Healing of interfacial surfaces in polymer systems

Literature data on the problems related to the healing of interfacial surfaces in polymers are revisited. Specific features and behavior of the contacting surfaces of polymer films in the rubbery and glassy states, as well as in heterophase polymer systems, are analyzed. Particular details associated with the healing of interfacial surfaces in polymers, which are capable of chemical interactions with each other, are considered. Special attention is focused on the analysis of the phenomena taking place on the newborn interfaces formed owing to the deformation of polymers in different physical states. Processes providing healing of shear bands and crazes during annealing of deformed polymer glasses are discussed. The above phenomena are shown to present evident practical interest from the viewpoint of the development of advanced nanocomposites based on polymer matrices.     

Ligand-receptor interactions between surfaces: the role of binary polymer spacers

The interactions between a receptor-modified planar surface and a surface grafted with a bimodal polymer layer, where one of the polymer species is ligand functionalized, are studied using a molecular theory. The effects of changing the binding energy of the ligand-receptor pair, the polymer surface coverage, the composition, and molecular weight of both the unfunctionalized and ligand functionalized polymers on the interactions between the surfaces are investigated. Our findings show that bridging exists between the surfaces including when the molecular weight of the ligand-bearing polymer is smaller than that of the unfunctionalized polymer, even though the ligand is initially buried within the polymer layer. The distance at which the surfaces bind depends only on the molecular weight of the ligand-modified polymer, while the strength of the interaction at a given surface separation can be tuned by changing the molecular weight of the polymers, the total polymer surface coverage, and the fraction of ligated polymers. The composition of the bimodal layer alters the structure of the polymer layer, thereby influencing the strength of the steric repulsions between the surfaces. Our theoretical results show good agreement with experimental data. The present theoretical study can be used as guidelines for the design of surfaces with tailored abilities for tunning the binding strength and surface-ligand separation distances for polymer-grafted surfaces bearing specific targeting ligands.     

Surface structure of polymers for biomedical applications

Biological reactions with synthetic polymers are strongly influenced by the surfaces of those materials. The surfaces are often substantially different in composition and structure from the bulk. By using contemporary surface analysis methods, we can understand polymer surfaces. The surfaces of polymers can also be modified to generate desired biological responses. These points are illustrated with examples involving polyurethanes and RF plasma-deposited films.     

Effect of associating polymer on the viscosity behavior of suspensions consisting of particles with different surface properties

Associating polymers which consist of water-soluble long-chain molecules containing a small fraction of hydrophobic groups (hydrophobes) behave as flocculants in aqueous suspensions. The effects of associating polymers on the rheological behavior are studied for single suspensions of particles with hydrophilic and hydrophobic surfaces, and their mixtures. For particles with hydrophilic surfaces, the suspensions are highly flocculated by a bridging mechanism, because the water-soluble chains adsorb onto hydrophilic surfaces. On the other hand, the particles with hydrophobic surfaces cannot be dispersed in water without polymer and the additions of a small amount of polymer are required for preparation of homogeneous suspensions. The associating polymer acts as a dispersant at low concentrations. However, further additions of polymer lead to a drastic increase in viscosity. Since the hydrophobes on one end of molecules adsorb onto hydrophobic surfaces and other hydrophobes tending from the particles can form micelles, the particles are connected by linkage of interchain associations. By mixing two suspensions of particles with hydrophilic and hydrophobic surfaces, the viscosity is substantially reduced and the flow becomes nearly Newtonian. The associating polymer in complex suspensions acts as a binder between the hydrophilic and hydrophobic surfaces. The hetero-flocculation which leads to the formation of composite particles may be responsible for the viscosity reduction of complex suspensions.     

Adsorption of comb copolymers on weakly attractive solid surfaces

In this work continuum and lattice Monte Carlo simulation methods are used to study the adsorption of linear and comb polymers on flat surfaces. Selected polymer segments, located at the tips of the side chains in comb polymers or equally spaced along the linear polymers, are attracted to each other and to the surface via square-well potentials. The rest of the polymer segments are modeled as tangent hard spheres in the continuum model and as self-avoiding random walks in the lattice model. Results are presented in terms of segment-density profiles, distribution functions, and radii of gyration of the adsorbed polymers. At infinite dilution the presence of short side chains promotes the adsorption of polymers favoring both a decrease in the depletion-layer thickness and a spreading of the polymer molecule on the surface. The presence of long side chains favors the adsorption of polymers on the surface, but does not permit the spreading of the polymers. At finite concentration linear polymers and comb polymers with long side chains readily adsorb on the solid surface, while comb polymers with short side chains are unlikely to adsorb. The simple models of comb copolymers with short side chains used here show properties similar to those of associating polymers and of globular proteins in aqueous solutions, and can be used as a first approximation to investigate the mechanism of adsorption of proteins onto hydrophobic surfaces.     

