Surface segregation of polypeptide-based block copolymer micelles: An approach to engineer nanostructured and stimuli responsive surfaces

We describe the surface segregation of polypeptide-based block copolymer micelles to produce stimuli-responsive nanostructures at the polymer blend/air interface. Such structures were obtained by simultaneous surface migration and self assembly at the surface of diblock copolymer/homopolymer blends. We employed blends composed of homopolymer (PS) and an amphiphilic block copolymer polystyrene-b-poly(l-glutamic acid) (PS-b-PGA). The surface was functionalized based on the preferential segregation to the polymer blend/air interface of the hydrophilic PGA block of the diblock copolymer upon annealing to water vapor. The surface migration of the diblock copolymer to the interface was demonstrated both by XPS and contact angle measurements. As a consequence, the PGA interfacial attraction leads to a large surface excess on diblock copolymer which in turn, through macrophase and microphase separation, produced separated domains at the surface with regions composed either of homo or block copolymer. Herein we demonstrate that the use of asymmetric diblock copolymers with a higher content in PS lead to spherical micellar assemblies randomly distributed at the surface. As observed by AFM imaging the blend composition, i.e. the amount of block copolymer within the blend influences the density of micelles at the surface. Finally, when exposed to water, the pH affects the surface morphology. The PGA segments are collapsed at low pH values and extended at pH values above 4.8, thus inducing variations on the topography of the films at the nanometer scale.     

Elucidation of protein adsorption behavior on polymeric surfaces: toward high-density, high-payload protein templates

The elucidation of protein adsorption behavior on polymeric surfaces is very important, since their use as arrays and carriers of biomolecules is ever growing for a wide variety of bioapplications. We evaluate protein adsorption characteristics on chemically homogeneous and heterogeneous polymeric surfaces by employing polystyrene-block-polymethylmethacrylate (PS-b-PMMA) diblock copolymer, PS homopolymer, PMMA homopolymer, and PS/PMMA blend as protein templates. We also investigate distance-dependent protein adsorption behavior on the interfacial region between PS and PMMA. We observe selective protein adsorption exclusively onto PS areas for the chemically heterogeneous PS-b-PMMA and PS/PMMA blend templates. On blend films, protein adsorption is highly favored on the PS regions located near the PS:PMMA interface over that on the PS areas situated away from the interface. Protein density on PS domains is inversely proportional to the separation distance between two neighboring PS:PMMA interfaces. We also observe a higher protein density on the PS-b-PMMA than on the PS or PMMA homopolymer templates. This effect is due to the fact that chemically heterogeneous PS-b-PMMA presents periodically spaced PS:PMMA interfaces on the nanometer scale, whereas no such interfaces are present on homopolymer films. The density of protein molecules on the heterogeneous PS-b-PMMA surface is approximately 3-4-fold higher than on the homogeneous PS surface for the identical experimental conditions. These results demonstrate that self-assembling, chemically heterogeneous, nanoscale domains in PS-b-PMMA diblock copolymers can be used as excellent, high-payload, high-density protein templates. The unique advantages of the diblock copolymer may prove the spontaneously constructed protein nanotemplates to be highly suitable as functional substrates in many proteomics applications.     

聚苯乙烯溶胀聚苯乙烯－聚丁二烯－聚苯乙烯三嵌段共聚物微区的研究

嵌段共聚物/均聚物共混体系,各嵌段会形成各自的相,并且嵌段间的连接点一定在两相之间的界面上,这一要求极大地影响了嵌段共聚物/均聚物共混体系的链构象和相行为.     

