The Interplay of Modulus,Strength, and Ductility in Adhesive Design Using Biomimetic Polymer Chemistry

High‐performance adhesives require mechanical properties tuned to demands of the surroundings. A mismatch in stiffness between substrate and adhesive leads to stress concentrations and fracture when the bonding is subjected to mechanical load. Balancing material strength versus ductility, as well as considering the relationship between adhesive modulus and substrate modulus, creates stronger joints. However, a detailed understanding of how these properties interplay is lacking. Here, a biomimetic terpolymer is altered systematically to identify regions of optimal bonding. Mechanical properties of these terpolymers are tailored by controlling the amount of a methyl methacrylate stiff monomer versus a similar monomer containing flexible poly(ethylene glycol) chains. Dopamine methacrylamide, the cross‐linking monomer, is a catechol moiety analogous to 3,4‐dihydroxyphenylalanine, a key component in the adhesive proteins of marine mussels. Bulk adhesion of this family of terpolymers is tested on metal and plastic substrates. Incorporating higher amounts of poly(ethylene glycol) into the terpolymer introduces flexibility and ductility. By taking a systematic approach to polymer design, the region in which material strength and ductility are balanced in relation to the substrate modulus is found, thereby yielding the most robust joints.     

A Biomimetic Mussel‐Inspired ε‐Poly‐l‐lysine Hydrogel with Robust Tissue‐Anchor and Anti‐Infection Capacity

In situ hydrogels have attracted considerable attention in tissue engineering because of their minimal invasiveness and ability to match the irregular tissue defects. However, hydrous physiological environments and the high level of moisture in hydrogels severely hamper binding to the target tissue and easily cause wound infection, thereby limiting the effectiveness in wound care management. Thus, forming an intimate assembly of the hydrogel to the tissue and preventing wound infecting still remains a significant challenge. In this study, inspired by mussel adhesive protein, a biomimetic dopamine‐modified ε‐poly‐l ‐lysine‐polyethylene glycol‐based hydrogel (PPD hydrogel) wound dressing is developed in situ using horseradish peroxidase cross‐linking. The biomimetic catechol–Lys residue distribution in PPD polymer provides a catechol–Lys cooperation effect, which endows the PPD hydrogels with superior wet tissue adhesion properties. It is demonstrated that the PPD hydrogel can facilely and intimately integrate with biological tissue and exhibits superior capacity of in vivo hemostatic and accelerated wound repair. In addition, the hydrogels exhibit outstanding anti‐infection property because of the inherent antibacterial ability of ε‐poly‐l ‐lysine. These findings shed new light on the development of mussel‐inspired tissue‐anchored and antibacterial hydrogel materials serving as wound dressings.     

Supramolecular β‐Sheet Suckerin–Based Underwater Adhesives

Nature has evolved several molecular strategies to ensure adhesion in aqueous environments, where artificial adhesives typically fail. One recently‐unveiled molecular design for wet‐resistant adhesion is the cohesive cross‐β structure characteristic of amyloids, complementing the well‐established surface‐binding strategy of mussel adhesive proteins based on 3,4‐l ‐dihydroxyphenylalanine (Dopa). Structural proteins that self‐assemble into cross β‐sheet networks are the suckerins discovered in the sucker ring teeth of squids. Here, light is shed on the wet adhesion of cross‐β motifs by producing recombinant suckerin‐12, naturally lacking Dopa, and investigating its wet adhesion properties. Surprisingly, the adhesion forces measured on mica reach 70 mN m^?1, exceeding those measured for all mussel adhesive proteins to date. The pressure‐sensitive adhesion of artificial suckerins is largely governed by their cross‐β motif, as evidenced using control experiments with disrupted cross‐β domains that result in complete loss of adhesion. Dopa is also incorporated in suckerin‐12 using a residue‐specific incorporation strategy that replaces tyrosine with Dopa during expression in Escherichia coli. Although the replacement does not increase the long‐term adhesion, it contributes to the initial rapid contact and enhances the adsorption onto model oxide substrates. The findings suggest that suckerins with supramolecular cross‐β motifs are promising biopolymers for wet‐resistant adhesion.     