Patterning molecularly thin films of polymers—new methods for photolithographic structuring of surfaces

Three novel photolithographic processes for patterning of molecularly thin polymer films are described. The polymer monolayers are prepared by immobilization of initiator molecules to surfaces of solid substrates followed by thermally or photochemically activated radical chain polymerization. Thus polymer chains which are covalently linked to the surfaces of the substrates are obtained. The films can be patterned using appropriate masks and deep or near UV irradiation before, during or after polymer formation. The procedures described in this paper allow the chemical tailoring of surfaces with high spatial resolution. Step-and-repeat procedures, which take advantage of the covalent linking of the polymers to the surfaces, permit the preparation of multifunctional polymer patterns.     

Rheological behavior of silica suspensions in aqueous solutions of associating polymer

Associating polymers are hydrophilic long-chain molecules containing a small amount of hydrophobic groups. The aqueous solutions show viscoelastic responses above some critical concentrations because a three-dimensional structure is formed by association of hydrophobic groups. When the associating polymers are added to silica suspensions at low concentrations, the flocculation is induced by bridging mechanisms, and the flow of suspensions become shear-thinning. For suspensions prepared with polymer solutions in which the associating network is developed, the viscosity decreases, shows a minimum, and then increases with increasing particle concentration. The viscosity decrease may arise from the breakdown of associating network due to adsorption of polymer chains onto the silica surfaces. As the particle concentration is increased, the polymer concentration in solution is decreased, and finally, all polymer chains are adsorbed on the surfaces. Beyond this point, the partial coverage of particle surfaces takes place and strong interactions are generated between particles by polymer bridging. Since the stable suspensions are converted to highly flocculated systems, the viscosity is increased and the flow becomes shear-thinning. The concentration effect of silica particles on the viscosity behavior of suspensions can be explained by a combination of viscosity decrease in solution due to polymer adsorption and viscosity increase due to flocculation.     

Advances in reactive polymeric surfactants for interface modification

Continued development of up-to-date polymer composite materials demands the design of certain interfacial layers in composite structure. The aim of this paper was to review recent advances in the synthesis of reactive polymeric surfactants (RPSs) and the application of 14 different RPSs for the modification of the interface in aqueous dispersions of polymers, reinforced polymer-based composites, and polymer blends. The activation (peroxidation) of planar polymer surfaces with RPSs for their further modification in order to impart specific surface properties was discussed as well. In the paper method of compatibilization of the blends of thermodynamically immiscible polymers through the formation in situ of a universal compatibilizer based on RPS was introduced. Finally, the features of the RPS macromolecules' adsorption on the surface of latex particles, inorganic filler particles, and planar polymer surfaces along with the formation of adsorbed reactive polymer layers are discussed.     

Thermally responsive chromatographic materials using functional polymers

Functional polymers that respond to small changes in environmental stimuli with large changes in their structure and properties are often called "intelligent" polymers. We have modified material surfaces with such polymers and used them in separation systems. Silica beads were modified with the temperature-responsive polymer poly(N-isopropylacrylamide) (PNIPAAm). PNIPAAm-grafted surfaces exhibited temperature-driven alterations of hydrophilic-hydrophobic surface-properties. Using this feature, PNIPAAm and related temperature-responsive polymers have been used to generate temperature-sensitive stationary phases for chromatographic separations. We attached several different functional polymers, including temperature- and pH-responsive polymers, to silica beads. These temperature-responsive stationary phases are useful in development of separation methods since adjusting the temperature represents an extra tool for optimizing the selectivity. Applications of thermally responsive columns for separations in the HPLC mode are demonstrated.     

Tethered polymer chains: surface chemistry and their impact on colloidal and surface properties

In this review the grafting of polymer chains to solid supports or interfaces and the subsequent impact on colloidal properties is examined. We start by examining theoretical models for densely grafted polymers (brushes), experimental techniques for their preparation and the properties of the ensuing structures. Our aim is to present a broad overview of the state of the art in this field, rather than an in-depth study. In the second section the interactions of surfaces with tethered polymers with the surrounding environment and the impact on colloidal properties are considered. Various theoretical models for such interactions are discussed. We then review the properties of colloids with tethered polymer chains, interactions between planar brushes and nanocolloids, interactions between brushes and biocolloids and the impact of grafted polymers on wetting properties of surfaces, using the ideas presented in the first section. The review closes with an outlook to possible new directions of research.     

