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Polymers, Volume 9, Issue 8 (August 2017)

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Cover Story (view full-size image) Threadings are architecture-specific topological constraints that give rise to complex and [...] Read more.
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Open AccessReview Characterization of Cell Scaffolds by Atomic Force Microscopy
Polymers 2017, 9(8), 383; https://doi.org/10.3390/polym9080383
Received: 30 July 2017 / Revised: 13 August 2017 / Accepted: 16 August 2017 / Published: 21 August 2017
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Abstract
This review reports on the use of the atomic force microscopy (AFM) in the investigation of cell scaffolds in recent years. It is shown how the technique is able to deliver information about the scaffold surface properties (e.g., topography), as well as about
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This review reports on the use of the atomic force microscopy (AFM) in the investigation of cell scaffolds in recent years. It is shown how the technique is able to deliver information about the scaffold surface properties (e.g., topography), as well as about its mechanical behavior (Young’s modulus, viscosity, and adhesion). In addition, this short review also points out the utilization of the atomic force microscope technique beyond its usual employment in order to investigate another type of basic questions related to materials physics, chemistry, and biology. The final section discusses in detail the novel uses that those alternative measuring modes can bring to this field in the future. Full article
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Open AccessRetraction Retraction: Abdalla, S., et al. A Bio Polymeric Adhesive Produced by Photo Cross-Linkable Technique. Polymers 2016, 8, 292, doi:10.3390/polym8080292 and Abdalla, S., et al. Controlled Light Cross-Linking Technique to Prepare Healable Materials. Polymers 2017, 9, 241, doi:10.3390/polym9060241
Polymers 2017, 9(8), 382; https://doi.org/10.3390/polym9080382
Received: 17 August 2017 / Revised: 17 August 2017 / Accepted: 17 August 2017 / Published: 21 August 2017
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Abstract
These two articles [1,2] published in Polymers will be marked as retracted.[...] Full article
Open AccessArticle Light-Driven Liquid Crystal Circular Dammann Grating Fabricated by a Micro-Patterned Liquid Crystal Polymer Phase Mask
Polymers 2017, 9(8), 380; https://doi.org/10.3390/polym9080380
Received: 27 June 2017 / Revised: 11 August 2017 / Accepted: 17 August 2017 / Published: 21 August 2017
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Abstract
As one of the diffractive optical elements, circular Dammann grating has shown its excellent versatility in practical applications. The electrically switchable Dammann grating has been extensively investigated; however, the research on the optically tunable circular Dammann grating has received less attention and reports
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As one of the diffractive optical elements, circular Dammann grating has shown its excellent versatility in practical applications. The electrically switchable Dammann grating has been extensively investigated; however, the research on the optically tunable circular Dammann grating has received less attention and reports on this subject have been insufficient in the past decade. In this paper, three-order and eight-order binary-phase liquid crystal circular Dammann gratings with two mutually orthogonal photo-induced alignments in every two adjacent alignment domains, fabricated by a micro-patterned liquid crystal polymer phase mask, are proposed to generate annular uniform-intensity patterns in the far field. A simple maskless optical tuning of an eight-order liquid crystal circular Dammann grating is demonstrated by controlling the polarization of an ultraviolet light as well as the energy dose. The proposed liquid crystal circular Dammann gratings with high efficiencies and desirable uniformities exhibit outstanding optical as well as electrical tunabilities, enabling the widespread prospective applications in adaptive photonic chips stimulated flexibly by only light or by the combination of light and electric field. Full article
(This article belongs to the Special Issue Photo-Responsive Polymers)
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Open AccessArticle Increased X-ray Visualization of Shape Memory Polymer Foams by Chemical Incorporation of Iodine Motifs
Polymers 2017, 9(8), 381; https://doi.org/10.3390/polym9080381
Received: 3 August 2017 / Revised: 18 August 2017 / Accepted: 18 August 2017 / Published: 20 August 2017
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Abstract
Shape memory polymers can be programmed into a secondary geometry and recovered to their primary geometry with the application of a controlled stimulus. Porous shape memory polymer foam scaffolds that respond to body temperature show particular promise for embolic medical applications. A limitation
