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Poly(ethylene glycol) diacrylate (PEGDA) hydrogels are biocompatible and photo-cross-linkable, with accessible values of elastic modulus ranging from kPa to MPa, leading to their wide use in biomedical and soft material applications. However, PEGDA gels possess complex microstructures, limiting the use of standard polymer theories to describe them. As a result, we lack a foundational understanding of how to relate their composition, processing, and mechanical properties. To address this need, we use a data-driven approach to develop an empirical predictive framework based on high-quality data obtained from uniaxial compression tests and validated using prior data found in the literature. The developed framework accurately predicts the hydrogel shear modulus and the strain-stiffening coefficient using only synthesis parameters, such as the molecular weight and initial concentration of PEGDA, as inputs. These results provide simple and reliable experimental guidelines for precisely controlling both the low-strain and high-strain mechanical responses of PEGDA hydrogels, thereby facilitating their design for various applications.

Thanks to many promising properties, including biocompatibility and the ability to experience large deformations, poly(ethylene glycol) diacrylate (PEGDA) hydrogels are excellent candidate materials for a wide range of applications. Interestingly, the polymerization of PEGDA leads to a network microstructure that is fundamentally different from that of the “classic” polymeric gels. Specifically, PEGDA hydrogels comprise PEG chains that are interconnected by multifunctional densely grafted rod-like polyacrylates (PAs), which serve as cross-linkers. In this work, we derive a microstructurally motivated model that captures the essential features which enable deformation in PEGDA hydrogels: (1) entropic elasticity of PEG chains, (2) deformation of PA rods, and (3) PA–PA interactions. Expressions for the energy-density functions and the stress associated with each of the three contributions are derived. The model demonstrates the microstructural evolution of the network during loading and reveals the role of key microscopic quantities. To validate the model, we fabricate and compress PEGDA hydrogel discs. The model is in excellent agreement with our experimental findings for a broad range of PEGDA compositions. Interestingly, we show that the response of PEGDA hydrogels with short PEG chains and long PA rods is governed by PA–PA interactions, whereas networks with longer PEG chains are dominated by entropy. To enable design, we employ the model to investigate the influence of key microstructural quantities, such as the length of the PEG and the PA chains, on the macroscopic properties and response. The findings from this work pave the way to the efficient design of PEGDA hydrogels with tunable properties and behaviors, which will enable the optimization of their performance in various applications.

Spider silk is a protein material that exhibits extraordinary and nontrivial properties such as the ability to soften and decrease its length by up to ∼60% upon exposure to high humidity. This process is commonly called supercontraction and is the result of a transition from a highly oriented glassy phase to a disoriented rubbery phase. In this work, we derive a microscopically motivated and energy-based model that captures the underlying mechanisms that give rise to supercontraction. We propose that the increase in relative humidity and the consequent wetting of a spider silk have two main consequences: (1) the dissociation of hydrogen bonds and (2) the swelling of the fiber. From a mechanical viewpoint, the first consequence leads to the formation of rubbery domains. This process is associated with an entropic gain and a loss of orientation of chains in the silk network, which motivates the contraction of the spider silk. The swelling of the fiber is accompanied by the extension of chains in order to accommodate the influx of water molecules. Supercontraction occurs when the first consequence is more dominant than the second. The model presented in this work allows us to qualitatively track the transition of the chains from glassy to rubbery states and determine the increase in entropy, the loss of orientation, and the swelling as the relative humidity increases. We also derive explicit expressions for the stiffness and the mechanical response of a spider silk under given relative humidity conditions. To illustrate the merit of this model, we show that the model is capable of capturing several experimental findings. The insights from this work can be used as a microstructural design guide to enable the development of new materials with unique spider-like properties.

We investigated the morphology, topology, and mechanical characteristics of a loosely cross-linked epoxy network as a function of the varying content of catechol moieties capable of forming reversible, ionic iron–catecholate cross-links. The primary epoxy network structure was kept fixed by a constant mole ratio of difunctional poly(ethylene glycol), monofunctional diluent, and diamine cross-linking agent in all samples. We then systematically replaced the catechol monoepoxide diluent by methyl glycidyl ether, which is incapable of participating in ionic complex formation. This allows the effects of the catechol content on network properties to be isolated and analyzed. Our results support a model in which increasing the concentration of catechol moieties promotes the formation of closely spaced iron–catecholate complex sites. This enables cooperative interactions between netpoints and produces a dramatic improvement in tensile properties. Such ionic interactions are thus a promising approach to creating stiff, strong, and tough load-bearing polymer networks.

β-Sheet protein structures and domains are widely found in biological materials such as silk. These assemblies play a major role in the extraordinary strength and unique properties of biomaterials. At the molecular level, the single β-sheet structure comprises polypeptide chains in zig-zag conformations that are held together by hydrogen bonds. β-sheet domains comprise multiple β-sheets that originate from hydrophobic interactions between sheets and are held together by van der Waals interactions. In this work, we introduce molecular models that capture the response of such domains upon mechanical loading and illustrate the mechanisms behind their collapse. We begin by modeling the force that is required to pull a chain out of a β-sheet. Next, we employ these models to study the behavior of β-sheets that are embedded into and connected to an amorphous protein matrix. We show that the collapse of a β-sheet occurs upon the application of a sufficiently high force that is transferred from the chains in the matrix to individual chains of the β-sheet structure and causes shear. With the aim of understanding the response of β-sheet domains, we derive models for the interactions between β-sheets. These enable the study of critical forces required to break such domains. As opposed to molecular dynamics simulations, the analysis in this work yields simple expressions that shed light on the relations between the nanostructure of β-sheet domains and their mechanical response. In addition, the findings of this work suggest how β-sheet domains can be strengthened.