Mussel Inspired Dynamic Cross‐Linking of Self‐Healing Peptide Nanofiber Network

A general drawback of supramolecular peptide networks is their weak mechanical properties. In order to overcome a similar challenge, mussels have adapted to a pH‐dependent iron complexation strategy for adhesion and curing. This strategy also provides successful stiffening and self‐healing properties. The present study is inspired by the mussel curing strategy to establish iron cross‐link points in self‐assembled peptide networks. The impact of peptide‐iron complexation on the morphology and secondary structure of the supramolecular nanofibers is characterized by scanning electron microscopy, circular dichroism and Fourier transform infrared spectroscopy. Mechanical properties of the cross‐linked network are probed by small angle oscillatory rheology and nanoindentation by atomic force microscopy. It is shown that iron complexation has no influence on self‐assembly and β‐sheet‐driven elongation of the nanofibers. On the other hand, the organic‐inorganic hybrid network of iron cross‐linked nanofibers demonstrates strong mechanical properties comparable to that of covalently cross‐linked network. Strikingly, iron cross‐linking does not inhibit intrinsic reversibility of supramolecular peptide polymers into disassembled building blocks and the self‐healing ability upon high shear load. The strategy described here could be extended to improve mechanical properties of a wide range of supramolecular polymer networks.     

Mussel‐Inspired Hydrogels for Self‐Adhesive Bioelectronics

Wearable and implantable bioelectronics are receiving a great deal of attention because they offer huge promise in personalized healthcare. Currently available bioelectronics generally rely on external aids to form an attachment to the human body, which leads to unstable performance in practical applications. Self‐adhesive bioelectronics are highly desirable for ameliorating these concerns by offering reliable and conformal contact with tissue, and stability and fidelity in the signal detection. However, achieving adequate and long‐term self‐adhesion to soft and wet biological tissues has been a daunting challenge. Recently, mussel‐inspired hydrogels have emerged as promising candidates for the design of self‐adhesive bioelectronics. In addition to self‐adhesiveness, the mussel‐inspired chemistry offers a unique pathway for integrating multiple functional properties to all‐in‐one bioelectronic devices, which have great implications for healthcare applications. In this report, the recent progress in the area of mussel‐inspired self‐adhesive bioelectronics is highlighted by specifically discussing: 1) adhesion mechanism of mussels, 2) mussel‐inspired hydrogels with long‐term and repeatable adhesion, 3) the recent advance in development of hydrogel bioelectronics by reconciling self‐adhesiveness and additional properties including conductivity, toughness, transparency, self‐healing, antibacterial properties, and tolerance to extreme environment, and 4) the challenges and prospects for the future design of the mussel‐inspired self‐adhesive bioelectronics.     

Physical Double‐Network Hydrogel Adhesives with Rapid Shape Adaptability,Fast Self‐Healing,Antioxidant and NIR/pH Stimulus‐Responsiveness for Multidrug‐Resistant Bacterial Infection and Removable Wound Dressing

Developing physical double‐network (DN) removable hydrogel adhesives with both high healing efficiency and photothermal antibacterial activities to cope with multidrug‐resistant bacterial infection, wound closure, and wound healing remains an ongoing challenge. An injectable physical DN self‐healing hydrogel adhesive under physiological conditions is designed to treat multidrug‐resistant bacteria infection and full‐thickness skin incision/defect repair. The hydrogel adhesive consists of catechol–Fe³⁺ coordination cross‐linked poly(glycerol sebacate)‐co‐poly(ethylene glycol)‐g‐catechol and quadruple hydrogen bonding cross‐linked ureido‐pyrimidinone modified gelatin. It possesses excellent anti‐oxidation, NIR/pH responsiveness, and shape adaptation. Additionally, the hydrogel presents rapid self‐healing, good tissue adhesion, degradability, photothermal antibacterial activity, and NIR irradiation and/or acidic solution washing‐assisted removability. In vivo experiments prove that the hydrogels have good hemostasis of skin trauma and high killing ratio for methicillin‐resistant staphylococcus aureus (MRSA) and achieve better wound closure and healing of skin incision than medical glue and surgical suture. In particular, they can significantly promote full‐thickness skin defect wound healing by regulating inflammation, accelerating collagen deposition, promoting granulation tissue formation, and vascularization. These on‐demand dissolvable and antioxidant physical double‐network hydrogel adhesives are excellent multifunctional dressings for treating in vivo MRSA infection, wound closure, and wound healing.     

