Forces between two layers of adsorbed polystyrene immersed in cyclohexane below and above the θ temperature

Israelachvili, Jacob N.; Tirrell, Matthew; Klein, Jacob; Almog, Yaacov

doi:10.1021/ma00132a015

Cited by 138 publications

(82 citation statements)

References 8 publications

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“…This type of "solidification" was predicted by molecular dynamics and experimentally measured. [7][8][9]39,40 The reported extent of solidification from solution or from melt has been remarkably similar. Furthermore, the model was quite successful for interpretation of not only the PVT behavior 2 but also the strongly nonlinear viscoelastic flows.…”

Section: Model Of Molten Pncmentioning

confidence: 76%

“…The failure originates in the well-known adsorption on the high-energy surface of crystalline montmorillonite (MMT) platelets. For example, Israelachvili et al 7 and Horn and Israelachvili 8 used the surface force analyzer (SFA) to measure the viscosity of PS solutions. The authors reported a solidlike behavior for the first 2-9 nm thick surface layer and then a progressive decrease of viscosity with distance from the platelet.…”

Section: Introductionmentioning

confidence: 99%

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Pressure−Volume−Temperature Dependence of Polypropylene/Organoclay Nanocomposites

Utracki

Simha

2004

Macromolecules

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Received August 24, 2004; Revised Manuscript Received October 7, 2004 ABSTRACT: The pressure-volume-temperature (PVT) dependencies of commercial polypropylene melt (PP) and its nanocomposites containing X wt % of organoclay (Cloisite-15A, or C15) and 2X w t%o fa compatibilizer were determined at T ) 450-530 K and P ) 0.1-190 MPa. C15 was used at concentrations: X ) 0, 2, and 4 wt %. Three functionalized PP's were used as compatibilizers: two maleated and one grafted with glycidyl methacrylate. Incorporation of X ) 2 wt % C15 into PP resulted in reduction of specific volume by ∆V ≈ 1%, but that of free volume (hole) fraction by ∆h ≈ 5%. The latter quantity was computed from the Simha-Somcynsky lattice-hole equation of state. Furthermore, at constant T and P the hole fraction was found to be linearly related to the bulk-average energetic interaction parameter and to be a sensitive indicator of structural changes. In binary (polymer + organoclay) systems ∆h is linearly related to the interlayer spacing, d 001. So, where statements from the previous paper are repeated or there are similarities, this is done for purposes of comparison. In three-component systems (with a compatibilizer) the proportionality has been preserved, but large changes of ∆h result in relatively small changes of d001. Mechanical properties hardly correlate with either ∆h or d001, as polymer/ compatibilizer morphology and crystallinity complicate the behavior.

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Section: Model Of Molten Pncmentioning

confidence: 76%

Section: Introductionmentioning

confidence: 99%

Pressure−Volume−Temperature Dependence of Polypropylene/Organoclay Nanocomposites

Utracki

Simha

2004

Macromolecules

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“…The technique involves the direct measurement of the intermolecular forces between two separate RNase A layers (each on a different smooth mica surface) as a function of separation distance (6,7). It is the same method as that used recently to elucidate the intermolecular forces and conformation of adsorbed molecules between mica surfaces covered with surfactants (8-10), polymers (11)(12)(13)(14)(15)(16)(17)(18), lipid mono and bilayers (19,20), and large flexible rod-like proteins such as bovine submaxillary mucin (4 x 106 daltons) and collagen (13,21).…”

Section: Methodsmentioning

confidence: 99%

Changing activity of ribonuclease A during adsorption: a molecular explanation.

Lee

Belfort

1989

Proc. Natl. Acad. Sci. U.S.A.

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The activity of ribonuclease A (RNase A) during adsorption onto molecular smooth mica increases from 16% to 78% in a period of 24 h when compared to its activity in free solution at pH 5 and 20 + 0.5MC. From electropotential plots, the tertiary structure of RNase A, the characteristics of the mica surface, and direct measurements of the intermolecular forces between two adsorbed enzyme layers, a molecular explanation is offered for the changing activity with time.Initially, the RNase A molecules lie flat-on the mica with their smallest axis perpendicular to and their active site facing the surface. As adsorption proceeds, the molecules slowly reorient until at long times they lie end-on with their largest axis perpendicular to the surface and their active site partially exposed to the free solution. A translational diffusion process is indicated for the phase transition and molecular reorientation of the RNase A molecules.The propensity for proteins to adsorb onto solid surfaces depends on their molecular properties, including size, charge, and chemical and physical structure. It also depends on the surface characteristics of the solid, the nature of the interactions between the surface and the proteins, and the solubility of the proteins in the solution. Although much of the literature deals with the amount of protein adsorbed as a function of solution concentration (isotherms), attention has recently been given to the mechanisms of adsorption and the structure and stability of the adsorbed molecules (1).The activity of biocatalytic molecules such as enzymes at solution-solid interfaces depends on their structural stability (2). Solid surfaces are able to disrupt intramolecular disulfide and hydrogen bonds and hence the "breathing" structure of enzymes. Intense interactions with surfaces can denature proteins (3), whereas weak interactions often leave the protein conformationally stable.In this report, we present a molecular explanation for the changing activity of a well-known conformationally stable protein, bovine pancreas ribonuclease A (RNase A) during the adsorption period onto mica. The four disulfide bonds and a very strong hydrogen bonding network support the rigidity of RNase A (4). Electropotential plots and the well-known crystal structure of RNase A together with the charge condition of the mica surface at pH 5 and 20°C are used to determine the probable orientation of the enzyme molecules at solid-liquid interfaces. Direct measurements of the adsorption kinetics of RNase A onto two curved mica surfaces and ofthe intermolecular forces between two separate RNase A layers (each on a different surface) during the adsorption process are described and used to quantitatively estimate the amount of enzyme associated with the surface and the thickness of the adsorbed layers, respectively. The kinetics of the change in enzyme activity and molecular reorientation of the surface is followed. MATERIALS AND METHODSMaterials. KCI salt was purchased from Aldrich and was of suprapure grade (99.99+%). RNase...

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“…First direct quantitative measurements were made with the SFA (e.g. [820][821][822][823]). Reviews are given in Refs.…”

Section: Steric Forcesmentioning

confidence: 99%

Force measurements with the atomic force microscope: Technique, interpretation and applications

Butt

Cappella

Kappl

2005

Surface Science Reports

3,210

2,949

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Forces between two layers of adsorbed polystyrene immersed in cyclohexane below and above the θ temperature

Cited by 138 publications

References 8 publications

Pressure−Volume−Temperature Dependence of Polypropylene/Organoclay Nanocomposites

Pressure−Volume−Temperature Dependence of Polypropylene/Organoclay Nanocomposites

Changing activity of ribonuclease A during adsorption: a molecular explanation.

Force measurements with the atomic force microscope: Technique, interpretation and applications

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