"Polyelectrolyte multilayer (PEM) thin films prepared via the Layer-by-Layer (LbL) deposition technique are of special interest in this research. The purpose of this study is to replace current mechanical closure systems, based on hook-and-loop type fasteners (i.e. Velcro), with PEM thin film systems. The technique is simple, cheap, versatile and environmental friendly; as a consequence a variety of thin films can be easily fabricated. By proposing PEMs as non-mechanical and nanoscopic molecular closures, we aim to obtain hermetic sealing, good adhesive strength, and peel off ease. Atomic force microscopy (AFM) and colloidal probe techniques were used to characterize the morphology, roughness and adhesive properties of PEMs. AFM measurements were conducted in air, necessarily requiring careful control of ambient humidity. PEMs were formed by consecutive deposition of polyanions and polycations on a charged polyethylene terephthalate (PET) solid surface, the result of which was stable nanostructured films. By systemically varying the parameters of PEM build-up process: different combinations of polyelectrolytes, different numbers of bilayers (polyanion/polycation pairs), and miscellaneous types and concentrations of salts (NaCl, NaBr and NaF salts at 0.5 M and 1.0 M concentrations), the adhesion and morphology of PEMs were thoroughly investigated. The PEM thin films specifically investigated include poly(ethyleneimine) (PEI), poly(styrene sulfonate) (PSS), poly(allylamine hydrochloride) (PAH), poly(acrylic acid) (PAA), and poly(diallydimethylammonium chloride) (PDADMAC). Silica colloidal probes were utilized in the investigation, some of which were functionalized with COOH and/or coated with PEI-PSS. Silica colloidal probes were used in order to quantify interaction forces on the PEMs. A functionalized silica colloidal probe (a probe with COOH surface chemistry) and a silica colloidal probe coated with PEI-PSS were used to simulate PEM-PEM interactions. The results suggest that adhesion in the PEMs depend on the number of layers, the salt concentration and the salt type used during the build-up process, the environmental conditions where the adhesion force measurements were made, and the choice of probe. "

The adhesion or bonding of two contacting surfaces is essential for a variety of processes, both natural and artificial. For example, the ability of insects and lizards to move on vertical walls requires their legs to adhere to the surface of the wall. To name a few technical processes: medical prosthetics, soldering, and surface coatings all have adhesion at their core. Thus, such an abundant phenomenon requires a tool to access and accurately study adhesion at a variety of interfaces. Atomic force microscopy (AFM) enables the measurement of adhesion at the nano-/microscale due to its high accuracy in force detection and lateral position sensitivity. Polymers are a suitable substrate for studying adhesion peculiarities due to their stimuli-responsiveness, which allows for fine-tuning of material properties. Therefore, for the sake of a broader comparison, the adhesion of the polymer interfaces is studied here with different AFM-based techniques on the microscale to select the most accurate one. The AFM study of adhesion is based on the mechanical contact between the indenter on the cantilever and the sample. Thus, increasing the contact area between the indenter and the sample allows for an increase in the accuracy of the measurement because the measured force is larger. Therefore, the use of a soft deformable particle attached to the end of the cantilever, called a soft colloidal probe, increases the accuracy of the measurement. However, the use of a soft colloidal probe can introduce non-linear effects during the rupture of the contact between the probe and the substrate. The main goal of this work is to measure the thermodynamic work of adhesion, regardless of these effects. First, we aimed to demonstrate the applicability of soft colloidal probe AFM to complex substrates. To achieve this, we applied the soft colloidal probe AFM to an artificial polymer with a structure like a mussel foot protein (a-mfp) distributed on a glass surface. The polymer was synthesized having a functional group sensitive to the pH change from 5.5 to 6.8. The change in pH induced a change in the structure of the polymer. The soft colloidal probe AFM revealed that remarkably, the a-mfp coating was 5 times less adhesive at pH 5.5 than at pH 6.8 when the experiments were conducted separately using different substrates for each pH value. However, when we changed the pH in situ during the measurement, we detected only 2-2.5 higher adhesion values for the case of pH 6.8. We attribute this result to the deposition of a-mfp on the surface of the colloidal probe. The second step was to use the PNIPAM anchored to the substrate (PNIPAM brush) as a sample sensitive to the non-solvent effect. Previously, we