Papers by Patricia McGuiggan
He2, Patricia McGuiggan3, Xi Zhang1, 1Department of Earth and Planetary Sciences, University of C... more He2, Patricia McGuiggan3, Xi Zhang1, 1Department of Earth and Planetary Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 ([email protected]). 2Department of Earth and Planetary Sciences, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218. 3Department of Materials Science and Engineering, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218.
Journal of Tribology, 1989
A new technique is described for sliding (shearing) two molecularly smooth surfaces laterally pas... more A new technique is described for sliding (shearing) two molecularly smooth surfaces laterally past each other in liquids while monitoring their exact contact area, the normal and transverse forces, and the surface separation. First, we show that the elastic deformations of two initially curved surfaces in adhesive contact are the same under static and dynamic (i.e., sliding) conditions. Detailed results are then presented of how the shear properties of thin films of water and a simple nonpolar liquid are “quantized” with the number of layers. Results with water as the intervening liquid, as well as the effects of humidity on sliding in air, reveal that more complex mechanisms are operating than with simple liquids which appear to be related to the complex “hydration” forces between two surfaces in water or in aqueous salt solutions. The results suggest a close correlation between the static forces and shear properties of very thin liquid films, and the molecular structure of the liq...
Science, 1988
An experimental technique is described for simultaneously measuring the static and dynamic intera... more An experimental technique is described for simultaneously measuring the static and dynamic interactions of very thin liquid films between two surfaces as they are moved normally or laterally relative to each other. Film thickness can be measured and controlled to 1 angstrom. Initial results are presented of the transition in the physical properties of liquid films only one molecular layer thick to thicker films whose properties are practically indistinguishable from the bulk. In particular, the results show that two molecularly smooth surfaces, when close together in simple liquids, slide (shear) past each other while separated by a discrete number of molecular layers, and that the frictional force is "quantized" with the number of layers. T HE PROPERTIES OF SUBMICROSCOP- ic quantities ofmatter, and especially of liquids confined to very small spaces, are of increasing interest, both for a fundamental understanding of molecular systems as well as from a practical need to understand and control many colloidal, in- terfacial, and material engineering processes. Examples abound, ranging from the formation of small liquid droplets, polymer clus- ters, or surfactant micelles in solution, to the properties of liquids in very narrow pores or trapped between two solid surfaces (essen- tial to understanding interfacial adhesion, the properties ofconcentrated dispersions of particles, and lubrication), and to the prop- erties of thin monolayer or bilayer films of surfactants and lipids (the basic structure of biological membranes). Fundamentally, it is important to ascertain how the physical properties ofsuch submicroscopic structures differ from those of the bulk materials, and in particular the size dependence of this variation. Certain bulk, or continuum, prop- erties such as refractive index, dielectric constant, and surface energy appear to be al- ready applicable to individual molecules or to very small clusters of molecules (1). In contrast, the results of direct measurements of interaction forces, such as the van der Waals forces between surfaces in liquids, are well described by continuum theories only at large distances, but fail drastically when two surfaces are closer than a few molecular diameters ofthe intervening liquid (solvent) molecules (1-5). This effect is due to the induced (or enhanced) ordering into dis- crete liquid molecular layers brought about
Molecular mechanisms and forces involved in the adhesion and fusion of amphiphilic bilayers
Science, 1989
The surface forces apparatus technique was used for measuring the adhesion, deformation, and fusi... more The surface forces apparatus technique was used for measuring the adhesion, deformation, and fusion of bilayers supported on mica surfaces in aqueous solutions. The most important force leading to the direct fusion of bilayers is the hydrophobic interaction, although the occurrence of fusion is not simply related to the force law between bilayers. Bilayers do not need to "overcome" some repulsive force barrier, such as hydration, before they can fuse. Instead, once bilayer surfaces come within about 1 nanometer of each other, local deformations and molecular rearrangements allow them to "bypass" these forces.
Proceedings of the National Academy of Sciences, 2006
Geckos can run rapidly on walls and ceilings, requiring high friction forces (on walls) and adhes... more Geckos can run rapidly on walls and ceilings, requiring high friction forces (on walls) and adhesion forces (on ceilings), with typical step intervals of ≈20 ms. The rapid switching between gecko foot attachment and detachment is analyzed theoretically based on a tape model that incorporates the adhesion and friction forces originating from the van der Waals forces between the submicron-sized spatulae and the substrate, which are controlled by the (macroscopic) actions of the gecko toes. The pulling force of a spatula along its shaft with an angle θ between 0 and 90° to the substrate, has a “normal adhesion force” contribution, produced at the spatula-substrate bifurcation zone, and a “lateral friction force” contribution from the part of spatula still in contact with the substrate. High net friction and adhesion forces on the whole gecko are obtained by rolling down and gripping the toes inward to realize small pulling angles θ between the large number of spatulae in contact with t...
