Symmetric Triblock Copolymers Research Articles

Coarse-graining in simulations of multicomponent polymer systems.

We investigate the mapping required between the interaction parameters of two different coarse-grained simulation models to ensure a match of the long-range structural characteristics of multicomponent polymeric system. The basis for our studies is the recent work of Morse and workers, which demonstrated the existence of a mapping between the interaction parameters of different coarse-grained simulation models which allow for a matching of the peak of the disordered state structure factor in symmetric diblock copolymers. We investigate the extensibility of their results to other polymeric systems by studying a variety of systems, including, asymmetric diblock copolymers, symmetric triblock copolymers, and diblock copolymer-solvent mixtures. By using the mapping deduced in the context of symmetric diblock copolymers, we observe excellent agreement for peak in the inverse structure between both two popular coarse grained models for all sets of polymeric melt systems investigated, thus showing that the mapping function proposed for diblock copolymer melts is transferable to other polymer melts irrespective of the blockiness or overall composition. Interestingly, for the limited parameter range of polymer-solvent systems investigated in this article, the mapping functions developed for polymer melts are shown to be equally effective in mapping the structure factor of the coarse-grained simulation models. We use our findings to propose a methodology to create ordered morphologies in simulations involving hard repulsive potentials in a computationally efficient manner. We demonstrate the outcomes of methodology by creating lamellar and cylindrical phases of diblock copolymers of long chains in the popularly used Kremer-Grest simulation model.

Asymmetric block copolymers for supramolecular templating of inorganic nanospace materials.

This review focuses on polymeric micelles consisting of asymmetric block copolymers as designed templates for several inorganic nanospace materials with a wide variety of compositions. The presence of chemically distinct domains of asymmetric triblock and diblock copolymers provide self-assemblies with more diverse morphological and functional features than those constructed by EOn POm EOn type symmetric triblock copolymers, thereby affording well-designed nanospace materials. This strategy can produce unprecedented nanospace materials, which are very difficult to prepare through other conventional organic templating approaches. Here, the recent development on the synthesis of inorganic nanospace materials are mainly focused on, such as hollow spheres, tubes, and porous oxides, using asymmetric triblock copolymers.

Small angle neutron scattering study of complex coacervate micelles and hydrogels formed from ionic diblock and triblock copolymers.

A complex coacervate is a fluid phase that results from the electrostatic interactions between two oppositely charged macromolecules. The nature of the coacervate core structure of hydrogels and micelles formed from complexation between pairs of diblock or triblock copolymers containing oppositely charged end-blocks as a function of polymer and salt concentration was investigated. Both ABA triblock copolymers of poly[(allyl glycidyl ether)-b-(ethylene oxide)-b-(allyl glycidyl ether)] and analogous poly[(allyl glycidyl ether)-b-(ethylene oxide)] diblock copolymers, which were synthesized to be nearly one-half of the symmetrical triblock copolymers, were studied. The poly(allyl glycidyl ether) blocks were functionalized with either guanidinium or sulfonate groups via postpolymerization modification. Mixing of oppositely charged block copolymers resulted in the formation of nanometer-scale coacervate domains. Small angle neutron scattering (SANS) experiments were used to investigate the size and spacing of the coacervate domains. The SANS patterns were fit using a previously vetted, detailed model consisting of polydisperse core-shell micelles with a randomly distributed sphere or body-centered cubic (BCC) structure factor. For increasing polymer concentration, the size of the coacervate domains remained constant while the spatial extent of the poly(ethylene oxide) (PEO) corona decreased. However, increasing salt concentration resulted in a decrease in both the coacervate domain size and the corona size due to a combination of the electrostatic interactions being screened and the shrinkage of the neutral PEO blocks. Additionally, for the triblock copolymers that formed BCC ordered domains, the water content in the coacervate domains was calculated to increase from approximately 16.8% to 27.5% as the polymer concentration decreased from 20 to 15 wt %.