Polymer‐Based Surfaces Designed to Reduce Biofilm Formation: From Antimicrobial Polymers to Strategies for Long‐Term Applications

Contact‐active antimicrobial polymer surfaces bear cationic charges and kill or deactivate bacteria by interaction with the negatively charged parts of their cell envelope (lipopolysaccharides, peptidoglycan, and membrane lipids). The exact mechanism of this interaction is still under debate. While cationic antimicrobial polymer surfaces can be very useful for short‐term applications, they lose their activity once they are contaminated by a sufficiently thick layer of adhering biomolecules or bacterial cell debris. This layer shields incoming bacteria from the antimicrobially active cationic surface moieties. Besides discussing antimicrobial surfaces, this feature article focuses on recent strategies that were developed to overcome the contamination problem. This includes bifunctional materials with simultaneously presented antimicrobial and protein‐repellent moieties; polymer surfaces that can be switched from an antimicrobial, cell‐attractive to a cell‐repellent state; polymer surfaces that can be regenerated by enzyme action; degradable antimicrobial polymers; and antimicrobial polymer surfaces with removable top layers.     

Confinement free energy of surfaces bearing end-grafted polymers in the mushroom regime and local measurement of the polymer density

End-tethered polymer chains usually adopt mushroomlike structures on the surface when their density is low. The behaviors of these surface-attached hemicoils are described by existing polymer theory. Dolan and Edwards derived the free energy of a single polymer chain confined between two planar surfaces. Their theory was used to approximate the steric interaction free energy, E, of two identical surfaces bearing polymers in the mushroom regime and to compare with experimental data obtained from surface force measurements. However, because of a mislabeled plot in the original paper, experimental force profiles did not seem to fit the free energy approximation satisfactorily. We have correctly relabeled the involved plot and derived a new simple expression for E. In order to verify this expression, we have performed experiments on PEG45 polymers incorporated in lipid bilayers using a surface force apparatus. The measured force profiles are in perfect agreement with the prediction. We show that such measurements can be used to determine the local density of grafted polymer with good precision.     

What really enhances the adsorption of polymers onto chemically nonuniform surfaces: surface randomness or its heterogeneity?

We theoretically perform a comparative analysis of the adsorption of polymers onto the regularly and randomly nonuniform surfaces. By developing and making use of the self-consistent perturbation expansion we calculate the surface excesses of the polymers adsorbed on the random and periodically patterned surfaces. In both cases the enhancement of the polymer adsorption is indicated, as compared to the adsorption onto the homogeneous surface that has the same average affinity for polymers. Moreover, the results obtained for the randomly nonuniform and periodically patterned adsorbing surfaces show striking quantitative similarity, when compared at the same characteristic sizes of inhomogeneities of these surfaces. This finding leads to the conclusion that the adsorption ability of the nonuniform surface primarily depends on the characteristic size of the surface inhomogeneity, rather than on the spatial distribution of the inhomogeneities on this surface. In all cases, the calculated total surface excess is found to be a decaying function of the ratio of the radius of gyration of polymers to the characteristic size of the surface inhomogeneity. The effect of the excluded volume is found to reduce the polymer adsorption.     

“intelligent” polymers in medicine and biotechnology

One can define “intelligent” polymers as those polymers which respond with large property changes to small physical or chemical stimuli. These polymers may be in various forms, such as in solution, on surfaces, or as solids. One may also combine “intelligent” aqueous polymer systems with biomolecules, to yield a large family of polymers which respond “intelligently” to physical, chemical or biological stimuli. This article overviews such interesting and versatile polymer systems.     

Behavior of polymers at surfaces and interfaces as observed in simulated systems

Cooperative motion algorithm (CMA) is used to simulate polymer chains in three types of dense systems reflecting special cases of polymer behavior at surfaces and interfaces: polymer brushes with variable grafting density in the range 0–1, both in a neutral solvent and in a polymer melt, layers of end-functionalized polymers between parallel end-adsorbing walls, and copolymers of various distributions of comonomer units (random, block and gradient copolymers) at interfaces with noncompatible polymers.     