Peptide‐Enhanced Selective Surface Deposition of Polymer‐Based Fragrance Delivery Systems

Surface deposition is a critical step in the application of fragrance‐containing products. This contribution presents a novel strategy to enhance the deposition of polymer‐based fragrance delivery systems onto cotton substrates from the application medium using phage display identified peptides. Following the identification of cotton binding peptide ligands under fabric softening conditions via phage display, the strongest binding peptide ligand is incorporated into two model polymer‐based fragrance delivery systems, viz., polymer profragrances and polymer nanoparticles. The model polymer profragrance used is a linear, water soluble poly(N‐(2‐hydroxypropyl)methacrylamide) conjugate, while poly(styrene‐co‐acrylic acid) (PS‐co‐PAA) nanoparticles prepared via miniemulsion polymerization are chosen as the second model system. The incorporation of the cotton binding peptide ligand into these fragrance delivery systems enhances their surface deposition two‐ to three‐fold, as evidenced by fluorescence intensity measurements. In the case of the fragrance‐containing PS‐co‐PAA nanoparticles, the enhanced surface deposition also translates into an increased fragrance release from the cotton surface according to dynamic headspace sampling measurements.     

Hyaluronic Acid Catechol: A Biopolymer Exhibiting a pH‐Dependent Adhesive or Cohesive Property for Human Neural Stem Cell Engineering

Nature has developed materials that are integrated and effective at controlling their properties of adhesiveness and cohesiveness; the chemistry of these materials has been optimized during evolution. For example, a catechol moiety found in the adhesive proteins of marine mussels regulates its properties between adhesion and cohesion, rapidly adapting to environmental conditions. However, in synthetic materials chemistry, introduced chemical moieties are usually monofunctional, either being adhesive or cohesive; typically, this is not effective compared to natural materials. Herein, it is demonstrated that hyaluronic acid‐catechol (HA‐catechol) conjugates can exhibit either adhesiveness, functionalizing the surface of materials, or cohesiveness, building 3D hydrogels. Up to now, catechol‐conjugated polymers have shown to be useful in one of these two functions. The usefulness of the polymer in stem cell engineering is demonstrated. A platform for neural stem cell culture may be prepared, utilizing the adhesive property of HA‐catechol, and hydrogels are fabricated to encapsulate the neural stem cells, utilizing the cohesive property of the HA conjugate. Moreover, the HA‐catechol hydrogels are highly neural stem cell compatible, showing better viability compared to existing methods based on HA hydrogels.     

Polymorph Switching of Calcium Carbonate Crystals by Polymer‐Controlled Crystallization

Polymer‐controlled crystallization of calcium carbonate crystals in solution by a gas diffusion method has been carried out in the presence of poly(sodium 4‐styrene sulfonate‐co‐N‐isopropylacrylamide) (PSS‐co‐PNIPAAM), and for the first time all three anhydrous polymorphs, calcite, vaterite, and aragonite could be selectively produced with a single additive. The selective polymorph synthesis can be nicely adjusted simply by concentration variations of polymer and calcium ions in the present reaction system. The simplicity of the system reveals the influence of Ca²⁺ and polymer concentration on the nucleation and crystal growth of CaCO₃ via the balance between thermodynamic and kinetic reaction control. A single mechanistic framework employing particle mediated as well as ion mediated crystallization for polymorph control is proposed.     