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Shape memory polymers can be programmed into a secondary geometry and recovered to their primary geometry with the application of a controlled stimulus. Porous shape memory polymer foam scaffolds that respond to body temperature show particular promise for embolic medical applications. A limitation for the minimally invasive delivery of these materials is an inherent lack of X-ray contrast. In this work, a triiodobenzene containing a monomer was incorporated into a shape memory polymer foam material system to chemically impart X-ray visibility and increase material toughness. Composition and process changes enabled further control over material density and thermomechanical properties. The proposed material system demonstrates a wide range of tailorable functional properties for the design of embolic medical devices, including X-ray visibility, expansion rate, and porosity. Enhanced visualization of these materials can improve the acute performance of medical devices used to treat vascular malformations, and the material porosity provides a healing scaffold for durable occlusion. Full article
(This article belongs to the Special Issue Shape Memory Polymers)
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Open AccessArticle The Effect of Network Solvation on the Viscoelastic Response of Polymer Hydrogels
Polymers 2017, 9(8), 379; https://doi.org/10.3390/polym9080379
Received: 29 June 2017 / Revised: 11 August 2017 / Accepted: 15 August 2017 / Published: 19 August 2017
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Abstract
The majority of investigations consider the deformation response of hydrogels, fully controlled by the deformation behavior of their polymer network, neglecting the contribution caused by the presence of water. Here, we use molecular dynamics simulation in an attempt to include the effect of
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The majority of investigations consider the deformation response of hydrogels, fully controlled by the deformation behavior of their polymer network, neglecting the contribution caused by the presence of water. Here, we use molecular dynamics simulation in an attempt to include the effect of physically bound water via polymer chain solvation on the viscoelastic response of hydrogels. Our model allows us to control the solvation of chains as an independent variable. The solvation of the chain is independent of other factors, mainly the effect (pH) which interferes significantly in experiments. The solvation of hydrophilic chains was controlled by setting a partial charge on the chains and quantified by the Bjerrum length (BL). The BL was calculated from the partial electric charge of the solvent and macromolecular network. When the BL is short, the repulsive Van der Waals interactions are predominant in the vicinity of macromolecules and solvation is not observed. For a long BL, the water molecules in the solvation zone of network are in the same range as attractive intermolecular forces and the solvation occurs. The model also allows the consideration of molecules of water attached to two chains simultaneously, forming a temporary bridging. By elucidating the relations between solvation of the network and structural changes during the network deformation, one may predict the viscoelastic properties of hydrogels knowing the molecular structure of its polymer chains. Full article
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Open AccessArticle Mechanical Properties of Composite Hydrogels of Alginate and Cellulose Nanofibrils
Polymers 2017, 9(8), 378; https://doi.org/10.3390/polym9080378
Received: 27 June 2017 / Revised: 10 August 2017 / Accepted: 17 August 2017 / Published: 19 August 2017
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Abstract
Alginate and cellulose nanofibrils (CNF) are attractive materials for tissue engineering and regenerative medicine. CNF gels are generally weaker and more brittle than alginate gels, while alginate gels are elastic and have high rupture strength. Alginate properties depend on their guluronan and mannuronan
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Alginate and cellulose nanofibrils (CNF) are attractive materials for tissue engineering and regenerative medicine. CNF gels are generally weaker and more brittle than alginate gels, while alginate gels are elastic and have high rupture strength. Alginate properties depend on their guluronan and mannuronan content and their sequence pattern and molecular weight. Likewise, CNF exists in various qualities with properties depending on, e.g., morphology and charge density. In this study combinations of three types of alginate with different composition and two types of CNF with different charge and degree of fibrillation have been studied. Assessments of the composite gels revealed that attractive properties like high rupture strength, high compressibility, high gel rigidity at small deformations (Young’s modulus), and low syneresis was obtained compared to the pure gels. The effects varied with relative amounts of CNF and alginate, alginate type, and CNF quality. The largest effects were obtained by combining oxidized CNF with the alginates. Hence, by combining the two biopolymers in composite gels, it is possible to tune the rupture strength, Young’s modulus, syneresis, as well as stability in physiological saline solution, which are all important properties for the use as scaffolds in tissue engineering. Full article
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Open AccessArticle Effect of Sodium Hydroxide Treatments on the Tensile Strength and the Interphase Quality of Hemp Core Fiber-Reinforced Polypropylene Composites
Polymers 2017, 9(8), 377; https://doi.org/10.3390/polym9080377
Received: 21 July 2017 / Revised: 11 August 2017 / Accepted: 14 August 2017 / Published: 19 August 2017
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Abstract
The formulation of greener composite materials by substituting glass fibers with natural fibers is a current field of research. If such natural fiber reinforcements come from industrial side streams, as hemp core fibers (HCFs) come from the extraction of hemp strands for the