聚环氧琥珀酸及丙烯酸共聚物阻垢机理的分子动力学模拟

用分子动力学方法,模拟计算了聚环氧琥珀酸( PESA)和丙烯酸共聚物[P（AA-co-MA）]、[P(AA-co-HPA)]及[P(AA-co-MAE)]4种聚合物阻垢剂与方解石晶体(104)晶面、(1 (1) 0)晶面的相互作用.结果表明,聚合物与方解石两晶面结合能的大小排序均为PESA＞[P(AA-co-MA)]＞...     

Nanoscale actuation of electrokinetic flows on thermoreversible surfaces

We report on a novel approach for controlling nanohydrodynamic properties at the solid-liquid interfaces through the use of stimuli-responding polymer coatings. The end-tethered polymers undergo a phase separation upon external activation. The reversible change in the thickness and polarity of the grafted polymers yields in a dynamic control of the surface-generated, electrokinetic phenomena. Nonactivated, swollen polymers are thicker than the electrical double layer (EDL) and prohibit the development of an EOF even on charged surfaces. On the other hand, activated polymer chains shrink and become thinner than the EDL and allow for the EOF to build up unimpeded. We show here that, for given experimental conditions, the EOF velocity on the shrunken surface is 35 times greater than the one on the nonactivated surface. Furthermore, we reveal that coupling of such surfaces with dense arrays of thermal actuators developed in our laboratory can lead to novel micro- and nanofluidic devices.     

Immobilization of amphiphilic polycations by catechol functionality for antimicrobial coatings

A new strategy for preparing antimicrobial surfaces by a simple dip-coating procedure is reported. Amphiphilic polycations with different mole ratios of monomers containing dodecyl quaternary ammonium, methoxyethyl, and catechol groups were synthesized by free-radical polymerization. The polymer coatings were prepared by immersing glass slides into a polymer solution and subsequent drying and heating. The quaternary ammonium side chains endow the coatings with potent antibacterial activity, the methoxyethyl side chains enable tuning the hydrophobic/hydrophilic balance, and the catachol groups promote immobilization of the polymers into films. The polymer-coated surfaces displayed bactericidal activity against Escherichia coli and Staphylococcus aureus in a dynamic contact assay and prevented the accumulation of viable E. coli, S. aureus, and Acinetobacter baumannii for up to 96 h. Atomic force microscopy (AFM) images of coating surfaces indicated that the surfaces exhibit virtually the same smoothness for all polymers except the most hydrophobic. The hydrophobic polymer without methoxyethyl side chains showed clear structuring into polymer domains, causing high surface roughness. Sum-frequency generation (SFG) vibrational spectroscopy characterization of the surface structures demonstrated that the dodecyl chains are predominantly localized at the surface-air interface of the coatings. SFG also showed that the phenyl groups of the catechols are oriented on the substrate surface. These results support our hypothesis that the adhesive or cross-linking functionality of catechol groups discourages polymer leaching, allowing the tuning of the amphiphilic balance by incorporating hydrophilic components into the polymer chains to gain potent biocidal activity.     

Grafting acrylic polymers from flat nickel and copper surfaces by surface-initiated atom transfer radical polymerization

Acrylic polymers, including poly(methyl methacrylate), poly(2,2,2-trifluoroethyl methacrylate), poly( N,N'-dimethyaminoethyl methacrylate), and poly(2-hydroxyethyl methacrylate) were grafted from flat nickel and copper surfaces through surface-initiated atom transfer radical polymerization (ATRP). For the nickel system, there was a linear relationship between polymer layer thickness and monomer conversion or molecular weight of "free" polymers. The thickness of the polymer brush films was greater than 80 nm after 6 h of reaction time. The grafting density was estimated to be 0.40 chains/nm2. The "living" chain ends of grafted polymers were still active and initiated the growth of a second block of polymer. Block copolymer brushes with different block sequences were successfully prepared. The experimental surface chemical compositions as measured by X-ray photoelectron spectroscopy agreed very well with their theoretical values. Water contact angle measurements further confirmed the successful grafting of polymers from nickel and copper surfaces. The surface morphologies of all samples were studied by atomic force microscopy. This study provided a novel approach to prepare stable functional polymer coatings on reactive metal surfaces.     

Photo-responsive polymer materials for biological applications

In this review, we briefly summarized the remarkable progress of photo-responsive polymer materials from zero-dimensional micelles, twodimensional surfaces to three-dimensional hydrogels with irreversible or reversible moieties. Based on the photo-responsiveness, polymer have been designed, synthesized and applied for various biological fields including drug delivery and cell manipulation.