Nano-organized collagen layers obtained by adsorption on phase-separated polymer thin films

The organization of adsorbed type I collagen layers was examined on a series of polystyrene (PS)/poly(methyl methacrylate) (PMMA) heterogeneous surfaces obtained by phase separation in thin films. These thin films were prepared by spin coating from solutions in either dioxane or toluene of PS and PMMA in different proportions. Their morphology was unraveled combining the information coming from X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and water contact angle measurements. Substrates with PMMA inclusions in a PS matrix and, conversely, substrates with PS inclusions in a PMMA matrix were prepared, the inclusions being either under the form of pits or islands, with diameters in the submicrometer range. The organization of collagen layers obtained by adsorption on these surfaces was then investigated. On pure PMMA, the layer was quite smooth with assemblies of a few collagen molecules, while bigger assemblies were found on pure PS. On the heterogeneous surfaces, it appeared clearly that the diameter and length of collagen assemblies was modulated by the size and surface coverage of the PS domains. If the PS domains, either surrounding or surrounded by the PMMA phase, were above 600 nm wide, a heterogeneous distribution of collagen was found, in agreement with observations made on pure polymers. Otherwise, fibrils could be formed, that were longer compared to those observed on pure polymers. Additionally, the surface nitrogen content determined by XPS, which is linked to the protein adsorbed amount, increased roughly linearly with the PS surface fraction, whatever the size of PS domains, suggesting that adsorbed collagen amount on heterogeneous PS/PMMA surfaces is a combination of that observed on the pure polymers. This work thus shows that PS/PMMA surface heterogeneities can govern collagen organization. This opens the way to a better control of collagen supramolecular organization at interfaces, which could in turn allow cell-material interactions to be tailored.     

COMPUTER SIMULATION OF MISCIBILITY AND SELF-ASSEMBLY STRUCTURE FOR POLYMER-CONTAINING SYSTEMS WITH SPECIAL INTERACTIONS

The miscibility and structure of A-B copolymer/C homopolymer blends with special interactions were studied by aMonte Carlo simulation in two dimensions. The interaction between segment A and segment C was repulsive, whereas it wasattractive between segment B and segment C. In order to study the effect of copolymer chain structure on the morphologyand structure of A-B copolymer/C homopolymer blends, the alternating, random and block A-B copolymers were introducedinto the blends, respectively. The simulation results indicated that the miscibility of A-B block copolymer/C homopolymerblends depended on the chain structure of the A-B copolymer. Compared with alternating or random copolymer, the blockcopolymer, especially the diblock copolymer, could lead to a poor miscibility of A-B copolymer/C homopolymer blends.Moreover, for diblock A-B copolymer/C homopolymer blends, obvious self-organized core-shell smicture was observed inthe segment B composition region from 20% to 60%. However if diblock copolymer composition in the blends is less than40%, obvious self-organized core-shell structure could be formed in the B-segment component region from 10 to 90%.Furthermore, computer statistical analysis for the simulation results showed that the core sizes tended to increasecontinuously and their distribution became wider with decreasing B-segment component.     

聚氧化乙烯-聚苯乙烯-聚氧化乙烯三嵌段共聚物/聚苯醚共混物的相容性和结晶行为

 本工作对聚氧化乙烯-聚苯乙烯-聚氧化乙烯(PEO-PS-PEO)三嵌段共聚物与聚苯醚(PPO)均聚物共混物的相容性及结晶行为进行了研究。结果表明,共混体系的相容性与嵌段共聚物中苯乙烯段的含量有关,PS含量越高,PPO与共聚物PS段的相容性越好。共混体系的结晶行为也明显不同于一般均聚物共混体系。在DSC降温结晶过程中最多可出现三个结晶峰。     

聚氧化乙烯-聚苯乙烯-聚氧化乙烯三嵌段共聚物/聚苯醚共混物的相容性和结晶行为

本工作对聚氧化乙烯-聚苯乙烯-聚氧化乙烯(PEO-PS-PEO)三嵌段共聚物与聚苯醚(PPO)均聚物共混物的相容性及结晶行为进行了研究。结果表明,共混体系的相容性与嵌段共聚物中苯乙烯段的含量有关,PS含量越高,PPO与共聚物PS段的相容性越好。共混体系的结晶行为也明显不同于一般均聚物共混体系。在DSC降温结晶过程中最多可出现三个结晶峰。     

The Effect of Chain Architecture on the Dynamics of Copolymers in a Homopolymer Matrix: Lattice Monte Carlo Simulations using the Bond‐Fluctuation Model

