Longitudinal Eigenvibration of Multilayer Colloidal Crystals and the Effect of Nanoscale Contact Bridges

Longitudinal contact-based vibrations of colloidal crystals with a controlled layer thickness are studied. These crystals consist of 390 nm diameter polystyrene spheres arranged into close packed, ordered lattices with a thickness of one to twelve layers. Using laser ultrasonics, eigenmodes of the crystals that have out-of-plane motion are excited. The particle-substrate and effective interlayer contact stiffnesses in the colloidal crystals are extracted using a discrete, coupled oscillator model. Extracted stiffnesses are correlated with scanning electron microscope images of the contacts and atomic force microscope characterization of the substrate surface topography after removal of the spheres. Solid bridges of nanometric thickness are found to drastically alter the stiffness of the contacts, and their presence is found to be dependent on the self-assembly process. Measurements of the eigenmode quality factors suggest that energy leakage into the substrate plays a role for low frequency modes but is overcome by disorder- or material-induced losses at higher frequencies. These findings help further the understanding of the contact mechanics, and the effects of disorder in three-dimensional micro- and nano-particulate systems, and open new avenues to engineer new types of micro- and nanostructured materials with wave tailoring functionalities via control of the adhesive contact properties

Towards Understanding Nonlinear Wave Propagation in Three-Dimensional Microscale Granular Crystals

Thesis (Ph.D.)--University of Washington, 2020Elastic waves and vibrations play central roles in numerous engineering fields and technologies such as impact mitigation, vibration isolation, ultrasonic imaging, and even electronic filtering components. Enhanced control over such dynamics has the potential to enhance existing applications or create entirely new technologies, with one avenue of such control being waveform manipulation using dispersion and nonlinearity. An attractive approach that has seen significant advancement recently is the field of phononic crystals and acoustic metamaterials, which use structure to tailor existing, and enable new, effective material properties. One such structure is the granular crystal, defined as ordered arrays of discrete elastic particles in contact, which supports dispersion tailoring in addition to nonlinearity resulting from the contact mechanics between the particles. This interplay between dispersion and nonlinearity has produced a large amount of research recently, however, it has mostly been limited to macroscale systems with millimeter to centimeter-sized spheres. Such macroscale systems have limited applicability to many engineering solutions with size and weight constraints. Using microscale spheres to create architectured material with enhanced functionality is a promising idea, however, the dynamic behavior can not be assumed to be identical to macroscale systems because different physics are expected to become important at small scales, the most consequential being adhesive forces. This work experimentally investigates whether three-dimensional microgranular crystals support nonlinear dynamics analogous to their macroscale counterparts, which is currently an open question. Key elements known to allow wave tailoring in macroscale systems are studied individually before building up to direct analysis of nonlinear dynamics in three-dimensional microgranular crystals. First, a two-dimensional microgranular crystal monolayer adhered to a substrate is utilized to investigate, within linear dynamical regimes, interparticle vibrational modes and horizontal-rotational degrees of freedom, both known to affect propagation in three-dimensional systems. Using this experimental design, horizontal-rotational interparticle modes were observed, and described by a recently developed unified theory, for the first time in a microgranular crystal, with the key takeaway being that adhesive forces enhance the role of rotations and form interparticle networks that drastically alter the mode frequency. Next, the contact mechanics of a microsphere monolayer was studied with three different methods of estimating the adhesive force and compared by assuming an elastic contact mechanics model. This unique comparison found the measurements varied widely, suggesting adhesion-induced plasticity may play a major role for polymer microspheres. Subsequently, the behavior of a disordered three-dimensional assembly of microspheres was explored by controlling static and dynamic loading amplitudes, which directly reveal the nonlinear nature of the contact and the weakly nonlinear dynamics that result from it. It was discovered that the nonlinear behavior was drastically different from macroscale counterparts initially, however, the behavior was approximately similar after mechanical conditioning. Lastly, strongly nonlinear dynamics of an ordered three-dimensional microscale granular crystal was investigated in a preliminary study by characterizing the dependence of sound speed on acoustic wave amplitude and found to behave approximately similar to macroscale systems, though additional data is needed for a rigorous analysis. This finding bodes well for translating the promise of macroscale granular crystals to the microscale. The work contained in this thesis lays out a path to exploring even more complex microgranular crystal dynamics

