The Simultaneous Determination of the Forces and Viscoelastic Properties of Adsorbed Polymer Layers

An Investigation into the Rheology of Pharmaceutical Inter-granular Material Bridges at High Shear Rates

“…3 that tan δ is independent of the cantilever spring constant and probe geometry and so it is on this parameter that quantitative analysis will be based. Work reported here differs from previous work (3,(5)(6)(7) in that it is the cantilever and not the sample which is subjected to an oscillatory drive. In addition, this model does not account for adhesion forces.…”

“…1). This model is usually termed a Voigt model (5) and full derivations are detailed in the Appendix. G′ and G″ may be derived as:…”

Shear thinning and frequency dependent behaviour of adsorbed polymer layers

“…Extensive descriptions of the apparatus, calibration and operation in both oscillatory and non-oscillatory mode can be found elsewhere [4,18]. In essence though the entire AFM cantilever is immersed into the solution of interest and the surfaces are moved together either smoothly when performing a "static" experiment or by superimposing an oscillatory motion onto the drive when operating in a dynamic mode.…”

“…In addition there are also dynamic interactions which arise from the rheological behaviour of the adsorbed polymer layers. However, there seems to be a wide gap in our understanding between these static and dynamic interactions, which is reflected in the vast amount of experimental [1][2][3][4][5][6] and theoretical [7][8][9][10][11] information readily available in the literature regarding static interactions between adsorbed polymer layers in a plethora of polymeric systems, compared to the relatively slow advancement made in the area pertaining to the viscoelastic properties of such layers [12][13][14][15][16][17][18][19][20][21]. Therefore, the impetus of this study was to further explore the intriguing area related to the rheological properties of adsorbed polymer layers.…”

“…Rheological properties of adsorbed polymer layers at the nanoscopic level can be obtained from a force-sensing apparatus such as a surface force apparatus (SFA) or an atomic force microscope (AFM), by adapting these techniques to act in a dynamic mode, thus effectively enabling them to act as rheometers [12][13][14][15][16][17][18][19][20][21]. This technique, which is aptly described by the term 'nanorheology', involves applying a small-amplitude sinusoidal motion to one surface.…”