Molecular arrangement of symmetric and non-symmetric triblock copolymers of poly(ethylene oxide) and poly(isobutylene) at the air/water interface

The behavior of a series of amphiphilic triblock copolymers of poly(ethylene oxide) (PEO) and poly(isobutylene) (PIB); including both symmetric (same degree of polymerization (DP) of the terminal PEO blocks) PEOm-b-PIBn-b-PEOm and non-symmetric (different DP of the terminal PEO blocks) PEOm-b-PIBn-b-PEOz, is investigated at the air/water interface by measuring surface pressure vs mean molecular area isotherms (π vs mmA), Langmuir–Blodgett (LB) technique, and infrared reflection–absorption spectroscopy (IRRAS). The block copolymer (PEO32-b-PIB160-b-PEO32) with longer PEO segments forms a stable monolayer and the isotherm reveals a pseudo-plateau starting at π∼5.7mN/m, also observed in the IRRAS, which is assigned to the pancake-to-brush transition related to the PEO dissolution into the subphase and subsequent PEO brush dehydration. Another plateau is observed at π∼40mN/m, which is attributed to the film collapse due to multilayer formation. The pancake-to-brush transition could not be observed for samples with smaller PEO chains. The isotherms for block copolymers, with short PEO chains, both symmetric (PEO3-b-PIBn-b-PEO3) and non-symmetric (PEO12-b-PIBn-b-PEO3), reveal another transition at π∼20–25mN/m. This is interpreted to be due to the conformational transition from a folded state where the middle PIB block is anchored to the water surface at both ends by the terminal hydrophilic segments to an unfolded state with PIB anchored to the water surface at one end. It is assumed that this transition involves the removal of PEO3 chains from the water surface in case of non-symmetric PEO12-b-PIB85-b-PEO3 and in case of symmetric, probably one PEO3 of each PEO3-b-PIB85-b-PEO3 chain. Because of the weaker interaction of the short PEO3 chains with the water surface as compared with the relatively longer PEO12 chains, the film of PEO3-b-PIB85-b-PEO3 collapses at much lower surface pressure after the transition as compared with the PEO12-b-PIB85-b-PEO3. The AFM images reveal the formation of microdomains of almost uniform height (6–7nm) in LB films of PEO3-b-PIB85-b-PEO3 and PEO12-b-PIB85-b-PEO3 after transferring onto silicon surfaces. These domains are assumed to be the mesomorphic domains of ordered and folded PIB chains.

Self-consistent field theoretic simulations of amphiphilic triblock copolymer solutions: Polymer concentration and chain length effects

Using the self-consistent field lattice model, polymer concentration $\bar{\phi}_{{P}}$ and chain length $N$ (keeping the length ratio of hydrophobic to hydrophilic blocks constant) the effects on temperature-dependent behavior of micelles are studied, in amphiphilic symmetric ABA triblock copolymer solutions. When chain length is increased, at fixed $\bar{\phi}_{{P}}$, micelles occur at higher temperature. The variations of average volume fraction of stickers $\bar{\phi}_\textrm{co}^\textrm{s}$ and the lattice site numbers $N_\textrm{co}^\textrm{ls}$ at the micellar cores with temperature are dependent on $N$ and $\bar{\phi}_{{P}}$, which demonstrates that the aggregation of micelles depends on $N$ and $\bar{\phi}_{{P}}$. Moreover, when $\bar{\phi}_{{P}}$ is increased, firstly a peak appears on the curve of specific heat $C_V$ for unimer-micelle transition, and then in addition a primary peak, the secondary peak, which results from the remicellization, is observed on the curve of $C_V$. For a long chain, in intermediate and high concentration regimes, the shape of specific heat peak markedly changes, and the peak tends to be a more broad peak. Finally, the aggregation behavior of micelles is explained by the aggregation way of amphiphilic triblock copolymer. The obtained results are helpful in understanding the micellar aggregation process.