Summary: The effects of copolymer sequence distribution on the dynamics of a copolymer in a homopolymer matrix are studied using computer simulations within the framework of the bond‐fluctuation model on blends containing low concentrations (10%) of copolymers dispersed in a homopolymer matrix. The sequence distribution of the two copolymer components was changed while maintaining the overall copolymer composition at 50/50. Our results indicate that copolymers with disordered sequence distributions exhibit dynamics that are faster than that of a homopolymer melt, while those with ordered sequence distributions exhibit a tendency to form aggregates that lead to slower dynamics as well as phase separation. Analysis of the structure suggests that copolymers with an alternating sequence distribution form large aggregates that are short‐lived, while diblocks form permanent micelle‐like structures. Analysis of the local composition around a copolymer molecule indicates that aggregation between copolymer chains has a direct impact on the local composition. This in turn has a significant impact on system dynamics. Our results indicate that the dynamics of random, random‐blocky, and alternating copolymers are nearly identical and are faster than that of a homopolymer melt. However, alternating copolymers form aggregates and hence are not uniformly distributed throughout the matrix phase. Thus, alternating copolymers are at a disadvantage in their ability to be effective compatibilizers. From a dynamic perspective, copolymers with random and random‐blocky copolymers seem to be ideal compatibilizers since they are distributed uniformly throughout the system and move rapidly through the matrix phase.

Snapshots of aggregates of alternating copolymer chains. Dark and bright spheres represent A and B monomers, respectively.     

Flory状态方程理论研究PS/PMMA/SAN相行为

将改进的Flory状态方程理论(EOS)引入含“分子内链段排斥性相互作用”的高分子共混物中,研究含无规共聚物的三元共混体系聚苯乙烯(PS)/聚甲基丙烯酸甲酯(PMMA)/聚苯乙烯-丙烯腈(SAN)无规共聚物的相行为,建立相应的适用于含无规共聚物三元共混体系Spinodal方程.用PS、PMMA、PAN的特征参数及其链段间相互作用参数分别计算相应共聚物的特征参数,由二元相互作用模型计算均聚物-共聚物间的相互作用能参数.在运用EOS理论研究三元均聚物共混体系相行为基础上,进一步预测PS/PMMA/SAN体系的相行为,计算并绘制不同温度下的Spinodal曲线并进行实验验证,理论计算与实验结果吻合.结果表明,EOS理论可以克服经典平均场理论的缺陷,成功描述含分子内排斥作用共混体系相行为与共聚物组成及温度之间的关系.     

Molecular design of multicomponent polymer systems. VII. Emulsifying effect of poly(ethylene–b–styrene) copolymer in high-density polyethylene/polystyrene blends

Poly(butadiene–b–styrene) copolymers containing a pure, 1,4-PB block have been synthesized by a “living” coordination process. The complete hydrogenation of the PB chain leads accordingly to a high-density polyethylene (HDPE) block. The emulsifying efficiency of such a copolymer (H-7) in HDPE/PS blends is compared with that of a previously reported poly(ethylene–butene–b–styrene) copolymer (SE-7) obtained by the PB hydrogenation of an anionically prepared PB–b–PS. Microscopy examinations demonstrate unambiguously the interfacial activity of both copolymers in HDPE/PS blends. The tensile mechanical properties of the blends are significantly but also differently modified by the two emulsifiers. The copolymer H-7 gives rise to the highest strengths, but, contrary to the copolymer SE-7, provides a poor ductility to the blends. This different behavior is assumed to result in part from the different characteristics of the hydrogenated PB blocks. The elastomeric HPB chain of SE-7 should form at the interface a more or less extended soft zone whereas a rigid interface would result from the cocrystallization of the HPB chain of H-7 with the HDPE homopolymer.     