relied only on the calculation of the force required to break the contact between the probe and the sample to access the adhesion properties. However, for the contact between elastic deformable bodies (i.e. soft colloidal probe, polymeric sample), the rupture of the contacts depends on the parameters of the rupture: the speed of the contact rupture and the pressure during the contact. Nevertheless, the use of the soft colloidal probe allowed an optical measurement of the contact area, which allowed us to access the work of adhesion without the rupture of the contact. In this way, we were able to compare the two approaches: The AFM-based measurement of the pull-off force (contact rupture) and the optical measurement of the contact radius (no rupture). It was found that the results of the two approaches were drastically different: the values of the work of adhesion from the pull-off force were around 10 times larger. The significant dependence of the pull-off-based work of adhesion on the contact history and the parameters of the pull-off event with the very short time scale of the pull-off event makes the values of the work of adhesion from the pull-off force very far from the equilibrium values. At the same time, the measurement of the contact area does not rely on fast processes. Thus, the adhesion work values from the contact area measurements were found to be much closer to the equilibrium values and therefore more accurate. We found that the work of adhesion of the PNIPAM brush was higher in the swollen state than in the collapsed state and attributed it to the adaptability of the polymer chains to change their conformation under contact. In other words, the freedom of movement of the chains significantly affects the work of adhesion of the PNIPAM brush. To further investigate this idea, we carried out a preliminary study on the PNIPAM hydrogel with redox stimuli-responsive and non-responsive cross-links, which allowed us to control the degree of cross-linking in situ. The decrease in the degree of crosslinking under the redox stimuli made the hydrogel more adhesive both in water and under co-nonsolvency conditions. Thus, we can conclude that the freedom of movement of the chain in the case of PNIPAM is crucial for its adhesive properties. Ultimately, this work demonstrates that the optical measurement of the contact area, rather than the theoretical prediction of the contact area, is critical to accessing the work of adhesion accurately and close to equilibrium. In addition, we have demonstrated that such measurements are applicable even to complex polymer systems.

No description available.

Doctor of Philosophy / Department of Physics / Bruce M. Law / Three diverse first author surfaces science experiments conducted by Sean P. McBride 1-3 will be discussed in detail and supplemented by secondary co-author projects by Sean P. McBride, 4-7 all of which rely heavily on the use of an atomic force microscope (AFM). First, the slip length parameter, b of liquids is investigated using colloidal probe AFM. The slip length describes how easily a fluid flows over an interface. The slip length, with its exact origin unknown and dependencies not overwhelming decided upon by the scientific community, remains a controversial topic. Colloidal probe AFM uses a spherical probe attached to a standard AFM imaging tip driven through a liquid. With the force on this colloidal AFM probe known, and using the simplest homologous series of test liquids, many of the suspected causes and dependencies of the slip length demonstrated in the literature can be suppressed or eliminated. This leaves the measurable trends in the slip length attributed only to the systematically varying physical properties of the different liquids. When conducting these experiments, it was realized that the spring constant, k, of the system depends upon the cantilever geometry of the experiment and therefore should be measured in-situ. This means that the k calibration needs to be performed in the same viscous liquid in which the slip experiments are performed. Current in-situ calibrations in viscous fluids are very limited, thus a new in-situ k calibration method was developed for use in viscous fluids. This new method is based upon the residuals, namely, the difference between experimental force-distance data and Vinogradova slip theory. Next, the AFM’s ability to acquire accurate sub nanometer height profiles of structures on interfaces was used to develop a novel experimental technique to measure the line tension parameter, τ, of isolated nanoparticles at the three phase interface in a solid-liquid-vapor system. The τ parameter is a result of excess energy caused by the imbalance of the complex intermolecular forces experienced at the three phase contact line. Many differences in the sign and magnitude of the τ parameter exist in the current literature, resulting in τ being a controversial topic.