Self-assembled morphologies of ABA triblock copolymer brushes in selective solvents

A simulated annealing method is used to investigate the self-assembled morphologies of symmetric ABA triblock copolymer brushes, formed by one end of the A-blocks tethered onto a planar surface, immersed in a solvent selective for the middle B-blocks. The morphological dependences of the brushes on polymer grafting density and block lengths are investigated systematically. Phase diagrams for systems with different grafting densities are constructed. The simulation results show that the grafted amphiphilic triblock copolymers can self-assemble to form a variety of complicated morphologies which can be classified in terms of the number of A-rich layers in the morphology. In particular, the formation of the structures with one A-rich layer or called "folded" brush structures is consistent with the speculation from the experimental studies of ABA triblock copolymer brushes. More detailed structures depend on the grafting density and the lengths of the blocks. Furthermore, at a high grafting density, the effects of the lengths of blocks and the interaction energies between different species in the system on the conformation of chains are investigated to illustrate the formation mechanisms of self-assembled morphologies of the amphiphilic triblock copolymer brushes.

Solubilization and Release of a Model Drug Nimesulide from PEO–PPO–PEO Block Copolymer Core–Shell Micelles: Effect of Size of PEO Blocks

The commercially available polypropylene oxide (PPO)–polyethylene oxide (PEO) symmetrical triblock copolymers (Pluronics®) have been recognized as pharmaceutical excipients and used in a variety of applications. This paper reports studies on micellar and solubilization behavior of three PEO–PPO–PEO block copolymers, viz. P103, P104 and P105 (same PPO mol. wt = 3250 g·mol−1 but different % PEO = 30, 40 and 50 %, respectively) in aqueous solutions. Critical micellization concentrations (CMCs), critical micellization temperatures (CMTs), and micelle size/polydispersity for copolymers with and without the drug, nimesulide (NIM), are reported. The solubilization of NIM is significantly enhanced with increasing hydrophobicity (P103 > P104 > P105), concentration, temperature and in the presence of added salt. The copolymer hydrophobicity, temperature and the drug loading strongly affect micelle behavior. The micelle–water partition coefficient (P) and thermodynamic parameters of solubilization, viz. Gibbs energy (\( \Updelta G_{s}^{\text{o}} \)), enthalpy (\( \Updelta H_{s}^{\text{o}} \)) and entropy (\( T\Updelta S_{s}^{\text{o}} \)), were calculated. The solubilization site of the drug in different micellar solutions and its release from Pluronics® micelles in phosphate buffer saline (PBS) solution at 37 °C were examined. The kinetics of NIM exhibits burst release characteristics, which are believed to be controlled by degradation of the copolymers. These studies were carried out to investigate the feasibility of using Pluronics® as a release vehicle of nimesulide in vitro. From the results, it was concluded that Pluronic® based formulations might be practical for drug delivery.

Physiologically relevant, pH-responsive PEG-based block and statistical copolymers with N,N-diisopropylamine units.

In order to impart pH-responsiveness within a physiologically-relevant context to PEG-based biomaterials, a new tertiary amine containing repeat unit, N,N-diisopropyl ethanolamine glycidyl ether (DEGE), was developed and incorporated into statistical and block copolymers with ethylene oxide (EO), and allyl glycidyl ether (AGE) via anionic ring-opening polymerization. The reactivity of this novel monomeric building block in copolymerizations with EO was investigated by spectroscopy with observed reactivity ratios of rDEGE = 1.28 ± 0.14 and rEO = 0.82 ± 0.10. It was further demonstrated that DEGE containing copolymers could serve as building blocks for the formation of new pH-responsive materials with a pKa of ca. 9, which allowed macroscopic hydrogels to be prepared from symmetric triblock copolymers PDEGE5.3k-b-PEO20k-b-PDEGE5.3k. The triblock copolymers exhibited clear sol-to-gel transitions in a physiologically-relevant critical gelation range of pH 5.8-6.6 and pH-dependent viscoelastic properties. On the nanometer scale, the preparation of pH-responsive micro- or nanogels was demonstrated by crosslinking P(DEGE-co-AGE) copolymers in miniemulsion droplets stabilized by PEO-b-P(DEGE-co-AGE) diblock terpolymers. These nanoparticles exhibited a reversible pH-dependent swelling profile with a volume phase transition at physiological pH 6.5-7.5.

