Lawrence Schultz

Shape deposition manufacturing of heterogeneous structures

Abstract To date, the most widely recognized advantage of the layered manufacturing methodology is the relative ease of automatically planning and executing the fabrication of complex geometric shapes. But building shapes using selective material-additive processes has a second, far-reaching advantage—the creation of heterogeneous structures composed of multimaterial regions and with prefabricated devices embedded into the structure. The capability to fabricate heterogeneous structures is important because it enables the realization of new, complex designs. Shape deposition manufacturing, a layered manufacturing process described in this paper, addresses how to build multimaterial, embedded structures such as advanced tooling and embedded electronic devices.

Robust gold nanoparticles stabilized by trithiol for application in chemiresistive sensors

The use of gold nanoparticles coated with an organic monolayer of thiol for application in chemiresistive sensors was initiated in the late 1990s; since then, such types of sensors have been widely pursued due to their high sensitivities and reversible responses to volatile organic compounds (VOCs). However, a major issue for chemical sensors based on thiol-capped gold nanoparticles is their poor long-term stability as a result of slow degradation of the monothiol-to-gold bonds. We have devised a strategy to overcome this limitation by synthesizing a more robust system using Au nanoparticles capped by trithiol ligands. Compared to its monothiol counterpart, the new system is significantly more stable and also shows improved sensitivity towards different types of polar or non-polar VOCs. Thus, the trithiol-Au nanosensor shows great promise for use in real world applications.

Robot-assisted shape deposition manufacturing

Solid freeform fabrication and shape deposition are rapid manufacturing processes which build parts by incremental material deposition and fusion of cross-sectional layers. In this paper, several thermal deposition processes are described for directly fabricating prototype metal shapes using robotically manipulated material deposition systems. A robotic palletizing/part transfer system is also described which integrates multiple deposition and shaping processes into a single facility for rapidly manufacturing functional shapes.<<ETX>>

Arc-sprayed steel-faced tooling

A process for building arc-sprayed steel-faced tooling is described. Strategies to create matched die sets for injection molding applications are presented, and the issues involving backing materials, spray con-ditions, and wear resistance are discussed. Examples of stainless steel tools built with this process demon-strate improved durability over more conventional sprayed zinc-faced tools.

Volatile organic compound discrimination using nanostructured polythiophene sensors

New synthesis methods have allowed us to make many semiconducting polythiophenes polymers with different side and end groups. Also, co-polymers combining a polythiophene chain attached to another polymer chain were synthesized. This design freedom brings a new dimensionality to the sensing properties of the materials. Single chip micro sensor resistor arrays, utilizing multiple polymers, were fabricated and then tested in an automated system. The sensors demonstrated ppm level sensitivity to various volatile organic compounds (VOCs) including both polar and non-polar materials. Polymers with different chemical structures show strong selectivity to different VOCs. By applying pattern recognition algorithms, the sensor response clearly discriminates between the tested VOCs allowing us to conjecture as to the role molecular modification have in determining response to specific VOCs

Nanostructure Dependence of Conductive Polymer Chemical Sensors

It is shown that the resistive sensing properties of conductive polymers are highly dependent on the material nanostructure. The sensing properties of regioregular poly(3-hexylthiophene) (P3HT) polymer thin films with porous nanofibrile structure, dense nanofibrile structure and nano-granular structure show very different conductance changes, in terms of both response amplitude and sign, upon exposure to various VOC vapors. This implies that multiple sensing mechanisms, such as both grain boundary and intra-grain effects, exist and the dominant sensing mechanism can vary with different material nanostructures. Possible mechanisms for these effects, and their correlation with observed material nanostructures, are also discussed.

Regioregular polythiophene nanowires and sensors

We have developed and synthesized highly conductive regioregular poly(3-alkylthiophene) (rr-PAT) derivatives for use in sensor arrays on a chip. Poly(3-alkylthiophene)s are ideally suited for this application because of their excellent electrical properties, solution processability and our ability to modify their chemical structure. Here, we synthesized rr-PATs that have different side chains and different end groups. The polymers were ink-jetted onto ChemFET devices on a chip and their chemical sensing properties were tested to a variety of volatile organic compounds (VOCs). The sensors demonstrated ppm level sensitivity and selectivity to all VOCs tested, including both polar and non-polar compounds.