Macromolecular motion is reduced in crowded polymer nanocomposites. Tracer diffusion is measured for deuterated polystyrene (dPS) into a polystyrene (PS):silica nanoparticle (NP) matrix using elastic recoil detection. This nanocomposite is ideal for studying diffusion in a crowded system because the interparticle distance (ID) that defines confinement can be varied from much greater than to much less than the size of the dPS chain, which is described by 2R g, the radius of gyration, and varies from 10 to 40 nm in this study. Diffusion is observed to be significantly slower than that predicted by the Maxwell model. The tracer diffusion coefficient of dPS in the nanocomposite relative to the pure PS matrix (D/D 0) plotted against the NP separation relative to probe size (i.e., ID/2R g) falls on a master curve, indicating that crowding is a property of both the dPS size and confinement in the nanocomposite. Moreover, the normalized diffusion coefficient decreases more rapidly when ID/2R g is less than ∼1, suggesting strong confinement conditions. The scaling of the diffusion coefficient with chain length is in excellent agreement with the entropic barrier model that accounts for the slowing down associated with the loss of chain entropy due to constrictive bottlenecks.

Diffusion of deuterated poly(methyl methacrylate) (dPMMA) is slowed down in a PMMA matrix filled with hydroxyl-capped spherical silica nanoparticles, from 13 to 50 nm in diameter and at loadings up to 40 vol %. At constant T − T g = 75 K, the normalized diffusion coefficients (D/D 0 ) collapse onto a master curve, when plotted against the confinement parameter, ID/2R g , where ID is interparticle distance and 2R g is probe size. This result suggests that the confinement parameter captures the effect of nanoparticle size, size polydispersity, and volume fraction on polymer dynamics for the PMMA composite. For ID < 2R g , the master curve exhibits a strongly confined region where D/D 0 decreases by up to 80%, whereas for ID > 2R g , the curve falls in a weakly confined region where D/D 0 decreases only moderately by up to 15%. Surprisingly, D/D 0 is reduced even when ID is 8 times larger than 2R g . A comparison between the master curves for PMMA and polystyrene nanocomposites indicates that attractive interactions in the PMMA system do not significantly alter the centerof-mass diffusion of macromolecules in polymer nanocomposites.

The tracer diffusion of deuterated polystyrene (dPS) is measured in a polystyrene nanocomposite containing silica nanoparticles (NPs), with number average diameters d n of 28.8 nm and 12.8 nm, using elastic recoil detection. The volume fractions of the large and small NPs (f NP ) range from 0 to 0.5, and 0 to 0.1, respectively. At the same volume fraction of NPs, the tracer diffusion of dPS is reduced as NP size decreases because the interparticle distance between NPs (ID) decreases. The reduced diffusion coefficient, defined as the tracer diffusion coefficient in the nanocomposite relative to pure PS (D/D 0 ), plotted against the confinement parameter, namely ID(d n ) relative to tracer size, ID(d n )/2R g , nearly collapses onto a master curve, although D/D 0 is slightly greater for the more polydisperse, smaller NPs. Using a log normal distribution of NP size from SAXS, the average ID of the smaller NPs is shown to increase by 25% at f NP ¼ 0.1 as polydispersity (s) increases from 1 to 1.39. By accounting for polydispersity, the confinement parameter better represents the effect of NP spacing on polymer diffusion. These experiments demonstrate that polymer tracer diffusion in polymer nanocomposites is empirically captured by the confinement parameter and that an increase in the average ID due to NP polydispersity has a secondary effect on model NP systems with a narrow distribution of sizes. However, for commercial systems, where polydispersity can be quite large, the effect of size distribution can significantly increase ID which in turn will influence polymer dynamics.1=3 À1 !(1)

Skin-like health care patches (SHPs) are next-generation health care gadgets that will enable seamless monitoring of biological signals in daily life. Skin-conformable sensors and a stretchable display are critical for the development of standalone SHPs that provide real-time information while alleviating privacy concerns related to wireless data transmission. However, the production of stretchable wearable displays with sufficient pixels to display this information remains challenging. Here, we report a standalone organic SHP that provides real-time heart rate information. The 15-μm-thick SHP comprises a stretchable organic light-emitting diode display and stretchable organic photoplethysmography (PPG) heart rate sensor on all-elastomer substrate and operates stably under 30% strain using a combination of stress relief layers and deformable micro-cracked interconnects that reduce the mechanical stress on the active optoelectronic components. This approach provides a rational strategy for high-resolution stretchable displays, enabling the production of ideal platforms for next-generation wearable health care electronics.

Strategies to improve stretchability of polymer semiconductors, such as introducing flexible conjugation-breakers or adding flexible blocks, usually result in degraded electrical properties. In this work, we propose a concept to address this limitation, by introducing conjugated rigid fused-rings with optimized bulky side groups and maintaining a conjugated polymer backbone. Specifically, we investigated two classes of rigid fusedring systems, namely, benzene-substituted dibenzothiopheno[6,5b:6′,5′-f ]thieno[3,2-b]thiophene (Ph-DBTTT) and indacenodithiophene (IDT) systems, and identified molecules displaying optimized electrical and mechanical properties. In the IDT system, the polymer PIDT-3T-OC12-10% showed promising electrical and mechanical properties. In fully stretchable transistors, the polymer PIDT-3T-OC12-10% showed a mobility of 0.27 cm 2 V −1 s −1 at 75% strain and maintained its mobility after being subjected to hundreds of stretching−releasing cycles at 25% strain. Our results underscore the intimate correlation between chemical structures, mechanical properties, and charge carrier mobility for polymer semiconductors. Our described molecular design approach will help to expedite the next generation of intrinsically stretchable high-performance polymer semiconductors.