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It is highly demanded to understand the confinement effect on nanoconfined polymers. Recent studies reported a strong perturbation of local dynamics and substantial alteration of glass transition temperature Tg at nanoscale. However, how confinement affects the mechanical properties of polymers is not fully understood. Here, we show that the modulus of thin polymer films could be remarkedly altered through a polymer–polymer interface. The modulus of a thin polystyrene (PS) film next to a polydimethylsiloxane (PDMS) was determined from the PS–PDMS bilayer bulging test. A series of experiments show that the modulus of PS can be increased up to 37%, when the modulus of the neighboring PDMS varies from 1.04 to 4.88 MPa. The results demonstrate a strong sensitivity of mechanical properties of thin polymers to the hard/soft environment, which we attribute to the change of high-mobility layer by the polymer–polymer interface. [ABSTRACT FROM AUTHOR]

The demand for applications, such as coatings, separation filters, and electronic packaging, has greatly driven the research of polymer films. At nanometer scale, mechanical properties of thin polymer films can significantly deviate from bulk. Despite outstanding progresses, there still lack deep discussions on nonlinear viscoelastic–viscoplastic response and their interactions under nanoconfinement. In this work, by conducting measurements via the bubble inflation method and modelling using Schapery and Perzyna equations, we demonstrate nonlinear viscoelastic–viscoplastic properties of freely standing thin polystyrene (PS) films. The results show the unchanged glassy compliance and the rubbery stiffening phenomenon for thin PS films, where the lower rubbery plateau in rubbery stiffening may originate from the induced molecular orientation by plastic deformation. With decreasing film thickness, viscosity and yield stress in viscoplasticity increase in an exponential and a linear trend, respectively, indicating the significant role of nanoconfinement effect on viscoplastic properties. These findings may reveal that there are many properties from linear viscoelasticity to nonlinear viscoelasticity–viscoplasticity that need to be explored and unveiled for sufficient understanding of the nanoconfinement effect on altering mechanical behavior of polymers. [ABSTRACT FROM AUTHOR]

Nanoscale polymeric thin films are widely used in diverse modern applications, where a satisfactory mechanical performance is a requirement to their full functionality. The mechanical response of polymer films is strongly affected by the size effects under nanoconfinement; however, the mechanism of such response in terms of molecular configurations and chain conformations has yet to be determined. In this work, we reveal the conformational origin of the stiffening behavior of crosslinked polymeric nanofilms via coarse-grained molecular dynamics and tailored experiments. We find that the biaxial modulus changes follow the alteration of polymer conformations, decoupled from size and thickness. We propose a theory to quantitatively link the elastic properties of the polymers to the distribution of their chain end-to-end distances, predicting a stiffening effect on uncoiled chains. Finally, we use such insight to obtain several PDMS nano-films of the same thickness but with a variability of two orders of magnitudes in their moduli. The mechanical response of polymer films is affected by size effects under nanoconfinement, but the mechanism of such response in terms of molecular configurations and chain conformations has proven elusive. The authors reveal the conformational origin of the stiffening behavior in crosslinked polymeric nanofilms via simulations and experiments. [ABSTRACT FROM AUTHOR]

Polymer nanowire (NW) organic field-effect transistors (OFETs) integrated on highly aligned large-area flexible substrates are candidate structures for the development of high-performance flexible electronics. This work presents a universal technique, coaxial focused electrohydrodynamic jet (CFEJ) printing technology, to fabricate highly aligned 90-nm-diameter polymer arrays. This method allows for the preparation of uniformly shaped and precisely positioned nanowires directly on flexible substrates without transfer, thus ensuring their electrical properties. Using indacenodithiophene-co-benzothiadiazole (IDT-BT) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8-BT) as example materials, 5 cm2 arrays were prepared with only minute size variations, which is extremely difficult to do using previously reported methods. According to 2D-GIXRD analysis, the molecules inside the nanowires mainly adopted face-on π-stacking crystallite arrangements. This is quite different from the mixed arrangement of thin films. Nanowire-based OFETs exhibited a high average hole mobility of 1.1 cm2 V−1 s−1 and good device uniformity, indicating the applicability of CFEJ printing as a potential batch manufacturing and integration process for high-performance, scalable polymer nanowire-based OFET circuits. This technique can be used to fabricate various polymer arrays, enabling the use of organic polymer semiconductors in large-area, high-performance electronic devices and providing a new path for the fabrication of flexible displays and wearable electronics in the future. [ABSTRACT FROM AUTHOR]