Analyse vibratoire de structures sandwiches stratifiees

SIGLECNRS AR 11469 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Longitudinal eigenvibration of multilayer colloidal crystals and the effect of nanoscale contact bridges

International audienceLongitudinal contact-based vibrations of colloidal crystals with a controlled layer thickness are studied

Electrolyte-free Amperometric Immunosensor using a Dendritic Nanotip

Electric detection using a nanocomponent may lead to platforms for rapid and simple biosensing. Sensors composed of nanotips or nanodots have been described for highly sensitive amperometry enabled by confined geometry. However, both fabrication and use of nanostructured sensors remain challenging. This paper describes a dendritic nanotip used as an amperometric biosensor for highly sensitive detection of target bacteria. A dendritic nanotip is structured by Si nanowires coated with single-walled carbon nanotubes (SWCNTs) for generation of a high electric field. For reliable measurement using the dendritic structure, Si nanowires were uniformly fabricated by ultraviolet (UV) lithography and etching. The dendritic structure effectively increased the electric current density near the terminal end of the nanotip according to numerical computation. The electrical characteristics of a dendritic nanotip with additional protein layers was studied by cyclic voltammetry and I–V measurement in deionized (DI) water. When the target bacteria dielectrophoretically captured onto a nanotip were bound with fluorescence antibodies, the electric current through DI water decreased. Measurement results were consistent with fluorescence- and electron microscopy. The sensitivity of the amperometry was 10 cfu/sample volume (10 3 cfu/mL), which was equivalent to the more laborious fluorescence measurement method. The simple configuration of a dendritic nanotip can potentially offer an electrolyte-free detection platform for sensitive and rapid biosensors

Amperometric immunosensor for rapid detection of Mycobacterium tuberculosis

Tuberculosis (TB) has been a major public health problem, which can be better controlled by using accurate and rapid diagnosis in low-resource settings. A simple, portable, and sensitive detection method is required for point-of-care (POC) settings. This paper studies an amperometric biosensor using a microtip immunoassay for a rapid and low-cost detection of Mycobacterium tuberculosis (MTB) in sputum. MTB in sputum is specifically captured on the functionalized microtip surface and detected by electric current. According to the numerical study, the current signal on the microtip surface is linearly changed with increasing immersion depth. Using a reference microtip, the immersion depth is compensated for a sensing microtip. On the microtip surface, target bacteria are concentrated and organized by a coffee-ring effect, which amplifies the electric current. To enhance the signal-to-noise ratio, both the sample processing and rinsing steps are presented with the use of deionized water as a medium for the amperometric measurement. When applied to cultured MTB cells spiked into human sputum, the detection limit was 100 CFU mL−1, comparable to a more labor-intensive fluorescence detection method reported previously

Amperometric immunosensor for rapid detection of Mycobacterium tuberculosis

Tuberculosis (TB) has been a major public health problem, which can be better controlled by using accurate and rapid diagnosis in low-resource settings. A simple, portable, and sensitive detection method is required for point-of-care (POC) settings. This paper studies an amperometric biosensor using a microtip immunoassay for a rapid and low cost detection of Mycobacterium Tuberculosis (MTB) in sputum. MTB in sputum is specifically captured on the functionalized microtip surface and detected by electric current. According to the numerical study, the current signal on microtip surface is linearly changed with increasing immersion depth. Using a reference microtip, the immersion depth is compensated for a sensing microtip. On the microtip surface, target bacteria are concentrated and organized by a coffee ring effect, which amplifies the electric current. To enhance the signal-to-noise ratio, both the sample processing- and rinsing steps are presented with use of deionized water as a medium for the amperometric measurement. When applied to cultured MTB cells spiked into human sputum, the detection limit was 100 CFU/mL, comparable to a more labor-intensive fluorescence detection method reported previously