Kinetics of aggregation in micellar solutions of thermoresponsive triblock copolymers – influence of concentration, start and target temperatures

In aqueous solution, symmetric triblock copolymers with a thermoresponsive middle block and hydrophobic end blocks form flower-like core–shell micelles which collapse and aggregate upon heating through the cloud point (CP). The collapse of the micellar shell and the intermicellar aggregation are followed in situ and in real-time using time-resolved small-angle neutron scattering (SANS), while heating micellar solutions of a poly((styrene-d8)-b-(N-isopropyl acrylamide)-b-(styrene-d8)) triblock copolymer in D2O rapidly through their CP. The influence of polymer concentration as well as of the start and target temperatures is addressed. In all cases, the micellar collapse is very fast. The collapsed micelles immediately form small clusters which contain voids. They densify which slows down or even stops their growth. For low concentrations and target temperatures just above the CP, i.e. shallow temperature jumps, the subsequent growth of the clusters is described by diffusion-limited aggregation. In contrast, for higher concentrations and/or higher target temperatures, i.e. deep temperature jumps, intermicellar bridges dominate the growth. Eventually, in all cases, the clusters coagulate which results in macroscopic phase separation. For shallow temperature jumps, the cluster surfaces stay rough; whereas for deep temperature jumps, a concentration gradient develops at late stages. These results are important for the development of conditions for thermal switching in applications, e.g. for the use of thermoresponsive micellar systems for transport and delivery purposes.

Morphologies and phase diagrams of ABC star triblock copolymers confined in a spherical cavity

The morphologies and phase diagrams exhibited by symmetric ABC star triblock copolymer nanoparticles are investigated by using the real-space self-consistent field theory. A variety of three-dimensional morphologies, such as spherically concentric lamellae and ring-like structures, are identified in the triangular phase diagrams for the polymeric nanoparticles, depending on the volume fractions of the components and the interaction between the polymers and the confining spherical surface. We first study a number of examples where the confining radius and degree of interactions between the polymer and the spherical surface are fixed. A neutral surface that has no energetic preference on any ABC component induces ring-like structures in axisymmetry in an orbicular region of the phase diagram, which surrounds the central region where distorted cylinder phases are stable; a spherical surface that attracts one of the three polymer components induces distorted cylinders into the ring-like structures in a central region of the phase diagram; a spherical surface that repels one of the components stabilizes a lamella-like structure in spherical symmetry in a large region of the phase diagrams. We then focus on an example of polygonal tiling morphologies to study the effects due to variations of the spherical radius and the degree of interactions between the polymer and the spherical surface. The results show that the degree of interactions can obviously influence the formation of morphologies but the spherical radius only affects the polygonal tiling morphologies through slightly adjusting their natural arrangement in the neutral surface case.

Effect of polymer concentration and length of hydrophobic end block on the unimer-micelle transition broadness in amphiphilic ABA symmetric triblock copolymer solutions

The effects of the length of each hydrophobic end block N_{st} and polymer concentration \bar{\phi}_{P} on the transition broadness in amphiphilic ABA symmetric triblock copolymer solutions are studied using the self-consistent field lattice model. When the system is cooled, micelles are observed, i.e.,the homogenous solution (unimer)-micelle transition occurs. When N_{st} is increased, at fixed \bar{\phi}_{P}, micelles occur at higher temperature, and the temperature-dependent range of micellar aggregation and half-width of specific heat peak for unimer-micelle transition increase monotonously. Compared with associative polymers, it is found that the magnitude of the transition broadness is determined by the ratio of hydrophobic to hydrophilic blocks, instead of chain length. When \bar{\phi}_{P} is decreased, given a large N_{st}, the temperature-dependent range of micellar aggregation and half-width of specific heat peak initially decease, and then remain nearly constant. It is shown that the transition broadness is concerned with the changes of the relative magnitudes of the eductions of nonstickers and solvents from micellar cores.

