Showing papers by "Xingcheng Xiao published in 2009"

Revealing Triple-Shape Memory Effect by Polymer Bilayers

Abstract: Bilayer polymers that consist of two epoxy dual-shape memory polymers of well-separated glass transition temperatures have been synthesized. These bilayer epoxy samples exhibit a triple-shape memory effect (TSME) with shape fixities tailorable by changing the ratio between the two layers. The triple-shape fixities of the bilayer epoxy polymers can be explained by the balance of stress between the two layers. Based on this work, it is believed that the following three molecular design criterions should be considered in designing triple-shape memory polymers with optimum TSME: 1) well-separated thermal transitions, 2) a strong interface, and 3) an appropriate balance of moduli and relative ratios between the layers (or microphases).

Reversible dry micro-fibrillar adhesives with thermally controllable adhesion

Abstract: This work reports thin-film terminated micro-fibrillar adhesives made of adhesive polymers and shape memory polymers as reversible dry adhesives with thermally controllable adhesion. Structurally different adhesives were fabricated by coating a continuous thin layer of an elastomeric adhesive polymer onto either a flat or a fibrillar shape memory polymer surface. Experimental results exhibited that pull-off forces of the adhesives can be up to four times different depending on thermal conditions. These differences originate from the temperature dependence of either the intrinsic adhesion properties of the adhesive polymer and/or the stiffness of the sub-surface shape memory polymer.

Intercalation electrode based on ordered graphene planes

Abstract: An intercalation electrode includes an electron current collector and graphene planes deposited normal to the surface of the current collector substrate. The graphene planes are deposited on the current collector substrate from a carbon-precursor gas using, for example, chemical vapor deposition. In an embodiment of an anode for a lithium-ion battery, the graphene planes are intercalated with lithium atoms. A lithium-ion battery may include this anode, a cathode, and a non-aqueous electrolyte. In repeated charging and discharging of the anode, lithium atoms and ions are readily transported between the graphene planes of the anode and the electrolyte.

Shape memory polymer and adhesive combination and methods of making and using the same

Abstract: One exemplary embodiment includes a thermo-reversible polymer adhesive including a dry adhesive layer and shape memory polymer layer, the shape memory polymer material capable of transitioning from a first shape to a second shape upon heating and imposition of a load to conform to the surface topography of a substrate to which the adhesive is applied.

Seal performance for hydrogen storage and supply systems

Abstract: The performance and durability of static and dynamic seals for hydrogen storage and supply systems has been improved by utilizing a spring-energized and plastic coated radial seal in combination with at least a mating surface that has been treated by one of a variety of procedures. These procedures include applying to the mating surface a low-friction, hard, and hydrogen impervious coating, chemically polishing the mating surface, and electrochemically polishing the mating surface. Each of these procedures significantly reduces, on a microscopic scale, the surface roughness of the mating surface. The seal can thus form a tighter and more gas-tight seal with the smoother mating surface so as to decrease the loss of hydrogen gas across the seal. The smoother mating surface can also improve seal life by reducing seal surface wear.

Remote activation of thermo-reversible dry adhesives

Abstract: A thermo-reversible dry adhesive, having shape memory polymer characteristics, introduces one or more particles of micro- or nano-particles to at least one layer of the at least one layer of shape memory polymer. These particles may be remotely activated to induct heat sufficient to transform the dry adhesive material from its temporary shape to its permanent shape in the absence of load, which allows the dry adhesive to be reversibly coupled to one or more substrates, wherein the degree of adhesion is greater when the dry adhesive is in the temporary shape than in the permanent shape.

Impact of surface chemistry on grain boundary induced intrinsic stress evolution during polycrystalline thin film growth.

Abstract: First principles calculations were integrated with cohesive zone and growth chemistry models to demonstrate that adsorbed species can significantly alter stresses associated with grain boundary formation during polycrystalline film growth. Using diamond growth as an example, the results show that lower substrate temperatures increase the hydrogen content at the surface, which reduces tensile stress, widens the grain boundary separations, and permits additional atom insertions that can induce compressive stress. More generally, this work demonstrates that surface heteroatoms can lead to behavior which is not readily described by existing models of intrinsic stress evolution.

Nanographene layers and particles and lubricants incorporating the same

Abstract: A method of making at least one nanographene layer is disclosed herein. The method includes selecting X hydrocarbon precursor and Y hydrogen gas (H2) such that a ratio of X/Y ranges from 0.5 to 1, the hydrocarbon precursor including at least one of CH4, C2H2 or C3H8. The method further includes submitting the hydrocarbon precursor to chemical vapor deposition using the hydrogen gas and argon gas (Ar). As a result, i) the hydrocarbon precursor reacts with the hydrogen gas and argon gas (Ar) according to the following reaction: X hydrocarbon precursor+YH2+ZAr→2X graphene+(Y+2X)H2+ZAr, where Z ranges from 5*(X+Y) to 10*(X+Y), and ii) the hydrocarbon precursor decomposes and self-assembles to form the at least one nanographene layer.