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The formulation of greener composite materials by substituting glass fibers with natural fibers is a current field of research. If such natural fiber reinforcements come from industrial side streams, as hemp core fibers (HCFs) come from the extraction of hemp strands for the textile industry, an additional advantage can be identified. Nonetheless, such by-product fibers show some drawbacks, such as high lignin contents, which can make it difficult to obtain a good interphase between the fibers and the matrix and to obtain a good fiber individualization. A digestion treatment at different NaOH contents is proposed to eliminate soluble lignin and extractives from the surface of the fibers. At the same time, the use of a coupling agent solves incompatibilities between the fibers and the matrix. The composites were tensile tested and the impact of the proposed treatments is evaluated and discussed. Later, the Kelly-Tyson modified equation and a modified rule of mixtures—the micro-mechanic models—is used to study the impact of such treatments on the quality of the interphase between the polymer and the reinforcement. Both treatments showed a high impact on the tensile strength and the quality of the interphase, obtaining competitive composite materials reinforced with HCFs derived from a by-product. Full article
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Open AccessArticle Effect of Catechol Content in Catechol-Conjugated Dextrans on Antiplatelet Performance
Polymers 2017, 9(8), 376; https://doi.org/10.3390/polym9080376
Received: 26 June 2017 / Revised: 17 August 2017 / Accepted: 17 August 2017 / Published: 19 August 2017
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Abstract
The surface coating of solid substrates using dextrans has gained a great deal of attention, because dextran-coated surfaces show excellent anti-fouling property as well as biocompatibility behavior. Much effort has been made to develop efficient methods for grafting dextrans on solid surfaces. This
[...] Read more.
The surface coating of solid substrates using dextrans has gained a great deal of attention, because dextran-coated surfaces show excellent anti-fouling property as well as biocompatibility behavior. Much effort has been made to develop efficient methods for grafting dextrans on solid surfaces. This led to the development of catechol-conjugated dextrans (Dex-C) which can adhere to a number of solid surfaces, inspired by the underwater adhesion behavior of marine mussels. The present study is a systematic investigation of the characteristics of surface coatings developed with Dex-C. Various Dex-C with different catechol contents were synthesized and used as a surface coating material. The effect of catechol content on surface coating and antiplatelet performance was investigated. Full article
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Open AccessArticle Correlation-Based Multiplexing of Complex Amplitude Data Pages in a Holographic Storage System Using Digital Holographic Techniques
Polymers 2017, 9(8), 375; https://doi.org/10.3390/polym9080375
Received: 30 June 2017 / Revised: 9 August 2017 / Accepted: 15 August 2017 / Published: 18 August 2017
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Abstract
Holographic recording media can store the amplitude and the phase, or the complex amplitude, of a beam on the basis of holography. Owing to this characteristic, digital data can be encoded onto the complex amplitude of a signal beam in holographic data storage.
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Holographic recording media can store the amplitude and the phase, or the complex amplitude, of a beam on the basis of holography. Owing to this characteristic, digital data can be encoded onto the complex amplitude of a signal beam in holographic data storage. However, most of conventional holographic storage systems encode digital data onto the amplitude alone because there are difficulties for modulating and detecting the phase. To solve the difficulties, a holographic storage system using digital holographic techniques has been proposed. With the help of digital holographic techniques, it is possible to modulate and detect the complex amplitude of a signal beam. Moreover, the proposed system can modulate the complex amplitude of a reference beam. In this paper, by making use of the capability, a correlation-based multiplexing with uncorrelated reference beams is demonstrated in the proposed system. Multiple holograms can be recorded in the same volume of a recording medium with no need for mechanical movements. Experimental results show that the proposed system with a correlation-based multiplexing can improve the storage capacity and can utilize the full potential of a recording medium without crosstalk noise stem from the optical setup. Full article
(This article belongs to the Special Issue Photo-Responsive Polymers)
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Open AccessArticle Bacterial Nanocellulose from Side-Streams of Kombucha Beverages Production: Preparation and Physical-Chemical Properties
Polymers 2017, 9(8), 374; https://doi.org/10.3390/polym9080374
Received: 15 July 2017 / Revised: 11 August 2017 / Accepted: 14 August 2017 / Published: 18 August 2017
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Abstract
We focused on preparing cellulose nanofibrils by purification, separation, and mechanical treatment of Kombucha membranes (KM) resulted as secondary product from beverage production by fermentation of tea broth with symbiotic culture of bacteria and yeast (SCOBY). We purified KM using two alkaline solutions,
[...] Read more.