Physical Review E, 2007
Jamming and force networks observed in electrorheological ͑ER͒ fluids bear many similarities to t... more Jamming and force networks observed in electrorheological ͑ER͒ fluids bear many similarities to those observed in various granular and colloidal systems. We have measured the time evolution ͑transient stresses͒ of filamentous networks of colloidal particles in suspensions subjected to continuous tensile strain concomitant with the switching on and off of electric fields. The density of particle chains was found to increase exponentially with the applied tensile strain via a rapid formation of single chains followed by a slower coarsening ͑aggregation͒ of the chains. The two processes can be ascribed to the field-induced short-range and long-range interparticle forces, respectively, along with the tensile viscous force.
Liquid to solidlike transitions of molecularly thin films under shear
The Journal of Chemical Physics, 1990
Page 407. Liquid to solidlike transitions of molecularly thin films under shear Michelle L. Gee, ... more Page 407. Liquid to solidlike transitions of molecularly thin films under shear Michelle L. Gee, Patricia M. McGuiggan, and Jacob N. Israelachvili Department of Chemical and Nuclear Engineering, and Materials Department, University ...
Biochemistry, 1992
With the aim of gaining more insight into the forces and molecular mechanisms associated with bil... more With the aim of gaining more insight into the forces and molecular mechanisms associated with bilayer adhesion and fusion, the surface forces apparatus (SFA) was used for measuring the forces and deformations of interacting supported lipid bilayers. Concerning adhesion, we find that the adhesion between two bilayers can be progressively increased by up to two orders of magnitude if they are stressed to expose more hydrophobic groups. Concerning fusion, we find that the most important force leading to direct fusion is the hydrophobic attraction acting between the (exposed) hydrophobic interiors of bilayers; however, the occurrence of fusion is not simply related to the strength of the attractive interbilayer forces but also to the internal bilayer stresses (intrabilayer forces). For all the bilayer systems studied, a single basic fusion mechanism was found in which the bilayers do not "overcome" their short-range repulsive steric-hydration forces. Instead, local bilayer deformations allow these repulsive forces to be "bypassed" via a mechanism that is like a first-order phase transition, with a sudden instability occurring at some critical surface separation. Some very slow relaxation processes were observed for fluid bilayers in adhesive contact, suggestive of constrained lipid diffusion within the contact zone. %e traditional view of the fusion of two amphiphilic layers (e.g., two vesicles) is that the two surfaces first overcome their We thank the National Science Foundation for supporting this work under Grant No. CBT87-21741. Christiane Helm is grateful to the Deutsche Forschungsgemeinschaft for a postdoctoral research scholarship.
Forces between surfaces in liquids
Advances in Colloid and Interface Science, 1982
Recent developments in the direct measurements of forces between surfaces in liquids at the ångst... more Recent developments in the direct measurements of forces between surfaces in liquids at the ångstrom resolution level are reviewed. The results reveal a rich variety of interactions and interaction potentials that depend on the nature of the surfaces and intervening liquids. These results also shed new insights into liquid structure adjacent to surfaces and the interactions occurrig in complex systems, with implications in many different areas of chemical physics, biology, and technology. The origin of some important fundamental interactions, such as repulsive "hydration" forces and attractive "hydrophobic" forces, are still not understood and offer a challenge for experimental and theoretical work in this area.
Titan, the largest moon of Saturn, is characterized by gigantic linear dunes and an active dust c... more Titan, the largest moon of Saturn, is characterized by gigantic linear dunes and an active dust cycle. Much like on Earth, these and other aeolian processes are caused by the wind-driven mobilization of surface grains, known as saltation. To date, very little is known about the conditions that allow for the occurrence of saltation on Titan. In fact, Titan saltation may be fundamentally different from Earth saltation given the denser atmosphere, the lower gravity, and the cohesion of its surface grains. Here, we draw on experiments, theory, and modeling to progress towards a comprehensive understanding of saltation on Titan. We find that aerodynamic lifting of surface grains requires strong wind speeds due to the high cohesion of the grains. However, saltation may be sustained through granular splash at wind speeds much smaller than those required to initiate grain motion. This suggests that most saltation transport on Titan is intermittent rather than continuous. We account for thes...