Mechanical properties of polymeric nanostructures fabricated through directed self-assembly of symmetric diblock and triblock copolymers

Grating arrays of polystyrenic nanostructures were fabricated by directed assembly of lamellae-forming poly(styrene-b-methyl methacrylate) diblock and poly(methyl methacrylate-b-styrene-b-methyl methacrylate) triblock copolymer films on chemical patterns and subsequent removal of polyacrylic regions by soft x-ray blanket exposure and fluid development. The collapse of gratings induced by capillary forces in a fluid rinse was observed when the aspect ratio of gratings was above a critical value or the critical aspect ratio of collapse (CARC). In stark contrast to the performance of traditional polymer photoresists, the CARC of gratings fabricated from block copolymers decreased monotonically with increasing LS. For a given pattern period (LS), the CARC of polystyrenic gratings fabricated from diblock copolymers was larger than that of gratings fabricated from an analogous triblock copolymer. The apparent elastic moduli of gratings that were calculated from CARC data using an elastic cantilever beam bending model decreased monotonically with increasing LS/L0 ratio, where L0 is the natural domain period of the block copolymer. This result is discussed in terms of possible LS-dependent changes in chain conformation, line width roughness, and domain shape of nanostructures fabricated from self-assembled block copolymer films.

Diblock and triblock copolymer thin films on a substrate with controlled selectivity

Using self-consistent field theory (SCFT), morphology development in symmetric linear ABC triblock copolymer films on neutral and selective substrates has been studied, and it is compared with the triblock copolymer morphologies in bulk. In particular, the effects of the substrate preferable to B (interior) block on nanopattern formation of the copolymer films are of our central interest. Here, we report various nanopatterns with tunable square morphologies. The domain patterns are much more diverse than those parallel to the substrate with substrate selectivity for end-block or those vertical to the substrate without substrate selectivity. Furthermore, in order to figure out an economical and efficient way to fabricate useful passive pattern transfer layers, which have potential applications in microelectronic processes and ultrahigh density storage media, we propose a two-step strategy and scrutinize the conditions for generating square symmetries using cylinder-forming or lamella-forming AB diblock copolymers deposited on substrates created from ABC triblock copolymer films. It is found that a thinner film with weak incompatibility can produce square patterns.

Boundary Lubrication of PEO-PPO-PEO Triblock Copolymer Physisorbed on Polypropylene, Polyethylene, and Cellulose Surfaces

In situ lateral force microscopy (LFM) and X-ray photoelectron spectroscopy (XPS) were used to probe the lubrication behavior of an aqueous solution of poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) (PEO-PPO-PEO) symmetric triblock copolymer on thin films of polypropylene (PP), polyethylene (PE), and cellulose. LFM experiments were carried out while the substrates were immersed in water and in solutions of the copolymer. The friction coefficient on PP and PE was reduced after adsorption from the PEO-PPO-PEO aqueous solution while the opposite effect was observed for cellulose surfaces. A critical normal loading force, at which the friction coefficient of the lubricated and unlubricated surfaces is equal, was identified and related to the affinity of the polymer with the substrate. Further experiments were performed to mimic practical operations involving lubricant addition during manufacturing and postprocessing removal. XPS was used to verify the presence of the lubricant on the polymeric substra...

Experimental and Computational Study of the Effect of Alcohols on the Solution and Adsorption Properties of a Nonionic Symmetric Triblock Copolymer

This study investigates the effect of alcohols on the solution and adsorption properties of symmetric triblock nonionic copolymers comprising blocks of ethylene oxide (EO) and propylene oxide (PO) (EO(37)PO(56)EO(37)). The cloud point, surface tension, critical micelle concentration (CMC), and maximum packing at the air-water interface are determined, and the latter is compared to the amount of polymer that adsorbs from solution onto polypropylene (PP) and cellulose surfaces. The interaction energy and radius of micelles are calculated by using molecular dynamics (MD) simulations. Equivalent MD bead parameters were used in dynamic density functional theory (DDFT) simulations to study the influence of alcohols on the phase behavior of EO(37)PO(56)EO(37) and its adsorption on PP from aqueous solutions. The simulation results agree qualitatively with the experimental observations. Ethanol acts as a good cosolvent for EO(37)PO(56)EO(37) and reduces the amount of EO(37)PO(56)EO(37) that adsorbs on PP surfaces; however, little or no influence is observed on the adsorption on cellulose. Interestingly, longer chain alcohols, such as 1-pentanol, produce the opposite effect. Overall, the solution and adsorption properties of nonionic symmetric triblock copolymers in the presence of alcohols are rationalized by changes in solvency and the hydrophobic effect.