Multivalent‐Ion‐Mediated Stabilization of Hydrogen‐Bonded Multilayers

Hydrogen‐bonding interactions are an important alternative to electrostatic interactions for assembling multilayer thin films of uncharged components. Herein, a new method is reported for rendering such films stable at pH values close to physiological conditions. Multilayer films based on hydrogen bonding are assembled by the alternate deposition of poly[(styrene sulfonic acid)‐co‐(maleic acid)] (PSSMA) and poly(N‐isopropylacrylamide) (PNiPAAm) at pH 2.5. The use of PSSMA results in multilayers that contain free styrene sulfonate groups, as these moieties do not interact with the PNiPAAm functional groups. Subsequent infiltration of a multivalent ion (Ce⁴⁺ or Fe³⁺) leads to an increase in the total film mass, with little impact on the film morphology, as determined by using atomic force microscopy. To examine the film stability, the resulting films have been exposed to elevated pH (7.1). While there is substantial swelling of the multilayers (25 % and 55 % for Ce⁴⁺‐ and Fe³⁺‐stabilized films, respectively), film loss is negligible. This provides a stark contrast with non‐stabilized films, which disassemble almost immediately upon exposure to pH 7.1. This method represents a simple and effective strategy for stabilizing hydrogen‐bonded structures non‐covalently. Further, the multivalent ions also render the films responsive to changes in the local redox environment, as demonstrated by film disassembly after exposure of Fe³⁺‐treated films to iodide solutions.     

Positively Thermo‐Sensitive Monodisperse Core–Shell Microspheres

In this paper, we report on a novel family of monodisperse thermo‐sensitive core–shell hydrogel microspheres that is featured with high monodispersity and positively thermo‐responsive volume phase transition characteristics with tunable swelling kinetics, i.e., the particle swelling is induced by an increase rather than a decrease in temperature. The microspheres were fabricated in a three‐step process. In the first step, monodisperse poly(acrylamide‐co‐styrene) seeds were prepared by emulsifier‐free emulsion polymerization. In the second step, poly(acrylamide) or poly[acrylamide‐co‐(butyl methacrylate)] shells were fabricated on the microsphere seeds by free radical polymerization. In the third step, the core–shell microspheres with poly‐ (acrylamide)/poly(acrylic acid) based interpenetrating polymer network (IPN) shells were finished by a method of sequential IPN synthesis. The proposed monodisperse core–shell microspheres provide a new mode of the phase transition behavior for thermo‐sensitive “smart” or “intelligent” monodisperse micro‐actuators that is highly attractive for targeting drug delivery systems, chemical separations, sensors, and so on.     

Room‐Temperature Self‐Healing and Recyclable Tough Polymer Composites Using Nitrogen‐Coordinated Boroxines

In this paper, nitrogen‐coordinated boroxines are exploited for the fabrication of self‐healing and recyclable polymer composites with enhanced mechanical properties. The 3D polymer networks cross‐linked with nitrogen‐coordinated boroxines are first synthesized through the trimerization of ortho‐aminomethyl‐phenylboronic acid groups at the terminals of poly(propylene glycol) (PPG) chains, and subsequently, the mechanically robust polymer composites are fabricated by utilizing the complexation of nitrogen‐coordinated boroxine‐containing PPG (N‐boroxine‐PPG) with poly(acrylic acid) (PAA) and hydrogen‐bonding interactions between them. The N‐boroxine‐PPG is soft with a tensile strength of 0.19 MPa, whereas the tensile strengths of N‐boroxine‐PPG/PAA composites can be tailored to range from 1.7 to 12.7 MPa by increasing the PAA contents in the polymer composites. It is revealed that the amine ligands can facilitate the formation and dissociation of nitrogen‐coordinated boroxines at room temperature. Moreover, the reversibility of nitrogen‐coordinated boroxines and hydrogen‐bonding interactions enable multiple cycles of healing and recycling of the damaged N‐boroxine‐PPG/PAA composites. The healed and recycled N‐boroxine‐PPG/PAA polymer composites regain most of their mechanical strength.     