Adhesion between different objects is happening everywhere. Without it, simple procedures like walking or holding something in a hand or attaching a postage stamp would be impossible. The life itself depends on adhesion on all levels, starting from the interactions between the living cells. Adhesion between two substrates is a complex phenomenon, which at present is still not well understood. There are several factors determining the strength of adhesion: (i) molecular interactions at interface, (ii) mechanical properties of adhesive, and (iii) area of contact between adhesive and probing surface. Two surfaces are tacky when they possess the right balance between these factors. Controlling the adhesion of materials is important in many fields ranging from industrial purposes to biomedical applications and everyday usage. There is a demand for “smart” materials with integrated functionalities that make them responsive, switchable, biocompatible, anti-bacterial, more energy efficient, or autonomous. In particular, materials for such cutting-edge applications like cell culture, drug delivery, tissue engineering, biosensors, anti/biofouling, microfluidics, climbing robots, sport equipment and many others require adjustable/tuneable adhesive properties. Many efforts were directed towards fabrication of materials with either weak or strong adhesion depending on the field of application. However, design of “smart” surfaces with reversibly switchable/controllable adhesion is still a highly challenging task. Therefore, the thesis aims on design of smart polymeric materials with responsive / adaptive adhesion properties. For this, fabrication and investigation of two types of switchable polymer layers based on stimuli-responsive polymer brushes will be performed. The first group is dealing with thermoresponsive polymer brushes: poly-(N-isopropylacrylamide) and two types of biocompatible polyethylene glycol-based systems. These polymer layers undergo phase transition below and above LCST between hydrophilic and hydrophobic states. The second part of the work is related to solvent-responsive comb-like and block copolymer brushes consisted of hydrophilic PEG and hydrophobic PDMS biocompatible and biodegradable polymers.

The SCP-RICM assay employs the measurable surface energy (or adhesive work W_adh) of a micrometer-sized polymeric sphere (soft colloidal probe, SCP) interacting with a glass chip using reflection interfer-ence contrast microscopy (RICM). Depending on those two interacting surfaces' nature and functional-ization, the SCP will deform, creating a contact area with the hard glass chip. This contact area is clearly distinguishable from the sphere’s interference ring pattern and can be measured. The adhesive surface energy W_adh can be calculated from the size of the contact area. An immobilization can be overcome by choosing a two-component analyte-dependent interaction, here presented for the copper (Cu) detection. The detection of Cu was chosen as a proof-of-concept system. However, detecting metal ions is an essential endeavor because, in excessive amounts, they present a severe threat to health and the environment. The copper-dependent interaction of the yeast chaperones yCox17 (also Cox17) and ySco1 (also Sco1) were chosen as the two-component analyte-dependent interaction. The chaperones partic-ipate in vivo in the formation of the electron transport chain of S. cerevisiae and interact in the mito-chondrial inner membrane to transfer one Cu(I) ion from Cox17 to Sco1. It was necessary to immobilize one protein to the SCPs and one to the chip surface, to transfer the copper chaperones' interaction into the SCP-RICM assay core detection components. The unique self-assembling characteristics of the class I hydrophobin Ccg-2 from N. crassa were used to immobilize one interaction partner to the chip surface. Class I hydrophobins are known for the formation of re-sistant and uniform layers at hydrophilic/hydrophobic interfaces. Initial SCP-RICM assay measurements with Sco1Δ95_a-SCPs and the Cox17_c-chips indicate that copper detection using the proposed mechanism is possible (Figure 39-3). Measurements can be differentiated between 0 and 0.1 mM Cu(I) concentration in solution. Further screening of concentrations be-low 