The structure of adsorption layers of amphiphilic block and blocklike copolymers of polyisobornyl acrylate and polyacrylic acid on the surface of hydrophilic titanium dioxide and hydrophobic copper phthalocyanine CuPc pigments in an aqueous dispersion has been studied by the electrokinetic sonic amplitude ESA method. The electroacoustic behaviour of the polyelectrolyte block copolymercoated particles could be described in the context of the polymer gel layer theory. The polymer layer around the particles was found to be much thinner for CuPc as compared to the TiO2substrate. This is attributed to differences in the adsorption mechanism and the composition of the adsorption layer normal to the substrate surface. Adsorption models were established that consider effects of the copolymer structure.

Amphiphilic block and “blocklike” copolymers based on polyisobornyl acrylate and polyacrylic acid were used as stabilizers for hydrophilic titanium dioxide and hydrophobic copper phthalocyanine pigments. As reflected by the dispersion stabilities and electrokinetic sonic amplitude ESA measurements, the molecular architecture of the copolymer is of great importance for its interaction with the pigment surface. It was observed that irrespective of polymer composition, blocklike copolymers exhibit lower stabilization ability and quite different adsorption behavior in comparison to block copolymers with sharp block boundaries. Models for the adsorption behavior of both block and blocklike copolymers are proposed.

New poly(aryl-ethynylene) polymers of tuned rigidity/flexibility were synthesized by a palladium-catalyzed polycondensation. The Sonogashira–Hagihara-type coupling reaction of 2,5-diethynyl-4-dodecyltoluene with 2,5- and/or 3,5-dibromopyridine led to polymers of different rigidity/flexibility simply by varying the ratio of 2,5- to 3,5-dibromopyridine charged in the polycondensation reaction. The ratio of para–meta linkages at the pyridine moiety in the polymer backbone was determined by NMR spectroscopy. The combination of molecular weight data obtained from vapor pressure osmometry and the use of oligomeric model compounds allowed us to establish a polymer-specific gel permeation chromatography calibration. Information about the molecular conformation of the polymers in solution were obtained by small-angle X-ray scattering (SAXS) experiments. The glass-transition and melting temperatures varied systematically with the degree of rigidity/flexibility and could be directly related to the conformational changes as reflected from the SAXS data. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1919–1933, 2004

The scratch resistance of automotive clear coats was investigated by a single and multi scratch test procedure. New data characteristic for the reflow capability, the scratch hardness and the lateral scratch resistance were generated and evaluated. A correlation between single and multi scratch data was established.

Additive manufacturing enables the fabrication of bio-inspired materials possessing intricate architectures across broad length scales leading to systems that are simultaneously stiff, tough, and lightweight. A digital light processing (DLP) strategy was used to additively manufacture polymer foams with controlled porosity through the incorporation of thermally expandable microspheres. Following initial photopolymerization, a subsequent thermal processing step reproducibly allows access to a broad range of foam densities. Using uniaxial compression, we investigated how foaming impacts the mechanics of the composite material, including modulus, Poisson’s ratio, and energy dissipation. It was observed that the 3D-printed foams are remarkably resilient under cyclic loading, with sustained values of both modulus and energy dissipation under repeated loading at large deformations.

The photochemical and thermal cis-trans isomerization of 4,4 -(diamido)azobenzene derivative built in the polyester segment of a segmented poly(ester urethane) has been investigated.

Der Schwerpunkt der Synthese hat sich von neuen Polyreaktionen auf die gezielte Darstellung von Makromolekülsystemen mit spezieller molekularer Geometrie sowie geordneten Strukturen in kondensierter Phase verlagert. Bei Polymeren mit Funktionseigenschaften werden über zielgerichtete Polymersynthesen vielfältige Morphologien angestrebt. In den so erzeugten Mikrophasen können dann ionische, photonische oder elektronische Vorgänge realisiert werden. Wirtschaftliche Aspekte beschließen diesen Trendbericht. Der Schwerpunkt der Synthese hat sich von neuen Polyreaktionen auf die gezielte Darstellung von Makromolekülsystemen mit spezieller molekularer Geometrie sowie geordneten Strukturen in kondensierter Phase verlagert. Bei Polymeren mit Funktionseigenschaften werden über zielgerichtete Polymersynthesen vielfältige Morphologien angestrebt. In den so erzeugten Mikrophasen können dann ionische, photonische oder elektronische Vorgänge realisiert werden. Wirtschaftliche Aspekte beschließen diesen Trendbericht.

The thermal stability of molecularly uniform oligourethanes based on 1,5-naphthalene diisocyanate (NDI) and 1,4-butanediol (BDO), which served as model compounds for the hard segment domains of technologically relevant NDI-based polyurethane (PUR) elastomers, was investigated by a series of complementary analytical methods. The NDI/BDO oligourethanes were characterized by high melting points above 250°C, so that thermal decomposition interfered with the melting process. The decomposition could be associated with the disruption of hydrogen bonds between the urethane NH and CO groups and proceeded in the disordered regions of the microcrystalline oligomers; this was also reflected from the end group effect on the melting. The temperature limit for the thermal stability of the urethane linkage in the crystalline state was about 230°C. For disordered regions, retro-urethanization reactions were already observed beginning at temperatures in the range of 210°C. The generated free isocyanate formed allophanate crosslinks, and with increasing temperature carbodiimide formation and conversion into polymeric carbodiimide structures were observed.