Bioinspired Double‐Dynamic‐Bond Crosslinked Bioadhesive Enables Post‐Wound Closure Care

Most existing bioadhesives, even those showing superiority in wound closure effectiveness, do not assist in the post‐wound closure process. A bioinspired, in situ formed, double‐dynamic‐bond crosslinked hydrogel bioadhesive that is capable of efficiently closing open wounds and enabling post‐wound closure care is reported. Catechol‐modified ε‐poly‐l ‐lysine and oxidized dextran are employed as natural polymer backbones and they are in situ crosslinked using Schiff's base dynamic bond and catechol? Fe coordinate dynamic bond through a process inspired by that used to cure marine mussel glue, forming a hydrogel bioadhesive. The unique double‐dynamic‐bond crosslinked structure endows the bioadhesive with higher mechanical and adhesive strength while retaining quick dissociation and good self‐healing capacities. Accordingly, the bioadhesive can exhibit multiple desirable functions, such as dissolution on demand, repeatable adhesiveness, adhesive and mechanical strength sufficient for wound closure, injectability, and good biocompatibility (DREAMING). After efficiently closing skin incisions, the bioadhesive can be facilely removed or repeatedly close the reopened wounds, thus enabling post‐wound closure care. On the basis of favorable functions in wound closure and the ability to enable post‐wound closure care, the bioadhesive demonstrates great potential in dealing with skin wounds.     

Interface Modification to Improve Hole‐Injection Properties in Organic Electronic Devices

The performance of organic electronic devices is often limited by injection. In this paper, improvement of hole injection in organic electronic devices by conditioning of the interface between the hole‐conducting layer (buffer layer) and the active organic semiconductor layer is demonstrated. The conditioning is performed by spin‐coating poly(9,9‐dioctyl‐fluorene‐co‐N‐ (4‐butylphenyl)‐diphenylamine) (TFB) on top of the poly(3,4‐ethylene dioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) buffer layer, followed by an organic solvent wash, which results in a TFB residue on the surface of the PEDOT:PSS. Changes in the hole‐injection energy barriers, bulk charge‐transport properties, and current–voltage characteristics observed in a representative PFO‐based (PFO: poly(9,9‐dioctylfluorene)) diode suggest that conditioning of PEDOT:PSS surface with TFB creates a stepped electronic profile that dramatically improves the hole‐injection properties of organic electronic devices.     

A Biomimetic Actuator Based on an Ionic Networking Membrane of Poly(styrene‐alt‐maleimide)‐Incorporated Poly(vinylidene fluoride)

A novel electro‐active polymer actuator employing the ionic networking membrane of poly(styrene‐alt‐maleimide) (PSMI)‐incorporated poly(vinylidene fluoride) (PVDF) was developed to improve the electrical and mechanical performance of the artificial muscles. The main drawback of the previous ionic polymer‐metal composite actuator was the straightening‐back and relaxation under the constant voltage excitation. The present ionic networking membrane actuator overcomes the relaxation of the ionic polymer‐metal composite actuator under the constant voltage and also shows much larger tip displacement than that of the Nafion‐based actuator. Under the simple harmonic stimulus, the measured mechanical displacement was comparable to that of the Nafion‐based actuator. The excellent electromechanical response of the current polymer actuator is attributed to two factors: the inherent large ionic‐exchange capacity and the unique hydrophilic nano‐channels of the ionic networking membrane. The electro‐active polymer actuator of PSMI‐incorporated PVDF can be a promising smart material and may possibly diversify niche applications in biomimetic motion.     