0.1 mM is still necessary. The presented proof-of-principle system for the indirect detection of copper shows copper-dependent behavior. These positive results give rise to many more options to use the SCP-RICM assay as an indirect detection system. The application range of the SCP-RICM assay could be enlarged for different analytes such as other heavy metals, bacteriophages, biomarkers, et cetera, and is relevant for fields from medicine to environmental monitoring.:TABLE OF CONTENT Table of Content I List of Figures VII List of Tables IX List of Abbreviations XI 1 Introduction 1 1.1 Biosensors 1 1.2 Analytical Detection Methods: Copper 2 1.3 SCP-RICM Assay 3 1.3.1 Sensor Chip Surface 4 1.3.2 Soft Colloidal Probes 5 1.3.3 Reflection Interference Contrast Microscopy 6 1.4 Hydrophobins 9 1.4.1 Structure and Functions of Hydrophobins 9 1.4.2 Ex vivo Applications of Hydrophobins 11 1.4.3 Class I Hydrophobin: Ccg-2 12 1.5 Mitochondrial Respiratory Chain 14 1.5.1 Copper Transport in Yeast 14 1.5.2 S. cerevisiae Sco1 protein 18 1.5.3 S. cerevisiae Cox17 protein 21 1.6 SCP-RICM Assay for Copper Detection 23 1.7 Aim of the Study 24 2 Materials and Methods 25 2.1 Laboratory Equipment 25 2.1.1 Devices 25 2.1.2 Chemicals 26 2.1.3 Consumables 28 2.1.4 Antibodies 29 2.1.5 Enzymes 30 2.1.6 Molecular Weight Standards 30 2.1.7 DNA Oligonucleotides 31 2.1.8 Plasmids and Vectors 32 2.2 Microorganisms 33 2.2.1 Strains 33 2.2.2 Cultivation of Microorganisms 34 2.2.3 Preparation of Electrocompetent E. coli Cells 36 2.2.4 Preparation of E. coli Glycerol Stocks 36 2.3 Protein Design 37 2.4 Molecular Cloning Methods 38 2.4.1 Vector Template Preparation 38 2.4.2 Agarose Gel Electrophoresis 40 2.4.3 DNA Extraction from Agarose Gels 41 2.4.4 Polymerase Chain Reaction 41 2.4.5 DNA Restriction Digest 42 2.4.6 DNA Dialysis 43 2.4.7 Ligation of DNA Fragments 43 2.4.8 Isolation of DNA from E. coli 44 2.4.9 DNA Sequencing 45 2.4.10 Transformation of E. coli via Electroporation 45 2.5 Protein Detection and Quantification 46 2.5.1 SDS PAGE 46 2.5.2 Coomassie Staining 50 2.5.3 Western Blot Analysis 51 2.5.4 Immunological Detection 51 2.5.5 Protein Quantification: Lowry Assay 52 2.5.6 Protein Quantification: Bradford Assay 53 2.5.7 Protein Quantification: NanoDrop Measurement 53 2.6 Protein Purification and Storage 54 2.6.1 Expression Analysis of Recombinant Proteins 54 2.6.2 Solubility Analysis 54 2.6.3 Protein Purification by Ni2+ Affinity Chromatography 55 2.6.4 Quantification of Purified Proteins 64 2.6.5 Dialysis of Purified Proteins 65 2.7 Glass Surface Functionalization 65 2.7.1 Glass Surface Preparation 66 2.7.2 Hydrophobin and Fusion Protein-Based Coating 66 2.7.3 Contact Angle Measurement 67 2.7.4 DRoPS Test 67 2.7.5 Atomic Force Microscopy 67 2.8 SCP Functionalization 68 2.8.1 Functionalization of SCPs with Proteins 68 2.8.2 Validation of SCP Functionalization with FITC Staining 69 2.9 SCP-RICM Assay and Its Analysis 69 3 Results 73 3.1 Generation of Recombinant Fusion Proteins 73 3.1.1 Sco1 and Sco1∆95 73 3.1.2 Cox17 84 3.1.3 Ccg-2 88 3.1.4 Overview: Optimization of Expression and Purification of Recombinant Proteins 90 3.2 His-Tag Cleavage 92 3.3 Chip Surface Functionalization 94 3.3.1 Optimization of the Glass Chip Preparation 94 3.3.2 Macroscopic Properties of the Functionalized Chip Surface 95 3.3.3 AFM Measurements 102 3.3.4 Theoretical Package of Hydrophobin Ccg-2 on the Chip Surface 103 3.4 SCP Functionalization 104 3.4.1 SCP Functionalization and FITC Staining 104 3.4.2 Theoretical Package of Proteins on SCPs 106 3.5 SCP-RICM Assay 107 4 Discussion and Further Prospectives 113 4.1 Discussion: SCP-RICM Assay and Protein-Protein Interaction 113 4.2 Outlook and Further Prospects 119 4.2.1 Heterologous Protein Expression and Purification: Methods, Cleavage and Refolding 119 4.2.2 Further Analysis of Chip Surface Functionalization 124 4.2.3 Alternative Chip Surface Functionalization Methods 126 4.2.4 SCP-RICM Assay: Data Acquisition and Evaluation 128 4.2.5 SCP-RICM Assay: Copper Detection 130 4.2.6 Exploiting the SCP-RICM Assay using Protein-Protein Interactions 131 4.2.7 Exploiting the SCP-RICM Assay with Alternative Interactions 133 5 Summary 137 6 Bibliography 141 7 Appendix 165 7.1 Sequences of Protein Constructs 165 7.1.1 Sequences of the Protein Construct Cox17_a 165 7.1.2 Sequences of the Hydrophobin-Cox17 Fusion Protein Cox17_b 165 7.1.3 Sequences of the Hydrophobin-Cox17 Fusion Protein Construct Cox17_c 166 7.1.4 Sequences of the Protein Construct Sco1_a and Sco1Δ95_a 167 7.1.5 Sequences of the Hydrophobin-Sco1 Fusion Protein Constructs Sco1_b and Sco1Δ95_b 169 7.1.6 Sequences of the Hydrophobin-Sco1 Fusion Protein Constructs Sco1_c and Sco1Δ95_c 171 7.1.7 Sequences of the Hydrophobin Ccg-2 173 7.2 pET-28b(+): Plasmid Map 173 7.3 Nickel Removal During Dialysis 175 7.4 DGR Assay 176 7.5 SCP diameter 179 Acknowledgements 181 Declaration of Authorship 183

