Centrifugal casting and fast curing of polydimethylsiloxane (PDMS) for the manufacture of micro and nano featured components

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 237-248).The thermosetting resin polydimethylsiloxane (PDMS) is commonly used to prototype micro and nano featured components. In the field of microfluidics, PDMS-based devices have been used for cell sorting, cell culturing, microbioreactors, DNA sequencing, and immunoassays. In energy-related applications, PDMS has been used in fuel cell assemblies and as a material for transferring carbon nanotubes in the construction of solar cells. In addition, PDMS is the fundamental material of soft lithography and microcontact printing. Given the widespread use of PDMS in micro/nano technology, biology, and chemistry, the motivation of this thesis is to outline a viable manufacturing process for thermosetting resins such as PDMS that could be scaled-up for the large-scale production of micro/nano featured components. With respect to rate of PDMS device production, the two time-limiting steps in the typical prototyping process are degassing (bubble removal) and curing. To improve the degassing step, a novel centrifugal casting method is introduced, which permits simultaneous patterning of multiple surfaces and precise thickness control of a PDMS part. To improve the curing step, a custom-designed thermal management system heats and cools the PDMS. In centrifugal casting, the spinning time required to produce a bubble-free part is dependent on a distribution of critical bubble sizes, the centrifuge's spin speed profile, geometry, and fluid properties. A physical model predicting the spin time for bubble removal is verified by high speed video imaging and the production of bubble-free parts.(cont.) In addition to producing bubble-free parts, the PDMS centrifugal casting technique is utilized to produce micro and nano featured components.by Aaron D. Mazzeo.Ph.D

Accurate capacitive metrology for atomic force microscopy

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.Includes bibliographical references (p. 219-224).This thesis presents accurate capacitive sensing metrology designed for a prototype atomic force microscope (AFM) originally developed in the MIT Precision Motion Control Lab. The capacitive measurements use a set of commercial capacitance sensors intended primarily for use against a flat target. In our design, the capacitance sensors are used with a spherical target in order to be insensitive to target rotations. The moving AFM probe tip is located approximately at the center of the spherical target to make the capacitive sensing insensitive to the probe tip assembly's undesirable rotation on the order of 3 x 10⁻⁴ rad for 10 [mu]m of lateral travel [48]. To accurately measure displacement of the spherical target relative to the capacitance sensors, models for the capacitance between a sphere and a circular disc were developed with the assistance of Katherine Lilienkamp. One of the resulting non-linear models was combined with the appropriate kinematic transformations to accurately perform measurement scans on a 20 [mu]m x 20 [mu]m surface with step heights of 26.5 nm. The probe tip positions during these scans were also calculated in real- time using Lilienkamp's non-linear capacitance model with a set of transformations and 3-D interpolation techniques implemented at 10 kHz. The scans were performed both in tapping and shear detection modes.(cont.) Localized accuracy on the order of 1 nm with RMS noise of approximately 3 nm was attained in measuring the step heights. Surface tracking control and speed were also improved relative to an earlier prototype. Lateral speeds of approximately 0.8 [mu]m/s were attained in the tapping mode. In addition to improving the original prototype AFM's scan speed and ability to attain dimensional accuracy, a process for mounting an optical fiber probe tip to a quartz tuning fork was developed. This mounting process uses Post-it notes. These resulting probe-tip/tuning-fork assemblies were tested in both the tapping and shear modes. The tests in the tapping mode used the magnitude of the fork current for accurate surface tracking. The tests performed in the shear mode used the magnitude and phase of the fork current for accurate surface tracking.by Aaron David Mazzeo.S.M

Paper-based electroanalytical devices for accessible diagnostic testing

Microfluidic paper-based analytical devices (μPADs) use the passive capillary-driven flow of aqueous solutions through patterned paper channels to transport a sample fluid into distinct detection zones that contain the reagents for a chemical assay. These devices are simple, affordable, portable, and disposable; they are, thus, well suited for diagnostic applications in resource-limited environments. Adding screen-printed electrodes to the detection zones of a μPAD yields a device capable of performing electrochemical assays (an EμPAD). Electrochemical detection has the advantage over colorimetric detection that it is not affected by interferences from the color of the sample, and can be quantified with simple electronics. The accessibility of EμPADs is, however, limited by the requirement for an external potentiostat to power and interpret the electrochemical measurement. New developments in paper-based electronics may help loosen some of this requirement. This review discusses the current capabilities and limitations of EμPADs and paper-based electronics, and sketches the ways in which these technologies can be combined to provide new devices for diagnostic testing.Chemistry and Chemical Biolog