Multifunctional Core/Shell Nanoparticles Self‐Assembled from pH‐Induced Thermosensitive Polymers for Targeted Intracellular Anticancer Drug Delivery

Core/shell nanoparticles that display a pH‐sensitive thermal response, self‐assembled from the amphiphilic tercopolymer, poly(N‐isopropylacrylamide‐co‐N,N‐dimethylacrylamide‐co‐10‐undecenoic acid) (P(NIPAAm‐co‐DMAAm‐co‐UA)), have recently been reported. In this study, folic acid is conjugated to the hydrophilic segment of the polymer through the free amine group (for targeting cancer cells that overexpress folate receptors) and cholesterol is grafted to the hydrophobic segment of the polymer. This polymer also self‐assembles into core/shell nanoparticles that exhibit pH‐induced temperature sensitivity, but they possess a more stable hydrophobic core than the original polymer P(NIPAAm‐co‐DMAAm‐co‐UA) and a shell containing folate molecules. An anticancer drug, doxorubicin (DOX), is encapsulated into the nanoparticles. DOX release is also pH‐dependent. DOX molecules delivered by P(NIPAAm‐co‐DMAAm‐co‐UA) and folate‐conjugated P(NIPAAm‐co‐DMAAm‐co‐UA)‐g‐cholesterol nanoparticles enter the nucleus more rapidly than those transported by P(NIPAAm‐co‐DMAAm)‐b‐poly(lactide‐co‐glycolide) nanoparticles, which are not pH sensitive. More importantly, these nanoparticles can recognize folate‐receptor‐expressing cancer cells. Compared to the nanoparticles without folate, the DOX‐loaded nanoparticles with folate yield a greater cellular uptake because of the folate‐receptor‐mediated endocytosis process, and, thus, higher cytotoxicity results. These multifunctional polymer core/shell nanoparticles may make a promising carrier to target drugs to cancer cells and release the drug molecules to the cytoplasm inside the cells.     

The Contribution of DOPA to Substrate-Peptide Adhesion and Internal Cohesion of Mussel-Inspired Synthetic Peptide Films

Mussels use a variety of 3, 4-dihydroxyphenyl-l-alanine (DOPA) rich proteins specifically tailored to adhering to wet surfaces. Synthetic polypeptide analogues of adhesive mussel foot proteins (specifically mfp-3) are used to study the role of DOPA in adhesion. The mussel-inspired peptide is a random copolymer of DOPA and N(5) -(2-hydroxyethyl)-l-glutamine synthesized with DOPA concentrations of 0-27 mol% and molecular weights of 5.9-7.1 kDa. Thin films (3-5 nm thick) of the mussel-inspired peptide are used in the surface forces apparatus (SFA) to measure the force-distance profiles and adhesion and cohesion energies of the films in an acetate buffer. The adhesion energies of the mussel-inspired peptide films to mica and TiO(2) surfaces increase with DOPA concentration. The adhesion energy to mica is 0.09 μJ m(-2) mol(DOPA) (-1) and does not depend on contact time or load. The adhesion energy to TiO(2) is 0.29 μJ m(-2) mol(DOPA) (-1) for short contact times and increases to 0.51 μJ m(-2) mol(DOPA) (-1) for contact times >60 min in a way suggestive of a phase transition within the film. Oxidation of DOPA to the quinone form, either by addition of periodate or by increasing the pH, increases the thickness and reduces the cohesion of the films. Adding thiol containing polymers between the oxidized films recovers some of the cohesion strength. Comparison of the mussel-inspired peptide films to previous studies on mfp-3 thin films show that the strong adhesion and cohesion in mfp-3 films can be attributed to DOPA groups favorably oriented within or at the interface of these films.     

pH‐Based Regulation of Hydrogel Mechanical Properties Through Mussel‐Inspired Chemistry and Processing

The mechanical holdfast of the mussel, the byssus, is processed at acidic pH yet functions at alkaline pH. Byssi are enriched in Fe³⁺ and catechol‐containing proteins, species with chemical interactions that vary widely over the pH range of byssal processing. Currently, the link between pH, Fe³⁺‐catechol reactions, and mechanical function is poorly understood. Herein, it is described how pH influences the mechanical performance of materials formed by reacting synthetic catechol polymers with Fe³⁺. Processing Fe³⁺‐catechol polymer materials through a mussel‐mimetic acidic‐to‐alkaline pH change leads to mechanically tough materials based on a covalent network fortified by sacrificial Fe³⁺‐catechol coordination bonds. These findings offer the first direct evidence of Fe³⁺‐induced covalent cross‐linking of catechol polymers, reveal additional insight into the pH dependence and mechanical role of Fe³⁺‐catechol interactions in mussel byssi, and illustrate the wide range of physical properties accessible in synthetic materials through mimicry of mussel‐protein chemistry and processing.     