Synthesis of thermo‐responsive poly(N‐vinylcaprolactam)‐containing block copolymers by cobalt‐mediated radical polymerization

AbstractThermo‐responsive block copolymers based on poly(N‐vinylcaprolactam) (PNVCL) have been prepared by cobalt‐mediated radical polymerization (CMRP) for the first time. The homopolymerization of NVCL was controlled by bis(acetylacetonato)cobalt(II) and a molecular weight as high as 46,000 g/mol could be reached with a low polydispersity. The polymerization of NVCL was also initiated from a poly(vinyl acetate)‐Co(acac)2 (PVAc‐Co(acac)2) macroinitiator to yield well‐defined PVAc‐b‐PNVCL block copolymers with a low polydispersity (Mw/Mn = 1.1) up to high molecular weights (Mn = 87,000 g/mol), which constitutes a significant improvement over other techniques. The amphiphilic PVAc‐b‐PNVCL copolymers were hydrolyzed into unprecedented double hydrophilic poly(vinyl alcohol)‐b‐PNVCL (PVOH‐b‐PNVCL) copolymers and their temperature‐dependent solution behavior was studied by turbidimetry and dynamic light scattering. Finally, the so‐called cobalt‐mediated radical coupling (CMRC) reaction was implemented to PVAc‐b‐PNVCL‐Co(acac)2 precursors to yield novel PVAc‐b‐PNVCL‐b‐PVAc symmetrical triblock copolymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Conformational evolution under steady shear flow: a comparison between cyclic and linear block copolymers

Cyclic block copolymer is a special type of block copolymer having no free ends. Comparison of the dynamic behavior between cyclic and linear block copolymers enables an understanding of the role of chain ends in dynamics of the latter. In relation to this point, analysis was made on the conformational dynamics for a cyclic bead-spring type diblock copolymer chain, AoB, under the steady shear flow. Further comparison was made on the conformational behavior of the AoB chain and that of two symmetric linear triblock copolymer chains, A–B–A and B–A–B. For these chains, the mobility was set to be higher for the A segments than the B segments. Thus, for the AoB chain under the steady shear flow, the segments of the A block exhibit less orientational anisotropy than those of the B block. This orientational contrast is enhanced for the A–B–A chain partly because the constraint for the motion of the segments is less near the chain ends than near the chain center. Nevertheless, for the B–A–B chain, the segmental orientation over the A block becomes more anisotropic than that over the B block. Detailed analysis shows that this result is attributable to a high orientational correlation for the segments of two end B blocks, in particularly for those near the block junctions. The correlated B segments exert a tensile force on the A block thereby significantly enhancing the orientational anisotropy of the A segments.

New Thiol‐Responsive Mono‐Cleavable Block Copolymer Micelles Labeled with Single Disulfides

Thiol-responsive symmetric triblock copolymers having single disulfide linkages in the middle blocks (called mono-cleavable block copolymers, ss-ABP(2)) were synthesized by atom transfer radical polymerization in the presence of a disulfide-labeled difunctional Br-initiator. These brush-like triblock copolymers consist of a hydrophobic polyacrylate block having pendent oligo(propylene oxide) and a hydrophilic polymethacrylate block having pendent oligo(ethylene oxide). Gel permeation chromatography and (1)H NMR results confirmed the synthesis of well-defined mono-cleavable block copolymers and revealed that polymerizations were well controlled. Because of amphiphilic nature, these copolymers self-assembled to form colloidally stable micelles above critical micellar concentration of 0.032 mg · mL(-1). In response to reductive reactions, disulfides in thiol-responsive micelles were cleaved. Atomic force microscopy and dynamic light scattering analysis suggested that the cleavage of disulfides caused dissociation of micelles to smaller-sized assembled structures in water. Moreover, in a biomedical perspective, the mono-cleavable block copolymer micelles are not cytotoxic and thus biocompatible.