Reconfigurable Self-Assembly of Mesoscale Optical Components at a Liquid-Liquid Interface

Magnetic fields template the self-assembly of 2D mesoscale optical components consisting of magnetically responsive parts at a liquid–liquid interface. These optical components are tiles of reflective diffraction gratings. Their orientations, and the resulting optical effects, are reconfigurable by a change in the magnetic field. Transferring the assembled structure onto solid substrates generates optically functional coatings or films.Chemistry and Chemical Biolog

Soft Robotics for Chemists

Soft robots: A methodology based on embedded pneumatic networks (PneuNets) is described that enables large-amplitude actuations in soft elastomers by pressurizing embedded channels. Examples include a structure that can change its curvature from convex to concave, and devices that act as compliant grippers for handling fragile objects (e.g., a chicken egg).Chemistry and Chemical Biolog

Predictive Modeling of Fast-Curing Thermosets in Nozzle-Based Extrusion

This work presents an approach to modeling the dynamic spreading and curing behavior of thermosets in nozzle-based extrusions. Thermosets cover a wide range of materials, some of which permit low-temperature processing with subsequent high-temperature and high-strength working properties. Extruding thermosets may overcome the limited working temperatures and strengths of conventional thermoplastic materials used in additive manufacturing. This project aims to produce technology for the fabrication of thermoset-based structures leveraging advances made in nozzle-based extrusion, such as fused deposition modeling (FDM), material jetting, and direct writing. Understanding the synergistic interactions between spreading and fast curing of extruded thermosetting materials will provide essential insights for applications that require accurate dimensional controls, such as additive manufacturing [1], [2] and centrifugal coating/forming [3]. Two types of thermally curing thermosets -- one being a soft silicone (Ecoflex 0050) and the other being a toughened epoxy (G/Flex) -- served as the test materials in this work to obtain models for cure kinetics and viscosity. The developed models align with extensive measurements made with differential scanning calorimetry (DSC) and rheology. DSC monitors the change in the heat of reaction, which reflects the rate and degree of cure at different crosslinking stages. Rheology measures the change in complex viscosity, shear moduli, yield stress, and other properties dictated by chemical composition. By combining DSC and rheological measurements, it is possible to establish a set of models profiling the cure kinetics and chemorheology without prior knowledge of chemical composition, which is usually necessary for sophisticated mechanistic modeling. In this work, we conducted both isothermal and dynamic measurements with both DSC and rheology. With the developed models, numerical simulations yielded predictions of diameter and height of droplets, along with width and height of extruded lines cured at varied temperatures. Experimental results carried out on a goniometric platform and a nozzle-based 3D printer showed agreement with the numerical simulations. Finally, this presentation will show how the models are adaptable to the planning of tool paths and designs in additive manufacturing

FLEXBLE ROBOTIC ACTUATORS

Some embodiments of the disclosed subject matter includes a laminated robotic actuator. The laminated robotic actuator includes a strain-limiting layer comprising a flexible, non extensible material in the form of a sheet or thin film, a flexible inflatable layer in the form of a thin film or sheet in facing relationship with the Strain-limiting layer, wherein the inflatable layer is selectively adhered to the strain-limiting layer, and wherein a portion of an un-adhered region between the strain-limiting layer and the inflatable layer defines a pressurizable channel, and at least one fluid inlet in fluid communication with the pressurizable channel. The first flexible non-extensible material has a stiffness that is greater than the stiffness of the second flexible elastomeric material and the flexible elastomer is non-extensible under actuation conditions

Millimeter-Scale Contact Printing of Aqueous Solutions Using a Stamp Made Out of Paper and Tape

This communication describes a simple method for printing aqueous solutions with millimeter-scale patterns on a variety of substrates using an easily fabricated, paper-based microfluidic device (a paper-based “stamp”) as a contact printing device. The device is made from inexpensive materials, and it is easily assembled by hand; this method is thus accessible to a wide range of laboratories and budgets. A single device was used to print over 2500 spots in less than three minutes at a density of 16 spots per square centimeter. This method provides a new tool to pattern biochemicals—reagents, antigens, proteins, and DNA—on planar substrates. The accuracy of the volume of fluid delivered in simple paper-to-paper printing is low, and although the pattern transfer is rapid, it is better suited for qualitative than accurate, quantitative work. By patterning the paper to which the transfer occurs using wax printing or an equivalent technique, accuracy increases substantially.Chemistry and Chemical Biolog