Adhesion between different objects is happening everywhere. Without it, simple procedures like walking or holding something in a hand or attaching a postage stamp would be impossible. The life itself depends on adhesion on all levels, starting from the interactions between the living cells. Adhesion between two substrates is a complex phenomenon, which at present is still not well understood. There are several factors determining the strength of adhesion: (i) molecular interactions at interface, (ii) mechanical properties of adhesive, and (iii) area of contact between adhesive and probing surface. Two surfaces are tacky when they possess the right balance between these factors. Controlling the adhesion of materials is important in many fields ranging from industrial purposes to biomedical applications and everyday usage. There is a demand for “smart” materials with integrated functionalities that make them responsive, switchable, biocompatible, anti-bacterial, more energy efficient, or autonomous. In particular, materials for such cutting-edge applications like cell culture, drug delivery, tissue engineering, biosensors, anti/biofouling, microfluidics, climbing robots, sport equipment and many others require adjustable/tuneable adhesive properties. Many efforts were directed towards fabrication of materials with either weak or strong adhesion depending on the field of application. However, design of “smart” surfaces with reversibly switchable/controllable adhesion is still a highly challenging task. Therefore, the thesis aims on design of smart polymeric materials with responsive / adaptive adhesion properties. For this, fabrication and investigation of two types of switchable polymer layers based on stimuli-responsive polymer brushes will be performed. The first group is dealing with thermoresponsive polymer brushes: poly-(N-isopropylacrylamide) and two types of biocompatible polyethylene glycol-based systems. These polymer layers undergo phase transition below and above LCST between hydrophilic and hydrophobic states. The second part of the work is related to solvent-responsive comb-like and block copolymer brushes consisted of hydrophilic PEG and hydrophobic PDMS biocompatible and biodegradable polymers.

Adhesive processes in aqueous media play a crucial role in nature and are important for many technological processes. However, direct quantification of adhesion still requires expensive instrumentation while their sample throughput is rather small. Here we present a fast, and easily applicable method on quantifying adhesion energy in water based on interferometric measurement of polymer microgel contact areas with functionalized glass slides and evaluation via the Johnson–Kendall–Roberts (JKR) model. The advantage of the method is that the microgel matrix can be easily adapted to reconstruct various biological or technological adhesion processes. Here we study the suitability of the new adhesion method with two relevant examples: (1) antibody detection and (2) soil release polymers. The measurement of adhesion energy provides direct insights on the presence of antibodies showing that the method can be generally used for biomolecule detection. As a relevant example of adhesion in technology, the antiadhesive properties of soil release polymers used in today’s laundry products are investigated. Here the measurement of adhesion energy provides direct insights into the relation between polymer composition and soil release activity. Overall, the work shows that polymer hydrogel particles can be used as versatile adhesion sensors to investigate a broad range of adhesion processes in aqueous media.