We focused on preparing cellulose nanofibrils by purification, separation, and mechanical treatment of Kombucha membranes (KM) resulted as secondary product from beverage production by fermentation of tea broth with symbiotic culture of bacteria and yeast (SCOBY). We purified KM using two alkaline solutions, 1 and 4 M NaOH, which afterwards were subjected to various mechanical treatments. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), dynamic light scattering (DLS), X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) were employed to evaluate the purification degree, the size and aspect of cellulose fibrils after each treatment step, the physical-chemical properties of intermediary and final product, and for comparison with micro-crystalline cellulose from wooden sources. We determined that 1 M NaOH solution leads to approx. 85% purification, while a higher concentration assures almost 97% impurities removal. XRD analysis evidenced an increase in crystallinity from 37% to 87% after purification, the characteristic diffractograms of Iα and Iβ cellulose allomorphs, and a further decrease in crystallinity to 46% after microfluidization, fact correlated with a drastically decrease in fibrils’ size. FTIR analysis evidenced the appearance of new chain ends by specific transmission bands at 2941 and 2843cm−1. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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Open AccessCommunication Synthesis of Humin-Phenol-Formaldehyde Adhesive
Polymers 2017, 9(8), 373; https://doi.org/10.3390/polym9080373
Received: 27 May 2017 / Revised: 11 August 2017 / Accepted: 14 August 2017 / Published: 18 August 2017
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Abstract
Humins are low-value-added byproducts from the biomass acid hydrolysis process. In the present work, humins were first employed as a phenol replacement for synthesis of modified phenol-formaldehyde adhesives through a two-step process. In this process, humins were first utilized to obtain alkaline soluble
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Humins are low-value-added byproducts from the biomass acid hydrolysis process. In the present work, humins were first employed as a phenol replacement for synthesis of modified phenol-formaldehyde adhesives through a two-step process. In this process, humins were first utilized to obtain alkaline soluble products, mainly consisting of phenolics, through a hydrothermal process. The obtained alkaline soluble products then reacted with phenol and formaldehyde to produce humin-phenol-formaldehyde adhesive (HPFA). The physicochemical properties of HPFA, including viscosity, bonding strength, pH, free formaldehyde level, free phenol level and solid content, met the requirements of the GB/T 14732-2006 Chinese National Standard. Full article
(This article belongs to the collection Polymeric Adhesives)
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Open AccessArticle Microstructural and Mechanical Implications of Microscaled Assembly in Droplet-based Multi-Material Additive Manufacturing
Polymers 2017, 9(8), 372; https://doi.org/10.3390/polym9080372
Received: 30 June 2017 / Revised: 15 August 2017 / Accepted: 16 August 2017 / Published: 18 August 2017
Cited by 2 | PDF Full-text (11670 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
To reveal the potential and limits of multi-material three-dimensional (3D) printed parts in droplet-based additive manufacturing, a study combining tensile experiments and 3D imaging technique is proposed. A polymeric composite structure made of acrylonitrile butadiene styrene and thermoplastic polyurethane is manufactured using a
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To reveal the potential and limits of multi-material three-dimensional (3D) printed parts in droplet-based additive manufacturing, a study combining tensile experiments and 3D imaging technique is proposed. A polymeric composite structure made of acrylonitrile butadiene styrene and thermoplastic polyurethane is manufactured using a two extrusion head printer. The quality of the interface between the two thermoplastics is quantified by adjusting the number of intertwining droplets at the interface. Tensile experiments assisted with digital image correlation are performed with two-interface orientation to discriminate shearing and traction at the interface. The 3D imaging results, which are based on X-ray micro-tomography, show the distinct features of droplet-based additive manufacturing in terms of porosity content and connectivity. Interface properties are found to control, in an incomparable way, the mechanical response. It is found that the interface quality is determinant for enhancing the ultimate performance whereas the interface orientation is found to be the perfect leverage for varying the slope of the linear part. Full article
(This article belongs to the Special Issue Three-Dimensional Structures: Fabrication and Application)
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Open AccessArticle Surface Modification of Poly(lactic acid) Fabrics with Plasma Pretreatment and Chitosan/Siloxane Polyesters Coating for Color Strength Improvement
Polymers 2017, 9(8), 371; https://doi.org/10.3390/polym9080371
Received: 12 July 2017 / Revised: 3 August 2017 / Accepted: 16 August 2017 / Published: 18 August 2017
Cited by 4 | PDF Full-text (1289 KB) | HTML Full-text | XML Full-text
Abstract
As people in the 21st century become increasingly environmentally aware, environmentally friendly products have come into focus. As such, environmentally friendly textiles and eco-textiles have become an international trend in research and development. Poly(lactic acid) fiber, which is biodegradable, holds much promise, but
[...] Read more.