Intermolecular Interactions of Perylene diimides in Photovoltaic Blends of Fluorene Copolymers: Disorder Effects on Photophysical Properties,Film Morphology and Device Efficiency

In the present work, we correlate the photophysical and photovoltaic properties with the respective film morphologies of three different blends made of the fluorene copolymers poly(9,9′‐dioctylfluorene‐co‐benzothiadiazole) (F8BT), poly[9,9′‐dioctylfluorene‐co‐N‐(4‐butylphenyl)diphenylamine] (TFB), and poly[9,9′‐dioctyfluorene‐co‐bis‐N,N′‐(4‐butylphenyl)‐bis‐N,N‐phenyl‐1,4‐phenylenediamine] (PFB) when blended with a perylene tetracarboxylic diimide (PDI) derivative. Additional photophysical studies in reference PDI blends of the electronically inert poly(styrene) matrix address the enhanced PDI intermolecular solid‐state interactions. We resolve the process of resonance energy transfer from excited polymer hosts to PDI and the process of photoinduced hole transfer from PDI to the polymer hosts. We deduce the efficiency of charge‐transfer PDI photoluminescence (PL) quenching and we discuss the power‐law PL kinetics seen in the as‐spun systems. Next we determine the dependence of the device external quantum efficiency (EQE) of these blends, in a range of annealing temperatures and PDI loadings. Differential scanning calorimetry enables precise selection of annealing temperatures. Optical microscopy shows that annealing enhances the order characteristics in the PDI aggregates in the F8BT:PDI system. In the case of the TFB:PDI and PFB:PDI blends, AFM studies suggest the formation of PDI‐rich domains on the film/air interface. The degree of order in the π–π stacking of the PDI monomers is inferred by the UV–Vis and PL spectra of the blends. The extent of order characteristics in PDI aggregates is correlated with the thermal properties of the hosts that control PDI molecular mobility upon annealing. The efficient dispersion of disrupted PDI crystallites is proposed to form appropriate percolation networks that favor balanced extraction of photogenerated carriers.     

Adhesion and Surface Interactions of a Self‐Healing Polymer with Multiple Hydrogen‐Bonding Groups

The surface properties and self‐adhesion mechanism of self‐healing poly(butyl acrylate) (PBA) copolymers containing comonomers with 2‐ureido‐4[1H]‐pyrimidinone quadruple hydrogen bonding groups (UPy) are investigated using a surface forces apparatus (SFA) coupled with a top‐view optical microscope. The surface energies of PBA–UPy4.0 and PBA–UPy7.2 (with mole percentages of UPy 4.0% and 7.2%, respectively) are estimated to be 45–56 mJ m^?2 under dry condition by contact angle measurements using a three probe liquid method and also by contact and adhesion mechanics tests, as compared to the reported literature value of 31–34 mJ m^?2 for PBA, an increase that is attributed to the strong UPy–UPy H‐bonding interactions. The adhesion strengths of PBA–UPy polymers depend on the UPy content, contact time, temperature and humidity level. Fractured PBA–UPy films can fully recover their self‐adhesion strength to 40, 81, and 100% in 10 s, 3 h, and 50 h, respectively, under almost zero external load. The fracture patterns (i.e., viscous fingers and highly “self‐organized” parallel stripe patterns) have implications for fabricating patterned surfaces in materials science and nanotechnology. These results provide new insights into the fundamental understanding of adhesive mechanisms of multiple hydrogen‐bonding polymers and development of novel self‐healing and stimuli‐responsive materials.