The object of this work is to obtain a fundamentalunderstanding of the principal issues concerning the handlingof an aqueous WC-Co powder suspension. The WO3 surface layer on the oxidised tungsten carbidepowder dissolves at pH&gt;3 with the tungsten concentrationincreasing linearly with time. Adding cobalt powder to thetungsten carbide suspension resulted in a significant reductionof the dissolution rate at pH&lt;10. Electrokinetic studiesindicated that the reduced dissolution rate may be related tothe formation of surface complexes; the experiments showed thatCo species in solution adsorb on the oxidised tungsten carbidepowder. The surface forces of oxidised tungsten and cobalt surfaceswere investigated using the atomic force microscope (AFM)colloidal probe technique. The interactions at various ionicstrengths and pH values are well described by DLVO theory. Theadsorption of cobalt ions to tungsten oxide surfaces resultedin an additional non-DLVO force and a reduced absolute value ofthe surface potential. It was shown that the adsorption ofpoly(ethylene imine) (PEI) to the WO3 surfaces induces anelectrosteric repulsion. The properties of spray-dried WC-Co granules were related tothe WC primary particle size, and the poly(ethylene glycol)(PEG) binder and PEI dispersant content in aqueous WC-Cosuspensions. The granule characterisation includes a new methodfor measuring the density of single granules. The increase inthe fracture strength of granules produced from suspensionsthat were stabilised with PEI was related to a more densepacking of the WC-Co particles. The AFM was used to study the friction and adhesion ofsingle spray-dried WC-Co granules containing various amounts ofPEG binder. The adhesion and friction force between two singlegranules (intergranular friction) and between a granule and ahard metal substrate (die-wall friction) have been determinedas a function of relative humidity. The granule-wall frictionincreases with binder content and relative humidity, whereasthe granule-granule friction is essentially independent of therelative humidity and substantially lower than the granule-wallfriction at all PEG contents. Key words:Hard Metal, Cemented Carbide, WC-Co, TungstenCarbide, Cobalt, Oxidation, Dissolution, Surface Complexation,XPS, AFM, Colloidal Probe, Hamaker Constant, Cauchy, WO3,CoOOH, ESCA, Zeta-Potential, Surface Potential, Poly(ethyleneimine), PEI, Suspension, van der Waals, Steric, Spray-Dried,Poly(ethylene glycol), Strength, Density, Friction, Adhesion,Granule, PEG, Pressing, FFM. / <p>QC 20161027</p>

The object of this thesis is to apply scanning probemicroscopy (SPM) to the field of advanced powder processing.Measurement of interparticle surface forces at conditionsrelevant to ceramic processing has been performed together withthorough studies of powder friction. Surface force measurements between silicon nitride andsilica surfaces in 1-bromonaphtalene and diiodomethane resultedin an attractive van der Waals force in both media for thesymmetric systems and a repulsive van der Waals force for theasymmetric systems. This agreed well with theoreticalpredictions from Lifshitz theory. Measurements in electrolytesolutions between silicon nitride surfaces with a varyingdegree of oxidation showed that silanol groups dominated theinteractions at a high degree of oxidation, whereas theinfluence of amine species became stronger after surfaceetching. Surface charge, surface potential and density ofsurface groups have been extracted from DLVO computer modellingof the experimental force curves. Surface force measurementshave been carried out using a nitrided silica sphere as acolloidal probe, representative for commercial silicon nitridepowders. Adsorption of poly(acrylic acid) above the isoelectricpoint generated a thin polymer layer of an essentially flatconformation. Friction force measurements were attainable via novelcalibration procedures of both the lateral photodetectorresponse and the cantilever torsional spring constant.Combining the method for detector calibration with evaluationof static friction slopes simplified the choice of appropriatecontact mechanics theory to evaluate the friction measurements.Applying the method on friction measurements between ironsurfaces coated with commercial lubricants showed a substantialsurface deformation not seen from the friction force alone. Thenanorheological properties of silica surfaces coated with twodifferent stearic acids have been evaluated from friction forcemeasurements. Steady sliding motion was replaced by highlyregular stick-slip motion at a critical load and velocity. Thestick-slip motion was successfully described and fitted to aphenomenological model. The contact area evaluated fromMaugis-Dugdale theory revealed the contact diameter to be veryclose to the stick-slip periodicity. Friction measurements were carried out between individualspray-dried ceramic granules as a function of binderconcentration and relative humidity. The hygroscopic nature ofthe binder resulted in a higher adhesion force but lowerfriction coefficient with increasing humidity. This effect wasascribed to softening of the binder and a lowering of the shearstrength of the binder rich surface layer on the granules.Comparison of the friction force between two granules and agranule and a hard metal surface confirmed that resistance toflow during the initial stages of powder pressing is dominatedby granule-wall friction and adhesion. Keywords: Atomic force microscope, AFM, SPM, van der Waalsinteraction, DLVO-theory, surface forces, colloidal probe,force curve, friction, adhesion, stick-slip, cantilever,calibration, spring constant, silicon nitride, iron,silica.