When a dielectric object is placed between two opposed, nonfocused laser beams, the total force acting on the object is zero but the surface forces are additive, thus leading to a stretching of the object along the axis of the beams. Using this principle, we have constructed a device, called an optical stretcher, that can be used to measure the viscoelastic properties of dielectric materials, including biologic materials such as cells, with the sensitivity necessary to distinguish even between different individual cytoskeletal phenotypes. We have successfully used the optical stretcher to deform human erythrocytes and mouse fibroblasts. In the optical stretcher, no focusing is required, thus radiation damage is minimized and the surface forces are not limited by the light power. The magnitude of the deforming forces in the optical stretcher thus bridges the gap between optical tweezers and atomic force microscopy for the study of biologic materials.

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Polyamide (nylon) 11 (PA11) and 12 (PA12) were melt-blended, dispersing low concentrations of nanoparticles, namely nanoclays (NCs), carbon nanofibers (CNFs), and nanosilicas (NSs) via twin-screw extrusion. To enhance their thermal and flame-retardant (FR) properties, an intumescent FR additive was added to the mechanically superior NC and CNF PA11 formulations. For neat and nanoparticle-reinforced PA11 and PA12, as well as for PA11 reinforced by both intumescent FR and select nanoparticles (NC or CNF), decomposition and heat deflection temperatures were measured, as were the peak heat release rates while burning the composites. All PA11 polymer systems infused with both nanoparticles and FR additive had higher decomposition temperatures than those infused with solely FR additive. For the PA11/FR/NC polymer blends, only the 20 wt% FR and 7.5 wt% clay formulation passed the UL 94 V-0 requirement, while all PA11/FR/ CNF formulations passed UL 94 V-0 requirement.

Polyamide (nylon) 11 (PA11) were melt-blended by dispersing low concentrations of nanoparticles (NPs), namely nanoclays (NCs) and carbon nanofibers (CNFs) via twin-screw extrusion. To enhance their thermal and flame retardant (FR) properties, an intumescent FR additive was added to the mechanically superior NC and CNF PA11 formulations. For neat and NP-reinforced PA11 as well as for PA11 reinforced by both intumescent FR and select NPs (NC or CNF), decomposition temperatures by TGA, flammability properties by UL 94, and cone calorimetry values were measured. All PA11 polymer systems infused with both NPs and FR additive had higher decomposition temperatures than those infused with solely FR additive. For the PA11/FR/NC polymer blends, Exolit® OP 1312 (FR2) is the preferred FR additive to pass the UL 94 V-0 requirement with 20 wt%. For the PA11/FR/CNF formulations, all Exolit® OP 1311 (FR1), OP 1312 (FR2), and OP 1230 (FR3) FR additives passed the UL 94 V-0 requirement with 20 wt%.

This paper identifies the material and processing parameters which most significantly influence the development of in-plane waviness in laminates. Thin laminates of unidirectional, T300 carbon-fiber/polysulfone matrix prepreg were processed in an autoclave and a custom-made water-cooled chamber, which allowed fast cooling rates. Multivariate regression analysis of process-induced waviness was performed for combinations of the select process variables and their interactions to identify those factors responsible for waviness development. Of the eight parameters investigated – hold temperature, hold time, pressure, length, width, thickness, cooling rate, and tool plate material – only three affected the development of fiber waviness: length, cooling rate, and tool plate material. Length affects not only the number of wrinkles and wrinkle distribution, but also the average amplitude of the waviness. Cooling rate affects the wavelength and amplitude of the waviness, as well as the number of wrinkles. Tool plate material primarily affects the number of wrinkles, without showing a significant effect on the average wave geometry. There is also an interaction between tool plate material and cooling rate in producing fiber waviness. For the three relevant parameters, the possible waviness-inducing mechanisms are tool plate/part coefficient of thermal expansion (CTE) mismatch, temporal temperature gradients (or cooling rates), and spatial temperature gradients. The tool plate/part CTE mismatch proved to be the most important mechanism driving fiber waviness in plates, although changes in cooling rates also dramatically affected the quantity of waviness which developed. Spatial temperature gradients were negligible for this study. The tool plate/part CTE mismatch-driven axial buckling loads on the fibers were substantial in the outermost laminate plies, or skin, but negligible in the laminate core. Waviness was limited to the surface or skin plies, even in identically-processed thick laminates. This study confirmed that if the fibers experience axial loads – albeit a small fraction of their Young’s modulus – while the matrix is unable to provide some level of transverse fiber support, the fibers will microbuckle resulting in waviness (in-plane or out-of-plane depending upon the laminate constraint).