Influence of Phase Separation Behaviour on Toughness of Compression Moulded SBS Star Block Copolymer/Polystyrene Blends

The influence of homopolymer molecular weight and compression moulding on morphology formation and deformation behaviour of binary blends of polystyrene-polybutadiene based star block copolymer and polystyrene (PS) homopolymer was investigated. The samples used were a polystyrene-(polystyrene-co-polybutadiene)-polystyrene (S-S/B-S) star block copolymer and anionically prepared polystyrene (aPS). The techniques used were transmission electron microscopy (TEM) and uniaxial tensile testing. A wide range of segregation behaviour was observed depending on the ratio of the length of aPS chains relative to that of corresponding outer blocks of the block copolymer. For the first time, the formation of macrophase-separated ‘droplet-like’ morphology has been reported, which endows the block copolymer/polystyrene blends with higher toughness. The mechanical properties of blends are discussed in the light of micromechanical processes of deformation. The micromechanical mechanisms and their dependence with inter domain distance are similar to the mechanisms found in rubber network toughened systems.     

Dewetting behavior of a block copolymer/homopolymer thin film on an immiscible homopolymer substrate

Numerous previous studies have established that the addition of a microphase-ordered AB diblock copolymer to a thin homopolymer A (hA) film can slow, if not altogether prevent, film rupture and subsequent film dewetting on a hard substrate such as silica. However, only a few reports have examined comparable phenomena when the hA/AB blend resides on a soft B-selective surface, such as homopolymer B (hB). In this work, the dewetting kinetics of thin films composed of polystyrene (PS) and a symmetric poly(styrene-b-methyl methacrylate) (SM) diblock copolymer on a poly(methyl methacrylate) substrate is investigated by hot-stage light microscopy. Without the SM copolymer, the dewetting rate of the PS layer is constant under isothermal conditions and exhibits Arrhenius behavior with an apparent activation energy of approximately 180 kJ/mol. Addition of the copolymer promotes a crossover from early- to late-stage dewetting kinetics, as evidenced by measurably different dewetting rates. Transmission electron microscopy reveals the morphological characteristics of dewetted PS/SM films as functions of film thickness and SM concentration.     

Nanostructured carbon black filled polypropylene/polystyrene blends containing styrene-butadiene-styrene copolymer: Influence of morphology on electrical resistivity

This paper is part of a comprehensive study on using selective localization of carbon black (CB) at the interface of immiscible polymer blends in order to reduce the percolation threshold concentration and enhance the conductivity of the blends. CB was successfully localized at the interface of polypropylene/polystyrene (PP/PS) blend by introducing styrene-butadiene-styrene (SBS) tri-block copolymer to the blend. In CB-PP/PS/SBS blends, CB has higher affinity for the polybutadiene (PBD) section of the SBS copolymer, whereas in CB-PP/PS blends, CB prefers the PS phase. PP/PS interface is one of the preferred locations for the SBS copolymer in the (PP/PS) blend; at which the PBD section of the SBS copolymer forms a few nanometers thick layer able to accommodate the CB nano-particles. The influence of SBS addition on the morphology and electrical properties of various PP/PS blends filled with 1 vol% CB were studied. SBS influence on the conductivity of PP/PS blends was found to be a function of the PP/PS volume ratio and SBS loading. The most dramatic increase in conductivity was found in the (60/40) and (70/30) PP/PS blends upon the addition of 5 vol% SBS. 5 vol% SBS was found to be the optimum loading for most blends. Using 10 vol% of SBS was reported to deteriorate electrical conductivity of the conductive co-continuous PP/PS blends. For all blends studied, SBS addition was found to compatibilize the blends. Finer morphologies were obtained by increasing SBS loading.     

Influences of organometallic polymer‐derived catalyst dispersion on SWNT growth

Catalyst formation kinetics of a ferrocene‐containing homopolymer, polyferrocenylethylmethylsilane (PFEMS), is investigated as it relates to the catalysis of single walled carbon nanotubes (SWNTs) through a chemical vapor deposition (CVD) process. The formation and efficiency of the PFEMS‐based iron catalyst is compared with that of the corresponding polystyrene (PS)‐b‐PFEMS diblock copolymer. The PFEMS homopolymer contains 23 wt % iron, while PS‐b‐PFEMS, with a 25 vol % PFEMS content, is only 6% iron. Despite its lower iron content, spin‐cast PS‐b‐PFEMS films on SiO₂/Si substrates produce more active iron sites than spin‐cast PFEMS films during CVD growth of SWNTs. This is related to the self‐assembly of the block copolymer, where PFEMS domains are well dispersed in the PS matrix, which degrades at a CVD temperature of 920 °C to leave catalytically active elemental iron behind. On the contrary, the pure PFEMS films contain a high percentage of iron and silicon, which tend to transform into ceramic‐coated iron at this high temperature, thus rendering the iron inactive towards SWNT growth. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 758–765, 2007     