As people in the 21st century become increasingly environmentally aware, environmentally friendly products have come into focus. As such, environmentally friendly textiles and eco-textiles have become an international trend in research and development. Poly(lactic acid) fiber, which is biodegradable, holds much promise, but it is difficult to deep dye. This study used chitosan, succine anhydride, siloxane, and polyethylene glycol to produce a series of chitosan/siloxane polyesters that have a hydrophilic component (chitosan) and a hydrophobic component (siloxane), and this chitosan/siloxane polyester can be coated on poly(lactic acid) fiber, which we had subjected to Argon plasma treatment to increase their antimicrobial properties and to increase the fibers dyeing efficiency. The study shows that, after the surface plasma treatment, longer PEG chain lengths resulted in higher K/S values. This result suggests that the surface plasma pretreatment and chitosan/siloxane polyesters coating showed that lower ∆E values result in more leveling dyeing of poly(lactic acid) fiber. Full article
(This article belongs to the Special Issue Biodegradable and Biobased Polyesters)
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Open AccessArticle Molecular Dynamics Study on the Effect of Surface Hydroxyl Groups on Three-Phase Wettability in Oil-Water-Graphite Systems
Polymers 2017, 9(8), 370; https://doi.org/10.3390/polym9080370
Received: 30 June 2017 / Revised: 15 August 2017 / Accepted: 15 August 2017 / Published: 18 August 2017
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Abstract
In this paper, a hydroxylated graphite surface is generated as a hydrophilic oleophobic material for the application of oil-water separation, and the effects of hydroxyl density on the three-phase wettability are studied in oil-water-graphite systems. We analyze the adsorption of water molecules on
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In this paper, a hydroxylated graphite surface is generated as a hydrophilic oleophobic material for the application of oil-water separation, and the effects of hydroxyl density on the three-phase wettability are studied in oil-water-graphite systems. We analyze the adsorption of water molecules on the hydroxylated surfaces and obtain the relationship between water-oil-solid interfacial properties and the hydroxyl density, which results from the synthetic effects of the orientation of molecules and hydrogen bonds. With the increase of hydroxyl density, the water-solid contact angle first decreases rapidly, and then remains constant. The density of the hydrogen bond formed between hydroxyls and water molecules in the adsorption layer can explain the regularity of the three-phase wettability. The orientation of the water molecules in the adsorption layer shows insignificant variation, owing to the hydrogen bond network formed between the water molecules; thus, little change is observed in the hydrogen bond density in the adsorption layer. Full article
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Open AccessArticle Constraining Polymers into β-Turns: Miscibility and Phase Segregation Effects in Lipid Monolayers
Polymers 2017, 9(8), 369; https://doi.org/10.3390/polym9080369
Received: 28 July 2017 / Revised: 11 August 2017 / Accepted: 13 August 2017 / Published: 17 August 2017
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Abstract
Abstract: Investigation of model biomembranes and their interactions with natural or synthetic macromolecules are of great interest to design membrane systems with specific properties such as drug-delivery. Here we study the behavior of amphiphilic β-turn mimetic polymer conjugates at the air–water interface
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Abstract: Investigation of model biomembranes and their interactions with natural or synthetic macromolecules are of great interest to design membrane systems with specific properties such as drug-delivery. Here we study the behavior of amphiphilic β-turn mimetic polymer conjugates at the air–water interface and their interactions with lipid model membranes. For this endeavor we synthesized two different types of conjugates containing either hydrophobic polyisobutylene (PIB, Mn = 5000 g·mol−1) or helical poly(n-hexyl isocyanate) (PHIC, Mn = 4000 g·mol−1), both polymers being immiscible, whereas polyisobutylene as a hydrophobic polymer can incorporate into lipid membranes. The conjugates were investigated using Langmuir-film techniques coupled with epifluorescence microscopy and AFM (Atomic Force Microscopy), in addition to their phase behavior in mixed lipid/polymer membranes composed of DPPC (dipalmitoyl-sn-glycero-3-phosphocholine). It was found that the DPPC monolayers are strongly disturbed by the presence of the polymer conjugates and that domain formation of the polymer conjugates occurs at high surface pressures (π > 30 mN·m−1). Full article
(This article belongs to the Special Issue From Amphiphilic to Polyphilic Polymers)
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