Scaling Issues in the Measurement of Monolayer Films
Fundamentals of Tribology and Bridging the Gap Between the Macro- and Micro/Nanoscales, 2001
An atomic force microscope (AFM), a surface forces apparatus (SFA), and a ball-on- inclined plane... more An atomic force microscope (AFM), a surface forces apparatus (SFA), and a ball-on- inclined plane (BOIP) apparatus were used to measure the mechanical properties of thin lubricant films. The frictional force of a set of four samples with different lubricant chemistries was measured by an AFM using a conventional sharp silicon nitride tip. Very little difference was observed among the different chemistries. A careful study using different tip sizes on two model compounds on mica was compared to results obtained with the SFA and suggested a tip size effect (scaling issue).
Maximized Hole Trapping in a Polystyrene Transistor Dielectric from a Highly Branched Iminobis(aminoarene) Side Chain
ACS Applied Materials & Interfaces
Surface Energy of the Titan Aerosol Analog “Tholin”
The Astrophysical Journal
Restaurator. International Journal for the Preservation of Library and Archival Material
The ability to determine the condition of paper (e.g. its brittleness) and its permanence is a ne... more The ability to determine the condition of paper (e.g. its brittleness) and its permanence is a need in libraries and archives. This study investigates various bend tests and applies these tests to aged paper with the goal of finding easy, non-destructive tests to determine the mechanical properties of paper. The cantilever test was previously shown to accurately assess mechanical properties of paper-based materials, such as elastic and bending moduli as well as the bending length. This work investigates the hanging pear loop and clamped fold tests and compares the results with those found with the cantilever test. The results show that the strain and curvature induced by the two tests are much larger than those experienced in the cantilever test. This large strain and curvature induce plastic behaviour and make the hanging pear loop and clamped fold tests inappropriate for use on paper-based materials.
Earth and Planetary Science Letters
Sand electrification is important for aeolian sediment transportation on terrestrial bodies with ... more Sand electrification is important for aeolian sediment transportation on terrestrial bodies with silicate sand as the main sediment composition. However, it has not been thoroughly studied for icy bodies such as Titan with organic sand as the main dune-forming material. We used the colloidal probe atomic force microscopy (AFM) technique to study triboelectric charging processes using Titan and Earth sand analogs. We found that it is easy to generate triboelectric charges between naphthalene (a simple aromatic hydrocarbon), polystyrene (an aromatic hydrocarbon polymer), and borosilicate glass (Earth silicate sand analog). Strong electrostatic forces can be measured after contact and/or tribocharging. In contrast, tholin, a complex organic material, does not generate any detectable electrostatic forces with contact or tribocharging within the detection limit of the instrument. If Titan sand behaves more like tholin, this indicates that the tribocharging capacity of Titan sand is much weaker than Earth silicate sand and much less than previously measured by Méndez-Harper et al., (2017), where only simple organics were used for Titan sand analogs. Thus, triboelectrification may not contribute to increasing interparticle forces between sand particles on Titan as much as on Earth. Interparticle forces generated by other electrostatic processes or other interparticle forces such as van der Waals and capillary cohesion forces could be the dominant interparticle forces that govern Titan sand formation and sediment transportation on the surface. Titan sand is also unlikely to produce large electrical discharge through tribocharging to affect future missions to Titan's surface.
Stewing in Its Own Juices? The Permeability of PET by Water and Acetic Acid
Restaurator. International Journal for the Preservation of Library and Archival Material
Historic documents are frequently protected by placing them in a sealed polyethylene-terephthalat... more Historic documents are frequently protected by placing them in a sealed polyethylene-terephthalate (PET) envelope. Although the paper is mechanically stabilized, the PET film may limit transmission of moisture or acidic degradation by-products of the paper. This creates a microenvironment for the encapsulated document. The permeation of water and acetic acid vapor through the PET film was measured to understand the microenvironment within an encapsulated enclosure. For encapsulation with a 102 μm (4 mil) PET film, the water vapor mass flux through the encapsulated film was measured. The water vapor was found to flow into or out of the PET film depending on the sample and environmental conditions. Because the encapsulated paper needed a longer time to dry than paper in open air, PET encapsulation provides a microenvironment that will buffer the encapsulated object from large swings in humidity. Acetic acid either did not diffuse through the PET, or it diffused at such a slow rate as ...
Direct Measurement of Interparticle Forces of Titan Aerosol Analogs (“Tholin”) Using Atomic Force Microscopy
Journal of Geophysical Research: Planets
The breathability of PET to water vapor: Thickness effects
Journal of the American Institute for Conservation
Where Does Titan Sand Come From: Insight From Mechanical Properties of Titan Sand Candidates
Journal of Geophysical Research: Planets
The disastrous copper. Comparing extraction and chelation treatments to face the threat of copper-containing inks on cellulose
Carbohydrate Polymers
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Papers by Patricia McGuiggan