The Effects of Terminal Groups on Elastic Asymmetries in Hybrid Molecular Materials

An asymmetric elastic modulus is a recently discovered and unexpected property of hybrid molecular materials that has significant implications for their underlying thermomechanical reliability. Elastic asymmetries are inherently related to terminal groups in the molecular structure, which limit network connectivity. Terminal groups sterically interact to stiffen the network in compression, while they disconnect the network and interact significantly less in tension. Here we study the importance of terminal group molecular weight and size (OH, methyl, vinyl, and phenyl) on the resulting elastic asymmetries and find that increasing the terminal group size actually leads to even larger degrees of asymmetry. As a result, we develop a molecular design criterion to predict how molecular structure affects the mechanical properties, a vital step toward integrating hybrid molecular materials into emerging nanotechnologies

Carbon-Bridge Incorporation in Organosilicate Coatings Using Oxidative Atmospheric Plasma Deposition

Carbon-bridges were successfully incorporated into the molecular structure of inorganic silicate films deposited onto polymer substrates using an oxidative atmospheric plasma deposition process. Key process parameters that include the precursor chemistry and delivery rate are discussed in the context of a deposition model. The resulting coating exhibited significantly improved adhesion and a 4-fold increase in moisture resistance as determined from the threshold for debonding in humid air compared to dense silica or commercial sol–gel polysiloxane coatings. Other important parameters for obtaining highly adhesive coating deposition on oxidation-sensitive polymer substrates using atmospheric plasma were also investigated to fully activate but not overoxidize the substrate. The resulting carbon molecular bridged adhesive coating showed enhanced moisture resistance, important for functional membrane applications

Heterogeneous Solution Deposition of High-Performance Adhesive Hybrid Films

Interfaces between organic and inorganic materials are of critical importance to the lifetime of devices found in microelectronic chips, organic electronics, photovoltaics, and high-performance laminates. Hybrid organic/inorganic materials synthesized through sol–gel processing are best suited to address these challenges because of the intimate mixing of both components. We demonstrate that deposition from <i>heterogeneous</i> sol–gel solutions leads to the unique nanolength-scale control of the through-thickness film composition and therefore the independent optimization of both the bulk and interfacial film properties. Consequently, an outstanding 3-fold improvement in the adhesive/cohesive properties of these hybrid films can be obtained from otherwise identical precursors

Toward Sustainable Multifunctional Coatings Containing Nanocellulose in a Hybrid Glass Matrix

We report on a sustainable route to protective nanocomposite coatings, where one of the components, nanocellulose fibrils, is derived from trees and the glass matrix is an inexpensive sol–gel organic–inorganic hybrid of zirconium alkoxide and an epoxy-functionalized silane. The hydrophilic nature of the colloidal nanocellulose fibrils is exploited to obtain a homogeneous one-pot suspension of the nanocellulose in the aqueous sol–gel matrix precursors solution. The mixture is then sprayed to form nanocomposite coatings of a well-dispersed, random in-plane nanocellulose fibril network in a continuous organic–inorganic glass matrix phase. The nanocellulose incorporation in the sol–gel matrix resulted in nanostructured composites with marked effects on salient coating properties including optical transmittance, hardness, fracture energy, and water contact angle. The particular role of the nanocellulose fibrils on coating fracture properties, important for coating reliability, was analyzed and discussed in terms of fibril morphology, molecular matrix, and nanocellulose/matrix interactions

Engineering the Mechanical Properties of Polymer Networks with Precise Doping of Primary Defects

Polymer networks are extensively utilized across numerous applications ranging from commodity superabsorbent polymers and coatings to high-performance microelectronics and biomaterials. For many applications, desirable properties are known; however, achieving them has been challenging. Additionally, the accurate prediction of elastic modulus has been a long-standing difficulty owing to the presence of loops. By tuning the prepolymer formulation through precise doping of monomers, specific primary network defects can be programmed into an elastomeric scaffold, without alteration of their resulting chemistry. The addition of these monomers that respond mechanically as primary defects is used both to understand their impact on the resulting mechanical properties of the materials and as a method to engineer the mechanical properties. Indeed, these materials exhibit identical bulk and surface chemistry, yet vastly different mechanical properties. Further, we have adapted the real elastic network theory (RENT) to the case of primary defects in the absence of loops, thus providing new insights into the mechanism for material strength and failure in polymer networks arising from primary network defects, and to accurately predict the elastic modulus of the polymer system. The versatility of the approach we describe and the fundamental knowledge gained from this study can lead to new advancements in the development of novel materials with precisely defined and predictable chemical, physical, and mechanical properties

Broadband Emission with a Massive Stokes Shift from Sulfonium Pb–Br Hybrids

Broadband Emission with a Massive Stokes Shift from Sulfonium Pb–Br Hybrid

Broadband Emission with a Massive Stokes Shift from Sulfonium Pb–Br Hybrids

Broadband Emission with a Massive Stokes Shift from Sulfonium Pb–Br Hybrid

Broadband Emission with a Massive Stokes Shift from Sulfonium Pb–Br Hybrids

Broadband Emission with a Massive Stokes Shift from Sulfonium Pb–Br Hybrid

Molecular-Scale Understanding of Cohesion and Fracture in P3HT:Fullerene Blends

Quantifying cohesion and understanding fracture phenomena in thin-film electronic devices are necessary for improved materials design and processing criteria. For organic photovoltaics (OPVs), the cohesion of the photoactive layer portends its mechanical flexibility, reliability, and lifetime. Here, the molecular mechanism for the initiation of cohesive failure in bulk heterojunction (BHJ) OPV active layers derived from the semiconducting polymer poly­(3-hexylthiophene) [P3HT] and two monosubstituted fullerenes is examined experimentally and through molecular-dynamics simulations. The results detail how, under identical conditions, cohesion significantly changes due to minor variations in the fullerene adduct functionality, an important materials consideration that needs to be taken into account across fields where soluble fullerene derivatives are used

Cross-Linkable, Solvent-Resistant Fullerene Contacts for Robust and Efficient Perovskite Solar Cells with Increased <i>J</i>_SC and <i>V</i>_OC

The active layers of perovskite solar cells are also structural layers and are central to ensuring that the structural integrity of the device is maintained over its operational lifetime. Our work evaluating the fracture energies of conventional and inverted solution-processed MAPbI₃ perovskite solar cells has revealed that the MAPbI₃ perovskite exhibits a fracture resistance of only ∼0.5 J/m², while solar cells containing fullerene electron transport layers fracture at even lower values, below ∼0.25 J/m². To address this weakness, a novel styrene-functionalized fullerene derivative, <b>MPMIC</b>_<b>60</b>, has been developed as a replacement for the fragile PC₆₁BM and C₆₀ transport layers. <b>MPMIC</b>_<b>60</b> can be transformed into a solvent-resistant material through curing at 250 °C. As-deposited films of <b>MPMIC</b>_<b>60</b> exhibit a marked 10-fold enhancement in fracture resistance over PC₆₁BM and a 14-fold enhancement over C₆₀. Conventional-geometry perovskite solar cells utilizing cured films of <b>MPMIC</b>_<b>60</b> showed a significant, 205% improvement in fracture resistance while exhibiting only a 7% drop in PCE (13.8% vs 14.8% PCE) in comparison to the C₆₀ control, enabling larger <i>V</i>_OC and <i>J</i>_SC values. Inverted cells fabricated with <b>MPMIC</b>_<b>60</b> exhibited a 438% improvement in fracture resistance with only a 6% reduction in PCE (12.3% vs 13.1%) in comparison to those utilizing PC₆₁BM, again producing a higher <i>J</i>_SC