Adsorption of PEO–PPO–PEO Triblock Copolymers with End-Capped Cationic Chains of Poly(2-dimethylaminoethyl methacrylate)

We study the adsorption of a symmetric triblock copolymer of ethylene oxide, EO, and propylene oxide, PO, end-capped with quarternized poly(2-dimethylaminoethyl methacrylate), DMAEMA (DMAEMA(24)-EO(132)PO(50)EO(132)-DMAEMA(24)). Light scattering and tensiometry are used to measure the relative size of the associated structures and surface excess at the air-liquid interface. The adsorbed amount, the amount of coupled water, and the viscoelasticity of the adsorbed polymer layer are measured on hydrophobic and hydrophilic surfaces (polypropylene, cellulose, and silica) by using quartz crystal microgravimetry (QCM) and surface plasmon resonance (SPR) at different ionic strengths and temperatures. The results of the experiments are compared with those obtained after adsorption of the uncharged precursor copolymer, without the cationic end-caps (EO(132)PO(50)EO(132)). DMAEMA(24)-EO(132)PO(50)EO(132)-DMAEMA(24) possesses higher affinity with the negatively charged silica and cellulose surfaces while the uncharged copolymer adsorbs to a larger extent on polypropylene surfaces. In this latter case, adsorption increases with increasing solution ionic strength and temperature. Adsorption of EO(132)PO(50)EO(132) on silica surfaces has little effect on the water contact angle (WCA), while adsorption of DMAEMA(24)-EO(132)PO(50)EO(132)-DMAEMA(24) increases the WCA of silica to 32°, indicating a large density of exposed PPO blocks upon adsorption. After adsorption of EO(132)PO(50)EO(132) and DMAEMA(24)-EO(132)PO(50)EO(132)-DMAEMA(24) on PP, the WCA is reduced by ≈14° and ≈28°, respectively, due to the exposed hydrophilic EO and highly water-soluble DMAEMA segments on the surfaces. The extent of surface coverage at saturation at the polypropylene/liquid interfaces (≈31 and 40 nm(2)/molecule obtained by QCM and SPR, respectively) is much lower, as expected, when compared with results obtained at the air/liquid interface, where a tighter packing is observed. The percentage of water coupled to the adsorbed cationic polymer decreases with solution ionic strength. Overall, these observations are ascribed to the effects of electrostatic screening, polymer hydrodynamic size, and solvency.

Adsorption and Association of a Symmetric PEO-PPO-PEO Triblock Copolymer on Polypropylene, Polyethylene, and Cellulose Surfaces

The association of a symmetric polyoxyethylene-polyoxypropylene-polyoxyethylene (PEO(19)-PPO(29)-PEO(19)) triblock copolymer adsorbed from aqueous solutions onto polypropylene (PP), polyethylene (PE), and cellulose surfaces was probed using Atomic Force Microscopy (AFM). Significant morphological differences between the polyolefin substrates (PP and PE) and the cellulose surfaces were observed after immersion of the films in the PEO(19)-PPO(29)-PEO(19) solutions. When the samples were scanned, while immersed in solutions of the triblock copolymer, it was revealed that the structures adsorbed on the polyolefin surfaces were smoothed by the adsorbed PEO(19)-PPO(29)-PEO(19). In contrast, those structures on the hydrophilic cellulose surfaces were sharpened. These observations were related to the roughness of the substrate and the energy of interaction between the surfaces and the PEO and PPO polymer segments. The interaction energy between each of the blocks and the surface was calculated using molecular dynamics simulations. It is speculated that the associative structures amply reported in aqueous solution at concentrations above the critical micelle concentration, CMC, are not necessarily preserved upon adsorption; instead, it appears that molecular arrangements of the anchor-buoy type and hemimicelles prevail. The reported data suggests that the roughness of the surface, as well as its degree of hydrophobicity, have a large influence on the nature of the resulting adsorbed layer. The reported observations are valuable in explaining the behavior of finishing additives and lubricants commonly used in textile and fiber processing, as well as the effect of the morphology of the boundary layers on friction and wear, especially in the case of symmetric triblock copolymers, which are commonly used as antifriction, antiwear additives.