High hardness nanocomposite coatings on cemented carbide

Abstract: A method of creating adherent surface coatings on carbide cutting tools or other workpiece substrates through the development of polycrystalline diamond coatings or composite coatings comprising a refractory metal carbide and polycrystalline diamond is described. The coating is deposited through a sequenced chemical vapor deposition process, first using a specified gas mixture of hydrogen and a refractory metal halide to deposit a base layer of a refractory metal carbide. This step is followed by a second step in which polycrystalline diamond is deposited from a gas mixture comprising a hydrocarbon and hydrogen. Co-deposition of refractory metal carbide and diamond in the second step to create a toughened diamond coating is also contemplated.

Nanocomposite coatings on cemented carbide

Abstract: A method of creating adherent, fracture-toughened polycrystalline diamond coatings on carbide cutting tools or other workpiece substrates through the development of composite coatings comprising polycrystalline diamond and carbon nanotubes is described. The coating is deposited through a chemical vapor deposition process using a pre-determined hydrocarbon-hydrogen gas mixture suitable for nucleating diamond on the carbide particles and carbon nanotubes on the metallic binder. The deposited coating, which may be up to 30 micrometers in thickness, is typically characterized by a diamond or diamond-like carbon matrix in which carbon nanotubes are distributed as fiber-like filler materials.

Product useful for joining substrate such as automotive body trim piece, comprises thermo-reversible dry adhesive comprising first layer containing dry adhesive and second layer containing shape memory polymer

Abstract: A product (10) comprises a thermo-reversible dry adhesive comprising a first layer (12) containing a dry adhesive; a second layer (14) containing a shape memory polymer; where the thermo-reversible dry adhesive has a first shape at a first temperature and a second shape at a second temperature with a load applied Independent claims are included for the following: (1) preparing a thermo-reversible dry adhesive containing at least one dry adhesive layer and at least one shape memory polymer layer involving heating the thermo-reversible dry adhesive to a temperature higher than the glass transition temperature of the shape memory polymer layer; imposing a load on the thermo-reversible dry adhesive while cooling to a temperature below the glass transition temperature of the shape memory polymer layer, so that the dry adhesive layer conforms to a corresponding topography of an underlying substrate to form a strong adhesive bond to the underlying substrate; and releasing the thermo-reversible dry adhesive from the underlying substrate by heating the thermo-reversible dry adhesive to a temperature above the glass transition temperature of the shape memory polymer to cause the shape memory polymer to revert to its original shape, and causing the dry adhesive layer to return to its original shape; and (2) forming a thermo-reversible dry adhesive involving forming a first layer by curing a first component, a second component, and a third component; forming a second layer over the first layer involving pouring a mixture of a fourth component and a fifth component over the first layer and curing the second layer; and post-curing the first and second layers to form the thermo-reversible adhesive having a curved structure at a first temperature and having a relatively flat structure at a second temperature with a load applied

Enhance diamond coating adhesion by oriented interlayer microcracking

Abstract: In this paper, we report a microcrack toughening mechanism for enhancing the adhesion of diamond coating. The oriented microcracks were formed within the TiC interlayer to dissipate strain energy and accommodate deformation via the crack opening-closing mechanism, thus enhancing the coating/substrate interfacial toughness. The delamination of diamond coating was effectively prevented when the parallel microcracks were confined within the interlayer and arrested at interfaces of coating/interlayer/substrate. Density functional theory calculations revealed that the highly anisotropic fracture strength of the TiC phase energetically favors crack initiation and propagation along (100) planes only, which are 54.7° away from the interface. These microcracks are constrained inside the interlayer by the two strong interfaces in the substrate/interlayer/coating system. The new microcrack toughening mechanism with these combined features has a wide application to enhance the adhesion of thin-film coatings.

Reversible welding process for polymers

Abstract: One exemplary method includes providing a first polymer and a second polymer each comprising a first shape memory polymer backbone having at least one surface free side chain, the first polymer and the second polymer each transformable between a permanent shape and a temporary shape; creating an adhesive bond between the first polymer and the second polymer, wherein the creating of the adhesive bond transforms the first polymer to its temporary shape and transforms the second polymer to its temporary shape; and wherein the at least one surface free chain of the first polymer in its temporary shape is interdiffused with the at least one surface free chain of the second polymer in its temporary shape by the creation of the adhesive bond.

Reversible dry adhesives for wet and dry conditions

Abstract: One embodiment includes a dry adhesive material including catechol chemically attached to the surface of a shape memory polymer molecule. The catechol content may allow the dry adhesive to be utilized in both dry and wet conditions to bond objects together. The shape memory polymer may allow the dry adhesive to be reversibly attached to the objects.

Haftfuß mit thermoreversiblem Kleber und Verfahren zum Herstellen und Verwenden desselben

Abstract: Eine Ausfuhrungsform sieht einen Haftfus vor, der einen mehrschichtigen thermoreversiblen Kleber mit einer Formgedachtnispolymerschicht und einer Trockenkleberschicht umfasst, die unter der Formgedachtnispolymerschicht liegt, wobei der mehrschichtige thermoreversible Kleber eine gekrummte Oberflache aufweist, wenn sich die Formgedachtnispolymerschicht unter ihrer Glasubergangstemperatur befindet und nicht von einer Belastung beeinflusst wird; und ein Mittel zum gleichmasigen Aufbringen einer Belastung und/oder einer Trennkraft auf dem Umfang des mehrschichtigen thermoreversiblen Klebers umfasst, welches eine Feder umfasst.