We present the design and validation of an apparatus, which is developed based on micro-vibration in cyclic bulge and contraction, to determine dynamic mechanical properties of ultrathin polymer films. By controlling air pressure acting on a polymer membrane, the apparatus exerts simple harmonic or other type periodic stresses on the film, and the resultant real-time deformation of the freely standing film is recorded by using a high-speed CCD camera. From the image frame sequences and the gas pressure data, the real-time stress and strain of the polymer film are attained. Consequently, the dynamic mechanical properties, including biaxial storage and loss moduli, and loss factor can be determined for polymer films with thickness down to 20 nm. This apparatus could also be used to determine other mechanical properties such as fatigue and yield for nanoconfined films of soft matter. [ABSTRACT FROM AUTHOR]

Abstract: Ammonia/amine gas sensors have received increasing attention in recent years, due to their applications in monitoring of meat and seafood spoilage and air pollution as well as diagnosis of chronic diseases. Herein, a new conjugated polymer PTTEH is developed, which is composed of thieno[3,4‐b]thiophene units, with very low bandgap. The low bandgap and the existence of radical state endow the polymer thin film with good electrical conductivity. As a result, PTTEH is successfully utilized for construction of a field‐effect transistor (FET) sensor for ammonia and amines at low driving voltages, which are advantageous for practical applications. Moreover, this FET sensor shows good selectivity and high sensitivity (down to 10 ppb) toward ammonia and amines. Accordingly, the real‐time monitoring of meat spoilage is achieved with this FET sensor. These studies will open a new venue to fabricate sensitive, portable, and small size sensors for real‐time monitoring of chemical vapors. [ABSTRACT FROM AUTHOR]

For nearly the past two decades, significant effort has been devoted to pursuing an understanding of the glass transition temperature and associated dynamics of polymers confined to the nanoscale. Without question, we know more about the glassy properties of confined polymers today than we knew two decades ago or even a decade ago. Much of our understanding has been obtained via studies on thin polymer films, as they are facile to process and are of substantial technological importance. Nevertheless, studies on polymers confined to other geometries are becoming increasingly more important as we pursue questions difficult to address using thin films and as technology demands the use of confined polymers beyond thin films. In this feature article, we highlight the impact of nanoscale confinement on the glassy properties of polymer nanoparticles. Although the emphasis is placed on contributions from our work, a discussion of the related literature is also presented. Our aim is to elucidate commonalities or fundamental differences in the deviations of glassy properties from the bulk for polymers confined to different geometries. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013 [ABSTRACT FROM AUTHOR]

Abstract: Dithienothiophene-phenylene cooligomers with n-hexyloxy or n-dodecyloxy substituents have been synthesized and compared to the previously reported unsubstituted parent compound. The effect of substituents on the thermal, electronic, optical, thin film structure and field-effect transistor (OFET) properties was investigated. Structural phase transitions from highly-ordered nanocrystalline to liquid crystalline were observed at 241 and 213 °C for n-hexyloxy- and n-dodecyloxy-substituted compounds respectively, different from the parent compound. For the alkoxy-substituted compounds, the absorption spectra in thin film blue shift 50 nm, while the fluorescence spectra in thin film red shift 88–100 nm compared to those in solution. The OFET devices based on the alkoxy-substituted compounds exhibit mobilities as high as ca 0.02 cm2V−1s−1 and their performance is sensitive to the alkoxy substituents and substrate temperatures. [Copyright &y& Elsevier]

We demonstrated a polymeric thin film fabrication process in which molecular-scale crystallization proceeds with additive film growth, by employing an innovative vapor-assisted deposition process termed matrix-assisted pulsed laser evaporation (MAPLE). In comparison to solution-casting commonly adopted for the deposition of polymer thin films, this physical vapor deposition (PVD) methodology can prolong the time scale of film formation and allow for the manipulation of temperature during deposition. For the deposition of molecular and atomic systems, such a PVD manner has been demonstrated to facilitate molecular ordering and delicately manipulate crystalline morphology during film growth. Here, using MAPLE, we deposited thin films of a model polymer, poly(ethylene oxide) (PEO), atop a temperature-controlled substrate with an average growth rate of less than 10 nm/h. The mechanism of deposition is sequential addition of nanoscale liquid droplets. We discovered that the deposition process leads to the formation of two-dimensional (2D) PEO crystals, composed of monolamellar crystals laterally grown from larger nucleus droplets. The 2D crystalline coverage and crystal thickness of the films can be manipulated with two processing parameters, deposition time, and temperature. [ABSTRACT FROM AUTHOR]