and dynamics of blends of self-suspended hairy silica nanoparticles grafted with poly(ethylene glycol) (PEG) and poly(methyl methacrylate) (PMMA). We find that favorable enthalpic attraction between tethered PEG and PMMA chains augment previously reported entropic attractions between tethered polymer chains in self-suspended suspensions to enhance particle-particle correlations, increase jamming, and slow down chain dynamics. As with their single-component counterparts, the hairy SiO2-PEG/SiO2-PMMA nanoparticle blends exhibit soft glassy rheological behavior and both the energy dissipated at yielding and the plateau elastic modulus display strong maxima in the symmetric case. A comparison of the small angle X-ray scattering (SAXS) measurements with theoretical analysis from density functional theory (DFT) reveals that the addition of SiO2-PMMA to a self-suspended SiO2-PEG suspension initially leads to a higher degree of stretching of the corona chains, which produces stronger interdigitation of the tethered chains, enhanced jamming, and slower polymer relaxation than observed in the single-component materials. By means of an analysis of the heat of mixing released upon blending tethered and untethered PEG and PMMA chains, we find that the strong enthalpic attraction between the grafted polymer chains enhances entropic attractive forces produced by the space-filling constraint on tethered ligands in self-suspended suspensions to produce entangled-polymer-like physical properties in polymers with molecular weights below the thresholds normally associated with the transition to an entangled state.

Physical aging and glass transition of hairy nanoparticle assemblies

ABSTRACTMatrix free assemblies of polymer‐grafted, “hairy” nanoparticles (aHNP) exhibit novel morphology, dielectric, and mechanical properties, as well as providing means to overcome dispersion challenges ubiquitous to conventional polymer‐inorganic nanocomposite blends. Physical aging of the amorphous polymer glass between the close‐packed nanoparticles (NPs) will dominate long‐term stability; however, the energetics of volume recovery within the aHNPs is unknown. Herein, we compare glass transition temperature (Tg) and enthalpy recovery of aHNPs to NP‐polymer blends, across different nano‐silica loadings (0–50 v/v%) and canopy architecture of polystyrene (PS) grafted silica. For aHNPs, the grafting of PS to silica imposes an additional design constraint between silica volume fraction, graft density, and graft molecular weight. At low and intermediate silica volume fraction, the Tg of blended nanocomposites is independent of silica content, reflecting a neutral polymer‐NP interface. For aHNPs, the Tg decreases with silica content, implying that chain tethering decreases local segment density more than the effect of molecular weight or polymer‐NP interactions. Additionally, the Tg of the aHNPs is higher than a linear matrix of comparable molecular weight, implying a complementary effect to local segment density that constrains cooperativity. In contrast, enthalpy recovery rate in the blend or aHNP glass is retarded comparably. In addition, a cross‐over temperature, Tx, emerges deep within the glass where the enthalpy recovery process of all nanocomposites becomes similar to linear unfilled matrices. Differences between structural recovery in aHNP and blended nanocomposites occur only at the highest silica loadings (∼ 50 v/v%), where enthalpy recovery for aHNPs is substantially suppressed relative to the blended counterparts. The absence of physical aging at these loadings is independent of brush architecture (graft density or molecular weight of tethered chains) and indicates that the impact of chain tethering on effective bulk structural relaxation starts to appear at particle‐particle surface separations on the order of the Kuhn length. Overall, these observations can be understood within the context of how three separate structural characteristics impact local segment density and relaxation processes: the dimension and architecture of the tethered polymer chains, the separation between NP surfaces, and the confinement imposed by chain tethering and space filling within the aHNP. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 319–330

New Class of Synthetic Membranes: Organophilic Pervaporation Brushes for Organics Recovery

Isolating and concentrating volatile organics such as fuels and intermediate chemicals from aqueous solutions is important for environmental synthesis and processing. We have prepared a new class of easy-to-synthesize polymeric membranes comprising hydrophobic brush-like structures as a selective layer, and have tested them using pervaporation of isobutanol from water. These brush structures were prepared by graft-induced polymerization of hydrophobic vinyl monomers from light-sensitive poly(ether sulfone) nanofiltration support membranes (grafting from) without initiating agents. Graft-induced tethered polymer chains with multiple C18 alkane side-chains out-performed the industry gold standard silicone rubber membrane with selectivities of α = 10.1 ± 0.9 and 6.7 ± 0.1, respectively, at comparable permeation fluxes of 0.7–1.0 ± 0.1 L/m2-h. Preparation of these brush membranes is simpler and easier to scale-up than current methods of preparing asymmetric and composite membrane structures. These brush struc...

