Development of quantitative theory of adsorption-induced deformation is important, e.g., for enhanced coalbed methane recovery by CO2 injection. It is also promising for the interpretation of experimental measurements of elastic properties of porous solids. We study deformation of mesoporous silica by n-pentane adsorption. The shape of experimental strain isotherms for this system differs from the shape predicted by thermodynamic theory of adsorption-induced deformation. We show that this difference can be attributed to the difference of disjoining pressure isotherm, responsible for the solid−fluid interactions. We suggest the disjoining pressure isotherm suitable for n-pentane adsorption on silica and derive the parameters for this isotherm from experimental data of n-pentane adsorption on nonporous silica. We use this isotherm in the formalism of macroscopic theory of adsorption-induced deformation of mesoporous materials, thus extending this theory for the case of weak solid−fluid interactions. We employ the extended theory to calculate solvation pressure and strain isotherms for SBA-15 and MCM-41 silica and compare it with experimental data obtained from small-angle X-ray scattering. Theoretical predictions for MCM-41 are in good agreement with the experiment...
Micro-cantilever sensors are widely used to detect biomolecules, chemical gases, and ionic species. However, the theoretical descriptions and predictive modeling of these devices are not well developed, and lag behind advances in fabrication and applications. In this paper, we present a novel multiscale simulation framework for nanomechanical sensors. This framework, combining density functional theory (DFT) calculations and finite element method (FEM) analysis, is capable of analyzing molecular adsorption-induced deformation and stress fields in the sensors from the molecular scale to the device scale. Adsorption of alkanethiolate self-assembled monolayer (SAM) on the Au(111) surface of the micro-cantilever sensor is studied in detail to demonstrate the applicability of this framework. DFT calculations are employed to investigate the molecular adsorption-induced surface stress upon the gold surface. The 3D shell elements with initial stresses obtained from the DFT calculations serve as SAM domains in the adsorption layer, while FEM is employed to analyze the deformation and stress of the sensor devices. We find that the micro-cantilever tip deflection has a linear relationship with the coverage of the SAM domains. With full coverage...
This thesis uses surface sensitive tools to characterize the effect of a solid surface on immobilized biomacromolecules. This includes understanding how the surface can change the affinity of these macromolecules to small molecules compared to bulk studies. Two classes of immobilized biomacromolecules, the supported lipid bilayer (SLB) and the Lac repressor protein (LacI), are characterized using microcantilever sensors and quartz crystal microbalance with dissipation (QCM-D). The first part of this thesis reports the use of microcantilever beams, an ultrasensitive sensor for measuring the surface free energy changes on a substrate induced by molecular adsorptions, to probe the interaction between a solid surface and a phospholipid bilayer. This sensing method integrates two well-developed techniques: solid-supported lipid bilayers (SLBs) and the microcantilever (MC) sensors. Studying the adsorption free energy of lipid bilayers on a solid surface allows better characterizing of the formation and stability of SLBs. Microcantilever converts the Gibbs free energy change taking place on its surface into a mechanical deformation. As molecules physisorb or chemisorb onto the surface of the microcantilevers, the microcantilevers bend, either due to induced compressive or tensile stresses...
A nanoclay based masterbatch was mixed with polypropylene (PP) and injection moulded by conventional (CIM) and shear controlled orientation (SCORIM) injection moulding techniques. The aim was to correlate the morphologies induced by SCORIM and CIM processing with the thermal, mechanical and fracture performance of thick PP/nanoclay mouldings. In SCORIM, two extreme shear levels were applied by changing processing conditions. A complete characterization is reported, and statistical analysis was carried out to obtain a relationship between moulding properties. Nanoclay acted as a polymer morphology director, and in combinationwith SCORIM it induced the formation of the γ polymorph of PP. The nanoclay has a strong positive effectonthe thermal degradation of PP under anoxidative atmosphere,dueto the barrier effect of clay and the physico-chemical adsorption of volatile degradation products on the silicates, but there were no differences between processing techniques. SCORIM samples of neat PP showed nonlinear brittle behaviour, while nanocomposites exhibited quasi-stable behaviour induced by a large deformation capability of the skin. Although fracture initiates at practically the same loading levels, the overall propagation energy values varied with processing conditions. Statistical analysis indicates that the decrement of the core region achieved by SCORIM processing...
We study water adsorption-induced deformation of a monolithic, mesoporous
silicon membrane traversed by independent channels of $\sim$8 nm diameter. We
focus on the elastic constant associated with the Laplace pressure-induced
deformation of the membrane upon capillary condensation, i.e. the pore-load
modulus. We perform finite-element method (FEM) simulations of the
adsorption-induced deformation of hexagonal and square lattices of cylindrical
pores representing the membrane. We find that the pore-load modulus weakly
depends on the geometrical arrangement of pores, and can be expressed as a
function of porosity. We propose an analytical model which relates the
pore-load modulus to the porosity and to the elastic properties of bulk silicon
(Young's modulus and Poisson's ratio), and provides an excellent agreement with
FEM results. We find good agreement between our experimental data and the
predictions of the analytical model, with the Young's modulus of the pore walls
slightly lower than the bulk value. This model is applicable to a large class
of materials with morphologies similar to mesoporous silicon. Moreover, our
findings suggest that liquid condensation experiments allow one to elegantly
access the elastic constants of a mesoporous medium.; Comment: 5 pages...
We investigate adsorption of a gas on the surface of a deformable adsorbent
taking into account thermal fluctuations and analyze in detail the influence of
thermal fluctuations on the adsorbent deformation in adsorption. The condition
for the coexistence of two states of the bistable system of adsorbed particles
is derived. We establish the specific properties of the adsorption-induced
surface relaxation of an adsorbent caused by thermal fluctuations. The mean
transition times between two stable states of the bistable system are derived
in the parabolic approximation and in the general case.; Comment: 23 pages, 5 figures
The Derjaguin - Broekhoff - de Boer theory of capillary condensation is
employed to describe deformation of mesoporous solids in the course of
adsorption-desorption hysteretic cycles. We suggest a thermodynamic model,
which relates the mechanical stress induced by adsorbed phase to the adsorption
isotherm. Analytical expressions are derived for the dependence of the
solvation pressure on the vapor pressure. The proposed method provides a
description of non-monotonic hysteretic deformation during capillary
condensation without invoking any adjustable parameters. The method is
showcased drawing on the examples of literature experimental data on adsorption
deformation of porous glass and SBA-15 silica.; Comment: 21 pages, 3 figures