The properties of polymers near an interface are altered relative to their bulk value due both to chemical interaction and geometric confinement effects. For the past two decades, the dynamics of polymers in confined geometries (thin polymer film or nanocomposites with high-surface area particles) has been studied in detail, allowing progress to be made toward understanding the origin of the dynamic effects near interfaces. Observations of mechanical property enhancements in polymer nanocomposites have been attributed to similar origins. However, the existing measurement methods of these local mechanical properties have resulted in a variety of conflicting results on the change of mechanical properties of confined polymers. Here, an atomic force microscopy (AFM)-based method is demonstrated that directly measures the mechanical properties of polymers adjacent to a substrate with nanometer resolution. This method allows us to consistently observe the gradient in mechanical properties away from a substrate in various materials systems, and paves the way for a unified understanding of thermodynamic and mechanical response of polymers. This gradient is both longer (up to 170 nm) and of higher magnitude (50% increase) than expected from prior results. Through the use of this technique, we will be better able to understand how to design polymer nanocomposites and polymeric structures at the smallest length scale, which affects the fields of structures, electronics, and healthcare.

Polymers are used in a wide range of applications for microelectronics, [1] medical engineering, [2] and structural composite engineering [3][4][5][6] where local polymer behavior due to interactions with free surfaces, substrates, or embedded surfaces has a significant impact on polymer response and function. For example, poly(methyl methacrylate) (PMMA) containing very small amounts of functionalized graphenebased sheet (FGS) [3] has shown increased glass transition temperature (T g ) of nearly 30 8C at only 0.05 wt% loading and increased elastic modulus by 33% at 0.01 wt% loading, well above the upper bound of stiffness predicted by traditional composite theory. Remarkable improvements of this magnitude cannot be attributed to a linear property combination of the polymer host and nanoparticles. Thus, interphase -the polymer near nanoparticle-polymer interfaces in which chain mobility and polymer dynamics substantially alter from the neat polymer -plays a critical role in the significant increases in thermodynamic and mechanical properties.Work in the last 15 years has demonstrated in a number of elegant experiments and modeling that T g of polymers can undergo dramatic changes near interfaces, [7][8][9][10] where negative or positive shift of this transition temperature depends upon the nature of the polymer-surface interaction. Thin films on substrates typically show changes in T g for film thicknesses of order 100 nm while for doubly supported thin films the deviation from bulk T g can be sensed up to film thicknesses of 500 nm. [8][9][10] The impact of the surface on the dynamics of the polymer propagates away from the surface significantly due to the macromolecular nature of polymers. Immediately COMMUNICATION [*] L.The mechanical properties of polymers near interfaces are important in a number of different fields. For almost two decades, the local dynamics of thin polymer films have been studied in great detail. However, development of an understanding of local mechanical properties has been hindered by the necessary proximity of stiff substrates: mechanical measurements are confounded by interaction with the substrate, convoluting polymer, and substrate properties. In this paper, local elastic properties of thin polymer films near interfaces are directly probed for the first time via nanoindentation experiments on thin films coupled with finite element modeling. A comprehensive set of experimental and numerical modeling results are presented for poly(methyl methacrylate) (PMMA) revealing separately the effects of substrate and interphase polymer. Results indicate the attractive surface significantly affects the properties up to hundreds of nanometers. This new, direct approach to measure local mechanical properties provides new fundamental understanding of interfacial and small-scale behaviors in polymers and soft matter for application advances in nanocomposites, microelectronics, and biopolymers. 400 wileyonlinelibrary.com ß

A seismic site classification microzonation for the city of Port-au-Prince is presented herein. The microzonation is based on 35 shear wave velocity ( VS) profiles collected throughout the city and a new geologic map of the region. The VS profiles were obtained using the multichannel analysis of surface waves (MASW) method, while the geologic map was developed from a combination of field mapping and geomorphic interpretation of a digital elevation model (DEM). Relationships between mean shear wave velocity over the upper 30 m of the subsurface ( VS30) and surficial geologic unit have been developed, permitting code-based seismic site classification throughout the city. A site classification map for the National Earthquake Hazards Reduction Program/International Building Code (NEHRP/IBC) classification scheme is provided herein. Much of the city is founded on deposits that classify as either NEHRP Site Class C or D, based on VS30. Areas of the city requiring additional subsurface information for accurate site classification are noted.

o-Toluidine, 6% (v/v) in glacial acetic acid, is used to determine glucose in biologic material after deproteinization with 3% (w/v) trichloracetic acid. A stable green color develops after heating at 1000 for 10 mm., and the absorbance is determined at 630 or 635 mp. The reagent is stable for many months at room temperature, and the reaction follows Beer's Law over a very wide range of concentrations. The development of the procedure is discussed, as is the specificity of the method for glucose.

For centuries, physicians have relied on touch to palpate tissue and detect abnormalities throughout the body. While this time-tested method has provided a simple diagnostic exam for large, superficial abnormalities, it does not permit quantifiable measurements of stiffness in deeper, small organs. Advances in noninvasive imaging to measure tissue rigidity represent important extensions of manual palpation techniques. Tissue fibrosis occurs with age in many organs; in the ovary, it is thought to be a marker of polycystic ovary syndrome (PCOS) and age-related idiopathic infertility, although quantitative assessment of fibrosis in this deep, abdominal tissue has not been possible. We used noninvasive methods to quantify ovarian tissue rigidity and clarify the role of tissue stiffness in reproductive health. With proper validation against accepted standards, noninvasive imaging techniques may become the quantitative counterpart to interior probing palpation methods and invasive (surgical) diagnoses, with applications across many clinical settings, including evaluation of adolescent and young adult ovarian function.