Critical conditions of polymer chromatography: An insight from SCFT modeling

In polymer chromatography, chain molecules are separated by molecular weight, size, and chemical composition due to adsorption and exclusion in nanoporous substrates. Three regimes of separation are distinguished depending on the adsorption strength and the pore size. In the regime of size exclusion chromatography, the adsorption energy is weak and the separation is entropy-driven with larger molecules having shorter retention times. On the opposite, in the regime of adsorption chromatography, enthalpy gain due to strong adsorption energy prevails over entropy loss, and the retention time of smaller molecules is shorter. We study the intermediate regime of so-called critical conditions, at which the entropic and enthalpic effects are mutually compensated, and the partition coefficient does not depend on the polymer molecular weight. Using the self-consistent field theory of tethered polymer chains, we confirm that for ideal chains the critical conditions are justified, albeit they depend on the pore size. However, for real chains with the excluded volume effect, the critical conditions hold only approximately, and the discrepancy increases as the pore size decreases. We show that it is important to consider three characteristic adsorption states: chains adsorbed at the external surface, chains adsorbed completely inside the pores, and partially translocated chains or "flowers" with a "root" adsorbed inside the pore and a "stem" hanging outside. The interplay of different adsorption mechanisms and the pore size distribution inherent to real substrates may lead to the manifestation of apparent critical adsorption conditions within the inherent deviation of experimental data.

Stretching tethered polymer chains: Density functional approach

We propose application of density functional theory to calculate the force acting on a selected segment of a tethered polymer chain that leads to stretching the chain. The density functional allows one to determine the effects due to the presence of other chains and solvent molecules. For high and moderate solvent densities the plot of the force versus the distance of the segment from the surface exhibits oscillatory behavior that has not been predicted by other approaches.

Impact of solvation on equilibrium conformation of polymer brushes in solvent mixtures

We have investigated the response of dextran brushes in aqueous dimethyl sulfoxide (DMSO) mixtures under normal compression using the extended surface forces apparatus. The hydrophilic, tethered polymer chains extend significantly in the studied aqueous mixtures and two brush-covered surfaces exhibit repulsive forces upon compression against each other; these attributes are relevant for both anti-biofouling and lubrication properties. An estimation of the height of the dextran brushes with varying solvent quality is made from measurements of the onset of the repulsion: the brush swells significantly in pure water, a decrease in swelling being observed with an increase in DMSO concentration (up to ∼50 vol%), followed by a more pronounced swelling at higher DMSO concentrations. This behavior is in qualitative agreement with the solubility of bulk dextran polymer in aqueous DMSO solutions. Besides the conformational changes, an increase in the compressibility of the dextran brushes upon increasing the DMSO concentration was observed and explained by the change in the solvation structure of the polymer brush. We describe the equilibrium configuration of the polymer brush under marginal/good solvent conditions with the help of a mean-field approach, considering both solvent quality and a solvation-structure-dependent bond length. This work shows that an appropriate selection of polymer brush and solvent mixture can be used to tune the conformational properties of the polymer brushes at the interface, as well as the consequent repulsive and frictional forces.

Steric Forces of Tethered Polymer Chains as a Function of Grafting Density: Studies with a Single Diblock Molecular Weight

The normal force to compress opposing polymer brushes as a function of grafting density was measured using a surface force apparatus. In contrast to conventional methods where grafting density has been varied by changing polymer molecular weight, in this work high grafting densities ranging from 1.4 to 7.6 mg/m2 were obtained by spin-coating different concentrations of a single diblock copolymer. Measured force profiles at low grafting density, σ < 4 mg/m2, were analogous to previous studies and consistent with Milner–Witten–Cates (MWC) theoretical predictions once chain polydispersity was accounted for. At higher grafting densities the experimentally measured repulsive interaction energy or force showed scaling behavior where the nondimensionalized force curves fall on top of each other; however, the behavior is distinctly different from the low grafting density regime and cannot be modeled using theory developed for the dilute/semidilute regime.

Tethered Nanoparticle–Polymer Composites: Phase Stability and Curvature

Phase behavior of poly(ethylene glycol) (PEG) tethered silica nanoparticles dispersed in PEG hosts is investigated using small-angle X-ray scattering. Phase separation in dispersions of densely grafted nanoparticles is found to display strikingly different small-angle X-ray scattering signatures in comparison to phase-separated composites comprised of bare or sparsely grafted nanoparticles. A general diagram for the dispersion state and phase stability of polymer tethered nanoparticle-polymer composites incorporating results from this as well as various other contemporary studies is presented. We show that in the range of moderate to high grafting densities the dispersion state of nanoparticles in composites is largely insensitive to the grafting density of the tethered chains and chemistry of the polymer host. Instead, the ratio of the particle diameter to the size of the tethered chain and the ratio of the molecular weights of the host and tethered polymer chains (P/N) are shown to play a dominant role. Additionally, we find that well-functionalized nanoparticles form stable dispersions in their polymer host beyond the P/N limit that demarcates the wetting/dewetting transition in polymer brushes on flat substrates interacting with polymer melts. A general strategy for achieving uniform nanoparticle dispersion in polymers is proposed.

