Polymer semiconductors such as the alkyl-substituted polythiophenes have long been recognized as solution-processable materials for device applications, but the carrier mobility of polymers is typically lower than insoluble organic small molecules such as pentacene. The lower mobility is generally attributed to less structural order; specifically the smaller and less-aligned crystals typical of polymer semiconductors should exhibit reduced intermolecular p-orbital overlap at grain boundaries.[1] The more disordered nature of polymer semiconductors has made it challenging to determine the details of their thin-film crystal structure.[2] Structure measurements are further complicated by the small volume of the thin, 20-50 nm, polymer semiconductor films used in organic field effect transistors. [3,4] X-ray diffraction (XRD) usually provides only primary index peaks, most often the and <0l0> series, that reveal crystal structure, orientation, and size, but exact atomic positions can rarely be determined. Moreover, it is clear that the thin-film crystal structure can differ from single crystal or powder structure.[5]Alkyl-substituted polythiophenes feature a backbone of sequentially bonded thiophene rings with linear alkane chains attached to their sides. In thin films, they self-assemble into lamellae; comparing typical unit-cell dimensions to molecular dimensions leads to a generally accepted layer-packing motif where planar backbones p stack in aromatic lamellae vertically segregated from lamellae of side chains. [6][7][8] Two critical but poorly characterized aspects of the crystal structure are the conjugated-plane tilt and the alkane side-chain configuration. In the lamellar motif, the conjugated planes must be roughly vertical (orthogonal to the lamella) so that they can p stack face-to-face within a quasi two-dimensional sheet. However, a variety of conjugated-plane tilts and a rich possibility of side-chain configurations-distinguished by varying tilt and degree of interdigitation-are consistent with this layer-packing motif and available diffraction data. Greater structural detail will support the development of new synthetic and processing strategies, because carrier transport critically depends on the intermolecular overlap of carrier band orbitals, which is controlled by the conjugated-plane spacing and tilt. Recently, poly(2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophenes) (pBTTT) have been reported to exhibit hole mobility comparable to that of many small molecule semiconductors [9] and rivaling what is achievable in amorphous silicon. The structure of this material is indicated schematically in the insets of Figures 1 and 3a. The high performance of the pBTTTs was attributed to greater structural order than typical polymer semiconductors, and XRD indicated large and well-oriented crystals.[9] Here we exploit this crystallinity to study structural detail within ca. 25 nm thick films of a pBTTT with tetradecyl side chains (pBTTT-C 14 ). From first-principles energy minimization using density f...

Robot-assisted devices are becoming a popular alternative to manual facilitation in stroke rehabilitation. These devices have the potential to reduce therapist burden and treatment costs; however, their effectiveness in terms of functional recovery remains in question. This pilot study compared the outcomes of a stroke rehabilitation program that incorporates robot-assisted gait training (RAGT) with a more traditional therapy program that does not. Twenty hemiparetic stroke patients were recruited at a rehabilitation hospital in Houston, Texas, and were randomly assigned to 2 groups. The control group (n = 10) received 24 1-hour sessions of conventional physical therapy, whereas the RAGT group (n = 10) received 24 1-hour sessions of conventional physical therapy combined with RAGT on a treadmill. Gait function was assessed before and after treatment by an 8-m walk test, a 3-minute walk test, and the Tinetti balance assessment. Both groups showed significant improvement in all 3 outcome measures following treatment (P < .05), but there was no difference between groups. It is concluded that RAGT may provide improvements in balance and gait comparable with conventional physical therapy. A larger multicenter trial is required to investigate the effectiveness of RAGT in hemiparetic stroke.

This article details the design, construction, and operation of flexible system that modulates light exposure for the purpose of fabricating continuous and discrete gradient combinatorial libraries. Designed for versatility, the device combines "off the shelf" components, modular accessories, and flexible computer control, so that it can be used for a variety of combinatorial research applications. Salient aspects and capabilities of the instrument are illustrated through two practical examples. The first case demonstrates how user defined exposure functions can be used to create continuous surface energy gradient libraries with a linear profile. The second example illustrates the creation of continuous and discrete libraries for mapping exposure-property functions in a photocurable polymer system.

Semiconducting 6,7,15,16-tetrakis(dodecylthio)quinoxalino[2′,3′:9,10]phenanthro [4,5-abc]phenazine (TQPP-12) has been synthesized as a candidate solution-processable semiconductor for organic electronics applications. We characterize the microstructure of TQPP-12 in films using a combination of polarized photon absorption spectroscopies (X-ray, vis, and infrared), X-ray diffraction, and scanning probe techniques. This characterization strategy allowed for the determination of molecular orientation and packing style within thin films of this complex molecule. The TQPP-12 molecules are arranged within layers, and the aromatic cores are separated from the alkane side chains. Both the core long axes and side chains are highly tilted with respect to surface normal, and the conjugated planes of the core are cofacially packed.