Structured multistimuli‐responsive functional polymer surfaces obtained by interfacial diffusion of amphiphilic block copolymers

Herein, we report the preparation of structured multistimuli‐responsive surfaces able to change reversibly both their chemical composition depending on the environment and their surface behavior by varying either/both the pH or/and the temperature. For that purpose, we took advantage of the surface segregation in homopolymer/diblock copolymer blends, composed of either polystyrene‐block‐poly(N,N′‐dimethylaminoethylmethacrylate) (PS‐b‐PDMAEMA) or polystyrene‐block‐poly (N,N′‐diethylaminoethylmethacrylate) (PS‐b‐PDEAEMA) and high molecular weight polystyrene used as a matrix. The variations of the surface composition as a function of the environment of exposure (air or water vapor) was investigated were investigated by XPS and contact angle measurements. The water‐annealed surfaces contain PDMAEMA or PDEAEMA at the surface and are additionally able to respond both to pH and temperature as demonstrated by the Wilhelmy technique. Both PDMAEMA and PDEAEMA can switch from a hydrophilic state to a collapsed hydrophobic state increasing the temperature above the LCST. More interestingly, as a result of the microphase separation of the block copolymers at the interface, the surfaces of the blends exhibit structuration. Thus, either micellar structures or “donut‐like” morphologies were obtained by using THF or toluene, respectively, as solvent. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1952–1961, 2010     

Morphology and deformation behaviour of SBS/PS blends: a combined microscopic and spectroscopic study

Correlation between morphology and micromechanical deformation behaviour of blends consisting of a lamellae-forming linear styrene/butadiene block copolymer and polystyrene homopolymer (hPS) was studied by different microscopic techniques (transmission electron microscopy and scanning electron microscopy) and rheo-optical Fourier transformed infrared spectroscopy. Attributable to a change in morphology from well-ordered lamellae to a distorted one, a transition in deformation mechanism from homogeneous plastic flow of the lamellae to formation of local craze-like deformation zones was observed on addition of hPS. The latter led to a drastic reduction in elongation at break. An abrupt depression in the degree of orientation of the polystyrene (PS) and the polybutadiene (PB) phases in the blends suggested that the failure occurs at the interface between the added hPS and PS blocks of the block copolymer.     

Compatabilization of polystyrene/polypropylene blends by styrene–butadiene block copolymers with differing polystyrene block lengths

Compatibilization of polystyrene/polypropylene (PS/PP) blends, by use of a series of butadiene–styrene block copolymers was studied by means of small‐angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM). The compatibilizers used differ in molar mass and the number of blocks. It was shown that the ability of a block copolymer (BC) to participate in the formation of an interfacial layer (and hence in compatibilization) is closely associated with the molar mass of styrene blocks. If the styrene blocks are long enough to form entanglements with the styrene homopolymer in the melt, then the BC is trapped inside this phase of the PS/PP blends, and its migration to the PS/PP interface is difficult. In this case, the BC does not participate in the formation of the interfacial layer nor, consequently, in the compatibilization process. On the other hand, the BC's with the molar mass of the PS blocks below the critical value are proved to be localized at the PS/PP interface. This preferable entrapping of some styrene–butadiene BC's in the PS phase of the PS/PP blend is, of course, connected to the differing miscibility of the BC blocks with corresponding components of this blend. Although the styrene block is chemically identical to the styrene homopolymer in the blend, the butadiene block is similar to the PP phase. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1647–1656, 1999     