Electrophoretic stretching of tethered polymer chains by travelling-wave electric fields: tunable stretching, expedited coil–stretch transition, and a new paradigm of dynamic molecular probing

The use of low-frequency travelling wave fields in electrophoretic stretching of charged polymer chains is investigated theoretically. We find, using a simple elastic dumbbell model, that the stretching behavior with and without fluctuations can show a number of distinctive features that cannot be seen in usual steady or alternating current electric fields. In the deterministic study without fluctuations, we show that an end-tethered charged polymer chain can be pulled by asymmetric strokes generated by a travelling wave field and kept extended along the wave. It is found that while the averaged chain extension can be increased by raising the field strength, it can be decreased by increasing the wave speed. This is a new example that stretching a polymer chain can be realized in a time periodic field with zero mean. As the free energy landscape here acts like a vibrating harmonic oscillator having double or multiple wells, a stretched chain trapped in an energy groove created by a travelling wave field can hop back to the lower energy coil state due to fluctuations. In this stochastic study, we develop a theory and carry out Brownian dynamics simulations to show that as long as the wave speed does not exceed the damping threshold and fluctuations do not prevail to diminish stretching, increasing the wave speed can help the chain maintain its stretch by preventing it from hopping to the coil state. In addition, two distinct hopping kinetics, Arrhenius and Kramers modes, can exist to govern the respective coil–stretch transitions in the double-well and multiple-well scenarios, depending on the extent of stretching. These features are the results of cooperative effects of travelling wave fields and fluctuations, and further manifested by tongue-like coil–stretch phase diagrams. Applications of the present stretching to dynamic molecular probing are also illustrated by monitoring and regulating the molecular transport over a cyclically stretching polymer chain at the nanoscale or single-molecule level.

Toughening of epoxy resin with poly(methyl methacrylate) grafted silica core-shell particles

AbstractStructurally well-defined core-shell particles were prepared by modifying the surface of silica with initiators for atom transfer radical polymerization (ATRP), and followed by using these initiator-modified particles as ATRP macro-initiators for methyl methacrylate. These particles were characterized with Fourier-transform infrared spectroscopy (FT-IR), thermo-gravimetric analysis (TGA) and scanning electron microscopy (SEM). The tethered polymer chains on the grafted silica particles were cleaved with hydrofluoric acid and measured with gel permeation chromatography (GPC). The results showed that poly(methyl methacrylate) (PMMA) chains grew from the particle surfaces in form of individual particles comprising of a hard silica core and a well-defined, densely grafted outer polymer layer. Diglycidyl ether of bisphenol-A (DGEBA) based epoxy resin was toughened with various doses of the synthesized PMMA-grafted silica particles. Resulting composite materials were characterized by tensile testing, SEM, dynamic mechanical analysis (DMA) and TGA. The results indicated that the incorporation of the core-shell particles improved the toughness of the composites without any significant deterioration of its thermal properties.

Computational entropy estimation of linear polyether-modified surfaces and correlation with protein resistant properties of such surfaces

The non-specific adsorption of proteins on surfaces is a well-known and mostly undesirable phenomena, which is reduced by a surface coating with the linear polyether poly(ethylene glycol) (PEG) as the current benchmark material. However, the molecular mechanism of protein-resistant surfaces is still not fully understood. Two main hypotheses are generally applied. The first one is steric repulsion of the highly flexible tethered polymer chains, leading to an entropic penalty by adsorption of proteins due to the reduction in polymer chain mobility. The second one argues with well-hydrated polymer chains generating a repulsive interfacial water layer. In this article, we compare the three different protein-resistant polyether structures PEG, linear polyglycerol (LPG(OH)) and linear poly(methyl glycerol) (LPG(OMe)) to get new insights into the molecular mechanism behind protein resistance. In a theoretical approach, we apply an entropy estimator that assesses the conformational states of the tethered polyethers from MD simulations. It reveals the entropy differences between these polyethers to be in the order PEG>LPG(OH) > LPG(OMe). Moreover, experiments on fibrinogen adsorption of these surfaces via surface plasmon resonance spectroscopy are performed and correlated with the theoretical studies. We find that protein resistant properties of surfaces are likely to arise from an interplay of different factors.