Roll-Casting of block copolymers and of block copolymer-homopolymer blends

An improved technique for casting highly oriented films of block copolymers from solutions subjected to flow is presented. Polymer solutions were rolled between two counter-rotating adjacent cylinders while at the same time the solvent was allowed to evaporate. As the solvent evaporated, the block copolymers microphase separated into globally oriented structures. Using this method known as ‘roll-casting’ we present in this paper a study of the morphology of polystyrene-polybutadiene-polystyrene (PS/PB/PS) triblock copolymer cast with and without additional high molecular weight homopolymers. The pure copolymer films consisted of polystyrene cylinders assembled on a hexagonal lattice in a polybutadiene matrix in a near single-crystal structure. Blends of copolymer with high molecular weight polystyrene and/or polybutadiene, phase separated into ellipsoidal regions of homopolymer embedded in an oriented block copolymer matrix. Annealing the films resulted in conversion of the homopolymer regions to spheres accompanied by some misalignment of the copolymer microdomains. The morphology of these films as revealed by TEM is discussed. A brief discussion of the flow field that develops in the experimental system is also presented and its similarity to the flow field of our previous work is shown. © 1994 John Wiley & Sons, Inc.     

Multitechnique characterization of thin films of immiscible polymer systems: PS–b‐PMMA diblock copolymers and PS–PMMA symmetric blends

Immiscible polymer systems are known to form various kinds of phase‐separated structures capable of producing self‐assembled patterns at the surface. In this study, different surface characterization methods were utilized to study the surface morphology and composition produced after annealing thin polymer films. Two different SIMS techniques—static time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and dynamic nano‐SIMS—were used, complemented by x‐ray photoelectron spectrometry (XPS) and atomic force microscopy (AFM). Thin films (spin‐coated onto silicon wafers) of polystyrene (PS)–poly(methyl methacrylate) (PMMA) symmetric blends and diblock copolymers of similar molecular weight were investigated. Surface enrichment by PS was found on all as‐cast samples. The samples were annealed at 160 °C for different time periods, after which the blend and the copolymer films exhibited opposite behaviour as seen by ToF‐SIMS and XPS. The annealed blend surface presented an increase in the PMMA concentration whereas that of copolymers showed a decrease in PMMA concentration compared with the as‐cast sample. For blends, the nano‐SIMS as well as AFM images revealed the formation of phase‐separated domains at the surface. The composition information obtained from ToF‐SIMS and XPS, as well as the surface mapping by nano‐SIMS and AFM, allowed us to conclude that PS formed phase separated droplet‐like domains on a thin PMMA matrix on annealing. The three‐dimensional nano‐SIMS images showed that the PS droplets were supported inside a rim of PMMA and that these droplets continued from the surface like columnar rods into the film until the substrate interface. In the case of annealed copolymer samples, the AFM images revealed topographical features resembling droplet‐like domains on the surface but there was no phase difference between the domains and the matrix. In the case of copolymers, owing to the covalent bonding between the blocks, complete phase separation was not possible. The three‐dimensional nano‐SIMS images showed domain structures in the form of striations inside the film, which were not continuous until the substrate interface. Information from the different techniques was required to gain an accurate view of the surface composition and topographical changes that have occurred under the annealing conditions. Copyright © 2005 John Wiley & Sons, Ltd.     

Thin films of PS/PS‐b‐pnipam and ps/pnipam polymer blends with tunable wettability

We developed thin films of blends of polystyrene (PS) with the thermoresponsive polymer poly(N‐isopropylacrylamide) (PNIPAM) (PS/PNIPAM) and its diblock copolymer polystyrene‐b‐poly(N‐isopropylacrylamide) (PS/PS‐b‐PNIPAM) in different blend ratios, and we study their surface morphology and thermoresponsive wetting behavior. The blends of PS/PNIPAM and PS/PS‐b‐PNIPAM are spin‐casted on flat silicon surfaces with various drying conditions. The surface morphology of the films depends on the blend ratio and the drying conditions. The PS/PS‐b‐PNIPAM films do not show an increase in their water contact angles with temperature, as it is expected by the presence of the PNIPAM block. All PS/PNIPAM films show an increase in the water contact angle above the lower critical solution temperature of PNIPAM, which depends on the ratio of PNIPAM in the blend and is insensitive to the drying conditions of the films. The difference between the wetting behavior of PS/PS‐b‐PNIPAM and PS/PNIPAM films is due to the arrangement of the PNIPAM chains in the film. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 670–679